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Hazardous Chemicals Handbook

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Hazardous Chemicals HandbookSecond edition

Phillip CarsonPhD MSc AMCT CChem FRSC FIOSH

Head of Science Support Services, Unilever Research Laboratory,Port Sunlight, UK

Clive MumfordBSc PhD DSc CEng MIChemEConsultant Chemical Engineer

Oxford Amsterdam Boston London New York Paris San DiegoSan Francisco Singapore Sydney Tokyo

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Butterworth-HeinemannAn imprint of Elsevier ScienceLinacre House, Jordan Hill, Oxford OX2 8DP225 Wildwood Avenue, Woburn, MA 01801-2041

First published 1994Second edition 2002

Copyright © 1994, 2002, Phillip Carson, Clive Mumford. All rights reserved

The right of Phillip Carson and Clive Mumford to be identified as theauthors of this work has been asserted in accordance with the Copyright,Designs and Patents Act 1988

No part of this publication may be reproduced in any material form (includingphotocopying or storing in any medium by electronic means and whetheror not transiently or incidentally to some other use of this publication) withoutthe written permission of the copyright holder except in accordance with theprovisions of the Copyright, Designs and Patents Act 1988 or under the terms ofa licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road,London, England W1T 4LP. Applications for the copyright holder’s writtenpermission to reproduce any part of this publication should be addressedto the publishers

British Library Cataloguing in Publication DataA catalogue record for this book is available from the British Library

Library of Congress Cataloguing in Publication DataA catalogue record for this book is available from the Library of Congress

ISBN 0 7506 4888 0

For information on all Butterworth-Heinemann publications visit our website at www.bh.com

Typeset at Replika Press Pvt Ltd, Delhi 110 040, IndiaPrinted and bound in Great Britain

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Preface to the second edition ix

Preface to the first edition xi

1 Introduction 1

2 Terminology 10

3 General principles of chemistry 21Introduction 21Atoms and molecules 21Periodic table 22Valency 23Chemical bonds 24Oxidation/Reduction 25Physical state 26Acids 26Bases 27Halogens 28Metals 29Oxygen and sulphur 30Nitrogen, phosphorus, arsenic and antimony 31pH 32Salts 32Organic chemistry 32Combustion chemistry 40Chemical reactivity 42

4 Physicochemistry 45Vapour pressure 45Gas–liquid solubility 46Liquid-to-vapour phase change 47Solid-to-liquid phase change 47Density differences of gases and vapours 47Density differences of liquids 49Immiscible liquid–liquid systems 49Vapour flashing 50

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Effects of particle or droplet size 50Surface area effects in mass transfer or heterogeneous reactions 50Enthalpy changes on mixing of liquids 52Critical temperatures of gases 52Chemical reaction kinetics 53Corrosion 54Force and pressure 56Expansion and contraction of solids 60

5 Toxic chemicals 67Introduction 67Hazard recognition 67Types of toxic chemicals 67Hazard assessment 81Risk assessment of carcinogens 119Risk control 120Control of substances hazardous to health 137Specific precautions 147

6 Flammable chemicals 178Ignition and propagation of a flame front 178Control measures 219Fire extinguishment 221Fire precautions 223

7 Reactive chemicals 228Water-sensitive chemicals 228Toxic hazards from mixtures 229Reactive hazards from mixtures 231Oxidizing agents 234Explosive chemicals 235General principles for storage 243Hazards arising in chemicals processing 243

8 Cryogens 258Liquid oxygen 259Liquid nitrogen and argon 261Liquid carbon dioxide 261Liquefied natural gas 263

9 Compressed gases 265Acetylene 273Air 274Ammonia 276Carbon dioxide 277Carbon monoxide 279Chlorine 280Hydrogen 282Hydrogen chloride 284


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Hydrogen sulphide 286Liquefied petroleum gases 287Methane 291Nitrogen 293Nitrogen oxides 295Oxygen 301Ozone 303Sulphur dioxide 304

10 Monitoring techniques 307Selected general analytical techniques for monitoring environmental pollution 308Gases and vapours 308Particulates 312Monitoring water quality 313Monitoring land pollution 314Monitoring air pollution 314Flammable gases 319Toxic particulates 321Official methods 357Sampling strategies 359Selected strategies for determining employees’ exposure to airborne chemicals 363Pollution monitoring strategies in incident investigation 387

11 Radioactive chemicals 390Hazards 391Types of radiation 391Control measures 392

12 Safety by design 396Design procedures 396Layout 397Storage 401Equipment design 404Piping arrangements 404Fire protection 410Installation and operation 411

13 Operating procedures 412Commissioning 413Operation 413Maintenance 413Pressure systems 423Emergency procedures 424Spillage 427First aid 429Personal protection 433Medical screening 441Monitoring standards 442Training 442


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14 Marketing 443Classification 443Packaging 445Labelling 447Information 451

15 Transport of chemicals 460Road transport 461Rail transport 468Air transport 470Sea transport 471Modes of transport for liquids, gases and solids 481Loading and unloading 484Container filling/discharging 487

16 Chemicals and the environment: sources and impact 488Atmospheric emissions 501Liquid effluents 503Solid wastes 507

17 Chemicals and the environment: monitoring and protection 512Legislative control 512Waste management 517Environmental Impact Assessment 526Control of atmospheric emissions 528Liquid effluent treatment operations 529Control of solid waste 533Monitoring and auditing 533

18 Conversion tables and measurement data 543

19 Bibliography 552

Appendix: Selected UK legislation relevant to environmental protection andoccupational health and safety in relation to chemicals 593

Index 599


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Preface to the second edition

The aim of this book remains as for the first edition, namely to provide an initial point of readyreference for the identification of hazards and precautions for dangerous chemicals. It is targetednot only at those in the chemical and process industries, but also anyone likely to work withchemicals within industry and in the service sector, e.g. hospitals, universities, research laboratories,engineering, agriculture, etc. It embraces the entire life-cycle of chemicals during transport,storage, processing, marketing, use and eventual disposal and should appeal to chemists, occupationaland environmental health practitioners and students, engineers, waste handlers, safety officersand representatives, and health care professionals. Clearly, more detailed texts or professionaladvice may need to be consulted for specific applications.

Since the first edition in 1994 there have been no significant changes in the fundamentals ofchemistry, physics and toxicology upon which the safe handling of chemicals are based. Therehas, however, been some increase in knowledge relating to the chronic toxicological and potentialenvironmental effects of specific chemicals, and in legislation and government guidelines. Theseare reflected in the second edition. In general, within the UK the predominant legislation relatingto substances hazardous to health, the Control of Substances Hazardous to Health Regulations1999 and its accompanying Approved Code of Practice, incorporate significant changes since the1988 (and 1994) versions. There has been an increase in the controls applicable to the marketingand transportation of different classes of chemicals. Those applicable to major hazards havechanged under the Control of Major Accident Hazard Regulations 1999. Other legislation hasbeen introduced: e.g. the Confined Spaces Regulations 1997, the Reporting of Injuries, Diseasesand Dangerous Occurrences Regulation 1995, the Health and Safety (Safety Signs and Signals)Regulations 1996, and the Pressure Systems Safety Regulations 2000 which is of importance tothe scope of this text. Increased concern as to the possible environmental impacts of chemicaldischarges and disposal has been accompanied by more comprehensive legislation for control.General safety legislation was expanded by the introduction of various separate regulations in1993, including that dealing with management of health and safety at work; workplace health,safety and welfare; workplace equipment; and personal protective equipment. These improvementsare, in general, now reflected in industry.

The opportunity has been taken to improve each chapter and to update the information. Themain changes include an expansion of the terminology in Chapter 2 and provision of an introductionto basic chemical principles for non-chemists in a new Chapter 3. Chapter 4 on Physicochemistrycontains additional examples. Chapter 5 on Toxic chemicals has been enlarged and the table ofhygiene standards updated. Chapters 6, 7 and 8 on Flammable chemicals, Reactive chemicals andCryogens, respectively, have been updated and expanded. The scope of Chapter 9 on Compressedgases has been widened to include additional examples together with the basic techniques ofpreparing gases in situ. Chapter 10 summarizes techniques for monitoring air quality and employeeexposure. It has also been expanded to provide guidance on monitoring of water and land pollution.

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The chapter on Radioactive chemicals (Chapter 11) has been updated. Considerations of safety indesign (Chapter 12) are presented separately from systems of work requirements, i.e. Operatingprocedures (Chapter 13). The considerations for Marketing and transportation of hazardous chemicalsare now addressed in two separate chapters (Chapters 14 and 15). Chemicals and the Environmentare now also covered in two chapters (Chapters 16 and 17) to reflect the requirement that theimpact of chemicals on the environment should be properly assessed, monitored and controlled.Although a substantial contribution to atmospheric pollution is made by emissions from roadvehicles and other means of transport, and this is now strictly legislated for, this topic is outsidethe scope of this text. Chapter 18 provides useful conversion factors to help with the myriad ofunits used internationally.

Whilst the hazards identified, and the principles and practice for the control of risks areuniversal, i.e. they are independent of location, in order to assist quick-reference an appendix ofrelevant contemporaneous UK legislation has been added as a guide together with a much-expanded Bibliography in Chapter 19. Finally, for convenience of use, the Index has been enlarged.

It is hoped that the improvements will help to achieve the objectives for which the text wasoriginally conceived, i.e. to summarize in relatively basic terms the hazards associated withchemicals and how the ensuing risks can be controlled, and to provide sufficient detailed informationto supplement that obtainable from suppliers, government publications, trade associations, andcomputerized data banks where recourse to specialized textbooks may be premature, difficult orunnecessary.



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Preface to the first edition

The aim of this handbook is to provide a source of rapid ready reference to help in the oftencomplex task of handling, using and disposing of chemicals safely and with minimum risk topeople’s health or damage to facilities or to the environment.

The range of chemicals and chemical mixtures in common use in industry is wide: it isobviously impossible to list them all in a concise handbook, or to refer to all their proprietarynames. The approach here has been to avoid ‘random listing’ and to arrange by type of hazard,dealing with the most widely used substances and those properties and characteristics of behaviourthat are directly relevant to common use and to compliance with safety legislation. Numeroussources not restricted to those in the Bibliography were searched for information and although notlisted, to achieve conciseness, these are acknowledged. The multiplicity of data sources alsomeans that minor variations occur due to differences in the procedures and methods for theirdetermination; however they provide general guidance. Whilst the data quoted in this text hasbeen carefully collated, its accuracy cannot be warranted. For this reason, and to avoid overlookingconsideration of other chemical-specific hazards or location-dependent legislation, it is advisableto refer to a Chemical Safety Data Sheet before using any chemical. These are readily availablefrom suppliers (e.g. in the UK under S.6 of the Health & Safety at Work etc. Act 1974). Forexhaustive treatment of physical, toxicological, flammable/explosive and reactive properties, andthe background to – and limitations of – their determination or prediction, the reader is referredto standard textbooks (see Bibliography) such as:

The Safe Handling of Chemicals in Industry (Carson and Mumford)Dangerous Properties of Industrial Materials (Sax and Lewis)Handbook of Reactive Chemical Hazards (Bretherick)Handbook of Toxic and Hazardous Materials (Sittig)Patty’s Industrial Hygiene and Toxicology (Clayton and Clayton)

The identification, assessment, control and monitoring of chemical-related hazards andenvironmental pollution control are, of course, required under a wide range of statutory legislation,dependent upon the country concerned. For example, in the UK the Health and Safety at Worketc. Act 1974, the Control of Substances Hazardous to Health Regulations 1988, the HighlyFlammable Liquids and Liquefied Petroleum Gases Regulations 1972, the Control of PollutionAct 1974 and the Environmental Protection Act 1990 are supplemented by a wide variety of othermeasures. Legislative controls tend to change frequently and it is important to ensure that a checkis made on current requirements and constraints in any specific situation involving chemicals.

It is hoped that this book will prove valuable to safety advisers, environmental health officers,emergency services personnel, safety representatives and those engaged in the transport or disposalof wastes – in fact, to anyone involved with chemicals ‘in the field’, i.e. away from ready access

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to chemical safety data sheets, detailed texts, library facilities or computerized databanks. It alsoprovides a useful summary for those who may need to make only passing reference to thehazardous properties and potential effects of chemicals, such as general engineering students andoccupational health nurses.



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Industrial hazards cover a wide spectrum including fire and explosion, mechanical hazards (e.g.from moving machinery), electrical hazards, occupational exposures to ionizing and non-ionizingradiation, biological hazards (e.g. acute or chronic infections, parasitism, and toxic or allergicreactions to plant and animal matter), physical hazards (e.g. tripping, falling, impact from vehiclesor falling objects) and ergonomical hazards (e.g. lifting or carrying heavy or awkward loads orfrom repetitive operations). Work-related stress can also lead to mental and physical ill-health.Different hazards may be associated with the manufacture, storage, transport, use, and disposal ofchemicals. Environmental hazards, through persistent or accidental losses of chemicals, may alsobe related to these operations.

Working with pathogenic micro-organisms bears passing similarity to chemicals. Hence, in theUK micro-organisms are classified as hazardous substances under the Control of SubstancesHazardous to Health Regulations and there is an accompanying Code of Practice. However,biological hazards arising from the working environment or from more specialized activities, e.g.working with pathogenic organisms in laboratories, are beyond the scope of this book. This textdeals solely with occupational, industrial and environmental hazards associated only with chemicals.It includes fires and explosions since they inevitably involve chemical compounds.

Chemicals are ubiquitous as air, carbohydrates, enzymes, lipids, minerals, proteins, vitamins,water, and wood. Naturally occurring chemicals are supplemented by man-made substances.There are about 70 000 chemicals in use with another 500–1000 added each year. Their propertieshave been harnessed to enhance the quality of life, e.g. cosmetics, detergents, energy fuels,explosives, fertilizers, foods and drinks, glass, metals, paints, paper, pesticides, pharmaceuticals,plastics, rubber, solvents, textiles; thus chemicals are found in virtually all workplaces. Besidesthe benefits, chemicals also pose dangers to man and the environment. For example:

• Of the many industrial fires in the UK in 1997 each of some 411 cost more than £50 000 withtotal losses amounting to £186m. These spanned a wide range of industrial and related premisesas shown in Table 1.1. The most common sources of ignition (see Chapter 6) that year areshown in Table 1.2.

• In the UK alone occupational health risks due to chemicals are illustrated by:– 152 incidents in 1998 involving supply and use of flammable gas with around 70% causing

carbon monoxide poisoning and 30 fires/explosions;– 554 new cases of pneumoconiosis (excluding asbestosis) and 3423 assessed cases of bronchitis

or emphysema (in coal miners) during the same period;– annually there are 4500 cases of work-related skin disease (80% contact dermatitis), ca 1500

cases of occupational asthma (mainly from solder flux, isocyanates, wood dust, spray painting,metal treatment, plastics), ca 200 cases of allergic rhinitis;

– between 2% and 8% of all cancer deaths are of occupational origin;

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Table 1.1 Breakdown of U.K. fires causing more than £50 000 damage in 1997

Occupancy No. of fires Loss £000 % of total costof all fires

Agriculture, forestry and fishing 27 3282 2Paper, printing and publishing 14 6480 3Food, drink and tobacco 13 7235 4Rubber and plastic 7 5371 3Textiles, footwear and clothing 7 1894 1Timber and wood products excluding furniture 6 1042 1Chemicals and allied products 5 4543 2Construction 5 515 –Metal manufacture 4 871 –Engineering 4 545 –Other manufacturing industries 25 20249 11Retail distribution 27 15021 8Transport and communications 18 13390 7Wholesale distribution 8 26250 14Education 39 23407 13Recreational/cultural 30 6946 4Clubs and public houses 19 4668 3Cafes/restaurants 14 2431 1Insurance, banking and business services 10 1730 1Hotels/boarding houses 6 2516 1Hospitals 4 925 –Public admin./defence/law enforcement 3 430 –Hostels/holiday camps 1 99 –Homes for disabled 1 100 –Domestic dwellings 63 9970 5Other 26 434 518 14

Table 1.2 Accidental fires (UK) in 1997: sources of ignition

Ignition source No. of fires % of all fires Loss £000 % of total cost ofall fires

Electrical appliances 110 26.8 55 491 29.8Smokers’ materials 17 4.1 2138 1.1Gas appliances 10 2.4 2595 1.4

(excluding blowlamps and welding)Blowlamps: all fuels 7 1.7 2176 1.2Welding and cutting appliances 7 1.7 1340 0.7Oil and petroleum appliances 6 1.5 714 0.4

(excluding blowlamps and welding)Unspecified appliances 5 1.2 578 0.3Rubbish burning 4 1 417 0.2Chimney, stovepipe and flue 2 0.5 303 0.2Natural occurrence 2 0.5 215 0.3Ashes/soot 1 0.2 50 0.1Other 22 5.4 3789 2Total 193 47 69 806 37.7

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– ca 1760 cases per year of acute poisonings and injuries from chemicals, the most common beingfrom acids, caustic, and gases, with process operatives and tradesmen being at greatest risk;

– an estimated 9000 cases of sick building syndrome per year.• The UK Environment Agency deals with over 6000 oil pollution incidents each year. One

estimate suggests that the chemical industry contributes to 50% of all air pollution with proportionsapproximating to sulphur dioxide (36%), carbon dioxide (28%), nitrogen oxides (18%), carbonmonoxide (14%) and black smoke (10%). Motor spirit refining is responsible for ca 26% ofemissions of volatile organic compounds to the atmosphere. In 1996 there were over 20 000reports of water pollution incidents with 155 successful prosecutions.

• The EC produces in excess of 2 billion tonnes of waste each year. 414 million tonnes arise inthe UK and a further 68 million tonnes of hazardous waste are imported. All wastes must bedisposed of safely.

Society must strike a balance between the benefits and risks of chemicals. In the workplace it isa management responsibility to ensure practices control the dangers, and it is for employees tocollaborate in implementing the agreed procedures. Management must also prevent uncontrolledenvironmental releases and ensure all wastes are disposed of safely and with proper regard fortheir environmental impact. The aims of this book are to raise awareness and to help usersidentify, assess and control the hazards of chemicals to permit optimum exploitation whilstminimizing the dangers.

The hazards of ‘chemicals’ stem from their inherent flammable, explosive, toxic, carcinogenic,corrosive, radioactive or chemical-reactive properties. The effect of exposure on personnel maybe acute, e.g. in a flash-fire or due to inhalation of a high concentration of an irritant vapour.Alternatively, prolonged or intermittent exposure may result in an occupational disease or systemicpoisoning. Generally acute effects are readily attributable; chronic effects, especially if theyfollow a long latency period or involve some type of allergic reaction to a chemical, may be lesseasy to assign to particular occupational exposures. The possible permutations of effects can bevery wide and exposure may be to a combination of hazards. For example, personnel exposed toa fire may be subject to flames, radiant heat, spilled liquid chemicals and vapours from them,leaking gases, and the pyrolytic and combustion products generated from chemical mixturestogether with oxygen deficient atmospheres. However, whether a hazardous condition develops inany particular situation also depends upon the physical properties of the chemical (or mixture ofchemicals), the scale involved, the circ*mstances of handling or use, e.g. the processes involvedand degree of containment, and upon the control measures prevailing, e.g. provision of controland safety devices, local exhaust ventilation, general ventilation, personal protection, atmosphericmonitoring and systems of work generally.

Hazard recognition and assessment always start from a knowledge of the individual propertiesof a chemical. What this may include is exemplified by Table 1.3. Additional properties, includingthose in Table 1.4, are relevant to environmental hazards, e.g. relating to behaviour on spillage oremission, and determination of permissible levels for disposal to air, land or water systems. Otherproperties may be relevant, e.g. odour which can serve as an, albeit often unreliable, means ofdetection. (Refer to Table 5.12.)

An elementary introduction to chemistry is given in Chapter 3; this serves only to providebackground and for more advanced consideration reference will be necessary to specific textbooks, e.g. as listed in the Bibliography. A brief discussion of the relevance of physicochemicalprinciples to hazard identification is given in Chapter 4. Relevant toxic and flammable properties,and summaries of appropriate precautions to cater for them during handling, use and disposal, areprovided in Chapters 5 and 6, respectively. Reactive hazards are discussed in Chapter 7. Thespecial problems with cryogenic materials and chemicals under pressure, typified by compressed

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Table 1.3 Comprehensive information possibly required for a hazardous chemical

Name of chemical; other namesUsesGeneral description of hazardsGeneral description of precautions

Fire-fighting methodsRegulationsSources of advice on precautions

Characteristics: evaluate as appropriate under all process conditionsFormula (chemical structure)Purity (identity of any contaminants), physical state, appearance, other relevant informationConcentration, odour, detectable concentration, taste

Physical characteristicsMolecular weight Particle size; size distributionVapour density Foaming/emulsification characteristicsSpecific gravity Critical temperature/pressureMelting point Expansion coefficientBoiling point Surface tensionSolubility/miscibility with water Joule–Thompson effectViscosity Caking properties

CorrosivityContamination factors (incompatibility), oxidizing or reducing agent, dangerous reactions

Flammability informationFlash point Vapour pressureFire point Dielectric constantFlammable limits (LEL, UEL) Electrical resistivityIgnition temperature Electrical groupSpontaneous heating Explosion properties of dust in a fireToxic thermal degradation products

Reactivity (instability) informationAcceleration rate calorimetry Drop weight testDifferential thermal analysis (DTA) Thermal decomposition testImpact test Influence testThermal stability Self-acceleration temperatureLead block test Card gap test (under confinement)Explosion propagation with detonation JANAF

Critical diameterPyrophoricity

Toxicity informationToxic hazard ratingHygiene standard (e.g. OEL, TLV)Maximum allowable concentration (MAC)Lethal concentration (LC50)Lethal dose (LD50)

Biological properties

Exposure effectsInhalation (general)Respiratory irritationIngestionSkin/eye irritationSkin and respiratory sensitizationMutagenicityTeratogenicityCarcinogenicity

Radiation informationRadiation surveyAlpha/beta/gamma/neutron exposure and contamination

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gases, are dealt with in Chapters 8 and 9. The unique problems associated with radioactivechemicals are described in Chapter 11.

The foregoing relates mainly to normal laboratory or commercial quantities of chemicals.Additional considerations arise with those quantities of flammable, explosive, reactive, bulktoxic, or hypertoxic chemicals which constitute major hazards, i.e. which may pose a hazard toneighbouring factories, residents, services etc. or a more substantial potential risk to the environment.Within the UK the Control of Major Accident Hazards Regulations 1999 requires that the operatorof any establishment where a dangerous substance listed in column 1 of Parts 2 or 3 of Schedule1 (reproduced here as Tables 1.5 and 1.6) is present in a quantity equal to or greater than that listedin column 2 of those Parts shall notify the competent authority. Detailed procedures and precautionsare then applicable to such sites depending partly upon whether they are ‘lower tier’ or ‘uppertier’, i.e. sites at which the quantity present is equal to or exceeds that listed in column 3. Thespecial considerations with such installations are detailed in specialist texts noted in the Bibliography.In the UK the Planning (Hazardous Substances) Regulations 1992 also require the holder toobtain a ‘hazardous substances consent’ for any site on which it is intended to hold a bulk quantityof any of 71 substances above a ‘controlled quantity’ (Table 1.7).

Table 1.4 Typical data on hazards to the environment

Aquatic toxicity (e.g. to fish, algae, daphnia)Terrestrial toxicity (to plants, earthworms, bees, birds)Biotic degradationAbiotic degradationPhotodegradationBiochemical oxygen demandChemical oxygen demandHydrolysis as a function of pHBioaccumulationOil/water partition coefficient

To proceed to assess, and recommend control strategies for, any operation involving a mixtureof chemicals – e.g. a chemical process, welding fume, mixed effluents – can be a complexexercise. It can rarely be solved by rigidly following a checklist, although checklists, examples ofwhich are given in the various chapters, can provide useful guidelines. And although associatedhazards are not covered here, the control of chemical hazards in the workplace cannot be achievedin isolation from a consideration of electrical, mechanical, ergonomic, biological and non-ionizingradiation hazards. Hence these must be included in any hazard analysis and control system.

To ensure that an operation is under control may necessitate environmental monitoring; this issummarized in Chapter 10. Principles of safe design are given in Chapter 12. General safetyconsiderations, administration and systems of work requirements, including elementary first aid,are summarized in Chapter 13. For example, the recommended strategy is to include provision forappropriate first aid procedures within the system of work before specific chemicals are broughtinto use; to so order work practices that the risk of exposure is minimized; and in the event of anaccident involving any but the most trivial injuries – with no foreseeable likelihood of complicationsor deterioration – to seek immediate medical assistance.

Additional considerations, e.g. relating to labelling, information supply and emergency procedures,arise when marketing and transporting chemicals. While – as with Chapter 13 and with controlmeasures generally – what is required will vary with specific legislation and basic requirementsare summarized in Chapters 14 and 15.

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Table 1.5 Schedule 1 Part 2 of the COMAH Regulations Named Substances (Explanatory notes omitted)

Column 1 Column 2 Column 3Dangerous substances Quantity in tonnes Quantity in tonnes

Ammonium nitrate (as described in Note 1 of 350 2500this Part)

Ammonium nitrate (as described in Note 2 of 1250 5000this Part)

Arsenic pentoxide, arsenic (V) acid and/or salts 1 2Arsenic trioxide, arsenious (III) acid and/or salts 0.1 0.1Bromine 20 100Chlorine 10 25Nickel compounds in inhalable powder form 1 1

(nickel monoxide, nickel dioxide, nickelsulphide, trinickel disulphide, dinickel trioxide)

Ethylenimine 10 20Fluorine 10 20Formaldehyde (concentration ! 90%) 5 50Hydrogen 5 50Hydrogen chloride (liquefied gas) 25 250Lead alkyls 5 50Liquefied extremely flammable gases (including LPG) 50 200

and natural gas (whether liquefied or not)Acetylene 5 50Ethylene oxide 5 50Propylene oxide 5 50Methanol 500 50004,4-Methylenebis (2-chloroaniline) and/or 0.01 0.01

salts, in powder formMethylisocyanate 0.15 0.15Oxygen 200 2000Toluene diisocyanate 10 100Carbonyl dichloride (phosgene) 0.3 0.75Arsenic trihydride (arsine) 0.2 1Phosphorus trihydride (phosphine) 0.2 1Sulphur dichloride 1 1Sulphur dioxide 15 75Polychlorodibenzofurans and 0.001 0.001

polychlorodibenzodioxins (including TCDD),calculated in TCDD equivalent

The following CARCINOGENS:

4-Aminobiphenyl and/or its salts, 0.001 0.001Benzidene and/or its salts,Bis(chloromethyl) ether,Chloromethyl ether,Dimethylcarbamoyl chloride,Dimethylnitrosoamine,Hexamethylphosphoric triamide,2-Naphthylamine and/or its salts,1.3-Propane sultone, 4-Nitrodiphenyl

Automotive petrol and other 5000 50 000petroleum spirits

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Table 1.6 Schedule 1 Part 3 of the COMAH Regulations. Categories of substances and preparations not specificallynamed in Part 2. (Explanatory notes omitted)

Column 1Column 2 Column 3Categories of dangerous substances Quantity in tonnes Quantity in tonnes

1. VERY TOXIC 5 20

2. TOXIC 50 200

3. OXIDIZING 50 200

4. EXPLOSIVE (Where the 50 200substance or preparationfalls within the definitiongiven in Notes 2a)

5. EXPLOSIVE (Where the 10 50substance or preparationfalls within the definitiongiven in Notes 2b)

6. FLAMMABLE (Where the 5000 50 000substance or preparationfalls within the definitiongiven in Notes 3a)

7a. HIGHLY FLAMMABLE 50 200(Where the substance orpreparation falls within thedefinition given in Notes 3bi)

7b. HIGHLY FLAMMABLE 5000 50 000(Where the substance orpreparation falls within thedefinition given in Notes 3bii)

8. EXTREMELY FLAMMABLE 10 50(Where the substance orpreparation falls within thedefinition given in Notes 3c)

9. DANGEROUS FOR THEENVIRONMENT incombination with riskphrases(i) R50: Very toxic to 200 500

aquatic organisms(ii) R51: Toxic to 500 2000

aquatic organismsand R43: maycause long-termadverse effects inthe aquaticenvironment

10. ANY CLASSIFICATION notcovered by those given abovein combination with risk phrases(i) R14: Reacts 100 500

violently with water(including R15)

(ii) R29: In contact with water, 50 200liberates toxic gas

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Table 1.7 Planning (Hazardous Substances) Regulations 1992Hazardous substances and controlled quantities

Hazardous substance Controlled quantity

Part A Toxic substances1. Acetone cyanohydrin (2-cyanopropan-2-ol) 200 t2. Acrolein (2-propenal) 200 t3. Acrylonitrile 20 t4. Allyl alcohol (2-propen-1-ol) 200 t5. Allylamine 200 t6. Ammonia (anhydrous or as solution containing more than 50% by weight of ammonia) 100 t7. Arsenic trioxide, arsenious (III) acid and salts 1 t8. Arsine (arsenic hydride) 1 t9. Bromine 40 t

10. Carbon disulphide 20 t11. Chlorine 10 t12. Ethylene dibromide (1,2-dibromoethane) 50 t13. Ethyleneimine 50 t14. Formaldehyde (>90%) 50 t15. Hydrogen chloride (liquefied gas) 250 t16. Hydrogen cyanide 20 t17. Hydrogen fluoride 10 t18. Hydrogen selenide 1 t19. Hydrogen sulphide 50 t20. Methyl bromide (bromomethane) 200 t21. Methyl isocyanate 150 kg22. Nickel tetracarbonyl 1 t23. Nitrogen oxides 50 t24. Oxygen difluoride 1 t25. Pentaborane 1 t26. Phosgene 750 kg27. Phosphine (hydrogen phosphide) 1 t28. Propyleneimine 50 t29. Selenium hexafluoride 1 t30. Stibine (antimony hydride) 1 t31. Sulphur dioxide 20 t32. Sulphur trioxide (including the sulphur trioxide content in oleum) 15 t33. Tellurium hexafluoride 1 t34. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) 1 kg35. Tetraethyl lead 50 t36. Tetramethyl lead 50 t

Part B Highly reactive substances and explosive substances

37. Acetylene (ethyne) when a gas subject to a pressure "620 millibars above that of the 50 tatmosphere, and not otherwise deemed to be an explosive by virtue of Order inCouncil No 30,(a) as amended by the Compressed Acetylene Order 1947,(b) or whencontained in a hom*ogeneous porous substance in cylinders in accordance with Orderof Secretary of State No 9,(c) made under the Explosives Act 1875.(d)

38. Ammonium nitrate and mixtures containing ammonium nitrate where the nitrogen 500 tcontent derived from the ammonium nitrate >28% of the mixture by weight other than:(i) mixtures to which the Explosives Act 1875 applies;(ii) ammonium nitrate based products manufactured chemically for use as fertilizer

which comply with Council Directive 80/876/EEC;(e) or(iii) compound fertilizers.

39. Aqueous solutions containing >90 parts by weight of ammonium nitrate per 100 parts 500 tby weight of solution.

40. Ammonium nitrate based products manufactured chemically for use as fertilizers which 1000 tcomply with Council Directive 80/876/EEC and compound fertilizers where thenitrogen content derived from the ammonium nitrate >28% of the mixture by weight.

41. 2,2-Bis(tert-butylperoxy)butane (>70%) 5 t42. 1,1-Bis(tert-butylperoxy)cyclohexane (>80%) 5 t

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43. tert-Butyl peroxyacetate (>70%) 5 t44. tert-Butyl peroxyisobutyrate (>80%) 5 t45. tert-Butyl peroxyisopropylcarbonate (>80%) 5 t46. tert-Butyl peroxymaleate (>80%) 5 t47. tert-Butyl peroxypivalate (>77%) 5 t48. Cellulose nitrate other than:

(i) cellulose nitrate to which the Explosives Act 1875 applies; or 50 t(ii) solutions of cellulose nitrate where the nitrogen content of the cellulose

nitrate "12.3% by weight and the solution contains "55 parts of cellulosenitrate per 100 parts by weight of solution.

49. Dibenzyl peroxydicarbonate (>90%) 5 t50. Diethyl peroxydicarbonate (>30%) 5 t51. 2,2-Dihydroperoxypropane (>30%) 5 t52. Di-isobutyryl peroxide (>50%) 5 t53. Di-n-propyl peroxydicarbonate (>80%) 5 t54. Di-sec-butyl peroxydicarbonate (>80%) 5 t55. Ethylene oxide 5 t56. Ethyl nitrate 50 t57. 3,3,6,6,9,9-Hexamethyl-1,2,4,5-tetroxacyclononane (>75%) 5 t58. Hydrogen 2 t59. Liquid oxygen 500 t60. Methyl ethyl ketone peroxide (>60%) 5 t61. Methyl isobutyl ketone peroxide (>60%) 5 t62. Peracetic acid (>60%) 5 t63. Propylene oxide 5 t64. Sodium chlorate 25 t65. Sulphur dichloride 1 t

Part C Flammable substances (unless specifically named in Parts A and B)

66. Liquefied petroleum gas, such as commercial propane and commercial butane, and 25 tany mixtures thereof, when held at a pressure >1.4 bar absolute.

67. Liquefied petroleum gas, such as commercial propane and commercial butane, and 50 tany mixture thereof, when held under refrigeration at a pressure "1.4 bar absolute.

68. Gas or any mixture of gases which is flammable in air, when held as a gas. 15 t69. A substance or any mixture of substances, which is flammable in air, when held 25 t

above its boiling point (measured at 1 bar absolute) as a liquid or as a mixture ofliquid and gas at a pressure >1.4 bar absolute.

70. A liquefied gas or any mixture of liquefied gases, which is flammable in air and 50 thas a boiling point <0°C (measured at 1 bar absolute), when held underrefrigeration or cooling at a pressure "1.4 bar absolute.

71. A liquid or any mixture of liquids not included in entries 68 to 70 above, which 10 000 thas a flash point <21°C.

(a)S.R. & O. 1937/54.(b)S.R. & O. 1947/805.(c)S.R. & O. 1919/869.(d) 1875 c.17.(e)OJ No L250, 23.9.80, p. 7.

All chemical operations produce waste either as solid wastes (including pastes, sludge anddrummed liquids), liquid effluents, or gaseous emissions (including gases, particulate solids,mists and fogs). Relevant data are summarized in Chapters 16 and 17.

Since data have been collated from a variety of sources, and tend to be presented in mixedunits, and because rapid conversion of units is an advantage in many on-site situations, conversiontables are included in Chapter 18. Finally, since safety with chemicals cannot be addressedexhaustively in a handbook, selected sources of reliable current information on chemical hazardsand their control are listed in Chapter 19.

Table 1.7 Cont’d

Hazardous substance Controlled quantity

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ACID A chemical compound whose aqueous solution turns blue litmus paper red, reacts with anddissolves certain metals to form salts, and reacts with bases to produce salts and water. They arecapable of transferring a hydrogen ion (proton) in solution.

ACUTE Describes a severe and often dangerous condition in which relatively rapid changes occur.

ACUTE TOXICITY Adverse health effects occurring within a short time period of exposure to a singledose of a chemical or as a result of multiple exposures over a short time period, e.g. 24 hours.

AEROSOL A colloidal suspension of liquid or solid particles dispersed in gas.

AFFF, AQUEOUS FILM-FORMING FOAM Fire-fighting foam which flows on burning liquid as a film,providing rapid knock-down.

ALCOHOL-RESISTANT FOAM Foam for use against fires involving liquids miscible with water, e.g.alcohol, acetone.

ANION A negatively charged atom or group of atoms, or a radical which moves to the positive pole(anode) during electrolysis.

ANOXIA Deficient supply of oxygen to tissues.

ANTIBODY A modified protein circulating in the serum of an animal, synthesized in response to aforeign molecule (antigen) that has entered the body.

ANTIGEN A foreign substance (usually a protein) that stimulates formation of antibody.

ASPHYXIA The result of a diminished supply of oxygen to the blood and tissues and interferencewith the respiratory function. Simple anoxia may be caused by ‘inert gases’, e.g. nitrogen, andsome flammable gases, e.g. methane. Toxic anoxia may be caused by certain substances, e.g.carbon monoxide and hydrogen cyanide, which interfere with the body’s ability to transfer orutilize oxygen in the tissues. Rapid unconsciousness and death can occur in either case.

ASTHMA Periodic attacks of wheezing, chest tightness and breathlessness resulting from constrictionof the airways.

ATOM The smallest unit of an element incapable of further subdivision in the course of a chemicalreaction.

ATOMIC NUMBER The number of protons in an atomic nucleus.

ATOPY Hypersensitivity where tendency to allergy is inherited.

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AUTO-IGNITION TEMPERATURE The minimum temperature required to initiate or cause self-sustainedcombustion of material in the absence of any external source of energy. (Values may changesignificantly with geometry, gas/vapour concentration, and presence of catalyst.) Any ignitionsource must be at a temperature of, or greater than, the ignition temperature of the specificsubstance.

BASE A chemical compound whose aqueous solution turns red litmus paper blue and is capableof accepting or receiving a proton from another substance. They react with acids to form salts andwater.

BATNEEC Term used in the Environmental Protection Act and other legislation. Certain pollutingprocesses are required to use the Best Available Techniques Not Entailing Excessive Cost(BATNEEC) to reduce the environmental impact of a prescribed process as far as possible.Environment Agency inspectors determine what constitutes BATNEEC for each application andare to change the definition as improved technologies or techniques become available.

BIOCHEMICAL OXYGEN DEMAND (BOD) Official term given to measure how polluting organic industrialeffluent is when it is discharged into water. This effluent is feed for bacteria which consumeoxygen, making it more difficult for plant and fish life to survive. The lower the BOD level, theless polluting the effluent.

BLACK LIST The Black List was introduced by the EC in Directive 76/464/EEC on dangeroussubstances released into water as list I. It contains substances selected mainly on the basis of theirtoxicity, persistence and accumulation in living organisms and in sediment.

BEST PRACTICABLE ENVIRONMENTAL OPTION (BPEO) Organizations may be encouraged to undertakesystematic decision processes with a view to seeking the BPEO that provides the most benefit (orleast damage) to the environment, at an acceptable cost.

BLEVE, BOILING LIQUID EXPANDING VAPOUR EXPLOSION Instantaneous release and ignition of flammablevapour upon rupture of a vessel containing flammable liquid above its atmospheric boiling point.

BLOWING AGENT Chemical liable to decomposition at low temperature to produce a large volumeof gas.

CARCINOGEN An agent (whether chemical, physical or biological) capable of increasing the incidenceof malignant neoplasms. Defined in Regulation 2 of the Control of Substances Hazardous toHealth Regulations 1999 as:

(a) any substance or preparation which if classified in accordance with the classification providedfor by Regulation 5 of the Chemicals (Hazard Information and Packaging for Supply) Regulations1994 would be in the category of danger, carcinogenic (category 1) or carcinogenic (category2) whether or not the substance or preparation would be required to be classified under thoseRegulations; or

(b) any substance or preparation:(i) listed in Schedule 1, or

(ii) arising from a process specified in Schedule 1 which is a substance hazardous to health.

CATION A positively charged atom or group of atoms, or a radical which moves to the negativepole (cathode) during electrolysis.

CHEMICAL BOND Strong forces of attraction holding atoms together in molecules or crystallinesalts.

CHLOROFLUOROCARBONS (CFCS) Organic substances containing chlorine and fluorine which were

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initially thought to be harmless and found extensive use, e.g., as propellants because they arelargely non-flammable. Some CFCs have since been found to be one of the main sources ofatmospheric ozone depletion and a greenhouse gas. Until recently they were used extensively asaerosol propellants, solvents, refrigerants and in foam making. Many countries have now agreedto eliminate CFCs as soon as possible.

CHLORINATED HYDROCARBONS Hydrocarbons containing chlorine atoms, e.g. trichloroethylene. Someof these chemicals accumulate in the food chain and do not readily degrade. Some plastics whichcontain certain chlorinated hydrocarbons release dioxins into the air, when burnt at low temperatures.

CHRONIC Occurring for a prolonged period.

CHRONIC TOXICITY Adverse health effects resulting from repeated daily exposures to a chemical fora significant period.

CLASS A FIRE A fire involving solids, normally organic, in which combustion generally occurs withthe formation of glowing embers.

CLASS A POISON (USA) A toxic gas/liquid of such a nature that a very small amount of the gas, orvapour of the liquid, in air is dangerous to life.

CLASS B FIRE A fire involving liquids or liquefiable solids.

CLASS B POISON (USA) Any substance known to be so toxic that it poses a severe health hazardduring transportation.

CLASS C FIRE A fire involving gases or liquefied gases in the form of a liquid spillage, or a liquidor gas leak.

CLASS D FIRE A fire involving metals.

CNS DEPRESSANT Substances, e.g. anaesthetics and narcotics, which depress the activity of thecentral nervous system. Symptoms following exposure include headache, dizziness, loss ofconsciousness, respiratory or cardiac depression, death.

CONFINED SPACE A space which is substantially, although not always entirely, enclosed and wherethere is a reasonably foreseeable risk of serious injury from hazardous substances or conditionswithin the space or nearby. The risks may include flammable substances; oxygen deficiency orenrichment; toxic gases, fume or vapour; ingress or presence of liquids; free-flowing solids;presence of excessive heat. For the purpose of the Confined Spaces Regulations 1997 a ‘confinedspace’ means any place, including any chamber, tank, vat, silo, pit, trench, pipe, sewer, flue, wellor other similar space in which, by virtue of its enclosed nature, there arises a reasonably foreseeablespecified risk.

CONTACT DERMATITIS Inflammation of the skin due to exposure to a substance that attacks itssurface.

CONTROLLED WASTE All household, industrial or commercial waste of any quantity or description.

CORROSIVE A substance that chemically attacks a material with which it has contact (body cells,materials of construction).

COSHH (CONTROL OF SUBSTANCES HAZARDOUS TO HEALTH) The Control of Substances Hazardous toHealth Regulations 1999 establish the responsibilities of employers with regard to all substanceswhich pose a health hazard in the workplace.

CRYOGEN A substance used to obtain temperatures far below freezing point of water, e.g. < – 78°C.

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CVCE (CONFINED VAPOUR CLOUD EXPLOSION) Explosion of a gas or vapour which is initially ‘confined’within a vessel, building, piping, etc.

DANGEROUS SUBSTANCES (UK) Defined substances which may be hazardous to the fire services in anemergency. (Dangerous Substances (Notification and Marking of Sites) Regulations 1990.)

Defined substances over which control is exercised for conveyance in all road tankers orin tank containers >3 m3 capacity. (The Carriage of Dangerous Goods by Road Regulations1996.)

Defined substances covered by a comprehensive system to inform consumers of potentialdangers and to reduce the hazard when carried by road. The Chemical (Hazard Information andPackaging for Supply Regulations 1994).

Defined substances, including all toxic gases, all flammable gases, asbestos and most hazardouswastes, for which carriage in packages or in bulk is controlled. (The Carriage of DangerousGoods by Road Regulations 1996).

DETONATION Explosion in which the flamefront advances at more than supersonic velocity.

DISCHARGE CONSENTS Permission to discharge trade effluent directly into controlled waters is givenby the National Rivers Authority in the form of a discharge consent which will specify amountsand conditions. Discharges to public sewers are controlled by discharge consents by one of the tenWater Service Companies.

DUST Solid particles generated by mechanical action, present as airborne contaminant (e.g. <75µm in size).

DUTY OF CARE The concept of the duty of care for waste is set out in Section 34 of the EnvironmentalProtection Act (1990) which states that it is the duty of any person who imports, produces, carries,keeps, treats or disposes of controlled waste to keep that waste properly under control.

ECOTOXICOLOGY The study of toxic effects of chemical and physical agents on living organisms aswell as human beings, especially on populations and communities within defined ecosystems.

ENDOTHERMIC REACTION A chemical reaction resulting in absorption of heat.

ENVIRONMENT AGENCY The Environment Agency provides a comprehensive approach to the protectionand management of the environment by combining the regulation of land, air and water. Itscreation is a major and positive step, merging the expertise of the National Rivers Authority, HerMajesty’s Inspectorate of Pollution, the Waste Regulation Authorities and several smaller unitsfrom the Department of the Environment.

EPIDEMIOLOGY The study in populations of health factors affecting the occurrence and resolutionof disease and other health-related conditions.

ERYTHEMA Reddening of skin, inflammation.

EXOTHERMIC REACTION A chemical reaction in which heat is released and, unless temperature iscontrolled, may lead to runaway conditions.

FIBROSIS Scarring, usually of lung tissue.

FIRE POINT The minimum temperature at which a mixture of gas/vapour and air continues to burnin an open container when ignited. The value is generally above the flash point.

FLAMMABLE RANGE The concentrations of flammable gas or vapour between the LEL and UEL ata given temperature.

FLASH POINT The lowest temperature required to raise the vapour pressure of a liquid such that

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vapour concentration in air near the surface of the liquid is within the flammable range, and assuch the air/vapour mixture will ignite in the presence of a suitable ignition source, usually aflame. (Open cup values are approximately 5.5° to 8.3°C higher than the closed cup values.)

FOG (MISTS) Liquid aerosols formed either by condensation of a liquid on particulate nodes in airor by uptake of liquid by hygroscopic particles.

FUME Airborne solid particles (usually <0.1µm) that have condensed from the vapour state.

HAZARD The inherent property of a substance capable of causing harm (e.g. toxicity, radioactivity,flammability, explosivity, reactivity, instability). In a broader context anything that can causeharm, e.g. electricity, oxygen-deficiency, machinery, extreme temperature.

HAZARDOUS WASTE An unofficial class of industrial wastes which have to be disposed of withparticular care. In the UK the closest definition is for ‘special wastes’. Certain toxic organicwastes, such as PCBs, have to be burned in high-temperature incinerators.

HEAVY METALS A group of metals which are sometimes toxic and can be dangerous in highconcentrations. The main heavy metals covered by legislation are cadmium, lead, and mercury.Industrial activities such as smelting, rubbish burning, waste disposal and adding lead to petrolincrease the amount of toxic heavy metals in the environment.

HUMIDIFIER FEVER A flu-like illness caused by inhalation of fine droplets of water from humidifiersthat have become contaminated.

HYDROCARBONS Organic compounds that contain only hydrogen and carbon. The major sources ofhydrocarbons in the atmosphere are vehicle emissions (unburned fuel) and gas leaks. Contributesto acid rain.


INERTING Depression of the flammable limits of a flammable gas/vapour–air mixture by theaddition of an inert gas, e.g. nitrogen, carbon dioxide, or similar mixtures, to render it non-flammable.

ION An isolated electron or positron, or an atom or molecule, which by loss or gain of one or moreelectrons has acquired a net electric charge.

IONIZING RADIATION The transfer of energy in the form of particles or electromagnetic waves of awavelength of 100 nanometers or less or a frequency of 3 ! 1015 hertz or more capable ofproducing ions directly or indirectly.

ISOTOPE One of two or more atoms having the same atomic number but different massnumber.

IPC (INTEGRATED POLLUTION CONTROL) Under this new integrated approach to pollution control land,water and air are to be treated collectively rather than as separate environmental media. Industriesare given consents to pollute with the effect on all three media being taken into consideration. IPCwas introduced by the Environmental Protection Act (1990) and an EC system of IntegratedPollution, Prevention and Control is being introduced.

JET FIRE Fuel burning as a flame when flammable gas or vapour issues from a pipe, or otherorifice, and burns on the orifice.

KINETICS The branch of physical chemistry concerned with measuring and studying the rates andmechanisms of chemical reactions.

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LANDFILL Disposal of waste in the ground. This method is commonly used for both domesticwaste and more hazardous chemical waste. Landfill sites used for difficult and potentially-dangerouswastes are now engineered, managed and monitored to prevent poisons leaking out.

LC50 The calculated concentration of a substance that causes death in 50% of a test populationunder prescribed conditions in a prescribed period of time (normally expressed as ppm or mg/m3

for gases, mg/1 for liquids).

LD50 The calculated dose of chemical (mg per kg body weight) causing death in 50% of testpopulation. (The species of animal, route of administration, any vehicle used to dissolve orsuspend the material, and the time period of exposure should be reported.)

LEACHATE Liquid that leaks from waste disposal sites. (In a broader sense liquid, e.g. solution,removed from a solid by a solvent, such as water.)

LEGIONNAIRES’ DISEASE Infection caused by inhaling a fine spray of airborne water carrying Legionellapneumophila bacteria.

LEL (LOWER EXPLOSIVE, OR FLAMMABLE, LIMIT) The minimum concentration of a gas, vapour, mistor dust in air at a given pressure and temperature that will propagate a flame when exposed toan efficient ignition source. Generally expressed as % by volume for gases and vapours, and asmg/m3 for mists or dusts.

LPG (LIQUEFIED PETROLEUM GAS) Petroleum gas stored or processed as a liquid in equilibrium withvapour by refrigeration or pressurization. The two LPGs in general use are commercial propaneand commercial butane supplied to product specifications, e.g. BS 4250. (These, or mixturesthereof, comprise LPG for the purpose of the Highly Flammable Liquids and Liquefied PetroleumGas Regulations 1972.)

MAJOR ACCIDENT An occurrence (including in particular, a major emission, fire or explosion) resultingfrom uncontrolled developments in the course of operation of any establishment and leading toserious danger to human health or the environment, and involving one or more dangerous substances.Requirements with respect to the control of major accident hazards involving dangerous substancesapply to defined establishments under the Control of Major Accident Hazards Regulations 1999.

MASS NUMBER The sum of the number of protons and neutrons in the nucleus of an atom.

MEL, MAXIMUM EXPOSURE LIMIT (UK) The maximum concentration of an airborne substance (averagedover a reference period) to which employees may be exposed by inhalation under any circ*mstances.(Listed in ‘Occupational exposure limits’, EH40/–HSE.)

METAL FUME FEVER Non-specific, self-limiting illness resembling an attack of influenza causedmainly by exposure to fumes of zinc, copper, or magnesium and less frequently due to exposureto other metal fumes. Exposures occur from molten metals, e.g. in smelting, galvanizing, welding.

METALWORKING FLUID Fluid applied to a tool and workpiece to cool, lubricate, carry away particlesof waste and provide corrosion protection. Generally comprising neat mineral oils, or water-basedmaterials, or a mixture of the two. Fluids may also contain emulsifiers, stabilizers, biocides,corrosion inhibitors, fragrances and extreme pressure additives.

MINERAL OIL Oil derived from petroleum. Includes a wide range of hydrocarbons from light oils,kerosene and gas oils, to the heavier fuel and lubricating oils.

MOLECULES Groups of atoms held together by strong chemical forces and forming the smallestunit of a compound. The atoms may be identical, e.g. H2 or different, e.g. H2O.

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MULTIPLE CHEMICAL SENSITIVITY An acquired disorder characterized by recurrent symptoms, referableto multiple organ systems, occurring in response to many chemically-unrelated compounds atdoses far below those established in the general population to cause harmful effects. No singlewidely accepted test of physiologic function can be shown to correlate with symptoms.

MUTAGEN A chemical or physical agent that can cause a change (mutation) in the genetic materialof a living cell.

NARCOSIS Drowsiness or sleepiness.

NATURAL GAS Flammable gas consisting essentially of methane with very minor proportions ofother gases. Flammable limits approximately 5–15%. Odourized for commercial distributionwithin the UK.

NRA (NATIONAL RIVERS AUTHORITY) The National Rivers Authority were the body responsible for themanagement of water resources and the control of water pollution in England and Wales. They arenow part of the Environment Agency.

ODOUR THRESHOLD The minimum concentration of a substance at which the majority of testsubjects can detect and identify the substance’s characteristic odour.

OES, OCCUPATIONAL EXPOSURE STANDARD (UK) The concentration of an airborne substance (averagedover a reference period) at which, according to current knowledge, there is no evidence that it islikely to be injurious to employees if they are exposed by inhalation, day after day. (Specified byHSC in Guidance Note EH40.)

OXIDIZING AGENT Compound that gives up oxygen easily or removes hydrogen from anothercompound. It may comprise a gas, e.g. oxygen, chlorine, fluorine, or a chemical which releasesoxygen, e.g. a nitrate or perchlorate. A compound that attracts electrons.

OXYGEN DEFICIENCY Depletion of oxygen content in an atmosphere to below the normal 21%.Exposure to <18% must not be permitted. Concentrations 6% to 10% oxygen can lead to loss ofconsciousness.

OXYGEN ENRICHMENT Increase in oxygen content of air to above the normal 21%. Enrichmentwithin a room to >25% can promote or accelerate combustion.

OZONE A reactive form of oxygen the molecule of which contains 3 atoms of oxygen. In the ozonelayer it protects the earth by filtering out ultra-violet rays. At ground level, as a constituent ofphotochemical smog, it is an irritant and can cause breathing difficulties.

OZONE LAYER A thin layer of ozone that lies about 25 kilometres above the earth in the stratosphere.Forms a protective screen against harmful radiation by filtering out ultra-violet rays from the sun.

PARAOCCUPATIONAL EXPOSURE Exposure of workers to an airborne contaminant from a nearbyprocess or operation not forming part of their jobs. Also termed ‘neighbourhood exposure’.

PCBS (POLYCHLORINATED BIPHENYLS) Toxic synthetic chemicals with excellent heat resistance andlow electrical conductivity properties. Now little used but considerable quantities remain in oldelectrical equipment. Produces dioxins and polychlorinated dibenzo-furans when burned below1200°C. PCBs are toxic and bio-accumulative.

PERCUTANEOUS ABSORPTION Absorption via the skin, e.g. due to local contamination or a splash ofchemical.

PERMIT-TO-WORK A document needed when the safeguards provided in normal production are

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unavailable and the manner in which a job is done is critical to safety. Identifies conditionsrequired for safe operation.

PNEUMOCONIOSIS A group of lung diseases of a chronic fibrotic character due to the inhalation andretention in the lungs of a variety of industrial dusts. The main diseases are asbestosis, silicosis,coalworkers’ pneumoconiosis and mixed-dust pneumoconiosis; less common pneumoconiosesare associated with talc, clay or aluminium.

POOL FIRE A fire involving a flammable liquid spillage onto ground or onto water, or within astorage tank or trench. The pool size depends upon the scale and local topography. Fire engulfmentand radiant heat pose the main risks.

PRACTICABLE Capable of being done in the light of current knowledge and invention.

PRESCRIBED DISEASE A disease prescribed for the purpose of payment of disablement benefit underthe Social Security Act 1975 and the Social Security (Industrial Injuries) (Prescribed Diseases)Regulations 1985 and subsequent amendments. (Conditions due to physical agents, biologicalagents and miscellaneous conditions are classified in addition to conditions due to chemicalagents.)

PRESCRIBED PROCESS Industrial process which requires an official authorization because of thelikelihood of causing pollution under the provisions of the Environmental Protection Act (1990).

PRESCRIBED SUBSTANCE A substance controlled by Section I of the Environmental Protection Act(1990) because of its potential to pollute. Different substances are prescribed for release todifferent environmental media.

PRESSURE SYSTEM Defined in the Pressure System Safety Regulations 2000 as a system containingone or more pressure vessels of rigid construction, any associated pipework and protective devices;the pipework with its protective devices to which a transportable gas container is, or is intendedto be, connected; or a pipeline and its protective devices which contains or is liable to contain arelevant fluid, but does not include a transportable gas container. Here ‘relevant fluid’ is steam;any fluid or mixture of fluids which is at a pressure of >0.5 bar above atmospheric pressure, andwhich fluid or a mixture of fluids is a gas, or a liquid which would have a vapour pressure of >0.5bar above atmospheric pressure when in equilibrium with its vapour at either the actual temperatureof the liquid or 17.5oC; or a gas dissolved under pressure in a solvent contained in a poroussubstance at ambient temperature and which could be released from the solvent with the applicationof heat.

PULMONARY OEDEMA Production of watery fluid in the lungs.

PYROPHORIC SUBSTANCE A material that undergoes such vigorous oxidation or hydrolysis (oftenwith evolution of highly-flammable gases) when exposed to atmospheric oxygen or to water, thatit rapidly ignites without an external source of ignition. This is a special case of spontaneouscombustion.

REASONABLY PRACTICABLE The implication that the quantum of risk is balanced against the sacrificeor cost in terms of money, time and trouble necessary to avert that risk. If the risk outweighs thesacrifice or cost, additional precautions are necessary.

RECYCLING The use of materials, usually after further processing, which otherwise would bethrown away. Becoming common practice in industry, especially with expensive commoditiessuch as chemical solvents although many products require a commercial subsidy in order to makerecycling viable.

RED LIST The Red List was drawn up by the UK Government in 1989 in response to international

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conferences of the states bordering the North Sea. The aim was to reduce inputs of Red Listsubstances by 50% by 1995, from 1985 levels. All those substances listed on the Red List areincluded on the EC Black List.

Authorizations to discharge Red List substances are dealt with by the Environment Agencyunder Integrated Pollution Control (IPC).

REDUCING AGENT A material that adds hydrogen to an element or compound; a material that addsan electron to an element or compound.

REPORTABLE DISEASE (UK) A disease which must be reported to the authorities when linked tospecified types of work. (The Reporting of Injuries Diseases and Dangerous Occurrences Regulations1995.)

RESPIRABLE DUST That fraction of total inhalable dust which penetrates to the gas exchange regionof the lung (usually considered to be in the range 0.5 µm–7 µm).

RESPIRATORY SENSITIZER (ASTHMAGEN) A substance which can cause an individual’s respiratorysystem to develop a condition which makes it ‘over-react’ if the substance is inhaled again. Suchan individual is ‘sensitized’; over-reaction is then likely to occur at concentrations of the substancewhich have no effect on unsensitized persons and lead to characteristic symptoms, e.g. rhinitis (arunny nose), conjunctivitis or in severe cases asthma or alveolitis.

RISK The likelihood that a substance will cause harm in given circ*mstances.

SAFE SYSTEM OF WORK A formal procedure resulting from systematic examination of a task toidentify all the hazards. Defines safe methods to ensure that hazards are eliminated or riskscontrolled.

SEALED SOURCE A source containing any radioactive substance whose structure is such as toprevent, under normal conditions of use, any dispersion of radioactive substances into the environment,but it does not include any radioactive substance inside a nuclear reactor or any nuclear fuelelement.

SENSITIZATION DERMATITIS Inflammation of the skin due to an allergic reaction to a sensitizer.

SENSITIZER A substance that causes little or no reaction in a person upon initial exposure but whichwill provoke an allergic response on subsequent exposures.

SICK BUILDING SYNDROME A group of symptoms more common in workers in certain buildings andwhich are temporarily related to working in them. Symptoms include lethargy, tiredness, headache;also sore/dry eyes, dry throat, dry skin, symptoms suggestive of asthma, blocked or runny nose.Cause is multifunctional but does include agents encountered in the workplace.

SMOKE Particulate matter (usually <0.5 µm in diameter) in air resulting usually from combustion,including liquids, gases, vapours and solids.

SOLVENTS Liquids that dissolve other substances. Chemical solvents are used widely in industry:e.g. by pharmaceutical makers to extract active substances; by electronics manufacturers to washcircuit boards; by paint makers to aid drying. Solvents can cause air and water pollution and somecan be responsible for ozone depletion.

SPECIAL WASTE Controlled waste which is subject to special regulations regarding its control anddisposal because of its difficult or dangerous characteristics. The UK definition of special wasteis similar, but not identical, to the EC’s hazardous waste.

SPONTANEOUS COMBUSTION Combustion that results when materials undergo atmospheric oxidation

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at such a rate that the heat generation exceeds heat dissipation and the heat gradually builds upto a sufficient degree to cause the mass of material to inflame.

STEAM EXPLOSION Overpressure associated with the rapid expansion in volume on instantaneousconversion of water to steam.

SUBSTANCE HAZARDOUS TO HEALTH As defined in Regulation 2 of the Control of Substances Hazardousto Health Regulations 1999,

(a) a substance which is listed in Part 1 of the approved supply list as dangerous for supply withinthe meaning of the Chemicals (Hazard Information and Packaging for Supply) Regulations1994 and for which an indication of danger specified for the substance in Part V of that listis very toxic, toxic, harmful, corrosive or irritant;

(b) a substance for which the Health and Safety Commission has approved a maximum exposurelimit or an occupational exposure standard;

(c) a biological agent;(d) dust of any kind except of a substance within para. (a) or (b) above, when present at a

concentration in air equal to or greater than:(i) 10 mg/m3, as a time-weighted average over an 8-hr period, of total inhalable dust, or

(ii) 4 mg/m3, as a time-weighted average over an 8-hr period of respirable dust;(e) a substance, not covered by (a) or (b) above, which creates a hazard to the health of any

person which is comparable with the hazards created by substances mentioned in those sub-paragraphs.

SYNERGISTIC When the combined effect, e.g. of exposure to a mixture of toxic chemicals, is greaterthan the sum of the individual effects.

SYSTEMIC POISONS Substances which cause injury at sites other than, or as well as, at the site ofcontact.

TERATOGEN A chemical or physical agent that can cause defects in a developing embryo or foetuswhen the pregnant female is exposed to the harmful agent.

THERMODYNAMICS The study of laws that govern the conversion of one form of energy to another.

TLV-C, THRESHOLD LIMIT VALUE – CEILING (USA) A limit for the atmospheric concentration of achemical which may not be exceeded at any time, even instantaneously in workroom air.

TLV-STEL, THRESHOLD LIMIT VALUE – SHORT TERM EXPOSURE LIMIT (USA) A maximum limit on theconcentration of a chemical in workroom air which may be reached, but not exceeded, on up tofour occasions during a day for a maximum of 15 minutes each time with each maximumexposure separated by at least one hour.

TLV-TWA, THRESHOLD LIMIT VALUE – TIME WEIGHTED AVERAGE (USA) A limit for the atmosphericconcentration of a chemical, averaged over an 8-hr day, to which it is believed that most peoplecan be exposed without harm.

TOTAL INHALABLE DUST Airborne material capable of entering the nose and mouth during breathingand hence available for deposition in the respiratory tract.

TOXIC WASTE Poisonous waste, usually certain organic chemicals such as chlorinated solvents.

TRADE EFFLUENT Any waste water released from an industrial process or trade premises with theexception of domestic sewage.

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UEL, UPPER EXPLOSIVE (OR FLAMMABLE) LIMIT The maximum concentration of gas, vapour, mist ordust in air at a given pressure and temperature in which a flame can be propagated.

UVCE (UNCONFINED VAPOUR CLOUD EXPLOSION) Explosion which may occur when a large mass offlammable vapour, normally >5 tonnes, after dispersion in air to produce a mixture within theflammable range is ignited in the open. Intense blast damage results, often causing ‘dominoeffects’, e.g. secondary fires.

VALENCY The number of potential chemical bonds that an element may form with other elements.

VOCs (VOLATILE ORGANIC COMPOUNDS) Gaseous pollutants whose sources include vehicle emissionsand solvents.

WDAs (WASTE DISPOSAL AUTHORITIES) Body responsible for planning and making arrangements forwaste disposal in their area with the waste disposal companies and for providing household wastedumps under the Environmental Protection Act 1990.

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General principles of chemistry


This chapter provides a brief insight into selected fundamental principles of matter as a backgroundto the appreciation of the hazards of chemicals.

Chemistry is the science of chemicals which studies the laws governing their formation,combination and behaviour under various conditions. Some of the key physical laws as theyinfluence chemical safety are discussed in Chapter 4.

Atoms and molecules

Chemicals are composed of atoms, discrete particles of matter incapable of further subdivision inthe course of a chemical reaction. They are the smallest units of an element. Atoms of the sameelement are identical and equal in weight. All specimens of gold have the same melting point, thesame density, and the same resistance to attack by mineral acids. Similarly, all samples of iron ofthe same history will have the same magnetism. Atoms of different elements have differentproperties and differ in weight.

Atoms are comprised of negatively charged electrons orbiting a nucleus containing positively-charged protons and electrically-neutral neutrons as described in Chapter 11. The orbits of electronsare arranged in energy shells. The first shell nearest to the nucleus can accommodate two electrons,the second shell up to eight electrons, the third 18 electrons, and the fourth 32 electrons. Thisscheme is the ‘electronic configuration’ and largely dictates the properties of chemicals. Examplesare given in Table 3.1.

Chemicals are classed as either elements or compounds. The former are substances whichcannot be split into simpler chemicals, e.g. copper. There are 90 naturally-occurring elements and17 artificially produced. In nature the atoms of some elements can exist on their own, e.g. gold,whilst in others they link with other atoms of the same element to form molecules, e.g. twohydrogen atoms combine to form a molecule of hydrogen. Atoms of different elements cancombine in simple numerical proportions 1:1, 1:2, 1:3, etc. to produce compounds, e.g. copperand oxygen combine to produce copper oxide; hydrogen and oxygen combine to produce water.Compounds are therefore chemical substances which may be broken down to produce more thanone element. Molecules are the smallest unit of a compound.

Substances such as brass, wood, sea water, and detergent formulations are mixtures of chemicals.Two samples of brass may differ in composition, colour and density. Different pieces of wood ofthe same species may differ in hardness and colour. One sample of sea water may contain moresalt and different proportions of trace compounds than another. Detergent formulations differ

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between brands. It is possible to isolate the different chemical components from mixtures byphysical means.

Periodic table

The number of protons plus neutrons in an atom is termed the mass number. The number ofprotons (which also equals the number of electrons) is the atomic number. When elements arearranged in order of their atomic numbers and then arranged in rows, with a new row starting aftereach noble gas, the scheme is termed the periodic table. A simplified version is shown in Table 3.2.

The following generalizations can be made. Period 2 elements at the top of Groups I to VIItend to be anomalous. Atomic and ionic radii decrease across a period but increase down a group.Elements in a period have similar electronic configurations and those in groups have the sameouter electronic arrangements. Elements at the top of a group tend to differ more from thesucceeding elements in the group than they do from one another. Metals are on the left of the tableand non-metals on the right. Elements such as silicon and germanium are borderline. Elementsbecome less metallic on crossing a period and more metallic on descending a group. The GroupI elements are alkali metals with reactivity increasing from top to bottom of the table. So theexothermic reaction of potassium (K) with water is more vigorous than that of lithium (Li).

Electronegativities increase across a period to a maximum with Group VII, the halogens, forwhich reactivity decreases from top to bottom of the table. Elements in Group 0 are unreactive

Table 3.1 Electronic configuration of selected elements

Element Symbol Atomic No. electrons No. electrons No. electrons No. electrons in(proton) in 1st shell in 2nd shell in 3rd shell 4th shellnumber

Hydrogen H 1 1Helium He 2 2Lithium Li 3 2 1Beryllium Be 4 2 2Boron B 5 2 3Carbon C 6 2 4Nitrogen N 7 2 5Oxygen O 8 2 6Fluorine F 9 2 7Neon Ne 10 2 8Sodium Na 11 2 8 1Magnesium Mg 12 2 8 2Aluminium Al 13 2 8 3Silicon Si 14 2 8 4Phosphorus P 15 2 8 5Sulphur S 16 2 8 6Chlorine Cl 17 2 8 7Argon Ar 18 2 8 8Potassium K 19 2 8 8 1Calcium Ca 20 2 8 8 2Scandium Sc 21 2 8 9 2Titanium Ti 22 2 8 10 2Vanadium Va 23 2 8 11 2Chromium Cr 24 2 8 13 1Manganese Mn 25 2 8 13 2

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and termed ‘inert’, or ‘noble’, gases. Elements 21–30, 39–48 and 72–80 are termed ‘transitionelements’ whilst those between 57 and 71 are termed ‘lanthanides’ or ‘rare earth’ elements, andelements 89–102 the ‘actinides’.


Atoms combine to form molecules or compounds by linking together using chemical bonds. Thenumber of bonds that elements are able to produce is termed their valency. Chemical changes aremost conveniently represented by use of symbols and formulae in chemical equations. Atoms ofeach element are represented by a symbol. The chemical formula of a compound is merely acomposite of its constituent atoms together with numerical indications of the ratio of the combiningelements. If a number of atoms of one kind are present in a molecule the number is indicated bya subscript. So carbon dioxide is CO2, ammonia NH3, nitric acid HNO3 and ammonium nitrate isNH4NO3.

Chemical equations are used to describe reactions between compounds. The formulae of thereactants are written on the left-hand side of the equation and the formulae of the products on theright. If a number of molecules of one kind take part in the reaction the number is written as acoefficient in front of the formulae. The two sides of the equation must balance.

To illustrate, both hydrogen and chlorine have a valency of one. Elemental hydrogen consistsof two hydrogen atoms linked to form a molecule of hydrogen written as H2. Elemental chlorinecomprises molecules of two atoms, Cl2. One molecule of hydrogen can react with one moleculeof chlorine to produce two molecules of hydrogen chloride:

H2 + Cl2 = 2HCl

Table 3.2 Periodic table of the elements

Group I II III IV V VI VII 0Period1 H He

1 2

2 Li Be B C N O F Ne3 4 5 6 7 8 9 10

3 Na Mg Al Si P S Cl Ar11 12 Transition elements 13 14 15 16 17 18

4 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

5 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54

6 Cs Ba * Hf Ta W Re Os Ir Pt Au Hg TI Pb Bi Po At Rn55 56 57–71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86

7 Fr Ra **87 88 89–102

*Lanthanide La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Luseries 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71

**Actinide Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No series 89 90 91 92 93 94 95 96 97 98 99 100 101 102

6 744444444 844444444


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Oxygen has a valency of two, nitrogen three and carbon four. Thus, elemental oxygen consists ofmolecules comprising two oxygen atoms. Because of their valencies, oxygen and hydrogen willco-react in a ratio of 1:2 respectively, i.e. one molecule of oxygen reacts with two molecules ofhydrogen to form two molecules of water:

2H2 + O2 = 2H2O

Whereas some atoms have only one valency, others have several, e.g. sulphur has valencies oftwo, four and six and can form compounds as diverse as hydrogen sulphide, H2S (valency two),sulphur dioxide, SO2 (valency four) and sulphur hexafluoride, SF6 (valency six). Clearly somecompounds comprise more than two different elements. Thus hydrogen, sulphur and oxygen cancombine to produce sulphuric acid, H2SO4. From the structure it can be seen that hydrogenmaintains its valency of one, oxygen two and sulphur is in a six valency state.





Chemical bonds

Chemical bonds are strong forces of attraction which hold atoms together in a molecule. There aretwo main types of chemical bonds, viz. covalent and ionic bonds. In both cases there is a shift inthe distribution of electrons such that the atoms in the molecule adopt the electronic configurationof inert gases.

Ionic bonds are formed by the transfer of electrons between atoms. For example, calcium hastwo outer electrons, whilst chlorine has seven. By transfer of its two outer electrons, one to eachchlorine atom, the calcium atom becomes doubly positively charged (a cation), Ca++, and has thestable configuration of inert argon. The chlorine atoms each having gained an electron becomenegatively charged (an anion), 2Cl–, also with the stable configuration of argon. The negatively-charged chlorine atoms then become electrostatically attracted to the positively charged calciumion to form calcium chloride, CaCl2.

Covalent bonds form when non-metallic atoms combine by sharing, rather than transferring,electrons. This is achieved by overlapping of their electronic shells. The overlapping regionattracts both atomic nuclei and bonds the atoms. For example, hydrogen atoms have one electron.In the hydrogen molecule each atom contributes one electron to the bond thereby allowing eachhydrogen atom control of two electrons giving it the electron configuration of the inert gashelium. In a water molecule, the oxygen atom, with six outer electrons, gains control of an extratwo electrons supplied by two atoms of hydrogen and gives it the configuration of the inert gasneon.

Bonds may also be broken symmetrically such that each atom retains one electron of the pairthat formed the covalent bond. This odd electron is not paired like all the other electrons of theatom, i.e. it does not have a partner of opposite spin. Atoms possessing odd unpaired electrons aretermed ‘free radicals’ and are indicated by a dot alongside the atomic or molecular structure. Thechlorination of methane (see later) to produce methyl chloride (CH3Cl) is a typical free-radicalreaction:

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UV lightCl2 = 2Cl• (Chlorine free radicals)

Cl• + CH4 = HCl + CH3• (Methyl free radicals)

CH3• + Cl2 = CH3Cl + Cl•

When many molecules combine the macromolecule is termed a polymer. Polymerization can beinitiated by ionic or free-radical mechanisms to produce molecules of very high molecular weight.Examples are the formation of PVC (polyvinyl chloride) from vinyl chloride (the monomer),polyethylene from ethylene, or SBR synthetic rubber from styrene and butadiene.


+ CH==CH|Cl

+ CH==CH|Cl

= (—CH—CH —)|Cl

2 2 2 2 n

Vinyl chloride Polyvinyl chloride

Hydrogen bound covalently to nitrogen, oxygen or fluorine may bond with another atom of oneof these elements by a unique linkage known as the ‘hydrogen bond’. Since the hydrogen nucleuscannot control more than two electrons this is not a covalent bond but a powerful dipole–dipoleinteraction, traditionally indicated by dotted lines. It occurs in water, hydrofluoric acid, undissociatedammonium hydroxide and many hydrates, e.g.:

Hydrogen bonding accounts for the abnormally high boiling points of, e.g., water, hydrogenfluoride, ammonia, and many organic compounds (see later) such as alcohols.


Processes which involve oxygen as reactant are termed oxidation reactions. Some are beneficial,e.g. the burning of fuels in the body to produce energy, the manufacture of chemical intermediates,e.g. cyclohexanone in the manufacture of nylon. Some are detrimental such as the oxidation offood to make it rancid: anti-oxidants are added to retard this. Compounds that give up oxygeneasily or remove hydrogen from another compound are classed as oxidizing agents. They maycomprise a gas, e.g. oxygen, chlorine, fluorine, or a chemical which releases oxygen, e.g. a nitrateor perchlorate. Thus copper becomes oxidized when it reacts with oxygen to form copper oxide:

2Cu + O2 = 2CuO

Reactions which involve the use of hydrogen as a reactant are termed reductions, e.g. the additionof a molecule of hydrogen across the unsaturated C==C in olefins to produce saturated alkanes.The material which adds hydrogen, or removes oxygen, is termed the reducing agent.

Clearly oxidation and reduction always occur together. The oxidation of copper by oxygen isaccompanied by reduction of the oxygen to copper oxide. Similarly, whilst metal oxides such asCuO, HgO, SnO and PbO are reduced to the metal by hydrogen the latter becomes oxidized towater during the process:

CuO + H2 = Cu + H2O

The reactions are therefore termed redox reactions. Redox reactions can also be explained at the


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Cl2(aq) + 2I– (aq) = 2Cl– (aq) + I2



Physical state

Chemicals exist as gases, liquids or solids. Solids have definite shapes and volume and are heldtogether by strong intermolecular and interatomic forces. For many substances, these forces arestrong enough to maintain the atoms in definite ordered arrays, called crystals. Solids with littleor no crystal structure are termed amorphous.

Gases have weaker attractive forces between individual molecules and therefore diffuse rapidlyand assume the shape of their container. Molecules can be separated by vast distances unless thegas is subjected to high pressure. Their volumes are easily affected by temperature and pressure.The behaviour of any gas is dependent on only a few general laws based upon the properties ofvolume, pressure and temperature as discussed in Chapter 4.

The molecules of liquids are separated by relatively small distances so the attractive forcesbetween molecules tend to hold firm within a definite volume at fixed temperature. Molecularforces also result in the phenomenon of interfacial tension. The repulsive forces between moleculesexert a sufficiently powerful influence that volume changes caused by pressure changes can beneglected i.e. liquids are incompressible.

A useful property of liquids is their ability to dissolve gases, other liquids and solids. Thesolutions produced may be end-products, e.g. carbonated drinks, paints, disinfectants or theprocess itself may serve a useful function, e.g. pickling of metals, removal of pollutant gas fromair by absorption (Chapter 17), leaching of a constituent from bulk solid. Clearly a solution’sproperties can differ significantly from the individual constituents. Solvents are covalent compoundsin which molecules are much closer together than in a gas and the intermolecular forces aretherefore relatively strong. When the molecules of a covalent solute are physically and chemicallysimilar to those of a liquid solvent the intermolecular forces of each are the same and the soluteand solvent will usually mix readily with each other. The quantity of solute in solvent is oftenexpressed as a concentration, e.g. in grams/litre.

Important common physical properties related to these states of matter are summarized inTable 3.3.


Acids and bases (see later) are interrelated. Traditionally, acids are compounds which containhydrogen and which dissociate in water to form hydrogen ions or protons, H+, commonly written as:

electronic level. Thus, the conversion of atomic copper to the oxide produces Cu++ ions as copperatoms have lost electrons. The reduction of lead oxide by hydrogen entails removal of electronsfrom the oxide to produce neutral metallic lead. Oxidizing agents are therefore chemicals whichattract electrons, and reducing agents chemicals that add electrons to an element or compound.Using these definitions the presence of either oxygen or hydrogen is not required, e.g. sincechlorine is a stronger oxidizing agent than iodine it displaces iodine from iodides:

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HX = H+ + X–

Examples include hydrochloric acid, nitric acid, and sulphuric acid. These are strong acids whichare almost completely dissociated in water. Weak acids, such as hydrogen sulphide, are poorlydissociated producing low concentrations of hydrogen ions. Acids tend to be corrosive with asharp, sour taste and turn litmus paper red; they give distinctive colour changes with otherindicators. Acids dissolve metals such as copper and liberate hydrogen gas. They also react withcarbonates to liberate carbon dioxide:

2HCl + Cu = CuCl2 + H2

2HCl + CaCO3 = CaCl2 + CO2 + H2O

Both acids and alkalis are electrolytes. The latter when fused or dissolved in water conduct anelectric current (see page 55). Acids are considered to embrace substances capable of acceptingan electron pair. Mineral acids have wide usage as indicated by Table 3.4.


Alkalis tend to be basic compounds which dissociate in water to produce hydroxyl ions, OH–


XOH = X+ + OH–

Specifically, an alkali is a hydroxide of one of the alkali or alkaline earth metals. Examplesinclude the hydroxides of potassium, sodium, and calcium (where X is K, Na, and Ca, respectively).

Table 3.3 Important common physical properties

GasDensityCritical temperature, critical pressure (for liquefaction)Solubility in water, selected solventsOdour thresholdColourDiffusion coefficient

LiquidVapour pressure–temperature relationshipDensity; specific gravityViscosityMiscibility with water, selected solventsOdourColourCoefficient of thermal expansionInterfacial tension

SolidMelting pointDensityOdourSolubility in water, selected solventsCoefficient of thermal expansionHardness/flexibilityParticle size distribution/physical form, e.g. fine powder, flakes, granules, pellets, prills, lumpsPorosity


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The first two are very soluble in water but the last is less so. Weaker bases include ammoniumhydroxide where X is NH4. In fact every acid can generate a base by loss of a proton and thedefinition now includes any compound capable of donating electron pairs, e.g. amines. Bases turnlitmus paper blue and show characteristic effects on other indicators. They are soluble in water,tarnish in air, and in concentrated form are corrosive to the touch. Common examples are givenin Table 3.5.

Table 3.4 Industrial uses of mineral acids

Acid Main uses

Hydrochloric acid (HCl) Chemical manufacture, chlorine, food and rubber production, metal cleaning, petroleumwell activation

Nitric acid (HNO3) Ammonium nitrate production for fertilizers and explosives, miscellaneous chemicalproduction

Phosphoric acid (H3PO4) Detergent builders and water treatment, foods, metal industries

Sulphuric acid (H2SO4) Alkylation reactions, caprolactam, copper leaching, detergents, explosives, fertilizers,inorganic pigments, textiles

Hydrofluoric acid (HF) Etching glass

Table 3.5 Common bases

Base Properties

Sodium hydroxide (NaOH) White deliquescent solid. Sticks, flakes, pellets.(caustic soda) Dissolution in water is highly exothermic.

Strongly basic. Severe hazard to skin tissue

Potassium hydroxide (KOH) White deliquescent solid. Sticks, flakes, pellets.(caustic potash) Dissolution in water is highly exothermic.

Strongly basic. Severe hazard to skin tissue

Calcium hydroxide (Ca(OH)2) White powder soluble in water yielding lime water. Alkaline(slaked lime)

Ammonium hydroxide (NH4OH) Weakly alkaline. Emits ammonia gas. Severe eye irritant(aqueous ammonia solution)


The halogens comprise fluorine, chlorine, bromine and iodine. They are remarkable for theirsimilarity in chemical behaviour and for the gradation in physical properties. They are highlyreactive and form covalent links with hydrogen, carbon, silicon, nitrogen, phosphorus, sulphurand oxygen, and with other halogen atoms. The halogen atoms also produce ionic bonds withmetals. The elements tend to be toxic.

Fluorine is a greenish-yellow gas which condenses to a yellow liquid and pale yellow solid. Itis the most chemically active of all the elements.

Chlorine (see page 280) is a heavy greenish-yellow gas with a choking smell. It combinesdirectly with nearly all elements, exceptions being carbon, nitrogen and oxygen. It will reactspontaneously with phosphorus, arsenic, antimony and mercury. Most metals will react with itwhen wet or on heating. It has a powerful affinity for hydrogen and will attack hydrocarbons.

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Bromine is a dark red volatile liquid with a pungent odour. The vapour attacks the eyes andmucous membranes. It combines spontaneously and with deflagration with phosphorus, arsenicand potassium and with many other elements when warmed. It bleaches litmus and turns starchpaper orange/yellow.

Iodine is a dark grey solid which is easily vaporized to a deep blue/violet vapour. It is sparingsoluble in water but dissolves in aqueous potassium iodide to give a brown solution. It combinesdirectly with many elements.


A metal is an electropositive element. There are over 70 metals in the earth’s crust. Examplesinclude copper, gold, iron, platinum, silver and tungsten. Chemically, in solution, a metal atomreleases an electron to become a positive ion. In bulk metals are solids and tend to have highmelting and boiling points (an exception is mercury). They are lustrous, relatively dense, malleable,ductile, cohesive and highly conductive to both electricity and heat.

Metals are crystalline in structure and the individual crystals contain positive metal ions. Theouter valency electrons appear to be so loosely held that they are largely interspersed amongst thepositive ions forming an electron cloud which holds the positive ions together. The mobility ofthis electron cloud accounts for the electrical conductivity. The crystal structure also explains thehardness and mechanical strength of metals whereas the elasticity is explained by the ability ofthe atoms and ions to slide easily over each other. Metals can be blended with other metals toproduce alloys with specific properties and applications. Examples include:

• Brass (alloy of copper and zinc) used for ship’s propellers, screws, wind instruments.• Bronze (alloy of copper and tin) used for coins, medals, statues, church bells.• Duralumin (alloy of aluminium, magnesium, copper and manganese) used for structural purposes,

e.g. in aircraft construction.• Nichrome (alloy of nickel, iron and chromium) used for heating elements.• Solder (alloy of tin and lead) used for joining metals, e.g. in electrical circuits.• Stellite (alloy of cobalt, tungsten, chromium, and molybdenum) used for surgical instruments.

(Variations in physical properties occur with changes in relative proportions.)

Group I metals are good conductors of heat and electricity and are so soft that they can be cutwith a knife. As a result of their low specific gravities, Li, Na, and K float on water. They reactvigorously with electronegative elements such as O, S and Cl. Indeed the ease with which theouter electron is detached from the atom explains their highly-reactive nature. This is exemplifiedby sodium which can only be handled if air is excluded, e.g. by nitrogen blanketing, or undervacuum, or submersed in oil.

Group IIA metals include Be, Mg, Ca, Sr, Ba and Ra which are grey, moderately-hard, highmelting-point substances. Like the alkali metals they attack water to liberate hydrogen but withless vigour. The salts of the alkaline earths are generally less stable towards heat and water thanthose of alkali metals, and less water soluble.

Group IIB includes Zn, Cd and Hg. Zinc has some resemblance to magnesium but the othermetals in the group have little in common. At room temperature mercury is unaffected by air,water or non-oxidizing agents whereas zinc is more reactive, albeit tempered by a protectivehydroxide film, a property utilized in galvanizing.


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Compounds tend to be covalent. Metals form complex ions and their oxides are only weaklybasic. Mercury forms no hydride.

Aluminium is an extremely light, white metal and whilst hard is malleable and ductile. Onexposure to air the metal forms a protective oxide film which reduces its reactivity. Its compoundstend to be covalent in nature: the sulphate is hydrolysed in solution and the trichloride is volatile.

Both tin and lead from Group IV can form valency two and four compounds. Two of the fourouter electrons can behave as inert when the atoms are bivalent. Bivalent tin (stannous) derivativesare covalent whereas the nitrate and sulphate of bivalent lead (plumbous) are ionic. Some tetavalentcompounds such as the hydrides and chloride are unstable, e.g.:

PbCl4 + 2H2O = PbO2 + 4HCl

Whereas stannic oxide is neither oxidizing nor reducing, plumbic oxide is a powerful oxidizer.Tin finds widespread use because of its resistance to corrosion, or as foil or to provide protective

coats/plates for other metals. Properties of lead which make industrial application attractivesurround its soft, plastic nature permitting it to be rolled into sheets or extruded through dies. Inthe finely-divided state lead powder is pyrophoric; in bulk form the rapidly-formed protectiveoxide layer inhibits further reaction. It dissolves slowly in mineral acids. Industrial uses includeroofing material, piping, and vessel linings, e.g. for acid storage.

The transition metals Cr, Mn, Fe, Co and Ni possess bi- and trivalent states. Chromium is ahard, malleable, white metal capable of high polish and does not tarnish in air. It is used forplating steel. Together with nickel it is also used in grades of stainless steel. Manganese is a greymetal which decomposes water and dissolves in dilute acids. Its chief use is in steel to removetrace quantities of oxygen and sulphur and to produce tough steel. Iron is a white, soft, malleable,ductile magnetic metal when pure and is used mainly in steel production. It is attacked by oxygenor steam to produce an oxide, Fe3O4. When exposed to ordinary atmospheric conditions it becomescovered with rust, i.e. hydrated ferric oxide, 2Fe2O3.3H2O. Cobalt does not oxidize in air at roomtemperature but oxidizes slowly if heated to yield cobaltous oxide, CoO. It dissolves slowly inacids becoming passive in concentrated nitric acid. Nickel is silver grey, hard, malleable, capableof high polish and resistant to attack by oxygen at room temperature but yields the oxide onheating. It dissolves in dilute nitric acid but is rendered passive by the concentrated acid. It formsthe volatile, toxic tetra carbonyl with carbon monoxide.

The metals copper, silver and gold from Group IX are sometimes termed coinage metals. Theypossess characteristic metallic lustre, take high polish and resist attack by air. They are extremelymalleable and ductile and excellent conductors of heat and electricity. All are attacked by chlorine;copper alone is attacked by oxygen. None of the metals displace hydrogen from acids. Copper hasa characteristic red colour. It is used for cooking utensils and wires in telegraphs, telephones,power lines, and electrical machinery. Silver is a lustrous, white metal capable of high polish. Itis tough, malleable, ductile and an efficient conductor of heat and electricity. Whilst resistant toattack by oxygen, on exposure to air it is slowly covered with a black film of silver sulphide. Usesinclude electroplating, mirrors, silverware, and crucibles. Gold is a yellow, malleable, ductilemetal which does not tarnish in air and is inert to any mineral acid. It reacts with halogens andaqua-regia (a mixture of hydrochloric and nitric acids in the ratio of 4:1).

Oxygen and sulphur

Oxygen is the first member of Group IV with six electrons in the outer shell. It is a colourless,tasteless and odourless gas which condenses to a blue liquid and freezes to a blue solid under

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cryogenic conditions (discussed in Chapter 8). The oxygen atom exerts covalent, ionic, or co-ionic characteristics. The principle types of compounds are those in which the oxygen atom

• exerts two ionic bonds by accepting two electrons from the same or different atoms, e.g. Ca++

O–;• exerts two covalent bonds by sharing electron pairs, e.g. H2O;• exerts co-ionic character by combining with another atom which already has the inert configuration

but of which at least one pair of electrons is unshared, e.g.


P+ O–

Thus oxygen can feature in a wide variety of compounds including ozone, oxides, water,hydrogen peroxide, carbonates, nitrates/nitrites, etc. It comprises about 21% of normal air (byvolume).

Sulphur molecules are S8 and it can exist in several forms. Its compounds are more acidic thanthose of oxygen and it may assume covalency up to six. It forms a series of oxides and oxyacidsof diverse chemistry. Combustion yields mainly SO2, a cause of atmospheric pollution fromsulphur-bearing fossil fuels.

Nitrogen, phosphorus, arsenic and antimony

None of these elements from Group V form cations of the type N+++++ due to loss of all fivevalency electrons. All the elements are strongly electronegative and readily form covalent bondswith other elements.

Nitrogen is a colourless, tasteless, odourless gas which is slightly soluble in water (see alsopage 296). It is non-toxic and inert and comprises about 79% of normal air (by volume). It neitherburns nor supports combustion and at room temperature does not react with any substance. Onheating, however, it combines with oxygen to produce nitric oxide NO, with hydrogen to produceammonia NH3, and with silicon to form silane SiH4, with calcium carbide to form calciumcyanamide CaCN2 and with metals such as lithium, calcium, barium, magnesium and aluminiumto form the corresponding nitrides.

Phosphorus exists as white and red phosphorus. The former allotrope may be preserved in thedark at low temperatures but otherwise reverts to the more stable red form. The white form is awaxy, translucent, crystalline, highly-toxic solid subliming at room temperature and inflaming inair at 35°C, so it is handled under water. The red form is a reddish violet crystalline solid whichvaporizes if heated at atmospheric pressure and condenses to give white phosphorus. The redform ignites in air at 260°C. Both are insoluble in water, and white phosphorus can be storedbeneath it. Phosphorus forms a host of compounds such as phosphine, tri- and penta-halides,tri-, tetra- and penta-oxides, oxyacids including hypophosphorous, orthophosphorous andorthophosphoric acids.

Arsenic exists as grey, yellow and black forms of differing physical properties and susceptibilitiestowards atmospheric oxygen. The general chemistry is similar to that of phosphorus but whereasphosphorus is non-metallic, the common form of arsenic is metallic. Traces of arsenides may bepresent in metallic residues and drosses; these may yield highly toxic arsine, AsH3, with water.

Antimony is a bluish white metal with good lustre but poor heat conducting ability. It is stablein air and resistant to dilute acids but attacked by halogens, sulphur, phosphorus and arsenic.


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The strength of acids and bases is measured on a pH (potential of hydrogen) scale:

pH = –log10 [H+]

The hydrogen ion concentration of a normal solution of a strong acid is about 1 gram-ion per litreand that of a typical strong base is 10–14 gram-ion per litre. Because of the vast range of possibleconcentrations it is convenient to use a logarithmic scale to express the hydrogen ion concentrationof a solution. The symbol pH is used to denote the degree of acidity of a solution. Pure waterwhich dissociates slightly to produce 10–7 gram-ions of H+ per litre is taken as the standard ofneutrality. Thus water has a pH of 7. Solutions of pH less than 7 are acidic and those greater than7 are alkali. The pH of a solution can be determined electrically using a hydrogen or glass electrodeand reference electrode (e.g. calomel electrode) or by chemical indicators. The pH scale is shownin Figure 5.1.


Acids and alkalis react with each other to produce salts and water, e.g.:

HCl + NaOH = NaCl + H2O

Thus salts are compounds formed by replacement of hydrogen in an acid by a metal. Clearly non-metals can also be involved, e.g.:

NH4OH + HCl = NH4Cl + H2O

Salts are non-volatile and in the fused state or in solution conduct an electric current. Many saltsare hydrated in the solid state with water of crystallization.

These reactions are exothermic and must be carefully controlled if the reactants are concentrated,since the rates can be very rapid.

Organic chemistry

Carbon is in the same group in the periodic table as silicon, germanium, tin and lead. Theelectronic structures are characterized by the presence of four electrons in the external quantumshell. The elements, however, do not form ions of the type X++++ and compounds are covalent inthe quadrivalent state. Lead and tin may be bivalent when lead forms ionic valencies. Carbondiffers from the other elements in this group by forming an enormous range of compounds, thechemistry of which is a special discipline, organic chemistry. There are over a million knownorganic compounds, including sugar, starch, alcohol, resins and mineral oil. The versatility ofcarbon arises from:

• the stability of the compounds produced whether from electropositive elements such as hydrogen,or from electronegative elements such as oxygen or fluorine;

• the ability of carbon to covalently link with other carbon atoms with one, two or three bonds,e.g. H3C—CH3 (ethane), H2C ==CH2 (ethylene), HC !! CH (ethyne, or acetylene). These linksmay be in the form of chain or ring skeletons. Compounds comprising mainly carbon andhydrogen are termed hydrocarbons.

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Carbon–carbon groups Carbon–nitrogen groups

Carbon–oxygen groups

Carbon–sulphur groups










Acyl chloride

Fatty acid

Primary amine

Secondary amine

Tertiary amine


Nitrile (or cyanide)



Sulphonic acid






Tables 3.6 and 3.7 illustrate some of the key organic groupings. For convenience organic compoundscan be classified as either aliphatic or aromatic.

Table 3.6 Examples of aliphatic organic structures

Aliphatic compounds

Aliphatic compounds are straight chain or acyclic compounds and are characterized by additionand free-radical chemistry.


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Beta naphthylamine





Trinitro toluene(TNT)


Methyl benzene(Toluene)

Hydroxy benzene(Phenol)Benzene


Amino benzene(Aniline)


Benzoic acid


Benzene sulphonic acid




Carbon/carbon compounds


Compounds containing only carbon and hydrogen are termed paraffins or alkanes. The generalformula for these compounds is CnH2n+2 where n is an integer. When only single bonds arepresent between carbon atoms they are classified as ‘saturated’. Examples include, ethane, propane,and butane; the last two are common fuel gases:

CH4 methane (natural gas)

CH3—CH3 ethane

CH3—CH2—CH3 propane commonly used as

CH3—CH2—CH2—CH3 butane liquefied petroleum gas

Table 3.7 Selected aromatic compounds





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The alkanes are almost insoluble in water, sodium hydroxide and sulphuric acid but soluble innon-polar solvents. The liquid density increases as the size of the paraffin molecule increases buttends to level off at 0.8, i.e. all alkanes are less dense than water; therefore they will float andspread as thin films on water. The boiling points and melting points increase as the number ofcarbon atoms rises. The physical properties of cyclic aliphatic hydrocarbons resemble those of thestraight-chain counterparts, although the boiling points and densities of the cyclic compounds aresomewhat higher. The strong carbon–carbon and carbon–hydrogen bonds render paraffins relativelyunreactive and the few reactions they undergo require forcing conditions and tend to producemixtures. On heating between 400 and 600°C they can undergo thermal degradation or ‘cracking’to produce simpler alkanes, olefins and hydrogen; this can increase the flammable hazards.


When carbon atoms are linked by a double bond the compounds are called olefins. Since thesemolecules contain less than the maximum quantity of hydrogen they are termed unsaturated.Examples include ethylene, propylene, and butylene. Note that the latter can exist in severalforms:

CH2 ==CH2 ethylene

CH3CH ==CH2 propylene

CH3—CH2—CH ==CH2 1-butylene

CH3—CH ==CH—CH3 2-butylene

(CH3)2C ==CH2 iso-butylene


Their physical properties are essentially those of the alkanes. It is the unsaturated linkages thatdominate the chemistry and the main reaction is one of addition (e.g. hydrogen, halogen, andhydrogen halides) across the double bond to produce saturated compounds. This reactivity isutilized in the manufacture of long-chain polymers, e.g. polyethylene and polypropylene.


Compounds with even less hydrogen to carbon than olefins are acetylenes or alkynes as exemplifiedby:

HC !! CH acetylene

CH3C !! CH propyne

CH3CH2C !! CH 1-butyne

CH3C !! CCH3 2-butyne

Physical properties are similar to alkanes and the chemistry is dictated by the carbon triple bond.This bond is less reactive than the olefin double bond towards electrophilic reagents, but more


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reactive towards chemicals that are themselves electron rich. Some metals, e.g. copper, react toform metal acetylides. If allowed to dry out the heavy metal acetylides are prone to explode(Chapter 7).

Carbon/Halogen compounds

One or several hydrogen atoms in hydrocarbons can be substituted by halogen to produce alkylhalides. This significantly alters the toxicity, e.g. substitution of a chlorine atom in a hydrocarbonleads to an increase in the potential narcotic and anaesthetic effects. Because of the increasedmolecular weight, alkyl halides have considerably higher boiling points than the correspondinghydrocarbon. For a given alkyl group the boiling point increases with increasing atomic weightof halogen, with fluorides having the lowest boiling point and iodides the highest. Increasing thehalogen content also reduces the ease with which some compounds undergo chemical or biologicaloxidation and hence they can accumulate in the environment. Some halogenated organic substancesreact with ozone in the upper atmosphere and deplete the planet of this gas which provides aprotective shield against harmful ultra-violet light.

Some alkyl halides are toxic, e.g. trichloromethane or chloroform (CHCl3) and tetrachloromethaneor carbon tetrachloride (CCl4). Progressive chlorination of hydrocarbons gives liquids and/orsolids of increasing non-flammability, density, viscosity, solvent power and decreasing specificheat, dielectric constant and water solubility. So perchloroethylene, CCl2 ==CCl2, is a commondry-cleaning solvent and trichloroethylene, CHCl ==CCl2, is widely used in vapour degreasing ofmetal components. Despite being polarized molecules they are insoluble in water.

As with other groups, halogens can substitute hydrogen in organic compounds containingadditional functional moieties such as carboxylic acids to form acid chlorides, e.g. acetyl chlorideCH3COCl. These are reactive acidic compounds liberating hydrochloric acid on contact withwater.

Carbon/Nitrogen compounds

Of the organic compounds of sufficient basicity to turn litmus paper blue amines are the mostsignificant. These compounds have trivalent nitrogen bonded directly to carbon by single bondswith the general formula RNH2, R2NH or R3N where R is an alkyl or aryl group. The first areclassed as primary amines, the next secondary amines and the last tertiary amines. The chemistryis influenced by the number of hydrogen atoms attached to the nitrogen.

Amines, like ammonia NH3, are polar compounds and, except for tertiary amines, formintermolecular hydrogen bonds leading to higher boiling points than non-polar compounds of thesame molecular weight, but lower boiling points than alcohols or acids. The smaller molecules,containing up to about six carbon atoms, dissolve in water. Aliphatic amines are similar inbasicity to ammonia and form water-soluble salts with acids:

RNH2 + HCl = RNH3+Cl–

Nitriles, or alkyl cyanides, are compounds in which carbon is bound to nitrogen by triple bonds.They tend to be stable, neutral substances with pleasant smells and are less toxic than hydrogencyanide. The smallest compounds are water soluble liquids and all are soluble in organic solvents.

Tertiary amines can be oxidized to form amine oxides in which the amino nitrogen atom islinked to a single oxygen atom. The resulting compounds are basic dissolving in water thus:

R3N" O + H2O = [R3N—OH]+ OH–

When nitrogen linked to two oxygen atoms is bound to carbon the compounds are termed

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nitroparaffins. When pure these compounds are colourless liquids with pleasant smells. They aresparingly soluble in water and most can be distilled at atmospheric pressure. The lower membersare used as solvents for oils, fats, cellulose esters, resins, and dyes. Nitroparaffins are also usedas raw materials for the synthesis of other chemicals such as pesticides, drugs, explosives, fuels(e.g. nitromethane in drag racing fuel). Some nitroparaffins are explosive as described in Chapter 7.

Carbon/Oxygen compounds

Compounds containing oxygen linked to a carbon and a hydrogen atom are termed alcohols.Simple examples are methyl and ethyl alcohol, CH3OH and C2H5OH, respectively. Reactions ofalcohols are characterized by the replacement of either the OH hydrogen atom or the entire OHgroup:

2CH OH + 2Na = 2CH ONa + H3methyl alcohol

3sodium methoxide


CH OH + HCl = CH Cl + H O3 3methyl chloride


Compounds in which oxygen bridges two carbon atoms are termed ethers, e.g. diethyl ether,CH3CH2—O—CH2CH3. This is used as a solvent and an anaesthetic. Generally, ethers are unreactivecompounds but on standing they can react with atmospheric oxygen to produce explosive peroxides,e.g. diethyl peroxide, CH3CH2—O—O—CH2CH3.

Oxygen can link solely to carbon atoms by double bonds to form carbonyl compounds containingthe C ==O group. If the same carbonyl group is linked to another carbon the compounds areclassed as ketones, if connected to a hydrogen atom they are aldehydes, and if connected to OHgroups they are carboxylic acids. The C ==O carbon can also be bonded to other atoms such ashalogens, nitrogen and sulphur. The carbonyl group tends to dominate the chemistry of aldehydesand ketones since it can be oxidized to carboxylic acids, reduced to alcohols or undergo additionreactions. Carboxylic acids are acidic in nature, typically reacting with bases to form salts or withalcohols to produce often sweet-smelling esters:

CH CO H + NaOH = CH CO Na + H O3 2acetic acid sodium hydroxide 3 2

sodium acetate2


CH CO H + CH OH = CH CO CH + H O3 2 3 3 2 3methyl acetate


Carbon/Sulphur compounds

Since sulphur is in the same group as oxygen in the periodic table it replaces oxygen in organicstructures to produce ‘thio’ analogues such as:

R—S—H thio alcohols or alkyl thiols

R—S—R thioethers or alkyl sulphides


—SH thioacids


—SH dithioacids


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R—C—R thioketones


—H thioaldehydes

With the exception of methanethiol, which is a gas, thiols are colourless, evil-smelling liquids.Their boiling points are lower than those of the corresponding alcohols, reflecting their reducedassociation and degree of hydrogen bonding between hydrogen and sulphur. For the same reasonthiols are less water soluble than their oxygen counterparts. The chemistry of thiols resemblesthat of alcohols but they are more acidic, reflecting the stronger acidity of hydrogen sulphide overwater, of which alcohols can be regarded as alkyl derivatives. They are used as feedstocks inrubber and plastics industries and as intermediates in agricultural chemicals, pharmaceuticals,flavours and fragrances. Because they react with rubber-containing materials selection of hoseand gasket material is crucial.

Alkyl sulphides are the sulphur analogues of ethers from which they differ considerably inchemistry. They are unpleasant-smelling oils, insoluble in water but soluble in organic solvents.They tend to be comparatively inert. Mustard gas, ClCH2CH2—S—CH2CH2Cl, an oily liquidboiling at 216°C with a mustard-like smell, is highly poisonous and a vesicant, and for this reasonfound use in chemical warfare.

Alkyl sulphoxides occur widely in small concentrations in plant and animal tissues. No gaseoussulphoxides are known and they tend to be colourless, odourless, relatively unstable solids solublein water, ethyl alcohol and ether. They are freely basic, and with acids form salts of the type(R2SOH)+ X–. Because sulphoxides are highly polar their boiling points are high. Their main useis as solvents for polymerization, spinning, extractions, base-catalysed chemical reactions and forpesticides.

Thioketones and aldehydes readily polymerize to the trimer and isolation of the monomer isdifficult.

Thioacids have a most disagreeable odour and slowly decompose in air. Their boiling pointsare lower than those of the corresponding oxygen counterparts and they are less soluble in water,but soluble in most organic solvents. An important dithioacid is dithiocarbonic acid (HO—CS2H).Whilst the free acid is unknown, many derivatives have been prepared such as potassium xanthategiving a yellow precipitate of copper xanthate with copper salts:

KOH + CS + C H OH = C H O—CS K + H Opotassiumhydroxide



2 5ethyl alcohol


2 5 2 2potassium xanthate

Unlike oxygen, sulphur can exist in higher valency states and as a result can be incorporated intoorganic structures in additional ways. Examples include:

R— S||O


—R Alkyl sulphones

RSO3H Sulphonic acids

Sulphones are colourless, very stable, water-soluble solids that are generally resistant to reduction.The most important sulphones are sulpholane (1) and sulpholene (2):

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Compound 1 is used as a solvent in the food, paint, resin/plastics, soap and woodpulp/paperindustries, and as a plasticizer. Compound 2 is used as an intermediate for the manufacture ofhydraulic fluid additives and cosmetics. Sulphonal (2:2-bis(ethylsulphonyl)-propane), anotherimportant sulphone, is a colourless solid, stable to acids and alkalis, with hypnotic properties.

Sulphonic acids are water soluble, viscous liquids. Their acidity is akin to that of sulphuricacid; they form salts with bases but fail to undergo esterification with alcohols. Their propertiesvary according to the nature of R: some are prone to thermal decomposition. They are used assurfactants and in the dye industry; some have biological uses. 2-Amino-ethanesulphonic acid isthe only naturally occurring sulphonic acid.

Aromatic compounds

Aromatic compounds are benzene and its derivatives and compounds that resemble benzene intheir behaviour in a chemistry dominated by ionic substitution. Benzene has the formula C6H6commonly written as the ring:















In reality all carbon atoms share equally the pool of electrons which constitute the doublebonds and benzene resists addition across the double bonds which would otherwise destroy itsunique structure and stability. Single or multiple hydrogen atoms can be substituted to form a hostof derivatives containing similar functional groups to those above, e.g. saturated and unsaturatedaliphatic chains, amino, carboxylic acidic, halogeno, nitro, and sulphonic acid groups as shownin Table 3.6.

Aromatic compounds find wide industrial use as exemplified by Table 3.8.Benzene and alkylbenzenes possess low polarity with similar physical properties to hydrocarbons.

They are insoluble in water but soluble in non-polar solvents such as ether. They are less densethan water (Table 6.1) and boiling points rise with increasing molecular weight (ca 20–30°Cincrement for each carbon atom). Since melting point depends not only on molecular weight butalso on molecular shape, the relationship to structure is more complicated. Benzene itself is acolourless liquid boiling at 80°C and freezing at 5.4°C. It is highly flammable with a flash pointof –11°C but with a narrow flammable range of 1.4–8%. It is acutely toxic producing narcoticeffects comparable to toluene but it also poses chronic effects on bone marrow which may leadto anaemia or even leukaemia. Similar effects are not proven for pure toluene, but in the pastcommercial toluol was contaminated with benzene.


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Combustion chemistry

In biological systems the oxidation of fuels by oxygen is a fundamental reaction by which energyis created, along with by-products such as water and carbon dioxide:

3O2 + 2(—CH2—) == 2CO2 + 2H2O + ENERGY

Anything that interferes with this mechanism in humans can result in reduced well-being or evendeath. Silicosis or asbestosis may impair oxygen transport from lungs to blood. Inhaled carbonmonoxide may combine with haemoglobin and prevent it from carrying oxygen. Waste productsmay not be removed efficiently when kidney function is damaged by toxic chemicals such asmercury and phenolic substances. Fuels such as glucose may be prevented from entering cells dueto inactivation of the necessary catalytic enzymes by, e.g., toxic metals or fluoracetate.

The oxidation of fuels is common outside living systems, combustion being the extremeexample. Combustion is a chemical reaction between a fuel and usually oxygen, with the liberationof energy often as heat. A flame is produced when sufficient energy is liberated, usually in thevisible range of the spectrum though some are in the infra-red or ultra-violet region and invisible.Chemical combustion processes are initiated by heat, light, sparks, etc. As the temperature of thecombustible substance rises it reaches the ignition temperature specific to the material and to thepressure, and the combustion process begins. It spreads from the ignition source to the adjacentlayer of gaseous mixture of fuel and oxidant (usually oxygen in air). In turn the burning layerignites the next layer until equilibrium is reached between the total heat energies of reactants andproducts when the combustion process ceases. When the rate of heat lost from the mass is less

Table 3.8 Industrial uses of selected aromatic compounds

Compound Use

Aniline (amino benzene) Agrochemicals, dyes and pigments,C6H5NH2 pharmaceuticals, photographic chemicals,

polymers, rubbers

Benzene Production of ethyl benzene, cumene, cyclohexane,C6H6 maleic anhydride, nitrobenzene, chlorobenzene,


Benzene (and alkylbenzene) Detergents, phenols, dyessulphonic acidsC6H5SO3H

Benzoic acid Alkyl resins, chemical intermediate, oil drillingC6H5CO2H additive, medicines

Nitro benzene Production of aniline, para-aminophenol, and dyesC6H5NO2

Phenol (hydroxy benzene) Phenolic resins as adhesives and for the car industry,C6H5OH caprolactam

Toluene (methyl benzene) Automotive fuels additive, organic solvent, productionC6H5CH3 of benzene, styrene, and terephthalic acid

Styrene (vinyl benzene) Polymers (C8H8)n for audio and video cassettes, carpetC6H5CH==CH2 backing, domestic appliances, packaging, food

containers, furniture, toys, vehicle parts

Xylenes (di methyl benzene) Plasticizers, polymer fibres and resins, solventsC6H4(CH3)2

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than the heat liberated by the combustion process an explosion occurs. When combustion increasesprogressively such that the flame front advances supersonically, compression from the shockwavecauses an increase in temperature and self-ignition of the fuel, i.e. detonation. The requirementsfor chemicals to burn are discussed in Chapter 6.

Most organic materials will burn; the smaller molecules may be highly flammable. In thesimplest form carbon (e.g. charcoal) in the presence of a surplus of oxygen will produce carbondioxide:

C + O2 = CO2

Usually, however, fuels are hydrocarbons and the products of combustion can be complex anddepend upon the nature of the fuel, the amount of oxygen present, and the temperature. A greatdeal of energy is required to break carbon–carbon and carbon–hydrogen bonds such as the hightemperatures of flames. Once the energy barrier is surmounted the subsequent chain of eventsproceeds readily with the evolution of energy, often sufficient to keep the combustion reaction inprogress. Simple hydrocarbons in excess oxygen will produce carbon dioxide and water:

2C2H6 + 7O2 = 4CO2 + 6H2O

If nitrogen or sulphur is present in the fuel then the mixture of combustion products may includeoxides of these elements. In the absence of excess oxygen incomplete oxidation occurs to producepartially oxidized carbon compounds such as aldehydes, ketones, phenols, and carbon monoxide.Carbon monoxide is extremely toxic and some of the other compounds are respiratory irritants.

Since air comprises about 21% oxygen and 79% nitrogen, with traces of other gases, e.g. CO2,complete combustion of methane (i.e. natural gas) in air can be represented as:

CH4 + 2O2 + 8N2 = CO2 + 2H2O + 8N2

This demonstrates how the oxygen is depleted resulting, as summarized in Chapter 6, in anirrespirable atmosphere rich in nitrogen. High temperature combustion may also result in thegeneration of oxides of nitrogen, NOx, which are respiratory irritants.

Under certain conditions some inorganic materials will burn. Magnesium metal as powder orribbon when heated to its melting point in oxygen burns to produce magnesium oxide, and in airto produce a mixture of magnesium oxide and magnesium nitride. Aluminium also burns in air athigh temperatures to produce a mixture of the oxide and nitride. Dust explosion characteristics ofvarious inorganic materials are included in Table 6.1.

Some materials such as oil-impregnated cotton and iron pyrites are prone to spontaneouscombustion, whilst selected materials such as metal alkyls and metals in a finely divided stateburn on immediate contact with water or air. These are termed ‘pyrophoric’. Examples andprecautions for their control are described in Chapter 6.

Dangers arising from fires therefore include:

• Burns from heat radiation, or fire engulfment.• Asphyxiation due to consumption of oxygen until the concentration is <18%.• Poisoning from toxic combustion products. In chemical fires, particularly those involving

mixtures, an extremely complex mixture of gases and particulates, e.g. smoke may be produced.The composition depends upon the initial compounds involved, the temperatures attained andthe oxygen supply, and is hence often unpredictable. Some gaseous compounds may derivefrom thermal breakdown, i.e. pyrolysis, of the chemicals rather than oxidation as illustrated inTables 3.9 and 3.10.

• Injury from collapse of weakened structures.• Explosions (see Chapter 6).


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Chemical reactivity


Energy cannot be created or destroyed but is converted from one form to another. Thermodynamicsis the study of energy transfer during reactions and on the work done by chemical systems. Itdefines the energy required to start a reaction or the energy given out during the process. Thischange in energy is denoted #U. During chemical reactions energy may be absorbed or liberated.If this is in the form of heat, and since most reactions are performed at constant pressure, this istermed enthalpy and denoted by H. The enthalpy change (or heat of reaction) is:

#H = H2 – H1

where H1 is the enthalpy of reactants and H2 the enthalpy of the products (or heat of reaction).When H2 is less than H1 the reaction is exothermic and #H is negative, i.e. temperature

increases. When H2 is greater than H1 the reaction is endothermic and the temperature falls. Theheat of reaction is usually expressed in the equation as #H, e.g.

2H2 (gas) + O2 (gas) = 2H2O (liquid) #H (298K) = –571.6 kJmole–1

Data exist for the enthalpy of chemical reactions, formation of substances from their constituentelements, combustion, fusion, neutralization, solution, vaporization, etc.


When strips of reactive metals such as zinc are placed in water a potential difference, the electromotiveforce (emf), is set up; the metal becomes negatively charged due to the transfer of zinc ions to thesolution and the build-up of electrons on the metal. The metal strips or rods are termed the

Table 3.9 Classes of pyrolysis products produced during fires

Chemical type involved in a fire Pyrolysis product

Halogenated plastic Polyaromatic hydrocarbonsAliphaticsSubstituted benzenesHalogenated aliphaticsDioxins and furans

Non-halogenated plastics Polycyclic aromatic compoundsAliphaticsSubstituted benzenesHeavy metals

Halogenated chemicals Polycyclic aromatic hydrocarbonsAliphaticsSubstituted benzenesHalogenated aliphaticsDioxins and furans

Non-halogenated chemicals Polycyclic aromatic hydrocarbonsAliphaticsSubstituted benzenes

Metal-based pesticides Range of organicsHeavy metals

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Table 3.10 Compounds liberated from a range of materials during fires

Fire material CO HCN HCl P2O5 Isocyanate Irritants, HF PAHs NOxe.g. andacrolein HBr

Chlorine EmissionsOn-site NA NA NA NA NA NA NA NA NAOff-site

Oil refineries Emissions + – – – – ++ – +++ –(storage tanks) On-site – – – – – ++ – –

Off-site – – – – – +

Paints and Emissions +++ – ++ + ++ ++ – ++ –solvents On-site – + – ++ + – –

Off-site – – – – + – – – –

Petrol Emissions ++ – – – – ++ – + –On-site – – – – – + – –Off-site – – – – – – – – –

Phosphorus Emissions +++ – + +++ ++ ++ – ++ –On-site – + ++ ++ + – –Off-site – – – + + – – – –

Plastics Emissions +++ +++ +++ + ++ ++ + ++ ++On-site ++ – ++ ++ +Off-site – – + – + + – –

Resins and Emissions +++ ++ + – ++ ++ + ++ ++adhesives On-site + – ++ ++ +

Off-site – – – – + + – – –

Rubber Emissions +++ + + – – +++/++ – ++ +On-site + – – ++/+ –Off-site – – – – – + – – –

Upholstery Emissions +++ +++ +++ – ++ ++ + ++ ++(polyurethane) On-site ++ – ++ ++ +

Off-site – – + – + + – – –

Vegetation Emissions + – – – – + – + +(forests) On-site – – – – – + –

Off-site – – – – – – – – –

Waste tips Emissions – + + – + ++ + + +On-site – + – + +Off-site – – – – – – – – –

KeyNA Not applicable since chlorine is the main riskEmissions Total emissions during a fireOn-site Exposure of workers and emergency service personnelOff-site Exposure of the general public and the wider environment– Zero or little emission or exposure+ Likely to be some emission or exposure++ Likely to be low level emission or exposure+++ Likely to be greatest emission or exposure

electrode and the potential difference is termed the electrode potential. The latter depends uponthe identity of the metal, the temperature and the concentration of metal ions in solution. Thuscopper is less reactive than zinc so that if the two metals are immersed in water and connected bya wire electrons will flow through the external circuit from Zn (cathode) to Cu (anode). Theprocess is termed electrolysis and the arrangement by which chemical energy is converted into











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electrical energy is termed a ‘chemical’ or ‘galvanic cell’. To standardize conditions emfs aredetermined at 25°C of cells containing a molar metallic electrode (i.e. a rod of metal immersedin a solution containing 1 gram-ion of the metallic ion per litre) opposed to a molar hydrogenelectrode (i.e. a plate of platinum covered with a thin film of hydrogen to simulate a rod ofhydrogen).

The ease with which an atom gains or loses electrons is termed the electronegativity ofthe element. Tabulation of the elements in order of ease by which they lose electrons is called theelectrochemical series and is shown in Table 6.10. Chapter 4 explains the importance of this to theformation and control of corrosion, and Chapter 6 discusses the relevance to predicting reactivityof metals towards water and their potential to become pyrophoric.

Other industrial applications of electrolysis include extraction/purification of metals from ores,electroplating, and the manufacture of certain chemicals such as sodium hydroxide. In the latter,sodium chloride solution when electrolysed is converted to sodium hydroxide to produce chlorineat the anode and hydrogen at the cathode. Both of these gaseous by-products are collected forindustrial use; chlorine is used in the production of bleach and PVC; hydrogen is used as a fuel,to saturate fats, and to make ammonia.

Rates of chemical reaction

Whereas thermodynamics describes the energy requirements of a reaction, the speed at which itprogresses is termed kinetics. It is important to be able to control the rate of chemical reactionsfor commercial and safety reasons. If a reaction takes too long to progress the rate at which aproduct is manufactured would not be viable. Alternatively, if reactions progress too fast and‘runaway’ out of control there could be dangers such as explosions. The rate at which reactionstake place can be affected by the concentration of reactants, pressure, temperature, wavelengthand intensity of light, size of particles of solid reactants, or the presence of catalysts (i.e. substanceswhich alter the speed of reactions without being consumed during the reaction) or impurities.Catalysts tend to be specific to a particular reaction or family of reactions. Thus nickel is used tofacilitate hydrogenation reactions (e.g. add hydrogen to C==C double bonds) whereas platinumis used to catalyse certain oxidation reactions. Sometimes care is needed with the purity ofreactants since impurities can act as unwanted catalysts; alternatively, catalysts can be inactivatedby ‘poisoning’.

The effect of temperature on different types of reaction is shown in Figure 7.5.For reactions which progress slowly at room temperature it may be necessary to heat the

mixture or add a catalyst for the reaction to occur at an economically-viable rate. For very fastreactions the mixture may need to be cooled or solvent added to dilute the reactants and hencereduce the speed of reaction to manageable proportions. In general the speed of reaction

• doubles for every 10°C rise in temperature;• is proportional to the concentration of reactants in solution;• increases with decreased particle size for reactions involving a solid;• increases with pressure for gas phase reactions.

Chapter 4 discusses reaction kinetics further.

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Hazards from processes using chemicals are assessed on the basis of:

• Inherent chemical properties Toxic, flammable/explosive, reactive, unstable• Chemical form Liquid, solid (briquette, flake, powder), gas, vapour, air-

borne particulate (including mist, fume, froth, aerosol,dust)

• Quantity In storage, held up in process stages, in the workingatmosphere, as wastes, etc.

• Processing conditions Use of high or low temperature, high pressure, vacuumor possible hazardous reactions (polymerization,oxidation, halogenation, hydrogenation, alkylation,nitration, etc.)

Hazards can often be foreseen from basic physicochemical principles, as summarized below.

Vapour pressure

The vapour pressure of a chemical provides an indication of its volatility at any specific temperature.As an approximation, the vapour pressure p! of a pure chemical is given by

logc p! = (A/T) + B

where A and B are empirically determined constants and T is the absolute temperature.Hence the vapour pressure of a chemical will increase markedly with temperature.For a component ‘a’ in a mixture of vapours, its partial pressure pa is the pressure that would

be exerted by that component at the same temperature if present alone in the same volumetricconcentration. So with a mixture of two components, ‘a’ and ‘b’, the total pressure is

P = pa + pb

If an inert gas is also present, its pressure is additive:

P = pa + pb + pinert

In an ‘ideal mixture’ the partial pressure pa is proportional to the mole fraction ya of the componentin the gas phase:

pa = yaP

and this partial pressure is also related to the concentration in the liquid phase expressed as molefraction xa by:


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p p xa a a = !where !pa is the vapour pressure of component ‘a’ at the prevailing temperature. So, if all thecomponents are miscible in the liquid phase the total pressure P of a mixture is

P p x p x p x = + + a a b b c c! ! !As a result:

• The flash point of any flammable liquid will be lowered if it is contaminated with a morevolatile, flammable liquid.

• Application of heat to a flammable liquid (e.g. due to radiation or flame impingement in a fire,or because of ‘hot work’) can generate a flammable vapour–air mixture.

• Increase in temperature of a toxic liquid can create an excessive concentration of toxic vapourin air. This may occur as the result of an exothermic reaction.

• The pressure in the vapour space of an incompletely full, sealed vessel containing liquid cannotbe reduced by partially draining off liquid.

• The pressure in an incompletely full container of liquid will increase with temperature and can,in the extreme, result in rupture due to over-pressurization unless adequate relief is provided.(This may occur following an uncontrolled exothermic reaction.) Alternatively, partial ejectionof the contents can occur on opening.

• The composition of the vapour in equilibrium with a miscible liquid mixture at any temperature,e.g. on heating during distillation, will be enriched by the more volatile components. Thecomposition of the liquid phase produced on partial condensation will be enriched by the lessvolatile components. Such ‘fractionation’ can have implications for safety in that the flammabilityand relative toxicity of the mixtures can change significantly.

Gas–liquid solubility

For a dilute solution, the partial pressure exerted by a dissolved liquid (a solute) ‘a’ in a liquidsolvent is given by

pa = Hxa

where H is Henry’s law constant for the system and xa is the mole fraction of solute. A differentvalue of H is applicable to each gas–liquid system.As a result:

• The solubility of a gas generally decreases with any increase in temperature. So, if a solutionin a closed receptacle is heated above the filling temperature during transport or storage, lossof gas can result on opening or liquid discharge.

• With a ‘sparingly-soluble’ gas a much-higher partial pressure of that gas is in equilibrium witha solution of a given concentration than is the case with a highly soluble gas.

• Exposure of a solution to any atmosphere will lead to the take-up, or release, of gas untilequilibrium is eventually attained.

• Rapid absorption of a gas in a liquid in an inadequately-vented vessel can result in implosion,i.e. collapse inwards due to a partial vacuum.

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Liquid-to-vapour phase change

Evaporation of liquid to form vapour is accompanied by a considerable increase in volume. Forexample, at atmospheric pressure one volume of water will generate 1600 volumes of steam.Similarly 4.54 litres of gasoline will yield 0.93 m3 of neat vapour on complete vaporization. Thereverse process, condensation, is accompanied by a considerable – and often rapid – decrease involume. As a result:

• Contact of water with molten metals or salts or hot oil (above 100°C at atmospheric pressure)can result in a ‘steam explosion’, or a ‘boil-over’, with ejection of process materials. Similareffects occur with other volatile liquids.

• Evaporation of a relatively-small volume of liquid in an enclosed space can produce a flammableor toxic vapour hazard. Leakage, or spillage, of a chemical maintained as a liquid above itsatmospheric boiling point by pressure (e.g. liquefied petroleum gases) or as a liquid by refrigeration(e.g. ammonia) can result in a sizeable vapour cloud.

• Sudden cooling of a vapour-filled vessel which is sealed, or inadequately vented, may cause animplosion due to condensation to liquid.

• Cooling of vapour in a vented vessel may cause sucking-back of process materials or ingressof air.

• Vaporization in enclosed containers can produce significant pressure build-up and explosion.

In addition to volume changes the effect of temperature is also important. Thus the specificlatent heat of vaporization of a chemical is the quantity of heat, expressed as kJ/kg, required tochange unit mass of liquid to vapour with no associated change in temperature. This heat isabsorbed on vaporization so that residual liquid or the surroundings cool. Alternatively an equivalentamount of heat must be removed to bring about condensation. Thus the temperature above aliquefied gas is reduced as the liquid evaporates and the bulk liquid cools. There may be consequencesfor heat transfer media and the strength of construction materials at low temperatures.

Solid-to-liquid phase change

The phase change of a chemical from solid to liquid generally results in an expansion in volume.(Ice to water is one exception.) As a result:

• Ejection of liquid can occur from open pipelines when solid blockages are released by externalheating, e.g. by steam. (This hazard is increased if pressure is applied upstream of the constricton.)

• Melting of solid in a sealed system may exert a significant internal pressure.

Density differences of gases and vapours

As an approximation, at constant pressure,

density of a gas/vapour relative molecular massabsolute temperature"

Since few chemicals (e.g. hydrogen, methane, ammonia) have a molecular weight less than that


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of air, under ambient conditions most gases or vapours are heavier than air. For example, forcommon toxic gases refer to Table 4.1; for flammable vapours refer to Table 6.1. At constantpressure the density of a gas or vapour is, as shown, inversely proportional to the absolutetemperature. As a result:

• On release, vapours heavier than air tend to spread (i.e. to ‘slump’) at low level and willaccumulate in pits, sumps, depressions in ground, etc. This may promote a fire/explosionhazard, or a toxic hazard, or cause an oxygen-deficient atmosphere to form, depending on thechemical.

• Heavy vapour can remain in ‘empty’ vessels after draining out liquid and venting via the topwith similar associated hazards.

• On release, vapours which are less dense than air at ambient temperature may tend to spreadat low level when cold (e.g. vapour from liquid ammonia or liquefied natural gas spillages).

• Gases less dense than air may rise upwards through equipment, or buildings, and if unventedwill tend to accumulate at high level. This is an important consideration with piped natural gaswhich tends to diffuse upwards from fractured pipes, open valves or faulty appliances. Hydrogenfrom leakages in use, e.g. from cylinders (refer to Table 9.12), or from electrolytic processes,e.g. battery-charging, rapidly diffuses upwards.

• Hot gases rise by thermal lift. Hence in the open air they will disperse. Within buildings thisis a serious cause of fire escalation and toxic/asphyxiation hazards if smoke and hot gases areable to spread without restriction (or venting) to upper levels.

• A balanced flue can serve to effectively vent a combustion process in a gas-fired appliance, butmust be sound in construction and unrestricted to avoid leaks.

• Once a gas or vapour has been mixed with air, it is the mean density of the mixture which isimportant (similar considerations arise when mixing other gases). The mean density of a gasmixture is given by:

pp V p V

V Vmixtureg g a a

g a =

+ +

where Vg, Va are the volumes of gas and air, and pg, pa the densities of gas and air respectively.Clearly if Va is large relative to Vg, or if pg does not differ significantly from pa, the value ofpmixture approximates to pa. As a result:

• The density of air saturated with a chemical vapour may not differ significantly from that of airitself. Refer to Table 4.2. This is an important consideration when designing ventilation systems,i.e. both high- and low-level extract vents may be desirable.

Table 4.1 Densities of some toxic gases and vapours relative to air at 20°C

Density gas/ Relativedensity of air molecular mass

Bromine vapour 5.54 160Phosgene 3.43 99Chlorine 2.46 71Sulphur dioxide 2.22 64Acrylonitrile vapour 1.84 53Hydrogen cyanide vapour 0.94 27Hydrogen fluoride vapour 0.69 20Ammonia 0.59 17

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Density differences of liquids

The specific gravities (s.g.) of liquid chemicals vary widely, e.g. for the majority of hydrocarbonfuels s.g. <1.0 but for some natural oils and fats, chlorinated hydrocarbons, s.g. >1.0. Density isgenerally reduced by any increase in temperature. As a result:

• On heating up, thermal expansion of a liquid in sealed piping, equipment or a container mayexert sufficient hydraulic pressure to cause rupture or failure. (Hence specific filling ratios arefollowed with containers, e.g. road tankers.)

• A lighter liquid can spread over and, if immiscible, remain on top of a denser liquid. Thusliquid fuels and many organic liquids will spread on water; this may result in a hazard insumps, pits or sewerage systems and often precludes the use of water as a jet in fire-fighting.

• Stratification of immiscible liquids may occur in unagitated process or storage vessels.

Immiscible liquid–liquid systems

In a combination of two immiscible liquids, each exerts its own vapour pressure independently.The total pressure is then the sum of the vapour pressures,

P p p = + a b! !Also if a solute C is present in solvent A when it is mixed with solvent B, some transfer will occurof C to B. Eventually equilibrium will be attained between the concentrations of C in each phase.For many dilute solutions this is expressed by

y = mx

where x is the mass (or mole) fraction of C in A, y is the mass (or mole) fraction of C in B andm is the partition coefficient. In concentrated solutions the equilibria are better represented by adistribution curve. As a result of these equilibria:

• The boiling point of a mixture of immiscible liquids can be significantly lower than that ofeither chemical, so violent boiling may occur unexpectedly on mixing them whilst hot.

• Partition of solute into a second immiscible liquid (e.g. water) may result in its release if thelatter is subsequently exposed to air, e.g. in a sump or effluent drain.

• Trace contamination of an immiscible liquid can occur following accidental contact withanother liquid even if the mutual solubilities are considered insignificant.

Table 4.2 Relative densities of air saturated with selected chemicals at 25°C

Relative density of saturated air(air at 25°C)

Benzene 1.21Bromochloromethane 1.07Carbon tetrachloride 1.65Diisobutyl ketone 1.01Nitroethane 1.04Parathion 1.0


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Vapour flashing

If a liquid near its boiling point at one pressure is ‘let down’ to a reduced pressure, vapour flashingwill occur. This will cease when the liquid temperature is reduced, due to removal of the latentheat of vaporization, to a temperature below the saturation temperature at the new pressure.

As a result:

• Flashing of vapour containing entrained mist may occur on venting equipment or vesselscontaining volatile liquids. This may create a toxic or flammable hazard depending on thechemical; with steam the risk is of scalding. Rupture of equipment can produce a similar effect.

• Escapes or spillages of liquefied petroleum gas, or chlorine or ammonia, rapidly generate avapour cloud.

• Loss of containment, e.g. due to a crack or open valve, from beneath the liquid level in aliquefied gas vessel is potentially more serious than if it occurs from the gas space because themass flowrate is greater.

• Absorption of heat (auto-refrigeration) and consequent temperature reduction on flashing mayhave a serious effect on associated heat transfer media, upon the strength of materials ofconstruction, and result in frosting at the point of leakage. Exposure of personnel carries a riskof frostbite.

Effects of particle or droplet size

Airborne particulate matter may comprise liquid (aerosols, mists or fogs) or solids (dust, fumes).Refer to Figure 5.2. Some causes of dust and aerosol formation are listed in Table 4.3. In eithercase dispersion, by spraying or fragmentation, will result in a considerable increase in the surfacearea of the chemical. This increases the reactivity, e.g. to render some chemicals pyrophoric,explosive or prone to spontaneous combustion; it also increases the ease of entry into the body.The behaviour of an airborne particle depends upon its size (e.g. equivalent diameter), shape anddensity. The effect of particle diameter on terminal settling velocity is shown in Table 4.4. As aresult:

• All combustible solids can create a dust explosion hazard if dispersed in air as a fine dustwithin certain concentration limits. Refer to Table 6.2. The hazard increases with decreasingparticle size.

• Particles in the respirable size range, i.e. about 0.5–7 µm, will, once dispersed, remain airbornefor extended periods. Indeed since they are sensitive to slight air currents they may be permanentlysuspended.

• A dust cloud comprising a distribution of particle sizes soon fractionates, e.g. visible mattersettles to the ground in a few minutes. Hence the size distribution of airborne particles maydiffer significantly with time and from that of the source material. (This is particularly relevantto occupational hygiene measurements involving toxic dust emissions.)

Surface area effects in mass transfer or heterogeneous reactions

The rate of mass transfer across a phase boundary or interface can be expressed by

N = K. A (#C)m

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Table 4.3 Selected sources of dusts and aerosols

Particulate form Common sources

Dust • Crushing• Grinding• Milling• Sieving• Drying, e.g. spray, drum, fluidized bed drying• Powder mixing• Emptying bags of powder, or fines from bag filters• Powder transfer, e.g. conveyors• Brushing• Buffing

Aerosol • Droplet generation by air pressure differential across the film, e.g.bursting of liquid film in bubbles, froth across bottle mouths andpipette tips

• Formation of froth by mixing of gas and liquid in shake cultures,fermenters or test tubes

• Forceful ejection of the contents of pipettes or syringe, especially ifalready containing gas bubbles

• Vibration or twanging of hypodermic needles or platinum loops• Impact of a droplet on a liquid, e.g. from liquid falling under gravity• Separation of two moist surfaces, e.g. withdrawal of the plunger in a

syringe barrel or stopper from a tube• Centrifugal forces, e.g. escape of liquid from a centrifuge• Sizzling, e.g. when a platinum loop or inoculation tool is flamed or

plunged hot into liquid• Deliberate atomization in some humidification operations, gas

scrubbing, spray drying, spray painting• Leakage of liquids transferred under pressure, e.g. from flange joints,

pump glands• Misting during condensation (e.g. in distillations) gas absorption,

vaporizations• Use of propellants, e.g. hand-held aerosol cans• Electrolytic processes• Rapid liquid discharge from an orifice, e.g. shower heads, taps

Table 4.4 Terminal velocities of particles of different sizes

Diameter Rate of fall(µm) (m/s)

5000 91000 4500 3100 3 $ 10–1

50 75 $ 10–3

10 3 $ 10–3

5 75 $ 10–5

1 36 $ 10–6

0.5 10 $ 10–6

0.1 36 $ 10–8

(Particle density 1000 kg/m3; air at 20°C, 100 kPa.)


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where N is mass transferred/unit timeK is a mass transfer coefficientA is the interfacial area(#C)m is the mean concentration gradient, representing the deviation from equilibrium. Hence therate is directly related to coefficient K, which will generally increase with any increase in turbulencesuch as increased relative velocity between the phases or agitation; to the exposed surface area A;and to the concentration difference, whether it is a pressure or humidity differential or a solubilityrelationship. As a result:

• The rate of evolution of a toxic or flammable vapour from a liquid (e.g. in an open vessel, froma spillage or as a spray) is directly related to the exposed area. Therefore, the rate of vapourformation from solvent-impregnated rag, from solvent-based films spread over a large area,from foams or from mists can be many times greater than that from bulk liquid.

• All gas absorption processes are surface area dependent. Hence water fog may be an effectivemeans of dealing with emissions of soluble gases, e.g. ammonia or hydrogen fluoride.

• The rates of gas–solid reactions are surface area dependent, so finely-divided metals, coal etc.may be prone to oxidation leading to spontaneous combustion. A combustible dust will burnmuch more rapidly than the bulk sold, and if dispersed in air cause a dust explosion (refer toTable 6.2).

• The rates of gas–liquid reactions are surface area dependent. Hence in the spontaneous combustionof oil impregnating fibrous thermal insulation on hot equipment, oxidation is facilitated by thelarge exposed surface area and, since the dissipation of heat is restricted, the temperature canrise until the oil ignites spontaneously.

• The important factors, on exposure to chemicals that are toxic by absorption via the skin, arethe contact area and the duration of exposure (refer to Table 13.8).

Enthalpy changes on mixing of liquids

Mixing of two or more chemicals which have dissimilar molecular structures may be exothermic(liberating heat) or endothermic (absorbing heat). As a result:

• Unless controlled, the enthalpy release when some liquids are mixed may result in theirejection from equipment or, in the extreme, an explosion.

Critical temperatures of gases

Every gas has a critical temperature above which it cannot be liquefied by the application ofpressure alone. The critical pressure is that required to liquefy a gas at its critical temperature.Data for common gases are given in Table 4.5. As a consequence:

• Liquefied gases may be stored fully refrigerated, with the liquid at its bubble point at nearatmospheric pressure; fully pressurized, i.e. at ambient temperature; or semi-refrigerated withthe temperature below ambient but the vapour pressure above atmospheric pressure. Of thegases listed in Table 4.6, all those with critical temperatures below ambient must be maintainedunder refrigeration to keep them in the liquid phase.

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• If the temperature remains constant, the pressure within any cylinder containing liquefied gaswill remain constant as gas is drawn off (i.e. more liquid simply evaporates) so the quantity ofgas remaining cannot be deduced from the pressure.

Table 4.5 Critical temperature and pressure data for common gases

Critical CriticalTemperature (°C) pressure (bar)

Water (steam) 374 –Sulphur dioxide 157 219Chlorine 144 78Ammonia 132 77.7Nitrous oxide 39 –Carbon dioxide 31.1 73.1Oxygen –119 50Nitrogen –147 33.7Hydrogen –240 12.9

Table 4.6 Gases commonly stored in liquefied form

Gas Boiling point Liquid density Volume ratio gas Vapour Criticalat 1 bar abs. at boiling (1 bar abs., 20°C) pressure temperature

point to liquid at 38°C(°C) (kg/m3) (at boiling point) (bar abs.) (°C)

Can be stored without refrigerationEthylene oxide 11 883 425 2.7 195n-Butane 0 602 242 3.6 152Butadiene (1, 3) –4 650 280 4.1 152Butylene (%) –6 626 262 4.3 146Isobutane –12 595 241 5.0 135Ammonia –33 682 962 14.6 133Propane –42 582 315 13.0 97Propylene –48 614 347 15.7 92

Requires refrigerationEthane – 89 546 436 – 32Ethylene –104 568 487 – 9Methane (LNG) –162 424 637 – –82Oxygen –183 1140 860 – –119Nitrogen –196 808 696 – –147

Chemical reaction kinetics

The rate of chemical reaction is generally a function of reactant concentration and temperature.For many hom*ogeneous reactions therefore, if they are exothermic,

rate of generation " e rRT

where R is the gas constant and Tr is the absolute temperature. If the heat is removed by forcedconvection to a coolant in a jacket or coil,

rate of removal " Tr – Ta


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where Ta is the coolant temperature. Thus:

• Since the generation rate is exponential whereas the removal rate is linear, for any exothermicreaction in a specific reactor configuration a critical condition may exist, i.e. a value of Trbeyond which ‘runaway’ occurs.

• A reaction which is immeasurably slow at ambient temperature may become rapid if thetemperature is raised.

With some reactions which have a significant rate at ambient temperature, e.g. catalysed reactions,oxidations or self-polymerization of certain polymers, severe hazards may be associated with anelevation in temperature.

Exothermic reactions require control strategies which may involve temperature control, dilutionof reagents, controlled addition of one reagent, containment/venting and provision for emergencies.Refer to p. 248.

Many liquid phase or heterogeneous solid–liquid or gas–liquid reactions result in gaseous productsor byproducts. These products may be toxic (refer to Table 5.1) or flammable (refer to Table 6.1),or result in overpressurization of any sealed container or vessel. Unless pressure relief is provided,relatively small volumes of reactants – the presence of which may not be expected – may generatesufficient gas pressure to rupture a container. The causes of pressure build-up may be:

• Reactions with water, e.g. reaction of phosphorus oxychloride with water to produce gaseoushydrogen chloride:

POCl3 + H2O & H3PO4 + HCl (refer to Table 7.1)

• Electrolytic corrosion (see later).• Reaction due to contaminants, e.g. in reusable containers or in transfer pipelines.• Reaction with construction materials, e.g. nitric acid can produce nitric oxide gas on contact

with copper in pipes or copper windings in motors of canned pumps:

3Cu + 2HNO3 & 3 CuO + 2NO + H2O

• Slow decomposition of a chemical of limited stability. For example, the slow decomposition of98–100% formic acid to gaseous carbon monoxide in a full 2.5 litre bottle would produce 7 barpressure during one year at 25°C if unvented:


• Self-initiated reactions, e.g. pyruvic acid on storage can become oxidized by air (or airborneyeasts) to form sufficient gaseous carbon dioxide to overpressurize the container:

CH3COCO2H + [O] & CH3CO2H + CO2

Pyruvic acid should therefore be stored refrigerated with light and air excluded.

The precautions required can be any combination of those in Table 4.7.


Pure metals and their alloys interact gradually with the elements of a corrosive medium to formstable compounds and the resulting metal surface is considered to be ‘corroded’. The corrosionreaction comprises an anode and an electrode between which electrons flow. Table 6.10 shows the

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anodic–cathodic series, or electrochemical series, for selected metals and for hydrogen (since thedischarge of hydrogen ions takes place in most corrosion reactions). Metals above hydrogen inthe series displace hydrogen more easily than do those below it. As a general rule, when dissimilarmetals are used in contact with each other and are exposed to an electrically-conducting solution,combinations of metals should be chosen that are as close as possible to each other in the series.Coupling two metals widely separated in the series will generally produce accelerated attack onthe more active metal. Often, however, protective passive oxide films and other effects will tendto reduce galvanic corrosion. Insulating the metals from each other can prevent corrosion. Thedual action of stress and a corrodent may result in stress corrosion cracking or corrosion fatigue.

Corrosion may be uniform or be intensely localized, characterized by pitting. The mechanismscan be direct oxidation, e.g. when a metal is heated in an oxidizing environment, or electrochemical.Galvanic corrosion may evolve sufficient hydrogen to cause a hazard, due to:

• Formation of a flammable atmosphere with air in equipment or piping.• Build-up of internal pressure within a weakening container.• Production of atomic hydrogen as a species; this may penetrate metal to produce blistering or


The consumption of oxygen due to atmospheric corrosion of sealed metal tanks may cause ahazard, due to oxygen-deficiency affecting persons on entry.

Stresses may develop resulting from the increased volume of corrosion products, e.g. rustformation involves a seven-fold increase in volume.

Many salts are corrosive to common materials of construction, as demonstrated in Tables 4.8and 4.9. Corrosion may be promoted, or accelerated, by traces of contaminants.

Whereas corrosion of metals is due to chemical or substantial electrochemical attack, thedeterioration of plastics and other non-metals which are susceptible to swelling, cracking, crazing,softening etc. is essentially physicochemical rather than electrochemical.

Corrosion prevention

Corrosion prevention is achieved by correct choice of material of construction, by physical means(e.g. paints or metallic, porcelain, plastic or enamel linings or coatings) or by chemical means(e.g. alloying or coating). Some metals, e.g. aluminium, are rendered passive by the formation ofan inert protective film. Alternatively a metal to be protected may be linked electrically to a moreeasily corroded metal, e.g. magnesium, to serve as a sacrificial anode.

Some corrosion-resistant materials for concentrated aqueous solutions and acids are given inTables 4.10 and 4 .11. The resistance of some common polymers to organic solvents is summarizedin Table 4.12. The attack process is accelerated by an increase in temperature. The chemicalresistance of a range of common plastics is summarized in Table 4.13.

Table 4.7 Precautions applicable to reactions producing gaseous products or byproducts

Temperature controlAdequately sized pressure reliefElimination of contaminants, including metallic residues, from process streams and equipmentSelection of materials of construction compatible with the chemical(s) in use, properly cleaned and passivatedElimination of ingress of reactive chemicals, e.g. water, airDate labelling and inventory control in storageCleaning and inspection of reusable containers, tankers etc, before refilling


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Table 4.8 Comparison of corrosion rates by solutions of salts

Salts Corrosion rates for listed construction materials(type and examples)

Carbon 304 SS 316 SS Alloy 400 Nickel 200steel (65 Ni-32Cu)

Non-oxidizing non-halidesAlkaline (pH >10)

e.g. sodium carbonate L L L L LNeutral

e.g. sodium sulphate M L-M; SCC L-M L Lsodium nitrate L-M; SCC L; pits L, pits L L

Acide.g. nickel sulphate S L-M L-M M M; pits

Non-oxidizing halidesNeutral

e.g. sodium chloride M; pits M; SCC; pits M; SCC; pits M MAcid

e.g. zinc chloride S S; SCC; pits S; SCC; pits M Mammonium chloride S S; SCC; pits M; SCC; pits M M-S

Oxidizing non-halidesNeutral

e.g. sodium chromate L(1) L L L Lsodium nitrite L(1) L L L Lpotassium M M M M M


e.g. ferric sulphate S L L S –silver nitrate S; SCC M M S S

Oxidizing halidesAlkaline

e.g. sodium hypochlorite S S; pits S; pits M-S; pits M-S; pitsAcid

e.g. ferric chloride S; SCC S; pits S; pits S Scupric chloride S S; pits S; pits S Smercuric chloride S S; SCC; pits S; SCC; pits S; SCC S

L Low: <5 mpy, for all concentrations and temperatures <boilingM Moderate: <20 mpy, perhaps limited to lower concentrations and/or temperaturesS Severe: >50 mpy

SCC lnduces stress corrosion cracking(mpy = mils per year: 1 mil = 0.001 in = 25.4 µm)(1)Chemical acts as corrosion inhibitor if present in sufficient amounts, but may cause pitting if inlower amounts.

Force and pressure

Pressure is defined as force per unit area. (It may be expressed in a variety of units; refer toChapter 18.) So, pressure $ area = force.

As a result:

• A relatively small pressure can result in a very large force if it is applied over a large area.Inadequately vented atmospheric storage tanks may therefore rupture if, for some reason, e.g.a high inflow, they are subjected to a relatively low internal pressure. Large side-on structures,windows, etc. are particularly prone to damage from an explosion even at a significant distancefrom the epicentre.

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• High-pressure equipment, the walls of gas cylinders, etc., are subjected to very high forces.Hence metallurgical integrity is vital.

• Implosion of glass, plastic or inadequately designed metal equipment can occur under partialvacuum conditions.

Stored pressure energy

Any gas stored or transferred under pressure represents an energy source. If piping or equipmentfailure occurs, energy is given out as the gas rapidly expands down to virtually atmosphericpressure. Elastic strain energy in the walls is also given out, but, by comparison, this is relativelysmall.

For a perfect gas the energy content is:


P = ln o o


where W is the energy content (joules), V is the container volume (m3), and Po and Pa are theinternal and atmospheric pressure (Mpa), respectively. As a result:

• Pressure rupture of even a small piece of equipment may result in a serious explosion generatingmissiles travelling at high velocity. This is an important consideration when using laboratoryglassware or industrial glass equipment and pipework.

• A pressure not registered on a gauge may be sufficient to result in an accident.• Pneumatic testing of equipment should only be used when hydraulic testing is impracticable;

appropriate safeguards, e.g. pre-inspection, reduction of the internal gas space, pressure relief,and use of a blast pit or enclosure, are necessary.

• High inventories of stored pressure energy constitute a major accident hazard.

Table 4.9 Selected inorganic salts highly corrosive to carbon steel (Corrosion rate >50 mpy)

Aluminium sulphate Magnesium fluorosilicateAmmonium bifluoride Mercuric chlorideAmmonium bisulphite Nickel chlorideAmmonium bromide Nickel sulphateAmmonium persulphate Potassium bisulphateAntimony trichloride Potassium bisulphiteBeryllium chloride Potassium sulphiteCadmium chloride Silver nitrateCalcium hypochlorite Sodium aluminium sulphateCopper nitrate Sodium bisulphateCopper sulphate Sodium hypochloriteCupric chloride Sodium perchlorateCuprous chloride Sodium thiocyanateFerric chloride Stannic ammonium chlorideFerric nitrate Stannic chlorideFerrous ammonium sulphate Stannous chlorideFerrous chloride Uranyl nitrateFerrous sulphate Zinc chlorideLead nitrate Zinc fluorosilicateLithium chloride


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Table 4.10 Corrosion-resistant materials for concentrated aqueous solutions

Material Acids Alkalis Salts Organic Not recommended forsolvents

Oxidizing Reducing Organic Aqueoussolutions

Alloy C L L L R L L R R R R R R L R R Acid services >65°C,especially hydrochloricacid or acid solutionswith high chloridecontents

Tantalum V R R L R N R R N N R R R R R Hot oleum (>50°C),strong alkalis, fluoridesolutions, sulphurtrioxide

Glass/silicates R R R R R N R R L L R R R R R Strong alkalis,especially >54°C,distilled water >82°C,hydrofluoric acid, acidfluorides, hotconcentratedphosphoric acid,lithium compounds>177°C, severe shockor impact applications

Carbon, N L L – – L – – R R R R R – – Strong oxidizers, veryimpreg. with strong solventsfuranCarbon, N L L R R L R R N R R R R R R Strong alkalis, veryimpreg. with strong oxidizersphenolicFEP/TFE R R R R R R R R R R R R R R R(1) Molten alkali metals,

elemental fluorine,strong fluorinatingagents

Furan resin N N V R L N L L R R R V R R L(1) Strongly oxidizingsolutions, liquidbromine, pyridine

Phenolic resin N L V R R L L R N N R N L R L(1) Strong alkalis or alkalisalts, very strongoxidizers

Epoxy resin(2) N N V L R – L N R L R N R L L(1) Strong oxidizingconditions, very strongorganic solvents

R Recommended for full range concentrations up to boiling or to temperature limit of (non-metallic) product form.L Generally good service but limited in concentration and/or temperature.V Very limited in concentration and/or temperature for service.N Not recommended.

(1) See Table 4.12(2) Epoxy hardener will strongly affect chemical resistance.




% H








% H




% H



% H



tic a



ic a



H (












Cl 3







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Table 4.11 Construction materials for use with strong acids

Acid Construction material Important safety consideration

Acetic 316 L stainless steel Excess acetic anhydride in glacial acetic acid can acceleratecorrosion; chloride impurities (ppm levels) can cause pitting andstress-corrosion cracking

Copper/copper alloys Not for highly oxidizing conditionsAluminium alloys Sensitive to contaminants; requires very clean welding; attacked very

rapidly in concentrations near 100% or with excess acetic anhydride

Formic 304 L stainless steel For ambient temperature onlyCopper/copper alloys Not for oxidizing conditions, including air

Hydrochloric Rubber-lined steel Low tolerance for organic solvent impurities; temperature limited(natural rubber) according to hardness of rubber; steel fabrication must be properly

doneAlloy C Not for hot concentrated HClAlloy B Not for oxidizing conditions (test if reducing conditions are in doubt)Tantalum Not for fluoride impuritiesImpervious graphite FragileReinforced plastic HCl may attack or permeate laminate; temperature limited

(<65.5°C); requires excellent engineering design and fabrication quality

Hydrofluoric Alloy 400 Not for oxidizing conditions (test if in doubt)Copper Not for oxidizing conditions (test if in doubt); <65.5°C only.Cupro-nickel Not for oxidizing conditions (test if in doubt); concentration and

temperature slightly limitedCarbon steel Not below 60% concentration, depending on impuritiesImpervious graphite Fragile; limit to below 60% concentrationPolyvinylidene fluoride –

Nitric 304 L stainless steel Must use low-carbon (or stabilized grade) if welded; not for fumingacid concentrations above 65.5°C

High-silicon iron Casting only; limited shock resistance; only for concentrations above45% if temperatures over 71°C

Aluminium (e.g. 3003, Mostly for over 95% concentration, not for below 85%5052) concentration; requires very clean welding.Titanium May ignite in red-fuming nitric acid if water is below 1.5% and

nitrogen dioxide is above 2.5%

Oleum Carbon steel Not for 100–101% H2SO4 concentration; limited in temperatureGlass-lined steel Limited shock resistance

Phosphoric 316 L stainless steel Must use low-carbon or stabilized grade if welded, up to 85%concentration and 93°C

Sulphuric Carbon steel Not for below 70% concentration; ambient temperatures only; flowvelocities below 0.6 to 1.2 m/s

Alloy 20 variations Limited temperature at 65–75% concentrationHigh-silicon iron Castings only; limited shock resistanceChemical lead Soft and suffers from erosion; creeps at room temperature; limit to

below 90% concentrationGlass Limited shock resistanceAlloy C Better for reducing acid strengths (<60% concentration)Rubber-lined steel For dilute not concentrated (oxidizing) strengths; temperature limited

according to rubber hardness and acid concentration; steelfabrication must be properly done

Brick linings with Absorption of the corrosive by the masonry (use membranesilicate mortar substrate); poor properties in tension or shear (use in compression);

many brick linings ‘grow’ in service but if used in archlike contours,growth merely increases compression


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Table 4.12 Solvent resistance of polymers

Solvent Example Thermosetting resins Thermoplastics Elastomers

Alcohols Methanol G E G G G E P E E E E E E GAldehydes Formaldehyde G E G G G E E G E G G G G EAliphatics Heptane G E E G E E G P G G E P P GAliphatic amines Diethylamine G E P P P E P G G – G – – –Aromatics (and derivatives) Benzene E G G P P E G P G P G P P P

Aniline P G G P P E P G E P G G P PPhenol G G G F P E P G G P G P P PXylene G E E G G E G P F P G P P P

Chlorinated aliphatics Trichloroethylene G G E G P E G P P P E P P PEthylene chloride G G G P P E – P F P E P P P

Ketones Acetone G G P G G E G P G P P G P PMiscellaneous:

Pyridine P P P P P E F F E P F P P PTetrahydrofuran Aromatics – P – P – E F P F P F P P PFurfural G E P G P E – P P P F – – –

E Recommended to maximum temperature of product form.G Recommendation limited to somewhat lower temperature, or restricted in product from.F Very limited recommendation; for ambient temperature only.P Not recommended. Severe attack.

(Temperatures are approximate maxima.)


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Expansion and contraction of solids

Hazardous situations can develop with changes in volume with temperature. The effect of temperatureon gases and liquids is mentioned on pages 45 and 65, respectively.

The thermal expansion and contraction of solids can also have safety implications. For a givenmaterial the amount of its linear expansion, or contraction, in one direction is directly related totemperature and its original size (i.e. length, diameter, circumference). Thus:

change in length = %L#t

where % = thermal coefficient of linear expansion,#t = change in temperature, andL = original linear measurement.

Table 4.14 lists the coefficients of expansion for selected materials of construction.Thus, unacceptable stresses can arise in rigid construction materials in apparatus, equipment,

piping, etc. if subjected to large temperature fluctuations. For example, conventional glass isprone to failure due to thermal shock.

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Table 4.13 Chemical resistance of common plastics

Chemical Resins


Acetaldehyde GN GF GN GN EE FN GNAcetamide, sat. EE EE EE EE EE NN NNAcetic acid, 5% EE EE EE EE EE EG EEAcetic acid, 50% EE EE EE EE EE EG EGAcetone EE EE EE EE EE NN FNAdipic acid EG EE EE EE EE EE EGAlanine EE EE EE EE EE NN NNAllyl alcohol EE EE EE EG EE EG GFAluminium hydroxide EG EE EG EG EE FN EGAluminium salts EE EE EE EE EE EG EEAmino acids EE EE EE EE EE EE EEAmmonia EE EE EE EE EE NN EGAmmonium acetate, sat. EE EE EE EE EE EE EEAmmonium glycolate EG EE EG EG EE GF EEAmmonium hydroxide, 5% EE EE EE EE EE FN EEAmmonium hydroxide EG EE EG EG EE NN EGAmmonium oxalate EG EE EG EG EE EE EEAmmonium salts EE EE EE EE EE EG EGn-Amyl acetate GF EG GF GF EE NN FNAmyl chloride NN FN NN NN EE NN NNAniline EG EG GF GF EE FN NNAntimony salts EE EE EE EE EE EE EEArsenic salts EE EE EE EE EE EE EEBarium salts EE EE EE EE EE EE EGBenzaldehyde EG EE EG EG EE FN NNBenzene FN GG GF GF EE NN NNBenzoic acid, sat. EE EE EG EG EE EG EGBenzyl acetate EG EE EG EG EE FN FNBenzyl alcohol NN FN NN NN EE GF GFBismuth salts EE EE EE EE EE EE EEBoric acid EE EE EE EE EE EE EEBoron salts EE EE EE EE EE EE EEBrine EE EE EE EE EE EE EEBromine NN FN NN NN EE FN GNBromobenzene NN FN NN NN EE NN NNBromoform NN NN NN NN EE NN NNButadiene NN FN NN NN EE NN FNn-Butyl acetate GF EG GF GF EE NN NNn-Butyl alcohol EE EE EE EG EE GF GFsec-Butyl alcohol EG EE EG EG EE GF GGtert-Butyl alcohol EG EE EG EG EE GF EGButyric acid NN FN NN NN EE FN GNCadmium salts EE EE EE EE EE EE EECalcium hydroxide, conc. EE EE EE EE EE NN EECalcium hypochlorite, sat. EE EE EE EG EE FN GFCarbazole EE EE EE EE EE NN NNCarbon bisulphide NN NN EG FN EE NN NNCastor oil EE EE EE EE EE EE EECedarwood oil NN FN NN NN EE GF FNCellosolve acetate EG EE EG EG EE FN FNCaesium salts EE EE EE EE EE EE EEChlorine, 10% in air GN EF GN GN EE EG EEChlorine, 10% (moist) GN GF GN GN EE GF EGChloroacetic acid EE EE EG EG EE FN FN


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Table 4.13 Cont’d

Chemical Resins


p-Chloroacetophenone EE EE EE EE EE NN NNChloroform FN GF GF FN EE NN NNChromic acid, 10% EE EE EE EE EE EG EGChromic acid, 50% EE EE EG EG EE EG EFCinnamon oil NN FN NN NN EE GF NNCitric acid, 10% EE EE EE EE EE EG GGCitric acid, crystals EE EE EE EE EE EE EGCoconut oil EE EE EE EG EE EE GFCresol NN FN EG NN EE NN NNCyclohexane GF EG GF NN EE EG GFDecalin GF EG GF FN EE NN EGo-Dichlorobenzene FN FF FN FN EE NN GNp-Dichlorobenzene FN GF EF GF EE NN NNDiethyl benzene NN FN NN NN EE FN NNDiethyl ether NN FN NN NN EE NN FNDiethyl ketone GF GG GG GF EE NN NNDiethyl malonate EE EE EE EG EE FN GNDiethylene glycol EE EE EE EE EE GF FNDiethylene glycol ethyl ether EE EE EE EE EE FN FNDimethyl formamide EE EE EE EE EE NN FNDimethylsulphoxide EE EE EE EE EE NN NN1,4-Dioxane GF GG GF GF EE GF FNDipropylene glycol EE EE EE EE EE GF GFEther NN FN NN NN EE NN FNEthyl acetate EE EE EE EG EE NN FNEthyl alcohol EG EE EG EG EE EG EGEthyl alcohol, 40% EG EE EG EG EE EG EEEthyl benzene FN GF FN FN EE NN NNEthyl benzoate FF GG GF GF EE NN NNEthyl butyrate GN GF GN FN EE NN NNEthyl chloride, liquid FN FF FN FN EE NN NNEthyl cyanoacetate EE EE EE EE EE FN FNEthyl lactate EE EE EE EE EE FN FNEthylene chloride GN GF FN NN EE NN NNEthylene glycol EE EE EE EE EE GF EEEthylene glycol methyl ether EE EE EE EE EE FN FNEthylene oxide FF GF FF FN EE FN FNFluorides EE EE EE EE EE EE EEFluorine FN GN FN FN EG GF EGFormaldehyde, 10% EE EE EE EG EE EG GFFormaldehyde, 40% EG EE EG EG EE EG GFFormic acid, 3% EG EE EG EG EE EG GFFormic acid, 50% EG EE EG EG EE EG GFFormic acid, 98–100% EG EE EG EF EE EF FNFuel oil FN GF EG GF EE EG EEGasoline FN GG GF GF EE FF GNGlacial acetic acid EG EE EG EG EE GF EGGlycerine EE EE EE EE EE EE EEn-Heptane FN GF FF FF EE EG FNHexane NN GF EF FN EE FN GNHydrochloric acid, 1–5% EE EE EE EG EE EE EEHydrochloric acid, 20% EE EE EE EG EE EG EGHydrochloric acid, 35% EE EE EG EG EE GF GFHydrofluoric acid, 4% EG EE EG EG EE GF GF

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Hydrofluoric acid, 48% EE EE EE EE EE NN GFHydrogen EE EE EE EE EE EE EEHydrogen peroxide, 3% EE EE EE EE EE EE EEHydrogen peroxide, 30% EG EE EG EG EE EE EEHydrogen peroxide, 90% EG EE EG EG EE EE EGIsobutyl alcohol EE EE EE EG EE EG EGIsopropyl acetate GF EG GF GF EE NN NNIsopropyl alcohol EE EE EE EE EE EE EGIsopropyl benzene FN GF FN NN EE NN NNKerosene FN GG GF GF EE GF EELactic acid, 3% EG EE EG EG EE EG GFLactic acid, 85% EE EE EG EG EE EG GFLead salts EE EE EE EE EE EE EELithium salts EE EE EE EE EE GF EEMagnesium salts EE EE EE EE EE EG EEMercuric salts EE EE EE EE EE EE EEMercurous salts EE EE EE EE EE EE EEMethoxyethyl oleate EG EE EG EG EE FN NNMethyl alcohol EE EE EE EE EE FN EFMethyl ethyl ketone EG EE EG EF EE NN NNMethyl isobutyl ketone GF EG GF FF EE NN NNMethyl propyl ketone GF EG GF FF EE NN NNMethylene chloride FN GF FN FN EE NN NNMineral oil GN EE EE EG EE EG EGNickel salts EE EE EE EE EE EE EENitric acid, 1–10% EE EE EE EE EE EG EGNitric acid, 50% EG GN GN GN EE GF GFNitric acid, 70% EN GN GN GN EE FN FNNitrobenzene NN FN NN NN EE NN NNn-Octane EE EE EE EE EE GF FNOrange oil FN GF GF FF EE FF FNOzone EG EE EG EE EE EG EGPerchloric acid GN GN GN GN GF NN GNPerchloroethylene NN NN NN NN EE NN NNPhenol, crystals GN GF GN FG EE EN FNPhosphoric acid, 1–5% EE EE EE EE EE EE EEPhosphoric acid, 85% EE EE EG EG EE EG EGPhosphorus salts EE EE EE EE EE EE EEPine oil GN EG EG GF EE GF FNPotassium hydroxide, 1% EE EE EE EE EE FN EEPotassium hydroxide, conc. EE EE EE EE EE NN EGPropane gas NN FN NN NN EE FN EGPropylene glycol EE EE EE EE EE GF FNPropylene oxide EG EE EG EG EE GF FNResorcinol, sat. EE EE EE EE EE GF FNResorcinol, 5% EE EE EE EE EE GF GNSalicylaldehyde EG EE EG EG EE GF FNSalicylic acid, powder EE EE EE EG EE EG GFSalicylic acid, sat. EE EE EE EE EE EG GFSalt solutions EE EE EE EE EE EE EESilver acetate EE EE EE EE EE EG GGSilver salts EG EE EG EE EE EE EGSodium acetate, sat. EE EE EE EE EE EG GFSodium benzoate, 1% EE EE EE EE EE EE EE

Table 4.13 Cont’d

Chemical Resins



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Sodium hydroxide, 1% EE EE EE EE EE FN EESodium hydroxide, 50% to sat. EE EE EE EE EE NN EGSodium hypochlorite, 15% EE EE EE EE EE GF EEStearic acid, crystals EE EE EE EE EE EG EGSulphuric acid, 1–6% EE EE EE EE EE EE EGSulphuric acid, 20% EE EE EG EG EE EG EGSulphuric acid, 60% EG EE EG EG EE GF EGSulphuric acid, 98% EG EE EE EE EE NN NNSulphur dioxide, liq., 46 psi NN FN NN NN EE GN FNSulphur dioxide, wet or dry EE EE EE EE EE EG EGSulphur salts FN GF FN FN EE FN NNTartaric acid EE EE EE EE EE EG EGTetrachloromethane FN GF GF NN EE NN GFTetrahydrofuran FN GF GF FF EE NN NNThionyl chloride NN NN NN NN EE NN NNTitanium salts EE EE EE EE EE EE EEToluene FN GG GF FF EE FN FNTributyl citrate GF EG GF GF EE NN FNTrichloroethane NN FN NN NN EE NN NNTrichloroethylene NN FN NN NN EE NN NNTriethylene glycol EE EE EE EE EE EG GFTripropylene glycol EE EE EE EE EE EG GFTurkey red oil EE EE EE EE EE EG EGTurpentine FN GG GF FF EE FN GFUndecyl alcohol EF EG EG EG EE GF EFUrea EE EE EE EG EE NN GNVinylidene chloride NN FN NN NN EE NN NNXylene GN GF FN FN EE NN NNZinc salts EE EE EE EE EE EE EEZinc stearate EE EE EE EE EE EE EG

E 30 days of constant exposure cause no damage. Plastic may even tolerate exposure for years.G Little or no damage after 30 days of constant exposure to the reagent.F Some signs of attack after 7 days of constant exposure to the reagent.N Not recommended; noticeable signs of attack occur within minutes to hours after exposure. (However, actual failure

might take years.)First letter: at room temperature.Second letter: at 52°C.

ResinsCPE Conventional (low-density) polyethylene.LPE Linear (high-density) polyethylene.PP Polypropylene.PMP Polymethylpentene.FEP Teflon FEP (fluorinated ethylene propylene). Teflon is a Du Pont registered trademark.ETFE Tefzel ethylene-tetrafluoroethylene copolymer. (For chemical resistance, see FEP ratings.) Tefzel is a Du Pont registered

trademark.PC Polycarbonate.PVC Rigid polyvinyl chloride.

Table 4.13 Cont’d

Chemical Resins


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Table 4.14 Thermal coefficients of linear expansion

Material Coefficient of expansion per °C

Aluminium 0.000025Brass 0.000018Bronze 0.000018Copper 0.000017Glass (Pyrex) 0.000003Iron (cast) 0.000011Lead 0.000029Platinum 0.000009Silver 0.000021Steel (mild) 0.000012Tin 0.000025Zinc 0.000029

Table 4.15 Pressure increase of common liquids due to thermal expansion on 16.6°C temperature rise

Liquid P (psia)

Acetic acid 3200Acetone 3260Aniline 5190Benzene 3860n-Butyl alcohol 2590Carbon tetrachloride 3310Methyl alcohol 3900Petroleum (s.g. = 0.8467) 2340Toluene 3340Water 1100

Liquids can also exert pressure due to thermal expansion. Table 4.15 provides an indication ofpressure increases due to temperature increases for selected common liquids in full containers orpipes. Serious accidents can arise unless the design of rigid plant items such as pipework takesinto account the changes in volume of liquids with temperature fluctuation by the following orcombinations thereof:

• Expansion bellows.• Expansion joints.• Expansion loops or offset legs.• Positioning of equipment so as to exploit the inherent flexibility.• Supports, guides, anchors, piles.• Decrease in pipe wall thickness.

Consideration should be given to the effects of thermal expansion of liquids and pressure-reliefvalves installed unless:

• pipelines cannot become blocked or heated;• liquid temperature is controlled;• line is normally in service and can be vented and drained;• one end of valve is fitted with check valve.


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If pressure relief is important methods include:

• installation of pressure-relief valve;• bypass;• check valves;• ensuring liquid is drained before blockage can occur.

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Toxic chemicals


Chemicals may be encountered as reactants, solvents, catalysts, inhibitors, as starting materials,finished products, by-products, contaminants, or off-specification products. They may vary frompure, single substances to complex proprietary formulations.

Exposures to chemicals may involve solids, liquids, or airborne matter as mists, aerosols,dusts, fumes (i.e. µm-sized particulates), vapours or gases in any combination. Many situations,e.g. exposure to welding fumes or to combustion products from fossil fuels, include mixtures bothof chemicals and of physical forms. Quantification of exposure is then difficult.

An exposure to a specific chemical in relatively low concentrations over a period may resultin chronic effects. At higher concentrations, the effects may be acute. Some chemicals producelocal damage at their point of contact with, or entry into, the body; others produce systemiceffects, i.e. they are transported within the body to various organs before exerting an adverseeffect.

For a classification of airborne contaminants, refer to Table 5.1

Hazard recognition

The toxicity of a substance is its capacity to cause injury once inside the body. The main modesof entry into the body by chemicals in industry are inhalation, ingestion and absorption throughthe skin. Gases, vapours, mists, dusts, fumes and aerosols can be inhaled and they can also affectthe skin, eyes and mucous membranes. Ingestion is rare although possible as a result of poorpersonal hygiene, subconscious hand-to-mouth contact, or accidents. The skin can be affecteddirectly by contact with the chemicals, even when intact, but its permeability to certain substancesalso offers a route into the body. Chemicals accorded a ‘skin’ notation in the list of OccupationalExposure Limits (see Table 5.12) are listed in Table 5.2. Exposure may also arise via skin lesions.

Types of toxic chemicals

Irritant chemicals

Primary irritants cause inflammation. Inflammation is one of the body’s defence mechanisms. Itis the reaction of a tissue to harm which is insufficient to kill the tissue and is typified by

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Table 5.1 Classification of airborne contaminants

Classification Sub-groups Examples

IrritantsHave a corrosive or a vesicant(blistering) effect on moist ormucous surfaces.Concentration may be moreimportant than duration of exposure.Animals and man react similarly.

Vapour, gases, mists(a) Primary Upper respiratory Acrolein; sulphur dioxide, hydrogen

chloride, chromic acid; formaldehyde.Upper and lower respiratory Fluorine; chlorine; bromine; ozone;

cyanogen chloride.Lower respiratory Phosgene; nitrogen dioxide; arsenic

trichloride.Skin Inorganic acids (chromic, nitric); organic

acids (acetic, butyric); inorganic alkalis(sodium hydroxide, sodium carbonate);organic bases (amines); organicsolvents.

DustsDetergents; salts (nickel sulphate, zinc

chloride); acids, alkalis, chromates.(b) Secondary or allergens Skin sensitizers Epoxy-resins; picryl chloride; or chlor-2-

4-dinitrobenzene; p-phenyl diamine.Respiratory sensitizers Isocyanates; proteolytic enzymes;

p-phenylene diamine; complex salts ofplatinum; cyanuric chloride.

AsphyxiantsExert an effect by interference with Simple anoxia caused by oxygen Carbon dioxide; methane; hydrogen;oxidation of tissue. Animals and deficiency in inhaled air. nitrogen; helium.man react similarly.

Toxic anoxia caused by damage to Carbon monoxide; cyanogen, hydrogenthe body’s oxygen transport or cyanide; nitrites; arsine; aniline,utilization by adverse reaction of dimethyl aniline, toluidine;biologically active substances. nitrobenzene; hydrogen sulphide

(causes respiratory paralysis byimpairment of oxygen utilization inthe central nervous system).

Anaesthetics and narcoticsExert principal effects as simple Acetylene Decreasinganaesthesia, by a depressant action Olefins anaestheticon the central nervous system. Ether action

Paraffins comparedAliphatic ketones withAliphatic alcohols otherEsters effects.

Systemic poisonsSubstances which cause injury at Visceral organs in general Many halogenated hydrocarbonsother than the site of contact. Haematopoletic (i.e. and metals.

blood-forming system) Benzene; phenols.Nervous system

Carbon disulphide; methanol; phenol;n-hexane; methyl n-butyl ketone;organophosphorus compounds;tetra-alkyl lead compounds.





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Toxic inorganic substances e.g.Lead, manganese, cadmium, antimony,

beryllium, mercury; arsenic;phosphorus; selenium and sulphurcompounds, fluorides.

Respiratory fibrogens Fibrogenic dusts e.g.Free crystalline silica, (quartz, tridymite,

cristobalite), asbestos (chrysotile,amosite, crocidolite etc.), talc.

CarcinogensCancer-producing agents Skin Coal tar pitch dust; crude anthracene

dust; mineral oil mist; arsenic.Respiratory Asbestos; polycyclic aromatic

hydrocarbons; nickel ore; arsenic;bis-(chloromethyl) ether; mustard gas.

Bladder/urinary tract #-naphthylamine; benzidine;4-aminodiphenylamine.

Liver Vinyl chloride monomer.Nasal Mustard gas; nickel ore.Bone marrow Benzene.

Inerts GasesSimple asphyxiantsArgon; methane; hydrogen; nitrogen;

helium.Particulates e.g. cement, calcium


constriction of the small vessels in the affected area, dilation of the blood vessels, increasedpermeability of the vessel walls, and migration of the white blood and other defensive cells to theinvading harmful chemical. The aim is to concentrate water and protein in the affected area to‘dilute’ the effect and wash away the chemical. Production of new cells is speeded up andcontaminated surface cells are shed.

The respiratory system is the main target organ for vapour, gas or mist. Readily-soluble chemicals,e.g. chlorine or phosgene, attack the upper respiratory tract; less soluble gases, e.g. oxides ofnitrogen, penetrate more deeply into the conducting airways and, in some cases, may causepulmonary oedema, often after a time delay.

For example, sulphur dioxide is highly water soluble and tends to be absorbed in the airwaysabove the larynx. Responses at various concentrations are summarized in Table 5.3. However, inthe presence of particulate catalysts and sunlight, conversion to sulphur trioxide occurs and theirritant response is much more severe.

Other parts of the body are also vulnerable: the skin and eyes from direct contact/rubbing orfrom exposure to airborne material including splashes; the mouth and pharynx by ingestion ofsolid or liquid chemicals.

One effect of direct contact of liquid or solid, and less often vapour, with the skin is a contactirritant dermatitis. Some dusts can also act as primary irritants. Even chemically-inert dusts, e.g.from glass fibres, can induce a dermatitis due to abrasion; this is made worse if a reactivechemical, e.g. a synthetic resin binder, is also involved. Examples of primary irritants includeacids; alkalis; defatting compounds, e.g. organic solvents, surfactants; dehydrating agents; oxidizingagents and reducing agents.

Table 5.1 Cont’d

Classification Sub-groups Examples


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AcrylamideAcrylonitrileAldrinAllyl alcoholAnilineAzinphos-methylAziridineButan-1-ol2-Butoxyethanoln-Butylamine$-BHC (Lindane)BromoformBromomethaneButan-2-one2-sec-ButylphenolCarbon disulphideCarbon tetrachlorideChlorinated biphenyls2-Chlorobuta-1,3-diene1-Chloro-2,3-epoxy propane2-ChloroethanolChloroform1-Chloro-4-nitrobenzeneChlorpyrifosCresols, all isomersCumeneCyanidesCyclohexylamineDiazinon1,2-Dibromoethane2,2%-Dichloro-4,4%-methylene dianiline (MDOCA)1,3-DichloropropeneDichlorvosDieldrin2-DiethylaminoethanolDiethyl sulphateDi-isopropylamineN,N-DimethylacetamideN,N-DimethylanilineDimethyl formamideDimethyl sulphateDinitrobenzene2,4-Dinitrotoluene1,4-DioxaneDioxathionEndosulfanEndrin2-Ethoxyethanol2-Ethoxyethyl acetateEthylene dinitrate4-Ethylmorpholine2-Furaldehyde (furfural)Furfuryl alcoholGlycerol trinitrateHeptan-3-oneHeptan-2-oneHexahydro-1,3,5-trinitro-1,3,5-triazine

Hexan-2-oneHydrazineHydrogen cyanide2-Hydroxypropylacrylate2,2-Iminodi(ethylamine)IodomethaneMalathionMercury alkylsMethacrylonitrileMethanol2-Methoxyethanol2-Methoxyethyl acetate(2-Methoxymethylethoxy) propanolMethoxypropanol2-Methyl-4,6-dinitrophenol5-Methylhexan-2-one4-Methylpentan-2-ol4-Methylpentan-2-one1-Methyl-2-pyrrolidoneN-Methyl-N,-2,4,6-tetranitroanilineN-MethylanilineMevinphosMonochloroacetic acidMorpholineNicotine4-NitroanilineNitrobenzeneNitrotolueneOctachloronaphthaleneParathionParathion-methylPentachlorophenolPhenolPhoratePiperidinePolychlorinated biphenyls (PCB)Propan-1-olPropylene dinitrateProp-2-yn-1-olSodium fluoroacetateSulfotepTetrabromoethaneTetraethylpyrophosphateTetrahydrofuranTetramethyl succinonitrileThallium, soluble compoundsTin compounds, organicTolueneo-ToluidineTricarbonyl (eta-cyclopentadienyl) manganeseTricarbonyl (methylcyclopentadienyl) manganeseTrichlorobenzene1,1,2-TrichloroethaneTrichloroethylene2,4,6-TrinitrotolueneXyleneXylidine

Table 5.2 Materials with an ‘Sk’ notation in list of Occupational Exposure Limits

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Strong acid

Weak acid




pH water



In extreme cases irritant chemicals can have a corrosive action. Corrosive substances can alsoattack living tissue (e.g. to cause skin ulceration and, in severe cases, chemical burns withdegradation of biochemicals and charring), kill cells and possibly predispose to secondary bacterialinvasion. Thus whilst acute irritation is a local and reversible response, corrosion is irreversiblecell destruction at the site of the contact. The outcome is influenced by the nature of the compound,the concentration, duration of exposure, the pH (see Figure 5.1) and also, to some extent, byindividual susceptibility etc. Thus dilute mineral acids may be irritant whereas at higher concentrationsthey may cause corrosion.

Table 5.3 Typical effects of sulphur dioxide concentrations in air

Concentration Response(ppm)

0.5–0.8 Minimum odour threshold3 Sulphur-like odour detectable

6–12 Immediate irritation to nose and throat20 Reversible damage to respiratory system

>20 Eye irritationTendency to pulmonary oedema and eventually respiratory paralysis

10 000 Irritation to moist skin within a few minutes

Figure 5.1 The pH scale


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A summary of the more common corrosive chemicals is given in Table 5.4. Note that thisincludes many primary irritants, such as:

• Chemicals which give strong acid reactions, often on interaction with water, e.g. mineral acids.Some organic acids can also be corrosive. Phenolics can result in local anaesthesia so that thepain will be absent for a time, i.e. contact may go unheeded.

• Halogen compounds.• Acid anhydrides/halides which react with water to form their parent acids.• Common bases, which render aqueous solutions alkaline.• Certain oxidizing/reducing compounds and salts which, in the form of solid (bulk or dust) or

as solution, can produce irritation by thermal burns.

Strong acids and alkalis produce effects within moments: e.g. sulphuric and nitric acids quicklybecome hydrated by the water content of the skin/mucous membranes and combine with skinprotein to form albuminates, sometimes with charring. Some substances, e.g. certain organotinsor hydrofluoric acid, produce a more delayed reaction. Thus on the skin hydrofluoric acid producesan effect which varies, depending on concentration and duration of exposure, from mild erythemato severe burns and intense pain, sometimes delayed by several hours after the initial exposure. Atough white lump forms over the area of skin damage under which progressive destruction of celltissue continues. Burns under the finger nails are notable in this respect because of the difficultiesof treatment. Similarly, inhalation of the vapour can cause corrosion of the respiratory system andpulmonary oedema. If hydrofluoric acid is swallowed, burns to the mouth and pharynx can occurwith vomiting and ultimate collapse.


Generally sensitizers may not on first contact result in any ill effects, although cellular changescan be induced and the body’s immune system affected. (Some chemicals may act as primaryirritants as well as sensitizers.) Subsequent exposures to the same, or related, chemicals maybring about violent allergic responses: the person has become sensitized. Generally there is nomathematical relationship between the degree of exposure and the extent of the response. Sensitizationto a compound is usually highly specific and normally occurs within about 10 days, althoughthere have been cases of workers using a chemical for years without untoward effects beforedeveloping an allergic dermatitis. Sensitization is usually for life. Depending upon the toxicmechanism, atopics may be most vulnerable.

Thus with industrial skin sensitizers, e.g. chromates or amine curing agents, no effect is usuallyobserved on first exposure; subsequent exposure results in inflammation of the skin, not restrictedto the areas of contact. Refer to Table 5.5.

Respiratory sensitizers, e.g. isocyanates or formaldehyde, result, in mild cases, in a sense oftightness of the chest and occasionally a troublesome cough. Severe cases involve bronchialasthma. Refer to Table 5.6. With such sensitizers, complete cessation of contact is often followedby rapid recovery but no further exposure is generally permitted.


Asphyxiants interfere with the body’s oxygen uptake mechanisms. Air normally contains 21%oxygen. Oxygen deficiency in inhaled air, e.g. due to the presence of nitrogen, argon, or carbondioxide in a confined space, depending on the concentration and duration, may affect the bodyand ultimately cause death from simple anoxia (Table 5.7).

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Table 5.4 Common corrosive chemicals

Acids and Acetic acid Nitrohydrochloric acidanhydrides Acetic anhydride Perchloric acid

Acid mixtures Phenosulphonic acidBattery fluids Phosphorus pentoxideChloroacetic acid Propionic acidChlorosulphonic acid Selenic acidChromic acid Spent acidsDichloroacetic acid Sulphamic acidFluoroboric acid Sulphuric acid and oleumFluorosilicic acid (fuming sulphuric acid)Hydrobromic, hydrochloric, hydrofluoric Sulphurous acid

and hydroiodic acids Thioglycolic acidMethacrylic acid Trichloroacetic acidNitric acid

Akalis Ammonium hydroxidePotassium hydroxide (caustic potash)Quaternary ammonium hydroxidesSodium hydroxide (caustic soda)

Halogens and Aluminium bromide and chloride Phosphorus sulphochloridehalogen salts Ammonium bifluoride and (thiophosphoryl chloride)

other bifluorides Phosphorus trichloride and pentachlorideAntimony trichloride, pentachloride Potassium fluoride and bifluoride

and pentafluoride Potassium hypochloriteBeryllium chloride Pyrosulphuryl chlorideBoron trichloride Sodium chloriteBromine Sodium fluorideChlorine Sodium hypochloriteCalcium fluoride Stannic chlorideChromic fluoride Sulphur chlorideChromous fluoride Sulphuryl chlorideFluorine Thionyl chlorideIodine Titanium tetrachlorideIron chlorides (ferric chloride, Vanadium dichloride

ferrous chloride) Zinc chlorideLithium chloridePhosphorus oxybromide and

oxychloride (phosphoryl bromideand chloride)

Interhalogen Bromine trifluoride and pentafluoridecompounds Chlorine trifluoride

Iodine monochloride

Organic halides, Acetyl bromide p-Chlorobenzyl chlorideorganic acid halides, Acrylonitrile monomer Chloropropionyl chlorideesters and salts Allyl chloride Dibromoethane (ethylene bromide)

Allyl chloroformate 1,2-Dichloroethane (ethylene chloride)Allyl iodide Diisooctyl acid phosphateAmmonium thiocyanate Ethyl chloroformateAnisoyl chloride Ethyl chlorocarbonateBenzhydryl bromide Ethylene oxide

(diphenyl methyl bromide) Fumaryl chlorideBenzoyl chloride Iso-propylchloroformateBenzyl bromide Methyl chloroformateBenzyl chloride Methyl chlorocarbonateBenzyl chloroformate Propionyl chloride

(benzyl chlorocarbonate) Sodium fluorosilicateButyl acid phosphateChloracetyl chloride


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Chlorosilanes Allyl trichlorosilane Hexadecyl trichlorosilaneAmyl trichlorosilane Hexyl trichlorosilaneButyl trichlorophenyl-trichlorosilane Methyl trichlorosilaneCyclohexyl trichlorosilane Nonyl trichlorosilaneDichlorophenyl trichlorosilane Octadecyl trichlorosilaneDiethyl trichlorosilane Octyl trichlorosilaneDiphenyl dichlorosilane Phenyl trichlorosilaneDodecyl trichlorosilane Trimethyl trichlorosilane

Vinyl trichlorosilane

Miscellaneous Proprietary mixtures, e.g. cleaning, disinfecting, bleaching, degreasing solids or solutions,corrosive substances based on these chemicals are corrosive to a degree dependent upon dilution

Ammonium sulphide HydrazineBenzene sulphonyl chloride Hydrogen peroxideBenzyl dimethylamine Organic peroxidesBeryllium nitrate PhenolsCatechol Silver nitrateChlorinated benzenes and toluenes Soda limeChlorobenzaldehyde Sodium aluminateChlorocresols Sodium amideCresols Sodium bisulphateCyclohexylamine Sodium bisulphiteDibenzylamine Sodium chromate and dichromateDichlorophenol Sodium hydrideDiethyl sulphate Sodium pyrosulphateDiketene TriethyltetramineDimethyl sulphate Tritolyl borateHexamethylenediamine

Table 5.4 Cont’d

Table 5.5 Common industrial skin sensitizers

Coal-tar and its direct derivativesAcridineAnthraceneCarbazoleCresol(1)



DyesAmido-azo-benzeneAmido-azo-tolueneAniline blackAuramineBismarck brownBrilliant indigo, 4 G.ChrysoidineCrystal and methyl violet

Erio blackHydron blueIndanthrene violet, R.R.Ionamine, A.S.Malachite greenMetanil yellowNigrosineOrange YParamido phenolParaphenylendiaminePyrogene violet brownRosanilineSafranineSulphanthrene pink

Dye intermediatesAcridine and compoundsAniline and compoundsBenzanthrone and compoundsBenzidine and compoundsChloro compounds

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Naphthalene and compoundsNaphthylaminesNitro compounds

ExplosivesAmmonium nitrateDinitrophenolDinitrotoluolFulminate of mercuryHexanitrodiphenylamineLead styphnatePicric acid and picratesPotassium nitrateSensolSodium nitrateTrinitromethylnitramine (Tetryl)Trinitrotoluene

InsecticidesArsenic compouds(1)



Mercury compounds(1)

NicotineOrganic phosphatesPetroleum distillates(1)

Phenol compounds(1)


Natural resinsBurgundy pitchCopalDammarJapanese lacquerPine rosinWood rosin

OilsCashew nut oil(1)

Coconut oilConing oils (cellosolves, eugenols)Cutting oils (the inhibitor or antiseptic they contain)Essential oils of plants and flowersLinseed oilMustard oil(1)

Sulphonated tung oil

Photographic developersBichromates


PlasticizersButyl cellosolve stearateDiamyl naphthaleneDibutyl tin laurateDioctylphthalateMethyl cellosolve oleateMethyl phthalylethylglycolaPhenylsalicylatePropylene stearateStearic acidTriblycol di-(2,ethyl butyrate)

Rubber accelerators and anti-oxidantsGuanidinesHexamethylene tetramineMercapto benzo thiazoleOrtho-toluidinePara-toluidineTetramethyl thiuram monosulphide and disulphideTriethyl tri-methyl triamine

Synthetic resinsAcrylicAlkydChlorobenzolsChlorodiphenylsChloro-naphthalenesChlorophenolsCumaronEpoxiesMelamine formaldehydePhenol formaldehydePolyestersSulphonamide formaldehydeUrea formaldehydeUrethaneVinyl

OthersEnzymes derived from B. subtilis

Table 5.5 Cont’d

(1) Compounds which also act as primary irritants.


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Table 5.6 Some substances recognized as causing occupational asthma


IsocyanatesPlatinum saltsAcid anhydride and amine hardening agents,

including epoxy resin curing agents,e.g. ethylene diamine, triethylene tetramine

Fumes from the use of resin (colophony) as asoldering flux

Proteolytic enzymes

Animals, including insects and other arthropods ortheir larval forms

Dusts from barley, oats, rye, wheat or maize, ormeal or flour made from such grain

Antibiotics, e.g. cephalosporins, hydralizine, ampicillins,piperazine, spiramycin

CimetidineWood dusts; some hardwoods (e.g. iroko, mahogany);some softwoods (e.g. western red cedar)Ispaghula powderCastor bean dustIpecacuanhaAzodicarbonamide


Persulphate salts and hennaCrustaceansReactive dyesSoya beanTea dustGreen coffee bean dustFumes from stainless steel weldingNatural rubber latexWater-mix metalworking fluidsCertain cyanoacrylatesMethyl methacrylateDiazonium saltsParaphenylenediamineFormaldehydeCobaltNickelBromelein, papainAmylaseTriglycidyl isocyanurateAzodicarbonamideButadiene diepoxide2,3-expoxy-1-propanol (glycidol)

Examples of use

Plastic foam, synthetic inks, paints and adhesivesPlatinum refining workshops and some laboratoriesAdhesives, plastics, moulding resins and

surfaces coatings

The electronics industry

Biological washing powders and the baking,brewing, fish, silk and leather industries

Research and educational laboratories, pest controland fruit cultivation

The baking or flour milling industry or on farms

Manufacture, dispensing

Manufacture of cimetidine tabletsFurniture manufacture

Manufacture of bulk laxativesProcessingManufacture of ipecacuanha tabletsBlowing agent in the manufacture of expanded

foam plastics for wallcoverings, floor coverings,insulation and packaging materials

Hospitals, laboratories, cooling tower systems andleather tanning

Manufacture of hair care products and their applicationFish and food processing industriesDyeing, printing and textile industriesSoya bean processing and food industriesTea processing and food industriesCoffee processing and food industriesStainless steel fabrication operationsLatex gloves, adhesives, surgical apparatus and appliancesCoolants in metalworkingAdhesivesAdhesivesPolymer manufactureHair dyes and treatmentsPreserving, resin and foam manufactureHard metal manufacture and toolsElectroplatingMeat tenderizingFlour improverPolyester-based powder coatingsPlastics manufacture; flour improverPolymer manufactureOil stabilizer

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Levels below 19.5% oxygen can have detrimental effects if the body is already under stress, e.g.at high altitudes. Exposures below 18% should not be permitted under any circ*mstance. Otherchemicals, e.g. carbon monoxide, result in toxic anoxia due to damage of the body’s oxygentransport or utilization mechanism.

Anaesthetics and narcotics

Anaesthetics and narcotics, e.g. hydrocarbons and certain derivatives such as the various chlorinatedsolvents or ether, exert a depressant action on the central nervous system.

Systemic poisons

Systemic poisons attack organs other than the initial site of contact. The critical organs are thekidneys, liver, blood and bone marrow.

Respiratory fibrogens

The hazard of particulate matter is influenced by the toxicity and size and morphology of theparticle. Figure 5.2 gives typical particle size ranges for particles from various sources. Thecritical size of dust (and aerosol) particles is 0.5 to 7 µm, since these can become deposited in therespiratory bronchioles and alveoli. If dust particles of specific chemicals, e.g. silica or thevarious grades of asbestos, are not cleared from the lungs then, over a period, scar tissue (collagen)may build up; this reduces the elasticity of the lungs and impairs breathing. The characteristicdisease is classified as pneumoconiosis. Common examples are silicosis, asbestosis, coalpneumoconiosis and talc pneumoconiosis.

An appreciation of the composition and morphology of the dust is important in the assessmentof hazard. Thus, among silica-containing compounds, crystalline silicates and amorphous silicas(silicon dioxide) are generally not considered fibrogenic, whereas free crystalline silica andcertain fibrous silicates such as asbestos and talcs can cause disabling lung diseases. Table 5.8indicates the approximate free silica content of various materials; Table 5.9 lists a range of silica-containing materials according to type.


Cancer is a disorder of the body’s control of the growth of cells. The disease may be genetic orinfluenced by life style or exposure to certain chemicals, termed carcinogens. For a list ofexamples of human chemical carcinogens, and the relevant target organs, refer to Table 5.10.

Table 5.7 Typical effects of depleted oxygen levels in air

Oxygen concentration (%) Effect

16–21 No noticeable effect12–16 Increased respiration, slight diminution of coordination10–12 Loss of ability to think clearly6–10 Loss of consciousness, death


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Lower limitelectron


0.4–0.8 µmLower limitmicroscope


Lower limitof visibility


SmogMist, fog, cloudsRain

Atmospheric dust

Oil smoke




Pollen Bacteria Viruses

MolecularColloidalSuspended settleableCompacted

Solid wastes

Water and wastewater



(1 m) (1 mm) (1 nm)

Particle diameter (µm)

Coal dust Tobacco smoke

Foundry dust


Figure 5.2 Typical particle size ranges

Table 5.8 Crystalline SiO2 in various materials

Material Normal range crystalline SiO2(%)

Foundry moulding sand 50–90Potteryware body 15–25Brick and tile compositions 10–35Buffing wheel dressings 0–60Road rock 0–80Limestone (agricultural) 0–3Feldspar 12–25Clay 0–40Mica 0–10Talc 0–5Slate and shale 5–15

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Table 5.9 Types of silica-containing dusts

Crystalline free silica (SiO2, including microcrystalline forms)Chalcedony A heat-resistant, chemically inert form of microcrystalline quartz. A decorative material.

Rare in industry.Chert A microcrystalline form of silica. An impure form of flint used in abrasives.Cristobalite A crystalline form of free silica, extremely hard and inert chemically; very resistant to

heat. Quartz in refractory bricks and amorphous silica in diatomaceous earth arealtered to cristobalite when exposed to high temperatures (calcined). Cristobalite isextensively used in precision casting by the hot wax process, dental laboratory work,and certain speciality ceramics.

Flint A microcrystalline form of native quartz, more opaque and granular than chalcedony.Used as an abrasive and in ceramics.

Jasper A microcrystalline impure form of silica similar to chert. Used for decorative purposes.Rare in industry.

Quartz Vitreous, hard, chemically-resistant free silica, the most common form in nature. Themain constituent in sandstone, igneous rocks, and common sands.

Tridymite Vitreous, colourless form of free silica. Formed when quartz is heated to 870°C (1598°F).Tripoli (rottenstone) A porous siliceous rock resulting from the decomposition of chert or siliceous limestone.

Used as a base in soap and scouring powders, in metal polishing, as a filtering agent,and in wood and paint fillers. A cryptocrystalline form of free silica.

Amorphous free silica (Noncrystalline)Diatomaceous earth A soft, gritty amorphous silica composed of minute siliceous skeletons of small aquatic

plants. Used in filtration and decoloration of liquids, insulation, filler in dynamite,wax, textiles, plastics, paint, and rubber. Calcined and flux-calcined diatomaceousearth contains appreciable amounts of cristobalite, and dust levels should be the sameas for cristobalite.

Silica gel A regenerative absorbent consisting of the amorphous silica manufactured by theaction of HCl on sodium silicate. Hard, glossy, quartz-like in appearance. Used indehydrating and in drying and as a catalyst carrier.

Silicates (compounds made up of silicon, oxygen and one or more metals with or without hydrogen. Asbestos dust is the mosthazardous (page 148). Others, e.g. talc, mica, vermiculite, have caused a silicatosis on prolonged exposure.)Asbestos A hydrated magnesium silicate in fibrous form. The fibres are believed to be the more

hazardous component of asbestos dust.Clays A great variety of aluminium–silicate bearing rocks, plastic when wet, hard when dry.

Used in pottery, stoneware, tile, bricks, cements, fillers and abrasives. Kaolin is onetype of clay. Some clay deposits may include appreciable amounts of quartz.Commercial grades of clays may contain up to 20% quartz.

Feldspar Most abundant group of materials, composed of silicates of aluminium with sodium,potassium, calcium, and rarely barium. Most economically important mineral. Usedfor ceramics, glass, abrasive wheels, cements, insulation and fertilizer.

Fuller’s earth A hydrated silica–alumina compound, associated with ferric oxide. Used as a filtermedium and as a catalyst and catalyst carrier and in cosmetics and insecticides.

Kaolin A type of clay composed of mixed silicates and used for refractories, ceramics, tile andstoneware.

Mica A large group of silicates of varying composition, but similar in physical properties. Allhave excellent cleavage and can be split into very thin sheets. Used in electricalinsulation.

Portland cement Fine powder containing compounds of lime, alumina, silica and iron oxide. Used as aconstruction material.

Silicon carbide (carborundum) Bluish-black, very hard crystals. Used as an abrasive and refractory material.Talc A hydrous magnesium silicate used in ceramics, cosmetics, paint and pharmaceuticals,

and as a filler in soap, putty and plaster.Vermiculite An expanded mica (hydrated magnesium-aluminium-iron silicate). Used in lightweight

aggregates, insulation, fertilizer and soil conditioners, as a filler in rubber and paints,and as a catalyst carrier.


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Table 5.10 Chemicals associated with cancer in humans (not all those listed are still in industrial use)

Chemicals and industrial processes which are carcinogenic for humansSubstance or process Site affected and type of neoplasm

4-Aminobiphenyl Bladder – carcinomaArsenic and certain compounds Skin, lung, liver – carcinomaAsbestos Respiratory tract – carcinoma

Pleura and peritoneum –mesothelioma

Gastrointestinal tract – carcinomaAuramine manufacture Bladder – carcinomaBenzene Blood – leukaemiaBenzidene Bladder – carcinomaBis (chloromethyl) ether and technical Lung – carcinoma

grade chloromethyl etherChlornaphazine Bladder – carcinomaChromium and certain compounds Lung – carcinomaDiethylstilbestrol Female genital tract – carcinoma

(transplacental)Haematite mining (underground) Lung – carcinomaIsopropanol manufacture Respiratory tract – carcinoma

(strong acid process)Melphalan Blood – leukaemiaMustard gas Respiratory tract – carcinoma2-Naphthylamine Bladder – carcinomaNickel refining Respiratory tract – carcinomaSoots, tars, and mineral oils Skin, lung, bladder – carcinomaVinyl chloride Liver – angiosarcoma

BrainLung – carcinomaLymphatic system – lymphoma

Chemicals which are probably carcinogenic in humansSubstance Site affected (human)

Acrylonitrile Colon, lungAflatoxins LiverAmitrole Various sitesAuramine BladderBeryllium and certain compounds Bone, lungCadmium and certain compounds Kidney, prostate, lungCarbon tetrachloride LiverChlorambucil BloodCyclophosphamide Bladder, bloodDimethylcarbamoyl chlorideDimethyl sulphate LungEthylene oxide Gastrointestinal tract, bloodIron dextran Connective tissueNickel and certain compounds Respiratory tractOxymetholone LiverPhenacetin Kidney, bladderPolychlorinated biphenyls Skin, various sitesThiotepa Blood

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Hazard assessment

Indicators of toxicity hazards include LD50, LC50, plus a wide range of in vitro and in vivotechniques for assessment of skin and eye irritation, skin sensitization, mutagenicity, acute andchronic dermal and inhalation toxicity, reproductive toxicology, carcinogenicity etc.

The LD50 is the statistically derived single dosage of a substance that can be expected to causedeath in 50% of the sample population. It is therefore an indicator of acute toxicity, usuallydetermined by ingestion using rats or mice, although other animals may be used. LD50 is alsodetermined by other routes, e.g. by skin absorption in rabbits. The values are affected by species,sex, age, etc.

The LC50 is the lethal concentration of chemical (e.g. in air or water) that will cause the deathof 50% of the sample population. This is most appropriate as an indicator of the acute toxicity ofchemicals in air breathed (or in water, for aquatic organisms). Table 5.11 illustrates the use ofLD50 values to rank the toxicity of substances.

Table 5.11 Toxicity rating system

Toxicity Commonly LD50 4hr LD50 Probablerating used term Single oral Vapour exposure Skin for lethal dose

dose for rats causing 2 to 4 deaths rabbits for humans(g/kg) in 6-rat group (ppm) (g/kg)

1 Extremely &0.001 <10 &0.005 Tastetoxic (1 grain)

2 Highly toxic 0.001–0.05 10–100 0.005–0.043 1 teaspoon(4 ml)

3 Moderately 0.05–0.5 100–1000 0.044–0.340 1 oz (30 g)toxic

4 Slightly toxic 0.5–5.0 1000–10 000 0.35–2.81 1 pint(250 g)

5 Practically 5.0–15.0 10 000–100 000 2.82–22.6 1 quartnon-toxic (500 g)

6 Relatively >15.0 >100 000 >22.6 >1 quartharmless

Hygiene standards

Hygiene standards are employed as indicators of risk to man from inhalation of toxic or nuisancechemicals at work.

Some indication of risk of employee exposure to airborne chemicals can be gauged from ananalysis of the level of exposure for comparison with known human dose/response data such asthose for carbon monoxide and hydrogen sulphide listed in Tables 5.31 and 5.32. More commonlythe reference is to published hygiene standards based on human epidemiology, animal data andextrapolations from information on related chemicals, with built-in safety factors. Table 5.12 listshygiene standards published annually by the American Conference of Governmental IndustrialHygienists (ACGIH), known as threshold limit values (TLV), and the UK equivalents publishedby the Health and Safety Executive (HSE), known as Occupational Exposure Limits (OELs). Thetable is a useful first point of reference but the original publications should be consulted for mostup-to-date values, an indication of proposed changes, and more detailed guidance on theirinterpretation. It is also important to consult the latest documentation explaining the toxicologicalbackground to the values.


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Threshold limit values (TLV)

These values represent airborne concentrations of substances to which it is believed that nearly allworkers may be repeatedly exposed by inhalation day after day without adverse health effects.Because of the wide variation in individual susceptibility, however, a small percentage of workersmay experience discomfort from some substances at concentrations below the TLV. A smallerpercentage may experience aggravation of a pre-existing condition/illness. Age, genetic factors orpersonal habits may make some individuals hypersensitive. Physical factors, e.g. UV, ionizingradiation, humidity, abnormal atmospheric pressure (altitude), excessive temperatures, or overtimeworking may add stress to the body so that effects from exposure at a TLV may be altered.Therefore best occupational hygiene practice is to maintain levels of all airborne contaminants aslow as is reasonably practicable.

There are three categories of TLV:

1 Time-weighted average (TWA) TLV – the time-weighted average concentration for a normal8 hr work day and a 40 hr work week, to which it is believed that nearly all workers may berepeatedly exposed, day after day, without untoward effects. TWA TLVs permit excursionsabove the TLV provided that they are compensated for by equivalent excursions below the TLVduring the work day. The excursion above the TLV is a rule of thumb, as explained in thesource reference.

2 Short-term exposure limit (STEL) TLV – the concentration to which it is believed that workerscan be exposed continuously for a short period of time without suffering from irritation,chronic or irreversible tissue damage, or narcosis of sufficient degree to increase the likelihoodof accidental injury, impair self-rescue or materially reduce work efficiency, and provided thatthe daily TWA limit is not exceeded. A STEL is a 15 min TWA exposure which should not beexceeded at any time during the work day even if the TWA is within the TLV. It should notoccur more than four times per day or without at least one hour between successive exposures.

3 Ceiling TLV(C) – the concentration that should not be exceeded during any part of the workingexposure. If instantaneous monitoring is not possible then the TLV(C) can be assessed over a15 min sampling period, except for those substances that may cause immediate irritation whenexposures are short.

Occupational exposure limits (OEL)

Occupational exposure limits for airborne contaminants are reviewed annually in the UK by theHealth and Safety Executive. They are published as Guidance Note EH 40/-. The two types ofexposure limit are:

• Long-term exposure limits. These are concerned with the total intake of a contaminant (orcontaminants) over a long period. As such they are appropriate for protecting workers againstthe effects of long-term exposure, or reducing the risks to an insignificant level.

• Short-term exposure limits. These are concerned primarily with the avoidance of acute effects,or reducing the risk of the occurrence.

Long-term and short-term limits are expressed as time-weighted average concentrations. For along-term limit the normal period is eight hours (although for vinyl chloride it is 1 year); for ashort-term limit the normal period is 15 minutes.

Specific short-term exposure limits are listed by the HSE for those chemicals which pose a riskof acute effects such as eye irritation from brief exposures. For other chemicals a recommended


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guideline for controlling short-term excursions is to restrict them to 3 ' long-term exposure limitaveraged over a 15 min period.

Percutaneous absorption

For most chemicals, inhalation is the main route of entry into the body. Penetration via damagedskin (e.g. cuts, abrasions) should, however, be avoided. Certain chemicals (e.g. phenol, aniline,certain pesticides) can penetrate intact skin and so become absorbed into the body. This mayoccur through local contamination, e.g. from a liquid splash, or through exposure to high vapourconcentrations. Special precautions to avoid skin contact are required with these chemicals andpotential exposure via skin absorption has to be taken into account when assessing the adequacyof control measures.

Some chemicals able to penetrate intact skin are listed in Table 5.2.


In the UK (under the Control of Substances Hazardous to Health Regulations 1999) there aremaximum exposure limits (MEL) and occupational exposure standards (OES):

• Maximum exposure limit (MEL) – the maximum concentration of an airborne substance, averagedover a reference period, to which employees may be exposed by inhalation under any circ*mstance.Thus, exposure to a chemical assigned an MEL must be as low as is reasonably practicable and,in any case, below the MEL.

• Occupational exposure standard (OES) – the concentration of an airborne substance, averagedover a reference period, at which, according to current knowledge, there is no evidence that itis likely to be injurious to employees if they are exposed by inhalation, day after day, to thatconcentration. Exposure to a chemical assigned an OES must be at no greater than thatconcentration but there is, under the UK Control of Substances Hazardous to Health Regulations,no duty to reduce it further. (Also under COSHH, if the OES is in fact exceeded but anemployer has identified the reasons, and is taking appropriate action to remedy it as soon asreasonably practicable, control may be regarded as being adequate.) However,(a) exposure should preferably be reduced below the OES to ensure that the exposure of all

personnel does not exceed it;(b) further application of good occupational hygiene principles to reduce exposure below the

OES should not be discouraged.

The application of standards

Caution is necessary in the application of control limits because of:

• The effects of mixtures of chemicals, e.g. additive or synergistic.• The effects of extended working hours, exertion etc.• The variation between workers in susceptibility to the effects of chemical exposures, e.g.

inherently or due to a pre-existing medical condition.• Changes in limits with increasing knowledge of toxicology.• With some asthmagens, respiratory sensitization may occur at atmospheric concentrations

below published limits.

In any event, hygiene standards:

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(a) should not be used as an index of relative hazard or toxicity;(b) are not well-defined dividing lines between ‘safe’ and ‘dangerous’ airborne concentrations;(c) cannot be readily extrapolated to assess long-term, non-occupational exposures, e.g. to

environmental pollutants.

Calculation of exposure

(a) Single substances. Hygiene standards are quoted for pure substances. The 8 hr TWA is bestassessed by personal dosimetry (Chapter 10) in which exposure is continuously monitored throughoutthe work day wherever the operator goes. When data are available on the individual fluctuationsin exposure, e.g. from a variety of tasks, the 8 hr TWA exposure can be calculated as in thefollowing example:

Working period Exposure(mg/m3)

8.00–10.30 0.1610.30–10.45 0.0010.45–12.45 0.0712.45–13.30 0.0013.30–15.30 0.4215.30–15.45 0.0015.45–17.15 0.21

8 hr TWA exposure = 0.16 2.5 + 0.07 2 + 0.42 2 + 0.21 1.5 + 0 1.258

' ' ' ' '

= 0.40 + 0.14 + 0.84 + 0.328

= 0.21 mg/m3

(b) Mixtures. Often working practices result in exposures to mixtures of chemicals. The individualcomponents of the mixture can act on the body independently, additively, synergistically orantagonistically. The ACGIH publication on TLVs and a Chemicals Industries Association booklet(see Bibliography) provide elementary advice on calculating hygiene standards for mixtures.

For compounds behaving additively, the relationship for compliance with the TLV of themixture is given by









3 + + + . . = 1.

where C1, C2 and C3 are the concentrations of the different components and T1, T2 and T3 are theTLVs for each pure component.

Example. Air contains 200 ppm acetone (TLV = 750), 300 ppm sec-butyl acetate (TLV = 200) and200 ppm of methyl ethyl ketone (TLV = 200):

concentrationTLV of mixture = 200

750 + 300200 + 200

200 = 0.26 + 1.5 + 1 = 2.76

i.e. the TLV has been exceeded.


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For independent effects, the relationship for compliance with the TLV of the mixture is given by:









3 = 1, = 1, = 1 etc.

Example. Air contains 0.10 mg/m3 lead (TLV 0.15 mg/m3) and 0.9 mg/m3 sulphuric acid(TLV 1 mg/m3):

0.100.15 = 0.7 0.9

1.0 = 0.9

i.e. the TLV has not been exceeded.For chemicals behaving antagonistically or synergistically, expert advice from a hygienist and

toxicologist should be sought.

Biological exposure indices

Exposure levels to certain chemicals can be monitored by determination of levels of the substanceor its metabolites in exhaled breath or in body tissues or fluids such as urine, blood, hair, nails etc.For example, blood lead levels have long been used to determine operator exposure to thischemical. Alternatively, exposure to some chemicals can be gauged by measurement of modificationsto critical biochemical constituents, e.g. changes in activity of a key enzyme, or physiologicalchanges, e.g. vitalograph measurement. The advantage of biological monitoring over environmentalanalysis is that the former measures the actual amount of substance absorbed into the body andreflects the worker’s individual responses and overall exposure. Shortcomings, however, includewide variation in individual responses to a given chemical; the unpopularity of invasive techniques;and, most importantly, the fact that it reflects a reaction to an exposure that has already occurred.

Biological exposure indices (BEI) published by the ACGIH are given in Table 5.13. BEIsrepresent the levels of determinant which are most likely to be observed in specimens collectedfrom a healthy worker who has been exposed to chemicals to the same extent as a worker withinhalation exposure to the TLV. Due to biological variability it is possible for an individual’smeasurements to exceed the BEI without incurring increased health risk. If, however, levels inspecimens obtained from a worker on different occasions persistently exceed the BEI, or if themajority of levels in specimens obtained from a group of workers at the same workplace exceedthe BEI, the cause of the excessive values must be investigated and proper action taken to reducethe exposure.

BEIs apply to 8 hr exposures, five days a week. However, BEIs for altered working schedulescan be extrapolated on pharmaco*kinetic and pharmacodynamic bases. BEIs should not be applied,either directly or through a conversion factor, to the determination of safe levels for non-occupationalexposure to air and water pollutants, or food contaminants. The BEIs are not intended for use asa measure of adverse effects or for diagnosis of occupational illness.

There is also a framework for the use of biological monitoring in the UK. A biological monitoringguidance value has been set where it is likely to be of practical value, suitable monitoring methodsexist and sufficient data are available.

Two types of value are quoted in Table 5.14:

• A Health Guidance Value, set at a level at which there is no indication from the scientificevidence available that the substance is likely to be injurious to health.

• A Benchmark Guidance value, set as a hygiene-based guidance value – actually a level which90% of available validated data are below and therefore achievable by the great majority ofindustry with good workplace practices.

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Table 5.13 Adopted biological exposure determinants

Chemical determinant Sampling time Biological Notationexposure indices

ACETONEAcetone in urine End of shift 50 mg/l Ns

ACETYLCHOLINESTERASEINHIBITING PESTICIDESCholinesterase activity in red Discretionary 70% of individuals Nsblood cells baseline

ANILINETotal p-aminophenol in urine End of shift 50 mg/g creatinine NsMethemoglobin in blood During or end of shift 1.5% of haemoglobin B, Ns,

SqARSENIC, ELEMENTALAND SOLUBLE INORGANICCOMPOUNDSInorganic arsenic plus End of workweek 35 µg/g As/l Bmethylated metabolites inurine

BENZENES-Phenylmercapturic acid inurine End of shift 25 µg/g creatinine Bt,t-Muconic acid in urine End of shift 500 µg/g creatinine B

CADMIUM ANDINORGANIC COMPOUNDCadmium in urine Not critical 5 µg/g creatinine BCadmium in blood Not critical 5 µg/l B

CARBON DISULPHIDE2-Thiothiazolidine-4-carboxylic acid (TTCA) in End of shift 5 mg/gurine creatinine

CARBON MONOXIDECarboxyhaemoglobin in blood End of shift 3.5% of haemoglobin B, NsCarbon monoxide in end- End of shift 20 ppm B, Nsexhaled air

CHLOROBENZENETotal 4-chlorocatechol in urine End of shift 150 mg/g creatinine NsTotal p-chlorophenol in urine End of shift 25 mg/g creatinine Ns

CHROMIUM (VI), water-soluble fume Increase during shift 10 µg/g creatinine BTotal chromium in urine End of shift at end of 30 µg/g creatinine B


COBALTCobalt in urine End of shift at end of

workweek 15 µg/l BCobalt in blood End of shift at end of 1 µg/l B, Sq


N,N-DIMETHYLACETAMIDEN-Methylacetamide in urine End of shift at end of 30 mg/g creatinine


N,N-DEMETHYLFORMAMIDE(DMF)N-Methylformamide in urine End of shift 15 mg/lN-Acetyl-S-(N-methyl- Prior to last shift ofcarbamoyl) cysteine in urine workweek 40 mg/l Sq


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2-ETHOXYETHANOL(EGEE) and2-ETHOXYETHYLACETATE (EGEEA)2-Ethoxyacetic acid in urine End of shift at end of 100 mg/g creatinine


ETHYL BENZENEMandelic acid in urine End of shift at end of 1.5 g/g creatinine NsEthyl benzene in end- workweek Sqexhaled air

FLUORIDESFluorides in urine Prior to shift 3 mg/g creatinine B, Ns

End of shift 10 mg/g creatinine B, Ns

FURFURALTotal furoic acid in urine End of shift 200 mg/g creatinine B, Ns

n-HEXANE2,5-Hexanedione in urine End of shift 5 mg/g creatinine Nsn-Hexane in end-exhaled air Sq

LEAD (see note below)Lead in blood Not critical 30 µg/100 ml

MERCURYTotal inorganic mercury in Preshift 35 µg/g creatinine BurineTotal inorganic mercury in End of shift at end of 15 µg/l Bblood workweek

METHANOLMethanol in urine End of shift 5 mg/l B, Ns

METHEMOGLOBININDUCERSMethemoglobin in blood During or end of shift 1.5% of haemoglobin B, Ns,


2-METHOXYETHANOL(EGME) and 2-METHOXYETHYLACETATE (EGMEA)2-Methoxyacetic acid in urine End of shift at end of Nq


METHYL CHLOROFORMMethyl chloroform in end- Prior to last shift ofexhaled air workweek 40 ppmTrichloroacetic acid in urine End of workweek 10 mg/l Ns, SqTotal trichloroethanol in urine End of shift at end of

workweek 30 mg/l Ns, SqTotal trichloroethanol in End of shift at end ofblood workweek 1 mg/l Ns

4,4%–METHYLENE BIS(2-CHLOROANILINE)(MBOCA)Total MBOCA in urine End of shift Nq

Table 5.13 Cont’d

Chemical determinant Sampling time Biological Notationexposure indices

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METHYL ETHYL KETONE(MEK)MEK in urine End of shift 2 mg/l

METHYL ISOBUTYLKETONE (MIBK)MIBK in urine End of shift 2 mg/l

NITROBENZENETotal p-nitrophenol in urine End of shift at end of 5 mg/g creatinine Ns

workweekMethemoglobin in blood End of shift 1.5% of haemoglobin B, Ns,


PARATHIONTotal p-nitrophenol in urine End of shift 0.5 mg/g creatinine NsCholinesterase activity in red Discretionary 70% of individual’s B, Ns,cells baseline Sq

PENTACHLOROPHENOL(PCP)Total PCP in urine Prior to last shift of 2 mg/g creatinine B

workweekFree PCP in plasma End of shift 5 mg/l B

PERCHLOROETHYLENEPerchloroethylene in end- Prior to last shift of 5 ppmexhaled air workweekPerchloroethylene in blood Prior to last shift of 0.5 mg/l

workweekTrichloroacetic acid in urine End of shift at end of 3.5 mg/l Ns, Sq


PHENOLTotal phenol in urine End of shift 250 mg/g creatinine B, Ns

STYRENEManelic acid in urine End of shift 800 mg/g creatinine Ns

Prior to next shift 300 mg/g creatinine NsPhenylglyoxlic acid in urine End of shift 240 mg/g creatinine Ns

Prior to next shift 100 mg/g creatinineStyrene in blood End of shift 0.55 mg/l Sq

Prior to next shift 0.02 mg/l Sq

TETRAHYDROFURANTetrahydrofuran in urine End of shift 8 mg/l

TOLUENEo-Cresol in urine End of shift 0.5 mg/l BHippuric acid in urine End of shift 1.6 g/g creatinine B, NsToluene in blood Prior to last shift of 0.05 mg/l


TRICHLOROETHYLENETrichloroacetic acid in urine End of workweek 100 mg/g creatinine Ns

Trichloroacetic acid and End of shift at end of 300 mg/g creatinine Nstrichlorethanol in urine workweekFree trichloroethanol in blood End of shift at end of 4 mg/l Ns



Table 5.13 Cont’d

Chemical determinant Sampling time Biological Notationexposure indices

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Trichloroethylene in blood SqTrichloroethylene in end-exhaled air Sq

VANADIUM PENTOXIDEVanadium in urine End of shift at end of 50 µg/g creatinine Sq


XYLENES (technical-grade)Methylhippuric acids in urine End of shift 1.5 g/g creatinine

1Women of child-bearing potential, whose blood Pb exceeds 10 µg/dl are at risk of delivering a child with a blood Pb overthe current Centres for Disease Control guidelines of 10 g/dl. If the blood Pb of such children remains elevated, they may beat increased risk of cognitive deficits. The blood Pb of these children should be closely monitored and appropriate stepsshould be taken to minimize the child’s exposure to environmental lead. (CDC Preventing Lead Poisoning in Young Children,October 1991; see BEI and TLV documentation for lead.)Notations‘B’ = backgroundThe determinant may be present in biological specimens collected from subjects who have not been occupationally exposed,at a concentration which could affect interpretation of the result. Such background concentrations are incorporated in the BEIvalue.‘Nq’ = non-quantitativeBiological monitoring should be considered for this compound based on the review; however, a specific BEI could not bedetermined due to insufficient data.‘Ns’ = non-specificThe determinant is non-specific, since it is also observed after exposure to other chemicals.‘Sq’ = semi-quantitativeThe biological determinant is an indicator of exposure to the chemical, but the quantitative interpretation of the measurementis ambiguous. These determinants should be used as a screening test if a quantitative test is not practical or as a confirmatorytest if the quantitative test is not specific and the origin of the determinant is in question.It is essential to consult the specific BEI documentation before designing biological monitoring protocols and interpreting BEIs.

(Biological limits are also in force for lead and its compounds under the Control of Lead at WorkRegulations 1998; different blood lead action, and suspension from work, levels apply to womenof reproductive capacity, young persons and other employees.

Biological monitoring of cadmium workers is also recommended; guidance on interpretationof results is given in EH1 – Cadmium: health and safety precautions.)

Odour thresholds

Some materials possess low odour thresholds: their smell gives warning of impending danger.Others possess odour thresholds well in excess of the hygiene standard. Examples are included inTable 5.12.

Reliance on the nose as an indicator, however, can be hazardous since:

• Untrained exposees may not understand the significance of an odour.• Some materials with low odour thresholds may paralyse the olfactory nerves and cause the

sense of smell to be lost within minutes (e.g. hydrogen sulphide).• Some materials are odourless (e.g. nitrogen).• Some materials, such as arsine, phosphine, toluene di-isocyanate and stibine, may be present

in concentrations in excess of their hygiene standards yet undetectable by smell.• Published odour threshold values vary widely from source to source.

Table 5.13 Cont’d

Chemical determinant Sampling time Biological Notationexposure indices

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Table 5.14 UK biological monitoring guidance values

Substance Biological monitoring Monitoring scheduleguidance values

Butan-2-one 70 µmol butan-2-one/l in Post shifturine (HGV)

2-Butoxyethanol 240 mmol butoxyacetic acid/mol Post shiftcreatinine in urine (HGV)

N,N-Dimethylacetamide 100 mmol N-methyl Post shiftacetamide/mol creatininein urine (HGV)

Carbon monoxide 30 ppm carbon monoxide Post shiftin end-tidal breath (HGV)

Dichloromethane 30 ppm carbon monoxide Post shiftin end-tidal breath (HGV)

Lindane ($ BHC (ISO)) 35 nmol/l (10 ug/l) of RandomLindane in whole blood(equivalent to 70 nmol/l) ofLindane in plasma (BGV)

MbOCA 15 µmol total MbOCA/mol Post shift(2.2%-dichloro-4,4’- creatinine in urine (BGV)methylene dianiline)

Mercury 20 µmol mercury/mol Randomcreatinine in urine (HGV)

4,4’-Methylenedianiline 50 µmol total MDA/mol Post shift for inhalation(MDA) creatinine in urine (BGV) and pre-shift next day for

dermal exposure

4-Methylpentan-2-one 20 µmol 4-methylpentan-2- Post shiftone/l in urine (HGV)

HGV = Health Guidance ValueBGV = Benchmark Guidance Value

• Workers may become acclimatized to a commonly-occurring odour, or be suffering temporarilyfrom an impaired sense of smell, e.g. due to a cold.

• The odour of a toxic chemical may be masked by the odour from another substance, or amixture.

Risk assessment of carcinogens

Arguably, risk assessment from exposure to carcinogens merits special consideration because ofthe low levels of exposure capable of producing an adverse response in certain individuals coupledwith the often long time-lag (latency period) between exposure and onset of disease.

There are several formal lists of carcinogens. Thus, in the UK under the Control of SubstancesHazardous to Health Regulations 1999 (see later) carcinogens are defined as:

• Any substance or preparation which if classified in accordance with the classification providedfor by regulation 5 of the Chemicals (Hazard Information and Packaging for Supply) Regulations1994 (‘CHIPS’) as amended would be in the category of danger, carcinogenic (category 1) orcarcinogenic (category 2).

• Substances listed in Table 5.15.


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Table 5.15 Substances and processes to which the definition of ‘carcinogen’ relates

AflatoxinsArsenicAuramine manufactureCalcining, sintering or smelting of nickel copper matte or acid leaching or electrorefining of roasted matteCoal soots, coal tar, pitch and coal tar fumesHardwood dustsIsopropyl alcohol manufacture (strong acid process)Leather dust in boot and shoe manufacture, arising during preparation and finishingMagenta manufactureMustard gas (!, !’-dichlorodiethyl sulphide)Rubber manufacturing and processing giving rise to rubber process dust and rubber fumeUsed engine oils

Substances or preparations requiring to be labelled with the risk phrase ‘R45’ (may causecancer) or ‘R49’ (may cause cancer by inhalation) under ‘CHIPS’ are listed in Table 5.16 after the5th edition of the Approved Supply List (Information approved for the classification and labellingof substances and preparations dangerous for supply). This list excludes certain coal and oil-based substances which attract the phrase ‘R45’ only when they contain a certain percentage ofa marker substance (e.g. benzene).

A summary of the evaluation of carcinogenic risks to humans by the International Agency forResearch on Cancer is given in Table 5.17 together with the IARC reference. IARC classifycarcinogens into four groups thus:

Group 1: The agent (mixture) is carcinogenic to humans. The exposure circ*mstance entailsexposures that are carcinogenic to humans.Group 2: (two classifications):Group 2A: The agent (mixture) is probably carcinogenic to humans. The exposure circ*mstanceentails exposures that are probably carcinogenic to humans.Group 2B: The agent (mixture) is possibly carcinogenic to humans. The exposure circ*mstanceentails exposures that are possibly carcinogenic to humans.Group 3: The agent (mixture, or exposure circ*mstance) is unclassifiable as to carcinogenicity inhumans.Group 4: The agent (mixture, or exposure circ*mstance) is probably not carcinogenic to humans.

Table 5.17 lists only Groups 1 and 2.

Risk control

Exposures to chemicals, resulting in toxic effects or oxygen-deficient atmospheres, may arise ina variety of industrial situations. A summary of common sources is given in Table 5.18: clearlythis is not exhaustive since exposure may result whenever materials are mixed, machined, heated,dispersed or otherwise processed or used.

The precautions naturally vary in each case. For example, to avoid improper admixture ofchemicals will require:

• Adequate training, instruction and supervision of workers.• Identification of chemicals by name and code number.• Segregated storage of incompatible substances.

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Table 5.16 Substances assigned ‘R45’ or ‘R49’ risk phrases

Substances with the risk phrase ‘R45’ (may cause cancer)AcrylamideAcrylonitrile5-Allyl-1,3-benzodioxide4-Aminoazobenzene4-Aminobiphenyl* (4-Aminodiphenyl*)Salts of 4-Aminobiphenyl* (salts of 4-Aminodiphenyl*)4-Amino-3-fluorophenolArsenic acid and its saltsArsenic pentoxideArsenic trioxideAsbestos (all types)AzobenzeneBenzeneBenzidine*Salts of benzidine*Benzidine azo dyes (except those specified elsewhere in the Approved Supply List)Benzo-(a)-anthraceneBenzo-(a)-pyreneBenzo-(e)-pyreneBenzo-(b)-fluorantheneBenzo-(j)-fluorantheneBenzo-(k)-fluorantheneBeryllium compounds (except aluminium beryllium silicates)Bis(chloromethyl)ether (BCME)Butane [1], isobutane [2], containing "0.1% butadieneButa-1,3-dieneCadmium chlorideCadmium fluorideCadmium sulphateCalcium chromateCaptafol (ISO)Carbadox (INN)Chloroaniline2-Chloroallyl diethyldithiocarbamate (Sulfallate ISO)Chlorodimethyl ether1-Chloro-2,3-epoxypropane (epichlorohydrin)Chromium III chromate (chromic chromate)ChryeneCI Basic Red 9CI Direct Black 38CI Direct Blue 6CI Direct Red 28CI Disperse Blue 1Clarified oils (petroleum), catalytic crackedClarified oils (petroleum), hydrodesulphurized catalytic crackedCobalt dichlorideCobalt sulphateco*ke (coal tar), high temperature pitchco*ke (coal tar), mixed coal–high temperature pitchco*ke (coal tar), low temperature, high temperature pitchDiaminotolueneo-DianisidineSalts of o-dianisidineo-Dianisidine-based azodyesDiarsenic trioxideDiazomethaneDibenz(a,h)anthracene1,2-Dibromo-3-chloropropane


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1,2-Dibromoethane (ethylene dibromide)3,3’-DichlorobenzidineSalts of 3,3’-dichlorobenzidine1,4-Dichlorobut-2-ene1,2-Dichloroethane (ethylene dichloride)2,2’-Dichloro-4,4’-methylenedianiline (MbOCA)Salts of 2,2-dichloro-4,4#-methylenedianiline1,3-Dichloro-2-propanol1,2:3,4 DiepoxybutaneDiethyl sulphate3,3’-Dimethylbenzidine (o-tolidine)Salts of 3,3’-dimethylbenzidine (salts of o-tolidine)Dimethylcarbamoyl chloride1,2-DimethylhydrazineN,N-DimethylhydrazineDimethylnitrosamine (N-nitroso dimethylamine)Dimethylsulphamoyl chlorideDimethyl sulphate2,6-dinitrotoluene1,2-diphenyl hydrazineDisodium [5-((4’-((2.6-hydroxy-3-((2-hydroxy-5-sulphophenyl)azo)phenyl)azo)(1,1’-biphenyl)-4-yl)azo]salicylato(4)cuprate(2-)Distillates (petroleum), intermediate vacuumDistillates (petroleum), petroleum residues vacuumDistillates (petroleum), chemically neutralized heavy paraffinicDistillates (petroleum), hydrodesulphurized light catalytic crackedDistillates (petroleum), hydrodesulphurized full-range middleDistillates (petroleum), light paraffinicDistillates (petroleum), light vacuumDistillates (petroleum), vacuumDistillates (petroleum), hydrodesulphurized middle co*kerDistillates (petroleum), heavy naphthenicDistillates (petroleum), heavy steam crackedDistillates (petroleum), acid-treated light naphthenicDistillates (petroleum), acid-treated light paraffinicDistillates (petroleum), chemically neutralized light paraffinicDistillates (petroleum), chemically neutralized heavy naphthenicDistillates (petroleum), chemically neutralized light naphthenicDistillates (petroleum), light catalytic crackedDistillates (petroleum), intermediate catalytic crackedDistillates (petroleum), light thermal crackedDistillates (petroleum), light steam-cracked naphthaDistillates (petroleum), cracked steam-cracked petroleum distillateDistillates (petroleum), hydrodesulphurized thermal cracked middleDistillates (petroleum), acid-treated heavy paraffinicDistillates (petroleum), light catalytic cracked, thermally degradedDistillates (petroleum), light naphthenicDistillates (coal tar), benzole fractionDistillates (coal tar), heavy oilsDistillates (petroleum), intermediate catalytic cracked, thermally degradedDistillates (petroleum), acid treated heavy, naphthenicDistillates (petroleum), heavy catalytic crackedDistillates (petroleum), heavy thermal crackedDistillates (petroleum), heavy paraffinicDistillates (petroleum), hydrodesulphurized intermediate catalytic crackedDistillates (petroleum), hydrodesulphurized heavy catalytic cracked1,2-Epoxypropane2,3 Epoxypropan-1-olErionite

Table 5.16 Cont’d

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EthyleneimineEthylene oxideExtracts (petroleum), heavy naphthenic distillate solventExtracts (petroleum), heavy paraffinic distillate solventExtracts (petroleum), light naphthenic distillate solventExtracts (petroleum), light paraffinic distillate solventExtracts (petroleum), light vacuum gas oil solventFuel oil no. 6Fuel oil, heavy, high sulphurFuel oil, residues–straight-run gas oils, high sulphurFuel oil, residualGas oils (petroleum), thermal cracked, hydrodesulphurizedGas oils (petroleum), heavy atmosphericGas oils (petroleum), hydrodesulphurized co*ker heavy vacuumGas oils (petroleum), steam crackedGas oils (petroleum), hydrodesulphurized heavy vacuumGas oils (petroleum), heavy vacuumGas oils (petroleum), light vacuum, thermal-cracked hydrodesulphurizedGas oils (petroleum), hydrotreated vacuumGas oils (petroleum), catalytic-cracked naphtha depropanizer overhead, C3-rich acid-freeGasoline, coal solvent extn, hydrocracked naphthaHexachlorobenzeneHexamethylphosphoric triamideHydrazineSalts of hydrazineHydrazine bis (3-carboxy-4-hydroxybenzene sulphonate)HydrazobenzeneHydrocarbons C26–55, aromatic-richLead hydrogen arsenate2-Methylaziridine4,4’-Methylene dianiline (4,4’-diaminodiphenylmethane)4,4’-Methylenedi-o-toluidineMethyl acrylamidomethoxyacetate (containing "0.1% acrylamide)Methyl acrylamidoglycolate (containing "0.1% acrylamide)2-Methoxyaniline4-Methyl-phenylenediamine (2,-4-toluenediamine)1-Methyl-3-nitro-1-nitrosoguanidineMethyl-onn-azoxymethyl acetate (Methyl azoxy methyl acetate)2-Naphthylamine*Salts of 2-naphthylamine*5-Nitroacenaphthene2-Nitroanisole4-Nitrobiphenyl* (4-Nitrodiphenyl*)Nitrofen (ISO)2-Nitronaphthalene2-NitropropaneN-Nitrosodipropylamine2,2’-(Nitrosoimino) bis ethanolPetroleum gases, liquefied (various)Potassium bromate1,3-Propanesultone3-Propanolide (Propiolactone)Residual oils (petroleum)Residues (petroleum), co*ker scrubber, condensed-ring-arom-containingResidues (petroleum), hydrogenated steam-cracked naphthaResidues (petroleum), atm towerResidues (petroleum), vacuum, lightResidues (petroleum), steam-cracked naphtha distnResidues (petroleum), steam cracked


Table 5.16 Cont’d

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Residues (petroleum), heavy co*ker and light vacuumResidues (petroleum), catalytic reformer fractionatorResidues (petroleum), hydrodesulphurized atmospheric towerResidues (petroleum), topping plant, low sulphurResidues (petroleum), heavy co*ker gas oil and vacuum gas oilResidues (petroleum), thermal crackedResidues (petroleum), catalytic reformer fractionator residue distillationResidues (petroleum), catalytic crackingResidues (petroleum), steam-cracked lightResidues (petroleum), hydrocrackedResidues (petroleum), light vacuumResidues (petroleum), steam-cracked heat-soaked naphthaResidues (petroleum), steam crackedResidues (petroleum), steam cracked, distillatesResidues (petroleum), atmosphericResidues, steam cracked, thermally treatedStrontium chromateStyrene oxideTar, brown-coalTar, brown-coal, low temperatureTar, coal, low temperatureTar, coal, high temperatureTar, coal1,4,5,8-tetraamino-anthraquinoneToluene-2,4-diammonium sulphate (4-methyl-m-phenylenediamine sulphate)o-Toluidineo-Toluidine-based azodyesThioacetamide4-o-Tolyazo-o-toluidinea,a,a-TrichlorotolueneUrethane (INN)Vinyl chloride (Chloroethylene)Zinc chromates (including zinc potassium chromate)

Substances with the risk phrase ‘R49’ (may cause cancer by inhalation)BerylliumBeryllium compounds with the exception of aluminium beryllium silicatesCadmium oxideCadmium sulphateChromium (VI) compounds (with the exception of barium chromate and of compounds specified elsewhere in the Approved

Supply List)Chromium trioxideChromyl chloride (chromic oxychloride)Dinickel trioxideNickel dioxideNickel monoxideNickel subsulphideNickel sulphidePotassium chromatePotassium dichromateRefactory ceramic fibres or special purpose fibres, with the exception of those specified elsewhere in the Approved Supply

List (man-made vitreous (silicate) fibres with random orientation with alkaline oxide and alkali earth oxide (Na2O + K2O+ CaO + MgO + BaO) content less than or equal to 18% by weight)

The classification as a carcinogen need not apply to fibres with a length weighted geometric mean diameter less two standarderrors greater than 6 µm

Sodium dichromateSodium dichromate dihydrate

* The manufacture and use of these substances, or any substance containing them, in concentrations equal to or greater than0.1% by weight, is prohibited in the UK (COSHH Reg. 4(1)).

Table 5.16 Cont’d

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Table 5.17 Evaluation of carcinogenic risks to humans by the IARC, as at 2000

Group 1: Carcinogenic to humans (78)

Agents and groups of agentsAflatoxins, naturally occurring [1402-68-2] (Vol. 56; 1993)4-Aminobiphenyl [92-67-1] (Vol. 1, Suppl. 7; 1987)Arsenic [7440-38-2] and arsenic compounds (Vol. 23, Suppl. 7; 1987)(NB: This evaluation applies to the group of compounds as a whole and not necessarily to all individual compounds withinthe group)Asbestos [1332-21-4] (Vol. 14, Suppl. 7; 1987)Azathioprine [446-86-6] (Vol. 26, Suppl. 7; 1987)Benzene [71-43-2] (Vol. 29, Suppl. 7; 1987)Benzidine [92-87-5] (Vol. 29, Suppl. 7; 1987)Beryllium [7440-41-7] and beryllium compounds (Vol. 58; 1993)(NB: Evaluated as a group)N,N-Bis(2-chloroethyl)-2-naphthylamine (Chlornaphazine) [494-03-1] (Vol. 4, Suppl. 7; 1987)Bis(chloromethyl)ether [542-88-1] and chloromethyl methyl ether [107-30-2] (technical-grade)(Vol. 4, Suppl. 7; 1987)1,4-Butanediol dimethanesulfonate (Busulphan; Myleran) [55-98-1] (Vol. 4, Suppl. 7; 1987)Cadmium [7440-43-9] and cadmium compounds (Vol. 58; 1993)(NB: Evaluated as a group)Chlorambucil [305-03-3] (Vol. 26, Suppl. 7; 1987)1-(2-Chloroethyl)-3-(4-methylcyclohexyl)-1-nitrosourea (Methyl-CCNU; Semustine) [13909-09-6] (Suppl. 7; 1987)Chromium[VI] compounds (Vol. 49; 1990)(NB: Evaluated as a group)Cyclosporin [79217-60-0] (Vol. 50; 1990)Cyclophosphamide [50-18-0] [6055-19-2] (Vol. 26, Suppl. 7; 1987)Diethylstilboestrol [56-53-1] (Vol. 21, Suppl. 7; 1987)Epstein–Barr virus (Vol. 70; 1997)Erionite [66733-21-9] (Vol. 42, Suppl. 7; 1987)Ethylene oxide [75-21-8] (Vol. 60; 1994)(NB: Overall evaluation upgraded from 2A to 1 with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Etoposide [33419-42-0] in combination with cisplatin and bleomycin (Vol. 76; 2000)[Gamma Radiation: see X- and Gamma (g)-Radiation]Helicobacter pylori (infection with) (Vol. 61; 1994)Hepatitis B virus (chronic infection with) (Vol. 59; 1994)Hepatitis C virus (chronic infection with) (Vol. 59; 1994)Human immunodeficiency virus type 1 (infection with) (Vol. 67; 1996)Human papillomavirus type 16 (Vol. 64; 1995)Human papillomavirus type 18 (Vol. 64; 1995)Human T-cell lymphotropic virus type I (Vol. 67; 1996)Melphalan [148-82-3] (Vol. 9, Suppl. 7; 1987)8-Methoxypsoralen (Methoxsalen) [298-81-7] plus ultraviolet A radiation (Vol. 24, Suppl. 7; 1987)MOPP and other combined chemotherapy including alkylating agents (Suppl. 7; 1987)Mustard gas (Sulphur mustard) [505-60-2] (Vol. 9, Suppl. 7; 1987)2-Naphthylamine [91-59-8] (Vol. 4, Suppl. 7; 1987)Neutrons (Vol. 75; 2000)Nickel compounds (Vol. 49; 1990)(NB: Evaluated as a group)Oestrogen therapy, postmenopausal (Vol. 72; 1999)Oestrogens, nonsteroidal (Suppl. 7; 1987)(NB: This evaluation applies to the group of compounds as a whole and not necessarily to all individual compounds withinthe group)Oestrogens, steroidal (Suppl. 7; 1987)(NB: This evaluation applies to the group of compounds as a whole and not necessarily to all individual compounds withinthe group)Opisthorchis viverrini (infection with) (Vol. 61; 1994)Oral contraceptives, combined (Vol. 72; 1999)(NB: There is also conclusive evidence that these agents have a protective effect against cancers of the ovary and endometrium)Oral contraceptives, sequential (Suppl. 7; 1987)


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Radon [10043-92-2] and its decay products (Vol. 43; 1988)Schistosoma haematobium (infection with) (Vol. 61; 1994)Silica [14808-60-7], crystalline (inhaled in the form of quartz or cristobalite from occupational sources) (Vol. 68; 1997)Solar radiation (Vol. 55; 1992)Talc containing asbestiform fibres (Vol. 42, Suppl. 7; 1987)Tamoxifen [10540-29-1] (Vol. 66; 1996)(NB: There is also conclusive evidence that this agent (tamoxifen) reduces the risk of contralateral breast cancer)2,3,7,8-Tetrachlorodibenzo-para-dioxin [1746-01-6] (Vol. 69; 1997)(NB: Overall evaluation upgraded from 2A to 1 with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Thiotepa [52-24-4] (Vol. 50; 1990)Treosulfan [299-75-2] (Vol. 26, Suppl. 7; 1987)Vinyl chloride [75-01-4] (Vol. 19, Suppl. 7; 1987)X- and Gamma (g)-Radiation (Vol. 75; 2000)

MixturesAlcoholic beverages (Vol. 44; 1988)Analgesic mixtures containing phenacetin (Suppl. 7; 1987)Betel quid with tobacco (Vol. 37, Suppl. 7; 1987)Coal-tar pitches [65996-93-2] (Vol. 35, Suppl. 7; 1987)Coal-tars [8007-45-2] (Vol. 35, Suppl. 7; 1987)Mineral oils, untreated and mildly treated (Vol. 33, Suppl. 7; 1987)Salted fish (Chinese-style) (Vol. 56; 1993)Shale-oils [68308-34-9] (Vol. 35, Suppl. 7; 1987)Soots (Vol. 35, Suppl. 7; 1987)Tobacco products, smokeless (Vol. 37, Suppl. 7; 1987)Tobacco smoke (Vol. 38, Suppl. 7; 1987)Wood dust (Vol. 62; 1995)

Exposure circ*mstancesAluminium production (Vol. 34, Suppl. 7; 1987)Auramine, manufacture of (Suppl. 7; 1987)Boot and shoe manufacture and repair (Vol. 25, Suppl. 7; 1987)Coal gasification (Vol. 34, Suppl. 7; 1987)co*ke production (Vol. 34, Suppl. 7; 1987)Furniture and cabinet making (Vol. 25, Suppl. 7; 1987)Haematite mining (underground) with exposure to radon (Vol. 1, Suppl. 7; 1987)Iron and steel founding (Vol. 34, Suppl. 7; 1987)Isopropanol manufacture (strong-acid process) (Suppl. 7; 1987)Magenta, manufacture of (Vol. 57; 1993)Painter (occupational exposure as a) (Vol. 47; 1989)Rubber industry (Vol. 28, Suppl. 7; 1987)Strong-inorganic-acid mists containing sulphuric acid (occupational exposure to) (Vol. 54; 1992)

Group 2A: Probably carcinogenic to humans (63)

Agents and groups of agentsAcrylamide [79-06-1] (Vol. 60; 1994)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Adriamycin [23214-92-8] (Vol. 10, Suppl. 7; 1987)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Androgenic (anabolic) steroids (Suppl. 7; 1987)Azacitidine [320-67-2] (Vol. 50; 1990)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Benz[a]anthracene [56-55-3] (Vol. 32, Suppl. 7; 1987)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Benzidine-based dyes (Suppl. 7; 1987)

Table 5.17 Cont’d

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(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Benzo[a]pyrene [50-32-8] (Vol. 32, Suppl. 7; 1987)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Bischloroethyl nitrosourea (BCNU) [154-93-8] (Vol. 26, Suppl. 7; 1987)1,3-Butadiene [106-99-0] (Vol. 71; 1999)Captafol [2425-06-1] (Vol. 53; 1991)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Chloramphenicol [56-75-7] (Vol. 50; 1990)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)a-Chlorinated toluenes (benzal chloride [98-87-3], benzotrichloride [98-07-7], benzyl chloride [100-44-7]) and benzoylchloride [98-88-4] (combined exposures) (Vol. 29, Suppl. 7, Vol. 71; 1999)1-(2-Chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU) [13010-47-4] (Vol. 26, Suppl. 7; 1987)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)para-Chloro-ortho-toluidine [95-69-2] and its strong acid salts (Vol. 48, Vol. 77; 2000)(NB: Evaluated as a group)Chlorozotocin [54749-90-5] (Vol. 50; 1990)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Cisplatin [15663-27-1] (Vol. 26, Suppl. 7; 1987)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Clonorchis sinensis (infection with) (Vol. 61; 1994)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Dibenz[a,h]anthracene [53-70-3] (Vol. 32, Suppl. 7; 1987)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Diethyl sulphate [64-67-5] (Vol. 54, Vol. 71; 1999)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Dimethylcarbamoyl chloride [79-44-7] (Vol. 12, Suppl. 7, Vol. 71; 1999)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)1,2-Dimethylhydrazine [540-73-8] (Vol. 4, Suppl. 7, Vol. 71; 1999)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Dimethyl sulphate [77-78-1] (Vol. 4, Suppl. 7, Vol. 71; 1999)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Epichlorohydrin [106-89-8] (Vol. 11, Suppl. 7, Vol. 71; 1999)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Ethylene dibromide [106-93-4] (Vol. 15, Suppl. 7, Vol. 71; 1999)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)N-Ethyl-N-nitrosourea [759-73-9] (Vol. 17, Suppl. 7; 1987)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Etoposide [33419-42-0] (Vol. 76; 2000)(NB: Other relevant data taken into consideration in making the overall evaluation)Formaldehyde [50-00-0] (Vol. 62; 1995)Glycidol [556-52-5] (Vol. 77; 2000)(NB: Other relevant data taken into consideration in making the overall evaluation)Human papillomavirus type 31 (Vol. 64; 1995)Human papillomavirus type 33 (Vol. 64; 1995)


Table 5.17 Cont’d

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IQ (2-Amino-3-methylimidazo[4,5-f]quinoline) [76180-96-6] (Vol. 56; 1993)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Kaposi’s sarcoma herpesvirus/human herpesvirus 8 (Vol. 70; 1997)5-Methoxypsoralen [484-20-8] (Vol. 40, Suppl. 7; 1987)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)4,4#-Methylene bis(2-chloroaniline) (MbOCA) [101-14-4] (Vol. 57; 1993)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Methyl methanesulphonate [66-27-3] (Vol. 7, Suppl. 7, Vol. 71; 1999)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)N-Methyl-N#-nitro-N-nitrosoguanidine (MNNG) [70-25-7] (Vol. 4, Suppl. 7; 1987)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)N-Methyl-N-nitrosourea [684-93-5] (Vol. 17, Suppl. 7; 1987)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Nitrogen mustard [51-75-2] (Vol. 9, Suppl. 7; 1987)N-Nitrosodiethylamine [55-18-5] (Vol. 17, Suppl. 7; 1987)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)N-Nitrosodimethylamine [62-75-9] (Vol. 17, Suppl. 7; 1987)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Phenacetin [62-44-2] (Vol. 24, Suppl. 7; 1987)Procarbazine hydrochloride [366-70-1] (Vol. 26, Suppl. 7; 1987)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Styrene-7,8-oxide [96-09-3] (Vol. 60; 1994)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Teniposide [29767-20-2] (Vol. 76; 2000)(NB: Other relevant data taken into consideration in making the overall evaluation)Tetrachloroethylene [127-18-4] (Vol. 63; 1995)ortho-Toluidine [95-53-4] (Vol. 27, Suppl. 7, Vol. 77; 2000)Trichloroethylene [79-01-6] (Vol. 63; 1995)1,2,3-Trichloropropane [96-18-4] (Vol. 63; 1995)Tris(2,3-dibromopropyl) phosphate [126-72-7] (Vol. 20, Suppl. 7, Vol. 71; 1999)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Ultraviolet radiation A (Vol. 55; 1992)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Ultraviolet radiation B (Vol. 55; 1992)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Ultraviolet radiation C (Vol. 55; 1992)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Vinyl bromide [593-60-2] (Vol. 39, Suppl. 7, Vol. 71; 1999)(NB: Overall evaluation upgraded from 2B to 2A with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Vinyl fluoride [75-02-5] (Vol. 63; 1995)

MixturesCreosotes [8001-58-9] (Vol. 35, Suppl. 7; 1987)Diesel engine exhaust (Vol. 46; 1989)Hot mate (Vol. 51; 1991)

Table 5.17 Cont’d

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Non-arsenical insecticides (occupational exposures in spraying and application of) (Vol. 53; 1991)Polychlorinated biphenyls [1336-36-3] (Vol. 18, Suppl. 7; 1987)

Exposure circ*mstancesArt glass, glass containers and pressed ware (manufacture of) (Vol. 58; 1993)Hairdresser or barber (occupational exposure as a) (Vol. 57; 1993)Petroleum refining (occupational exposures in) (Vol. 45; 1989)Sunlamps and sunbeds (use of) (Vol. 55; 1992)

Group 2B: Possibly carcinogenic to humans (235)

Agents and groups of agentsA-a-C (2-Amino-9H-pyrido[2,3-b]indole) [26148-68-5] (Vol. 40, Suppl. 7; 1987)Acetaldehyde [75-07-0] (Vol. 36, Suppl. 7, Vol. 71; 1999)Acetamide [60-35-5] (Vol. 7, Suppl. 7, Vol. 71; 1999)Acrylonitrile [107-13-1] (Vol. 71; 1999)AF-2 [2-(2-Furyl)-3-(5-nitro-2-furyl)acrylamide] [3688-53-7] (Vol. 31, Suppl. 7; 1987)Aflatoxin M1 [6795-23-9] (Vol. 56; 1993)para-Aminoazobenzene [60-09-3] (Vol. 8, Suppl. 7; 1987)ortho-Aminoazotoluene [97-56-3] (Vol. 8, Suppl. 7; 1987)2-Amino-5-(5-nitro-2-furyl)-1,3,4-thiadiazole [712-68-5] (Vol. 7, Suppl. 7; 1987)Amitrole [61-82-5] (Vol. 41, Suppl. 7; 1987)Amsacrine [51264-14-3] (Vol. 76; 2000)ortho-Anisidine [90-04-0] (Vol. 73; 1999)Antimony trioxide [1309-64-4] (Vol. 47; 1989)Aramite® [140-57-8] (Vol. 5, Suppl. 7; 1987)Auramine [492-80-8] (technical-grade) (Vol. 1, Suppl. 7; 1987)Azaserine [115-02-6] (Vol. 10, Suppl. 7; 1987)Aziridine [151-56-4] (Vol. 9, Suppl. 7, Vol. 71; 1999)(NB: Overall evaluation upgraded from 3 to 2B with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Benzo[b]fluoranthene [205-99-2] (Vol. 32, Suppl. 7; 1987)Benzo[j]fluoranthene [205-82-3] (Vol. 32, Suppl. 7; 1987)Benzo[k]fluoranthene [207-08-9] (Vol. 32, Suppl. 7; 1987)Benzofuran [271-89-6] (Vol. 63; 1995)Benzyl violet 4B [1694-09-3] (Vol. 16, Suppl. 7; 1987)2,2-Bis(bromomethyl)propane-1,3-diol [3296-90-0] (Vol. 77; 2000)Bleomycins [11056-06-7] (Vol. 26, Suppl. 7; 1987)(NB: Overall evaluation upgraded from 3 to 2B with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Bracken fern (Vol. 40, Suppl. 7; 1987)Bromodichloromethane [75-27-4] (Vol. 52, Vol. 71; 1999)Butylated hydroxyanisole (BHA) [25013-16-5] (Vol. 40, Suppl. 7; 1987)b-Butyrolactone [3068-88-0] (Vol. 11, Suppl. 7, Vol. 71; 1999)Caffeic acid [331-39-5] (Vol. 56; 1993)Carbon black [1333-86-4] (Vol. 65; 1996)Carbon tetrachloride [56-23-5] (Vol. 20, Suppl. 7, Vol. 71; 1999)Catechol [120-80-9] (Vol. 15, Suppl. 7, Vol. 71; 1999)Ceramic fibres (Vol. 43; 1988)Chlordane [57-74-9] (Vol. 53; 1991)Chlordecone (Kepone) [143-50-0] (Vol. 20, Suppl. 7; 1987)Chlorendic acid [115-28-6] (Vol. 48; 1990)para-Chloroaniline [106-47-8] (Vol. 57; 1993)Chloroform [67-66-3] (Vol. 73; 1999)1-Chloro-2-methylpropene [513-37-1] (Vol. 63; 1995)Chlorophenoxy herbicides (Vol. 41, Suppl. 7; 1987)4-Chloro-ortho-phenylenediamine [95-83-0] (Vol. 27, Suppl. 7; 1987)Chloroprene [126-99-8] (Vol. 71; 1999)Chlorothalonil [1897-45-6] (Vol. 73; 1999)CI Acid Red 114 [6459-94-5] (Vol. 57; 1993)


Table 5.17 Cont’d

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CI Basic Red 9 [569-61-9] (Vol. 57; 1993)CI Direct Blue 15 [2429-74-5] (Vol. 57; 1993)Citrus Red No. 2 [6358-53-8] (Vol. 8, Suppl. 7; 1987)Cobalt [7440-48-4] and cobalt compounds (Vol. 52; 1991)(NB: Evaluated as a group)para-Cresidine [120-71-8] (Vol. 27, Suppl. 7; 1987)Cycasin [14901-08-7] (Vol. 10, Suppl. 7; 1987)Dacarbazine [4342-03-4] (Vol. 26, Suppl. 7; 1987)Dantron (Chrysazin; 1,8-Dihydroxyanthraquinone) [117-10-2] (Vol. 50; 1990)Daunomycin [20830-81-3] (Vol. 10, Suppl. 7; 1987)DDT [p,p#-DDT, 50-29-3] (Vol. 53; 1991)N,N#-Diacetylbenzidine [613-35-4] (Vol. 16, Suppl. 7; 1987)2,4-Diaminoanisole [615-05-4] (Vol. 27, Suppl. 7; 1987)4,4#-Diaminodiphenyl ether [101-80-4] (Vol. 29, Suppl. 7; 1987)2,4-Diaminotoluene [95-80-7] (Vol. 16, Suppl. 7; 1987)Dibenz[a,h]acridine [226-36-8] (Vol. 32, Suppl. 7; 1987)Dibenz[a,j]acridine [224-42-0] (Vol. 32, Suppl. 7; 1987)7H-Dibenzo[c,g]carbazole [194-59-2] (Vol. 32, Suppl. 7; 1987)Dibenzo[a,e]pyrene [192-65-4] (Vol. 32, Suppl. 7; 1987)Dibenzo[a,h]pyrene [189-64-0] (Vol. 32, Suppl. 7; 1987)Dibenzo[a,i]pyrene [189-55-9] (Vol. 32, Suppl. 7; 1987)Dibenzo[a,l]pyrene [191-30-0] (Vol. 32, Suppl. 7; 1987)1,2-Dibromo-3-chloropropane [96-12-8] (Vol. 20, Suppl. 7, Vol. 71; 1999)2,3-Dibromopropan-1-ol [96-13-9] (Vol. 77; 2000)para-Dichlorobenzene [106-46-7] (Vol. 73; 1999)3,3#-Dichlorobenzidine [91-94-1] (Vol. 29, Suppl. 7; 1987)3,3#-Dichloro-4,4#-diaminodiphenyl ether [28434-86-8] (Vol. 16, Suppl. 7; 1987)1,2-Dichloroethane [107-06-2] (Vol. 20, Suppl. 7, Vol. 71; 1999)Dichloromethane (methylene chloride) [75-09-2] (Vol. 71; 1999)1,3-Dichloropropene [542-75-6] (technical-grade) (Vol. 41, Suppl. 7, Vol. 71; 1999)Dichlorvos [62-73-7] (Vol. 53; 1991)1,2-Diethylhydrazine [1615-80-1] (Vol. 4, Suppl. 7, Vol. 71; 1999)Diglycidyl resorcinol ether [101-90-6] (Vol. 36, Suppl. 7, Vol. 71; 1999)Dihydrosafrole [94-58-6] (Vol. 10, Suppl. 7; 1987)Diisopropyl sulphate [2973-10-6] (Vol. 54, Vol. 71; 1999)3,3#-Dimethoxybenzidine (ortho-Dianisidine) [119-90-4] (Vol. 4, Suppl. 7; 1987)para-Dimethylaminoazobenzene [60-11-7] (Vol. 8, Suppl. 7; 1987)trans-2-[(Dimethylamino)methylimino]-5-[2-(5-nitro-2-furyl)-vinyl]-1,3,4-oxadiazole [25962-77-0] (Vol. 7, Suppl. 7; 1987)2,6-Dimethylaniline (2,6-Xylidine) [87-62-7] (Vol. 57; 1993)3,3#-Dimethylbenzidine (ortho-Tolidine) [119-93-7] (Vol. 1, Suppl. 7; 1987)1,1-Dimethylhydrazine [57-14-7] (Vol. 4, Suppl. 7, Vol. 71; 1999)3,7-Dinitrofluoranthene [105735-71-5] (Vol. 65; 1996)3,9-Dinitrofluoranthene [22506-53-2] (Vol. 65; 1996)1,6-Dinitropyrene [42397-64-8] (Vol. 46; 1989)1,8-Dinitropyrene [42397-65-9] (Vol. 46; 1989)2,4-Dinitrotoluene [121-14-2] (Vol. 65; 1996)2,6-Dinitrotoluene [606-20-2] (Vol. 65; 1996)1,4-Dioxane [123-91-1] (Vol. 11, Suppl. 7, Vol. 71; 1999)Disperse Blue 1 [2475-45-8] (Vol. 48; 1990)1,2-Epoxybutane [106-88-7] (Vol. 47, Vol. 71; 1999)(NB: Overall evaluation upgraded from 3 to 2B with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Ethyl acrylate [140-88-5] (Vol. 39, Suppl. 7, Vol. 71; 1999)Ethylbenzene [100-41-4] (Vol. 77; 2000)Ethylene thiourea [96-45-7] (Vol. 7, Suppl. 7; 1987)Ethyl methanesulfonate [62-50-0] (Vol. 7, Suppl. 7; 1987)Foreign bodies, implanted in tissues (Vol. 74; 1999)

Polymeric, prepared as thin smooth films (with the exception of poly(glycolic acid))Metallic, prepared as thin smooth filmsMetallic cobalt, metallic nickel and an alloy powder containing 66–67% nickel, 13–16% chromium and 7% iron

Table 5.17 Cont’d

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2-(2-Formylhydrazino)-4-(5-nitro-2-furyl)thiazole [3570-75-0] (Vol. 7, Suppl. 7; 1987)Furan [110-00-9] (Vol. 63; 1995)Glasswool (Vol. 43; 1988)Glu-P-1 (2-Amino-6-methyldipyrido[1,2-a:3#,2#-d]imidazole) [67730-11-4] (Vol. 40, Suppl. 7; 1987)Glu-P-2 (2-Aminodipyrido[1,2-a:3#,2#-d]imidazole) [67730-10-3] (Vol. 40, Suppl. 7; 1987)Glycidaldehyde [765-34-4] (Vol. 11, Suppl. 7, Vol. 71; 1999)Griseofulvin [126-07-8] (Vol. 10, Suppl. 7; 1987)HC Blue No. 1 [2784-94-3] (Vol. 57; 1993)Heptachlor [76-44-8] (Vol. 53; 1991)Hexachlorobenzene [118-74-1] (Vol. 20, Suppl. 7; 1987)Hexachloroethane [67-72-1] (Vol. 73; 1999)Hexachlorocyclohexanes (Vol. 20, Suppl. 7; 1987)Hexamethylphosphoramide [680-31-9] (Vol. 15, Suppl. 7, Vol. 71; 1999)Human immunodeficiency virus type 2 (infection with) (Vol. 67; 1996)Human papillomaviruses: some types other than 16, 18, 31 and 33 (Vol. 64; 1995)Hydrazine [302-01-2] (Vol. 4, Suppl. 7, Vol. 71; 1999)Indeno[1,2,3-cd]pyrene [193-39-5] (Vol. 32, Suppl. 7; 1987)Iron-dextran complex [9004-66-4] (Vol. 2, Suppl. 7; 1987)Isoprene [78-79-5] (Vol. 60, Vol. 71; 1999)Lasiocarpine [303-34-4] (Vol. 10, Suppl. 7; 1987)Lead [7439-92-1] and lead compounds, inorganic (Vol. 23, Suppl. 7; 1987)(NB: Evaluated as a group)Magenta [632-99-5] (containing CI Basic Red 9) (Vol. 57; 1993)MeA-a-C (2-Amino-3-methyl-9H-pyrido[2,3-b]indole) [68006-83-7] (Vol. 40, Suppl. 7; 1987)Medroxyprogesterone acetate [71-58-9] (Vol. 21, Suppl. 7; 1987)MeIQ (2-Amino-3,4-dimethylimidazo[4,5-f]quinoline) [77094-11-2] (Vol. 56; 1993)MeIQx (2-Amino-3,8-dimethylimidazo[4,5-f]quinoxaline) [77500-04-0] (Vol. 56; 1993)Merphalan [531-76-0] (Vol. 9, Suppl. 7; 1987)2-Methylaziridine (Propyleneimine) [75-55-8] (Vol. 9, Suppl. 7, Vol. 71; 1999)Methylazoxymethanol acetate [592-62-1] (Vol. 10, Suppl. 7; 1987)5-Methylchrysene [3697-24-3] (Vol. 32, Suppl. 7; 1987)4,4#-Methylene bis(2-methylaniline) [838-88-0] (Vol. 4, Suppl. 7; 1987)4,4#-Methylenedianiline [101-77-9] (Vol. 39, Suppl. 7; 1987)Methylmercury compounds (Vol. 58; 1993)(NB: Evaluated as a group)2-Methyl-1-nitroanthraquinone [129-15-7] (uncertain purity) (Vol. 27, Suppl. 7; 1987)N-Methyl-N-nitrosourethane [615-53-2] (Vol. 4, Suppl. 7; 1987)Methylthiouracil [56-04-2] (Vol. 7, Suppl. 7; 1987)Metronidazole [443-48-1] (Vol. 13, Suppl. 7; 1987)Mirex [2385-85-5] (Vol. 20, Suppl. 7; 1987)Mitomycin C [50-07-7] (Vol. 10, Suppl. 7; 1987)Mitoxantrone [65271-80-9] (Vol. 76; 2000)Monocrotaline [315-22-0] (Vol. 10, Suppl. 7; 1987)5-(Morpholinomethyl)-3-[(5-nitrofurfurylidene)amino]-2-oxazolidinone [3795-88-8] (Vol. 7, Suppl. 7; 1987)Nafenopin [3771-19-5] (Vol. 24, Suppl. 7; 1987)Nickel, metallic [7440-02-0] and alloys (Vol. 49; 1990)Niridazole [61-57-4] (Vol. 13, Suppl. 7; 1987)Nitrilotriacetic acid [139-13-9] and its salts (Vol. 73; 1999)(NB: Evaluated as a group)5-Nitroacenaphthene [602-87-9] (Vol. 16, Suppl. 7; 1987)2-Nitroanisole [91-23-6] (Vol. 65; 1996)Nitrobenzene [98-95-3] (Vol. 65; 1996)6-Nitrochrysene [7496-02-8] (Vol. 46; 1989)Nitrofen [1836-75-5] (technical-grade) (Vol. 30, Suppl. 7; 1987)2-Nitrofluorene [607-57-8] (Vol. 46; 1989)1-[(5-Nitrofurfurylidene)amino]-2-imidazolidinone [555-84-0] (Vol. 7, Suppl. 7; 1987)N-[4-(5-Nitro-2-furyl)-2-thiazolyl]acetamide [531-82-8] (Vol. 7, Suppl. 7; 1987)Nitrogen mustard N-oxide [126-85-2] (Vol. 9, Suppl. 7; 1987)Nitromethane [75-52-5] (Vol. 77; 2000)2-Nitropropane [79-46-9] (Vol. 29, Suppl. 7, Vol. 71; 1999)


Table 5.17 Cont’d

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1-Nitropyrene [5522-43-0] (Vol. 46; 1989)4-Nitropyrene [57835-92-4] (Vol. 46; 1989)N-Nitrosodi-n-butylamine [924-16-3] (Vol. 17, Suppl. 7; 1987)N-Nitrosodiethanolamine [1116-54-7] (Vol. 17, Suppl. 7, Vol. 77; 2000)N-Nitrosodi-n-propylamine [621-64-7] (Vol. 17, Suppl. 7; 1987)3-(N-Nitrosomethylamino)propionitrile [60153-49-3] (Vol. 37, Suppl. 7; 1987)4-(N-Nitrosomethylamino)-1-(3-pyridyl)-1-butanone (NNK) [64091-91-4] (Vol. 37, Suppl. 7; 1987)N-Nitrosomethylethylamine [10595-95-6] (Vol. 17, Suppl. 7; 1987)N-Nitrosomethylvinylamine [4549-40-0] (Vol. 17, Suppl. 7; 1987)N-Nitrosomorpholine [59-89-2] (Vol. 17, Suppl. 7; 1987)N#-Nitrosonornicotine [16543-55-8] (Vol. 37, Suppl. 7; 1987)N-Nitrosopiperidine [100-75-4] (Vol. 17, Suppl. 7; 1987)N-Nitrosopyrrolidine [930-55-2] (Vol. 17, Suppl. 7; 1987)N-Nitrososarcosine [13256-22-9] (Vol. 17, Suppl. 7; 1987)Ochratoxin A [303-47-9] (Vol. 56; 1993)Oestrogen–progestogen therapy, postmenopausal (Vol. 72; 1999)Oil Orange SS [2646-17-5] (Vol. 8, Suppl. 7; 1987)Oxazepam [604-75-1] (Vol. 66; 1996)Palygorskite (attapulgite) [12174-11-7] (long fibres, >5 micrometres) (Vol. 68; 1997)Panfuran S [794-93-4] (containing dihydroxymethylfuratrizine)(Vol. 24, Suppl. 7; 1987)Phenazopyridine hydrochloride [136-40-3] (Vol. 24, Suppl. 7; 1987)Phenobarbital [50-06-6] (Vol. 13, Suppl. 7; 1987)Phenolphthalein [77-09-8] (Vol. 76; 2000)Phenoxybenzamine hydrochloride [63-92-3] (Vol. 24, Suppl. 7; 1987)Phenyl glycidyl ether [122-60-1] (Vol. 47, Vol. 71; 1999)Phenytoin [57-41-0] (Vol. 66; 1996)PhIP (2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine) [105650-23-5] (Vol. 56; 1993)Polychlorophenols and their sodium salts (mixed exposures) (Vol. 41, Suppl. 7, Vol. 53, Vol. 71; 1999)Ponceau MX [3761-53-3] (Vol. 8, Suppl. 7; 1987)Ponceau 3R [3564-09-8] (Vol. 8, Suppl. 7; 1987)Potassium bromate [7758-01-2] (Vol. 73; 1999)Progestins (Suppl. 7; 1987)Progestogen-only contraceptives (Vol. 72; 1999)1,3-Propane sultone [1120-71-4] (Vol. 4, Suppl. 7, Vol. 71; 1999)b-Propiolactone [57-57-8] (Vol. 4, Suppl. 7, Vol. 71; 1999)Propylene oxide [75-56-9] (Vol. 60; 1994)Propylthiouracil [51-52-5] (Vol. 7, Suppl. 7; 1987)Rockwool (Vol. 43; 1988)Safrole [94-59-7] (Vol. 10, Suppl. 7; 1987)Schistosoma japonicum (infection with) (Vol. 61; 1994)Slagwool (Vol. 43; 1988)Sodium ortho-phenylphenate [132-27-4] (Vol. 73; 1999)Sterigmatocystin [10048-13-2] (Vol. 10, Suppl. 7; 1987)Streptozotocin [18883-66-4] (Vol. 17, Suppl. 7; 1987)Styrene [100-42-5] (Vol. 60; 1994)(NB: Overall evaluation upgraded from 3 to 2B with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Sulfallate [95-06-7] (Vol. 30, Suppl. 7; 1987)Tetrafluoroethylene [116-14-3] (Vol. 19, Suppl. 7, Vol. 71; 1999)Tetranitromethane [509-14-8] (Vol. 65; 1996)Thioacetamide [62-55-5] (Vol. 7, Suppl. 7; 1987)4,4#-Thiodianiline [139-65-1] (Vol. 27, Suppl. 7; 1987)Thiourea [62-56-6] (Vol. 7, Suppl. 7; 1987)Toluene diisocyanates [26471-62-5] (Vol. 39, Suppl. 7, Vol. 71; 1999)Toxins derived from Fusarium moniliforme (Vol. 56; 1993)Trichlormethine (Trimustine hydrochloride) [817-09-4] (Vol. 50; 1990)Trp-P-1 (3-Amino-1,4-dimethyl-5H-pyrido[4,3-b]indole) [62450-06-0] (Vol. 31, Suppl. 7; 1987)Trp-P-2 (3-Amino-1-methyl-5H-pyrido[4,3-b]indole) [62450-07-1] (Vol. 31, Suppl. 7; 1987)Trypan blue [72-57-1] (Vol. 8, Suppl. 7; 1987)

Table 5.17 Cont’d

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Uracil mustard [66-75-1] (Vol. 9, Suppl. 7; 1987)Urethane [51-79-6] (Vol. 7, Suppl. 7; 1987)Vinyl acetate [108-05-4] (Vol. 63; 1995)4-Vinylcyclohexene [100-40-3] (Vol. 60; 1994)4-Vinylcyclohexene diepoxide [106-87-6] (Vol. 60; 1994)Zalcitabine [7481-89-2] (Vol. 76; 2000)Zidovudine (AZT) [30516-87-1] (Vol. 76; 2000)

MixturesBitumens [8052-42-4], extracts of steam-refined and air-refined (Vol. 35, Suppl. 7; 1987)Carrageenan [9000-07-1], degraded (Vol. 31, Suppl. 7; 1987)Chlorinated paraffins of average carbon chain length C12 and average degree of chlorination approximately 60%(Vol. 48; 1990)Coffee (urinary bladder) (Vol. 51; 1991)(NB: There is some evidence of an inverse relationship between coffee drinking and cancer of the large bowel; coffeedrinking could not be classified as to its carcinogenicity to other organs)Diesel fuel, marine (Vol. 45; 1989)(NB: Overall evaluation upgraded from 3 to 2B with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Engine exhaust, gasoline (Vol. 46; 1989)Fuel oils, residual (heavy) (Vol. 45; 1989)Gasoline (Vol. 45; 1989)(NB: Overall evaluation upgraded from 3 to 2B with supporting evidence from other data relevant to the evaluation ofcarcinogenicity and its mechanisms)Pickled vegetables (traditional in Asia) (Vol. 56; 1993)Polybrominated biphenyls [Firemaster BP-6, 59536-65-1] (Vol. 41, Suppl. 7; 1987)Toxaphene (Polychlorinated camphenes) [8001-35-2] (Vol. 20, Suppl. 7; 1987)Welding fumes (Vol. 49; 1990)

Exposure circ*mstancesCarpentry and joinery (Vol. 25, Suppl. 7; 1987)Dry cleaning (occupational exposures in) (Vol. 63; 1995)Printing processes (occupational exposures in) (Vol. 65; 1996)Textile manufacturing industry (work in) (Vol. 48; 1990)

• Identification by labels, numbers, colour coding etc. of vessels, transfer lines and valves.• Clear, unambiguous operating instructions (updated and freely available).• Segregated disposal of residues, ‘empty’ sacks, containers, liquid effluents, solid wastes, floor-

washes etc.

Control strategies in general

Strategies for reducing the risk from a toxic chemical depends upon its nature (i.e. toxic, corrosive,dermatitic) and extent. A combination of the following measures may be appropriate.


Hazardous chemicals or mixtures may be replaceable by safer materials. These may be less toxicper se, or less easily dispersed (e.g. less volatile or dusty). Substitution is also applicable tosynthesis routes to avoid the use of toxic reactants/solvents or the production, either intentionallyor accidentally, of toxic intermediates, by-products or wastes.

Minimization of inventory

As a general rule, it is preferable to minimize the amounts of toxic chemicals in storage and inprocess. There may be an advantage in handling chemicals in the most dilute practicable concentration.


Table 5.17 Cont’d

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Mechanical handling

Release of, and exposure of personnel to, toxic chemicals can be reduced by appropriate mechanicalhandling and enclosed transfer, including:

• In-plant transfer via pipelines.• In-plant transfer in specially designed containers, e.g. tote bins, corrosion-resistant containers,

with provision for mechanical lifting.• Use of enclosed transfer by pressurization or vacuum, with appropriate balancing or venting,

Table 5.18 Common sources of toxic atmospheres

Source Examples

Improper storage, handling, use or Leakages(1)

disposal of specific chemicals Improper venting or draining(1)

Open handling(1)

Incorrect notification on disposalUse of wrong material

Accidental release, spillage Transport incidentsOverfilling of containersEquipment failureUnexpected reactionsRunaway reactions

Admixture of chemicals By mistake, e.g. wrongly identifiedIn wrong proportionsIn wrong circ*mstances(1)

In wrong sequence

Fires Pyrolysis productsCombustion products(1)

VaporizationThrough domino effects

Operation in confined spaces Improper isolationFrom residuesOxygen deficiency (inherent, from purging or from rusting)

Maintenance or cleaning of equipment ResiduesLoss of containment (breaking lines)Stripping insulationBurning-off paint, flame heating componentsReaction or vaporization of cleaning products

Wastes Anaerobic breakdownAdmixture of effluentsOpen handling of effluents or ‘wastes’Atmospheric ventingSolid wastesUncontrolled incineration

Fabrication, manufacturing or machining Welding fumes(1)

operations etc. Spray painting, curing of paints(1)

Use of adhesives, curing of adhesives(1)




Plastics forming or overheating(1)

(1) May result in long-term exposure (throughout operation or in workplace).

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(e.g. with knock-out and/or scrubbing, filtration or incineration for vapours/gases), or recovery(e.g. adsorption or vapour recompression) provisions.

• Use of enclosed belt conveyors, chutes or pneumatic conveyors for solids.• Enclosed transfer of solids using screw feeders.• Transfer of solids in sealed containers or plastic sacks in preset batch weights, so avoiding

emptying for reweighing.

Vessel or equipment cleaning can also be automated, e.g. using high-pressure liquid sprays. Thisis essential, whenever practicable, to avoid entry under the Confined Spaces Regulations 1997.

Process change

A modification to the chemical process or manufacturing operation can reduce risk, for example:

• Purification of raw materials.• Use of solutions, slurries, pellets, granules or ‘dust-free’ (i.e. partially-wetted) powders instead

of dry powders.• Centralized make-up of toxic chemicals in master batches for transfer in sealed containers or

impermeable bags.• Transfer of an active chemical agent in an inherently safer form (e.g. sulphur dioxide as sodium

metabisulphite, chlorine as sodium hypochlorite). Generation of an active agent in this mannerclearly reduces the inventory in use.


Release of liquids (as mists or sprays), of vapour or of dusts may be reduced in some cases bysuppression methods. Such practices include:

• Pre-wetting of powders or fibrous solids. This extends to wet sweeping (if vacuum cleaning isimpractical).

• Use of a cover on open-topped tanks, vats or portable containers when not in use, or othermethods to reduce the exposed liquid surface.

• Use of floating roof tanks.• Lowering the operating temperature of process liquids.• Provision of a partial seal on exposed liquid interfaces, e.g. a foam blanket or a layer of floating

inert spheres.• Provision of a vapour recovery system on storage tanks.

Monitoring of equipment operation and of process parameters

The use of appropriate instruments to monitor equipment operation and relevant process variableswill detect, and provide warning of, undesirable excursions. Otherwise these can result in equipmentfailure or escape of chemicals, e.g. due to atmospheric venting, leakage or spillage. Instrumentsmay facilitate automatic control, emergency action such as coolant or pressure relief or emergencyshutdown, or the operation of water deluge systems.

Parameters which may be monitored include:

• Electrical power drawn by prime movers.• Equipment vibration.


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• Coolant flow and temperatures (in and out); low flow and high temperature.• Composition of process and effluent streams.• Pressure or vacuum; high or low pressure.• Process temperature; high or low temperature.• Flow rates of process fluids; high or low flow.• Pressure drop.• Oxygen concentration.• pH; high or low pH.• Liquid (or particulate solid) level; high or low level.• Atmospheric concentration of specific pollutants.


Segregation is a common means of controlling toxic risks, or restricting the working area exposedto them. Segregation may be by any, or a combination, of:

• Distance, e.g. spacing of equipment, operating stations, storage, buildings.• Physical barriers, e.g. splashguards, screens, or use of separate rooms. In special cases equipment

enclosures and/or complete rooms may be maintained under a slight negative pressure.• Time, e.g. performance of cleaning, demolition or stripping operations ‘out-of-hours’. Rotation

of jobs, and limitation of exposure, e.g. in confined spaces, are also examples of partialsegregation.


Contamination of the working environment can be prevented by complete containment, i.e. completeenclosure as in glove boxes in a laboratory or operation in sealed equipment. For materialstransfer, balancing is preferred to venting. However, additional precautions are necessary forcleaning, emergency venting, sampling – foreseeable events which could result in unplannedleakage or spillage. Minimize pumping or blowing, sample points, pipe joints and equipmentrequiring maintenance, and avoid hoses unless reinforced and properly secured, e.g. armouredhose. Consider tank draining/recovery arrangements. Provide adequate instrumentation on storagetanks, e.g. temperature indicator, high temperature alarm, pressure indicator, high pressure alarmand level gauge, together with relief if necessary (safety valve backed up by rupture disk toprevent seepage). Provide bunds to contain spillages and protect drainage systems and sewers.

Local exhaust ventilation

Because complete containment is physically impracticable in many cases, local exhaust ventilationis often applied to remove contaminants. The objective is to extract pollutant as near as practicableto its source and before it enters, or passes through, a worker’s breathing zone. Vents should leadaway from personnel to a safe location, with scrubbing/filtering as appropriate. Common examplesare:

• Laboratory fume cupboards, operated with the front sash at the correct setting and providingthe requisite linear air velocity at the gap.

• Lip extraction at anticipated points of leakage (e.g. around open-topped tanks, sampling,drumming/packing points).

• Open-fronted extraction booths for spraying operations, or adhesive application operations.

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Typical minimum transport velocities are given in Table 12.13 and capture velocities for variousapplications in Table 12.12.

General ventilation, which relies upon dilution by a combination of fresh air make-up andremoval, is a secondary measure.

Personal protection

The provision and use of properly selected personal protective equipment is normally regarded asback-up for the previous measures. Refer to Chapter 13. In some situations it is the only reasonablypracticable measure to ensure personal safety and its use may be a legal requirement. Examplesare:

• For entry into a confined space which may contain toxic chemicals or be oxygen deficient.Refer to Figure 13.1.

• During certain maintenance operations.• During fire-fighting or emergency rescue operations.• As a standby for emergency use in case of accidental release of toxic materials, e.g. during

tanker unloading, or disconnection of temporary pipelines or when dealing with spillagesgenerally, or if other protective measures, e.g. local exhaust ventilation, fail in service.

• As protection against chemicals to which no exposure is permissible or desirable.

Personal hygiene

A good standard of personal hygiene is required to minimize exposure by ingestion or skinabsorption of chemicals. The measures include:

• Adequate washing facilities with hot and cold running water, soap or hand cleanser, and dryingprovisions all conveniently located.

• Supply of an appropriate barrier cream (i.e. for ‘wet’ or ‘dry’ work) and afterwork cream.• Adequate showering/bathing facilities.• Avoidance of use of solvents, abrasive powders or process chemicals for skin cleaning.• Provision of overalls of an appropriate type and their frequent laundering either in-house or by

an approved contractor, with a prohibition on their unauthorized removal from the workplaceor use in e.g. canteens. Disposable overalls are appropriate in some situations.

• Prompt attention to, and covering of, damaged or perforated areas of skin.• Avoidance of eating, drinking, the application of cosmetics, or smoking in the work area.

Medical supervision and biological monitoring may be appropriate.Training for all staff, covering both normal operation and emergency situations, is essential.The combination of measures used will depend upon the degree of hazard, and the scale and

nature of the processes. For example, dust and fume control measures in the rubber industry aresummarized in Table 5.19.

Control of substances hazardous to health

In Great Britain the COSHH Regulations cover virtually all substances hazardous to health.(Excluded are asbestos, lead, materials dangerous solely due to their radioactive, explosive, orflammable properties, or solely because of high or low temperatures or pressures, or where risk


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to health arises due to administration in the course of medical treatment, and substances belowground in mines, which have their own legislation.)

Substances ‘hazardous to health’ include substances labelled as dangerous (i.e. very toxic,toxic, harmful, irritant or corrosive) under any other statutory requirements, agricultural pesticidesand other chemicals used on farms, and substances with occupational exposure limits. Theyinclude harmful micro-organisms and substantial quantities of dust. Indeed any material, mixtureor compound used at work, or arising from work activities, which can harm people’s health isapparently covered.

The regulations set out essential measures that employers (and sometimes employees) have totake:

• Prohibit use of substances listed in Table 5.20.• Assess the risk to health arising from work, and what precautions are needed (see Figure 5.3).

Table 5.19 Combination of measures for dust and fume control in the rubber industry

Factory process Health hazard Control measures

Drug room Dust from ‘small drugs’ Substitution(complex organic compounds) Master batches

Preweighed, sealed bagsDust-suppressed chemicalsLocal exhaust ventilationCare in handling

Dust from bulk fillers and whitings Local exhaust ventilationCare in handling

Dust from carbon black Master batchesLocal exhaust ventilationTotally enclosed systemsNot by ‘careful handling’ alone

Skin contact with process oils Direct metering into mixerCare in handling and protective clothing.

Compounding Dust Local exhaust ventilationMaster batchesPreweighed, sealed bagsDust-suppressed chemicalsCare in handling

Fume Local exhaust ventilationRemoval of hot product from workroom –

cool before handlingSkin contact with process oils Direct metering

Care in handling and protective clothing

Moulding Fume Local exhaust ventilationRemoval of hot product from workroom –

cool before handlingDeflection by shields

Calendering and extruding Fume Local exhaust ventilationWater cooling of extrudate

Dust from release agents Substitution of wet methods(chalk stearate or talc) Enclosure and local exhaust ventilation

Curing Fume Local exhaust ventilation at autoclavedoor and storage racks

Allow autoclave to cool before opening

Spreading Fume Local exhaust ventilationCare in handling mixes

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Table 5.20 Prohibition of certain substances hazardous to health for certain purposes

Substance Purpose for which substance is prohibited

2-Naphthylamine; benzidene; 4-aminodiphenyl; 4-nitrodiphenyl; their salts and any substance containing anyof those compounds, in a total concentration equal to orgreater than 0.1% by mass

Sand or other substance containing free silica

A substance:(a) containing compounds of silicon calculated as silica to

the extent of more than 3% by weight of dry material,other than natural sand, zirconium silicate (zircon), calcinedchina clay, calcined aluminous fireclay, sillimanite, calcinedor fused alumina, olivine; or

(b) composed of or containing dust or other matter depositedfrom a fettling or blasting process

Carbon disulphide

Oils other than white oil, or of entirely animal or vegetableorigin or entirely of mixed animal and vegetable origin

Ground or powdered flint or quartz other than natural sand

Ground or powdered flint or quartz other than:(a) natural sand; or(b) ground or powdered flint or quartz which forms part of a

slop or paste

Dust or powder of a refractory material containing not lessthan 80% of silica other than natural sand

White phosphorus

Hydrogen cyanide

Benzene and any substance containing benzene in aconcentration equal to or greater than 0.1% by mass otherthan:(a) motor fuels covered by specific EEC(b) waste Directives

Manufacture and use for all purposes including anymanufacturing process in which the substance is formed

Use as an abrasive for blasting articles in any blasting apparatus

Use as a parting material in connection with the making ofmetal castings

Use in cold-cure process of vulcanizing in the proofing ofcloth with rubber

Use in oiling the spindles of self-acting mules

Use in relation to the manufacture or decoration of potteryfor the following purposes:(a) the placing of ware for the biscuit fire;(b) the polishing of ware;(c) as the ingredient of a wash for saggers, trucks, bats, cranks

or other articles used for supporting ware during firing;and

(d) as dusting or supporting powder in potters’ shops

Use in relation to the manufacture or decoration of potteryfor any purpose except:(a) use in a separate room or building for (i) the manufacture

of powdered flint or quartz or (ii) the making of frits orglazes or the making of colours or coloured slips for thedecoration of pottery;

(b) use for the incorporation of the substance into the bodyof ware in an enclosure in which no person is employedand which is constructed and ventilated to prevent theescape of dust

Use for sprinkling the moulds of silica bricks, namely bricksor other articles composed of refractory material and containingnot less than 80% of silica

Use in the manufacture of matches

Use in fumigation except when:(a) released from an inert material in which hydrogen cyanide

is absorbed;(b) generated from a gassing powder; or(c) applied from a cylinder through suitable piping and

applicators other than for fumigation in the open air tocontrol or kill mammal pests

Uses for all purposes except:(a) use in industrial processes; and(b) for the purposes of research and development or for the

purpose of analysis$%&


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• Introduce appropriate measures to prevent or control the risk.• Ensure that control measures are used and that equipment is properly maintained and procedures

observed.• Where necessary, monitor the exposure of the workers and carry out an appropriate form of

surveillance of their health.• Inform, instruct and train employees about the risks and the precautions to be taken.


The HSE provide elegant guidance and checklists for conducting and recording risk assessmentsin COSHH Essentials (see Bibliography). This is supplemented by guidance sheets on ventilation,engineering controls and containment for a variety of unit operations including charging reactors;dipping; filling/emptying sacks/kegs/drums; mixing; sieving; weighing.

The basic steps in any assessment include a review of:

1 What substances are present? In what form?

(a) Substances brought into the workplace.(b) Substances given off during any process or work activity.(c) Substances produced at the end of any process or work activity (service activities included).

Substances ‘hazardous to health’ can be identified by:

• for brought-in substances, checking safety information on labels and that legally obtainablefrom the suppliers, e.g. on their Material Safety Data sheet: making sure it is the most up-to-date version;

• use of existing knowledge, e.g. past experience, knowledge of the process, understanding ofrelevant current best industrial practice, information on related industrial health problems;

• seeking advice from a trade association, others in a similar business, consultants;• checking whether a substance is mentioned in any COSHH Regulations or Schedules, or listed

in Guidance Note EH 40;• examination of published trade data, HSE guidance information, literature or documentation;• checking Part 1 of the approved supply list under the Chemicals (Hazard Information and

Packaging for Supply) Regulations 1994. (Anything listed as very toxic, toxic, corrosive,harmful or irritant is covered by COSHH.)

Table 5.20 Cont’d

Substance Purpose for which substance is prohibited

The following substances:chloroform, carbon tetrachloride; 1,1,2-trichloroethane,1,1,2,2-tetratchloroethane; 1,1,1,2-tetrachloroethane;pentachloroethane, vinylidene chloride; 1,1,1-trichloroethaneand any substance containing one or more of those substancesin a concentration equal to or greater than 0.1% by mass,other than:

(a) medical products;(b) cosmetic products

Supply for use at work in diffusive applications such as insurface cleaning and the cleaning of fabrics except for thepurposes of research and development or for the purpose ofanalysis

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Project details/work procedureIdentify substances hazardous to health, quantities, grouping,mixtures

Establish how they could enter the body and potential effects

Consider• Who is exposed (remember general public, other groups of

employees, contractors etc.)?• Under what circ*mstances (include breakages and spills,

emissions to atmosphere)?• How much they would be exposed to and for how long?

Prevention of exposure – is it possible?• Elimination •Enclosure of equipment/apparatus• Substitution •Ventilation• Change the process •Exclusion of people from work area

If prevention is not possible, consider control measures, e.g.•Engineering controls•Safe systems of work•Personal hygiene needs

If PPE1 or RPE2 necessary, information on types required

Emergency procedures following spillage, including first aid

Routine exposure monitoring requirements

Health surveillance requirements

Personnel training needs

Storage arrangements for raw materials, disposalarrangements for products

Any further action needed to comply with the regulations

Review date for assessment

Keep test records

Keep RPE testrecords

Keep records

Keep records

2 What is the health hazard?

• if breathed in, on contact with the skin or eyes, or if ingested?• quantity of material used, i.e. small (grams or millilitres), medium (kilograms or litres), or

large (tonnes or cubic metres)?• how dusty or volatile is the substance?

Figure 5.3 COSHH assessment procedure1 PPE = Personal Protective Equipment2 RPE = Respiratory Protective Equipment


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3 Where and how are the substances actually used or handled?

• Where and in what circ*mstances are the substances handled, used, generated, released, disposedof etc.?

• What happens to them in use (e.g. does their form change – such as from bulk solid to dust bymachining)?

• Identify storage and use areas.• Identify modes of transport.

4 What harmful substances are given off etc.?

5 Who could be affected, to what extent and for how long?

Identify both employees and non-employees – including cleaners, security staff, employees,contractors, members of the public who could be affected.

6 Under what circ*mstances?

• Is some of the substance likely to be breathed in?• Is it likely to be swallowed following contamination of fingers, clothing etc.?• Is it likely to cause skin contamination or be absorbed through the skin? (NB some materials

have a definite Sk notation in EH 40.)• Is it reasonably foreseeable that an accidental leakage, spill or discharge could occur (e.g.

following an operating error or breakdown of equipment or failure of a control measure)?


• How are people normally involved with the substance?• How might they be involved (e.g. through misuse, spillage)?

7 How likely is it that exposure will happen?

Check control measures currently in use.

• Check on their effectiveness and whether they are conscientiously/continuously applied.

8 What precautions need to be taken to comply with the rest of the COSHH Regulations?

Having regard to

• who could be exposed,• under what circ*mstances,• the level and possible length of time,• how likely exposure is,• the environmental hazards,

together with knowledge about the hazards of the substance (i.e. its potential to cause harm),conclusions are reached about personal exposure.

The employer’s duty is to ensure that the exposure of employees to a hazardous substance isprevented or, if this is not reasonably practicable, adequately controlled. Duties under the Regulations

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extend with certain exceptions to other persons, whether at work or not, who may be affected bythe employers work.


Prevention of exposure should be given priority, e.g. by:

• changing the process or method of work to eliminate the operation resulting in the exposure;• process modification to avoid production of a hazardous product, by-product or waste product;• substitution of a hazardous substance by a new, or different form of the same, substance which

presents less risk to health.

If for a carcinogen prevention of exposure is not reasonably practicable by using an alternativesubstance or process there is a requirement to apply all the measures listed in Table 5.21. If thesemeasures do not provide adequate control then suitable personal protective equipment as willadequately control exposure must be provided.

Table 5.21 Measures for the control of exposure to carcinogens

• Total enclosure of the process and handling systems unless not reasonably practicable.• Use of plant, processes and systems of work which minimize the generation of, or suppress and contain, spills, leaks, dust,

fumes and vapours.• Limitation of quantities in the workplace.• Keeping the number of persons who might be exposed to a minimum.• Prohibition of eating, drinking and smoking in areas that may be contaminated.• Provision of hygiene measures including adequate washing facilities and regular cleaning of walls and surfaces.• Designation of those areas and installations which may be contaminated and the use of suitable and sufficient warning

signs.• Safe storage, handling and disposal, and use of closed and clearly labelled containers.

For hazardous substances not classified as carcinogens, where protection of exposure is notreasonably practicable, adequate control should be achieved by measures other than personalprotection, so far as is reasonably practicable. This is subject to the degree of exposure, circ*mstancesof use of the substance, informed knowledge about the hazards and current technical developments.Any combination of the measures listed in Table 5.22 are applicable.

Table 5.22 Measures for the control of exposure to hazardous substances not classified as carcinogens

• Totally enclosed process and handling systems.• Plant or processes or systems of work which minimize generation of, or suppress or contain, the hazardous dust, fume,

biological agent etc. and limit the area of contamination in the event of spills and leaks.• Partial enclosure with local exhaust ventilation.• Local extract ventilation.• Sufficient general ventilation.• Reduction of number of employees exposed.• Exclusion of non-essential access.• Reduction in the period of exposure for employees.• Regular cleaning of contamination from, or disinfection of, walls, surfaces etc.• Provision of means for safe storage and disposal.• Prohibition of eating, drinking, smoking, application of cosmetics etc. in contaminated areas.• Provision of adequate facilities for washing, changing and storage of clothing, with arrangements for laundering contaminated



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Again when the measures in Table 5.22 do not prevent, or provide adequate control of exposurethere is a requirement to provide suitable personal protective equipment to accomplish it. Thisincludes respiratory protection, protective clothing generally, footwear and eye protection which,in the UK, complies with the Personal Protective Equipment Regulations 1992. All routes ofexposure, e.g. inhalation, ingestion, absorption through the skin or contact with the skin, must beconsidered.

Control measures in existing work situations should be reviewed, extended or replaced asnecessary to achieve and sustain adequate control.

If leaks, spills or uncontrolled releases of a hazardous substance could occur, means arerequired for limiting the extent of health risks and for regaining adequate control as soon aspossible. Where appropriate means should include:

• establish emergency procedures;• safe disposal of the substance;• sufficient suitable personal protective equipment to enable the source of the release to be safely

identified and repairs to be made;• exclusion of all persons not concerned with the emergency action from the area of contamination;• in the case of carcinogens, ensuring that employees and other persons who may be affected by

an escape into the workplace are kept informed of the failure forthwith.

Exposure limits

Exposures require control such that nearly all people would not suffer any adverse health effectseven if exposed to a specific substance (or mixture of substances) day after day. For certainsubstances there are set occupational exposure limits: refer to page 78.

As noted earlier, routes other than inhalation must also be considered. Thus exposure to asubstance which can be hazardous upon ingestion, absorption through the skin or mucous membranes,or contact with skin or mucous membranes needs control to a standard such that nearly allthe population could be exposed repeatedly without any adverse health effect. (Note that thiswill not necessarily protect those who are atopic or with a relevant pre-existing condition, e.g.dermatitis.)

Maintenance, examination and testing of control measures

An employer has specific obligations to ensure all control measures are kept in an efficient state,efficient working order and good repair. Engineering controls should be examined and tested atsuitable intervals, e.g. local exhaust ventilation equipment must be tested at least once everyfourteen months, and more often for processes specified in Table 5.23, and a record kept. Respiratorsand breathing apparatus must also be examined frequently and the checks recorded.


The exposure of workers should be monitored in certain cases, e.g.

• substances or processes listed in Table 5.24;• where it is not certain that particular control measures are working properly;• where it is not possible to be sure that exposure limits are not being exceeded;• where there could be serious risks to health if control measures were to fail or deteriorate.

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Table 5.24 Specific substances and processes for which monitoring is required (Schedule 5, Reg. 10(2))

Substance or process Minimum frequency

Vinyl chloride monomer Continuous or in accordance with a procedure approvedby the Health and Safety Executive

Spray liberated from vessels at which an Every 14 days while the process is being carried onelectrolytic chromium process is carriedon, except trivalent chromium

A record should be kept of any monitoring for at least 5 years, unless it is representative ofpersonal exposure of identifiable employees when records must be retained for at least 40 years.

Personal/workplace air monitoring

Sampling strategies may include measurement of the hazardous substance:

• in the breathing zone of a worker (personal dosimetry); and/or• in the workplace air (see Chapter 10).

Biological monitoring

For a few substances exposure may be assessed using biological monitoring (see page 114).Depending upon the substance the sampling strategy varies from post shift, random, or pre-shiftthe day after exposure.

Health surveillance

If a known adverse health effect can reasonably be anticipated under the circ*mstances of work– and could readily be observed – some form of health surveillance is appropriate. This mayinvolve a doctor or trained nurse. It may include the checking of employees’ skin for dermatitisor asking questions relevant to any asthmatic condition where work is with recognized causativeagents (e.g. epoxy resin curing agents).

In the UK health surveillance is a statutory requirement for the agents, operations and processes

Table 5.23 Frequency of thorough examination and test of local exhaust ventilation plant used in certain processes(Schedule 4, Reg. 9(2)(a))

Process Minimum frequency

Blasting in, or incidental to cleaning of metal castings, 1 monthin connection with their manufacture

Processes, other than wet processes, in which metal 6 monthsarticles (other than gold, platinum or iridium) are ground,abraded or polished using mechanical power, in any roomfor more than 12 hours per week

Processes giving off dust or fume in which non-ferrous 6 monthsmetal castings are produced

Jute cloth manufacture 1 month


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Table 5.25 UK health surveillance requirements

Medical surveillance is required unless exposure is insignificant (Schedule 6 to COSHH Reg. 11(2)a and 5)

Substance Process

Vinyl chloride monomer (VCM) In manufacture, production, reclamation, storage, discharge,transport, use or polymerization

Nitro or amino derivatives of phenol and of benzene In the manufacture of nitro or amino derivatives ofor its hom*ologues phenol and of benzene or its hom*ologues and the

making of explosives with the use of any of thesesubstances

Potassium or sodium chromate or dichromate In manufacture

Orthotolidine and its salts In manufacture, formation or use of these substancesDianisidine and its saltsDichlorobenzidine and its salts

Auramine In manufactureMagenta

Carbon disulphide Processes in which these substances are used, or givenDisulphur dichloride off as vapour, in the manufacture of indiarubber orBenzene, including benzol of articles or goods made wholly or partially ofCarbon tetrachloride indiarubberTrichloroethylene

Pitch In manufacture of blocks of fuel consisting of coal, coaldust, co*ke or slurry with pitch as a binding substance

Health surveillance is appropriate unless exposure is insignificant (Control of Carcinogenic Substances ACOP,15–18)

Selected relevant legislationAsbestos Control of Asbestos at Work Regulations 1987 and

subsequent amendmentsCompressed air (other than diving operations) Work in Compressed Air Special Regulations 1958Diving operations Diving Operations at Work Regulations 1981 and

subsequent amendmentsFlint, quartz, transfers, colours, Approved Code of Practice. Control of substancesfrits, glazes, dusts hazardous to health in the production of pottery.

Control of substances hazardous to health regulations.Ionizing radiations Ionizing Radiations Regulations 1999Lead Control of lead at Work Regulations 1998Pesticides MAFF/HSC Code of Practice for the safe use of

pesticides on farms and holdings.Approved Code of Practice. Safe use of pesticides for

non-agricultural purposes. Control of substanceshazardous to health regulations.

summarized in Table 5.25. Advice on health surveillance is also given for the agents listed inTable 5.26.

Health records must be kept of the health surveillance carried out for at least 40 years after thelast entry. Appropriate action should be taken based upon the results, i.e. it should be establishedhow and when workers should be referred for further examination and how the results will beused to improve the management of health risks.

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Information supply

There is requirement to train and inform employees of:

• the risks arising from their work• the precautions to be taken• the results of any monitoring carried out• the collective (anonymous) results of any health surveillance carried out.

Specific precautions

Ways in which these principles are applied in practice are illustrated in the following sectionusing common potentially hazardous operations or substances:

• Everyday operations such as painting and welding.• Toxic dusts such as asbestos and catalysts.• Hyperpoisons such as cyanides.• Insecticides.• Primary irritants and corrosives.• Common gases such as oxides of carbon and nitrogen, hydrogen sulphide, and inert gases.• Liquids which pose a health hazard due to volatilization, e.g. mercury and degreasing with

chlorinated solvent, i.e. dry cleaning with perchloroethylene or metal cleaning withtrichloroethylene.

• Liquids posing problems because of the presence of impurities, e.g. mineral oils.• Use of a strong disinfectant/biocide, i.e. glutaraldehyde.• Machining operations on metals involving cooling by fluids.• Application of synthetic resins, e.g. epoxy resins.• Gases present in buildings, e.g. offices.

Table 5.26 Agents for which health surveillance is advised

Agent UK HSE Guidance Note

Agents liable to cause skin disease EH 26Antimony EH 19Arsenic EH 8Beryllium EH 13Cotton dust MS 9Agents causing genetic modification ACGM/HSE Note 4

Isocyanates EH 16MS 8

Mineral wool EH 46Platinum MS 22Talc dust EH 32

Biological monitoringCadmium EH 1

Mercury EH 17MS 12

Trichloroethylene EH 5

Biological effect monitoringOrganophosphorus pesticides MS 17




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(i) Asbestos

This ubiquitous material previously found use in construction materials, lagging, brake liningsetc. If inhaled, asbestos dust may result in serious respiratory disease (e.g. asbestosis, lung cancer,mesothelioma of the pleura). Therefore strict control must be exercised over all work with asbestosproducts which may give rise to dust. Within the UK, the Control of Asbestos at Work Regulations1987 as amended by the Control of Asbestos at Work (Amendment) Regulations 1992 and 1998,and Approved Codes of Practice apply to all such work, including manufacturing, processing,repairing, maintenance, construction, demolition, removal and disposal. Because of their widerrelevance their requirements are summarized in Table 5.27.

(ii) Catalysts

Catalysts are often used to increase the rate of reactions (Chapter 3). Like many chemicals theycan pose health risks to workers (Table 5.28) unless handled with care. They can be either:

• hom*ogeneous catalysts dispersed with reactants so that reaction takes place in a single phase.The catalyst is added to the reactor with other process ingredients and removed by the normalfinishing separation processes. Worker exposure is similar to those for other process materials;

• heterogeneous catalysts where the catalysis occurs at a solid interface, often used in the formof fixed beds. These must be regenerated or replaced periodically posing significant exposurerisks.

Heterogeneous catalysts are often located at the top of a reactor and manipulated with temporaryhandling equipment. To avoid exposure to toxic dust, local ventilation should be installed; if thisis impracticable, scrupulous use of personal protective equipment and rigid compliance withsystems-of-work are essential. Respiratory equipment may include self-contained or line-fedbreathing apparatus.

Skin protection may necessitate use of full protective suits. When catalysts are dumped fromreactors at the end of a process they may prove to be extremely dusty as a result of reduction inparticle size during the reaction process. Again, depending upon the nature of the hazard, ventilation,personal protection, and use of temporary enclosures to prevent contamination of the generalwork area should be considered. Some catalysts are pyrophoric and some catalyst beds are inertedwith the added possibility of fire, or release of inerting gas into the workplace which may causeasphyxiation.

Aluminium oxide may induce respiratory irritation upon inhalation of high concentrationsresulting in emphysema and flu-like symptoms. Some catalysts are sensitive to exposure to moistair. Aluminium alkyls may be pyrophoric and personal protection must be worn to prevent skinburns. Aluminium chloride reacts with moisture in air to produce steam and irritant hydrogenchloride and with moisture in the eyes, mucous membranes or skin. It is on the basis that 3 molesof hydrogen chloride with a ceiling TLV of 5 ppm hydrolyse from one mole of AlCl3, that an8 hr TWA TLV of 2 mg/m3 for AlCl3 as Al has been set to offer the same degree of freedom fromirritation that is provided by the TLV for HCl. The material should therefore be stored in a cool,dry, well-ventilated place and the bulk stocks must be waterproof and segregated from combustibles.Pressure build-up due to evolution of hydrogen chloride should be safely vented. Depending uponscale of operation, goggles, face-shield, gloves, shoes and overalls of acid-resistant materialsshould be worn. Transfer should be in dry air or under a nitrogen blanket. Process fumes/dustshould be collected via a scrubber. Spillages should be collected before washing the area withcopious volumes of water.

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Table 5.27 Summary of precautions for work involving asbestos

Assessment Before starting any work which is liable to expose employees to asbestos dust, an assessment of the workis required to help decide the measures necessary to control exposure. This should:

• Identify the type of asbestos (or assume that it is crocidolite or amosite, to which stricter controls areapplicable than to chrysotile).

• Determine the nature and degree of exposure.• Set out steps to be taken to prevent that exposure, or reduce it to the lowest level reasonably


The assessment should be in writing except if the work involves low level exposure and is simple, so thatthe assessment can be easily repeated and explained.

Control limits (Fibres per millimetre) 4 hrs 10 minchrysotile 0.3 0.9any other form of asbestos alone 0.2 0.6

or in mixtures

Employees should never breathe air containing a level of asbestos which exceeds these limits. Moreoverthe level should always be reduced so far as it reasonably can be. Use should be made of:

• Suitable systems of work.• Exhaust ventilation equipment.• Other technical measures.• All of these techniques if reasonably practicable.

If the dust level is, or could be, above the control limit an employer must:

• Provide suitable respiratory protective equipment and ensure that it is used properly.• Post warning notices that the area is a ‘respirator zone’.

Action levels Action levels are a measure of the total amount of asbestos to which a person is exposed within a 12week period. These are set in fibres/hr per millilitre:

over 12 weekswhere exposure is solely to chrysotile 72where exposure is to any other form of asbestos, 48

alone or in mixtureswhere both types of exposure occur in the 12 week a proportionate number

period at different times

When these are, or may be, exceeded the employer must ensure that the enforcing authority has beennotified, maintain a health record of exposed workers and make sure that they receive regular medicalexaminations, and identify work areas where the action level is liable to be exceeded as ‘asbestos areas’.

Other provisions There are also requirements for an employer to:

• Monitor the exposure of employees to asbestos where appropriate.• Ensure that employees liable to be exposed to asbestos receive adequate information, instruction and

training – so that they are aware of the risks and the precautions which should be observed.• Provide protective clothing for workers when a significant quantity of asbestos is liable to be deposited

on their clothes.• Check that the plant or premises where work with asbestos is carried out is kept clean.• Make sure that there are adequate washing and changing facilities.• Provide separate storage areas for any protective clothing and respiratory protective equipment

required, and for personal clothing.• Make sure that all asbestos articles, substances and products for use at work are specially labelled.• Keep raw asbestos and asbestos waste sealed and labelled.


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Chromium oxide and chromium supported on other oxides such as aluminium oxide are importantcatalysts for a wide range of reactions. Chromium forms several oxides, the most important ofwhich are Cr2O3, CrO2 and CrO3. None are without problems and whilst it is often thought thattrivalent Cr compounds are of low toxicity, dermatitis and pulmonary disease may result fromexposure. The hexavalent compounds such as CrO3 are more toxic with potential to cause irritantand allergic contact dermatitis, skin ulcers (including ‘chrome holes’), nasal irritation and kidneydamage. Some water-insoluble compounds have been associated with an increased risk of lungcancer. An 8 hr TWA MEL has been set at 0.05 mg/m3 for Cr VI compounds. CrO3 can react withreducing agents including organic compounds (e.g. acetic acid, aniline, quinoline, alcohol, acetone,thinners, and grease) vigorously to cause fires and explosions. On heating to 250°C it liberatesoxygen to further support combustion. Containment, or use of ventilation, and personal protectiveequipment such as rubber gloves, respirators, overalls, rubber aprons, rubber boots may be necessarydepending upon the risk and nature of exposure. If the process is routine, atmospheric analysisand biological monitoring backed up with health surveillance may also be required. Stocks shouldbe protected from physical damage, stored in a dry place away from combustible materials andeasily oxidizable substances. Avoid storage on wooden floors.

Table 5.28 Health effects of catalysts

Catalyst Uses Health effect

Aluminium oxide Hydrotreating petroleum feedstocks NuisanceFluid crackingAutoexhausts

Aluminium chloride Resin manufacture by polymerization Irritation due to formation ofof low molecular-weight hydrocarbons HCl with moistureFriedel–Crafts reactions to manufacturedetergent alkylate, agrochemicals, drugs

Aluminium alkyls Alkylations/Grignard reactions Acute thermal burns, lung damage

Chromic oxide Cr3+ may be converted to the moretoxic and carcinogenic Cr6+

Colbalt Hydrogenations of solid fuels and fuel oils Lung irritation (hard metalManufacture of terephthalic acid disease); respiratory sensitizationHigh pressure production of aldehydes

Ferric oxide Oxidations Siderosis

Molybdenum compounds Hydrodesulphurization and hydrotreating Irritation of eyes andof petroleum respiratory tractOxidation of methanol to formaldehdye PneumoconiosisEpoxidation of olefinsDecomposition of alkali metal nitrides

Nickel compounds Hydrogenations (e.g. Raney nickel) Carcinogenic (nickel subsulphide).Conversion of synthesis gas to methane Skin sensitizationReduction of organo nitro compoundsto amines

Nickel carbonyl Carbonylation of acetylene and alcohols to Acute respiratory failure;produce acrylic and methacrylic acids carcinogenic

Platinum compounds Hydrosilation cross-linking of silicone polymers Sensitization dermatitisHydrogenation, isomerization andhydroformylation of alkenesAutomobile exhaust catalyst

Vanadium Pollution control, e.g. removal of hydrogen Respiratory irritation; green–blacksulphide and in manufacture of sulphuric acid tongue (transient)

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Long-term exposure to ferric oxide dust can cause changes to the lungs which are detectableby X-rays. For this reason an 8 hr TWA TLV of 5 mg/m3 has been set. Good ventilation isimportant for processes involving this compound. For regular use routine medical examinationand exclusion of staff with pulmonary disease may be necessary.

Some nickel compounds may be irritant to skin and eyes and dermal contact with nickel canresult in allergic contact dermatitis. Nickel carbonyl is extremely toxic by inhalation and shouldbe handled in totally enclosed systems or with extremely efficient ventilation. Air monitors linkedto alarms may be required to detect leaks. Respiratory equipment must be available for dealingwith leaks. Biological checks (e.g. nickel in urine) should be considered for routine operationsinvolving nickel catalysts.

Platinum is used as a catalyst for nitric and sulphuric acid production, in petroleum refiningand in catalytic mufflers to control air pollution. Platinum salts can cause respiratory complaints,asthma, and ‘platinosis’, an allergic response. Allergic dermatitis may also result from exposureto soluble platinum salts and once subjects have been sensitized it generally precludes continuedoccupational exposure at any level. The 8 hr TWA OEL for platinum metal is 5 mg/m3 but forsoluble platinum salts it is only 0.002 mg/m3. Handling precautions must include containmentwhere possible, ventilation, personal protection, and the screening out of individuals who havebecome sensitized.

Vanadium as the pentoxide is used as a catalyst in the oxidation of sulphur dioxide, oxides ofnitrogen, and other substances. Vanadium is poisonous by any route in any but small doses andthe pentavalent state, such as V2O5, is the most hazardous. Upon inhalation, the main effects areon the respiratory passages causing tracheitis, bronchitis, emphysema, pulmonary edema, orbronchial pneumonia. Symptoms of acute exposure may include nausea, vomiting, high temperature,diarrhoea, nervous malfunction and frequent coughs whilst those of chronic exposure are paleskin, anaemia, vertigo, cough, high blood pressure, green discoloration of tongue, tremor offingers and nervous malfunction. In animal studies exposure to 70 mg/m3 V2O5 dust was fatalwithin a few hours. An 8 hr TWA TLV of just 0.05 mg/m3 has been set in the USA by the ACGIH.Clearly, processes must be designed such that dust formation is prevented. Where exposure ispossible ventilation, personal protection including respiratory protection, medical surveillance,atmospheric monitoring and high standards of personal hygiene should be considered to ensureexposure is controlled.

(iii) Common gases (see also Chapter 9)

(a) Carbon dioxideCarbon dioxide gas can act as an asphyxiant due to displacement of air, resulting in oxygendeficiency (page 262). Sources include:

• Fires, because it is inevitably a product of combustion from any carbon-based fuel.• Use as an inert gas.• Discharge of carbon dioxide extinguishers.• Use of solid ‘cardice’ as a cryogen (page 261).• Natural processes, e.g. fermentation.• Water from certain underground strata, due to de-gassing (page 46).• The neutralization of acids with carbonates or bicarbonates.• As a byproduct of the synthesis of ammonia, hydrogen.

The hazard is particularly acute in confined spaces.The gas is also toxic as exemplified by Table 5.29. Furthermore, the increased respiratory rate

may cause increased amounts of other toxic gases, e.g. carbon monoxide in fires, to be inhaled.


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The special precautions appropriate for entry into confined spaces are summarized in Chapter13. In fires, evacuation of burning buildings, prohibition on re-entry and the use of self-containedbreathing apparatus by fire-fighters are key precautions.

(b) Carbon monoxideCarbon monoxide is a colourless, odourless gas and – without chemical analysis – its presence isundetectable. It is produced by steam reforming or incomplete combustion of carbonaceous fuels;typical carbon monoxide concentrations in common gases are given in Table 5.30.

Table 5.30 Typical carbon monoxide concentrations in gases

Gas Typical carbon monoxide concentration(%)

Blast furnace gas 20–25Coal and co*ke oven gas 7–16Natural gas, LPG (unburnt) nilPetrol or LPG engine exhaust gas 1–10Diesel engine exhaust gas 0.1–0.5

Table 5.29 Typical reactions of persons to carbon dioxide in air

Carbon dioxide concentration Effect(ppm) (%)

5000 0.5 TLV/OEL-TWA: can be tolerated for 8 hr exposure with no symptoms and nopermanent damage

15 000 1.5 OEL-STEL: 10 min20 000 2.0 Breathing rate increased by 50%30 000 3.0 TLV-STEL: breathing rate increased by 100%50 000 5.0 Vomiting, dizziness, disorientation, breathing difficulties after 30 min80 000 8.0 Headache, vomiting, dizziness, disorientation, breathing difficulties after short

exposure100 000 10.0 Headache, vomiting, dizziness, disorientation, unconsciousness, death after a

few minutes

Table 5.31 Typical reactions of persons to carbon monoxide in air

Carbon monoxide (ppm) Effect

30 Recommended exposure limit (8 hr time-weighted average concentration)200 Headache after about 7 hr if resting or after 2 hr exertion400 Headache with discomfort with possibility of collapse after 2 hr at rest or 45 min

exertion1200 Palpitation after 30 min at rest or 10 min exertion2000 Unconscious after 30 min at rest or 10 min exertion

Carbon monoxide is extremely toxic by inhalation since it reduces the oxygen-carrying capacityof the blood. In sufficient concentration it will result in unconsciousness and death. Typicalreactions to carbon monoxide in air are summarized in Table 5.31.

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The STEL is 200 ppm but extended periods of exposure around this, particularly withoutinterruption, raise concern for adverse health effects and should be avoided.

If a potential carbon monoxide hazard is identified, or confirmed by atmospheric monitoring,the range of control techniques summarized on page 280 must be applied.

(c) Hydrogen sulphideHydrogen sulphide occurs naturally, e.g. in gases from volcanoes, undersea vents, swamps andstagnant water. It is also a byproduct of many industrial processes, e.g. co*king and hydro-desulphurization of crude oil or coal. It is a highly toxic gas. Although readily detectable by odourat low concentrations, at high concentrations it paralyses the sense of smell and the nervoussystem controlling the lungs and hence acts as a chemical asphyxiant. Typical effects at differentconcentrations in air are summarized in Table 5.32.

Table 5.32 Typical effects or hydrogen sulphide concentrations in air

Concentration (ppm) Response

0.2 Detectable odour 20–150 Conjunctivitis

150 Olfactory nerve paralysis250 Prolonged exposure may cause pulmonary oedema500 Systemic symptoms may occur in 0.5 to 1 hr

1000 Rapid collapse, respiratory paralysis imminent5000 Immediately fatal

A hazard of hydrogen sulphide may be present in petroleum refining and recovery involvingsour crudes, due to chemical breakdown of sulphides (e.g. by acids), or from anaerobic decompositionof sulphur-containing materials, e.g. in wells, sewers or underground pumping stations. Furtherproperties and cylinder-handling precautions are given in Chapter 9. If hydrogen sulphide exposureis possible environmental levels should be monitored and if necessary ventilation provided andrespiratory protection worn.

(d) Inert gasesMost toxicologically inert gases, e.g. nitrogen, argon, helium (and indeed common flammablegases, e.g. hydrogen, methane, propane, butane, acetylene) can generate oxygen-deficientatmospheres. These occur most often within confined spaces but may also be present near ventsor open manways. The gases have no colour, smell or taste. Responses at given depleted oxygenlevels are summarized in Table 5.7: to reduce the oxygen content to a fatal level requires a simpleadded asphyxiant gas concentration of approximately 50%.

Oxygen deficiency may arise through, for example:

• Use of nitrogen or argon to exclude air from vessels.• Use of carbon dioxide fire extinguishers in a confined space.• Excessive generation of e.g. nitrogen or helium gas from cryogenic liquids.• Leakage of argon from an argon arc welding set in an unventilated enclosure.• Formation of rust inside a closed steel tank (oxygen is removed from the atmosphere by the

oxidation of iron).• Neutralizing vessel contents with carbonate or bicarbonate, displacing the air with carbon



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Entry into a confined space requires strict control (page 417). Whenever oxygen deficiencymay be encountered air quality checks should be made and appropriate breathing apparatus used.

(e) Oxides of nitrogenOxides of nitrogen comprise nitrous oxide (N2O), nitric oxide (NO), nitrogen dioxide (NO2),dinitrogen tetroxide (N2O4) and dinitrogen pentoxide (N2O5). N2O5 is a low-melting solid rapidlydecomposing in air to NO2/N2O4 and nitrogen hexoxide (NO3). (The last is stable only below–142°C above which it decomposes into oxygen and nitrogen dioxide.)

Nitrous oxide is a colourless, non-flammable, non-corrosive gas with sweetish odour and taste.It is generally considered to be non-toxic and non-irritating but one of its main applications is use,in combination with air or oxygen, as a weak anaesthetic in medicine and dentistry. At lowconcentrations it produces hysteria (hence the term ‘laughing gas’). A higher than expectedincidence of spontaneous abortions among female workers exposed directly to anaesthetic gaseshas been reported but the current 8 hr TWA OES (page 99) of 100 ppm is believed sufficiently lowto prevent embryofetal toxicity in humans. At high concentrations in the absence of air it is asimple asphyxiant. It is also used as a dispersing agent in whipping cream. It is oxidized in air tothe dioxide. ‘Nitrous fume’ exposure in the main involves the inhalation of airborne NO2/N2O4mixtures – usually in an equilibrium ratio of approximately 3:7 – which at high concentrationsexist as a reddish-brown gas. Sources of fume include:

• Fuming nitric acid.• Chemical reactions with nitrogen-based chemicals, including the firing of explosives.• Electric arc welding, flame-cutting using oxy-acetylene, propane or butane flames, or such

flames burning in air.• Forage tower silos.• The exhaust of metal-cleaning processes.• Fires, e.g. involving ammonium nitrate.• Exhausts from diesel vehicles.

The effects of this mixture of gases are insidious: several hours may elapse before lung irritationdevelops. It is feebly irritant to the upper respiratory tract due to its relatively low solubility.

Effects of given concentrations of nitrogen oxides are listed in Table 5.33: the margin betweenconcentrations that provoke mild symptoms and those proving to be fatal is small. A person witha normal respiratory function may be affected by exposure to as low as 5 ppm; diseases such asbronchitis may be aggravated by such exposures. The current 8 hr TWA OES is 3 ppm with anSTEL (page 99) of 5 ppm.

Table 5.33 Effects of nitrogen oxides

Concentration Effect(ppm in air)

<60 No warning effect (although the odour threshold is <0.5 ppm) 60–150 Can cause irritation and burning in nose and throat

100–150 Dangerous in 30–60 minutes200–700 Fatal on short exposure (*1 hour)

First-aid measures for people exposed to nitrogen dioxide are mentioned in Chapter 9. In anyevent, containment, ventilation and/or appropriate respiratory protection should be considereddepending upon scale of operation and level of exposure.

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(iv) Cyanides

As a group, the cyanides are among the most toxic and fast-acting poisons. (This is due to thecyanide ion which interferes with cellular oxidation.)

Hydrogen cyanide (prussic acid) is a liquid with a boiling point of 26°C. Its vapour is flammableand extremely toxic. The effects of acute exposure are given in Table 5.34. This material is a basicbuilding block for the manufacture of a range of chemical products such as sodium, iron orpotassium cyanide, methyl methacrylate, adiponitrile, triazines, chelates.

Table 5.34 Toxic effects of hydrogen cyanide

Concentration in air Effect(ppm)

2–5 Odour detectable by trained individual10 (UK MEL 10 mg/m3 STEL (SK))18–36 Slight symptoms after several hours45–54 Tolerated for 3–60 min without immediate or late effects

100 Toxic amount of vapours can be absorbed through skin110–135 Fatal after 30–60 min, or dangerous to life135 Fatal after 30 min181 Fatal after 10 min270 Immediately fatal

Although organocyanides (alkyl cyanides, nitriles or carbonitriles), in which the cyanide groupis covalently bonded, tend as a class to be less toxic than hydrogen cyanide, many are toxic intheir own right by inhalation, ingestion or skin absorption. Some generate hydrogen cyanideunder certain conditions, e.g. on thermal degradation.

The properties of selected cyanides of industrial importance are summarized in Table 5.35.Depending upon scale of operation, precautions for cyanides include:

• techniques to contain substances and avoid dust formation (solid cyanides), aerosol formation(aqueous solutions), and leakages (gas);

• gloves, face and hand protection;• high standards of personal hygiene;• ventilation and respiratory protection (dust or gaseous forms);• environmental monitoring for routine processes;• health surveillance.

(v) Glutaraldehyde

Glutaraldehyde (1,3-diformyl propane) is a powerful, cold disinfectant. It is used principally inaqueous solution as a biocide and chemical disinfectant. It has been widely used in the healthservices, e.g. in operating theatres, endoscopy units, dental units and X-ray film processing.

The hazards with glutaraldehyde are those of irritation to the skin, eyes, throat, and lungs. Itcan cause dermal and respiratory sensitization, resulting in rhinitis and conjunctivitis or asthma.In the UK the Maximum Exposure Limit is just 0.05 ppm (8 hr TWA limit) and 0.05 ppm (15 minSTEL) with a ‘Sen’ notation (p. 93).

Wherever practicable it is advisable for glutaraldehyde to be replaced by a less hazardouschemical, e.g. it should not be used as a general wipe-down disinfectant.


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Table 5.35 Selected cyano compounds

Chemical Toxicity Properties

Acetone cyanohydrin Highly toxic by inhalation or ingestion Colourless combustible liquid(Oxyisobutyric nitrile) Irritating and moderately toxic upon skin Flash point 73°C(CH3)2C(OH)CN contact Ignition temperature 68.7°C

Readily decomposes to HCN and acetone Completely soluble in waterat 120°C, or at lower temperatureswhen exposed to alkaline conditions

Acetonitrile Highly toxic by ingestion, inhalation or Colourless liquid with ether odour and(Methyl cyanide) skin absorption sweet burning tasteCH3CN Insufficient warning properties. Lethal Flash point 73°C

amounts can be absorbed without Ignition temperature 52.3°Cgreat discomfort Flammable limits 4.4%–16%

High concentrations rapidly fatalPossibility of severe delayed reactions

Acrylonitrile Closely resembles HCN in toxic action Colourless flammable liquid with mild,(Vinyl cyanide) Poisonous by inhalation, ingestion or faintly pungent odourCH2CHCN skin absorption Flash point 0°C. Dilute water solutions

Emits cyanides when heated or also have low flash pointscontacted by acids or acid fumes

Symptoms: flushed face, irritation of eyesand nose, nausea etc.

Adiponitrile Can behave as a cyanide when ingested Water-white, practically odourless liquid(Tetramethylene cyanide) or otherwise absorbed into the body Flash point 93°CCN(CH2)4CN Combustion products may contain HCN Specific gravity 0.97

Vapour density 3.7Calcium cyanide Reacts with air moisture to release HCN. Nonflammable white powder or crystalsCa(CN)2 If finely ground and the relative

humidity of the air is >35%, this canoccur fairly rapidly

Releases HCN slowly on contact withwater or CO2, or rapidly with acids

Do not handle with bare handsCyanogen Highly poisonous gas similar to HCN Colourless flammable gas with a pungent(Ethane dinitrile, Prussite) almondlike odour, becoming acrid in(CN)2 higher concentrations

Water solubleVapour density 1.8

Cyanogen bromide Extremely irritating and toxic vapours Transparent crystals with a penetrating(Bromine cyanide) Contact with acids, acid fumes, water or odourCNBr steam can produce toxic and Melting point 52°C

corrosive fumes Boiling point 61°CVapour density 3.6Water soluble

Cyanogen chloride Poisonous liquid or gas Colourless liquid with a strong irritating(Chlorine cyanide) Vapour highly irritating and very toxic smellCNCl Boiling point 13°C

Vapour density 2.1Potassium cyanide On exposure to air, gradually Nonflammable white lumps or crystalsKCN decomposes to release HCN Faint odour of bitter almonds

Poisonous by ingestion, inhalation or Completely water solubleskin absorption

Do not handle with bare hands. Strongsolutions may be corrosive to the skin

Sodium cyanide Poisonous by inhalation, ingestion or Nonflammable white granules, fusedNaCN skin absorption pieces or ‘eggs’

Do not handle with bare hands Odourless when dry; slight almondReleases HCN slowly with water, more odour in damp air

rapidly with acids Completely water soluble

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Basic precautions include those in Table 5.36.

Table 5.36 Basic precautions for handling gluteraldehyde

• Use with proper local extract ventilation or, as a minimum, in a well-ventilated area• Replace lids on buckets, waste bins and troughs• Use in a manner which enables splashes, skin contact and exposure to airborne droplets or fumes to be avoided• Use appropriate personal protective equipment, e.g. gloves, apron, visor or goggles• Automation of disinfection procedures, e.g. use of automatic machines, still with a good standard of general ventilation,

for disinfecting endoscopes• Establishment of a procedure to deal safely with any spillages

(vi) Insecticides

Insecticides may be in the form of liquid concentrates, requiring dilution in water or solvents;solutions, wettable powders, granules or pastes; or pressurized or liquefied gases. Applicationmay be as fumigants or fogs, sprays, dust or granules. Obviously all such chemicals are toxic tovarying degrees so that exposure via inhalation or ingestion, and in many cases via skin absorption,should be minimized.

The variation in toxicity of common organophosphate insecticides is exemplified in Table 5.37.The range of chlorinated hydrocarbon insecticides (Table 5.38) have, with the exception of Endrinand Isodrin, somewhat lower oral and dermal toxicities. The toxicities of a range of other insecticides,fungicides, herbicides and rodenticides are summarized in Table 5.39.

Essential precautions with insecticides are listed in Table 5.41.

(vii) Irritants and corrosives

As a class, primary irritants are the most widely encountered chemicals in industry and includeinorganic acids and alkalis, halogens and halogen salts, chlorosilanes, detergents, organic solventsand organic acids and many derivatives, e.g. acid chlorides and anhydrides. In extreme cases,many are also corrosive (Table 5.4) and, in the case of organic compounds, possibly flammable.The skin, eyes and mucous membranes are at greatest risk although the respiratory tract isaffected if the materials become airborne as dusts or aerosols, or if gaseous or volatile, e.g.halogens and inorganic anhydrous acids (Tables 5.42 and 5.43). Table 5.44 lists the properties ofselected organic acids.

Typical precautions for work with irritant and corrosive chemicals are listed in Table 5.45.

(viii) Mercury

Mercury is used in the manufacture of thermometers, barometers and switchgear, and in theproduction of amalgams with copper, tin, silver and gold, and of solders. A major use in thechemical industry is in the production of a host of mercury compounds and in mercury cells forthe generation of chlorine. Mercury has a significant vapour pressure at ambient temperature andis a cumulative poison.

The liquid attacks many metals, including aluminium, gold, copper and brass. Splashes breakup into very small, mobile droplets, making clean-up of spillages difficult.

Mercury should not be left exposed in a laboratory. Reservoirs etc. should be covered with alayer of water or oil and, if practicable, the neck of the vessel plugged. The risk is increased by


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Table 5.37 Organophosphate insecticides (see also Table 5.12)

Insecticide Oral LD50 Dermal LD50 UK OES(mg/kg) (mg/kg) 8 hr TWA value


Abate 8600–13 000 4000 —Azinphosmethyl (Guthion) 11–13 220 0.2 SKAzodrin 17.5–20 112–126 —Bidrin 22 225 —Carbophenothion 10–30 27–54 —Chlorthion 890–980 4100–4500 —Ciodrin 125 385 —Coumaphos (Co-Ral) 15.5–41 860 —Demeton (Systox) 2.5–6.2 8.2–14 —Diazinon 76–108 455–900 —Dicapthon 330–400 790–1250 —Dimethyldichlorovinyl Phosphate (DDVP) 56–80 75–107 —Dimethoate 215 400–610 —Dioxathion (Delnav) 23–43 63–235 0.2 SKDisulfoton (Di-Syston) 2.3–6.8 6–15 0.1O-ethyl-O-p-nitrophenyl Phenyl 7.7–36 25–230 —

Phosphonothioate (EPN)Ethion 27–65 62–245 8 SKFenthion (Baytex) 215–245 330 —Malathion 1000–1375 4444 10 SKMethyl Parathion 14–24 67 0.2 SKMethyl Trithion 98–120 190–215 —Naled 250 800 3 SKNemacide 270 — —NPD — 1800–2100 —Octamethyl Pyrophosphoramide (Schradan) 9.1–42 15–44 —Parathion 3.6–13 6.8–21 0.1 SKPhorate (Thimet) 1.1–2.3 2.5–6.2 0.05 SKPhosdrin (Mevinphos) 3.7–6.1 4.2–4.7 0.1 SKPhosphamidon 23.5 107–143 —Ronnel (Korlan) 1250–2630 5000 10Ruelene 460–635 — —Sulfotep, Tetraethyl Dithiopyrophosphate (TEDP) — — 0.2 SKTetraethyl Pyrophosphate (TEPP) 1.05 2.4 0.05 SKTrichlorfon (Dipterex) 560–630 2000 —

SK Can be absorbed through skin.The LD50 varies according to species of animal, sex, age and health.

heating, e.g. due to spillage on a hot surface; no glass blowing should therefore be done onmercury-contaminated glass.

Care is essential to avoid spillages. A fine capillary tube connected to a filter flask and filterpump should be used immediately to collect any spillage. Surfaces, e.g. floors, contaminated byminute mercury droplets should be treated with sulphur or zinc dust, or by use of a commercialclean-up kit.

Rooms in which mercury is regularly exposed should be subjected to routine atmosphericmonitoring. Personnel in such rooms should receive periodic medical examinations.

For routine laboratory precautions refer to Table 5.40.

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Table 5.38 Chlorinated hydrocarbon insecticides (see also Table 5.12)

Insecticide Oral LD50 Dermal LD50 UK OES(mg/kg) (mg/kg) 8 hr TWA value


Aldrin 39–60 98 0.25 SKBenzene Hexachloride (BHC) 1250 — —Chlordane 335–430 690–840 0.5 SKChlorobenzilate 1040–1220 <5000 —DDT 113–118 2510 1.0Dichloropropane-Dichloropropene 140 2100 —Dicofol (Kelthane) 1000–1100 1000–1230 —Dieldrin 46 60–90 0.25 SKDilan — 5900–6900 —Endosulfan (Thiodan) 18–43 74–130 —Endrin 7.5–17.8 15–18 0.1 SKEthylene Dibromide 117–146 300 —Ethylene Dichloride 770 3890 —Heptachlor 100–162 195–250 0.5 SKIsodrin 7.0–15.5 23–35 —Kepone 125 <2000 —Lindane 88–91 900–1000 0.5 SKMethoxychlor 5000 — 10Mirex 600–740 2000 —Para-Dichlorobenzene 1000 — —Perthane 4000 — —Strobane 200 5000 —TDE 4000 4000 —Telone 200–500 — —Toxaphene 80–90 780–1075 —

SK can be absorbed through skin.The LD50 varies according to species of animal, sex, age and health.

(ix) Mineral oil lubricants

Mineral oils, i.e. oils derived from petroleum, are widely used as lubricants, cutting oils, solubleoil coolants etc.

They have very low acute toxicities, i.e. oral LD50 values of around 10 g/kg. They are notabsorbed via the skin and are insufficiently volatile to produce harmful vapours at room temperature.Additives are used in small quantities for specific properties but these do not normally affect thehealth and safety characteristics. Dermatitis may be caused by repeated or prolonged contact ofmineral oils with the skin. Such contact with higher boiling fractions over many years can resultin warty growths which may become malignant, e.g. on the scrotum following contamination ofthe front of overalls, possibly from oily rags in trouser pockets. Carcinogenic activity is reducedby solvent refining of the base stocks but can increase with use. Oil mists at concentrationsnormally encountered are primarily a nuisance, but very high concentrations could, on inhalation,cause irritation of the lungs leading to pneumonia. Because of the carcinogenic potential theatmospheric concentration should be controlled below 5 mg/m3 as an 8 hr TWA concentration and10 mg/m3 as a 10 min STEL concentration. General recommendations for precautions withmineral oils are summarized in Table 5.46.


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Table 5.39 Insecticides, rodenticides, fungicides and herbicides (see also Table 5.12)

Substance Oral LD50 Dermal LD50 UK OES 8hr TWA value(mg/kg) (mg/kg) (mg/m3)

InsecticidesBinapacryl 58–63 720–810 —Calcium Arsenate 298 2400 —Carbaryl 500–850 4000 5Cryolite 200 — —DN-111 330 1000 —Lead Arsenate — 2400 0.15Metaldehyde 1000 — —Morestan 1800 — —Naphthalene 2400 2500 50Nicotine Sulphate 83 285 —Ovex 2050 — —Paris Green 100 2400 —Pyrethrum 1500 1800 —Rotenone 50–75 940 5Ryania 1200 4000 —Tetradifon 14 700 10 000 —Zineb 5200 — —

RodenticidesSodium Fluoroacetate 0.05 SKStrychnine 0.15Thallium Sulphate 0.1 as TI, SKWarfarin 0.1

FungicidesFerbam 17 000 — 10Formaldehyde — — 2.5 MELOrganic Mercurials — — 0.01Maneb 7500 — —Nabam 395 — —Pentachlorophenol — — 0.5 SKZiram 1400 — —

Herbicides2,4-D 375–700 — 10

(differentacids, saltsand esters)

2,4,5,-T 481–500 — 10(different acidsand esters)

Dinitrocresol (DNOC) 30 — 0.2 SK

SK Can be absorbed through skin.The LD50 varies according to species of animal, sex, age and health.

(x) Metalworking fluids

Metalworking fluids contain mineral oils (refer to p. 80) or synthetic lubricants; they are used neator in admixture with water. They may contain small amounts of biocides, stabilizers, emulsifiers,corrosion inhibitors, fragrances and extreme pressure additives. The formulations render themsuitable for application to metal being worked, generally from a recirculatory system, to providelubrication, corrosion protection, swarf removal and cooling of the tool and machined surface.

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Table 5.41 Guidance on safety with pesticides

Approval In the UK only approved pesticides may be supplied and usedEach product has an approval number and conditions of use

Storage Suitable sitingrequirements Adequate capacity and construction

Designed to hold spillageProperly lit and ventilatedFire- and frost-resistantDesigned so that containers can be safely stacked and movedClearly markedKept locked except when in use

Competence Every user must be competent (Certificate of Competence required in UK)

Information Workers must be supplied with sufficient information and guidance

Evaluation of Product selectionpossible How to comply with the conditions of approvalproblems Selection of protective clothing

How to avoid spray driftHow to avoid environmental damageNeed to warn neighbours and others who may be affected etc.

Training Pesticide legislationrequirements Decisions on whether a pesticide has to be used

Selection of appropriate pesticideInterpretation of labels and codes of practiceHazards and risks to human health/the environmentSelection and use of engineering controls and protective clothingCalibration and safe operation of application equipmentSafe storage and disposal of pesticidesEmergency action in case of poisoning or contaminationHow to contain and deal with accidental spillageConstraints imposed by weather or other factorsAppropriate record keepingNeed for exposure monitoring/health surveillance

Exposure control Use engineering/technical means, e.g.Low-level filling bowlsSuction probesClosed handling systemsSoluble packsIn-cab electronic sprayer controlsHydraulic boom-folding

(These measures should be used in preference to protective clothing)

Disposal Minimize disposal requirements by careful estimation of needs and correct measurementDispose of dilute pesticides by using as a spray, in accordance with ‘approval’, in a safe/approved areaConcentrated, unused pesticides should be stored, returned or disposed of as toxic waste

Table 5.40 Routine laboratory precautions with mercury

Avoid the use of mercury, if possibleStore in airtight containers or under water or liquid paraffinHandle over a suitable tray near to the apparatus in useAvoid wearing rings. Wear gloves. Wash the hands and gloves after handling mercuryUse catchpots under apparatus containing mercuryUse only apparatus strong enough to withstand the considerable force which may arise due to movements of mercury (e.g.

rigid pvc or polythene)Clean up all spillages immediately and check for pockets (e.g. in cracks and crevices) by monitoringDecontaminate equipment such as vacuum pumps and glassware prior to service/maintenance


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Table 5.42 Halogens

Halogen Melting point Boiling point Vapour density Threshold limit Reactivity and Appearance and Colour of(°C) (°C) (air = 1.0) value (ppm) oxidizing strength state at 21°C gas/vapour

Fluorine (F2) –217 –188 1.3 0.1 Extremely active Pale yellow gas Pale yellow

Chlorine (Cl2) –101 –34 2.5 1.0 Very active Greenish-yellow Greenish-yellowgas. Amberliquid at 5.8bar pressure

Bromine (Br2) –6.6 59 5.5 0.1 Active Dark red liquid Dark redto reddish-brown

lodine (I2) 113 185(1) 8.6 0.1 Least active Bluish-black Violetlustrous solid

(1) Readily sublimes at lower temperatures.

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Hand dispensing is also used but on most modern machines application is by a continuous jet,spray or mist.

Skin contact with metalworking fluids may cause skin irritation or a contact irritant dermatitis.Contact with neat oils may cause folliculitis (oil acne). Contact with some aqueous-mix fluidsmay, depending upon the additives, e.g. biocides, cause an allergic contact dermatitis. Formerlythe use of unrefined mineral oils posed a risk of skin cancer.

The fumes and mist from metalworking fluids may cause irritation of the eyes, nose and throat.

Table 5.43 Common anhydrous acids

Chemical Melting Boiling Typical cylinder Vapour Propertiespoint point pressure at 21°C density(°C) (°C) (bar) (air = 1.0)

Hydrogen bromide –86 –69 22 2.8 Colourless, corrosive nonflammable(Anhydrous hydrobromic acid) gas with an acrid odourHBr Highly irritating to eyes, skin and

mucous membranesFumes in moist air, producing

clouds with a sour tasteFreely soluble in water

Hydrogen chloride –111 –83 42.4 1.3 Colourless, corrosive nonflammable(Anhydrous hydrochloric acid) gas with a pungent odourHCl Considered somewhat more

dehydrating and more corrosivethan the mists and vapours ofhydrochloric acid

Fumes in airVery water soluble

Hydrogen fluoride –83 19 0.069 0.7 Colourless, corrosive nonflammable(Anhydrous hydrofluoric acid) liquid or gas with a penetratingHF odour

Highly irritating and poisonousVery soluble in water. Liquid

liberates heat as it dissolves inwater. The entrapment of waterin an anhydrous hydrogenfluoride cylinder can cause rapidgeneration of heat and pressurewhich can lead to an explosion.Containers should never beheated to >52°C. A liquidhydrogen fluoride spill areashould not be entered unlessprotective clothing (impervious tothe compound) and a self-contained gas mask are worn

Fumes in air

Hydrogen iodide –51 –35 Colourless, corrosive nonflammable(Anhydrous hydriodic acid) gas with an acrid odourHl Highly irritating to eyes, skin and

mucous membranesAttacks natural rubberDecomposed by lightExtremely soluble in waterFumes in moist air


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Breathing difficulties, i.e. bronchitis or asthma, arising from sensitization to bacterial contaminationor additive chemicals, have been reported.

The formation of nitrosamines, e.g. n-nitrosodiethanolamine, which are possible humancarcinogens, can occur in synthetic or semi-synthetic fluids which contain a nitrite salt anddiethanolamine or triethanolamine.

Basic precautions include those in Table 5.47.

(xi) Painting

Industrial painters may suffer adverse health effects from over exposure to paint by skin contactor accidental ingestion, from excessive inhalation of paint aerosol, solvent vapour, or of dust inthe case of electrostatically-applied powder coatings (e.g. polyesters containing triglycidylisocyanurate), or from exposure to thermal degradation products from heated paint or plasticcoatings (Table 5.48).

Precautions for paintwork are summarized in Table 5.49.

Table 5.44 Common organic acids

Acid Flash point Ignition Specific Vapour Boiling Properties(°C) temperature gravity density point

(°C) (water = 1.0) (air = 1.0) (°C)

Acetic acid (glacial) 40 426 1.05 2.07 118 Clear, colourless water-(Ethanoic acid) soluble mobile liquidCH3COOH Strong vinegar odour

Lower explosive limit 4%Glacial acetic is a

concentration of acetic acid>99%

Expands on freezing into anicelike solid at 16.6°C; canbreak container

Butyric acid 72 452 0.96 3.04 163 Colourless water-soluble oily(Butanoic acid) liquid with strong odourCH3(CH2)2COOH

Formic acid 69 601 1.22 1.59 100 Colourless water-solubleHCOOH fuming liquid with pungent

penetrating odourGlacial acid freezes at 8°CDecomposes slowly in

storage, liberating carbonmonoxide

Sufficient gas pressure canaccumulate in tightly sealedtank to cause rupture orleakage

Common concentrations all>90%

Propionic acid 54 512 0.99 2.56 141 Colourless liquid with(Methylacetic acid) slightly pungent and rancidCH3CH2COOH odour

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Table 5.45 Precautions in handling primary irritants/corrosives

Avoid contact Use in most dilute form practicableMinimize opportunity for contact and time of contactSelect appropriate constructional materials (flexible hoses)Allow for clearance of blockage (e.g. steaming)Containment

Avoid open tanks, even if only loose lids practicableProvide barriers

Use handling technique that avoids airborne contaminationMechanical handling

In-plant transfer preferably by pipelineAlternatively use special vessels, e.g. lined drums, or continuous arrangements for

enclosed transferDrums should be emptied using pumps/forklift trucks etc.Avoid manual tipping

Provide warning notices to identify containers and areas where corrosive chemicals arein use, and instructions regarding necessary protection, particularly eye protection areas

Identify vessels, pumps and pipelines (e.g. colour coding, numbering)Spillage

Retain with bunds etc.Neutralize or mop up immediatelyMaintain supplies of neutralizing chemicals, e.g. soda ash

Provide hosing-down facilities where appropriateMinimize joints, particularly drain and sample points, valves/pipe joints, flanges over

access waysAvoid flexible hoses where possible; otherwise secure, shield and maintainShield glass sectionsProvide separate FULL and EMPTY storage areasUse road or rail tanker for bulk transfer; if small containers are used, they should be

of correct design (free space, pressure, corrosion)Label containers according to hazard, precautions, first aidSegregate incompatible materialsMaintain good housekeeping

Personal protection Depending on scale of operation, use impervious rubber gloves, eye protection(glasses/goggles/face shield), rubber aprons, boots, armlets, protective suits

Provide respiratory protection against gases/dusts/fumesProvide shower and eyewash facilitiesUse protective/barrier creams and skin reconditioning creamsMaintain high standard of personal hygiene

First aid measures Investigate all complaintsIn the case of injury, obtain medical attention rapidly

Emergency measures Copiously flush eyes with water for up to 15 min, and skin with water and soap – exceptin the case of substances such as quicklime whose reaction with water is exothermic(1 g generates >18 kcal), titanium or tin tetrachloride, both of which rapidly hydrolizeto form hydrochloric acid

Therapeutic measures for specific chemicals include:White phosphorus. This element burns in air and can produce severe thermal and

chemical burns. It may reignite on drying. After washing, rapid but brief treatmentwith copper sulphate (to avoid systemic absorption and copper poisoning) is used toconvert the phosphorus to copper phosphide which is then removed

Hydrogen fluoride. This can form painful but delayed necrosis. Treat with calciumgluconate locally and monitoring of serum calcium levels, with administration ofcalcium where necessary


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Table 5.46 General precautions with mineral oils

Avoid all unnecessary contact with mineral and synthetic oils, e.g. by carefully designed work practicesAvoid extreme exposure to oil mist or vapoursWhen used as a machine coolant:

• substitute by oil-in-water emulsions (suds) or by nitrite-free synthetic coolants;• use of an adequate flow of cooling to minimize ’fuming’;• provide l.e.v.;• provide and use enclosures and splash guards wherever practicable;• regularly change coolant and machine system cleaning.• with solutions or emulsions control concentration in use.

For machine operation, use of protective clothing, e.g. impervious aprons with detachable absorbent fronts (see also below).Protective gloves may be helpful if they can be kept clean inside (porous gloves may prolong exposure)Impervious elasticated armlets may be appropriateProvide a readily available supply of disposable ragsDo not carry used rags in overall or trouser pocketsWear goggles if eye contact is likely

Wear clean work clothesConsider short-sleeved overalls for workers using metal cutting fluids (avoids skin friction from cuffs saturated with oil and

holding particles of swarf)Dry-clean oily overallsChange underclothes that become wet with oils, and wash thoroughly

Wash skin thoroughly to remove all traces of oilAvoid strong soaps, detergents, abrasive skin cleansersDo not use paraffin (kerosene), petrol (gasoline), chlorinated hydrocarbons or proprietary solvents to cleanse skinUse barrier cream before work and after washing hands (different barrier creams protect against different oils – a cream

intended for soluble oil does not protect against straight oils)Use skin reconditioning cream after washing hands at end of shiftSee that all cuts and scratches receive prompt medical attentionSeek medical advice as soon as an irritation or other skin abnormality appears

Maintain a high standard of housekeeping – a clean workplace encourages clean work practicesEncourage self-checks and provide the necessary information – e.g. leaflet MS(B)5 available free from HSEUse warning notices, placards etc. to promote good personal hygiene and good work practices

Table 5.47 Basic precautions for metalworking fluids

• Design, maintain and operate machine tools to minimize fumes and mist generation, splashing and skincontamination

• Provide local exhaust ventilation as appropriate• Control fluid quality during use, involving checks on correct dilution and make-up, concentration and freedom from

contamination in service, regular cleaning and fluid changing• Provide and use appropriate personal protective equipment• A high standard of personal hygiene• Regular skin inspections, e.g. at a frequency of once per month; monitoring of any respiratory problems by

simultaneous enquiries and completion of an annual questionnaire• Prohibit air lines for blowing clean components• Prohibit eating, drinking or smoking near machines• Remove swarf and fines from, and prevent hydraulic oil leakage into, recirculated fluid• Avoid the use of water-mix synthetic fluids containing nitrites if there is a technologically effective alternative.

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Table 5.48 Potential pollutants from heated paints or plastic coatings

Elements in resin Chemical classification of resin Possible products of pyrolysis

Carbon, hydrogen and possibly Resin and derivatives Carbon monoxideoxygen Natural drying oils Aldehydes (particularly

Cellulose derivatives formaldehyde, acrolein andAlkyd resins unsaturated aldehydes)Epoxy resins (uncured) Carboxylic acidsPhenol-formaldehyde resins PhenolsPolystyrene Unsaturated hydrocarbonsAcrylic resins Monomers, e.g. fromNatural and synthetic rubbers polystyrene and acrylic resins

Carbon, hydrogen, nitrogen and Amine-cured epoxy resins As above, but also variouspossibly oxygen Melamine resins nitrogen-containing compounds,

Urea-formaldehyde resins including nitrogen oxides,Polyvinyl pyridine or pyrrolidine hydrogen cyanide, isocyanatesPolyamidesIsocyanate (polyurethanes)Nitrocellulose derivatives

Carbon, hydrogen and possibly Polyvinyl halides As above, but also halogenatedhalogens, sulphur and nitrogen Halogenated rubbers compounds. These may be

PTFE and other fluorinated polymers particularly toxic when fluorineThiourea derivatives is presentSulphonamide resins Hydrogen halidesSulphochlorinated compounds Carbonyl chloride (phosgene)

Hydrogen sulphideSulphur dioxide

Table 5.49 Precautions in preparation and paintwork

Information (i.e. at least a safety data sheet and comprehensive container label) and training related to the hazards in thehandling and use of the range of chemicals.

Use where practicable of less harmful chemicals, e.g. water-based paints.Provision and use of appropriate health surveillance, e.g. for signs of dermatitis, asthma, effects of specific solvent exposures.Full use of any spray booth, enclosure, exhaust ventilation or dilution systems, and automatic handling equipment. (The

efficiency of all local exhaust ventilation and other control systems should be maintained, and checked by testing.)Where appropriate, atmospheric monitoring of airborne pollution levels.Full use, where appropriate, of ventilation, e.g. by opening doors, windows.Prompt attention to any damaged or malfunctioning equipment, e.g. general ventilation.Replacement of lids on containers.Correct disposal of paint, thinner, impregnated rags.Use, where appropriate, of a properly-fitting respirator with correct filter or air-fed equipment.Use of a vacuum cleaner or damping techniques to minimize dust generation.Avoidance of the use of unauthorised thinners for paint dilution, surface preparation or cleaning of spray guns/brushes/rollers.Avoidance of skin contact and ingestion of chemicals by:

• Use of protective clothing and eye protection.• Use of barrier cream and skin conditioning cream.• Removal of jewellery etc. which can trap chemicals in contact with the skin.• Avoidance of excessive skin contact with solvents, e.g. when cleaning brush, spray guns; not washing hands in solvents.• Avoidance of eating, drinking or smoking while painting.• A good standard of personal hygiene, i.e. washing hands before eating, and showering or bathing at the end of work.• Maintaining overalls and respiratory protection in a clean state.• Leaving protective clothing at work.


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This solvent has an ethereal odour with a detection threshold between 5 and 80 ppm. It can beabsorbed orally, by inhalation and through the skin, and small amounts of the compound can bedetected in the breath of humans several days after exposure. Overexposure by inhalation cancause central nervous system (CNS) depression – characterized by dizziness, light-headedness,inebriation and difficulty in walking – and liver damage. Minimal CNS effects occur at exposuresof about 100 ppm. Chronic exposure has resulted in peripheral neuropathy. Ingestion of largedoses can cause internal irritation, nausea, vomiting and diarrhoea; it can cause drowsiness orunconsciousness. Contact with the skin will result in degreasing, resulting in mild irritationpossibly leading to cracking and secondary infection; in extreme cases dermatitis may occur.

Eye contact with vapour above 100 ppm may cause irritation. Liquid splashes produce irritation.Studies on the carcinogenicity are inconclusive but IARC classify tetrachloroethylene as a

probable human carcinogen (Class 2A – see Table 5.17).Thermal degradation in contact with flame or red hot surfaces will produce highly-toxic gases,

e.g. acid chlorides and phosgene. Reaction with freshly-galvanized surfaces may producedichloroacetylene, which is also highly toxic.

The long-term OES is 50 ppm (8 hr TWA), set to protect against CNS effects, which will alsoprotect against liver or kidney damage and irritation. The short-term OES is 1000 ppm (15 minutereference period) to minimize exposures at irritant levels.

Tetratchloroethylene has been detected in the food chain as a contaminant: its volatility preventssignificant bioaccumulation but some transfer to aquatic sediments is possible. At low concentrationsit is slowly degraded under anaerobic conditions.

The precautions for the use of perchloroethylene correspond with those for trichloroethylene(Table 5.52). The dry cleaning process, and its safety measures comprise:

• cleaning in hot solvent in sealed machines;• drying with hot air (after centrifugal removal of liquid solvent) which passes over a lint filter

then cooled to condense solvent;• deodorization to remove last traces of solvent with fresh air with venting to atmosphere;• solvent recovery by distillation. Normal measures for solvent control use activated charcoal

absorption filters often as disposable cartridges. Still residues are usually removed manuallyfrom each machine at least once per week, or in some machines they are pumped directly to awaste storage vessel, often a lidded metal container located outside the building.

Table 5.50 Physical properties of perchloroethylene

Boiling point 121°CSaturated vapour concentration 1.5 + 104 ppm at 20°CSpecific gravity 1.623 at 20°CVapour density (air = 1) 5.83 at 74°CSolubility in water 0.015% w/w at 25°C

(xii) Perchloroethylene (tetrachloroethene, tetrachloroethylene)

Perchloroethylene is a clear, dense, non-flammable volatile chlorinated solvent. It is widely usedfor dry cleaning; small quantities are used in adhesives and cleaning agents. It is miscible withorganic solvents but only slightly soluble in water. Relevant physical properties are given inTable 5.50.

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(xiii) Trichloroethylene (trichloroethene)

Trichloroethylene is a colourless non-flammable chlorinated hydrocarbon liquid. It is mainlyused for degreasing of metals in the engineering and electrical appliance industries; other outletsare as a solvent in inks, in dry-cleaning, in varnishes and adhesives, and as a solvent in theextraction of fats and oils. Relevant physical properties are given in Table 5.51.

The solvent has a sweetish odour similar to chloroform detectable at about 30 ppm. It isprimarily a depressant of the central nervous system (CNS). Significant impairment of performancein behavioural tests and some CNS effects have occurred at 1000 ppm but not at 300 ppm;prenarcotic symptoms have occurred at mean levels of 200 ppm to 300 ppm.

Direct eye contact with liquid produces injury, generally transient, to the corneal epithelium.The liquid is mildly irritating to the skin due to the degreasing effect; repeated contact may causedermatitis. Ingestion of substantial quantities of liquid can damage the mucous membranes, andproduce acute effects ranging from mild discomfort to profound anaesthesia.

Evidence to indicate that exposure to trichloroethylene is associated with an increased incidenceof cancer in man or in adverse effects in the offspring of women workers exposed to the compound

Table 5.51 Physical properties of trichloroethylene

Boiling point 87°CSaturated vapour concentration 7.9 + 104 ppm at 20°CSpecific gravity 1.464 at 20°CVapour density (air = 1) 4.54Solubility in water 0.11% w/w at 25°C

Table 5.52 General safety precautions with trichloroethylene and tetrachloroethylene

Do notStore liquid in buckets or other open storage vessels.Lean into any vessel containing liquid or vapour.Use in any location which is not well ventilated, but avoid extraneous draughts.Enter any confined space, e.g. any tanks or pits, except in accordance with a permit-to-work system.

DoStore in the open air if possible, or at least in a well-ventilated area which is not below ground level.Provide and maintain efficient local exhaust ventilation, if enclosed plant cannot be used.Avoid smoking in proximity to any open system.Replace lids on any open-topped tanks.Wear eye protection if there is any risk of splashing.Avoid contact with the skin. If hand contact is likely, wear PVC gloves.Avoid contact of liquid or vapour with naked flames or red-hot surfaces.In vapour degreaser operation, do:

control vapour at the specified level within the tank;employ effective l.e.v. and prevent draughts in the workroom, e.g. by suitable screening;avoid overheating of solvent and uncontrolled vaporization, including prevention by the use of appropriate thermostats;lower and raise work loads slowly, to minimize vapour displacement;carefully position, or drain, hollow articles.

When cleaning plant, if plant is within a pit, do:ensure ventilation draws air from the bottom of the pit;distil off vapour in accordance with specific operating instructions;allow any liquid to cool to ambient temperature before drawing off into a suitable receptacle;remove sludge by raking through sump door, after allowing several hours for ventilation;restrict any entry, in accordance with the Confined Space Regulations 1997.


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is confused but IARC classify trichlorethylene as a probable human carcinogen, Class 2A (seeTable 5.17).

Decomposition of trichloroethylene can occur upon contact with naked flames, red-hot surfaces,hot elements of electric heaters, or intense UV light with the generation of acidic and highly-toxicproducts. The presence of reactive contaminants, e.g. acids, strong alkalis, highly-reactive metals,may also result in decomposition to similar products.

The Occupational Exposure Standards imposed for trichloroethylene are Maximum ExposureLimits of 100 ppm (8 hr TWA) and 150 ppm (15 minute reference period). A skin notation ‘Sk’is applicable because of the potential for skin absorption. Because of its volatility, trichloroethyleneis not recommended for cold cleaning; it is normally used in partially enclosed vapour degreasingequipment provided with local exhaust ventilation.

Typical precautions with trichloroethylene are summarized in Table 5.52. An important factoris that the vapours are much heavier than air; they will therefore spread and may accumulate atlow levels, particularly in undisturbed areas. Because of its volatility, releases to the environmentusually reach the atmosphere. Here it reacts with hydroxyl or other radicals (estimated half-lifefor reaction with hydroxyl radicals is less than a week) and is not therefore expected to diffuse tothe stratosphere to any significant extent. There is some evidence for both aerobic and anaerobicbiodegradation of trichloroethylene.

(xiv) Sick building syndrome

When working in certain buildings some workers suffer temporarily from a group of symptomsincluding:

• lethargy/tiredness;• irritability;• lack of concentration/mental fatigue;• headaches;• nausea/dizziness;• sore throats;• dry eyes and skin;• skin rash;• asthma;• blocked/runny nose.

The condition is usually non-specific and seldom traced to a single cause. This has been termedsick building syndrome. Despite much research, little has been proven but the building featuresassociated with the condition are:

• hermetically sealed, airtight shell;• mechanical heating, ventilation and air-conditioning;• use of materials and equipment that emit a variety of irritating and sensitizing toxic fumes and/

or dust;• fluorescent lights;• application of energy conservation measures;• lack of individual control over environmental conditions;• landscape plants;• VDUs;• draughts.

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Whilst the causative agent(s) have not been established it is thought to be multifunctional andpossibilities include physical factors (humidity, temperature, lighting), static electricity,electromagnetic radiation, air ion concentrations, fungi, noise, psychological stress, and chemicals.Chemicals which are not those involved in the normal work processes can become trapped withinthe building, albeit at concentrations below those known to cause ill-health effects, if:

• liberated from materials of construction or furnishings; or• they could enter from outside.

Examples of common pollutants are given in Table 5.53.

Table 5.53 Common pollutants that may be found in buildings

Chemical Source

Ammonia Cleaning solutionsPrintersCigarette smoke

Asbestos Pipe laggingAir duct liningsCeiling and roof tilesAsbestos cement sheeting

Benzene Synthetic fibresPlasticsCleaning solutionsTobacco smoke

Biocides Air-conditioning systemsWater treatmentHumidifiersDisinfectants

Carbon dioxide Exhaled breathVehicle exhaustsSmoking chimneysPortable heaters

Carbon monoxide Tobacco smokeGas cookersGas and oil heatersVehicle exhausts from loading bays or diesel trucks

Detergent dust Carpet cleanersEthyl alcohol Duplicating fluidsFibre glass InsulationFormaldehyde Insulation material

Ceiling tilesParticle boardPlywoodOffice furnitureCarpet gluesVarious plasticsSynthetic fibres and rugsUpholstery and other textilesPesticidesPaintPaperTobacco smoke

Hydrocarbons Paints, adhesivesSolventsSynthetic materials


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Floor and furniture polishesVehicle exhausts

Hydrochloric acid Electric stencil cutting machinesMethyl alcohol Spirit duplicating machinesMicro-organisms Duct work

HumidifiersOxides of nitrogen Vehicle exhausts

Tobacco smokeGas heaters

Ozone Electrical discharges from equipment such as photocopiers, electrostaticprecipitators, fluorescent lights

Paint fumes PaintPCBs Transformers

Ageing VDUsFluorescent lights

Pesticides Plant, timber and fabric treatmentsAir conditioning/ventilation units

Photochemical smog Reaction between chemicals and ozoneRadon Soil

ConcreteStoneWater supply

Solvents Typist correction fluidsAdhesives, gluesCleaning fluidsPaintFelt-tip pensStencil machinesInks

Sterilant gases HumidifiersAir-conditioning units

Sulphur dioxide Coal firesPower stationsChimneysVehicle exhausts

Vinyl chloride Plastic PVC pipesLight fittingsUpholsteryCarpets

Table 5.53 Cont’d

Chemical Source

Because the cause is unknown precautions are difficult to specify but general guidance includesthat in Table 5.54.

Temporary problems of building pollution may occur during construction and engineeringactivities, refurbishment, painting and decorating, and cleaning in internal, or sometimes external,areas. The sources are, generally, more easily traced.

(xv) Synthetic resins

Synthetic resins are extensively used, e.g., in surface finishes, in the fabrication and repair of boatand motor vehicle bodies, in the manufacture of laminated boards, for electrical components, inpattern making and in paints and varnishes. Non-rubber adhesives made from fish glues and fromcotton derivatives (e.g. cellulose acetate) tend not to be sensitizing but, depending upon compositionand the manner of use, many other types may pose significant dermatitic and fume hazards.

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Table 5.54 Precautions to avoid ‘sick buildings’

• Avoid nuisance noise• Provide adequate ventilation• Avoid high uniform temperatures• Avoid lack of air movement• Provide adequate humidity• Avoid uniform dull lighting and décor• Provide natural lighting: avoid tinted glass• Ensure staff are motivated• Consider possible cause at building design, construction and commissioning stages• ‘Bake out’ buildings to drive out pollutants• Investigate complaints, especially if there are pockets of complaints, or epidemics with related symptoms.

The monomers, catalysts or hardeners, or plasticizers can include chemicals with the potentialto irritate the skin, mucous membranes or respiratory tract. Some can promote skin or respiratorysensitization. The range of chemicals in use is extremely wide, so that reference should be madeto the Materials Safety Data Sheet for each specific formulation or variation of it identifiable byreference to the supplier’s proprietary name and code number. Some common resin types aresummarized in Table 5.55.

Table 5.55 Synthetic resin types

Type Examples

Acrylic Polymethyl methacrylate

Amino Melamine formaldehyde, urea formaldehyde, furfuryl alcohol – urea formaldehyde

Epoxy Epichlorohydrin with bisphenol A. The curing agents may pose significant health hazards, e.g.amines (triethylamine, p-phenylenediamine, diethylenetriamine) or acid anhydrides (pyromelliticdianhydride)

Phenolic Phenol formaldehyde. Formaldehyde is a respiratory irritant but is not classified as asthmagen.

Polyester Powder coatings containing triglycidyl isocyanurate are possible asthmagens (unclassified)

Polyurethane An organic isocyanate (MDI or a pre-polymer) with a hydroxy compound. The isocyanates are potentrespiratory sensitizers, the risk increasing with volatility

Vinyl Polyvinyl chloride, polyvinyl acetate.

With the exception of epoxy resins, when a resin is fully polymerized it loses any irritantproperties. However, associated materials, e.g. glass fibre used as a filler, or the dust fromplywood or veneers, may promote irritation. Partially-cured resins will retain some irritant properties.Traces of cutaneous or respiratory sensitizers liberated, e.g. by heating or machinery, may beproblematic.

Epoxy resins are often mixtures of the epoxy resin, a curing agent (hardener), solvents, reactivediluents, antioxidants and filler. Examples are given in Table 5.56. Curing agents usually compriseperoxides, amines or anhydrides. These may cure at room temperature or require elevatedtemperatures. They may be irritant or damage skin, eyes or lungs; certain amines and peroxidesare sensitizers. The solvents such as acetone, methyl ethyl ketone, toluene, xylene, glycol ethers,and alcohols pose both health and fire hazards. Glycidyl ethers are used as reactive diluents while


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Table 5.56 Typical exposure effects associated with epoxy resin systems

Resin type Examples Skin contact Inhalation Ingestion

Liquid epoxy based on the • mild to moderate • low volatility, low toxicityresin reaction product of irritants exposure unlikely

epichlorohydrin • mild to moderate unless heated,and bisphenol A or sensitizers sprayed, or spreadbisphenol F over large

unventilated surface

Solid epoxy resins based on the • mild to moderate • low volatility, low toxicityreaction product of irritants and mild exposure unlikelyepichlorohydrin and sensitizers unless crushed orbisphenol A or • not readily groundbisphenol F absorbed through


Modified liquid liquid epoxy resins • mild to moderate • low volatility, low toxicityepoxy resins with added reactive irritants exposure unlikely

diluents or solvents • moderate to unless heated,strong sensitizers sprayed, or spread

over large unventilatedsurfaces

Aliphatic and – • irritants, sensitizers, • respiratory irritants high toxicitycycloaliphatic corrosive, absorbedamine curing through skinagents

Aromatic amine – • sensitizers, long- • respiratory irritants moderate tocuring agents term health • sensitizers high toxicity

effects, absorbedthrough skin

Anhydride curing – • corrosive, severe • dusts may be high toxicityagents sensitizers sensitizers

Reactive diluents glycidyl ethers • moderate to • moderate low toxicitystrong sensitizers volatility, exposure


Solvents acetone, methyl • defats and dries • high volatility, low to highethyl ketone (MEK), skin exposure possible toxicity, long-toluene, xylene, • some may be • irritation term effectsglycol, ethers, absorbed • central nervousalcohol • may carry other system depression

components (e.g. dizziness, lossthrough skin of coordination)

Fillers fibreglass, silicas, • some may be • dust inhalation low toxicitycalcium carbonate, absorbedpowdered metal • potentialpigments primary irritant

phenols, phosphites, amines and thiobisphenols are employed as antioxidants in, e.g., polypropene,polyethylene and polystyrene resins. Typical precautions are summarized in Table 5.57.

Numerous alternatives to low-solid, solvent-based coatings traditionally used by, e.g., thewood furniture industry are shown in Table 5.58 with the estimated reduction in volatile organiccompound emissions.

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Table 5.57 General precautions with synthetic resins

Substitution using non-irritant resins and constituents, or less hazardous or less volatile constituents.

Limitation of skin contact, e.g. by covering benches, pre-mixing of resins, good housekeeping, mechanization.

Prevent or limit dust and vapour production.

Partial enclosure with local exhaust ventilation, or local exhaust ventilation, of working position: separate hazardous processesfrom other work, e.g. spray-painting with epoxy-containing sensitizing and carcinogenic compounds,

Enclose curing and mixing rooms.

Consider in advance procedures to be used for cleaning tools used in the process.

Provision and use of protective clothing, e.g. gloves, gauntlets, armlets, long-sleeved overalls; storage apart from ordinaryclothing.

Provision and use of appropriate barrier cream.

Health surveillance on a regular basis covering skin inspections, enquiries/tests relating to respiratory function: consider theneed to screen out staff with medical histories of allergic reactions.

Provision of first-aid treatment even for trivial injuries to the skin.

Provision of adequate washing facilities including resin-removal cream; enforce high standards of personal hygiene.

Limitation of the use of respiratory protection to those situations where control of exposure by inhalation cannot becontrolled by other means.

Provision of a good standard of general ventilation.

Prohibition of eating, drinking, smoking or application of cosmetics in the workplace.

Plan and organize collection and disposal of waste.

Limit stocks, some ingredients such as MbOCA and MEK have potential for major accidents.

Table 5.58 Alternative wood glues

Coating type VOC reduction (%)

Aqueous base 90–95High solids (e.g. nitrocellulose) 17–40UV cured 80–100Polyester 80–100Polyurethane 80–100

(xvi) Welding fume

Almost all welding, brazing, gas cutting, burning and similar processes produce polluting fumeand gases which can be harmful. The composition of the fume varies and the quantity generateddepends upon the type of process. A summary of the possible emissions is given in Figure 5.4.Generally the fume will comprise very fine particles of metals and their oxides. Gases such ascarbon monoxide and nitrogen oxides may be generated and mix with any inert shielding gasesused. The hazard may be increased if the metal is painted (e.g. if lead-based paint is present thefume will contain lead oxide) or coated (e.g. plastic coatings will emit thermal degradationproducts). (Examples are given in Table 5.48.) Metal coatings will also emit thermal degradationproducts, e.g. zinc oxide fumes from galvanized steel, lead oxide from steel painted with red leadfor corrosion protection.

Measures to control welding fume include process modifications, engineering controls, systemof work and administrative action as summarized in Figure 5.5.


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Carbon dioxide

Carbon monoxide

Non- pulmonary


Primary pulmonary

Welding fumes and gases


Pulmonaryirritant ortoxic inhalants


Fibrotic Nonfibrotic






















Oxides of nitrogen



Figure 5.4 Possible constituents in welding fumes and their effects

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Figure 5.5 Measures to control welding fume


Assess welding process:is control of exposure




Can fume becontrolled by process

modifications? YES






Can improvedwork methodsreduce fume?

Use ventilation tocontrol fume as faras reasonablypracticable







Is exposureadequatelycontrolled?

Train welders inthe use of allcontrol measures

Ensureadequatefit for RPE


Assessrequirementsfor RPE




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Table 5.12 Hygiene standards (see key and notes on pages 108–110)

Threshold limit values (USA) Occupational exposure limits (UK) Air odourSubstance TWA STEL TWA(c) STEL(c) threshold

(ppm)(a) (mg/m3)(b) (ppm)(a) (mg/m3)(b) (ppm) (mg/m3) (ppm) (mg/m3) (ppm; v/v)

Acetaldehyde – – C25 – 20 37 50 92 2000Acetic acid 10 25 15 37 10 25 15 37 21Acetic anhydride 5C – – – 0.5 0.1 2 0.4 39Acetone 500 – 750 – 750 1810 1500 3620 57Acetone cyanohydrin – – SKC4.7 – – – – – –Acetonitrile 40 67 60 101 40 68 60 102 0.23Acetophenone 10 – – – – – – – –Acetylene – (d) – – – (d) – – 230Acetylene dichloride, see 1,2-DichloroethyleneAcetylene tetrabromide 1 14 – –Acetylsalicylic acid (aspirin) – 5 – – – 5 – –Acrolein – – C0.1 – 0.1 0.25 0.3 0.8 0.61Acrylamide SK – 0.03(e) – – SK – 0.3 MEL – –Acrylic acid SK 2 5.9 – – 10 30 20 60 110Acrylonitrile SK 2(e) 4.3(e) – – SK 2 4.4 MEL – – 0.12Adipic acid – 5 – – – – – – –Adiponitrile 2 – – – – – – – –Aldrin SK – 0.25 – – SK – 0.25 – 0.75Allyl alcohol SK 0.5 – – – SK 2 4.8 4 9.7 1.8Allyl chloride 1 3 2 6 – – – – 0.84Allyl glycidyl ether (AGE) 1 – – – SK 5 24 10 47Allyl propyl disulphide 2 12 3 18 – – – –!-Alumina, see Aluminium oxideAluminium

Total inhalable dust – – – – – 10 – –Respirable dust – – – – – 4 – –Metal dust – 10 – – – – – –Pyro powders, as Al – 5 – – – – – –Welding fumes, as Al – 5 – – – – – –Alkyls (NOC-d), as Al – 2 – – – – – –

Aluminium oxidesTotal inhalable dust – 10 – – – 10 – –Respirable dust – – – – – 4 – –

Aluminium salts (soluble) – 2 – – – 2 – –4-Aminodiphenyl SK – (g) – – – – – –2-Aminoethanol, see Ethanolamine2-Aminopyridine 0.5 2 – – 0.5 2 2 8Amitrole – 0.2 – – – – – –Ammonia 25 17 35 24 25 18 35 25 4.8

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Ammonium chloride fume – 10 – 20 – 10 – 20Ammonium perfluorooctanoate SK – 0.01 – – – – – –Ammonium sulphamate – 10 – – – 10 – 20Amosite, see Asbestosn-Amyl acetate 50 – 100 – 50 270 100 541 1800sec-Amyl acetate 50 – 100 – 50 270 100 541 61000Aniline and hom*ologues SK 2 7.6 – – SK 1 4 – – 1.9Anisidine (o-, p-isomers) SK 0.1 0.5 – – SK 0.1 0.5 – –Antimony and antimony compounds

except stibine (as Sb) – 0.5 – – – 0.5 – –Antimony hydride (Stibine) 0.1 – – – 0.1 0.52 0.3 1.6Antimony trioxide production (g) – – – – – –

p-Aramid respirable fibres (1) – – – –ANTU – 0.3 – – – – – –Argon – (d) – – – (d) – –Arsenic elemental and inorganic – 0.01(g) – – – – – –

compounds As (except arsine)Arsenic trioxide production – (e) – – – – – –Arsine 0.05 0.16 – – 0.05 0.16 – – 0.10Asbestos, all forms(g) 0.1 (j)


Asphalt (petroleum) fumes – 0.5 – – – 5 – 10Atrazine – 5 – – – 10 – –Azinphos-methyl SK – 0.2 – – SK – 0.2 – 0.6Azodicarbonamide – – – –SEN – 1.0 – 3 MELBarium, soluble – 0.5 – – – 0.5 – –

compounds, as BaBarium sulphate

Respirable dust – – – – – 4 – –Total inhalable dust – 10 – – – 10 – –

Benomyl – 10 – – – 10 – 15Benzene 0.5(g) – 2.5 – 5 15 MEL – – 0.85Benz(a)anthrene (e)

Benzenethiol – – – – 0.5 2.3 – –Benzene-1,2,4-tricarboxylic – – – C0.04 SEN – 0.04 – 0.12

acid 1,2-anhydrideBenzidine SK – (g) – – – – – –p-Benzoquinone, see QuinoneBenzo(b)fluoanthene (e)

Benzoyl peroxide – 5 – – – 5 – –Benzo(a)pyrene – (e) – – – – – –Benzotrichloride SK (e) – C0.1 – – –Benzoyl chloride – – C0.5 – – – –

(1) p-Aramid respirable fibres are subject to an OES of 0.5 fibres/ml, 8 hr TWA

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Table 5.12 Cont’d

Threshold limit values (USA) Occupational exposure limits (UK) Air odourSubstance TWA STEL TWA(c) STEL(c) threshold

(ppm)(a) (mg/m3)(b) (ppm)(a) (mg/m3)(b) (ppm) (mg/m3) (ppm) (mg/m3) (ppm; v/v)

Benzyl acetate 10 – – – – –Benzyl butyl phthalate – – – – – 5 – –Benzyl chloride 1 5.2 – – 0.5 2.6 1.5 7.9 23Beryllium and compounds, – 0.002(g) – 0.01 – 0.002 –

as BeBiphenyl 0.2 1.3 – – 0.2 1.3 0.6 3.8 2402,2-Bis(p-chlorophenyl)- – – – – – 1 – 3

1,1,1-trichloroethanesee Diglycidyl ether

Bis(2-dimethylamino-ethyl) ether 0.05 – 0.15 – – – – –Bis(2-ethyl hexyl) phthalate – – – – – 5 – 10Bismuth telluride – 10 – – – 10 – 20

Se-doped – 5 – – – 5 – 10Borates, tetra, sodium salts

Anhydrous – 1 – – – 1 – –Decahydrate – 5 – – – 5 – –Pentahydrate – 1 – – – 1 – –

Bornan-2-one 2 – 4 – 2 13 3 19Boron oxide – 10 – – – 10 – 20Boron tribromide – – C1 – – – 1 10Boron trifluoride – – C1 – – – 1 2.8Bromacil – 10 – – 1 11 2 22Bromine 0.1 0.66 2 1.3 0.1 0.7 0.3 2Bromine pentafluoride 0.1 0.72 – – 0.1 0.7 0.3 2.2 2.0Bromochloromethane, see

ChlorobromomethaneBromoethane, see Ethyl bromideBromoform SK 0.5 5.2 – – SK 0.5 5 – – 0.39Bromomethane, see Methyl bromideBromotrifluoromethane 1000 6190 – – 1000 6190 1200 74301,3-Butadiene 2(e) – – – 10 22 MEL – – 640Butane 800 1900 – – 600 1450 750 1810 0.29Butanethiol, see Butyl mercaptan2-Butanone, see Methyl ethyl ketone

(MEK)trans-But-2-enal – – – – 2 6 6 182-Butoxyethanol (EGBE) SK 20 – – – SK 25 123 MEL – – 250n-Butyl acetate 150 713 200 950 150 724 200 966 390sec-Butyl acetate 200 950 – – 200 966 250 1210

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tert-Butyl acetate 200 950 – – 200 966 250 1210Butyl acrylate 2 – – – 10 53 – – 290n-Butyl alcohol SK – – C50 – SK – – 50 154 60sec-Butyl alcohol 100 303 – – 100 308 150 462 38tert-Butyl alcohol 100 303 – – 100 308 150 462 2.1Butylamine SK – – C5 – SK – – 5 15 2.7n-Butyl chloroformate – – – – 1 5.6 – –tert-Butyl chromate, as CrO3 SK – – – C0.1 – – – –Butylated hydroxy toluene – 10 – – – 10 – –n-Butyl glycidyl ether (BGE) 25 133 – – 25 135 – –n-Butyl lactate 5 30 – – 5 30 – – 0.71Butyl mercaptan 0.5 1.8 – – – – – – 510o-sec-Butylphenol SK 5 31 – – SK 5 30 – –p-tert-Butyltoluene 1 6 20 121 – – – – 2.0Cadmium dusts and salts, as Cd

elemental – 0.01(e) – – –compounds, as Cd – 0.002(e) – – (except


Cadmium oxide pigments)fume, as Cd – – – – – 0.025 MEL 0.05 MEL

Cadmium sulphide pigments, – – – – – 0.03 MEL – –respirable dust, as Cd

Caesium hydroxide – 2 – – – 3 – –10 (total

inhalable dust) –– 4 – –

(respirable dust)Calcium chromate – 0.001(e) – – – – – – –Calcium cyanamide – 0.5 – – – 0.5 – 1Calcium hydroxide – 5 – – – 5 – –Calcium oxide – 2 – – – 2

10 (totalinhalable dust) – –

4(respirable dust)

10 (total(inhalable dust) – –

4 (respirable dust)

Camphor, synthetic, see Bornan-2-oneCaprolactam

Dust – 1 – 3 – 1 – 3Vapour 5 23 10 47 5 23 10 47




Calcium sulphate – 10(f) – – –




Calcium silicate – 10(f) – – –




Calcium carbonate – 10(f) – –

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Table 5.12 Cont’d

Threshold limit values (USA) Occupational exposure limits (UK) Air odourSubstance TWA STEL TWA(c) STEL(c) threshold

(ppm)(a) (mg/m3)(b) (ppm)(a) (mg/m3)(b) (ppm) (mg/m3) (ppm) (mg/m3) (ppm; v/v)

Captafol SK – 0.1 – – SK – 0.1 – –Captan – 5 – – – 5 – 15Carbaryl – 5 – – – – – –Carbofuran – 0.1 – – – 0.1 – –Carbon black – 3.5 – – – 3.5 – 7Carbon dioxide 5000 9150 30 000 54800 5000 9150 15 000 27 400 0.067Carbon disulphide SK 10 32 – – SK 10 32 MEL – – 92Carbon monoxide 25 28 – – 30 35 200 232 0.00050Carbon tetrabromide 0.1 1.4 0.3 4.1 0.1 1.4 0.3 4Carbon tetrachloride SK 5(e) 31(e) 10 62 SK 2 13 – – 0.052Carbonyl chloride, see PhosgeneCarbonyl fluoride 2 5.4 5 13 – – – –Catechol SK 5 23 – – 5 23 – –

10 (total – 20inhalable dust)

4 – –(respirable dust)

Chlordane SK – 0.5 – – SK – – – –Chlorinated camphene SK – 0.5 – 1 – – – –Chlorinated diphenyl oxide – 0.5 – – – – – –Chlorine 0.5 1.5 1 2.9 0.5 1.5 1 2.9 3.2Chlorine dioxide 0.1 0.28 0.3 0.83 0.1 0.3 0.3 0.9 0.011Chlorine trifluoride – – C0.1 0.38C – – 0.1 0.38Chloroacetaldehyde – – C1 3.2C – – 1 3.3Chloroacetone SK – – C1 C3.8 – – – –!-Chloroacetophenone 0.05 0.32 – – 0.05 0.32 – – 1.4Chloroacetyl chloride 0.05 0.23 0.15 0.7 – – – –Chlorobenzene 10 – – – 50 234 – – 110o-Chlorobenzylidene SK – – C0.05 C0.39 – – – –

malononitrileChlorobromomethane 200 1060 – – 200 1060 250 1340 0.502-Chloro-1,3-butadiene, see

&-ChloropreneChlorodifluoromethane 1000 3590 – – 1000 3590 – –Chlorodiphenyl (42% chlorine) SK – 1 – –Chlorodiphenyl (54% chlorine) SK – 0.5 – – SK – 0.1 – –

1-Chloro-2,3-epoxy propane, seeEpichlorohydrin




Cellulose (pure) – 10 – – –


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2-Chloroethanol, see Ethylenechlorohydrin

Chloroethylene, see Vinyl chlorideChloroform 10(e) 49(e) – – 2 9.9 – – 0.12bis(Chloromethyl)ether 0.001(g) 0.005 – – 0.001 0.005 – –Chloromethyl methyl ether (e) (e) – – – – – –1-Chloro-4-nitrobenzene – – – – SK – 1 – 21-Chloro-1-nitropropane 2 10 – – – – – –Chloropentafluoroethane 1000 6420 – – 1000 6420 – –Chloropicrin 0.1 0.67 – – 0.1 0.7 0.3 2 0.13&-Chloroprene SK 10 36 – – – – – – 0.683-Chloropropene – – – – 1 3 2 62-Chloropropionic acid 0.1 – – – – – – –o-Chlorostyrene 50 283 75 425 – – – –Chlorosulphonic acid – – – – – 1 – –o-Chlorotoluene 50 259 – – 50 264 – – 1502-Chloro-6-(trichloromethyl)pyridine,

see NitrapyrinChlorpyrifos – 0.2 – – SK – 0.2 – 0.6Chromite ore processing (Chromate), – 0.05(g) – – – – – –

as CrChromium metal – 0.5 – – – 0.5 – –Chromium (III) compounds, as Cr – 0.5 – – – 0.5 – –Chromium (VI) compounds, as Cr

Water soluble – 0.05(g) – – – 0.05 – –Water insoluble – 0.01(g) – –

Chromyl chloride 0.025 0.16 – – – – – –Chrysene (e) (e) – – – – – –Chrysotile, see AsbestosClopidol – 10 – – – – – –Coal dust – 2 – – – 2 – –

(respirable fraction) (respirable dust)Anthracite – 0.4 – – – – – –Bitumous – 0.9 – – – – – –

Coal tar pitch volatiles, as benzene – 0.2(g) – – – 0.14 – –solubles

Cobalt as Co, elemental and inorganic – 0.02 – – – 0.1 – –compounds (cobalt and

compounds)Cobalt carbonyl as Co – 0.1 – – – – – –Cobalt hydrocarbonyl as Co – 0.1 – – – – – –Copper

Fume – 0.2 – – – 0.2 – –Dusts and mists as Cu – 1 – – – 1 – 2

Cotton dust, raw – 0.2(l) – – – 2.5 – –

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Table 5.12 Cont’d

Threshold limit values (USA) Occupational exposure limits (UK) Air odourSubstance TWA STEL TWA(c) STEL(c) threshold

(ppm)(a) (mg/m3)(b) (ppm)(a) (mg/m3)(b) (ppm) (mg/m3) (ppm) (mg/m3) (ppm; v/v)

Cresol, all isomers SK 5 22 – – SK 5 22 – – 17 000(m-cresol)

Cristobalite, see Silica, crystallineCrocidolite, see AsbestosCrotonaldehyde – – C0.3 – – – – – 17 (trans)Crufomate – 5 – – – – – –Cryofluorane (INN) 1000 7110 – – 1000 7110 1250 8890Cumene SK 50 246 – – SK 25 125 75 375 570Cyanamide – 2 – – – 2 – –Cyanides as CN, see Hydrogen cyanide –Cyanogen 10 22 – – 10 22 – –Cyanogen chloride – – C0.3 C0.75 – – 0.3 0.77Cyclohexane 300 1030 – – 100 350 300 1050 25Cyclohexanol SK 50 206 – – 50 208 – – 0.15Cyclohexanone SK 25 100 – – 25 102 100 408 0.88Cyclohexene 300 1010 – – 300 1020 – – 0.18Cyclohexylamine 10 41 – – SK 10 41 – – 2.6Cyclonite SK – 0.5 – – SK – 1.5 – 3Cyclopentadiene 75 203 – – – – – – 1.9Cyclopentane 600 1720 – – – – – –Cyhexatin – 5 – – – 5 – 102,4-D – 10 – – – 10 – 20DDT (Dichloro- – 1 – – – 1 – 3

diphenyltrichloroethane)Decaborane SK 0.05 0.25 0.15 0.75 – – – –Demeton SK 0.01 0.11 – – – – – – 0.060Diacetone alcohol 50 238 – – 50 240 75 362 0.28Dialkyl 79 phthalate – – – – – 5 – –Diallyl phthalate – – – – – 5 – –2,2*-Diaminodiethylamine – – – – SK 1 4 – –1,2-Diaminoethane, see EthylenediamineDiammonium peroxydisulphate – – – – – 1 – –

as S2O8Diatomaceous earth, see Silica,

amorphousDiazinon SK – 0.1 – – SK – 0.1 – 0.3Diazomethane 0.2(e) 0.34 – – carcinogen – – –Diborane 0.1 0.11 – – 0.1 0.1 – – 2.5Dibromodifluoromethane – – – – 100 872 150 1310

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1,2-Dibromoethane, see Ethylenedibromide

2-N-Dibutylamino-ethanol SK 0.5 3.5 – – – – – –Dibutyl phenyl phosphate SK 0.3 3.5 – – – – – –Dibutyl phosphate 1 8.6 2 17 1 8.7 2 17Dibutyl phthalate – 5 – – – 5 – 106,6*-Di-tert-butyl-4-4*- – – – – – 10 – 20

thiodi-m-cresolDichloroacetylene – – C0.1 C0.39 – – 0.1 0.4o-Dichlorobenzene SK 25 152 50 153 – – 50 306 0.30p-Dichlorobenzene 10 31 – – 25 153 50 306 0.183-3*-Dichlorobenzidine – (e) – – – – – – –1,4-Dichloro-2-butene 0.005(e) – – – – – – –Dichlorodifluoromethane SK 1000 4950 – – 1000 5030 1250 62801,3-Dichloro-5,5-dimethyl hydonton – 0.2 – 0.4 – 0.2 – 0.41,1-Dichloroethane – – – – 200 823 400 16501,2-Dichloroethane, see Ethylene

dichloride1,1-Dichloroethylene see Vinylidene

chloride1,2-dichloroethylene 200 793 – – 200 806 250 1010 17

(trans)Dichloroethyl ether SK 5 29 10 58 – – – – 0.049Dichlorofluoromethane 10 42 – – 10 43 – –Dichloromethane 50 175 – – 100 350 MEL 300 10601,1-Dichloro-1-nitroethane 2 12 – – – – – –2,2*-Dichloro-4-4*-methylene – – – – SK – 0.005 MEL – –

dianiline (Mb OCA)Dichlorophenoxyacetic acid, see 2,4-D1,2-Dichloropropane, see Propylene

dichlorideDichloropropene SK 1 4.5 – – SK 1 5 10 502,2-Dichloropropionic acid – 5 – – – – – –Dichlorotetrafluoro-ethane, see

CryofluoraneDichlorvos SK – 0.90 – – SK 0.1 0.92 0.3 2.8Dicrotophos SK – 0.25 – – – – – –Dicyclohexyl phthalate – – – – – 5 – –Dicyclopentadiene 5 27 – – 5 27 – – 0.0057Dicyclopentadienyl iron, see FerroceneDieldrin SK – 0.25 – – SK – 0.25 – 0.75Diethanolamine – 2 – – 3 13 – – 0.27Diethylamine 5 – 25 75 10 30 25 75 0.132-Diethylamino-ethanol SK 2 – – – SK 10 49 – – 0.011Diethylene glycol – – – – 23 100 – –

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Table 5.12 Cont’d

Threshold limit values (USA) Occupational exposure limits (UK) Air odourSubstance TWA STEL TWA(c) STEL(c) threshold

(ppm)(a) (mg/m3)(b) (ppm)(a) (mg/m3)(b) (ppm) (mg/m3) (ppm) (mg/m3) (ppm; v/v)

Diethylene triamine SK 1 4.2 – – SK 1 4.3 – –Diethyl ether, see Ethyl etherDi(2-ethylhexyl)phthalate, see

Di-sec-octyl phthalateDiethyl ketone 200 716 300 1024 200 716 250 895 2.0Diethyl phthalate – 5 – – – 5 – 10Diethyl sulphate – – – – 0.05 0.32 – –Difluorodibromomethane 100 858 – – 100 860 150 1290Diglycidyl ether (DGE) 0.1 0.53 – – 0.1 0.5 – –Dihydroxybenzene, see HydroquinoneDiisobutyl ketone 25 145 – – 25 148 – – 0.11Diisoctyl phthalate – – – – – 5 – –Diisodecyl phthalate – – – – – 5 – –Diisononyl phthalate – – – – – 5 – –Diisopropylamine SK 5 21 – – 5 21 – – 1.8Diisopropyl ether, see Isopropyl etherDimethoxymethane, see MethylalDimethyl acetamide SK 10 36 – – SK 10 36 20 72 47Dimethylamine 5 9 15 27 2 3.8 6 11 0.34Dimethylaminobenzene, see XylideneDimethylamino ethanol – – – – 2 7.4 6 22Dimethylaniline SK 5 25 10 50 SK 5 25 10 50 0.013

(N,N-Dimethylaniline)Dimethylbenzene, see Xylene1,3-Dimethylbutyl acetate – – – – 50 300 100 600Dimethyl carbamoyl chloride (e) (e) – – – – – –Dimethyl-1,2-dibromo-2,2-dichloroethyl

phosphate, see NaledDimethyl ether – – – – 400 766 500 958N-N-Dimethylethylamine – – – – 10 30 15 45Dimethylethoxy silane 0.5 – 1.5 – – – – –Dimethylformamide SK 10 30 – – SK 10 30 20 60 2.22,6-Dimethyl-4-heptanone, see

Diisobutyl ketone1,1-Dimethyl hydrazine SK 0.01(e) – – – – carcinogen – – 1.7Dimethylnitrosoamine,

see N-NitrosodimethylamineDimethylphthalate – 5 – – – 5 – 10Dimethyl sulphate SK 0.1(e) 0.52(e) – – SK 0.05 0.25 – –

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Dinitolmide – 5 – – – – – –Dinitrobenzene (all isomers) SK 0.15 1 – – SK 0.15 1 0.5 3Dinitro-o-cresol SK – 0.2 – – SK – 0.2 – 0.61,2-Dinitroethane, see Ethylene

glycol dinitrate1,2-Dinitropropane – – – – SK – – – –3,5-Dinitro-o-toluamide, see DinitolmideDinitrotoluene SK – 0.2 – – SK – carcinogen – –Di-nonyl phthalate – – – – – 5 – –Dioxane SK 20 – – – SK 25 90 100 366 24Dioxathion SK – 0.2 – – SK – 0.2 – –Diphenyl, see BiphenylDiphenylamine – 10 – – – 10 – 20Diphenyl ether (vapour),

see Phenyl EtherDiphenylmethane diisocyanate, see

Isocyanates; Methylenebisphenyl isocyanate

Diphosphorus pentoxide – – – – – – – 2Dipotassium peroxydisulphate, – – – – – 1 – –

as S2O8Dipropylene glycol methyl ether SK 100 606 150 909 – – – –Dipropyl ketone 50 233 – – – – – –Diquat – 0.5 – – – 0.5 – 1Di-sec-octyl phthalate – 5 – – – 5 – 10Disodium disulphite – 5 – – – 5 – –Disodium peroxydisulphate, – – – – – 1 – –

as S2O8Disodium tetraborate

anhydrous – – – – – 1 – –decahydrate – – – – – 5 – –pentahydrate – – – – – 1 – –

Disulfiram – 2 – – – – – –Disulfoton – 0.1 – – – 0.1 – 0.3Disulphur dichloride – – C1 – – – 1 5.6Diuron – 10 – – – 10 – –Divinyl benzene 10 53 – – 10 54 – –Dusts (S)

10 (totalinhalable dust)

4 – –(respirable dust)

Endosulfan SK – 0.1 – – SK – 0.1 – 0.3Endrin SK – 0.1 – – SK – 0.1 – 0.3Enflurane 75 566 – – 50 383 – –




Emery – 10(i) – – –

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Table 5.12 Cont’d

Threshold limit values (USA) Occupational exposure limits (UK) Air odourSubstance TWA STEL TWA(c) STEL(c) threshold

(ppm)(a) (mg/m3)(b) (ppm)(a) (mg/m3)(b) (ppm) (mg/m3) (ppm) (mg/m3) (ppm; v/v)

Enzymes, see SubtilisinsEpichlorohydrin SK 0.5 1.9 – – SK MEL 0.5 1.9 1.5 5.8 0.93EPN SK – 0.1 – – – – – –1,2-Epoxypropane, see Propylene oxide2,3-Epoxy-1-propanol, see Glycidol2,3-Epoxypropyl isopropyl ether 50 240 75 360 50 240 75 360Ethane (d) (d) 120 000Ethanethiol, see Ethyl mercaptanEthanol, see Ethyl alcoholEthanolamine 3 7.5 6 15 3 7.6 6 15 2.6Ethion SK – 0.4 – – – – – –2-Ethoxyethanol (EGEE) SK 5 18 – – SK 10 37 MEL – – 2.72-Ethoxyethyl acetate (EGEEA) SK 5 27 – – SK 10 54 MEL – – 0.056Ethyl acetate 400 1440 – – 400 1460 – – 3.9Ethyl acrylate 5(e) 20(e) 15(g) 61(g) SK 5 20 15 60 0.0012Ethyl alcohol 1000 1880 – – 1000 1920 – – 84Ethylamine 5 9 – – 2 3.8 6 11 0.95Ethyl amyl ketone 25 131 – – 25 133 – – 6.0Ethyl benzene 100 441 125 552 100 441 125 552 2.3Ethyl bromide 5 – – – 200 906 250 1130 3.1Ethyl tert-butyl ether 5 – – – – – – –Ethyl butyl ketone 50 234 75 351 50 237 100 475Ethyl chloride 100 – – – 1000 2700 1250 3380 4.2Ethylchloroformate – – – – 1 4.4 – –Ethyl cyanoacrylate 0.2 – – – – – – 0.3 1.5Ethylene (d) 290Ethylene chlorohydrin SK – – C1 – SK – – 1 3.4Ethylenediamine 10 25 – – 10 25 – – 1.0Ethylene dibromide SK (e) (e) – – SK 0.5 4 MEL – – 2.5Ethylene dichloride 10 40 – – 5 21 – – 88


Ethylene glycol, vapour and mist – – – C100 – particulate – –60 125

vapourEthylene glycol dinitrate SK 0.05 0.31 – – SK 0.2 1.3 0.2 1.3Ethylene glycol methyl ether acetate,

see 2-Methoxyethyl acetateEthylene oxide 1(e) 1.8(e) – – SK 5 9.2 MEL – – 430Ethylene imine SK 0.5 0.88 – – SK carcinogen




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Ethyl ether 400 1210 500 1520 400 1230 500 1540 8.9Ethyl formate 100 303 – – 100 308 150 462 312-Ethylhexyl chloroformate – – – – 1 7.9 – –Ethylidene chloride, see

1,1-DichloroethaneEthylidene norbornene – – C5 – 0.014Ethyl mercaptan 0.5 1.3 – – 0.5 1.3 2 5.2 0.00076N-Ethylmorpholine SK 5 24 – – SK 5 24 20 96 1.4Ethyl silicate 10 85 – – 10 87 30 260 17Fenamiphos SK – 0.1 – – – – – –Fenchlorphos, see RonnelFensulfothion – 0.1 – – – – – –Fenthion SK – 0.2 – – – – – –Ferbam – 10 – – – 10 – 20Ferrocene – 10 – – – 10 – 20Ferrous foundry particulate

total inhalable dust – – – – – 10 – –respirable dust – – – – – 4 – –

Ferrovanadium dust – 1 – 3Fibrous glass dust – 10 – – – – – –Flour dust – 5 – – – – – –Fluorides as F – 2.5 – – – 2.5 – –Fluorine 1 1.6 2 3.1 – – 1 1.6 0.14Fluorotrichloromethane, see

TrichlorofluoromethaneFonofos SK – 0.1 – – – – – –Formaldehyde – – C0.3(e) – 2 2.5 MEL 2 2.5 MEL 0.83Formamide SK 10 18 – – 20 37 30 56Formic acid 5 9.4 10 19 5 9.6 – – 49Furfural SK 2 7.9 – – SK 2 8 5 20 0.078Furfuryl alcohol SK 10 40 15 60 SK 5 20 15 60 8.0Gasoline 300 890 500 1480 – – – –Germanium tetrahydride 0.2 0.63 – – 0.2 0.6 0.6 1.9Glass, fibrous or dust, see Fibrous

glass dustGlutaraldehyde – – C0.05 – SEN 0.05 0.2 0.05 0.2Glycerin mist – 10 – – – 10 – –Glycidol 2 – – – – – – –Glycol monoethyl ether, see

2-EthoxyethanolGlycerol trinitrate SK 0.05 – – – SK 0.2 1.9 0.2 1.9Grain dust (oat, wheat, barley) – 4 – – – – – –

10 (total – –Graphite, all forms – 2 – – – (inhalable dust)

except graphite fibres 4 – –(respirable dust)




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Table 5.12 Cont’d

Threshold limit values (USA) Occupational exposure limits (UK) Air odourSubstance TWA STEL TWA(c) STEL(c) threshold

(ppm)(a) (mg/m3)(b) (ppm)(a) (mg/m3)(b) (ppm) (mg/m3) (ppm) (mg/m3) (ppm; v/v)

Gypsum, see Calcium sulphateHafnium – 0.5 – – – 0.5 – 1.5Halothane 50 404 – – 10 82 – – 33Helium (f) (f)

Heptachlor SK – 0.5 – – – – – –Heptane (n-Heptane) 400 1640 500 2050 – – – – 1502-Heptanone, see Methyl n-amyl

ketone3-Heptanone, see Ethyl butyl

ketoneHexachlorobenzene – 0.002 – – – – – –Hexachlorobutadiene SK 0.02(e) 0.21(e) – – – – –Hexachlorocyclohexane, see LindaneHexachlorocyclo-pentadiene 0.01 0.11 – – – – – – 0.030

5 50 – – 0.15(vapour)

Hexachloroethane 1 9.7 – – – 10 (totalinhalable dust)

– 4 – –(respirable dust)

Hexachloronaphthalene SK – 0.2 – – – – – –Hexafluoroacetone SK 0.1 0.68 – – – – – –Hexahydro-1,3,5-trinitro-

1,3,5-triazine, see CycloniteHexamethylene diisocyanate 0.005 0.034 – – see IsocyanatesHexamethyl phosphoramide SK (e) (e) – – – – – –Hexane (n-hexane) 50 176 – – 20 72 – – 130

Other isomers 500 1760 1000 3500Hexanediamine 0.5 – – – – – –1,6-Hexanolactam, see Caprolactam2-Hexanone, see Methyl n-butyl ketone1-Hexene 30 – – – – – – –Hexone, see Methyl isobutyl ketonesec-Hexyl acetate 50 295 – – SK 50 205 75 300Hexylene glycol – – C25 – 25 123 25 123 50Hydrazine SK 0.01 – – – SK 0.02 0.03 0.1 0.13 MEL 3.7Hydrazoic acid, vapour – – – – – – 0.1 0.18Hydrogen (d) (d)

Hydrogenated terphenyls (non irradiated) 0.5 4.9 – – – – – –




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Hydrogen bromide – – C3 C9.9 – – 3 10 2.0Hydrogen chloride – – C5 C7.5 1 2 5 8 0.77Hydrogen cyanide and cyanide salts

(excluding cyanogen and cyanogenchloride)Hydrogen cyanide – C4.7 – – – MEL 10 11Calcium cyanide – – – C5Potassium cyanide – – – C5 – 5 – –Sodium cyanide – – – C5

Hydrogen fluoride as F – – C3 – – – 3 2.5 0.042Hydrogen peroxide 1 1.4 – – 1 1.4 2 2.8 0.30Hydrogen selenide as Se 0.05 0.16 – – 0.05 0.17 – – 0.0081Hydrogen sulphide 10 14 15 21 10 14 15 21Hydroquinone – 2 – – – 2 – 44-Hydroxy-4-methyl-2-pentanone, see

Diacetone alcohol2-Hydroxypropyl acrylate 0.5 2.8 – – SK 0.5 2.7 – –Indene 10 48 – – 10 48 15 72 0.015Indium and compounds as In – 0.1 – – – 0.1 – 0.3Iodine – – C0.1 – – – 0.1 1Iodoform 0.6 10 – – 0.6 9.8 1 16 0.005Iron oxide dust + fume (Fe2O3) as Fe (t) 5 – – – 5 – 10Iron pentacarbonyl as Fe 0.1 0.23 0.2 0.45 0.01 0.08 – –Iron salts, soluble, as Fe – 1 – – – 1 – 2Isoamyl acetate 50 266 100 532 50 270 100 541 0.025Isoamyl alcohol 100 361 125 452 100 366 125 458 0.042Isobutyl acetate 150 713 – – 150 724 187 903 0.64Isobutyl alcohol SK 50 152 – – 50 154 75 231 1.6Isocyanates, all, as-NCO – – – – SK – 0.02 MEL – 0.07 MELIsofluorane – – – – 50 383 – –Isooctyl alcohol SK 50 266 – – 50 270 – –Isopentyl acetate – – – – 50 270 100 541Isophorone – – C5 C28 – – 5 29 0.20Isophorone diisocyanate SK 0.005 0.045 – – see IsocyanatesIsopropoxyethanol 25 106 – – – – – –Isopropyl acetate 250 1040 310 1290 – – 200 849 2.7Isopropyl alcohol 400 983 500 1230 SK 400 999 500 1250 22Isopropylamine 5 12 10 24 – – – – 1.2N-Isopropylaniline SK 2 11 – – – – – –Isopropyl chloroformate – – – – 1 5 – –Isopropyl ether 250 1040 310 1300 250 1060 310 1310 0.017Isopropyl glycidyl ether (IGE), see

2,3-Epoxypropyl isopropyl etherKaolin – 2 – – – 2 – –Ketene 0.5 0.86 1.5 2.6 0.5 0.87 1.5 2.6


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Table 5.12 Cont’d

Threshold limit values (USA) Occupational exposure limits (UK) Air odourSubstance TWA STEL TWA(c) STEL(c) threshold

(ppm)(a) (mg/m3)(b) (ppm)(a) (mg/m3)(b) (ppm) (mg/m3) (ppm) (mg/m3) (ppm; v/v)

Lead, inorganic dusts and fumes, – 0.05 – –as Pb (k)

lead alkyls (k)

Lead arsenate as PbHAsO4 – 0.15 – –

Lead chromate as Cr – 0.05 as Pb(e)

0.012 as Cr(e)

Limestone, see Calcium carbonateLindane SK – 0.5 – – SK – 0.1 – –Lithium hydride – 0.025 – – – 0.025 – –Lithium hydroxide – – – – – – – 1LPG (Liquefied petroleum gas) 1000 1800 – – 1000 1750 1250 2180

– 10 (total – –

Magnesite – 10(I) – – – inhalable dust) – –4

(respirable dust)4 (fume, – 10

respirable dust)Magnesium oxide fume – 10 – – 10 (total

inhalable dust)Malathion SK – 10 – – SK – 10 – –Maleic anhydride 0.1 – – – – 1 – 3 MEL 0.32Manganese as Mn

Dust and compounds – – – – – 5 – –Fume – – – 3 – 1 – 3Elemental and inorganic compounds – 0.2 – – – – – –

Manganese cyclopenta-dienyl SK – 0.1 – – SK – 0.1 – 0.3tricarbonyl as Mn

Manganese methyl-pentadienyl – – – – SK – 0.2 – 0.6tricarbonyl

Manganese tetroxide – – – – – 1 – –Man-made mineral fibre – – – – – 5 MEL – –Marble, see Calcium carbonateMercaptoacetic acid, see

Thioglycolic acidMequinol (INN) – 5 – – – 5 – –Mercury, as Hg

Alkyl compounds – 0.01 – 0.03 – 0.01 – 0.03Aryl compounds – 0.1 – – – – – –








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Inorganic forms includingmetallic mercury – 0.025 – – – 0.025 – –

Mesityl oxide 15 60 25 100 15 61 25 102 0.45Methacrylic acid 20 70 – – 20 72 40 143Methacrylonitrile – – – SK 1 2.8 – –Methane (d) (d)

Methanethiol, see Methyl mercaptanMethanol, see Methyl alcoholMethomyl – 2.5 – – SK – 2.5 – –Methoxychlor – 10 – – – 10 – –2-Methoxyethanol (EGME) SK 5 16 – – SK 5 16 MEL – – 2.32-Methoxyethyl acetate (EGMEA) SK 5 24 – – SK 5 24 MEL – – –2-Methoxymethylethoxy propanol – – – – 50 308 – – SK4-Methoxyphenol, see Mequinol (INN)1-Methoxypropan-2-ol 100 375 150 560 SK 100 375 300 11201-Methoxypropyl acetate – – – – 50 274 150 822Methyl acetate 200 606 250 757 200 616 250 770 4.6Methyl acetylene 1000 1640 – – – – – – 50Methyl acetylene-propadiene 1000 1640 1250 2050 – – – –

mixture (MAPP)Methyl acrylate SK 2 7 – – 10 36 – – 0.0048Methylacrylonitrile SK 1 2.7 – – – – – – 7.0Methylal 1000 3110 – – 1000 3160 1250 3950Methyl alcohol SK 200 262 250 328 SK 200 266 250 333 100Methylamine 5 6.5 15 19.5 10 13 – – 3.2Methyl amyl alcohol, see Methyl

isobutyl carbinolMethyl n-amyl ketone 50 233 – – 50 237 100 475 0.35N-Methyl aniline SK 0.5 2.2 – – SK 0.5 2.2 – – 1.7Methyl bromide SK 1 4 – – SK 5 20 15 603-Methylbutan-1-ol – – – – 100 366 125 4581-Methylbutyl acetate – – – – 50 270 100 541Methyl-tert-butyl ether 40 – – – 25 92 75 275Methyl n-butyl ketone SK 5 20 10 40 SK 5 20 – – 0.076Methyl chloride SK 50 103 100 207 50 105 100 210Methyl chloroform 350 1910 450 2460 200 1110 400 2220 120Methyl cyanoacrylate 0.2 1 4 18 – – 0.3 1.4 2.2Methylcyclohexane 400 1610 – – – – – – 630Methylcyclohexanol 50 234 – – 50 237 75 356 500 (cis)o-Methylcyclohexanone 50 229 75 344 SK 50 233 75 350Methyl demeton SK – 0.5 – – – – – –2-Methyl-4,6-dinitrophenol – – – – SK – 0.2 – 0.6Methylene bisphenyl isocyanate (MDI) 0.005 0.051 – – see IsocyanatesMethylene chloride, see Dichloro-


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Table 5.12 Cont’d

Threshold limit values (USA) Occupational exposure limits (UK) Air odourSubstance TWA STEL TWA(c) STEL(c) threshold

(ppm)(a) (mg/m3)(b) (ppm)(a) (mg/m3)(b) (ppm) (mg/m3) (ppm) (mg/m3) (ppm; v/v)

4-4*-Methylene SK 0.01(e) 0.11(e) – – – 0.005 – –bis(2-chloroaniline)

Methylene bis(4-cyclo- 0.005 0.054 – – see Isocyanateshexylisocyanate)

4,4*-Methylenedianiline SK 0.1(e) 0.81(e) – – 0.01 0.08 – –Methyl ethyl ketone (MEK) 200 590 300 885 200 600 300 899 5.4Methyl ethyl ketone peroxide – – C0.2 – – – 0.2 1.5Methyl formate 100 246 150 368 100 250 150 375 6005-Methyl-3-heptanone, see Ethyl

amyl ketone5-Methylhexan-2-one – – – – 50 237 100 475Methyl hydrazine SK 0.1 – – – – – – – 1.7Methyl iodide SK 2(e) 12(e) – – SK 2 12 – –Methyl isoamyl ketone 50 234 – – 50 237 100 475 0.012Methyl isobutyl carbinol SK 25 104 40 167 SK 25 106 40 170 0.070Methyl isobutyl ketone 50 205 75 307 SK 50 208 100 416 0.68Methyl isocyanate SK 0.02 0.047 – – see Isocyanates 2.1Methyl isopropyl ketone 200 705 – – – – – – 1.9Methyl mercaptan 0.5 0.98 – – 0.5 1 – – 0.0016Methyl methacrylate 50 208 100 416 50 208 100 416 0.083Methyl parathion SK – 0.2 – – SK – 0.2 – 0.62-Methylpentane-2,4-diol – – – – 25 125 25 1254-Methylpentan-2-ol – – – – SK 25 100 40 1704-Methylpentan-2-one – – – – SK 50 205 100 4164-Methylpent-3-en-2-one – – – – 15 60 25 1002-Methylpropan-1-ol – – – – 50 150 75 225Methyl propyl ketone 200 705 250 881 200 716 250 895 111-Methyl-2-pyrrolidone – – – – 25 103 75 309Methyl silicate 1 6.3 – – 1 6.3 5 32Methyl styrene (all isomers except – – – – 100 491 150 736

!-methyl styrene)!-Methyl styrene 50 242 100 483 – – 100 491 0.29N-Methyl-N,2,4,6-tetranitroaniline – – – – – 1.5 – 3Methyl vinyl ketone – – C0.2 – – – – –Metribuzin – 5 – – – – – –Mevinphos SK 0.01 0.09 0.03 0.27 SK 0.01 0.1 0.03 0.28

– 10 (total – –Mica – 3 – – inhalable dust)

(respirable dust) – 0.8 – –(respirable dust)




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Mineral wool fibre – 10(i) – MEL – –Molybdenum as Mo

Soluble compounds – 5 – – – 5 – 10Metal and insoluble compounds – 10 – – – 10 – 20

Monochloroacetic acid – – – – SK 0.3 1.2 – –Monochlorobenzene, see ChlorobenzeneMonocrotophos – 0.25 – – – – – –Morpholine SK 20 71 – – SK 20 72 30 109 0.01Naled SK – 3 – – – 3 – 6Naphthalene 10 52 15 79 10 53 15 80 0.084&-Naphthylamine (g)

Neon (d) (f)

NickelMetal – 1.5 – – – 0.1 – –Insoluble compounds as Ni – 0.2(g) – – – 0.5 – –Soluble compounds as Ni – 0.1 – – – 0.1 – –

(inorganic)Nickel carbonyl as Ni 0.05 0.35 – – – – 0.1 0.24 0.30Nickel organic compounds as Ni – – – – – 1 – 3Nickel subsulphide – 0.1(g) – – – – – –Nickel sulphide roasting, fume and – 0.1 – – – – – –

dust, as Ni carcinogenNicotine SK – 0.5 – – SK – 0.5 – 1.5Nitrapyrin – 10 – 20 – 10 – 20Nitric acid 2 5.2 4 10 2 5 4 10Nitric oxide 25 31 – – 25 30 35 45p-Nitroaniline SK – 3 – – SK – 6 – –Nitrobenzene SK 1 5 – – SK 1 5 2 10 0.018p-Nitrochlorobenzene SK 0.1 0.64 – – – – – –4-Nitrodiphenyl (e)

Nitroethane 100 307 – – 100 310 – – 2.1Nitrogen (d) (d)

Nitrogen dioxide 3 5.6 5 9.4 3 5.7 5 9.6 0.39Nitrogen trifluoride 10 29 – – 10 30 15 45Nitroglycerin (NG), see Glycerol trinitrateNitromethane 20 50 – – 100 250 150 381 3.51-Nitropropane 25 91 – – 25 93 – – 11.02-Nitropropane 10(e) 36(e) – – 5 19 – – 70N-Nitrosodimethylamine SK – (e) – – – – – –Nitrotoluene SK 2 11 – – SK 5 30 10 57 0.045Nitrotrichloromethane, see ChloropicrinNitrous oxide 50 90 – – 100 183 – –Nonane 200 1050 – – – – – – 47Nuisance particulates, see Particulates

not otherwise classified (PNOC);Dusts

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Table 5.12 Cont’d

Threshold limit values (USA) Occupational exposure limits (UK) Air odourSubstance TWA STEL TWA(c) STEL(c) threshold

(ppm)(a) (mg/m3)(b) (ppm)(a) (mg/m3)(b) (ppm) (mg/m3) (ppm) (mg/m3) (ppm; v/v)

Octachloronaphthalene SK – 0.1 – 0.3 SK – 0.1 – 0.3Octane 300 1400 375 1750 300 1450 375 1800 48Oil mist, mineral – 5(w) – 10 – 5 – 10Osmium tetroxide as Os 0.0002 0.0016 0.0006 0.0047 0.0002 0.002 0.0006 0.006 0.0019Oxalic acid – 1 – 2 – 1 – 2Oxydiethanol – – – – 23 100 – –Oxygen difluoride 0.05C 0.11C – – – – – – 0.10Ozone

Heavy work 0.05 – – –Moderate work 0.08 – – – – – 0.2 0.4Light work 0.10 – – –Any work loads up to 2 hrs 0.20 – – –

Paracetamoltotal inhalable dust – – – – – 10 – –

Paraffin wax fume – 2 – – – 2 – 6Paraquat

total inhalable dust – 0.5 – – – – – –respirable – 0.1 – – – 0.08 – –

Parathion SK – 0.1 – – SK – 0.1 – 0.3Parathion-methyl – – – – SK – 0.2 – 0.6Particulate polycyclic aromatic

hydrocarbons (PPAH), seeCoal tar pitch volatiles

Particulates not otherwise classified – 10 – – see Dusts(PNOC)

Pentaborane 0.005 0.013 0.015 0.039 – – – – 0.96Pentachloronaphthalene – 0.5 – – – – – –Pentachlorophenol SK – 0.5 – – SK – 0.5 – 1.5

– 10 (total – 20

Pentaerythritol – 10 – – inhalable dust)– 4 – –

(respirable dust)Pentane 600 1770 750 22102-Pentanone, see Methyl propyl ketonePentyl acetate, see Amyl acetatesPerchloroethylene 50 339 200 1357 50 345 100 690 27Perchloromethyl mercaptan 0.1 0.76 – – – – – –Perchloryl fluoride 3 13 6 25 3 13 6 26Precipitated silica, see Silica, amorphous





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Perlite – 10(i) – – – – – –Petroleum distillates, see Gasoline;

Stoddard solvent; VM&P naphthaPhenacyl chloride, see

!-ChloroacetophenonePhenol SK 5 19 – – SK 5 19 10 38 0.040Phenothiazine SK – 5 – – – – – –N-Phenyl-&-naphthylamine (e) (e) – – – – – –p-Phenylenediamine SK – 0.1 – – SK – 0.1 – –Phenyl-2,3-epoxypropyl ether – – – – 1 6 – –Phenyl ether vapour 1 7 2 14 1 7 – – 0.0012Phenylethylene, see Styrene, monomerPhenyl glycidyl ether (PGE) 1 6.1 – – – – – –Phenylhydrazine SK 5(e) 22(e) 10(g) 44(g)

Phenyl mercaptan 0.5 2.3 – – – – – – 0.00094Phenylphosphine 0.05C 0.23C – – – – – –Phorate (ISO) SK – 0.05 – 0.2 SK – 0.05 – 0.02Phosdrin, see MevinphosPhosgene 0.1 0.40 – – 0.02 0.08 0.06 0.25 0.90Phosphine 0.3 0.42 1 14 – – 0.3 0.4 0.51Phosphoric acid – 1 – 3 – – – 2Phosphorus (yellow) 0.02 – – – – 0.1 – 0.3Phosphorus oxychloride 0.1 0.63 – – 0.2 1.3 0.6 3.8Phosphorus pentachloride 0.1 0.85 – – 0.1 0.87 – –Phosphorus pentasulphide – 1 – 3 – 1 – 3Phosphorus trichloride 0.2 1.1 0.5 2.8 0.2 1.3 0.5 2.9Phthalic anhydride 1 6.1 – – SEN – 4 – 12 0.053m-Phthalodinitrile – 5 – – – – – –Picloram – 10 – – – 10 – 20Picric acid – 0.1 – – SK – 0.1 – 0.3Pindone – 0.1 – – – – – –Piperazine dihydrochloride – 5 – – 5 – –Piperidine – – – – SK 1 3.5 – –2-Pivalyl-1,3-indandione, see PindonePlaster of Paris, see Calcium sulphatePlatinum

Metal – 1 – – – 5 – –Soluble salts (except certainhalogeno-platinumcompounds) as Pt – 0.002 – – SEN – MEL 0.002 – –

Polychlorobiphenyls, seeChlorodiphenyls

Polytetrafluoroethylene (m)

decomposition products

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Table 5.12 Cont’d

Threshold limit values (USA) Occupational exposure limits (UK) Air odourSubstance TWA STEL TWA(c) STEL(c) threshold

(ppm)(a) (mg/m3)(b) (ppm)(a) (mg/m3)(b) (ppm) (mg/m3) (ppm) (mg/m3) (ppm; v/v)

Polyvinyl chlorideTotal inhalable dust – – – – – 10 – –Respirable dust – – – – – 4 – –

Portland cementTotal inhalable dust – – – – – 10 – –Respirable dust – – – – – 4 – –

Potassium hydroxide – – – 2C – – – 2Propane – (d) – – – – – – 16 000Propane-1,2,-diol

Total (vapour + particulates) – – – – 150 474 – –Particulates – – – – – 10 – –

Propane sultone (e) (e)

Propargyl calcohol, see Prop-2-yn-1-ol)&-Propiolactone 0.5(e) 1.5(e) – – – – – –Propionic acid 10 30 – – 10 31 15 46 0.16Propoxur – 0.5 – – – 0.5 – 2Propranolol – – – – – 2 – 6n-Propyl acetate 200 835 250 1040 200 849 250 1060 0.67n-Propyl alcohol SK 200 492 250 614 SK 200 500 250 625 2.6isoPropyl alcohol – – – – 400 999 500 1250Propylene (d) 76Propylene dichloride 75 347 110 508 – – – – 0.25Propylene glycol dinitrate SK 0.05 – – – SK 0.2 1.4 0.2 1.4Propylene glycol monomethyl ether,

see 1-Methoxypropan-2-olPropylene imine SK (e) 4.7(e) – – – – – –Propylene oxide 20 48 – – 5 12 – – 44n-Propyl nitrate 25 107 40 172 – – – –Propyne, see Methyl acetyleneProp-2-yn-1-ol SK 1 2.3 – – SK 1 2.3 3 7Pulverized fuel ash

Total inhalable dust – – – – – 10 – –Respirable dust – – – – – 4 – –

Pyrethrins – – – – – 5 – 10Pyrethrum – 5 – – – – – –2-Pyridylamine, see 2-aminopyridinePyridine 5 16 – – 5 16 10 33 0.17Pyrocatechol, see CatecholQuartz, see Silica, crystalline

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Quinone 0.1 0.44 – – 0.1 0.4 0.3 1.3 0.084RDX, see CycloniteResorcinol 10 45 20 90 10 46 20 92Rhodium

Metal – 1 – – – 0.1 – 0.3(Fume and dust)

Insoluble compounds as Rh – 1 – – – – – –Soluble compounds as Rh – 0.01 – – – 0.001 – 0.003

Ronnel – 10 – – – 10 – –Rosin core solder, pyrolysis products – 0.1 – – SEN – 0.05 MEL – 0.15Rotenone (commercial) – 5 – – – 5 – 10

– 10 (total – –inhalable dust)

– 4 – –(respirable dust)

Rubber fume – – – – – 0.6 MEL – –Rubber process dust – – – – – 6 MEL – –Rubber solvent (naphtha) 400 1590 – – – – – –

(exceptSelenium and compounds as Se – 0.2 – – 0.1 hydrogen – –

selenide)Selenium hexafluoride as Se 0.05 0.16 – – – – – –Sesone – 10 – – – 10 – 20Silane, see Silicon tetrahydrideSilica, Amorphous

Total inhalable dust – 10(f) – – – 6 – –Respirable dust – 3(f) – – – 2.4 – –Precipitated – 10 – – – – – –

Silica fume (Respirable) – 2 – – – – – –Silica fused (Respirable) – 0.1 – – – 0.08 – –Silica, Crystalline (Respirable)

Cristobalite – 0.05 – –Quartz – 0.05(e) – – – 0.3 – –Tridymite – 0.05 – –Tripoli – 0.1 – –

– 10 (total – –

Silicon – 10(f) – – inhalable dust)– 4 – –

(respirable dust)– 10 (total – –

Silicon carbide – 10(f) – – inhalable dust)– 4 – –

(respirable dust)Silicon tetrahydride 5 6.6 – – 0.5 0.67 1 1.3




Rouge – 10(f) – –








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Table 5.12 Cont’d

Threshold limit values (USA) Occupational exposure limits (UK) Air odourSubstance TWA STEL TWA(c) STEL(c) threshold

(ppm)(a) (mg/m3)(b) (ppm)(a) (mg/m3)(b) (ppm) (mg/m3) (ppm) (mg/m3) (ppm; v/v)

SilverMetal – 0.1 – – – 0.1 – –Compounds as Ag – 0.01 – – – 0.01 – –

SoapstoneRespirable dust – 3 – – – – – –Total dust – 6(i) – – – – – –

Sodium azideas sodium azide – – – C0.29 – – – 0.3as hydrazoic acid vapour – – C0.11 –

Sodium bisulphite – 5 – – – 5 – –Sodium 2,4-dichloro-phenoxyethyl sulphate, see SesoneSodium fluoroacetate SK – 0.05 – 0.15 SK – 0.05 – 0.15Sodium hydroxide – – – C2 – – – 2Sodium metabisulphite, see Disodium disulphite

– 10 (total – –

Starch – 10 – – inhalable dust)– 4 – –

(respirable dust)Stearates – 10 – – – – – –Stibine, see Antimony hydrideStoddard solvent 100 525 – – – – – –Strontium chromate – 0.0005(e) – –Strychnine – 0.15 – – – 0.15 – 0.45Styrene, monomer SK 20 – 40 – 100 430 MEL 250 1080 MEL 0.32Subtilisins (proteolitic enzymes as – – – C0.00006 – 0.00006 – 0.00006

100% pure crystalline enzyme)Sucrose – 10 – – – 10 – 20Sulfotep SK – 0.2 – – SK – 0.2 – –Sulfometuron methyl – 5 – –Sulphur dioxide 2 5.2 5 13 2 5 5 13 1.1Sulphur hexafluoride 1000 5970 – – 1000 6070 1250 7590Sulphuric acid – 1(e) – 3 – 1 – –Sulphur monochloride, see Disulphur dichlorideSulphur pentafluoride – – C0.01 – 0.025 0.25 0.075 0.79Sulphur tetrafluoride – – C0.1 – 0.1 0.4 0.3 1.2Sulphuryl fluoride 5 21 10 42 5 21 10 42Sulprofos – 1 – – – – – –Systox, see Demeton2,4,5-T – 10 – – – 10 – 20




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Synthetic vitreous fibresContinuous filament glass fibres

Respirable – 1f/cc(h) – –Inhalable – 5mg/m3

Glass wool fibres – 1f/cc(h)

Rock wool fibres – 1f/cc(h)

Stag wool fibres – 1f/cc(h)

Special purpose glass fibres – 1f/cc(h)

Talc (containing no asbestos fibres) – 2 – – – 1 – –(respirable dust) (respirable dust)

Talc (containing asbestos fibres) Use asbestosTLV-TWA

Tantalum metal and oxide dusts – 5 – – – 5 – 10TEDP, see SulfotepTellurium and compounds, as Te – 0.1 – – – 0.1 (except – –

hydrogen telluride)Tellurium hexafluoride as Te 0.02 0.10 – – – – – –Temephos – 10 – – – – – –TEPP SK 0.004 0.047 – – SK 0.004 0.05 0.01 0.12Terephthalic acid – 10Terphenyls – – – C5 – – 0.5 51,1,2,2-Tetrabromoethane – – – – SK 0.5 7 – –1,1,1,2-Tetrachloro-2,2- 500 4170 – – 100 847 100 847

difluoroethane1,1,2,2-Tetrachloro-1,2- 500 4170 – – 100 847 100 847

difluoroethane1,1,2,2-Tetrachloroethane SK 1 6.9 – – – – – – 1.5Tetrachloroethylene, see

PerchloroethyleneTetrachloromethane, see Carbon

tetrachlorideTetrachloronaphthalene – 2 – – – 2 – 4Tetraethyl lead as Pb SK – 0.1 – – SEE NOTE (K)Tetraethyl orthosilicate,

see Ethyl silicateTetrafluoroethylene 2 – – –Tetrahydrofuran 200 590 250 737 100 300 200 599 2.0Tetramethyl lead as Pb SK – 0.15 – – SEE NOTE (K)Tetramethyl orthosilicate,

see Methyl silicateTetramethyl succinonitrile SK 0.5 2.8 – – SK 0.5 2.8 2 11Tetranitromethane 0.005 – – – – – – –Tetrasodium pyrophosphate

anhydride – 5 – –decahydrate – 5 – –

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Table 5.12 Cont’d

Threshold limit values (USA) Occupational exposure limits (UK) Air odourSubstance TWA STEL TWA(c) STEL(c) threshold

(ppm)(a) (mg/m3)(b) (ppm)(a) (mg/m3)(b) (ppm) (mg/m3) (ppm) (mg/m3) (ppm; v/v)

Tetryl – 2 – – SK – 1.5 – 3Thallium, soluble compounds,

as Tl SK – 0.1 – – SK – 0.1 – –4,4*-Thiobis(6-tert-butyl-m-cresol) – 10 – – – 10 – –Thioglycolic acid SK 1 3.8 – – 1 3.8 – –Thionyl chloride – – C1 C4.9 – – 1 5Thiram – 1 – – – 5 – 10Tin

Metal – 2 – – – – – –Oxide and inorganic compounds – 2 – – – 2 – 4except SnH4, as SnOrganic compounds as Sn SK – 0.1 – 0.2 SK – 0.1 – 0.2

(except Cyhexin)– 10 (total

inhalable dust)– 4 – –

(respirable dust)Toluene 50 191 150 565 SK 50 191 150 574 2.9Toluene-2,4-diisocyanate (TDI) 0.005 0.036 0.02 0.14 see Isocyanatesp-Toluenesulphonyl chloride – – – – – – – 5 0.17o-Toluidine SK 2(e) 8.8(e) – – 0.2 0.9 – – 0.25m-Toluidine SK 2 8.8 – – – – – –p-Toluidine SK 2(e) 8.8(e) – – – – – –Toluol, see TolueneToxaphene, see Chlorinated campheneTributyl phosphate 0.2 2.2 – – – 5 – 5Trichloroacetic acid 1 6.7 – –1,2,4-Trichlorobenzene – – C5 C37 1 7.6 – – 1.41,1,1-Trichlorobis (chlorophenyl)ethane – – – – – 1 – 31,1,1-Trichloroethane, see Methyl

chloroform1,1,2-Trichloroethane SK 10 55 – –Trichloroethylene 50 269 100 535 SK 100 550 MEL 150 820 MEL 28Trichlorofluoromethane – – C1000 C5710 1000 5710 1250 7140 5Trichloromethane, see ChloroformTrichloronaphthalene SK – 5 – – – – – –Trichloronitromethane, see Chloropicrin1,2,3-Trichloropropane SK 10 60 – – 50 306 75 4601,1,2-Trichloro-1,2,2-trifluoroethane 1000 7670 1250 9590 1000 7790 1250 9740 45




Titanium dioxide – 10(i) – –

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Tricyclohexyltin hydroxide,see Cyhexatin

Tridymite, see Silica, crystallineTriethanolamine – 5 – –Triethylamine 1 3 15 62 10 42 15 63 0.48Trifluorobromomethane, see

Bromotrifluoromethane1,3,5-Triglycidyl-s-triazinetrione – 0.05 – –Triglycidyl iso-cyanurate – – – – – 0.1 – –Trimellitic anhydride, see Benzene-

1,2,4-tricarboxylic acid 1,2-anhydrideTrimethylamine 5 12 15 36 10 25 15 37 0.00044Trimethyl benzene 25 123 – – 25 125 – – 0.553,5,5-Trimethylcyclohex-2-enone – – – – – – 5 29Trimethyl phosphite 2 10 – – 2 10 – – 0.000102,4,6-Trinitrophenol, see Picric acid2,4,6-Trinitrophenylmethylnitramine,

see Tetryl2,4,6-Trinitrotoluene (TNT) SK – 0.1 – – – 0.5 – –Triorthocresyl phosphate SK – 0.1 – – – 0.1 – 0.3Triphenyl amine – 5 – – – – – –Triphenyl phosphate – 3 – – – 3 – 6Tripoli, see Silica, crystallineTungsten as W

Insoluble compounds – 5 – 10 – 5 – 10Soluble compounds – 1 – 3 – 1 – 3

Turpentine 100 566 – – 100 566 150 850Uranium (natural)

Soluble and insoluble compounds – 0.2(g) – 0.6(g) – 0.2 – 0.6as U

n-Valeraldehyde 50 176 – – – – – – 0.028Vanadium pentoxide as V2O5

0.5 (total– inhalable dust) – –

Respirable dust and fume – 0.05 – – 0.04 (Fume– and respirable – –

dust) as VVegetable oil mists – 10 – – – – – –Vinyl acetate 10 35 15 52 10 36 20 72 0.50Vinyl benzene, see StyreneVinyl bromide 0.5(e) 2.2(e) – – 5 20 – –Vinyl chloride 1(g) 2.6(g) – – 7(l) – MEL – – 3000Vinyl cyanide, see AcrylonitrileVinyl cyclohexene dioxide SK 0.1 0.6 – – – – – –Vinyl fluoride 1(e) – – –




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Table 5.12 Cont’d

Threshold limit values (USA) Occupational exposure limits (UK) Air odourSubstance TWA STEL TWA(c) STEL(c) threshold

(ppm)(a) (mg/m3)(b) (ppm)(a) (mg/m3)(b) (ppm) (mg/m3) (ppm) (mg/m3) (ppm; v/v)

Vinylidene chloride 5 20 20 79 10 40 MEL – – 190Vinylidene fluoride 500 – – –Vinyl toluene 50 242 100 483 – – – – 10VM & P naphtha 300 1370 – – – – – –Warfarin – 0.1 – – – 0.1 – 0.3Welding fumes (NOC) – 5(i) – – – 5 – –White spirit – – – – see EH 40 for calculationWood dust (certain hardwoods e.g. – 1(g) – – SEN – 5 MEL – –

beech, oak)Softwood – 5 – 10 – 5 MEL – –

Wool process dust – – – – – 10 – –Xylene

o-,m-,p-isomers 100 434 150 651 SK 100 441 150 662 1.1 (meta)m-Xylene !, !*-diamine SK – – – C0.1 – – – –Xylidine, mixed isomers SK 0.5(e) 2.5(e) – – SK 2 10 10 50 0.056

(2,4-Xylidine)Yttrium, metal and compounds, as Y – – – – 1 – 3Zinc chloride fume – 1 – 2 – 1 – 2Zinc chromates as Cr – 0.01(g) – – – – – –Zinc distearate

Total inhalable dust – – – – – 10 – 20Respirable dust – – – – – 4 – –

Zinc oxideFume – 5 – 10 – 5 – 10Dust – 10 – – – – – –

Zirconium and compounds, as Zr – 5 – 10 – 5 – 10

C Ceiling limitMEL Maximum exposure limitNOC Not otherwise classifiedSEN Capable of causing respiratory sensitization; skin sensitizers have not been given a separate notationSK Can be absorbed through skinThis table is a useful guide but because standards are continually under review and many caveats apply reference should be made to the most recent edition of HSE EH40 and the AGGIH TLV list for current values and their interpretation. Often carcinogens are not assigned a hygiene standard.(a) Parts of vapour or gas per million parts of contaminated air by volume at 25°C and 760 torr (1.013 bar).(b) Milligrams of substance per m3 air.(c) Value shown is OES unless otherwise indicated as MEL.

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(d) Simple asphyxiant. Some gases and vapours present at high concentrations act as asphyxiants by reducing the oxygen content of air. Many of these are odourless andcolourless. Many also pose a fire or explosion risk, often at values below which asphyxiation can occur. (Although capable of asphyxiation, they are not considered tobe substances hazardous to health under COSHH.)(e) Suspected human carcinogens – see TLV Appendix A, Category A2 (below).(f) The value is for total dust containing no asbestos and <1% crystalline silica.(g) Confirmed human carcinogen – see TLV Appendix, A, Category A1 (below).(h) Fibres longer than 5 µm and with an aspect ratio +3:1 as determined by the membrane filter method at 400–450X magnification (4 mm objective) phase contrastillumination.(i) Welding fumes cannot be classified simply. The composition and quantity of both are dependent on the alloy being welded and the process and electrodes used.Reliable analysis of fumes cannot be made without considering the nature of the welding process and system being examined; reactive metals and alloys such asaluminium and titanium are arc-welded in a protective inert atmosphere such as argon. These arcs create relatively little fume, but they do create an intense radiationwhich can produce ozone. Similar processes are used to arc-weld steels, also creating a relatively low level of fumes. Ferrous alloys also are arc-welded in oxidizingenvironments that generate considerable fume and can produce carbon monoxide instead of ozone. Such fumes generally are composed of discrete particles ofamorphous slags containing iron, manganese, silicon, and other metallic constituents depending on the alloy system involved. Chromium and nickel compounds arefound in fumes when stainless steels are arc-welded. Some coated and flux-cored electrodes are formulated with fluorides and the fumes associated with them cancontain significantly more fluorides than oxides. Because of the above factors, arc-welding fumes frequently must be tested for individual constituents that are likely tobe present to determine whether specific TLVs are exceeded. Conclusions based on total fume concentration are generally adequate if no toxic elements are present inwelding rod, metal, or metal coating and conditions are not conducive to the formation of toxic gases.

Most welding, even with primitive ventilation, does not produce exposures inside the welding helmet above 5 mg/m3. That which does, should be controlled.(j) UK control limits for asbestos:

Chrysotile 0.3 fibres/ml of air averaged over any continuous 4 hr period0.9 fibres/ml of air averaged over any continuous 10 min period

Any other form of asbestos, 0.2 fibres/ml of air averaged over any continuous 4 hr periodalone or in mixtures 0.6 fibres/ml of air averaged over any continuous 10 min periodAction levels for cumulative exposures within a 12 week period:(a) for chrysotile, 72 fibre hours/ml of air(b) for any other form of asbestos, alone or in mixtures, 48 fibre hours/ml of air(c) for both types of exposure at different times within the period, a proportionate number of fibre hours/ml

The lack of limits should not be taken to imply an absence of hazard. In the absence of a specific OEL for a particular dust, exposure should be adequately controlledand where there is no indication of the need for a lower value, personal exposure should be kept below both 10 mg/m3 8 hr TWA total inhalable dust and 4 mg/m3

8 hr TWA respirable dust.(k) UK limits for lead are 8 hr TWA concentrations as follows:

Lead other than lead alkyls – 0.15 mg/m3 of airLead alkyls – 0.1 mg/m3 of air

These are ceiling values that must not be exceeded when calculating 8 hr TWA. They should be read in conjunction with biological limits for lead.(l) As measured by the vertical elutriator cotton-dust samples.(m) Polytetrafluoroethylene decomposition products: thermal decomposition of the fluorocarbon chain in air leads to the formation of oxidized products containingcarbon, fluorine and oxygen. Because these products decompose in part by hydrolysis in alkaline solution, they can be quantitatively determined in air as fluoride toprovide an index of exposure. No TLV is recommended pending determination of the toxicity of the products, but air concentration should be minimal. (Trade names:Algoflon, Fluon, Teflon, Tetran.)(n) In the UK vinyl chloride is also subject to an overriding annual maximum exposure limit of 3 ppm.(o) As sampled by a method that does not collect vapour.

TLV Appendix A: Carcinogens (excerpts)The Chemical Substances Threshold Limit Values Committee classifies certain substances found in the occupational environment as either confirmed or suspected human

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Table 5.12 Cont’d

carcinogens. The present listing of substances that have been identified as carcinogens takes two forms: those for which a TLV has been assigned and those for whichenvironmental and exposure conditions have not been sufficiently defined to assign a TLV. Where a TLV has been assigned, it does not necessarily imply the existenceof a biological threshold; however, if exposures are controlled to this level, we would not expect to see a measurable increase in cancer incidence or mortality.

Two categories of carcinogens are designated:

A1 – Confirmed Human Carcinogens. Substances, or substances associated with industrial process, recognized to have carcinogenic potential.A2 – Suspected human carcinogens. Chemical substances, or substances associated with industrial process, which are suspect of inducing cancer, based on their limitedepidemiological evidence or demonstration of carcinogenesis in one or more animal species by appropriate methods.

Exposures to carcinogens must be kept to a minimum. Workers exposed to A1 carcinogens without a TLV should be properly equipped to eliminate to the fullest extentpossible all exposure to the carcinogen. For A1 carcinogens with a TLV and for A2 carcinogens, worker exposure by all routes should be carefully controlled to levelsas low as reasonably achievable (ALARA) below the TLV.

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Flammable chemicals

Certain chemicals pose fire and explosion risks because:

• They ignite easily. Vapours often travel a considerable distance to an ignition source remotefrom the point of chemical escape.

• Considerable heat is generated. Many volatile substances liberate heat at a rate some ten timesfaster than burning wood.

• The fire spreads easily by, e.g., running liquid fire, a pool fire, a fire ball, heat radiation or thermallift (convection).

• Explosion: a confined vapour cloud explosion (CVCE) can result from ignition of vapourwithin a building or equipment; a boiling liquid expanding vapour explosion (BLEVE) canresult when unvented containers of flammable chemicals burst with explosive violence as aresult of the build-up of internal pressure; unconfined vapour cloud explosion (UVCE) canresult from ignition of a very large vapour or gas/air cloud.

Clearly, flammable chemicals also pose a health risk if the substance or its thermal degradationor combustion products are toxic, (e.g. carbon monoxide) or result in oxygen deficiency becauseoxygen is consumed. Hot smoke and other respiratory irritants, e.g. aldehydes, are also produced.

Ignition and propagation of a flame front

Normally flame propagation requires

(a) fuel, gas or vapour (or combustible dust) within certain concentration limits,(b) oxygen supply (generally from air) above a certain minimum concentration, and(c) ignition source of minimum temperature, energy and duration.

All three, represented by the three corners of a triangle (Figure 6.1), must generally be present.But no ignition source is needed if a material is above a specific temperature (see p. 214), and noadditional oxygen is required if an oxidizing agent is present or in a few cases when oxygen iswithin the fuel molecule (e.g. ethylene oxide).


Liquids and solids do not burn as such, but on exposure to heat vaporize or undergo thermaldegradation to liberate flammable gases and vapours which burn. Some chemicals undergospontaneous combustion (see page 214).

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FuelVapour/gasMist/frothDust of combustible solid

Ignition sourceFlamesSparks (of sufficient energy)Self heating etc.

OxygenAirOxidizing agentincluding e.g. chlorine

Flammable limits

Flammable gases and volatile liquids are particularly hazardous because of the relative ease withwhich they produce mixtures with air within the flammable range. An increase in the surface areaof any liquid facilitates vaporization. For each substance there is a minimum concentration of gasor vapour below which flame propagation will not occur (i.e. the mixture is too lean). There isalso a concentration above which the mixture is too rich to ignite. The limits of flammability areinfluenced by temperature and pressure (e.g. the flammable range expands with increasedtemperature). Generally, the wider the flammable range the greater the fire risk. Flammabilitylimits for a range of chemicals are summarized in Table 6.1.

The vapour pressure of a flammable substance also provides an indication of how easily thematerial will volatilize to produce flammable vapours; the higher the vapour pressure, the greaterthe risk. Lists of vapour pressures usually contain data obtained under differing conditions butinspection of boiling points (when the vapour pressure equals atmospheric pressure) gives a firstapproximation of the ease with which substances volatilize. Table 6.1 therefore includes bothboiling point and vapour pressure data.

Flash point

The flash point represents the minimum temperature at which an ignitable mixture exists abovea liquid surface. By definition, flash points are inapplicable to gases. Some solids, e.g. naphthaleneand camphor, are easily volatilized on heating so that flammable mixtures develop above the solidsurface and hence flash points can be determined. (However, although these substances can beignited, they generally need to be heated above their flash points in order for combustion to besustained: this is the ‘fire point’.)

Flash point determinations may be made in ‘closed’ or ‘open’ containers, giving different values;

Figure 6.1 Fire triangle


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these are non-equilibrium methods. Alternatively equilibrium methods are available. Typicalflash points are quoted in Table 6.1 and, unless otherwise stated, these relate to closed cupmeasurements. In general, the lower the flash point the greater the potential for fire: materialswith flash points at or below ambient temperature are highly flammable and can inflame atambient temperature on contact with ignition sources. Flash point is used to classify liquids undermany legislative systems: in the UK liquids with flash points <32°C (and which, when heatedunder specific test conditions and exposed to an external source of flame applied in a standardmanner, supports combustion) are defined as ‘highly flammable’ under the Highly FlammableLiquid and Liquefied Petroleum Gas Regulations.

Chemicals may ignite below their flash points if the substance:

• Is in the form of a mist (or froth).• Covers a large surface area (e.g. when absorbed on porous media).• Contains a small amount of a more volatile flammable liquid, e.g. due to deliberate or accidental


In addition

• Flash points are reduced by increases in ambient pressure. Thus the flash point of toluene at sealevel (101.3 kPa) is 4.5°C whereas at 83.3 kPa, e.g. in the mountains at 1685 m, the value is1°C.

• Materials with high flash points such as heavy oils and resins can produce flammable vapoursdue to thermal degradation on heating. Dangers therefore arise when welding, flame cuttingempty drums/vessels once used to contain such materials due to the presence of residues.

Substances may be heated to their flash points by other substances with lower flash points burningin close proximity. Storage of flammable chemicals, therefore, needs careful consideration.

Vapour density

The density of a vapour or gas at constant pressure is proportional to its relative molecular massand inversely proportional to temperature. Since most gases and vapours have relative molecularmasses greater than air (exceptions include hydrogen, methane and ammonia), the vapours slumpand spread or accumulate at low levels. The greater the vapour density, the greater the tendencyfor this to occur. Gases or vapours which are less dense than air can, however, spread at low levelwhen cold (e.g. release of ammonia refrigerant). Table 6.1 includes vapour density values.

Dust explosions

Increasing the surface area of a combustible solid enhances the ease of ignition. Hence dust burnsmore rapidly than the corresponding bulk solid; combustion of dust layers can result in rapidflame spread by ‘train firing’. Solid particles less than about 10 µm in diameter settle slowly inair and comprise ‘float dust’ (see p. 51 for settling velocities). Such particles behave, in someways, similarly to gas and, if the solid is combustible, a flammable dust–air mixture can formwithin certain limits. Larger particles also take part, since there is a distribution of particle sizes,and ignition can result in a dust explosion.

Dust explosions are relatively rare but can involve an enormous energy release. A primaryexplosion, involving a limited quantity of material, can distribute accumulations of dust in theatmosphere which, on ignition, produces a severe secondary explosion.

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Small particles are required, to provide a large surface-area-to-mass ratio and for the solid toremain in suspension. Surface absorption of air (oxygen) by the solid, or the evolution of combustiblegas or vapour on heating, may be a predisposing factor. The presence of moisture reduces thetendency to ignite: it also favours agglomeration to produce larger particles. An increase in theproportion of inert solid in particles tends to reduce combustibility.

The explosive range of dusts in air can be very wide. The limits vary with the chemicalcomposition and with the size of the particles. The lower limits are equivalent to a dense fog inappearance. The upper limits are ill defined but are not generally of practical significance. Theimportant characteristics are the ease of ignition, lower explosive limits, the maximum explosionpressure and the rates of pressure rise. Organic or carbonaceous materials, or easily oxidizablemetals (e.g. aluminium or magnesium) are more hazardous than nitrogenous organic materials.The least hazardous materials are those which contain an appreciable amount of mineral matter.

For a summary of data for a range of dusts refer to Table 6.2.

Oxygen requirements

Most substances require a supply of oxygen in order to burn. Air contains about 21% oxygen.Gases and vapours can produce flammable mixtures in air within certain limits. When the oxygencontent of air is increased (e.g. by enrichment with pure oxygen from a leaking cylinder) the firehazard is increased. Conversely, lowering the oxygen by, for instance, the presence of an inert gassuch as nitrogen, argon, or carbon dioxide, reduces the fire risk. Some chemicals contain theirown supply of oxygen (e.g. perchlorates) and can burn even in an oxygen-deficient atmosphere.Just as chemicals can react violently with oxygen to produce a fire, certain substances can inflameon reaction with other oxidizing agents (e.g. hydrocarbons with chlorine). Upper and lowerflammable limits exist for such systems. Oxidizing agents generally assist combustion (see page234).

There is a critical oxygen content below which ignition of combustible dusts or gases will notoccur and this can provide a means for safe operation under an inert atmosphere, i.e. ‘inerting’.

Ignition sources

Combustion is generally initiated by the introduction of a finite amount of energy to raise a finitevolume of the material to its ignition temperature. Potential ignition sources for vapour–airmixtures are listed in Table 6.3, and temperatures in Table 6.4. Heat sources can be chemicalenergy (spontaneous combustion, chemical reaction), mechanical energy (e.g. friction), radiantenergy, solar energy, static energy or electrical current. Thus heat is generated from electricalcurrent by resistance, arcing or sparking. Resistance arises when the current flow exceeds thecapacity of the wire. The result is often a blown fuse, tripped circuit breaker or heating of thecircuit wire. Arcing occurs when electrical current jumps from one point to another, e.g. in aswitch or connection box when wires separate from connections, or as a result of worn insulationbetween positive and neutral wires.

Common ignition sources include:

• Naked flames (e.g. Bunsen burners, welding torches, blow lamps, furnaces, pilot lights, matches,glowing cigarettes or embers).

• Sparks created by arcs in electrical switchgear, engines, motors, or by friction (e.g. lighterspark). Aluminium, magnesium, titanium and their alloys have an affinity for oxygen and in athermite reaction with rust produce temperatures !3000°C. A thermite flash can result from the


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Table 6.3 Sources of ignition

Mechanical sourcesFriction Metal to metal

Metal to stoneRotary impactAbrasive wheelBuffing discTools, drillBoot studsBearingsMisaligned machine partsBroken machine partsChocking or jamming of materialPoor adjustment of power drivesPoor adjustment of conveyors

Missiles Hot missilesMissile friction

Metal fracture Cracking of metal

Electrical sourcesElectrical current Switch gear

Cable breakVehicle starterBroken lightElectric motor

Electrostatic Liquid velocitySurface chargePersonal chargeRubbing of plastic or rubberLiquid spray generationMist formationWater jettingPowder flowWater settling

Lightning Direct strikeHot spotInduced voltage

Stray currents Railway linesCable breakArc welding

Radio frequency Aerial connectionIntermittent contact

Thermal sourcesHot surface Hot spot

Catalyst hot spotsIncandescent particles from incinerators, flarestacks, chimneysVehicle exhaustSteam pipesRefractory lining, hot slagForeign metal in crushing and grinding equipmentElectric heaterSmokingGlowing embers, brandsDrying equipmentMolten metal or glassHeat transfer saltHot oil/salt transfer lines


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Boiler ducts or fluesElectric lampsHot process equipmentWelding metalInduction brazingHot platesSoldering irons

Self-heating OxidationReactionActivated carbon

Flames Pilot lightPrimary fire involving liquid (running or pool), solid or gasMatches, cigarette lightersCutting, weldingPortable gas heatersStoves; natural gas, LPG, oil or solid fuel – firedBurnersArsonBlow torchesBrazing

Compression Pressure changePiston

Engines ExhaustEngine overrunHydraulic spray into air intake

Diffusion High pressure change

Chemical sourcesPeroxides Oxygen release


Polymerization Exothermic reactionCatalystLack of inhibitorCrystallization

Spontaneous Pyrophoric depositDepositsWater reactiveSulphidesOily rags, oil impregnation of laggingHeat transfer salt

Reaction with other substancesThermite reaction Rust

Exothermic reactions with aluminium, aluminium alloys

Unstable substances Acetylides

Decomposition InitiatorTemperatureCatalyst

striking of a smear or thin coating of alloy on rusty steel with a hammer. The glancing impactof stainless steel, mild steel, brass, copper–beryllium bronze, aluminium copper and zinc ontoaluminium smears on rusty steel can initiate a thermite reaction of sufficient thermal energy toignite flammable gas/vapour–air atmosphere or dust clouds.

Table 6.3 Cont’d

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Table 6.4 Approximate temperatures of common ignition sources

Flame/spark sources Ignition temperature (°C)Candles 640–940Matches 870Manufactured gas flame 900–1340Propane flame 2000Light bulb element 2483Methane flame 3042Electrical short circuit or arc 3870

Non-flame sourcesSteam pipes at normal pressure 100Steam pipes at 10 psi (0.7 bar) 115Light bulb, normal 120Steam pipes at 15 psi (1 bar) 121Steam pipes at 30 psi (2 bar) 135Steam pipes at 50 psi (3.5 bar) 148Steam pipes at 75 psi (5 bar) 160Steam pipes at 100 psi (7 bar) 170Steam pipes at 150 psi (10.5 bar) 185Steam pipes at 200 psi (14 bar) 198Steam pipes at 300 psi (21 bar) 217Steam pipes at 500 psi (35 bar) 243Steam pipes at 1000 psi (70 bar) 285Cigarette, normal 299Soldering iron 315–432Cigarette, insulated 510Light bulb, insulated 515

Petroleum vapour is unlikely to be ignited by impact of steel on steel produced by hand.Power operation can however produce incendive sparks. Hydrogen and perhaps ethylene,acetylene or carbon disulphide can be ignited by the impact of steel on steel using hand tools.If non-sparking tools are used, care must be taken to avoid embedded grit particles sinceimpact of steel on ‘rock’ poses a greater hazard. Impact on flint or grit can produce incendivesparks irrespective of striking material. Friction in bearings is a common ignition source.

• Radiant heat sources include furnaces, vats, cooking stoves and other hot surfaces. Solar heatfrom the direct rays of the sun may directly, or if magnified by, e.g., glass bottles or flasks,provide sufficient energy to raise the temperature of chemicals to their flash-point.

• Vehicular petrol engines are potential ignition sources by means of the spark-ignition system,dynamo or battery, or hot exhaust pipe. Non-flameproof diesel engines are potential ignitionsources due to a hot exhaust pipe or carbonaceous particles or flames from the exhaust.

• Spark due to static electricity associated with the separation of two dissimilar materials (Table6.5). The charges may be transported/conducted some distance after separation before there issufficient accumulation to produce a spark, e.g. in the flow of liquids or powders. The size ofthe charge is generally small but the potential difference may be very high such that a spark isof sufficient energy for ignition.

Electrostatic charge generated by a liquid flow through a pipe depends on the electricalconductivity of the liquid. With a liquid of high electrical conductivity, the charge is easilygenerated but quickly dissipated. Hazardous liquids are generally those with conductivities inthe range 0.1 to 1000 ps/m. The rate of charge generation increases with increase in flowrateand constrictions in the pipeline.

• Friction resulting from two surfaces rubbing together, e.g. drive belts in contact with their


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housing or guard, or metal surfaces rubbing against one another. Usually friction arises frompoor maintenance (e.g. loose guard, inadequate lubrication).

• Lightning. Protection is generally provided by earthing with low resistance, e.g. 7 ", whichshould be short and direct. The recommended value for protection of plant is !10 ".

A material that is above its autoignition temperature will ignite spontaneously on contact withair in the correct proportions (see Table 6.1 for minimum temperature of ignition source).

Ignition of a flammable dust–air mixture is more difficult than with flammable vapour–airmixtures. A larger source of heat is required, and a larger volume of fuel must be heated to theignition point. The same range of potential ignition sources is applicable as for air–vapour mixtures.

At certain temperatures compounds will explode without application of a flame, as illustratedby the selection in Table 6.6.

Spontaneous combustion

Certain materials which are generally considered to be stable at ordinary temperatures can inflameeven in the absence of normal ignition sources. Such spontaneous combustion results from exothermicautoxidation when the heat liberated exceeds that dissipated by the system. Materials prone toself-heating are listed in Table 6.7. In most cases, such fires involve relatively large, enclosed orthermally-insulated masses, and spontaneous combustion usually occurs after prolonged storage.

Pyrophoric chemicals

Pyrophoric chemicals are so reactive that on contact with air they undergo vigorous reaction withatmospheric oxygen (under ambient conditions or at elevated temperatures), or with water (Table6.9). Examples include:

• Certain metals/alloys – the alkali metals (lithium, potassium, sodium) and even some metals/alloys which undergo slow oxidation or are rendered passive in bulk form but which, in thefinely divided state, inflame immediately when exposed to oxygen (e.g. aluminium, magnesium,zirconium).

Table 6.5 Operations which may result in static charge generation

Solid–solid Persons walkingGrit blastingConveying of powdersBelts and pulleysFluidized beds

Solid–liquid Flow of liquids in pipelines/filtersSettling of particles in liquid (e.g. rust and sludge)

Gas–liquid Released gas (air) bubbles rising in a large tankMist formation from LPG evaporationSplash fillingCleaning with wet steamMist formation from high pressure water jets

Liquid–liquid Settling of water drops in oil

Solid–gas Mixing of immiscible liquidsPneumatic conveying of solidsFluidized beds

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• Phosphorus.• Certain phosphides, hydrides and silanes (e.g. hydrogen phosphide, silane).• Substances which react with water to liberate flammable gas, e.g. carbides (liberate acetylene),

alkali metals (hydrogen), organometallics (hydrocarbons – see Table 6.8), and where the heatof reaction is sufficient to ignite the gas. Thus metals which are less electronegative thanhydrogen (see Table 6.10) will displace this element from water or alcohols, albeit at differentrates.


Fires sometimes initiate, or are followed by, explosions resulting in blast damage, missiles etc.These may trigger secondary events, e.g. fires, toxic releases or further explosions.

Types of explosion

• Confined vapour cloud explosion: gas or vapour burns in a confined volume and rapid expansionof the combustion products is restrained until failure of the container or building occurs.

• Boiling liquid expanding vapour explosion: follows failure of a pressurized container of flammableliquid, e.g. LPG, or a sealed vessel containing volatile flammable liquids, under fire conditions.Ignition results in a fireball and missiles.

• Dust explosion (refer to page 220).• Explosion due to thermal deflagration or detonation of a solid or liquid.• Unconfined vapour cloud explosion: a large flammable gas or vapour–air cloud burns in free

space with sufficient rapidity to generate pressure waves, which propagate through the cloudand into the surrounding atmosphere. Such events are extremely rare.

Table 6.6 Approximate temperatures at which selected substances will explode, without the application of a flame

Solids Temperature(1) (°C)Gun cotton (loose) 137 139(2)

Cellulose dynamite 169 230Blasting gelatine (with camphor) 174Mercury fulminate 175Gun cotton (compressed) 186 201Dynamite 197 200Blasting gelatine 203 209Nitroglycerin 257Gunpowder 270 300

GasesPropylene 497 511Acetylene 500 515Propane 545 548Hydrogen 555Ethylene 577 599Ethane 605 622Carbon monoxide 636 814Manufactured gas 647 649Methane 656 678

(1) The value quoted is that at which the substance itself explodes, not the temperature at which its container ruptures withthe possible subsequent ignition of the contents.(2) The higher temperature is applicable when the heat rise is very rapid, i.e. if the rate of rise is slow then the explosion willoccur at the lower temperature.


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Table 6.7 Materials liable to self-heat

Liquid materials susceptible to self-heating when dispersed on a solidBone oil moderateCastor oil very slightCoconut oil very slightCod liver oil highCorn oil moderateCotton seed oil (refined) highFish oil highLard highLinseed oil (raw) very highMenhaden oil highNeatsfoot oil slightOleic acid very slightOleo oil very slightOlive oil slightPalm oil moderatePeanut oil moderatePerilla oil highPine oil moderateRape seed oil highRosin oil highSoya bean oil moderateSperm oil moderateTallow moderateTallow oil moderateTung oil moderateTurpentine slightWhale oil high

Solid materials susceptible to self-heating in airActivated charcoalAnimal feedstuffsBeansBone meal, bone blackBrewing grains, spentCarbonCelluloidColophony powder materialCopper powderCopraCorkCottonCotton wasteCottonseedDistillers dried grainFatsFertilizersFishmealFlaxFoam and plasticGrainsGrassGum rosinHayHempHidesIron filings/wool/boringsIron pyritesIxtle

Jaggery soapJuteLagging contaminated with oils etc.Lamp-blackLeather scrapMaizeManureMilk productsMonomers for polymerizationPalm kernelsPaper wastePeatPlastic, powdered (various)Rags, impregnatedRapeseedRice branRubber scrapSawdustSeedcakeSeedsSilageSisalSoap powderSoya beansStrawSulphurVarnished fabricWood chipsWood fibreboard

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Fibrous materials are subject to self-heating when impregnated with the following vegetable/animal oils(in decreasing order of tendency)Cod liver oilLinseed oilMenhaden oilPerilla oilCorn oilCottonseed oilOlive oilPine oilRed oilSoya bean oilTung oilWhale oilCastor oilLard oilBlack mustard oilOleo oilPalm oilPeanut oil

Other materials subject to self-heating (depending upon composition, method of drying, temperature, moisturecontent)Desiccated leatherLeather scrapsDried bloodHousehold refuseLeather meal

NB This list is not exclusive

Table 6.8 Characteristics of some organometallic compounds in common use

Alkyl magnesium halides (Grignard reagents) Usually prepared and handled in organic solventFor alkyl groups of !4 carbon atoms, the compounds react

vigorously with water and the resulting alkane ignites

Butyl lithium Pale yellow, caustic, extremely flammable liquidMay ignite if exposed to airReacts violently with water

Diethyl aluminium chloride Colourless corrosive liquidIgnites immediately upon contact with airReacts violently with water

Diethyl zinc Colourless malodorous liquids that are spontaneously flammableDimethyl zinc in air and react violently with water

Dimethyl arsine Colourless poisonous liquidIgnites in air

Nickel carbonyl Yellowish, volatile, toxic liquid, oxidizes in air andexplodes at ~60°C

Confirmed carcinogen

Sodium methylate White powder, sensitive to air and decomposed by water

Triethyl aluminium Colourless liquids which ignite in air and decomposeTriethyl aluminium ethereate explosively in cold waterTrimethyl aluminium


Wood flourWool waste

Zinc powder

Table 6.7 Cont’d

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Table 6.9 Pyrophoric chemicals in common use

Pyrophoric alkyl metals Carbonylpotassium Pyrophoric metal Triethylarsineand derivatives Carbonylsodium sulphides TriethylboraneGroups Dodecacarbonyldivanadium (Ammonium sulphide) TriethylphosphineAlkyl lithiums Dodecacarbonyltetracobalt Barium sulphide TriisopropylphosphineDialkylzincs Dodecacarbonyltriiron Calcium sulphide TrimethylarsineDiplumbanes Hexacarbonylchromium Chromium (II) sulphide TrimethylboraneTrialkylaluminiums Hexacarbonylmolybdenum Copper (II) sulphide TrimethylphosphineTrialkylbismuths Hexacarbonyltungsten Diantimony trisulphide

Nonacarbonyldiiron Dibismuth trisulphide Pyrophoric alkylCompounds Octacarbonyldicobalt Dicaesium selenide non-metal halidesBis-dimethylstibinyl oxide Pentacarbonyliron Dicerium trisulphide ButyldichloroboraneBis(dimethylthallium) acetylide Tetracarbonylnickel Digold trisulphide DichlorodiethylsilaneButyllithium Europium (II) sulphide DichlorodimethylsilaneDiethylberyllium Pyrophoric metals Germanium (II) sulphide Dichlor(ethyl)silaneDiethylcadmium (in finely-divided state) Iron disulphide Dichloro(methyl)silaneDiethylmagnesium Caesium Iron (II) sulphide lododimethylarsineDiethylzinc Calcium Manganese (II) sulphide Trichloro(ethyl)silaneDiisopropylberyllium Cerium Mercury (II) sulphide Trichloro(methyl)silaneDimethylberyllium Chromium Molybdenum (IV) Trichloro(vinyl)silaneDimethylbismuth chloride Cobalt sulphideDimethylcadmium Hafnium Potassium sulphide Pyrophoric alkylDimethylmagnesium Iridium Rhenium (VII) sulphide non-metalsDimethylmercury Iron Silver sulphide HydridesDimethyl-phenylethynylthallium Lead Sodium disulphide DiethylarsineDimethyl-l-propynlthallium Lithium Sodium polysulphide DiethylphosphineDimethylzinc Manganese Sodium sulphide DimethylarsineEthoxydiethylaluminium Nickel Tin (II) sulphide 1,1-DimethyldiboraneMethylbismuth oxide Palladium Tin (IV) sulphide 1,2-DimethyldiboraneMethylcopper Platinum Titanium (IV) sulphide DimethylphosphineMethyllithium Plutonium Uranium (IV) sulphide EthylphosphineMethylpotassium Potassium MethylphosphineMethylsilver Rubidium Pyrophoric alkyl MethylsilaneMethylsodium Sodium non-metalsPoly(methylenemagnesium) Tantalum Bis(dibutylborino)Propylcopper Thorium acetyleneTetramethyldistibine Titanium Bis-dimethylarsinyl oxideTetramethyllead Uranium Bis-dimethylarsinylTetramethylplatinum Zirconium sulphideTetramethyltin Bis-trimethylsilyl oxideTetravinyllead Alloys Dibutyl-3-methyl-3-Triethylantimony Aluminium–mercury buten-1-ynlboraneTriethylbismuth Bismuth–plutonium DiethoxydimethylsilaneTriethylgallium Copper–zirconium DiethylmethylphosphineTrimethylantimony Nickel–titanium EthyldimethylphosphineTrimethylgallium TetraethyldiarsineTrimethylthalium Pyrophoric non-metals TetramethyldiarsineTrivinylbismuth and metal carbides TetramethylsilaneVinyllithium Phosphorus Tribenzylarsine

Silane mixo-TributylboranePyrophoric carbonyl metals Phosphine TributylphosphineCarbonylithium Calcium carbide

Uranium carbide

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Rarely founduncombined

Other types of explosion involve,

• Pressure rupture, due to rapid release of high pressure. Blast is generated by rapid expansionof gas down to atmospheric pressure and rupture of the container generates missiles.

• Steam explosion: rapid vaporization of water within molten metal, molten salts or hot oil orthrough them contacting surface or adsorbed moisture (refer to page 47).

The last two types do not involve a combustion reaction but the damage they cause can similarlybe related to the overpressure generated at a given distance from the event.

Control measures

Strategies for handling flammable materials

• Minimize at the design stage the risk of fire/explosion, e.g. by substitution with a less volatilechemical or operation at lower temperature, avoidance of air ingress or use of inerting. Designto minimize leakages and avoidance of potential ignition sources.

Table 6.10 Electrochemical series

Metal Symbol Electro-negativity Occurrence Reactivity with water

Lithium Li 0.97Caesium Cs 0.86 React with cold water toPotassium K 0.91 Never found yield hydrogenBarium Ba 0.97 uncombinedStrontium Sr 0.99Calcium Ca 1.04Sodium Na 1.01

Magnesium Mg 1.23Aluminium Al 1.47 Burning metals decomposeManganese Mn 1.60 water and hot metalsZinc Zn 1.66 decompose steamChromium Cr 1.56Iron Fe 1.64Cadmium Cd 1.46

Cobalt Co 1.70Nickel Ni 1.75 Very little reaction unlessTin Sn 1.72 at white heatLead Pb 1.55

Hydrogen H 2.20Phosphorus P 2.06Oxygen O 3.50

Bismuth Bi 1.67Copper Cu 1.75 Sometimes foundMercury Hg 1.44 uncombinedSilver Ag 1.42 Inactive with water or steam

Platinum Pt 1.44 Found uncombinedGold Au 1.42 with other elements


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• Minimize the risk by appropriate systems of work.• Mitigate the effects of fire or explosion, e.g. by detection provision, spacing, appropriate

construction materials, shielding, venting, extinguishment, provision for evacuation of personnel.

Fire prevention

Theoretically, if one corner of the ‘fire triangle’ is eliminated a fire or explosion is impossible.However, in practice, if flammable gases or vapours are mixed with air in flammable concentrations,sooner or later the mixture is likely to catch fire or explode because of the difficulty of eliminatingevery source of ignition. For reliable control of flammable materials, including combustible dusts,the aim is to remove two corners from the fire triangle. This can include some combination of:

• Prevention of a mixture forming within the flammable range.• Elimination of ignition sources (see Table 6.3).

Fire control

Fire detection and suppression form the basis of fire control, with emergency back-up proceduresto mitigate the consequences. Selected key tactics for working with flammable chemicals aresummarized in Table 6.11.

Refer also to ‘Fire extinguishment’ (page 221).

Dust explosions

The avoidance, and mitigation of the effects, of a dust explosion may involve some combinationof:

• Elimination of ignition sources, which is inherently difficult to ensure.• Atmosphere control, e.g. controlling dust concentrations or inerting.• Containment of explosion overpressure, i.e. by designing plant capable of withstanding in

excess of the maximum explosion overpressure, or safe venting of forces, e.g. via blow-offpanels, doors, membranes.

• Limitation of inventory.• Restriction of spread by means of baffles, chokes or by advance inerting.• Use of water sprays or very rapid injection of suppressant gas or powder.• Good housekeeping, particularly to avoid a devastating secondary explosion, following redispersion

of any accumulations of combustible dust.

A similar logic is applicable to the control of explosions involving gas or vapour, but othermeasures, e.g. dispersion by steam or containment by water curtains, may be applicable to vapourclouds in the open air. Containment or diversion of a blast (e.g. by blast walls) and reducing itseffect by appropriate spacing of equipment, buildings etc. are also applicable.


Control measures to reduce the risk from handling pyrophorics include:

• Handling and storing the minimum quantities necessary at any time.

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• Segregation of the material from other chemicals, particularly‘fuels’, i.e. solvents, paper, clothetc.

• Handling in dry, chemically-inert atmospheres or beneath other appropriate media, e.g. dry oilor inert gas.

• Handling in solution (e.g. aluminium alkyls in petroleum solvents).• Immediate destruction and removal of spilled materials.• Careful selection and provision of appropriate fire extinguishers in advance.• Provision and use of appropriate eye/face protection, overalls and gloves.

Fire extinguishment


If a flammable gas or vapour is present, a pre-fire condition may be identified by a flammable-gas detector. This will actuate an alarm at a fraction of the LFL. Banks of detectors may beinstalled at high or low level depending, in part, upon the gas density. Fire detection may be by:

Table 6.11 Control measures for working with flammable chemicals

Substitute with less volatile/flammable material where possible (i.e. higher flash point/autoignition temperature, lowervapour pressure)

Check on legal requirements and relevant standards/codes etc.

Minimize quantities in use/in store

Keep below LEL, e.g. chill to lower airborne concentration, use exhaust ventilation, inerting, keep air out.

Design plant/equipment so as to contain the material and provide adequate dilution or exhaust ventilation asappropriate

Provide means to contain spillages, e.g. bund walls, kerbsEliminate ignition sources

Eliminate static

Consider need for inerting, flame arresters, pressure relief valves, explosion vents (venting to safe location)

Consider need for checks on oxygen levels or loss of inert medium

Apply appropriate zoning criteria, e.g. with respect to standards of electrical equipment (refer to Table 12.6)

Set up procedures to prevent inadvertent introduction of other ignition sources and to avoid oxygen enrichment:Physical segregation, e.g. fencesWarning signs to indicate flammable hazard, no smoking etc.Permits–to-work (including hot work permits)Safe systems of work to control plant modifications etc

Keep flammable chemicals apart from oxidizing agents

Design layout to avoid domino effects/fire spread

Segregate ‘empty’ and ‘full’ containers

Check for plant integrity/flammable leaks periodically or continuously on-line, as appropriate

Install appropriate fire/smoke detection, audible alarms

Provide adequate fire suppression systems

Deal with mishaps such as spillage immediately

Train staff in hazards and precautions, and practise emergency evacuation drills

Remember that flammable chemicals can also be toxic or asphyxiant


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• Personnel, e.g. operating, maintenance or security staff, or neighbours, or passers-by.• Heat sensing, as actual temperature or rate-of-temperature rise, and depending upon melting of

a metal (fusion); expansion of a solid, liquid or gas; electrical sensing.• Smoke detection depending upon absorption of ionizing radiation by smoke particles; light

scattering by smoke particles; light obscuration.• Flame detection by ultraviolet radiation or infra-red radiation sensing.

A combination of detectors may be appropriate. They may activate an alarm only, or actuate acombined alarm/extinguishment system. With a bank of detectors a voting system may be used toincrease reliability and reduce the frequency of spurious alarms. Detection/alarm systems mayalso be interlinked with, e.g., fire-check doors held back on electromagnetic catches such that thedoors close automatically upon activation of the detection system.


Removal of one of the corners of the fire triangle normally results in extinguishment of a fire.Propagation of a flame can also be stopped by inhibition of the chain reactions, e.g. using drypowders or organo–halogen vaporizing liquids.

Classification of fires

Class TypeA Fire involving solid materials, generally organic materials, in which combustion normally

takes place with the formation of glowing embers.B Fire involving a liquid or liquefiable solid (the miscibility or otherwise with water is

an important characteristic).C Fire involving a gas.D Fire involving a burning metal, e.g. magnesium, aluminium, sodium, calcium or zirconium.

An additional class not currently included in British Standard EN2 is Class F fires includingcooking oils or fats. Electrical fires are not classified since any fire involving, or initiated by,electrical equipment will fall within Class A, B or C.

Fire-extinguishing materials

The penetration and cooling action of water is required with Class A fires, e.g. those involvingpaper, wood, textiles, refuse. Water is applied in the form of a jet or spray; foam or multi-purposepowder extinguishers are alternatives. Extinguishment of a Class B fire can be achieved by thesmothering action of dry chemical, carbon dioxide or foam. Most flammable liquids will float onwater (refer to Table 6.1 under ‘Specific gravity’), so that water as a jet is unsuitable: a mist may,however, be effective. Water is also widely used to protect equipment exposed to heat. Drypowders are effective on flammable liquid or electrical fires.

Foam is a proportioned mixture of water and foam concentrate aspirated with air to causeexpansion, e.g. from 6 to 10 times the volume (low expansion foam) up to >100 times (highexpansion foam). It transports water to the surface of flammable liquids and enables it to float andextinguish the fire. An effective system depends upon:

• The type of flammable liquid – determines the type of foam, e.g. standard or alcohol-resistantgrade. Aqueous film-forming foam may be used for rapid ‘knock-down’.

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• The type of hazard – determines the method and rate of application, e.g. by fixed pourers,mobile monitors, portable foam-towers or fixed semi-subsurface systems.

• The size of the hazard – determines the requirements for foam concentrate and water.

Carbon dioxide is useful where the minimum damage should be caused to the materials at risk,on fires in liquid, solids or electrical fires but not where there is a high risk of reignition. It islikely to be ineffective outdoors due to rapid dispersal. It is unsuitable for reactive metals, metalhydrides or materials with their own oxygen supply, e.g. cellulose nitrate.

Dry powders are effective on flammable liquid or electrical fires. Special powders are availablefor use on metals. Dry powder extinguishers may be used on Class C fires, including gases andliquefied gases in the form of a liquid spillage or a liquid or gas leak. This must be accompaniedby other actions, e.g. stopping the leak; this is necessary to avoid accumulation of an unburnedflammable gas–air mixture which could subsequently result in an explosion. Activation may beautomatic by a detection system, or manual.

Vaporizing liquid halogen agents are electrically non-conductive and are effective on a widerange of combustibles, particularly flammable liquids and electrical fires. A ‘lock-off’ system isrequired on fixed installations to protect personnel, the normal extinguishing concentration being5% by volume. The use of such liquids is being phased out; except for defined essential uses theywill be banned from 31 December 2003.

Portable extinguishers and fire blankets are normally provided at strategic points in the workarea. The range of application of portable extinguishers is summarized in Table 6.12. BritishStandard EN3: Part 5 requires all new extinguisher bodies to be red. A zone of colour above, orwithin, the section used to provide operating instructions may be used to identify the type ofextinguisher. The colours used are:

Standard dry powder or multi-purpose dry powder blueAFFF (aqueous film-forming foam) creamWater redVaporizing liquid, including Halon greenCarbon dioxide black

Fixed installations for fire-fighting may be either:

• Manually operated for general protection, e.g. hose reels, hydrants and foam installations, or• Automatically operated for general protection, e.g. sprinklers, or for special-risk protection,

e.g. carbon dioxide installations.

The general requirements of such an installation are summarized in Table 6.13.

Fire precautions

A range of precautions are based on the principles summarized earlier. However, general precautions,applicable to the majority of work situations, are listed in Table 6.14, many of which are includedin legal requirements. In the UK duties under the Fire Precautions (Workplace) (Amendment)Regulations 1999 are to:

• carry out a fire risk assessment of the workplace;• identify significant findings and details of anyone specifically at risk;


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Table 6.12 Portable fire extinguishers

Extinguisher type Water Carbon dioxide Dry powder Foam Vaporizing liquid(3) Fire blanket Sand

Class A fireWood, cloth, paper Most suitable Small fires only Small fires only Yes Small fires only(1) No, except for No

or similar personalcombustible clothing onmaterial fire

Cooling by watermost effective

Class B fireFlammable liquids, Dangerous Most suitable Most suitable Most suitable(2) Small fires only(1) Most suitable Small fires only

petrol, oils, Small fires onlygreases, fats

Blanketing/smothering mosteffective

Electrical plant,electrical Dangerous Most suitable Most suitable No Yes(1) No Noinstallations

Non-conductivityof extinguishingagent mostimportant

(1) Toxic products may be produced: care must be exercised after use in confined spaces.(2) Special foam required for water-miscible liquids.(3) Subject to replacement.

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Table 6.13 General requirements for fixed fire-extinguishing systems (Activation may be automatic by a detectionsystem, or manual)

• Capability to control and extinguish the anticipated fire condition without recourse to outside assistance (unless plannedfor).

• Reliability, allowing for environmental features likely to be detrimental to operation, e.g. dust, corrosion, tar.• Agents must be compatible with the process, with each other, and with any other installed systems.• Consideration of the potential toxicity of the agent, any thermal degradation products, or products generated on contact

with chemicals present will dictate safety measures.• If manual fire-fighting is also anticipated following agent discharge, visibility in the fire zone requires consideration.

Table 6.14 General fire precautions

Area designation Zoning for electricsControl portable heaters etc.No smokingRestricted areas

Electrical equipment Regular inspection and maintenance by qualified electriciansProhibition of makeshift installations

Waste disposal Prevention of combustible waste accumulation in corners, passageways or other convenient‘storage’ areas

Storage Segregated storageUncongested storage of combustibles: gangways/adequate breaksMaterial stacked in the open should be away from windowsFlammable liquids in properly designed storerooms: bulk quantities in fixed, bunded,

adequately spaced tanks

Contractors Clearance Certificate control of contractors/temporary workersClose control of temporary heating, lighting, cooking etc.

Escape/access Escape doors and routes must be kept free of obstructionsAccess for emergency services must be maintained

Fire equipment Fire alarm and fire-fighting equipment must be regularly inspected, maintained and testedPortable extinguishers to have designated locations/be of correct type. Instructions must be

provided as to where and how to use them. Practice is necessary

Flues Passages for services or other ducts must be adequately fire-stopped to prevent their actingas flues for fire/smoke transmission

Sprinklers Maintain sprinkler systemsInstitute alterations if building is modified, use changes etc.Observe use specifications, e.g. for stack heights, fire loading

Prevention of arson Control access at all timesScreen employees and casual labourLock away flammable substances and keep combustibles away from doors, windows, fencesProvide regular fire safety patrols, even where automatic systems are providedSecure particularly storage and unmanned areas

Fire and smoke stop Ensure that fireproof doors and shutters are self-closingdoors Keep all doors free from obstruction

Ensure that fire check doors are kept closed


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1 Identify fire hazardsSources of ignitionSources of fuelWork processes

2 Identify the location of people at significant risk incase of fire

3 Evaluate the risksAdequacy of existing fire safety measuresControl of ignition sourcesControl of fuel sourcesFire detection/warningMeans of escapeMeans of fighting fireMaintenance and testing of fire precautionsFire safety training of all employees

Implement any if necessary

4 Record findings and take actionPrepare emergency planInform, instruct and train all employees in fireprecautions

5 Keep assessment under reviewRevise if situation changes

Figure 6.2 Action plan for fire risk assessment

• provide and maintain fire precautions to safeguard those at the workplace;• provide relevant information, instruction and training.

In the UK the Building Regulations impose fire safety requirements on:

• structural stability;• compartmentalization to restrict fire spread;• fire resistance of elements and structures;• reduction of spread of flame over surfaces of walls and ceilings;• space separation between buildings to reduce the risk of fire spread from one building to

another;• means of escape in case of fire;• access for fire appliances and assistance to the fire brigade.

An action plan for risk assessment is given in Figure 6.2.

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Table 6.15 Essentials for fire instruction and training

Action to be taken upon discovering a fireAction to be taken upon hearing the fire alarmRaising the alarm, including the location of alarm call points, internal fire alarm telephones and alarm indicator panelsCorrect method of calling the fire serviceThe location and use of fire-fighting equipmentKnowledge of the escape routesThe importance of fire doors and the need to close all doors at the time of a fire and on hearing the fire alarmStopping machines and processes and isolating power supplies where appropriateEvacuation of the building:

• procedures for alerting visitors, members of the public etc., including if necessary directing/escorting them to exits;• familiarity with how to open all escape doors and the use of any emergency fastenings;• understanding of the reason for not using lifts except those designated, and of special design, for evacuation of disabled


The minimum fire instruction and training needs are summarized in Table 6.15.


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Table 6.1 Properties of flammable chemicals

Substance Specific Vapour Flash Ignition Flammable Boiling Melting Solubility Vapourgravity density point(1) temp. limits(1) point point in water pressure

(air = 1) (°C) (°C) (%) (°C) (°C) (g/100 g) (mm Hg/°C)

Acetal 0.83 4.08 –21 230 1.6–10.4 103 –100 2120 10/8Acetaldehyde 0.78 1.52 –38 185 4–57 21 –124 ! –Acetanilide 1.21 4.7 174 546 – 304 114 – 1/114Acetic acid 1.05 2.1 43 426 4–16 118 17 ! 11.4/20Acetic anhydride 1.08 3.5 54 385 3–10 140 –73 ! 10/36Acetone 0.79 2.0 –18 538 3–13 56 –94 ! 400/40Acetone cyanohydrin 0.93 2.9 74 688 – 82 –19 v. sol –Acetonitrile 0.79 1.4 6 524 4–16 80 –45 ! 100/27Acetyl acetone, see

2,4-PentanedioneAcetyl chloride 1.1 2.7 4 390 – 51 –112 dec. –Acetylene 0.91 0.9 – 300 3–82 –83 Subl. sl. sol. 40 atm/17Acetylene dichloride, see

1,2-DichloroethyleneAcetyl peroxide 1.2 4.07 113oc – – 63exp. 30 sl. sol. –Acrolein 0.84 1.9 –26 278 3–31 53 –87 v. sol. –Acrolein dimer 1.1 – 48 – – 151 –73 sol. –Acrylic acid 1.05 2.5 52oc 429 – 142 12 ! 10/39Acrylonitrile 0.81 1.8 0oc 481 3–17 77 –83 sol. 100/23Adipic acid 1.4 5.04 191 422 – 334 153 sl. sol. 1/160Adiponitrile 0.97 3.73 93 – – 295 2.3 sl. sol. –Aerozine 50, see HydrazineAldrin – – 66 – – – 104 insol. –Allyl acetate 0.93 3.4 21oc 374 – 103 – sl. sol. –Allyl alcohol 0.85 2.0 21 378 3–18 97 –129 ! 10/10Allyl amine 0.76 2.0 –29 374 2–22 55 – ! –Allyl bromide 1.4 4.2 –1 295 4–7 70 –119 insol. –Allyl chloride 0.94 2.6 –32 392 3–11 45 –136 insol. –Allyl chloroformate 1.1 4.2 31 – – 110 – insol. –Allylene, see PropyneAllyl glycidyl ether 0.97 3.4 57 – – 154 –100 sol. –2-Aminoethanol, see

EthanolamineAminoethylethanol amine 1.03 3.6 129 368 – 244 – v. sol –Ammonia, anhydrous 0.77 0.59 – 651 16–25 –33 –78 89.9° 10 atm/26Ammonium nitrate 1.7 – – – exp. 210/11 mm dec. 169 118° –n-Amyl acetate 0.88 4.5 25 379 1–7.5 148 –79 sl. sol. –iso-Amyl acetate 0.88 4.5 23 380 1–7.5 142 – – –sec-Amyl acetate 0.86 4.5 32 – 1–7.5 121 – – –

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n-Amyl alcohol 0.82 3.0 33 300 1–10 137 –79 sl. sol. 1/14iso-Amyl alcohol 0.81 3.0 43 347 1–9 132 – sl. sol. –tert-Amyl alcohol 0.81 3.0 19 437 1–9 102 –12 sl. sol. –Amylamine 0.8 3.0 7oc – – 103 –55 ! –n-Amyl bromide 1.22 5.2 32 – – 130 –95 insol. –Amylene 0.66 2.4 –2 273 1.5–9 30 –124 insol. –n-Amyl ether 0.74 5.46 57 171 – 190 –70 insol. –iso-Amyl formate 0.89 4.0 26 – – 131 –74 sl. sol –Amyl mercaptan 0.84 3.59 18 – – 127 –76 insol. 13/25iso-Amyl nitrate 0.99 – 52 – – 152–7 – sl.sol. –Amyl nitrite 0.85 4.0 10 209 – 104 – sl. sol –Aniline 1.02 3.22 70 770 1.3 184 –6 sol. 1/35o-Anisaldehyde 1.12 – 118 – – 250 38 insol. –Anisole 1.0 3.72 52oc – – 154 –37 insol. 10/42Anthracene 1.25 6.15 121 540 0.6– 340 217 insol. 1/145Anthraquinone 1.44 7.16 185 – – 380 286 insol. 1/190Asphalt 1.1 – 204+ 485 – 370–470 – – –Aziridine 0.83 1.5 –11 322 3.6–46 56 –72 ! –Benzaldehyde 1.04 3.7 64 192 – 178 –26 sl. sol. 1/26Benzene 0.88 2.8 –11 562 1.4–8 80 5.4 sl. sol 10/26Benzene monochloride, see

ChlorobenzeneBenzoic acid 1.32 4.2 121 574 – 249 122 sl. sol. 1/96p-Benzoquinone, see QuinoneBenzonitrile 1.2 – 85oc – – 191 –13 – 1/28Benzotrifluoride 1.19 5.04 12 – – 101 –29 insol. 11/0Benzoyl chloride 1.22 4.88 72 – – 197 –0.5 dec. 1/32Benzoyl peroxide 1.33 – – 80 – exp. 106 sl. sol. –Benzyl acetate 1.06 5.1 102 461 – 214 –51.5 sl. sol. 1/45Benzyl alcohol 1.04 3.7 101 436 – 206 –15.3 4 1/58Benzylamine 0.98 – 63 – – 185 ! –Benzyl benzoate 1.11 7.3 148 481 – 323 21 insol. –Benzyl ‘Cellosolve’ 1.1 5.3 129 352 – 256 –75 – –Benzyl chloride 1.10 4.36 67 585 1.1– 179 –39 insol. –Benzylidene chloride, see Benzal

chlorideBenzyl mercaptan 1.06 4.3 70 – – 194 – insol. –Bicyclohexyl 0.9 5.7 74 244 1–5 240 2 – –Biphenyl 1.2 5.3 113 540 0.6–5.8 256 70 insol. –2-Biphenylamine 1.16 5.8 – 452 – 299 49 insol. –Borneol 1.01 5.31 66 – – – 212 subl insol. –Boron hydrides, see Di-, Penta-,

or Deca-BoranesBromobenzene 1.50 5.4 51 566 – 155 –31 insol. 10/401-Bromobutane, see Butyl bromide

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Bromoethane 1.46 3.76 none 511 6.7–11.3 38 –119 sl. sol. 400/21Bromomethane, see Methyl

bromideBromopentane, see Amyl bromideBromopropane, see Propyl

bromide3-Bromopropene, see Allyl

bromide3-Bromopyne, see Propargyl

bromideo-Bromotoluene 1.42 5.9 79 – – 181 –27 insol. –1,3-Butadiene 0.62 1.97 <–7 429 2–11.5 –4.7 –109 insol. 1840/21n-Butane 0.60 2.04 –60 405 1.9–8.5 –0.5 –138 v. sol. 2 atm/19iso-Butane 0.56 2.01 – 462 1.8–8.4 –12 –160 sol.n-Butanol, see n-Butyl alcoholButanone, see Methyl ethyl

ketone1-Butene 0.60 1.9 –80 384 1.6–9.3 –6.1 –130 insol. 3480/212-Butene 0.62 1.9 – 324 1.8–9.0 1.1 –127 insol. 1410/212-Butene (trans) 0.6 2.0 –73 324 2–10 2.5 –106 – 1592/212-Butoxyethanol, see Butyl

cellosolven-Butyl acetate 0.88 4.0 27 399 1.4–7.6 125 –76 sl. sol. 15/25iso-Butyl acetate 0.87 4.0 18 423 1.3–7.5 117 –99 sl. sol. –sec-Butyl acetate 0.86 4.0 31 – 1.7– 112 – insol. 24Butyl acetyl ricinoleate 0.9 13.7 110 385 – 220 –32 – –Butyl acrylate 0.9 4.4 49oc – – 69.50 mm –65 – 10/36n-Butyl alcohol 0.81 2.55 29 365 1.4–11 118 –89 sol. 6/20iso-Butyl alcohol 0.81 2.55 28 427 1.7–10.9 107 –108 1015 –sec-Butyl alcohol 0.81 2.55 24 406 1.7–9.8 99.5 –115 12.5 10/20tert-Butyl alcohol 0.78 2.55 10 478 2.4–8 83 25 ! 40/25Butylamine 0.76 2.5 –12 312 1.7–9.8 78 –50 ! 72/20tert-Butylamine 0.70 2.5 – – 1.7–8.9 45 –67 ! –iso-Butylamine 0.73 2.5 –9 378 – 66 –104 ! –n-Butyl benzene 0.9 4.6 71 412 1–6 182 –81 – 1/23iso-Butyl benzene 0.9 4.6 52 418 1–7 174 –83 – 1/19n-Butyl bromide 1.28 4.7 18 265 2–6.6 101 –112 0.06 –Butyl carbitol 1.0 5.6 78 228 – 231 –68 – 0.02/20Butyl carbitol acetate 1.0 – 116 299 – 247 –32 – <0.01/20

Table 6.1 Cont’d

Substance Specific Vapour Flash Ignition Flammable Boiling Melting Solubility Vapourgravity density point(1) temp. limits(1) point point in water pressure

(air = 1) (°C) (°C) (%) (°C) (°C) (g/100 g) (mm Hg/°C)

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Butyl cellosolve 0.91 4.1 61 244 1.1–12.7 171 <–40 ! 0.6/20n-Butyl chloride 0.88 3.2 7 471 1.9–10.1 78 –123 0.07 –tert-Butyl chloride 0.85 3.2 <21 – – 51 –27 sl. sol. –1,3-Butylene glycol 1.0 3.2 121 394 – 208 <–50 – 0.06/202,3-Butylene glycol 1.0 3.1 85 402 – 180 19 – 0.17/20Butylene oxides 0.8 2.5 –15 – 1.5–18.3 63 – – –Butyl ether, see Dibutyl ethern-Butyl formate 0.91 3.5 18 322 1.7–8 107 –90 sl. sol. 40/32iso-Butyl formate 0.89 – <21 – – 98 –95 1.122 –Butyl hydroperoxide 0.86 2.1 27 – – dec. 6 sol. –

in heptane 0.68 – –4 223 1.2–6.7 98 – – –in hexane 0.69 – –22 234 1.2–7.5 69 – – –in pentane 0.70 – –40 309 1.5–7.8 36 – – –

Butyl lactate 1.0 5.0 71 382 – 188 –43 – 0.4/20Butyl mercaptan 0.84 3.1 2 – – 98 –116 sl. sol. –Butyl methacrylate 0.89 4.8 52 294 2–8 163 – insol. 5/20Isobutyl methyl ketone 3.5 17 460 1.2–8 126 –57 – –tert-Butyl peracetate 0.93 – 27 – –tert-Butyl perbenzoate 1.0 – 88 – – 113dec – – 0.3/50Butyl peroxypivalate (in 75% sol. – >68 – – –19

of mineral spirits)Butyl peroxytrimethyl acetate, see

Butyl peroxypivalateButyl vinyl ether 0.77 3.4 –9 – – 94 –92 insol. –n-Butyraldehyde 0.82 2.5 –6.7 230 2.5– 76 –99 4 –iso-Butyraldehyde 0.79 2.5 –40 254 1.6–10.6 64 –66 4 –n-Butyric acid 0.96 3.0 66 452 2–10 164 –7.9 ! 0.4/20iso-Butyric acid 0.95 3.0 62 502 – 154 –47 2020 –n-Butyric anhydride 0.97 5.4 88 307 – 198 –73 dec. –2-Butyrolactone 1.05 3.0 98 – – 206 –44 ! –n-Butyronitrile 0.8 – 26 – – 117 –112 sl. sol. –Butyryl chloride 1.03 3.7 <21 – – 107 –89 dec. –Camphor 0.99 5.24 66 466 0.6–3.5 204 180 sl. sol. –Caproic acid 0.93 4.0 102 – – 205 –5.4 1.120 0.2/20Capryl alcohol, see 2-OctanolCaprylaldehyde 0.8 4.5 52 – – 168 – –Caprylic acid, see Octanoic acidCaprylic alcohol, see 1-OctanolCarbitol, see Diethylene glycol

monoethyl etherCarbolic acid, see PhenolCarbon disulphide 1.26 2.6 –30 100 1–44 46 –112 0.2° 400/28Carbon monoxide 0.81 0.97 – 609 12.5–74 –192 –207 0.004° –Carbon oxysulphide, see

Carbonyl sulphide

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Carbonyl sulphide 1.07 2.1 – – 12–29 –50 –138 8014

Carvene, see DipenteneCellosolve 0.93 3.10 41 238 1.7–15.6 135 – ! 3.8/20Cellosolve acetate 0.97 4.7 55 382 1.2–12.7 156 –62 v. sol. 1.2/20Cellulose nitrate 1.66 – 13 – – – – insol. –Chloral 1.51 5.1 none – – 98 –58 v. sol. –Chlordane ~1.6 – 56 – – 175 – – –Chlorine dioxide 3.09 2.3 – 100 – 9.9 –59 dec. –Chloroacetaldehyde 1.19 2.7 88 – – 85 –16 – 100/45

(40% solution)Chlorobenzene 1.11 3.9 29 638 1.3–7.1 132 –45 insol. 10/221-Chloro-1,1-difluoroethane 1.12 – – 632 9–14.8 –9.2 – – –1-Chloro-2,4-dinitrobenzene 1.7 – 194 432 2–22 315 43 insol. –Chlorodiphenyls ~1.4 – 176–80 – – 340–75 – – 30/2001-Chloro-2,3-epoxypropane, see

EpichlorohydrinChloroethane, see Ethyl chlorideChloroethanol, see Ethylene

chlorohydrinChloromethane, see Methyl

chlorideChloronaphthalene 1.19 5.6 132 >558 – 256 –20 insol. –Chloronitrobenzenes 1.37 – 127 – – 242 32–46 insol. –1-Chloro-1-nitropropane 1.21 4.3 62 – – 142 – sl. sol. –o-Chlorophenol 1.24 – 64 – – 175 7 v. sol. 1/12p-Chlorophenol 1.24 – 121 – – 220 43 sol. 1/49o-Chlorophenyl diphenyl 1.3 12.5 >215 – – 240–55/5 mm <0 – –

phosphateChloroprene 0.95 3.0 –20 – 4–20 59 – sl. sol. –Chlorotrifluoroethylene 1.31 – –27 – 8.4–39 –28 158 – –Cinnamaldehyde 1.05 – 49 – – 253 –7.5 sl. sol. –m-Cresol 1.03 3.7 94 559 1.06–1.35 203 12 sol. 1/52o-Cresol 1.05 3.7 81 599 1.35– 191 31 sol. (hot) 1/38p-Cresol 1.04 3.7 94 559 1.06–1.4 202 35 sol. (hot) –Creosote (mixed phenols) 1.07 – 74–82 336 – 200–250 – – –Cresylic acid, see o-CresolCrotonaldehyde 0.87 2.4 13 207 2.1–15.5 104 –76 v. sol. –Crotonitrile 0.83 2.3 <100 – – 110–116 –52 – –Crude oil (petroleum) 0.78–0.97 – (–7)–(+32) – – – <–46 – –

Table 6.1 Cont’d

Substance Specific Vapour Flash Ignition Flammable Boiling Melting Solubility Vapourgravity density point(1) temp. limits(1) point point in water pressure

(air = 1) (°C) (°C) (%) (°C) (°C) (g/100 g) (mm Hg/°C)

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Cumene 0.86 4.1 44 424 0.9–6.5 152 –96 insol. 10/38Cumene hydroperoxide 1.05 – 79 – – 153 – – –Cyanogen 0.95 1.8 – – 6–32 –21 –34 45020 –Cyclohexane 0.77 2.91 –20 260 1.3–8.4 80 4.1 insol. 100/60Cyclohexanol 0.96 3.45 68 300 – 161 25 3.6 1/21Cyclohexanone 0.95 3.4 44 420 1.1–8.1 156 –45 sl. sol. 10/39Cyclohexene 0.81 2.8 <–6 – – 83 –104 insol. 160/38Cyclohexylamine 0.87 3.4 32 293 – 135 –18 sol. –Cyclohexylbenzene 0.95 – 99 104 – 238 7.5 insol. 1/67Cyclopentane 0.75 2.42 –7 – – 49 –94 insol. 400/31Cyclopentanone 0.95 2.3 26 – – 131 –58 insol. –Cyclopropane 0.72 1.45 – 498 2.4–10.4 –33 –127 sl. sol. –p-Cymene 0.86 4.62 47 436 0.7–5.6 177 –68 insol. 1/17Decaborane 0.94 – 80 149 – 213 100 sl. sol. 19/100Decahydronaphthalene 0.87 4.76 57 250 0.7–4.9 186 –45 insol. –iso-Decaldehyde 0.8 5.4 85 – – 197 – – –Decalin, see

Decahydronaphthalenen-Decane 0.73 4.90 46 208 0.8–5.4 174 –30 insol. 1/17n-Decyl alcohol 0.83 5.3 82oc – – 229 7 insol. 1/170Diacetone alcohol 0.93 4.0 64 603 1.8–6.9 168 –50 ! 1/20Diaminoethane, see Ethylene

DiamineDiazomethane 1.45 – – 100exp. – –23 –145 dec. –Diborane 0.46 0.96 –90 145 0.9–98 –93 –165 dec. –Dibutylamine 0.50 4.46 52oc – – 159 –51 sol. 2/20Dibutyldichlorotin 1.36 10.5 355 – – 135 43 dec. –

at 10 mmDi-n-butyl ether 0.77 4.5 25 194 1.5–7.6 141 –98 insol. –Dibutyl oxalate 1.01 7.0 104 – – 246 –30 insol. –Dibutyl peroxide 0.79 5.0 18 – – 111 –40 insol. 20/20Dibutyl phosphite 0.97 6.7 49 – – 115 – – –

at 10 mmDibutyl phthalate 1.04 9.6 157 403 – 340 –35 insol. –Dibutyl tartrate 1.1 – 91 284 – 204/26 mm 21 – –Dibutyl tin dilaurate 1.05 21.8 235 – – – 27 insol. –Dichloroacetyl chloride 1.53 5.1 66 – – 107 – dec. –2,5-Dichloroaniline – 5.6 166 – – 251 50 sl. sol. –o-Dichlorobenzene 1.30 5.07 66 648 2–9 180 –18 insol. –

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1,4-Dichlorobutane 1.1 4.4 52 – – 162 –39 insol. 4/201,3-Dichloro-2-butene – 4.3 27 – – 123 – insol. –1,1-Dichloroethane 1.18 3.4 –6 458 5.6–11.4 57 –97 0.7° –1,2-Dichloroethane, see Ethylene

dichloride1,1-Dichloroethylene, see

Vinylidene chloride1,2-Dichloroethylene 1.3 3.3 2–4 – 9.7–12.8 48–60 –80 sl. sol. –2,2"-Dichloroethyl ether 1.22 4.9 55 369 – 178 –24 insol. –Dichloromethane 1.34 2.93 – 662 15.5–66 40 –97 220 –

in O2Dichloromonofluoromethane 1.48 3.8 – 552 – 9 –135 insol. –1,1-Dichloro-1-nitroethane 1.42 4.97 76 – – 124 – 0.520 –Dichloropentanes (mixed) 1.1 4.9 41 47 – 130 – – –2,4-Dichlorophenol 1.38 5.6 114 – – 210 45 sl. sol. 1/531,2-Dichloropropane 1.16 3.9 16 557 3.4–14.5 97 –100 sl. sol. 40/191,3-Dichloropropane 1.23 3.8 35 – – 104 – insol. –Dicyclohexylamine 0.93 6.3 99oc – – 256 –0.1 0.1628 –Dicyclopentadiene 0.93 4.55 35 – – 170 33 – 10/48Diethanolamine 1.09 3.6 152 662 – 270 28 v. sol. 5/1881,1-Diethoxyethane, see

AcetalDiethyladipate 1.01 – – – – 240–5 –21 0.4330 –Diethylamine 0.71 2.5 <–26 312 1.8–10.1 56 –48 v. sol. 400/382-Diethyl-amino-ethanol 0.88 4.03 60 – – 163 – ! –N,N-Diethylaniline 0.94 5.15 85 332 – 216 –38 1.412 1/50Diethylcarbonate 0.98 4.07 25 – – 126 –43 insol. 10/24Diethyl cellosolve 0.8 6.56 35oc 207 – 121 –74 – 9.4Diethylene glycol 1.12 3.66 124 229 2– 245 –8 sol. 1/92Diethylene glycol-monoethyl 1.11 4.6 96 204 1.2– 202 –10 ! –

etherDiethylenetriamine 0.95 3.5 102 399 – 207 –39 ! –Diethyl ether, see Ethyl etherDiethyl ethyl phosphonate 1.03 5.7 105 – – 83 – sl. sol. –

at 11 mmDiethyl ketone 0.82 2.96 13 452 – 101 –42 4.720 –Diethyl malonate 1.06 5.5 93 – – 199 –50 2.120 1/40o-Diethyl phthalate 1.1 7.7 163 – – 302 –40 insol. –p-Diethyl phthalate 1.1 7.7 117 – – 296 –5 insol. –

Table 6.1 Cont’d

Substance Specific Vapour Flash Ignition Flammable Boiling Melting Solubility Vapourgravity density point(1) temp. limits(1) point point in water pressure

(air = 1) (°C) (°C) (%) (°C) (°C) (g/100 g) (mm Hg/°C)

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Diethyl sulphate 1.18 5.3 104 436 – 208dec. –25 insol. 1/47Diglycol, see Diethylene glycol3,4-Dihydro-2H-pyran 0.92 2.9 –18 – – 86 – sol. –Diisobutyl ketone 0.81 4.9 60 – 0.8–6.2 168 – insol. –Diisobutyl carbinol 0.8 5 74 – 0.8–6.1 173 –65 – 0.3/20

(at 100°C)Diisopropyl amine 0.72 3.5 –1 – –84 83 –61 sl. sol. –Diisopropyl ether 0.72 3.5 –28 443 1.4–7.9 69 –86 sl. sol. 150/25Diisopropyl benzene 0.9 5.6 76oc 449 – 205 <–55 – –3,3"-Dimethoxybenzidine – 8.5 206 – – – 137 insol. –Dimethoxyethane 0.85 3.1 40 – – 65 –113 sol. –Dimethoxymethane 0.86 2.63 –18 237 – 46 –105 33 330/20Dimethoxypropane 0.85 3.6 –7 – – 95 – – –N,N-Dimethyl acetamide 0.94 3.0 77 354 1.8–13.8 165 –20 ! 1.3/25Dimethylamine 0.68 1.65 –50 (<–18) 402 (430) 2.8–14.4 7.4 –92 v. sol. –N,N-Dimethylaniline 0.95 4.17 63 371 – 193 2.5 sl. sol. 1/302,2-Dimethyl butane 0.65 3.00 –48 425 1.2–7.0 50 –98 insol. 400/312,3-Dimethyl butane 0.7 3.0 –29 420 1.2–7 58 –135 – 400/39Dimethyl carbonate 1.1 3.1 19 – – 90 0.5 insol. –Dimethyl chloracetal 1.1 4.3 43 232 – 130 – – –Dimethyl ether, see Methyl etherDimethylformamide 0.94 2.51 58 445 2.2–15.2 153 –61 ! 3.7/251,1-Dimethylhydrazine, see

Unsymmetrical dimethyl-hydrazine

2,6-Dimethyl-4-heptanone, seeDiisobutyl ketone

2,3-Dimethyl pentane 0.69 3.5 <–7 337 1–7 90 –135 – 40/14Dimethyl phthalate 1.19 6.7 146 556 – 288 – insol. 1/102,2-Dimethyl propane 0.61 2.48 <–7 450 1.4–7.5 9.5 –18 insol. 100/21Dimethyl sulphate 1.33 4.35 83 188 – 189dec. –31 sol. –Dimethyl sulphide 0.8 2.1 <–18 206 2.2–19.7 37 –83 insol. –Dimethyl sulphoxide 1.01 – 95 215oc 2.6–28.5 189 18 sol. 0.4/202,4-Dinitroaniline 1.62 6.3 244 – – – 188 insol. –m-Dinitrobenzene 1.58 – 150 severe explosion hazard when 291 90 0.399 –o-Dinitrobenzene 1.31 5.8 150 exposed to shock or flame 319 118 sl. sol. –p-Dinitrobenzene 1.63 – 150 – – 299 172 0.1838 –2,4-Dinitrotoluene 1.4 6.3 207 – – 300 70 0.0320 –Di-n-Octyl phthalate 0.97 14.4 219 – – 385 –30 – –Di-sec-Octyl phthalate 0.99 16 218 410 – 358 –55 – 1.2/2001,4-Dioxane 1.04 3.0 12 180 2–22.2 101 10 ! 40/25Dipentene 0.85 4.66 45 237 0.7–6.1 178 –97 insol. 1/14Dipentene, dioxide see p-Mentha-

1,8-dieneDipentene monoxide 0.93 4.45 67 – – 75 <–6 – –

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Diphenylamine 1.16 5.8 153 634 – 302 53 insol. 1/108Diphenylmethane 1.01 5.8 130 486 – 266 26 insol. 1/76Dipropylene glycol methyl ether 0.95 5.1 85 – – 189 – – –n-Dodecane 0.75 5.96 74 204 0.6– 216 –12 insol. 1/48Epichlorohydrin 1.18 3.29 41 – – 117 –48 <5 10/171,2-Epoxy-propane 0.83 2.0 –37 – 2.1–21.5 34 –104 v. sol. 400/18Ethane 0.57 1.04 – 515 3–12.5 –89 –183 insol. –Ethanediol, see Ethylene glycolEthanethiol 0.84 2.14 <27 299 2.8–18 37 –144 1.5 –Ethanoic acid, see Acetic acidEthanol 0.79 1.59 12 423 3.3–19 79 –114 ! 40/19Ethanolamine 1.02 2.11 85 – – 170 11 ! 6/60Ethoxy acetylene 0.79 2.4 <–7 100exp. – 50 – insol. –2-Ethoxy ethanol, see Cellosolve2-Ethoxy ethylacetate, see

Cellosolve acetateEthyl acetanilide 0.94 5.62 52 – – 258 54 insol. –Ethyl acetate 0.90 3.04 –4.4 427 2.18–11.5 77 –84 7.520 100/27Ethyl acetoacetate 1.03 4.48 84 – – 181 –45 1317 1/29Ethyl acrylate 0.92 3.5 16 273 1.8– 100 <–72 sol. 29/20Ethyl alcohol, see EthanolEthyl aldehyde, see AcetaldehydeEthylamine 0.80 1.56 <–18 384 3.5–14 17 –81 ! 400/2Ethyl amyl ketone 0.85 – 57 – – 161 – insol. –n-Ethyl aniline 0.96 4.18 85 – – 205 –64 insol. 1/38Ethyl benzene 0.9 3.7 15 432 1–6.7 136 –95 0.0115 10/26Ethyl benzoate 1.15 5.17 >96 – – 213 –35 insol. 1/40Ethyl bromide, see BromoethaneEthyl bromoacetate 1.51 5.8 48 – – 159 <–20 insol. –Ethyl butyl ketone 0.82 3.93 46 – – 148 –37 insol. –2-Ethyl butyraldehyde 0.8 3.5 21oc – 1–8 117 –90 – 14/20Ethyl butyrate 0.88 4.0 26 463 – 121 –97 0.6825 10/15Ethyl chloride 0.92 2.2 –50 519 3.6–15.4 12 –139 0.45° 1000/20Ethyl chloroacetate 1.26 4.3 66 – – 144 – 27 insol. 10/38Ethyl chloroformate 1.36 3.74 16 – – 95 –81 dec. –Ethyl crotonate 0.92 3.93 2 – – 143–7 45 insol. –Ethyl cyanoacetate 1.06 3.9 110 – – 206 –23 225 1/68Ethyl cyanide, see PropionitrileEthylene 0.001 1.0 – 450 3.1–32 –104 –169 260 –

Table 6.1 Cont’d

Substance Specific Vapour Flash Ignition Flammable Boiling Melting Solubility Vapourgravity density point(1) temp. limits(1) point point in water pressure

(air = 1) (°C) (°C) (%) (°C) (°C) (g/100 g) (mm Hg/°C)

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Ethylene chlorohydrin 1.21 2.78 60oc 425 4.9–15.9 128 –69 ! 10/30Ethylene diamine 0.90 2.07 43 – – 117 8.5 v. sol. 11/20Ethylene dichloride 1.26 3.4 13 413 6.2–15.9 83 –36 sl. sol. 100/29Ethylene glycol 1.11 2.14 111 413 3.2– 198 –13 ! 0.05/20Ethylene glycol monobutyl ether,

see Butyl cellosolveEthylene glycol monoethyl ether,

see CellosolveEthylene glycol monomethyl

ether, see Methyl cellosolveEthylenimine, see AziridineEthylene oxide 0.87 1.49 <–18 429 3–100 11 –111 sol. 1095/20Ethyl ether 0.71 2.55 –45 180 1.85–48 34 –123 7.520 442/20Ethyl ethynyl ether, see

EthoxyacetyleneEthyl formate 0.95 2.55 –20 455 2.7–13.5 54 –79 1118 100/52-Ethyl hexanol 0.83 4.49 84 – – 180–5 <–76 insol. 0.2/20Ethyl lactate 1.04 4.07 46 400 1.5–30 154 – ! –Ethyl malonate, see Diethyl

malonateEthyl mercaptan, see EthanethiolEthyl methyl ether 0.7 2.1 –37 190 2–10 11 – – –N-Ethylmorpholine 0.92 4.00 32 – – 138 – ! –Ethyl nitrite 0.90 2.59 –35 90(explodes) 4.1–50 17 – dec. –Ethyl oxalate 1.08 5.04 76 – – 186 –41 sl. sol. –Ethyl propionate 0.9 3.5 12 477 2–11 99 –73 – 40/272-Ethyl-3-propyl acrolein 0.85 4.35 68oc – – 175 <100 insol. 1/20Ethyl silicate 0.93 7.22 52 – – 165 110subl. dec. 1/20Ethyl vinyl ether 0.75 2.46 <–46 202 1.7–28 36 –115 sl. sol. –Fluoroethylene – – – – 2.6–21.7 –51 –160 insol.Formaldehyde 0.82 1.08 – 430 7.0–73 –19 –92 sol. –Formalin (39% formaldehyde 0.82 – 85 – – 101 – – –

methanol free)Formalin (37% formaldehyde- – – 50 – – 101 – – –

15% methanol)Formamide 1.13 – 155oc – – 211dec. 2.6 ! 30/129Form-dimethylamide, see

DimethylformamideFormic acid 1.22 1.59 69oc 601 18–57 101 8.2 ! 40/24Furan 0.94 2.35 <0 – 2–14 32 –86 insol –Furfural 1.16 3.31 60 316 2.1– 162 –37 9.113 –Furfuryl alcohol 1.13 3.37 75 491 1.8–16.3 171 –31 ! 1/32

(916)Gasoline (petrol) 0.8 3.0–4.0 –43 280–456 1.4–7.6 38–204 – – –Glycerol 1.26 3.17 160 354 – 290dec. 18 ! 1.26/20

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Heptane 0.68 3.45 –4 223 1.2–6.7 98 –91 insol. 40/222-Heptanone, see Methyl amyl

ketone3-Heptanone, see Ethyl butyl

ketonen-Heptylamine 0.77 4.0 54oc – – 158 –23 sl. sol. –Hexachlorobenzene 1.57 9.8 242 – – 322 230 insol. –2,4-Hexadienal 0.9 – 68oc – 1–8 170 – sl. sol. –1,4-Hexadiene 0.7 2.8 –21 2–6 64 – insol. –Hexane 0.66 2.97 –22 261 1.1–7.5 68 –96 insol. 100/16Hexanedioic acid, see Adipic acidHexanoic acid, see Caproic acidn-Hexanol 0.81 3.52 60 293 – 158 –45 sl. sol 1/242-Hexanone, see Methyl butyl

ketone1-Hexene 0.7 2.97 <–7 – 1.2–6.9 63 –139 insol. 310/382-Hexene 0.68 2.92 <–7 – – 69 –146 insol. –Hexone, see iso-Butyl methyl

ketonesec-Hexyl acetate 0.86 4.97 45 – – 141 –64 insol. 4/20Hexyl alcohol, see n-HexanolHexyl amine 0.76 3.49 29oc – – 129 –19 sl. sol. –Hydracrylic acid-#-lactone 1.15 2.5 74 – 2.9– 155 –33 dec. –Hydrazine 1.0 1.1 38 Varies with 4.7–100 113 1.4 v. sol. 14.4/25


Hydrocyanic acid 0.69 0.93 –18 538 6–41 26 –14 ! 400/10Hydrogen 0.09 0.069 – 585 4–75 –253 –259 2.1° –Hydrogen sulphide 1.5 1.2 – 260 4.3–46 –60 –83 437° 20 atm/25p-Hydroquinone 1.33 3.8 165 515 – 285 171 sol. 4/150Hydroquinone monomethyl ether 1.55 – 131 421 – 246 54 sol. –Hydroxylamine 1.20 – 129exp. – – 56 34 sol. –Isoprene 0.68 2.35 –54 220 – 34 –147 insol. –Kerosene 0.81 4.5 38 229 0.7–5 170–300 <–46 –

dependent uponspecific fraction

Lactonitrile 0.99 2.45 77 – – 182dec. –40 ! –Linseed oil 0.9 – 22 343 – – –19 – –Maleic anhydride 0.9 3.4 102 477 1.4–7.1 202 58 dec. 1/44

Table 6.1 Cont’d

Substance Specific Vapour Flash Ignition Flammable Boiling Melting Solubility Vapourgravity density point(1) temp. limits(1) point point in water pressure

(air = 1) (°C) (°C) (%) (°C) (°C) (g/100 g) (mm Hg/°C)

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p-Mentha-1,8-diene 3.84 7.4 45 237 0.7–6.1 170 <60 insol. –2-Mercaptoethanol 1.14 2.69 74oc – – 157 – sol. 1/20Mesityl oxide 0.86 3.5 31 344 – 130 –59 sol. 10/26$-Methacrylic acid 1.02 – 77oc – – 158 16 sol. 1/25Methane 0.42 0.6 – 537 5–15 –161 –183 sl. sol. –3-(3-Methoxypropoxy)-1-

propanol, see Dipropyleneglycol methyl ether

Methyl acetate 0.97 2.55 –9 502 3.1–16 57 –99 v. sol. 100/9.4Methyl acetylene, see PropyneMethyl acrylate 0.95 3.0 –3oc – 2.8–25 80 –75 sl. sol. 100/28Methylal, see DimethoxymethaneMethyl alcohol 0.79 1.11 12 464 6–36.5 65 –98 ! 100/21Methyl amyl alcohol 0.80 3.5 41 – 1–5.5 130 <–90 sl. sol. 3/20Methyl-n-amyl ketone 0.81 3.9 49oc 533 – 151 –35 sl. sol. 3/20Methyl bromide 1.73 3.27 – 537 10–16 4 –95 insol. –2-Methyl-1-butene 0.66 2.4 <–7 – – 39 –134 insol. –2-Methyl-2-butene 0.67 2.4 <–17 – – 38 –123 sl. sol. –3-Methyl-1-butene 0.67 2.42 <–57 365 1.5–9.1 20 –168 insol. –N-Methylbutylamine 0.74 3.0 13oc – – 91 – sol. –Methyl butyl ketone 0.81 3.45 35oc 533 1.2–8 126 –57 – 10/39Methyl butyrate 0.90 3.53 14 – – 102 <–97 sl. sol. 40/30Methyl cellosolve 0.97 2.62 46oc 288 2.5–14 125 –87 ! 6/20Methyl cellosolve acetate 1.01 4.07 56 394 1.7–8.2 145 –70 sol. –Methyl chloride 0.98 1.8 <0oc 632 10.7–17.4 –24 –98 sl. sol. –Methyl chloroform, see 1,-1,-

1-TrichloroethaneMethyl chloroformate 1.24 3.26 12 504 – 73 – dec. –Methyl cyanide, see AcetonitrileMethyl cyclohexane 0.77 3.39 –4 285 1.2– 100 –126 insol. 40/22%-Methyl cyclohexanol 0.92 3.93 68 296 – 165 –20 sl. sol. –2-Methyl cyclohexanone 0.92 3.86 48 – – 165 – insol. –4-Methyl cyclohexene 0.80 3.34 –1oc – – 103 –116 insol. 10/38Methylene chlorobromide, see

BromochloromethaneMethyl ether 0.66 1.56 –41 350 3.4–18 –24 –139 sol. –Methyl ethyl ether 0.73 2.07 –37 190 2–10.1 11 – sol. –Methyl ethyl ketone 0.81 2.5 –7 515 2–10 80 –87 v. sol. –Methyl formate 0.99 2.1 –19 456 5.9–20 32 –100 v. sol. 400/162-Methyl furan 0.92 2.8 –30 – – 63 –89 insol. 139/205-Methyl-3-heptanone, see Ethyl

amyl ketoneMethyl hydrazine 0.9 1.6 <27 – – 87 <–80 sol. –Methyl isobutyl ketone 0.80 3.5 23 460 1.4–7.5 117 –85 sl. sol. 16/20

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Methyl isobutyrate 0.86 3.5 13oc 482 – 92 –84 sl. sol. –Methyl mercaptan 0.87 1.66 <–18 – 3.9–21.8 7.6 –123 sl. sol. –Methyl methacrylate 0.94 3.6 10 421 2.1–12.5 100 –50 sl. sol. 40/251-Methylnaphthalene 1.03 – – 528 – 240–3 –22 insol. –2-Methyl-2-propanethiol, see

t-Butyl mercaptanMethyl-n-Propyl ketone 0.81 3.0 7 505 1.6–8.2 102 –78 sl. sol. –1-Methlpyrrole 0.91 2.8 16 – – 115 –57 insol. –Methyl salicylate 1.18 5.24 101 454 – 223 –8.3 sl. sol. 1/54a-Methyl styrene 0.92 4.08 54 574 1.9–6.1 167–70 –23 insol. –m,-p-Methyl styrene 0.89 4.08 57 494 0.9 170 –83 – –Methyl sulphate, see Dimethyl

sulphateMethyl sulphide, see Dimethyl

sulphideMethyl vinyl ether 0.77 2.0 –51 – – 8 –122 sl. sol. 1052/20Mixed acids – – None – None Varies Varies – –Monomethylamine – 1.1 –10 430 4.9–20.8 –6.3 –94 v. sol –Morpholine 0.99 3.00 38oc 310 – 128 –4.9 ! –Naphtha (coal tar) 0.87 – 42 277 – 149–216 – – –Naphtha (petroleum), see

Petroleum etherNaphtha, varnish makers and <1 4.1 10 232 0.9–6.7 116–43 – – –

painters, 50° flashNaphtha, varnish makers and <1 4.3 29 232 1–6 139–77 – – –

painters, high flashNaphtha, varnish makers and <1 – –2 232 0.9–6 100–60 – – –

painters, regularNaphthalene 1.15 4.42 79 526 0.9–5.9 210 80 insol. –2-Naphthol 1.22 4.97 153 – – 295 123 insol. 10/451-Naphthylamine 1.12 4.93 157 – – 301 50 sl. sol. –Natural gas – – – 482 3.8–17 – – – –Nickel carbonyl 1.32 ~6 – 60exp. 2– 43 –25 sl. sol. 400/26Nicotine 1.01 5.61 – 244 0.7–4.0 247 <–80 ! 1/62o-Nitroaniline 1.44 – 168oc 521 – 284 71 sl. sol. 1/104p-Nitroaniline 1.44 – 199 – – 336 146 insol. 1/124Nitrobenzene 1.20 4.24 88 482 1.8– 211 5 sl. sol. 1/44

at 93°Co-Nitrobiphenyl 1.44 6.9 143 180 – 330 35 insol. 2/140

Table 6.1 Cont’d

Substance Specific Vapour Flash Ignition Flammable Boiling Melting Solubility Vapourgravity density point(1) temp. limits(1) point point in water pressure

(air = 1) (°C) (°C) (%) (°C) (°C) (g/100 g) (mm Hg/°C)

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Nitroethane 1.05 2.58 38 360–415 3.4– 114 –90 sol. 16/20Nitromethane 1.14 2.11 35 418 7.3– 101 –28 sol. 28/20$-Nitronaphthalene 1.14 5.96 164 – – 304 60 insol. –1-Nitropropane 0.99 3.06 49oc 421 2.6– 131 –108 sl. sol. 8/202-Nitropropane 0.99 3.06 39oc 428 2.6– 120 –93 sl. sol. 10/16m-Nitrotoluene 1.15 4.7 106 – – 232 15 insol. 1/50o-Nitrotoluene 1.16 4.72 106 – – 220 –4.1 insol. 1/50p-Nitrotoluene 1.29 4.72 106 – – 238 52 insol. 1/54Nonyl phenol 0.95 7.6 141 – – 290–301 – – –Octane 0.70 3.86 13 220 1.0–4.66 125 –57 insol. 10/19Octanoic acid 0.91 5.0 132oc – – 240 16 sl. sol. –1-Octanol 0.83 4.5 81 – – 194 –17 sol. –2-Octanol 0.82 4.48 88 – – 178 –39 sl. sol. –Oil, lubricating – – >149oc 260–371 – 360 <–46 – –Oil, mineral oil mist 0.81 – 193oc – – 360 – – –Oil, olive 0.9 – 225 343 – – –6 – –Oil, peanut 0.9 – 282 470 – – 3 – –Oil, soybean 0.9 – 282 445 – – 22 – –Oil, vegetable <1 – 321 – – – –9–1 – –Oleic acid 0.89 – 189 363 – 360 14 insol. 1/77Paraffin wax 0.9 – 199 245 – >370 42–60 – –Paraformaldehyde 1.39 – 70 300 – – 120–170 – 145/25Paraldehyde 0.99 4.55 36oc 238 1.3– 128 12 v. sol. –Pentaborane 0.66 2.2 30 – 0.4– 58 –47 dec. 66/0n-Pentane 0.63 2.48 –49 309 1.4–8 36 –130 v. sol. 400/19iso-Pentane 0.62 2.48 –51 420 1.4–7.6 28 –161 insol. –1,5-Pentanediol 0.99 3.59 135 334 – 240 –16 sol. <0.01/202,4-Pentanedione 0.98 3.45 41oc – – 136–40 –23 v. sol. –n-Pentanol, see n-Amyl alcohol2-Pentanol 0.81 3.03 39 347 1.2–9.0 119 – v. sol. –2-Pentanone, see Methyl n-propyl

ketone3-Pentanone, see Diethyl ketonePentene, see Amylenen-Pentyl acetate, see n-Amyl

acetatesec-Pentyl acetate, see sec-AmylacetatePentyl alcohol, see n-Amyl

alcoholPentyl amine, see n-Amylamineiso-Pentyl nitrite, see Amyl nitritePeracetic acid (40% acetic acid 1.23 – 41 110exp. – 105 –30 v. sol. –

solution)Petroleum ethers 0.6 2.50 <–17 288 1–6 30–160 <–73 – –

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Phenol 1.07 3.24 79 715 1.5– 181 40 sol. –Phenyl acetate 1.09 4.7 80 – – 196 – sl. sol. –Phenylcyclohexane, see

Cyclohexylbenzenep-Phenylenediamine – 3.7 156 – – 267 140 sol. –Phenylethanolamine 1.09 – 152 – – 285 35 4.620 <0.01/20Phenyl ether 1.09 5.86 96oc 646 – 258 27 insol. 0.021/25Phenyl ether – Biphenyl mixture 1.06 – 124oc 610 – 257 12 – –Phenylhydrazine 1.09 3.7 89 174 – 243dec. 20 sol. 1/72o-Phenyl phenol 1.21 – 124 – – 286 57 insol. 1/100Phorone 0.88 4.8 85 – – 197 28 sl. sol. –iso-Phorone 0.93 4.77 96oc 462 0.8–3.8 215 –8 sl. sol. –Phosdrin 1.23 – 79oc – – 107 – – –

at 1 mmPhosphorus (white and yellow) 1.82 4.42 – 30 spontaneous ignition 280 44 sl. sol. 1/77

in dry airPhosphorus (red) 2.34 4.77 – 260 – 280 590 v. sol. –

at 43 atmPhosphorus pentasulphide 2.03 – – 142 – 514 276 insol. –Phosphorus tribromide 2.8 – – 100 – 173 –40 insol. 10/48Phthalic anhydride 1.53 5.10 151 584 1.7–10.4 284 131 sl. sol. 1/972-Picoline 0.95 3.2 39oc 538 – 129 –70 v. sol. 10/244-Picoline 0.96 3.21 57oc – – 143 4 ! –Picric acid 1.76 7.9 150 300 – >300exp. 122 sol. –2-Pinene 0.86 4.7 33 – – 156 –55 sl. sol. 10/37Piperidine 0.86 3.0 16 – – 106 –7 ! 40/29Piperylene 0.68 2.4 –43 – 2–8.3 42 –141 insol. –Propane 0.58 1.56 468 2.2–9.5 –45 –187 insol. –1,3-Propanediamine 0.86 2.56 24oc – – 136 –24 v. sol. –1,2-Propanediol 1.04 2.62 99 371 2.6–12.5 189 –59 ! –n-Propanol, see n-Propyl alcoholPropargyl alcohol 0.96 1.93 36oc – 3.4– 115 –17 sol. 12/20Propargyl bromide 1.56 4.1 10 324 3.0– 90 –61 – –Propene, see Propyleneiso-Propenyl acetate 0.91 3.45 16 – 1.9– 93 –93 sl. sol. –#-Propiolactone, see Hydracrylic

acid-#-lactonePropionaldehyde 0.81 2.0 –9oc 207 3–16 48 –81 sol. –Propionic acid 0.99 2.56 54 513 2.9– 141 –22 ! 10/40

Table 6.1 Cont’d

Substance Specific Vapour Flash Ignition Flammable Boiling Melting Solubility Vapourgravity density point(1) temp. limits(1) point point in water pressure

(air = 1) (°C) (°C) (%) (°C) (°C) (g/100 g) (mm Hg/°C)

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Propionitrile 0.77 1.9 2 – 3.1– 97 –93 v. sol. –Propionyl chloride 1.06 3.2 12 – – 80 –94 dec. –iso-Propyl acetate 0.87 3.52 4 460 1.8–7.8 93 –73 sol. –n-Propyl acetate 0.89 3.5 14 450 2–8 102 –95 sl. sol. 40/29n-Propyl alcohol 0.78 2.07 15 433 2.1–13.5 97 –127 v. sol. 10/15iso-Propyl alcohol 0.79 2.07 12 399 2.3–12.7 82 –89 ! –Propylamine 0.72 2.0 –37 318 2.0–10.4 49 –83 sol. 248/20iso-Propylamine 0.69 2.03 –37oc 402 2.3–10.4 32 –101 ! –Propyl benzene 0.86 4.14 30 450 0.8–6 159 –100 insol. 10/43iso-Propyl benzene, see Cumeneiso-Propyl benzoate 1.01 5.67 99 – – 218 –26 insol. –Propyl bromide 1.35 4.3 – 490 – 71 –110 sl. sol. –Propyl chloride 0.89 2.71 <–18 520 2.6–11.1 47 –123 sl. sol. –n-Propyl cyanide, see

ButyronitrilePropylene 0.51 1.5 –108 460 2–11.1 –48 –185 v. sol. 10 atm/20Propylene carbonate 1.21 3.5 135oc – – 242 –49 v. sol. 0.03/20Propylene dichloride, see 1,2-

Dichloropropaneiso-Propyl ether 0.72 3.5 –28 443 1.4–21 69 –60 sl. sol. 150/25n-Propyl formate 0.91 3.03 –3 455 2.3– 81 –93 sl. sol. 100/30iso-Propyl formate 0.88 3.0 –6 485 – 68 – sl. sol. –iso-Propyl glycidyl ether 0.92 4.15 – – – 137 – – –Propyl nitrate 1.06 – 20 177 2–100 111 <–100 sl. sol. –iso-Propyl toluene, see CymenePropyne 0.68 1.38 – – 1.7 –23 –105 sl. sol. 3876/20Pyridine 0.99 2.7 20 482 1.8–12.4 115 –42 ! 10/13Pyrrolidine 0.85 2.45 3 – – 89 –63 ! 128/39Pyruvic acid 1.23 – 3.0 – – 165 14 ! –Quinoline 1.09 4.45 – 480 1.2– 238 –20 sol. 1/60Quinone 1.32 – 293 – – – 116subl. sl. sol. –Resorcinol 1.27 3.79 127 608 1.4– 281 110 sol. 1/108

at 200°CSalicylaldehyde 1.15 – 78 – – 197 –10 sl. sol. 1/33Salicylic acid 1.44 4.8 157 545 – 211 at 203 mm 159 sl. sol. 1/114Silane 0.68 – – Spontaneously –112 –185 insol. –

flammable in airSodium 0.97 – – >115 spontaneous 892 98 dec. –

ignition in dry airSodium acetate 1.53 – – 607 – – 324 119° –Stearic acid 0.95 9.8 196 395 – 358–83 69 insol. 1/174Stoddard solvent 1.0 – 38–43 227–60 0.8–5 220–300 – – –Styrene 0.909 3.6 31 490 1.1–6.1 146 –33 insol. –Styrene monomer 0.905 1 31 490 1.1–6.1 145 –31 insol. –Succinonitrile 0.98 2.1 132 – – 266 58 v. sol. 2/100

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Sulphur 2.07 – 207 232 – 444 119 insol. 1/184Sulphur monochloride 1.69 4.7 118 234 – 136 –80 dec. 10/28Tallow 0.895 – 265 – – – 32 – –Tannic acid – – 199oc 527 – – 210dec. sol. –m-Terphenyl 1.16 – 135oc – – 365 87 insol. –o-Terphenyl 1.14 7.9 163oc – – 332 57 insol. –1,2,4,5-Tetrachlorobenzene 1.86 – 155 – – 243 139 insol. <0.1/25Tetradecane 0.76 6.8 100 202 0.5– 254 6 insol. 1/76Tetraethylenepentamine 0.99 – 163oc – – 333 – – –Tetraethyl lead 1.66 8.6 93 – – 170exp. –137 insol. 1/38Tetrahydrofuran 0.89 2.5 –14 321 2–11.8 65 –65 v. sol. 114/15Tetrahydronaphthalene 0.97 4.55 71 384 0.8–5 207 –30 insol. 1/38

at 150°C2,2"-Thiodiethanol 1.18 4.2 160oc – – 28 –11 ! –Thiophene 1.06 2.9 –1 – – 84 –38 – 40/12Toluene 0.87 3.1 4.4 536 1.4–6.7 111 –95 insol. 37/30Toluene-2,4-diisocyanate 1.2 6.0 132 – 0.9–9.5 251 20 – –m-Toluidine 0.99 3.9 86 482 – 203 –31 sl. sol. 1/41o-Toluidine 1.004 3.7 85 482 – 200 –16 sl. sol. 1/44p-Toluidine 1.046 3.9 87 482 – 200 44 sl. sol. 1/42Triamylamine 0.8 7.8 102 – – 232 – – –Tri-n-butyl amine 0.8 6.38 86 – – 216 –70 sl. sol. –Tributyl phosphate 0.97 9.2 146 – – 292 <–80 sol. –1,2,4-Trichlorobenzene 1.45 6.3 99 – – 214 17 insol. 1/381,1,1-Trichloroethane 1.34 4.6 none – – 74 –38 insol. 100/20Trichloroethylene 1.46 4.54 – 410 12–90 87 –73 sl. sol. 100/321,2,3-Trichloropropane 1.39 5.0 82 304 3.2–12.6 156 –15 sl. sol. 100/461,1,2-Trichloro-1,2,2-trifluoro 1.56 – – 680 – 48 –36 insol. –

ethaneTricresyl phosphate, see Tritolyl

phosphateTridecanol 0.82 6.9 121 – – 274 31 insol. –Triethyl aluminium 0.84 – <–53 <–53 – 194 –53 exp. H2O 4/83Triethyl amine 0.73 3.48 <–7 – 1.2–8.0 89 –115 sol. –Triethanolamine 1.13 – 179 – – 360 20 ! 10/205Triethylene glycol 1.13 5.17 177 371 0.9–9.2 276 –4 ! 1/114Triethylene-tetramine 0.98 – 135 338 – 267 12 sol. <0.01/20Triethyl o-formate 0.89 5.1 30 – – 146 – dec. 10/40Triisobutyl aluminium 0.79 – <0 <4 – 114 4 – –

Table 6.1 Cont’d

Substance Specific Vapour Flash Ignition Flammable Boiling Melting Solubility Vapourgravity density point(1) temp. limits(1) point point in water pressure

(air = 1) (°C) (°C) (%) (°C) (°C) (g/100 g) (mm Hg/°C)

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Trimethyl amine 0.66 2.0 –7 190 2–11.6 4 –117 v. sol. –Trimethyl borate 0.92 3.6 <27 – – 67 –29 dec. –3,5,5-Trimethyl-2-

cyclohexenone, seeiso-Phorone

2,2,4-Trimethyl pentane 0.69 3.9 –12 418 1.1–6.0 99 –107 insol. 41/212,4,4-Trimethyl-2-pentene 0.72 3.9 2 – – 112 –107 insol. 77/381,3,5-Trioxane 1.17 3.1 45 414 3.6–29 115 62 v. sol. 13/25Triphenyl phosphate 1.21 – 220 – – 245 49 insol. –

at 11mmTriphenyl phosphine 1.19 90 180 – – >360 80 insol. –Tripropylamine 0.75 4.9 41 – – 156 –94 sl. sol. –Tritolyl phosphate 1.17 12.7 225 385 – 410 11 – –Turpentine 0.87 4.6 35–39 253 0.8– 153–75 – – –Unsymmetrical dimethyl 0.79 1.94 ~–15 249 2–95 63 –58 v. sol. –

hydrazineValeraldehyde 0.81 3.0 12 – – 102 –92 sl. sol. –Valeric acid 0.94 3.5 96 – – 186 –35 sol. –Vinyl acetate 0.94 3.0 –8 427 2.6–13.4 73 –100 insol. 100/21Vinyl chloride 0.91 2.15 –78 472 4–22 –14 –154 sl. sol. 2600/25Vinyl cyanide, see AcrylonitrileVinyl ether 0.77 2.4 <–30 360 1.7–37 39 – – –Vinylidene chloride 1.3 3.4 –15oc 458 5.6–11.4 32 –122 insol. –Vinyl toluene, see Methyl styrenem-Xylene 0.87 3.7 29 528 1.1–7.0 139 –48 insol. 10/28o-Xylene 0.90 3.7 32 464 1.0–6.0 144 –26 insol. 10/32p-Xylene 0.86 3.6 27 529 1.1–7.0 138 13 insol. 10/27Xylidine 0.99 4.2 97 – – 224 <–15 sl. sol. –

dec. Decomposesexp. Explodes on contact with waterinsol. Insolubleoc Open cupsl. sol. Slightly soluble (<5 g /100 g )sol. Soluble (5–50 g /100 g)v. sol. Very soluble (>50g /100g)! Infinitely soluble (soluble in all proportions)Superscript indicates °C.(1) Unless otherwise stated, flammable limits relate to ambient temperature and atmospheric pressure and flash points relate to closed cup measurements.

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Table 6.2 Dust explosion characteristics of combustible solids

Dust Minimum ignition Minimum Minimum Maximum Maximum rate Maximum Notestemperature (°C) explosible ignition explosion of pressure oxygen————————— concentration energy pressure rise concentrationcloud layer (g/l) (mJ) (psi)(1) .(psi/s) to prevent

ignition(% by volume)

Acetamide 560 – – – – – – Group (b) dustAceto acetanilide 560 – 0.030 20 90 4800 –Acetoacet-p-phenetedide 560 – 0.030 10 87 >10 000 –Acetoacet-o-toluidine 710 – – – – – –2-Acetylamino-5-nitro thiazole 450 450 0.160 40 137 9000 –Acetyl-p-nitro-o-toluidine 450 – – – – – –Adipic acid 550 0.035 60 95 4000 –Alfalfa 460 200 0.100 320 88 1100 –Almond shell 440 200 0.065 80 101 1400 –Aluminium, atomized 650 760 0.045 50 84 >20 000 –Aluminium, flake 610 320 0.045 10 127 >20 000 –Aluminium–cobalt alloy 950 570 0.180 100 92 11 000 –Aluminium–copper alloy – 830 0.100 100 95 4000 –Aluminium–iron alloy 550 450 – – 36 300 –Aluminium–lithium alloy 470 400 <0.1 140 96 6000 –Aluminium–magnesium alloy 430 480 0.020 80 86 10 000 –Aluminium–nickel alloy 950 540 0.190 80 96 10 000Aluminum–silicon alloy 670 – 0.040 60 85 7500 –Aluminium acetate 560 640 – – 59 950 – Guncotton ignition

source in pressure testAluminium octoate 460 – – – – – –Aluminium stearate 400 380 0.015 10 86 >10 000 –2-Amino-5-nitrothiazole 460 460 0.075 30 110 5600 –Anthracene 505 Melts – – 68 700 –Anthranilic acid 580 – 0.030 35 84 6500 –Anthraquinone 670 – – – – – –Antimony 420 330 0.420 1920 28 300 –Antipyrin 405 Melts – – 53 –Asphalt 510 500 0.025 25 94 4800 –Aspirin 550 Melts 0.015 16 87 7700 –Azelaic acid 610 – 0.025 25 76 4700 –$, $"-Azo isobutyronitrile 430 350 0.015 25 134 8000 –Barley 370 – – – – – –Benzethonium chloride 380 410 0.020 60 91 6700 –Benzoic acid 600 Melts 0.011 12 95 10 300 –Benzotriazole 440 0.030 30 103 9200 –

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Benzoyl peroxide – – – 21 –Beryllium 910 540 – Did not – Contained 8% oxide

igniteBeryllium acetate, basic 620 – 0.080 100 87 2200 15 Inert gas carbon

dioxideBis(2-hydroxy-5-chlorophenyl)- 570 – 0.040 60 70 2000 13 Inert gas carbon

methane dioxideBis(2-hydroxy-3,5,6- Did not 450

trichlorophenyl)-methane igniteBone meal 490 230 11 100 Guncotton ignition

source in pressure testBoron 730 390 Did not ignite 41 200 Guncotton ignition

source in pressure testBread 450Brunswick green 360t-butyl benzoic acid 560 – 0.020 25 88 6500 –Cadmium 570 250 4000 7 100Cadmium yellow 390Calcium carbide 555 325 13Calcium citrate 470 Group (b) dustCalcium gluconate 550 Group (b) dustCalcium DL pantothenate 520 – 0.050 80 105 4600 –Calcium propionate 530 – – – 90 1900 –Calcium silicide 540 540 0.060 150 86 20 000 –Calcium stearate 400 0.025 15 97 >10 000 –Caprolactam 430 – 0.07 60 79 1700 8Carbon, activated 660 270 0.100 – 92 1700 – Guncotton ignition

source in min. expl.conc. and max.expl. pressure tests

Carbon, black 510Carboxy methyl cellulose 460 310 0.060 140 130 5000Carboxy methyl hydroxy ethyl 380 – 0.200 960 83 800 –

celluloseCarboxy polymethylene 520 – 0.115 640 76 1200 –Casein 460 – – – 89 1200 –Cellulose 410 300 0.045 40 117 8000 –Cellulose acetate 340 – 0.035 20 114 6500 5 Inert gas nitrogenCellulose acetate butyrate 370 – 0.025 30 81 2700 7Cellulose propionate 460 – 0.025 60 105 4700 –Cellulose triacetate 390 0.035 30 107 4300 –Cellulose tripropionate 460 – 0.025 45 88 4000 –Charcoal 530 180 0.140 20 100 1800 –Chloramine-T 540 150 – – 7 150 – Guncotton ignition

source in pressure test

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o-Chlorobenzmalono nitrile 0.025 90 >10 000o-Chloroaceto acetanilide 640 0.035 30 94 3900 –p-Chloroaceto acetanilide 650 – 0.035 20 85 5500 –Chloro amino toluene 650 – – – – – –

sulphonic acid4-Chloro-2 nitro aniline 590 120 <0.750 140 123 3500 –p-Chloro-o-toluidine 650 – – – – – –

hydrochlorideChocolate crumb 340 – – – – – –Chromium 580 400 – 140 56 5000Cinnamon 440 230 0.230 30 121 3900 –Citrus peel 500 330 0.060 100 51 1200 –Coal, brown 485 230 0.060 – – See also LigniteCoal, 8% volatiles 730 – – –Coal, 12% volatiles 670 240 – –Coal, 25% volatiles 605 210 0.120 120 62 400 –Coal, 37% volatiles 610 170 0.055 60 90 2300 Standard Pittsburgh coalCoal, 43% volatiles 575 180 0.050 50 92 2000Cobalt 760 370 – – – –Cocoa 500 200 0.065 120 69 1200 –Coconut 450 280 – – – –Coconut shell 470 220 0.035 60 115 4200 –Coffee 360 270 0.085 160 38 150 10 Inert gas carbon

dioxideCoffee, extract 600 – – – 47 – –Coffee, instant 410 350 0.280 Did not 68 500 –

igniteco*ke >750 430 – – – – –co*ke, petroleum, 13% volatiles 670 1.00 36 200 – Guncotton ignition

source in min. expl.conc. and max.expl. pressure tests

Colophony 325 Melts – –Copal 330 Melts – 68 – See also Gum manilaCopper 700 – – Did not Did not Did not –

ignite ignite ignite

Table 6.2 Cont’d

Dust Minimum ignition Minimum Minimum Maximum Maximum rate Maximum Notestemperature (°C) explosible ignition explosion of pressure oxygen————————— concentration energy pressure rise concentrationcloud layer (g/l) (mJ) (psi)(1) .(psi/s) to prevent

ignition(% by volume)

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Copper–zinc, gold bronze 370 190 1.00 – 44 1300 –Cork 460 210 0.035 35 96 7500Corn cob 450 240 0.045 45 127 3700Corn dextrine 410 390 0.040 40 124 7000Cornflour 390 – – – – – –Cornstarch 390 0.040 30 145 9500Cotton flock 470 – 0.050 25 94 6000Cotton linters 520 0.50 1920 73 400 5Cottonseed meal 530 200 0.055 80 89 2200 –Coumarone–indene resin 550 – 0.015 10 93 11 000 11Crystal violet 475 Melts – – – – –Cyclohexanone peroxide – – – 21 84 5600 –Dehydroacetic acid 430 – 0.030 15 87 8000 –Dextrin 410 440 0.050 40 99 9000Dextrose monohydrate 350 – – – – –Diallyl phthalate 480 – 0.030 20 90 8500 –Diamino stilbene disulphonic 550 – – – Group (b) dust

acidDiazo aminobenzene 550 – 0.015 20 114 >10 000 –Di-t-butyl-p-cresol 420 0.015 15 79 13 000 9Dibutyl tin maleate 600 –Dibutyl tin oxide 530Dichlorophene 770 72 30002,4-Dichlorophenoxy ethyl 540 0.045 60 84 2200

benzoateDicyclopentadiene dioxide 420 0.015 30 89 9500Dihydrostreptomycin sulphate 600 230 0.520 – 42 200 73,3"-Dimethoxy 4,4"-diamino – – 0.030 82 >10 000 –

diphenylDimethylacridan 540 –Dimethyl diphenyl urea 490Dimethyl isophthalate 580 0.025 15 84 8000Dimethyl terephthalate 570 0.030 20 105 12 000 6S-S"-Dimethyl xanthogene 400 0.300 3200 84 1500

thylene bis dithiocarbamateDinitro aniline 470 –3,5-Dinitrobenzamide 500 Melts 0.040 45 163 6500 –3,5-Dinitrobenzoic acid 460 – 0.050 45 139 4300Dinitrobenzoyl chloride 380 – – – – – –Dinitrocresol 340 Melts 0.030 –4,4"-Dinitro-sym-diphenyl urea 550 – 0.095 60 102 2500 –Dinitro stilbene disulphonic 450 – – – – – –

acidDinitrotoluamide 500 – 0.050 15 153 >10 000 –Diphenyl 630 – 0.015 20 82 3700 –

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Table 6.2 Cont’d

Dust Minimum ignition Minimum Minimum Maximum Maximum rate Maximum Notestemperature (°C) explosible ignition explosion of pressure oxygen————————— concentration energy pressure rise concentrationcloud layer (g/l) (mJ) (psi)(1) .(psi/s) to prevent

ignition(% by volume)

4,4"-Diphenyl di 590 140 0.065 30 143 5500sulphonylazide

Diphenylol propane 570 0.012 11 81 11 800 5 Inert gas nitrogen(Bisphenol-A)

Egg white 610 – 0.14 640 58 500Epoxy resin 490 – 0.015 9 94 8500 –Esparto grass – – – – 94 7300 –Ethyl cellulose 340 330 0.025 15 112 7000Ethylene diamine tetra acetic 450 – 0.075 50 106 3000

acidEthyl hydroxyethyl cellulose 390 – 0.020 30 94 2200Ferric ammonium ferrocyanide 390 210 1.500 17 100Ferric dimethyl dithio 280 150 0.055 25 86 6300

carbamateFerric ferrocyanide 370 82 1000Ferrochromium 790 670 2.00Ferromanganese 450 290 0.130 80 62 5000Ferrosilicon (45% Si) 640Ferrosilicon (90% Si) Did not 980 0.240 1280 113 3500

igniteFerrotitanium 370 400 0.140 80 55 9500Ferrous ferrocyanide 380 190 0.400Ferrovanadium 440 400 1.300 400Fish meal 485Fumaric acid 520 0.085 35 103 3000 –Garlic 360 – 0.10 240 57 1300 –Gelatin, dried 620 480 <0.5 – 78 1200 –Gilsonite 580 500 0.020 25 78 4500Graphite 730 580 –Grass 56 400Gum arabic 500 260 0.060 100 117 3000Gum Karaya 520 240 0.100 180 116 2500 –Gum manila (copal) 360 390 0.030 30 89 6000Gum tragacanth 490 260 0.040 45 123 5000 –Hexa methylene tetramine 410 – 0.015 10 98 11 000 11Horseradish – – <0.100 96 1600

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Hydrazine acid tartrate 570 0.175 460 30 200 –p-Hydroxy benzoic acid 620 – 0.040 – 37 – –Hydroxyethyl cellulose 410 – 0.025 40 106 2600 –Hydroxyethyl methyl cellulose 410 –Hydroxy propyl cellulose 400 – 0.020 30 96 2900 –Iron 430 240 – – – –Iron, carbonyl 420 230 0.105 100 47 8000Iron pyrites 380 280 1.00 8200 5 100 –Isatoic anhydride 700 0.035 25 80 4900 –Isinglass 520 – – Nil NilIsophthalic acid 700 – 0.035 25 78 3100Kelp 570 220 Did not ignite 19 200 –Lactalbumin 570 240 0.040 50 97 3500 –Lampblack 730 – – – – –Lauryl peroxide 12 90 6400Lead 790 290 Did not 3 100 – Flame ignition source

ignite in pressure testLeather 390 –Lignin 450 0.040 20 102 5000 7Lignite 450 200 0.030 30 94 8000 –Lycopodium 480 310 0.025 40 75 3100 9Magnesium 560 430 0.030 40 116 15 000Maize husk 430 – – 75 700Maize starch 410 – – – – – –Maleic anhydride 500 Melts – – – – –Malt barley 400 250 0.055 35 95 4400Manganese 460 240 0.125 305 53 4900 –Manganese ethylene bis dithio 270 – 0.07 35 –

carbamateManioc 430 –Mannitol 460 0.065 40 97 2800Melamine formaldehyde resin 410 0.02 50 93 1800DL Methionine 370 360 0.025 35 119 5700 71-Methylamino anthraquinone 830 Melts 0.055 50 71 3300Methyl cellulose 360 340 0.030 20 133 6000 –2,2-Methylene bis-4-ethyl-6-t- 310 76 7300 –

butyl phenolMilk 440 – – – – – –Milk, skimmed 490 200 0.050 50 95 2300 –Milk sugar 450 Melts – 31 –Molybdenum 720 360 – – – –Molydenum disulphide 570 290 – – – – –Monochloracetic acid 620 – – – – – –Monosodium salt of trichloro 540 – – – – – – Group (b) dust

ethyl phosphate

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Table 6.2 Cont’d

Dust Minimum ignition Minimum Minimum Maximum Maximum rate Maximum Notestemperature (°C) explosible ignition explosion of pressure oxygen————————— concentration energy pressure rise concentrationcloud layer (g/l) (mJ) (psi)(1) .(psi/s) to prevent

ignition(% by volume)

Moss, Irish 530 230 Did not ignite 21 300 –Naphthalene 575 Melts – – 87 – –#-Naphththalene-azo- 510 Melts 0.020 50 70 2300 –

dimethyl aniline#-Naphthol 670 – – – – – –Naphthol yellow 415 395 –Nigrosine hydrochloride 630 – – – –p-Nitro-o-anisidene 400 –p-Nitro-benzene arsonic acid 360 280 0.195 480 77 900 –Nitrocellulose – – – 30 >256 >20 900 –Nitro diphenylamine 480 – – – – – –Nitro furfural semi carbazone 240 – – – >143 8600 –Nitropyridone 430 Melts 0.045 35 111 >10 000 –p-Nitro-o-toluidine 470 – – – – – –m-Nitro-p-toluidine 470 – – – – –Nylon 500 430 0.030 20 95 4000 6Oilcake meal 470 285 – – – –Onion, dehydrated 410 – 0.130 Did not 35 500 –

ignitePaper 440 270 0.055 60 96 3600Para formaldehyde 410 – 0.040 20 133 13 000Peanut hull 460 210 0.045 50 116 8000Peat 420 295Peat, sphagnum 460 240 0.045 50 104 2200Pectin 410 200 0.075 35 132 8000Penicillin, N-ethyl piperidine 310

salt ofPenta erythritol 450 – 0.030 10 90 9500 7Phenol formaldehyde 450 0.015 10 107 6500Phenol furfural resin 530 – 0.025 10 88 8500 –Phenothiazine 540 – 0.030 56 3000 –p-Phenylene diamine 620 – 0.025 30 94 11 000 –Phosphorus, red 360 305 –Phosphorus pentasulphide 280 270 0.050 15 64 >10 000 –Phthalic acid 650 Melts – 62 –Phthalic anhydride 605 Melts 0.015 15 72 4200 11

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Phthalimide 630 – 0.030 50 89 4800Phthalodinitrile >700 Melts – – 43 – –Phytosterol 330 Melts 0.025 10 76 >10 000Piperazine 480 – 72 1400Pitch 710 – 0.035 20 88 6000Polyacetal 440 – 0.035 20 113 4100Polyacrylamide 410 240 0.040 30 85 2500Polyacrylonitrile 500 460 0.025 20 89 11 000Polycarbonate 710 0.025 25 96 4700 –Polyethylene 390 – 0.020 10 80 7500 –Polyethylene oxide 350 0.030 30 106 2100 5Polyethylene terephthalate 500 0.040 35 98 5500 –Poly isobutyl methacrylate 500 280 0.020 40 74 2800 –Poly methacrylic acid 450 290 0.045 100 97 1800Polymethyl methacrylate 440 0.020 15 101 1800 7Polymonochlorotrifluoro 600 720 Did not ignite –

ethylenePolypropylene 420 0.020 30 76 5500 –Polystyrene 500 500 0.020 15 100 7000Polytetrafluoro ethylene 670 570 Did not ignitePolyurethane foam 510 440 0.030 20 87 3700Polyurethane foam, fire 550 390 0.025 15 96 3700

retardantPolyvinylacetate 450 0.040 160 69 1000 11 Inert gas carbon

dioxidePolyvinyl alcohol 450 Melts 78Polyvinyl butyral 390 0.020 10 84 2000 5Polyvinyl chloride 670 Did not ignite 38 500 Flame ignition sourcePolyvinylidene chloride 670 Group (b) dustPolyvinyl pyrrolidone 465 Melts 15Potassium hydrogen tartrate 520Potassium sorbate 380 180 0.120 60 79 9500Potato, dried 450 97 1000Potato starch 430Provender 370 93 1400Pyrethrum 460 210 0.100 80 95 1500 –Quillaia bark 450Rape seed meal 465Rayon, viscose 420Rayon, flock 0.03Rice 440 240 0.050 50 105 2700Rosin 390 0.015 10 87 12 000Rubber 380Rubber, crude, hard 350 0.025 50 80 3800 13Rubber, crumb 440 84 3300

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Rubber, vulcanized 360 – – – 40 –Rye flour 415 325 – – 35 –Saccharin 690Salicylanilide 610 Melts 0.040 20 73 4800 –Salicylic acid 590 – 0.025 84 6800Sawdust 430 – – – 97 2000 –Sebacic acid – – – – 74 400 –Senna 440 0.010 105 49 300Shellac 400 – 0.020 10 73 3600 9Silicon Did not 760 <0.10 80 94 13 000 –

igniteSoap 430 600 0.085 100 77 2800Sodium acetate 590 0.030 35 90 4600Sodium amatol 580 Melts 0.140 – 65 800Sodium benzoate 560 680 0.050 80 91 3700Sodium carboxymethyl 320 – 1.10 440 49 400 5

celluloseSodium 2-chloro-5-nitro- 550 440 – – – – –

benzene sulphonateSodium 2,2-dichloro 500 – 0.260 220 68 500

propionateSodium dihydroxy naphthalene 510 – – – Group (b) dust

disulphonateSodium glucaspaldrate 600Sodium glucoheptonate 600Sodium monochloracetate 550 –Sodium m-nitrobenzene – – – – 92 400 –

sulphonateSodium m-nitrobenzoate – 87 2900 –Sodium pentachlorophenate Did not 360 Did not –

ignite igniteSodium propionate 479 70 700Sodium secobarbital 520 – 0.100 960 76 800Sodium sorbate 400 140 0.050 30 87 6500Sodium thiosulphate 510 330 – 11 <100 Guncotton ignition

source in pressure test

Table 6.2 Cont’d

Dust Minimum ignition Minimum Minimum Maximum Maximum rate Maximum Notestemperature (°C) explosible ignition explosion of pressure oxygen————————— concentration energy pressure rise concentrationcloud layer (g/l) (mJ) (psi)(1) .(psi/s) to prevent

ignition(% by volume)

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Sodium toluene sulphonate 530 – – – –Sodium xylene sulphonate 490 – – – – – –Soot >690 535 – – Did not –

igniteSorbic acid 440 460 0.020 15 106 >10 000 5 Inert gas nitrogenL-Sorbose 370 – 0.065 80 76 4700 –Soya flour 550 340 0.060 100 94 800 9Soya protein 540 0.050 60 98 6500 9Starch 470 – – – – – –Starch, cold water 490 – – – – – –Stearic acid 290 25 80 8500Steel 450 – –Streptomycin sulphate 700 – – – – – –Sucrose 420 Melts 0.045 40 86 5500 –Sugar 370 400 0.045 30 109 5000Sulphur 190 220 0.035 15 78 4700 –Tantalum 630 300 <0.20 120 55 4400 –Tartaric acid 350Tea 500 – 93 1700Tea, instant 580 340 Did not ignite 48 400Tellurium 550 340 – – – – –Terephthalic acid 680 – 0.050 20 84 8000 –Tetranitro carbazole 395 MeltsThiourea 420 Melts – – 29 100 –Thorium 270 280 0.075 5 79 5500 –Thorium hydride 260 20 0.080 3 81 12 000Tin 630 430 0.190 80 48 1700 –Titanium 375 290 0.045 15 85 11 000 Ignites

in carbondioxide

Titanium hydride 480 540 0.070 60 121 12 000 3Tobacco 485 290 – – – – –Tobacco, dried 320 – – – 85 1000 –Tobacco, stem 420 230 Did not ignite 53 400 –Tribromosalicyl anilide 880 Melts – – – – –Trinitrotoluene – – 0.070 75 63 2100s-Trioxane 480 – 0.143 – 85 600 –$,$"-Trithiobis (N, N-dimethyl- 280 230 0.060 35 96 6000

thioformamide)Tung 540 240 0.070 240 74 1900Tungsten 730 470 – – Did not

igniteUranium 20 100 0.060 45 69 5000Uranium hydride 20 20 0.060 5 74 9000Urea 900 Did not ignite Group (b) dust

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Urea formaldehyde moulding 460 0.085 80 89 3600 9powder

Urea formaldehyde resin 430 0.02 34 110 1600Vanadium 500 490 0.220 60 57 1000 10Vitamin B1 mononitrate 380 190 0.035 35 120 9000 –Vitamin C 460 280 0.070 60 88 4800Walnut shell 420 210 0.035 60 121 5500Wax, accra 260Wax, carnauba 340 –Wax, paraffin 340Wheat, flour 380 360 0.050 50 109 3700Wheat, grain dust 420 290 – – 43 –Wheat starch 430 0.045 25 100 6500Wood 360 – – 90 5700 5Wood, bark 450 250 0.020 60 103 7500Wood, flour 430 – 0.050 20 94 8500 7Wood, hard 420 315 – – 66Wood, soft 440 325 – – 63 –Yeast 520 260 0.050 50 123 3500Zinc 680 460 0.500 960 70 1800Zinc ethylene dithio carbamate 480 180 45 300Zinc stearate 315 Melts 0.020 10 80 10 000Zirconium 20 220 0.045 5 75 11 000 Ignites

in carbondioxide

Zirconium hydride 350 270 0.085 60 90 9500 3

(1) 1 psi = 0.069 bar = 6.9 kN/m2.

Table 6.2 Cont’d

Dust Minimum ignition Minimum Minimum Maximum Maximum rate Maximum Notestemperature (°C) explosible ignition explosion of pressure oxygen————————— concentration energy pressure rise concentrationcloud layer (g/l) (mJ) (psi)(1) .(psi/s) to prevent

ignition(% by volume)

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Reactive chemicals

From Chapter 3 all chemical reactions involve energy changes as a combination of activationenergy and reaction energy. Whilst in some cases the heat of reaction is absorbed into the productsand the reaction cools (endothermic reactions), most reactions evolve energy as heat (exothermicreactions), and sometimes as light and sound. When the heat liberated or absorbed cannot beaccommodated by the surrounding environment hazards are presented which can result in materialdamage. This can arise because either the amount of energy (thermodynamics) or the rate ofenergy release due to the speed of reaction (reaction kinetics) is excessive. The aim therefore isto establish the thermal stability of the system and then to control the extent and rate of heatrelease so as to minimize risk from energetic hazards. Thousands of reactive hazards have beendocumented by Bretherick (see Bibliography). The present chapter provides an insight into thehazards and the basic precautions to control the risk.

Reactive chemical hazards may arise from the inherent properties of the chemicals handled,used or disposed of and/or from their admixture or processing.

A hazard may arise with a chemical because of its tendency to decompose spontaneously or toreact violently on contact with other common chemicals, as illustrated in Figure 7.1. The case ofpyrophoric chemicals is summarized in Chapter 6; some dangerous reactions of compressed gasesare mentioned in Chapter 9; other cases are summarized here.

However, extreme caution is necessary with mixed chemical systems since many which arethermodynamically unstable exhibit considerable kinetic stability. The kinetic barrier to stabilitymay be overcome if traces of catalyst are present, and result in a violent reaction. The mostcommon catalysts derive from metals, or their compounds, and the unpredictable behaviour ofmany reactions arises from the unwitting presence of impurities. Other catalysts include acids,bases, organic free-radical precursors, etc. Hence any system must be treated with care which

(a) is thermodynamically unstable or(b) may contain a catalyst, or impurities which could serve as a catalyst.

Water-sensitive chemicals

Some chemicals are ‘water-sensitive’: in contact with water they can generate flammable or toxicgases and/or undergo a vigorous reaction. Refer to Table 7.1. Such reactions can cause overpressurein sealed equipment or pipework. Selected water-sensitive chlorine compounds are given in Table7.2. With flammable gas generation the heat of reaction may cause ignition, depending upon thecompound in question, as illustrated by the list of hydrides in Table 7.3.

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Reaction withwater

Ignition offlammable gases Inflames

Over-pressurization*of container

Admixture withanother specificchemical




Self-reaction ordecomposition Flammable gases



Over-pressurization of container*


Toxic gases


Over-pressurization*of container

Over-pressurization*of container

Exothermicreaction with air


*Unless venting/pressure relief is provided

Precautions for safe handling

• Store and use in such a way that accidental ingress of water, or contact with it, is avoided(roofs of storage areas should be regularly maintained to minimize leaks).

• Provide covered storage, off the ground, away from sprinkler systems, safety showers, overheadwater lines or condensate lines.

• Keep away from water taps or sinks.• Store under a chemically-inert medium when appropriate (stocks should be checked regularly

to ensure that an adequate level of inert medium is maintained).• Segregate from other flammable materials, e.g. solvents and combustibles.• Use appropriate eye/face protection, overalls and gloves.

Toxic hazards from mixtures

Undesirable emissions of toxic gases may occur as a result of mixing relatively common chemicals.Refer to Table 7.4. Chemicals which are incompatible in this way must be brought into contactonly under strictly controlled conditions.

Figure 7.1 Possible reactive chemical hazards (consequences are not mutually exclusive)


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Table 7.1 Water-sensitive chemicals: consequences of water contact

Acetyl bromide TAcetyl chloride T VAcetylcholine bromide TAluminium (powder) FAluminium alkyls F VAluminium isopropoxide FAluminium lithium hydride FAluminium selenide TAluminium phosphide F TBoron tribromide TCalcium (granules) FCalcium carbide FCalcium hydride FCalcium phosphide F TChlorosulphonic acid T VDisulphur dichloride T VEthoxides, alkaline VLithium (metal) F VLithium aluminium deuteride FLithium aluminium dihydride FLithium borohydride FLithium hydride FLithium methoxide FMagnesium (powder) FMagnesium alkyls FMagnesium phosphide F TMethoxides, alkaline F VNickel sulphide TPhosphorus pentasulphide F TPhosphorus sesquisulphide F TPhosphorus pentachloride TPhosphorus pentabromide TPotassium (metal) F VPotassium borohydride FPotassium methoxide FSilicon tetrachloride T VSodium (metal) F VSodium aluminium hydride FSodium borohydride F TSodium hydride FSulphur dichloride T VSulphuric acid, fuming (Oleum) T VSulphur tetrachloride T VSulphuryl chloride T VThionyl chloride T VTitanium tetrachloride T VTrichlorophenylsilane TTrichlorosilane FZinc (powder) FZinc alkyls T VZirconium (powder) F

F Flammable gasesT Toxic productsV Vigorous reaction

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• Provision of adequate training, instruction, and supervision.• Prohibition on unauthorized mixing, e.g. of cleaning agents or ‘wastes’.• Correct labels.• Segregated storage, to avoid accidental mixing.• Dispose of wastes and ‘empty’ containers by different routes.• Specific precautions against the inherent hazards of each individual chemical.

Reactive hazards from mixtures

Many chemicals are ‘incompatible’ because a violent reaction may occur on mixing. This can, insome conditions, result in an explosion. Refer to Table 7.5.

An appraisal is needed of all chemicals which may be present, even if unintentionally (e.g. asintermediates, byproducts or wastes) and how they can react under the most extreme conditions

Table 7.2 Examples of reactive chlorine compounds

Compound Description Reactivity

Acetyl chloride Colourless, fuming, corrosive liquid Decomposes violently with water toCH3COCI Flash point 4°C produce heat and toxic fumes: HCI

When heated, emits phosgene

Aluminium chloride Orange, yellow, grey or white Reacts with air moisture to form corrosive(anhydrous) powder which is a severe HCI gasAICI3 respiratory irritant and can cause Violent reaction when a stream of water hits

skin/eye burns a large amountDo not use water in vicinity

Benzoyl chloride Colourless, fuming, corrosive liquid Reacts strongly with water or waterC6H5COCI with a strong odour vapour, producing heat and toxic/corrosive

Combustible: flash point 72°C fumesGenerates phosgene gas when Use of water must be considered carefully


Calcium hypochlorite Water soluble white crystals or Water spray may be used but evolves CI2 gasCa(CIO)2 powder with strong chlorine freely at ordinary temperatures with

odour moistureNon-flammable but can evolve CI2

and O2May undergo decomposition

Sulphur monochloride Yellowish-red oily fuming liquid Decomposes when contacted by water, toS2CI2 with a strong odour produce heat and toxic/corrosive fumes

Combustible: flash point 118°C Do not allow water to enter containers:Ignition temp. 233°C reaction can be violentLiquid and vapours are irritating Wash down spills with flooding amounts

of water

Titanium tetrachloride Colourless to light yellow fuming Reacts vigorously with water, liberating heatTiCI4 corrosive liquid and corrosive HCI gas

Vapour is irritating Reacts more strongly with hot waterUse water spray to keep exposed containers

cool in fire


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Table 7.3 Variation in reactivity of hydrides with humid air or water

Substance Reaction (ambient temperature)

Humid air Water

Aluminium borohydride (Al(BH4)3) Explosive ExplosiveAluminium hydride (AlH3) Slow ModerateAntimony hydride (Stibine) (SbH3) Rapid Very slowArsenic hydride (Arsine) (AsH3) Moderate Very slowBarium hydride (BaH2) Rapid RapidBeryllium borohydride (Be(BH4)2) Explosive ExplosiveBeryllium hydride (BeH2) Slow SlowCalcium hydride (CaH2) Moderately fast RapidCerium hydride (CeH3) Pyrophoric SlowCaesium hydride (CsH) Inflames ViolentCopper hydride (CuH) Rapid SlowDiborane (B2H6) Explosive ModerateLead hydride (PbH4) Instant (unstable gas) —Lithium aluminium hydride (LiAH4) Rapid ViolentLithium borohydride (LiBH4) Rapid VigorousLithium hydride (LiH) Can ignite RapidMagnesium aluminium hydride (Mg(AlH4)2) Vigorous VigorousMagnesium borohydride (Mg(BH4)2) Very slow ViolentMagnesium hydride (MgH2) Known to ignite RapidPentaborane (B5H9) Ignites RapidPhosphorus hydride (Phosphine) (PH3) Pyrophoric Very slowPotassium borohydride (KBH4) Very slow Very slowPotassium hydride (KH) Inflames VigorousRubidium hydride (RbH) Inflames ViolentSilicon hydride (Silane) (SiH4) Explosive RapidSodium aluminium hydride (NaAlH4) Rapid Ignites, may explodeSodium borohydride (NaBH4) Slow SlowSodium hydride (NaH) Ignites ViolentUranium hydride (UH3) Pyrophoric Moderate

Table 7.4 Toxic hazards from incompatible chemical mixturesSubstances in column 1 must be stored/handled so that they cannot accidentally contact corresponding substances incolumn 2 because toxic materials (column 3) would be produced.

Column 1 Column 2 Column 3

Arsenical materials Any reducing agent ArsineAzides Acids Hydrogen azideCyanides Acids Hydrogen cyanideHypochlorites Acids Chlorine or hypochlorous acidNitrates Sulphuric acid Nitrogen dioxideNitric acid Copper, brass any heavy metals Nitrogen dioxide (nitrous fumes)Nitrites Acids Nitrous fumesPhosphorus Caustic alkalis or reducing agents PhosphineSelenides Reducing agents Hydrogen selenideSulphides Acids Hydrogen sulphideTellurides Reducing agents Hydrogen telluride

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Table 7.5 Reactive hazards of incompatible chemicalsSubstances in column 1 must be stored/handled so that they cannot contact corresponding substances in column 2 underuncontrolled conditions, or violent reactions may occur.

Column 1 Column 2

Acetic acid Chromic acid, nitric acid, hydroxyl-containing compounds, ethyleneglycol, perchloric acid, peroxides, or permanganates

Acetone Concentrated nitric and sulphuric acid mixturesAcetylene Chlorine, bromine, copper, silver, fluorine or mercuryAlkali and alkaline earth metals, Carbon dioxide, carbon tetrachloride, or other chlorinated

e.g. sodium, potassium hydrocarbons. (Also prohibit, water, foam and dry chemical on fireslithium, magnesium, calcium, involving these metals – dry sand should be available)powdered aluminium

Anhydrous ammonia Mercury, chlorine, calcium hypochlorite, iodine, bromine or hydrogen fluorideAmmonium nitrate Acids, metal powders, flammable liquids, chlorates, nitrites, sulphur,

finely-divided organics or combustiblesAniline Nitric acid, hydrogen peroxideBromine Ammonia, acetylene, butadiene, butane or other petroleum gases,

sodium carbide, turpentine, benzene, or finely-divided metalsCalcium oxide WaterCarbon, activated Calcium hypochloriteChlorates Ammonium salts, acids, metal powders, sulphur, finely-divided organics

or combustiblesChromic acid and chromium Acetic acid, naphthalene, camphor, glycerol, turpentine, alcohol or

trioxide other flammable liquidsChlorine Ammonia, acetylene, butadiene, butane or other petroleum gases,

hydrogen, sodium carbide, turpentine, benzene or finely-divided metalsChlorine dioxide Ammonia, methane, phosphine or hydrogen sulphideCopper Acetylene, hydrogen peroxideFluorine Isolate from everythingHydrazine Hydrogen peroxide, nitric acid, or any other oxidantHydrocarbons (benzene, butane, Fluorine, chlorine, bromine, chromic acid, peroxides

propane, gasoline, turpentine, etc.)Hydrocyanic acid Nitric acid, alkalisHydrofluoric acid, anhydrous Ammonia, aqueous or anhydrous

(hydrogen fluoride)Hydrogen peroxide Copper, chromium, iron, most metals or their salts, any flammable

liquid, combustible materials, aniline, nitromethaneHydrogen sulphide Fuming nitric acid, oxidizing gasesIodine Acetylene, ammonia (anhydrous or aqueous)Mercury Acetylene, fulminic acid (produced in ethanol – nitric acid mixtures), ammoniaNitric acid (conc) Acetic acid, acetone, alcohol, aniline, chromic acid, hydrocyanic acid,

hydrogen sulphide, flammable liquids, flammable gases, or nitratablesubstances, paper, cardboard or rags

Nitroparaffins Inorganic bases, aminesOxalic acid Silver, mercuryOxygen Oils, grease, hydrogen, flammable liquids, solids or gasesPerchloric acid Acetic anhydride, bismuth and its alloys, alcohol, paper, wood, grease, oilsPeroxides, organic Acids (organic or mineral), avoid friction, store coldPhosphorus (white) Air, oxygenPotassium chlorate Acids (see also chlorates)Potassium perchlorate Acids (see also perchloric acid)Potassium permanganate Glycerol, ethylene glycol, benzaldehyde, sulphuric acidSilver Acetylene, oxalic acid, tartaric acid, fulminic acid (produced in

ethanol–nitric acid mixtures), ammonium compoundsSodium See alkali metals (above)Sodium nitrite Ammonium nitrate and other ammonium saltsSodium peroxide Any oxidizable substance, such as ethanol, methanol, glacial acetic

acid, acetic anhydride, benzaldehyde, carbon disulphide,glycerol, ethylene glycol, ethyl acetate, methyl acetate or furfural

Sulphuric acid Chlorates, perchlorates, permanganates


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(e.g. concentration, agitation, temperature, pressure) likely to arise. Sometimes special testing isrequired.

For reactions with air or water, refer to pyrophoric chemicals (Chapter 6).In acid-base reactions, the heat of neutralization of aqueous acids and bases can be sufficient

to cause ‘spitting’ from containers when the concentrated reagents interact. This is also encounteredwhen concentrated sulphuric acid is diluted (refer to Table 7.1); the acid should always be addedcautiously to water and not vice versa. Eye and skin protection is obligatory when using such reagents.

Oxidizing agents

Oxidizing agents, although not normally spontaneously flammable, often represent a source ofoxygen that can support combustion. They will react readily in contact with reducing reagents.Hence an oxidizing agent will invariably accelerate the rate of burning of a combustible material.In finely divided state such mixtures may react explosively.

Some common oxidizing agents are classified according to stability in Table 7.6.

Table 7.6 Common oxidizing agents classified according to stability

Classification Example

Relatively stable Aluminium nitrate• Increase the burning rate of combustible materials Ammonium persulphate• Form highly flammable or explosive mixtures Barium nitrate/peroxide

with finely divided combustible materials Calcium nitrate/peroxideCupric nitrateHydrogen peroxide solutions (8–27.5% by weight)Lead nitrateLithium peroxide/hypochloriteMagnesium nitrate/perchlorateNickel nitrateNitric acid (concentrations !70%)Potassium dichromate/nitrate/persulphateSilver nitrateSodium dichromate/nitrate/nitrite/perborate/

persulphate/chlorite (!40% by weight)Strontium nitrate/peroxideZinc peroxide

Moderately unstable/reactive Ammonium dichromate• Undergo vigorous decomposition on heating Barium chlorate• Explode when heated in a sealed container Calcium chlorate/hypochlorite• Cause spontaneous heating of combustible Chromium trioxide (chromic acid)

materials Hydrogen peroxide solutions (27.5–91% by weight)Nitric acid (concentrations >70%)Potassium bromide/chlorate/permanganate/peroxideSodium chlorate/permanganate/peroxide/chlorite

(>40% by weight)Strontium chlorate

Unstable Ammonium chlorate/perchlorate/permanganate• Explode when catalysed or exposed to heat, Benzoyl peroxide

shock or friction Guanidine nitrate• Liberate oxygen at room temperatures Mercury chlorate

Methyl ethyl ketone peroxidePotassium superoxide

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Safe handling

• Handle and store the minimum quantities practicable for the process or experiments in progress.• Segregate the materials from other chemicals, particularly reducing agents, paper, straw, cloth

or materials of low flash point.• Handle in the most dilute form possible in clearly designated areas, away from potential

ignition sources.• Provide and use appropriate eye/face protection, overalls and gloves.

Hazards arising from the oxidation of organic compounds are greater when the reactants arevolatile, or present as a dust or an aerosol. Liquid oxygen and various concentrated acids, e.g.nitric, sulphuric or perchloric acid, and chromic acid are strong oxidizing agents. The use ofperchloric acid or perchlorates has resulted in numerous explosions; their use should be avoidedwhen possible (refer to Table 7.5).

Explosive chemicals

Explosions involving flammable gases, vapours and dusts are discussed in Chapter 6. In addition,certain chemicals may explode as a result of violent self-reaction or decomposition when subjectedto mechanical shock, friction, heat, light or catalytic contaminants. Substances containing theatomic groupings listed in Table 7.7 are thermodynamically unstable, or explosive. They includeacetylides and acetylenic compounds, particular nitrogen compounds, e.g. azides and fulminates,peroxy compounds and vinyl compounds. These unstable moieties can be classified further as inTable 7.8 for peroxides. Table 7.9 lists a selection of potentially-explosive compounds.

More specific definitions of ‘explosives’ appear in legislation, e.g. in the UK under the ExplosivesAct 1875 as amended, which covers:

• High explosives which detonate to produce shock waves. Materials which are easily detonatedby mechanical or electrical stimuli are termed ‘primary explosives’. Those requiring an impingingshock wave to initiate them are ‘secondary explosives’.

• Pyrotechnics which burn to produce heat, smoke, light and/or noise.• Propellants which burn to produce heat and gas as a means of pressurizing pistons, start

engines, propel projectiles and rockets.

The precautions with any particular explosive depends on the hazard. In the UK explosives areclassified as: 1 – Gunpowder; 2 – Nitrate mixture; 3 – Nitro compound; 4 – Chlorate mixture;5 – Fulminate; 6 – Ammunition and 7 – Fireworks.

For the purposes of safety distances in connection with the issue of licences for factories andmagazines, explosives have been categorized as: X – fire or slight explosion risks or both, withonly local effect; Y – mass fire risks or moderate explosion risk, but not mass explosion risk;Z – mass explosion risk with serious missile effect; ZZ – mass explosion risk with minor missileeffect.

Hazards can be illustrated by reference to Table 7.10 (showing the explosive effects of smallquantities of high explosives in a 6 m " 6 m single-storey building) and to Figure 7.2 (relating thesize of fireball to quantity of burning pyrotechnic, high explosive or propellant). With pyrotechnicsthe hazard is related to the violence with which the chemical burns. One scheme used to classifypyrotechnics is given in Table 7.11. This is used to restrict quantities in use/storage and for


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Hydroxylammonium salts– N+ – OH Z –



C C MetalC C X


N N=







C N O Metal




N – Metal

N – N = O

N – NO2

C – N = N – C

C – N = N – O – C

C – N = N – S – C

C – N = N – O – N = N – C

C – N = N – S – N = N – C

C – N = N – N – C


– N = N – N = N –

– C – O – O – H– C – CO – OOH

– C – O – O – C –– C – CO – OOR

– O – O – Metal

– O – O – Non–metal

N Cr – O2

– N3

C – N2+ O–

– C – N2+ S –

N+ – HZ–

Acetylenic CompoundsMetal AcetylidesHaloacetylene derivativesDiazirines

Diazo Compounds

Nitroso CompoundsNitroalkanes, C–Nitro and Polynitroaryl compounds

Polynitroalkyl compounds

Acyl or alkyl nitritesAcyl or alkyl nitrates


N–Metal Derivatives

Metal Fulminates or aci – nitro salts

Fluorodinitromethyl compounds

N–Nitroso Compounds

Azo Compounds

N–Nitro Compounds


Bis–arenediazo oxides

Arenediazo aryl sulphides

Trizazenes (R=H, –CN, –OH, –NO)

Bis–arenediazo sulphides

High–nitrogen compounds tetrazoles


Peroxides (cyclic, diacyl, dialkyl)

Metal peroxides, peroxoacid salts


Aminechromium peroxo–complexes

Azides (acyl, halogen, non–metal, organic)


Diazonium sulphides and derivatives, ‘xanthates’

Hydrazinium salts, oxosalts of nitrogenous bases



Table 7.7 Atomic groupings characterizing explosive compounds

Bond groupings Class

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Diazonium carboxylates or salts

Aminemetal oxosalts


Halogen Azides, N–Halogen compounds, N–Haloimides

Difluoroamino compounds

Alkyl perchlorates, Chlorite salts, Halogen oxides,Hypohalites, Perchloric acid, Perchloryl Compounds

– C – N2+ Z –

(N–Metal)+Z –
























contain the grouping:

ROOHRmQ(OOH)n(Q = metal or metalloid)


$-Oxy- and $-peroxy-hydroperoxides and peroxides



Diacyl peroxides


Table 7.7 Cont’d

Bond groupings Class

Table 7.8 Classification of organic peroxides

Peroxide class General structures or characteristic group


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Table 7.9 Selected potentially explosive compounds

(a) Peroxy compounds(i) Organic peroxy compoundsAcetyl cyclohexane-sulphonyl peroxide (70%)Acetyl cyclohexane-sulphonyl peroxide

(28% phthalate solution)o-Azidobenzoyl peroxidet-Butyl mono permaleate (95% dry)t-Butyl peracetate (70%)t-Butyl peroctanoatet-Butyl perpivalate (75% hydrocarbon solution)t-Butyl peroxy isobutyrateBis-hexahydrobenzoyl peroxideBis-monofluorocarbonyl peroxideBis-benzenesulphonyl peroxideBis-hydroxymethyl peroxideBis (1-hydroxycyclohexyl) peroxide2,2-Bis (t-butylperoxy) butane2,2-Bis-hydroperoxy diisopropylidene peroxideBarium methyl peroxideBenzene triozonideCyclohexanone peroxide (95% dry)Diacetyl peroxideDi-n-butyl perdicarbonate (25% hydrocarbon

solution)2:4-Dichlorobenzoyl peroxide

(50% phthalate solution)Dicaproyl peroxideDicyclohexyl perdicarbonateDi-2-ethylhexyl perdicarbonate

(40% hydrocarbon solution)Dimethyl peroxideDiethyl peroxideDi-t-butyl-di-peroxyphthalateDifuroyl peroxideDibenzoyl peroxideDimeric ethylidene peroxideDimeric acetone peroxideDimeric cyclohexanone peroxideDiozonide of phoroneDimethyl ketone peroxideEthyl hydroperoxideEthylene ozonideHydroxymethyl methyl peroxideHydroxymethyl hydroperoxide1-Hydroxyethyl ethyl peroxide1-Hydroperoxy-1-acetoxycyclodecan-6-oneIsopropyl percarbonateIsopropyl hydroperoxideMethyl ethyl ketone peroxideMethyl hydroperoxideMethyl ethyl peroxideMonoperoxy succinic acidNonanoyl peroxide (75% hydrocarbon solution)1-Naphthoyl peroxideOxalic acid ester of t-butyl hydroperoxideOzonide of maleic anhydridePhenylhydrazone hydroperoxidePolymeric butadiene peroxidePolymeric isoprene peroxide

Polymeric dimethylbutadiene peroxidePolymeric peroxides of methacrylic acid

esters and styrenePolymeric peroxide of asymmetrical diphenylethylenePeroxyformic acidPeroxyacetic acidPeroxybenzoic acidPeroxycaproic acidPolymeric ethylidene peroxideSodium peracetateSuccinic acid peroxide (95% dry)Trimeric acetone peroxideTrimeric propylidene peroxideTetraacetate of 1,1,6,6-tetrahydroperoxycyclodecane

(ii) Inorganic peroxy compoundsPeroxidesHydrogen peroxide (>30%)Mercury peroxide

PeroxyacidsPeroxydisulphuric acidPeroxynitric acidPeroxy ditungstic acid

Peroxyacid saltsSodium peroxyborate (anhydrous)Sodium triperoxychromateSodium peroxymolybdateSodium peroxynickelateSodium diperoxytungstatePotassium peroxyferratePotassium peroxynickelatePotassium hyperoxytungstatePotassium peroxy pyrovanadateCalcium diperoxysulphateCalcium peroxychromateZinc tetraaminoperoxydisulphateAmmonium peroxyborateAmmonium peroxymanganateAmmonium peroxychromate

SuperoxidesPotassium superoxideOzone (liquid >30%)Potassium ozonideCaesium ozonideAmmonium ozonide

Inorganic peracids and their salts (common exampleswhich are particularly hazardous)

Ammonium perchlorateAmmonium persulphateAmmonium pernitratePerchloric acid (>73%)Performic acidSilver perchlorateTropylium perchlorate

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(b) Halo-acetylenes and acetylidesLithium bromoacetylideDibromoacetyleneLithium chloroacetylideSodium chloroacetylideDichloroacetyleneBromoacetyleneChloroacetyleneFluoroacetyleneDiiodoacetyleneSilver trifluoromethylacetylideChlorocyanoacetyleneLithium trifluoromethylacetylide3,3,3-Trifluoropropyne1-Bromo-2-propyne1-Chloro-2-propyne1-lodo-1,3-butadiyne1,4-Dichloro-2-butyne1-lodo-3-penten-1-yne1,6-Dichloro-2,4-hexadiyne2,4-Hexadiynylene bischlorosulphiteTetra (chloroethynyl) silane2,4-Hexadiynylene bischloroformate1-lodo-3-Phenyl-2-propyne1-Bromo-1,2-cyclotridecadien-4,8,10-triyne

(c) Metal acetylidesDisilver acetylideSilver acetylide-silver nitrateDigold(I) acetylideBarium acetylideCalcium acetylide (carbide)Dicaesium acetylideCopper(II) acetylideDicopper(I) acetylideSilver acetylideCaesium acetylidePotassium acetylideLithium acetylideSodium acetylideRubidium acetylideLithium acetylide-ammoniaDipotassium acetylideDilithium acetylideDisodium acetylideDirubidium acetylideStrontium acetylideSilver trifluoromethylacetylideSodium methoxyacetylideSodium ethoxyacetylide1,3-Pentadiyn-1-ysilver1,3-Pentadiyn-1-ylcopperDimethyl-1-propynylthalliumTriethynylaluminiumTriethynylantimonyBis(Dimethylthallium) acetylideTetraethynylgermaniumTetraethynyltinSodium phenylacetylide

3-Buten-1-ynyldiethylaluminiumDimethyl-phenylethynylthallium3-Buten-1-ynyltriethyllead3-Methyl-3-buten-1-ynyltriethyllead3-Buten-1-ynyldiisobutylaluminiumBis(Triethyltin) acetylene

(d) Metal azidesAluminium triazideBarium diazideBoron triazideCadmium diazideCalcium diazideChromyl azideCopper(I) azideCopper(II) azideLead(II) azideLead(IV) azideLithium azideLithium boroazideMercury(I) azideMercury(II) azidePotassium azideSilicon tetraazideSilver azide

(e) Metal azide halidesChromyl azide chlorideMolybdenum azide pentachlorideMolybdenum azide tetrachlorideSilver azide chlorideTin azide trichlorideTitanium azide trichlorideTungsten azide pentabromideUranium azide pentachlorideVanadium azide dichlorideVanadyl azide tetrachloride

(f) Diazo compounds1,1 Benzoylphenyldiazomethane2 Butan-1-yl diazoacetatet-Butyl diazoacetatet-Butyl-2-diazoacetoacetateDiazoacetonitrile2-DiazocyclohexanoneDiazocyclopentadiene1-DiazoindineDiazomethane (The precursor of this compound

(N-Methyl-N-nitriso-toluene-4-sulphonamide)is available commercially)

DiazomethyllithiumDiazomethylsodiumDicyanodiazomethaneDinitrodiazomethaneIsodiazomethaneMethyl diazoacetate

(g) Metal fulminatesCadmium fulminate


Table 7.9 Cont’d

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Table 7.9 Cont’d

Copper fulminateDimethylthallium fulminateDiphenylthallium fulminateMercury(II) methylnitrolateMercury(II) formhydroxamateMercury(II) fulminateSilver fulminateSodium fulminateThallium fulminate

(h) Nitro compounds(i) C-Nitro compounds4-Chloro-2,6,-dinitroaniline2-Chloro-3,5-dinitropyridineChloronitromethane1-Chloro-2,4,6-trinitrobenzene (picryl chloride)Dinitroacetonitrile2,4-DinitroanilineDinitroazomethane1,2-Dinitrobenzene1,3-Dinitrobenzene1,4-Dinitrobenzene2,4-Dinitrobenzenesulphenyl chloride3,5-Dinitrobenzoic acid3,5-Dinitrobenzoyl chloride2,6-Dinitrobenzyl bromide1,1-Dinitro-3-butene2,3-Dinitro-2-butene3,5-Dinitrochlorobenzene2,4-Dinitro-1-fluorobenzene2,6-Dinitro-4-perchlorylphenol2,5-Dinitrophenol2,4-Dinitrophenylacetyl chloride2,4-Dinotrophenylhydrazine2,4-Dinitrophenylhydrazinium perchlorate2,7-Dinitro-9-phenylphenanthridine2,4-Dinitrotoluene1-Fluoro-2,4-dinitrobenzene4-Hydroxy-3,5-dinitrobenzene arsonic acid1-Nitrobutane2-Nitrobutane1-Nitro-3-buteneNitrocellulose1-Nitro-3 (2,4-dinitrophenyl) urea Nitroethane2-NitroethanolNitroglycerineNitromethane1-Nitropropane2-Nitropropane5-NitrotetrazolePicric acid (2,4,6-trinitrophenol)Potassium-4,6-dinitrobenzofuroxan hydroxide


Potassium-3,5-dinitro-2(1-tetrazenyl) phenolatePotassium trinitromethanide (‘Nitroform’ salt)Sodium 5-dinitromethyltetrazolideTetranitromethaneTrichloronitromethane (chloropicrin)2,2,4-Trimethyldecahydroquinoline picrateTrinitroacetonitrile1,3,5-Trinitrobenzene2,4,6-Trinitrobenzenesulphonic acid

(picryl sulphonic acid)Trinitrobenzoic acid2,2,2-TrinitroethanolTrinitromethane2,4,6-Trinitrophenol (picric acid)2,4,6-Trinitroresorcinol2,4,6-Trinitrotoluene (TNT)2,4,6-Trinitro-m-xylene

(ii) N-Nitro compounds1-Amino-3-nitroguanidineAzo-N-nitroformamidine1,2-Bis(difluoroamino)N-nitroethylamineN,N’ Diacetyl-N,N’-dinitro-1,2-diaminoethaneN,N’ Dinitro-1,2-diaminoethaneN,N’ Dinitro-N-methyl-1,2-diaminoethane1-methyl-3-nitro-1-nitrosoguanidineNitric amide (nitramide)1-Nitro-3(2,4-dinitrophenyl) ureaNitroguanidineN-NitromethylamineNitroureaN,2,4,6-Tetranitro-N-methylaniline (tetryl)1,3,5,7-Tetranitroperhydro-1,3,5,7-tetrazocine

(iii) Ammonium nitrate

(i) Reactive vinyl monomersAcrylic acidAcrylonitrilen-Butyl acrylaten-Butyl methacrylate4-ChlorostyreneDivinyl benzeneDodecyl methacrylateEthyl acrylateEthylene dimethacrylate2-Hydroxypropyl methacrylateMethyl acrylateMethyl methacrylate$-Methyl styreneMethyl vinyl etherStyreneVinyl acetateVinyl bromide

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0 5 10 15 20 25Quantity of explosive (kg)










Table 7.10 Explosive effects of small quantities of high explosive in a 6 m " 6 m room

Quantity of explosive Effect

1 g Serious injury to a person holding the explosive10 g Very serious injury to a person close to the explosive

1% of persons at a distance of 1.5 m are also liable to ear-drum rupture100 g 50% of windows in room likely to be blown out

1% ear-drum rupture at 3.5 m50% ear-drum rupture at 1.5 mAlmost certain death of persons in very close proximity (e.g. holding the explosive)

500 g Complete structural collapse of brick-built building probableProbable survival of steel of concrete-framed buildingAlmost certain death of persons very close to blastPersons close to blast seriously injured by lung and hearing damage, fragmentation effects,

and from being thrown bodilyEar-drum rupture of almost all persons within the room

Figure 7.2 Diameter of fireball versus quantity of explosive

selection of the appropriate safety precautions. Propellant hazards are akin to those for pyrotechnicsexcept that confinement can lead to detonation.


Expert advice is required before handling any of these materials, many of which are governed bylegislation regulating, e.g., licensing of premises, use, storage, transportation, import/export, sale,labelling, disposal. Some general considerations are given in Table 7.12. Table 7.13 summarizesbasic precautions for work on a laboratory scale.

Disposal of explosive waste and the repair or dismantling of contaminated plant need extremecare. Table 7.14 provides guidance on techniques for disposal of the more commonly encounteredexplosives by experts at proper disposal sites. Collection of the waste should be in well labelled,distinctive, specially designed containers. Cleaning and decontamination of plant comprises removalof gross contamination under wet or solvent conditions using tools made of soft material, finalcleaning with solvent or chemical reagent, and finally ‘proving’ of the equipment by heating totemperatures exceeding those for decomposition of the contaminant. Repair work should be thesubject of a permit-to-work system (Chapter 13); it should be assumed that explosives may havepenetrated threads, joints and other crevices and bolts, flanges etc. These should be thoroughlydecontaminated prior to dismantling. Operatives should be suitably trained and protected.


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Table 7.11 Classification of pyrotechnics

Composition Behaviour Artefacts Characteristics

Group 1Chlorate and metal Burn very Flash shells (maroons) Mass explosion risk

perchlorate report or violently Casings containing flashwhistling compositions compositions

Dry non-gelatinized Sealed hail-preventingcellulose nitrates rockets

Barium peroxide/zirconiumcompositions

Group 2Nitrate/metal/sulphur Burn violently Large firework shells Accelerating

compositions Fuse unprotected signal single-itemCompositions with >65% flares explosions

chlorate Non-pressed report bulletsBlack powder (bird scarers)Nitrate/boron compositions Report cartridges

(unpacked)Black matches (uncovered)

Group 3Nitrate/metal compositions Burn fast Large firework shells Burn very

without sulphur Fuse protected signal flares violently withCompositions with <35–65% Pressed report cartridges in single-item

chlorate primary packagings explosionsCompositions with black Quickmatches in transport

powder packagingsLead oxide/silicon with >60% Waterfalls; Silver wheels;

lead oxides VolcanoesPerchlorate/metal Black powder delays

compositions other thanreport

Group 4Coloured smoke compositions Low/medium Large firework shells Single-itemWhite smoke compositions speed burning without flash ignitions/explosions

(except those in Group 5) compositions in transportCompositions with <35% packagings

chlorate Signal ammunition withoutThermite compositions flash compositions,Aluminium/phosphorus !40 g of composition

pesticide compositions Small fireworks, fuseprotected (exceptvolcanoes and silverwheels)

Group 5Slow burning/heating Burn slowly Small fireworks in primary Slow single-item

compositions packagings ignitions/explosionsWhite smoke compositions Signal ammunition in

based on hexachloroethane transport packagingwith zinc, zinc oxide and Delays without black<5% aluminium or <10% powdercalcium silicon Coloured smoke devices

Sealed table bombsWhite smoke devices

unpacked (see Group 5composition)

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Table 7.12 General considerations for work with explosive chemicals

Consult with experts on the hazards and on technical, administrative and legal requirements.The chance of accidental initiation is related to the energy imparted to the substance and the sensitivity of the compound.

Hence the sensitivity of compounds should be established (e.g. Table 7.15) before devising appropriate control measures.(Many sensitive explosives have ignition energies of 1–45 mJ, while some very sensitive materials have ignition energies<1 mJ.)

Depending on scale, specially designed facilities may be required, remote from other buildings, accessways or populatedareas. Remote handling procedures may be required (Figure 7.3), possibly with closed-circuit TV monitoring utilizingconcrete outbuildings or bunkers.

Consider fire protection, detection and suppression requirements (Chapter 6), and means of escape, alarms, etc.Minimize stocks and segregate from other chemicals and work areas. Where appropriate, keep samples dilute or damp and

avoid formation of large crystals when practicable. Add stabilizers if possible, e.g. to vinyl monomers. Store in specially-designed, well-labelled containers in ‘No Smoking’ areas, preferably in several small containers rather than one largecontainer. Where relevant, store in dark and under chilled conditions, except where this causes pure material to separatefrom stabilizer (e.g. acrylic acid).

Do not decant in store.Consider need for high/low temperature alarms for refrigerated storage; these should be inspected and tested regularly.Consider need for mitigatory measures (fire, blast, fragment-resistant barricades/screens), electrical and electrostatic safeguards,

personal protection, disposal etc.Stores and work areas should be designated ‘No Smoking’ areas and access controlled. Depending upon scale, explosion-

proof electrics and static elimination may be required.Deal with spillages immediately and make provisions for first aid.All staff should be adequately trained, and written procedures provided.

Table 7.15 gives selected methods for testing explosives.There is also a range of chemicals, sometimes termed ‘blowing agents’ (e.g. hydrazides) which

decompose at low temperature producing large volumes of gas such as nitrogen and steam.Examples are listed in Table 7.16. Equipment for such products requires special design and aknowledge is required of activators, decomposition rates and temperatures.

General principles for storage

The general principles for storage of chemicals, which follow from previous summaries, are listedin Table 7.17. Those for compressed gases are given in Chapter 9.

Hazards arising in chemicals processing

Some factors contributing to chemical process hazards are summarized in Chapter 6: the roles ofindividual chemicals can be assessed from the preceding part of this chapter.

Chemical reaction hazards

Examples of hazardous reactions are given in Table 7.18. Table 7.19 gives basic precautions inmonomer storage; Table 7.20 lists properties of common monomers.

Reaction characteristics

• Reaction in gas, liquid (neat or in solution suspension/emulsion) or solid phase.• Catalytic or non-catalytic.


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What is thelikelihood ofinitiation?

Negligible/low High

Highe.g. slurry andemulsion explosivesmanufacturing

Negligible/lowe.g. handling smallquantities of insensitiveexplosives

What is the potentialfor harm to operators?

Negligible/lowe.g. pyrotechniccompositions insmall quantities

Highe.g. NG blasting,explosivesmanufacture andpropellant pressing


Provide:Safe designSafe systemof workSupervisionMonitoring


Provide:Safe systemof workSafeguards (eyeprotection asminimum)Against explosion:Hand/wrist protectionHeat protectionSafety screensAgainst fireball:Fire-protectivegloves/clothingHead/face protectionSafety screens


Processnot running


Preventaccess toprocess area Provide:

Protectiveclothing (ifappropriate)for access toprocess areae.g. while loading‘carpet rolls’ ofpropellant intopresses

What is the potentialfor harm to operators?

Figure 7.3 Remote versus non-remote manufacturing requirements and fire/explosion safeguards

• Exothermic, endothermic, or negligible heat loss/gain.• Reversible or irreversible.• First or second order or complex kinetics.

Reactors may be operated batchwise or continuously, e.g. in tubular, tubes in shell (with orwithout internal catalyst beds), continuous stirred tank or fluidized bed reactors. Continuousreactors generally offer the advantage of low materials inventory and reduced variation of operatingparameters. Recycle of reactants, products or of diluent is often used with continuous reactors,possibly in conjunction with an external heat exchanger.

Adequate heat removal facilities are generally important when controlling the progress ofexothermic chemical reactions. Common causes of thermal runaway in reactors or storage tanksare shown in Figure 7.4. A runaway reaction is most likely to occur if all the reactants are initiallymixed together with any catalyst in a batch reactor where heat is supplied to start the reaction.

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Chemical engineering operations

Many chemical engineering unit operations may be linked together in chemical processing. Thecommonest are:

Fluid mechanics

Pumping of liquids. Compression of gasesMixing (solids, liquids, gases; possibly multiphase)Atomization, dispersion

Table 7.13 Precautions for handling explosives in the laboratory

StorageThe quantities of potentially explosive materials in store and in use should be strictly limited.Stores should be specially designed, constructed of non-combustible material, and located away from other hazards (e.g.

brick ‘coal bunkers’ are suitable for small samples, but purpose-built constructions with explosion-proof lights etc. arerequired for larger quantities). They should be designated ‘No Smoking’ areas and be well labelled.

Stores should be used exclusively for these materials. Other combustible material such as fabric, paper, organic solventsshould not be stored there.

Generally the substances in this class are unstable when heated or exposed to light; they should be stored cool and in thedark. However, for liquids with added stabilizer cooling may cause separation of the material from the stabilizer.Similarly, precipitation of a potentially explosive compound from a diluent may occur on cooling. In both cases this canrepresent a hazardous situation.

Stores should be ventilated and sound, e.g. no cracks in floors, no rusty window frames, no water seepages, etc.Stores should be clean, tidy and locked. Contamination must be avoided and a high standard of housekeeping maintained.Heat sources should not be permitted nearby.Material should be purchased in several small containers rather than one large container and always stored in original

containers. Integrity of the labels should be checked.

UseUse must be restricted to experienced workers, aware of the hazards and the necessary precautions.Records of usage should be kept and stock rotated. Old material should be disposed of.Work should be on a scale of <0.5 g for novel but potentially explosive material until the hazards have been fully evaluated

and <5 g for established, commercially available, substances such as peroxide free-radical initiators.For the above scales, eye protection should be worn and work should be undertaken in a standard fume-cupboard behind

a well-anchored polycarbonate screen. It is advisable to wear a protective apron and hand protection; whether leathergauntlets or tongs should be used will be dictated by circ*mstances. Such measures are recommended but it should beensured that they do not precipitate a hazard as a result of loss of tactile sensitivity (e.g. dropping a flask, overtighteningclamps, exerting excessive pressure when assembling apparatus). The material of gloves needs consideration. (PVC butnot rubber is suitable for tert-butyl peroxide.)

For large-scale work, armour-plated fume cupboards are likely to be required.Skin contact, inhalation and ingestion must be avoided. Splashes in eyes or on skin should be washed away immediately with

copious quantities of water. Medical attention should be sought. If material is swallowed, medical aid is requiredimmediately.

Glass apparatus should be pickled (e.g. in nitric acid) and thoroughly rinsed after use.Sources of ignition such as hot surfaces, naked flames etc. must be avoided and smoking prohibited where explosives are

used. Accidental application of mechanical energy should be avoided (e.g. material should not be trapped in ground-glassjoints): seized stoppers, taps etc. must not be freed by the application of force. To minimize risk of static electricity,laboratory coats of natural fibre rather than synthetic fabrics are preferred. It is important to neutralize any spillage on thecoat immediately, since delay could result in the impregnated garment becoming a fire hazard.

To prevent glass fragments from flying in the event of an explosion, use should be made of metal gauzes to screen reactionflasks etc., or cages, e.g. for desiccators. Vessels of awkward size/shape may be covered with cling film.

Whenever possible a stabilizer or diluent should be used and separation of the pure material should be avoided.Any waste material (and contaminated cloths, tissues, clothing etc.) must be rendered safe by chemical means or by

controlled incineration of dilute solution where practical prior to disposal.In the event of fire, the area should be evacuated, the alarm raised and the fire brigade summoned. Only if it is clearly safe

to do so should the fire be tackled with an appropriate extinguisher.


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Table 7.14 Suggested methods of disposal for commonly encountered explosives

Burn Detone Dissolve Chemical Drowning

NG-based blasting explosive yes yes no no yesANFO yes yes yes no yesPyrotechnic compositions yes no yes no yesBlack powder yes no yes no yesDetonators yes yes no no noDetonating cord yes yes no no noNitroglycerine yes no no yes noSlurry explosive yes yes yes no yesContaminated paper waste yes no no no noFireworks (finished) yes no no no noInitiatory explosives no yes no yes noPropellants yes no no no noNon-NG-based

blasting explosives yes yes no no yesShotgun cartridges yes no no no noSporting/small arms ammunition yes no no no no

Table 7.15 Methods for testing explosives

Flame test A few crystals (or drop of solution) are heated in the non-luminous flame of a Bunsen burner.Melting with quiet burning is at one end of the spectrum; cracking, flashing-off or flaringare considered hazardous.

Impact Impact sensitivity can be gauged by striking a few crystals of the compound on a metal lastwith the ball of a ball-pein hammer. Ignition, smoking, cracking or other sign of decompositionare considered hazardous.

Differential If the decomposition reaction follows the general rate law, the activation energy,scanning heat of decomposition, rate constant and half-life for any given temperature cancalorimetry be obtained on a few milligrams using the ASTM method. Hazard indicators

Differential thermal include heats of decomposition in excess of 0.3 kcal/g, short half-lives, lowanalysis activation energies and low exotherm onset temperatures, especially if heat of

Hot stage decomposition is considerable.microscope The DTA or hot-stage microscope can be used under ignition conditions to obtain an

ignition temperature. The nature of the decomposition can also be observed at a range oftemperatures. Observations such as decomposition with evolution of gases prior to ignitionare regarded as potentially hazardous.

Bomb calorimetry Use of oxygen and an inert gas enables the heat of combustion and the heat of decompositionto be evaluated respectively.

Deflagration A melting point test has been described for diazo compounds. The first 1 mm of a melting-point tube filled with c. 10 mg of test compound is inserted in a melting-point apparatusheated at 270°C. Once decomposition starts, the tube is removed. The decompositionrapidly propagates through the entire mass for unstable diazo compounds; no such propagationis reported for stable versions.

Heat transfer

Convective heat exchange, natural or forcedRadiant heat transfer, e.g. furnacesEvaporation, e.g. in evaporatorsCondensation, e.g. in shell and tube heat exchangesHeat transfer to boiling liquids, e.g. in vaporizers, boilers, re-boilers

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Mass transfer operations (in which a material is transferred across aphase boundary or interface)

Distillation, either batchwise or continuousLiquid–liquid extraction (solvent extraction)Solid–liquid extraction (leaching)Gas absorption, scrubbing; desorption, strippingHumidification and water coolingDehumidification and air conditioningDrying of solids, solutions/slurriesAdsorption (in which a gas or liquid is taken up on a solid, e.g. activated charcoal, molecular

sieves)CrystallizationLess common means of separation, e.g. dialysis, ion-exchange, osmosis, chromatography,


Non-mass transfer operations

Filtration of suspensions, e.g. in filter presses, rotary vacuum filtersSedimentation, gravity settlingCentrifugation, for immiscible liquid or solid separation and recoveryClassification by sieving, screeningSize reduction, e.g. milling, crushing, grinding

Table 7.16 Substances with a high rate of decomposition

These substances decompose rapidly to produce large volumes of gas. They are substances not classified as deflagrating ordetonating explosives but exhibit violent decomposition when subject to heat.Material Trauzel lead Combustion properties

block value(cm3/g)

1:8, Bis (dinitrophenoxy)4,5-dinitro anthraquinone 18.5100% Dinitrosopentamethylene tetramine 18.52,4-Dinitroaniline 17.52-Amino-3,5-dinitrothiophene 13–17.51:5 Bis (dinitrophenoxyl) 4:8-dinitro anthraquinone 10.5 Combustion propagates fully and2-formylamino-3,5-dinitrothiophene 8 fast with flame2-acetyl-amino-3,5-dinitrothiophene 72-anisidine nitrate 680% DNPT 2.5

6-nitro-1-diazo-2-naphthol-sulphonic acid 5 Combustion propagates fully andfast by smouldering

Ammonium nitrate 232-bromo-4,6-dinitroaniline 17.5 Local decomposition – no6-bromo-2,4-dinitroaniline 17 propagation of the2-chloro-4,6-dinitroaniline 16.5 decomposition

This substance exhibits a high rate of decomposition without combustion when exposed to heat and certain initiators.Material Decomposition Property


P,P’-oxybis (benzenesulphonyl hydrazide) 150°C Decomposes and propagates










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Table 7.17 General principles for chemical storage

• Store minimum quantities• Control stock, i.e. first-in/first-out, move redundant stock• Segregate chemicals, e.g. from water, air, incompatible chemicals, sources of heat, ignition sources• Segregate ‘empties’, e.g. cylinders, sacks, drums, bottles• Monitor stock, e.g. temperature, pressure, reaction, inhibitor content, degradation of substance, deterioration of packaging

or containers/corrosion, leakages, condition of label, expiry date, undesirable by-products (e.g. peroxides in ethers)• Spillage control; bund, spray, blanket, containment. Drain to collection pit• Decontamination and first-aid provisions, e.g. neutralize/destroy, fire-fighting• Contain/vent pressure generated to a safe area• Store in ‘safest’ form, e.g. as pre-polymers, as chemical for generation of requirements (e.g. hypochlorites for chlorine) in

dilute form• Handle solids as prills or pellets rather than powders to minimize the possibility of dust formation• Split-up stocks into manageable lots, e.g. with reference to fire loading/spillage control. Limit stack heights; generally

chemicals should be stored off the ground (e.g. to facilitate cleaning, to keep above any ingress of water in the event offlooding)

• Select correct materials of construction; allow for reduction in resistance due to dilution/concentration, presence ofimpurities, catalytic effects

• Transport infrequently to minimize stocks for both safety and to reduce costs and environmental hazards arising from theneed to dispose of surplus or expired material

• Ensure appropriate levels of security, hazard warning notices, fences, patrols. Control access including vehicles• Segregate/seal drains• Appropriate gas/vapour/fume/pressure venting, e.g. flame arrestors, scrubbers, absorbers, stacks• Ensure adequate natural or forced general ventilation of the storage area• Provide adequate, safe lighting• Label (name and number); identify loading/unloading/transfer couplings• Facilitate sampling (for quality assurance and stock monitoring)• Provide appropriate fire protection (sprinkler, dry powder, gas)• Consider spacings from buildings, road, fence• Ensure adequate access for both normal and emergency purposes with alternative routes• Protect from vehicle impact, e.g. by bollards• Assign responsibility for administration, maintenance, cleaning and general housekeeping

Gas cleaning by filtration, demisting, electrostatic precipitation, wet collection of particulates,cyclonic separation.

Dependent upon the chemicals in-process, each of these may introduce a range of hazards, e.g.chemical, flammable or mechanical. These must be checked in every case. Safety features whichmay be required are summarized in Table 7.21.

Common reaction rate v. temperature characteristics for reactions are illustrated in Figure 7.5.To avoid runaway conditions (Fig. 7.5a) or an explosion (Figure 7.5c), control may involve:

• Use of dilute solutions, emulsions, or suspensions.• Feeding one reactant in at a controlled rate depending upon reactant’s temperature.• Refluxing of solvent from a condenser.• Imposing a limit on reactor size, to ensure adequate heat transfer area per unit volume.• Careful selection of reactant and coolant temperature.• Provision of efficient agitation.

Mitigation of a runaway reaction may involve:

• Emergency cooling.• Dumping of reactants into an empty vessel or one containing a compatible quenching liquid.

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Table 7.18 Characteristics of some different types of reaction

Oxidation Feedstocks generally hydrocarbonsHazard of fire/explosion arises from contact of flammable material with oxygenReactions highly exothermic: equilibrium favours complete reaction

Polymerization Exothermic reaction which, unless carefully controlled, can run-away and create a thermalexplosion or vessel overpressurization

Refer to Table 7.20 for common monomersCertain processes require polymerization of feedstock at high pressure, with associated

hazardsMany vinyl monomers (e.g. vinyl chloride, acrylonitrile) pose a chronic toxicity hazardRefer to Table 7.19 for basic precautions

Halogenation The commercially important halogens are chlorine, bromine, fluorine, iodine. Refer to Table5.19 for properties

All are highly toxicReactions are highly exothermic and chain reactions can occur, which may result in detonation

Hydroprocesses Hydrogen is chemically stable and relatively unreactive at ordinary temperatures; mostprocesses utilizing it require a catalyst. Above 500°C it reacts readily with oxygen andconfined flammable mixtures explode violently if ignited

Main hazards: fire, explosion, metallurgical problems arising from hydrogen attack

Nitration Hazards arise from the strong oxidizing nature of the nitrating agents used (e.g. mixture ofnitric and sulphuric acids) and from the explosive characteristics of some end products

Reactions and side reactions involving oxidation are highly exothermic and may occurrapidly

Sensitive temperature control is essential to avoid run-away

Alkylation Hazards arise from the alkylating agents, e.g. dimethyl sulphate (suspected human carcinogen),hydrogen fluoride (highly toxic irritant gas)

Thermal alkylation processes require higher temperatures and pressures, with associatedproblems

High pressure reactions High inventories of stored pressure (e.g. in pressurized reactors or associated plant) canresult in catastrophic failure of the pressure shell

Table 7.19 Basic precautions in monomer storage

IndoorsCool, well-ventilated areaNon-combustible constructionSegregated from other flammables/reactants

OutdoorsWell-spaced tanks, possibly with water cooling, refrigeration, buriedSome monomers (e.g. acrylic acid) may require provisions to avoid freezingProvision for inhibitor/stabilizer additionProvision for atmosphere inerting may be required

• Venting to a knock-out vessel, to remove non-gaseous substances. (This may be followed by ascrubbing unit for gases or a flare-stack.)

The kinetics and thermodynamics of the reaction, and of possible side reactions, need to be understood. The explosive potential of chemicals liable to exothermic reaction should be carefullyappraised.

A thorough assessment should be made before undertaking:


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Table 7.20 Properties of common monomers

Flash Ignition Flammable Specific Vapour Boiling Propertiespoint temp. limits gravity density point(°C) (°C) (% by vol. (Water (Air = 1.0) (°C)

in air) = 1.0)

Acetaldehyde –38 185 4.0–55.0 0.8 1.5 21 Colourless fuming liquid(Acetic aldehyde, Pungent odourethanal) IrritantCH3CHO Water soluble

Can polymerizeexothermically, formexplosive peroxides, orreact violently with otherchemicals

Acrolein –26 278 2.8–31.0 0.8 1.9 53 Colourless/yellow liquid(Allyl aldehyde, Pungent unpleasant odourpropenal) Water solubleCH2:CHCHO Irritant

Can polymerizeexothermically withstrong alkalis, heat or light

Can form peroxidesAcrylic acid 54 – – 1.1 2.5 140 Colourless, water soluble(Propenoic acid, liquidpropene acid) Freezing point 14°CCH2:CHCOOH Polymerizes readily with

oxygenMust be inhibited

Acrylonitrile 0 481 3.0–17.0 0.8 1.8 77 Colourless, partially water(Vinyl cyanide, soluble liquidpropenenitrile) Experimental carcinogenCH2:CHCN Polymerizes violently with

organic peroxides orconcentrated causticalkalis

Highly toxicUsually inhibited

1,3-Butadiene –76 450 2.0–11.5 0.6 1.9 –4 Colourless, odourless(Butadiene, liquefiable gasvinylethylene) Polymerizes readily,CH2:CHCH:CH2 particularly if O2 or

traces of catalyst presentCan form explosive peroxidesNormally contains inhibitor

(liquid phase) andantioxidant

Epichlorhydrin 32 – – 1.2 3.3 115 Colourless, partly water(Chloropropylene soluble liquidoxide) Highly toxicCH2:OCHCH2Cl Polymerizes exothermically

with acids, bases, certainsalts and catalysts

Can react with waterEthyl acrylate 15 – 1.8–– 1.2 – 100 Colourless liquidCH2:CHCOOC2H5 Acrid odour

Polymerizes readily,accelerated by heat, light,organic peroxides


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Ethylene oxide <–18 429 3.0–100 0.9 1.5 11 Colourless gas at roomCH2:CH2 temperature

Irritant to eyes and O respiratory tract, and an

experimental carcinogenPolymerizes uncontrollably

with immense explosiveforce on contact withcertain chemicals (e.g.ammonia)

Formaldehyde gas 430 7.0–73.0 – 1.1 –21 Colourless(Oxymethylene) Water soluble gas producingHCHO formalin solutions

Suffocating odourPolymerizes readilyHighly toxicRespiratory sensitizer

Methacrylic acid 77 – – – – 158 Colourless, water solubleCH2:C(CH3)COOH liquid

Polymerizes readily unlessinhibited or stored <15°C

IrritantMethyl acrylate –3 – 2.8–25.0 1.0 3.0 80 Colourless liquidCH2:CHCOOCH3 Acrid odour

Extremely irritating torespiratory system, skinand mucous membranes

Methyl methacrylate 29 – 2.1–12.5 0.9 3.4 101 Colourless liquidCH2:C(CH3)COOCH3 Acrid odourStyrene 32 490 1.1–6.1 0.9 3.6 145 Colourless/oily yellow liquid(Vinyl benzene) Penetrating odourC6H5CH:CH2 Polymerizes slowly in air or

light, accelerated by heator catalysts

Ignition/explosion possibleUsually inhibitedStore <21°C

Vinyl acetate –8 427 2.6–13.4 1.1 3.0 72 Colourless, partially waterCH3COOCH:CH2 soluble liquid

Faint odourPolymerizes with heat or

organic peroxidesVinyl chloride –78 472 4.0–22.0 1.0 2.1 –14 Colourless, sweet smelling(Chloroethene) liquefiable gasCH2:CHCl Polymerizes with light, heat,

air or catalystsNormally inhibitedHuman carcinogen

Vinylidene chloride –10 458 5.6–11.4 1.3 3.3 37 Colourless volatile liquid(Dichloroethylene-1,1) Polymerizes unless inhibitedCH2:CCl2 Decomposes at 457°C


Table 7.20 Cont’d

Flash Ignition Flammable Specific Vapour Boiling Propertiespoint temp. limits gravity density point(°C) (°C) (% by vol. (Water (Air = 1.0) (°C)

in air) = 1.0)

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(a) (b) (c)

(d) (e) (f)

Temperature Temperature Temperature

Temperature Temperature Temperature



n ra





Incorrect kineticassumptions

Incorrect initiation

Insufficient mixing

Temperature too low

Impurities (inhibitors)

Feed rate too fast

Accumulation ofreactants orintermediates


Emergency loss ofcooling, stirring

Impurities (catalysts)that accelerate rate

Incorrect assumptionson heat balance

Temperature of heattransfer fluid too high

Storage temperature too high

Triggering ofundesired reaction


Heat accumulation,uncontrollabletemperature rise

Thermal runaway

Figure 7.4 Common causes of thermal runaway in reactors or storage tanks

Figure 7.5 Types of reaction rate/temperature curvea Rapid increase with temperature – normal characteristicb Slow increase in rate with temperature – characteristic of some heterogeneous reactionsc Very rapid increase at one point – the ignition point in an explosiond Decrease in rate at higher temperature – characteristic of catalytic reactionse Decrease in rate at intermediate temperatures, followed by an increasef Slow decrease in rate with temperature

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Table 7.21 Safety features in chemical engineering operations

Inventory Reduce inventory of chemicals:Continuous operation may be preferable to batchLow residence time contacting equipment may be better than cheaper alternativesetc.

Monitoring Monitor temperature, pressure flow, composition, freedom from contamination and otherappropriate properties of all streams where relevant. Consider automatic control

Isolation Provide for isolation from upstream and downstream operations. Consider provision ofautomatic and/or remotely operated isolation. Consider isolation for cleaning needs

Contaminants Provide measures to remove unacceptable contaminants from feed materials, processstreams and services, e.g. entrained liquid, tramp metal, unwanted particulate solids

Pressure/temperature Operate at moderate temperature and pressure where possible. Avoid superheatedliquids, which will flash-off, if practicable

Allow for effects of over-/under-temperature, over-/under-pressure. Following assessment(e.g. by HAZOP)

Continuous flow With continuous flow operations consider (e.g. using a HAZOP procedure) the effects of:No flowReduced flowReverse flowIncreased flowContaminated flowFlow of a substituted material, etc.

Start-up/shutdown Provide for safe start-up, including purging if necessaryProvide for safe shutdown:

NormalBy a tripOn standbyIn various emergency situations, etc.

Instrumentation Provide safety instrumentation in addition to process instrumentationConsider high–high and low–low alarms. Consider automatic activation of emergency

responses, e.g. venting, emergency cooling, recycling, discharge of liquid streams,shutdownHigh/low temperature


linked to trips for automatic operation where appropriateProtective features Provide protective as well as control features, e.g. pressure and vacuum relief, explosion

suppression relief, advance inerting, containmentWaste streams Cater for routine and emergency, safe discharge of all waste streams, e.g. atmospheric

venting, possibly after treatment, discharge of liquid effluents including out-of-specificationstreams, discharges of particulate or bulk solids

Common-mode failure Avoid common-mode failure possibilities with services, control systems, safety systemsetc.

• Scale-up (since it may result in a decrease in heat transfer capacity per unit mass of reactant).• Modifications in reactor geometry, agitation and control (e.g. instrumentation, cooling, venting).• Changes in reaction materials, (e.g. source, purity, concentration), diluents, catalysts charging

procedures.• Changes in operating conditions.

The characteristics of some potentially hazardous reactions are summarized in Tables 7.18 and7.22.

Many processes require equipment designed to rigid specifications together with automaticcontrol and safety devices. Consideration should be given to the control, and limitation of theeffects, of equipment malfunction or maloperation including:


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Table 7.22 Hazard rating of chemical reactions

Reaction Degree of Reaction Degree ofhazard hazard

ReductionClemmensen DSodium-amalgam DZinc–acetic acid EZinc–hydrochloric acid EZinc–sodium hydroxide EFerrous ammonium sulphate ELead tetraacetate EMeerwein–Pondorff DLithium aluminium hydride BDialkyl aluminium hydride BRosenmund ACatalytic high pressure ACatalytic low pressure B

OxidationHydrogen peroxide – dilute aqueous EAir or I2 (mercaptan to

disulphide) DOppenauer DSelenium dioxide DAqueous solution nitric acid,

permanganate, manganicdioxide, chromic acid,dichromate E

Electrolytic BChromyl chloride COzonolysis ANitrous acids APeracids – low molecular

weight or two or morepositive groups A

Peracids – high molecularweight B

t-Butyl hypochlorite CChlorine C


Alkali metal CAlkali metal alcoholate DAlkali metal amides and hydrides CReformatsky EMichael EGrignard BOrganometallics, such as

dialkyl zinc or cadmium–alkyl or aryl lithium B

Alkali acetylides ADiels–Alder DArndt–Eistert ADiazoalkane and aldehyde AAldehydes or ketones and

hydrogen cyanide C

Carbon–oxygenWilliamson D

Formaldehyde – hydrochloricacid E

Ethylene oxide CDialkyl sulphate DDiazoalkane A

Carbon–nitrogenCyanomethylation CChloromethylation DEthylenimine CEthylene oxide CQuaternization D

CondensationErlenmeyer DPerkin DAcetoacetic ester DAldol DClaisen DKnoevenagel DCondensations using catalysts

such as phosphoric acid;AlCl3; KHSO4; SnCl4;H2SO4; ZnCl2 NaHSO2;POCl2; HCl; FeCl2 E

Acyloin CDiketones with hydrogen sulphide CDiketones with diamines)

quinazolines DDiketones with NH2OH)

isoxazolines DDiketones with NH2NH2)

pyrazoles CDiketones with semicarbazide

) pyrazoles DDiketones with ammonia)pyrazoles DCarbon disuphide with

aminoacetamide)thiazolone ANitriles and ethylene diamines

) imidazolines DAminationLiquid ammonia BAqueous ammonia EAlkali amides C

EsterificationInorganic EAlkoxy magnesium halides BOrganic:

Alcohol and acids or acidchloride or acid anhydride DAlkyl halide and silver salts of

acids EAlkyl sulphate and alkalimetal salt of acid DAlkyl chlorosulphates and

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alkali salts of carboxylic acid DEster-exchange DCarboxylic acid and diazomethane A

Acetylene and carboxylicacid-vinyl ester A

Hydrolysis, aqueous nitriles,esters E

Simple metathetical replacement D

Preparation and reaction ofperoxides and peracidsConcentrated ADilute D

PyrolysisAtmospheric pressure DPressure B

Schmidt B

Mannich D

HalogenationSO2X2, SOX2, SX, POX2, PX5 DHX DCl2, Br2 C

NitrationDilute DConcentrated B

Named reactions

Aldol reaction is the condensation of an aldehyde to produce longer-chain hydroxy aldehydes


3 2* )* +Arndt-Eistert reaction is used to convert an acid compound into the next higher hom*ologue by reaction with diazomethane

RCOCl + 2CH2N2 *) R · COCH2CO2H + 2N2 + CH3Cl

Claisen reaction is the condensation of benzaldehyde with aliphatic aldehydes and ketones containing $-hydrogen


6 5 2* )** +

C H CHO + CH COCH C H CH==CH CO CH + H O6 5 3 3

6 5 3 2* )* + +

Clemmensen reaction is the reduction of carbonyl compounds with amalgamated zinc and concentrated hydrochloric acid

R CO R RCH ReiH+2+ + * )*

Diels-Alder is the preparation of cyclic olefins from dienes and a dienophile

HazardousA Highly flammable

Develops high pressure instantlyHighly toxic

SpecialB Flammable, perhaps explosive, mixtures formC Flammable, or generates toxic ubstances

ConventionalD Slightly flammable

Generates or uses mildly toxicsubstances

E Non-flammableDoes not use or generate toxic



Table 7.22 Hazard rating of chemical reactions

Reaction Degree Reaction Degreeof ofhazard hazard























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Erlenmeyer reaction is the condensation of aromatic aldehydes with hippuric acid to form azlactones (important intermediatesin the preparation of amino- and keto-acids)







Grignard reaction is the use of alkyl magnesium halides to form a host of products by reaction with a variety of chemicals

RMgX + H2O *) RH + Mg(OH) · X

RMgX + R#OH *) RH + Mg(OR#) · XRMgX + NH3 *) RH + Mg(NH2) · X

RMgX + RN=C *) R—N(MgX)=CR + R—N=C(R)MgX

Knoevenagel reaction is the synthesis of $, ,-unsaturated acids by reaction of aldehydes and compounds with activemethylene groups in the presence of an organic base

RCHO + CH (CO C H ) R CH==C(CO C H ) + H O2 2 2 5

base 2 2 5 2 2* )* +



150–2002 2+ + . *** +°

Mannich reaction is the condensation between formaldehyde, ammonia, or a primary or secondary amine (preferably as thehydrochloride), and a compound containing at least one active hydrogen atom


CH NH HCl + H O2 4



2 2 2+ *)* +Meerwein-Pondorff reduction is the synthesis of alcohols by heating carbonyl compounds with aluminium isopropoxide inisopropanol and distilling off acetone by-product

R2C=O + (CH3)2CHOAl3 *) R2CHO Al3 + CH3CO CH3 *) R2CHOH

Michael condensation is the addition of a compound with an active methylene group to an $, ,-unsaturated keto-compound

CH (CO C H ) + (CH ) C==CH CO CH (CH ) C


CH COCH + C H O2 2 2 5 2 3 2 3C H O

3 2|

2 2 5

2 3 2 5–2 5

* )**

Oppenauer reaction is oxidation of secondary alcohols to ketones using aluminium t-butoxide

RCH(OH)R + CH COCH RCOR + CH CH(OH)CH3 3catalyst

3 3# * )** #Perkin condensation is the reaction between aromatic aldehydes and aliphatic acid anhydrides (in the presence of thesodium salt) to form ,-arylacrylic acid

C H CHO + (CH CO) O C H CH== CH CO H6 5 3 2CH CO Na

6 5 23 2* )****

Reformatsky reaction is the formation of ,-hydroxyesters by reaction of $-bromoacid ester and a carbonyl compound,usually in the presence of zinc

# * )* #R CO + RCH(Br)CO C H R C(OH)CHR CO C H2 2 2 5Zn

2 2 5

Rosenmund reaction is the action between acid chloride and hydrogen in the presence of palladium catalyst to producealdehydes

RCOCl + H R CHO + HCl2 Pd*)* +

Schmidt reaction is the reaction between carbonyl compounds and hydrazoic acid in the presence of e.g. concentratedsulphuric acid



2+ + * )** +

Williamson reaction is the synthesis of ethers by action of heat on a mixture of alkyl haldie and sodium or potassium alkoxide

ROK + R#X ) ROR# + KX

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• Stirrer failure, mechanical or electrical.• Attainment of abnormal reaction conditions, e.g. overpressure, over-temperature, segregation

of reactants, excessive reaction rate, initiation of side reactions.• Power failure, affecting agitator, pumps, instruments.• Error in valve, switch or associated equipment operation.• Failure to actuate agitation at the proper time.• Instrument failure, pressure, flow, temperature, level or a reaction parameter, e.g. concentration.• Failure of instrument air or electricity.• Loss of inert gas blanket.• Failure of relief devices, e.g. pressure relief valves or rupture discs.• Failure of coolant, refrigerant, or other utilities.• Failure of high or low pressure alarms or cut-outs.• Addition of wrong material or wrong quantities.• Addition of materials in incorrect sequence.• Failure to add material, e.g. short-stop or inhibitor, at correct stage.• Spillage of material.• Improper venting to atmosphere, i.e. other than via vents with flame arresters or scrubbers, or

via a knockout drum, or to the correct flare systems.• Restricted or blocked vent.• Restricted material flows in or out.• Leakage of materials out, e.g. due to a gasket failure, or air in.


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Cryogenics, or low-temperature technology, is the science of producing and maintaining very lowtemperatures usually below 120 K, as distinct from traditional refrigeration which covers thetemperature range 120 to 273.1 K. At or below 120 K, the permanent gases including argon,helium, hydrogen, methane, oxygen and nitrogen can be liquefied at ambient pressure as exemplifiedby Table 8.1. Any object may be cooled to low temperatures by placing it in thermal contact witha suitable liquefied gas held at constant pressure. Applications can be found in food processing,rocket propulsion, microbiology, electronics, medicine, metal working and general laboratoryoperations. Cryogenic technology has also been used to produce low-cost, high-purity gasesthrough fractional condensation and distillation. Cryogens are used to enhance the speed ofcomputers and in magnetic resonance imaging to cool high conductivity magnets for non-intrusivebody diagnostics. Low-temperature infrared detectors are used in astronomical telescopes.

Table 8.1 Properties of common cryogens

Gas Boiling point Volume of gas produced on evaporation(°C) of 1 litre of liquid (litres)

Helium – 269 757Hydrogen – 253 851Neon – 246 1438Nitrogen – 196 696Fluorine – 187 888Argon – 186 847Oxygen – 183 860Methane – 161 578Krypton – 151 700Xenon – 109 573Chlorotrifluoromethane – 81 –Carbon dioxide – 78.5 553

Every gas has a critical temperature above which it cannot be liquefied by application ofpressure alone (Chapter 4). As a result, gases used, e.g., as an inert medium to reduce oxygencontent of atmospheres containing flammable gas or vapour (Chapter 6) are often shipped andstored as cryogenic liquid for convenience and economy.

In the laboratory, a range of ‘slush baths’ may be used for speciality work. These are preparedby cooling organic liquids to their melting points by the addition of liquid nitrogen. Commonexamples are given in Table 8.2. Unless strict handling precautions are instituted, it is advisableto replace the more toxic and flammable solvents by safer alternatives.

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Table 8.2 Working temperatures of cryogenic slush baths

Bath liquid Temperature(°C)

Carbon tetrachloride – 23Chlorobenzene – 45Solid carbon dioxide – 63

in acetone or methylated spirits(1) – 78Toluene – 95Carbon disulphide – 112Diethyl ether – 120Petroleum ether – 140

(1)Liquid nitrogen is omitted from this mixture and the solvent is used to improve the heat transfer characteristics of cardice.

Typical insulating materials include purged rockwool or perlite, rigid foam such as foam-glassor urethane, or vacuum. However, because perfect insulation is not possible heat leakage occursand the liquefied gas eventually boils away. Uncontrolled release of a cryogen from storage orduring handling must be carefully considered at the design stage. The main hazards with cryogensstem from:

• The low temperature which, if the materials come into contact with the body, can cause severetissue burns. Flesh may stick fast to cold uninsulated pipes or vessels and tear on attemptingto withdraw it. The low temperatures may also cause failure of service materials due toembrittlement; metals can become sensitive to fracture by shock.

• Asphyxiation (except with oxygen) if the cryogen evaporates in a confined space.• The very large vapour-to-liquid ratios (Table 8.1) so that a large cloud, with fog, results from

loss of liquid.• Catastrophic failure of containers as cryogen evaporates to cause pressure build-up within the

vessel beyond its safe working pressure (e.g. pressures !280 000 kPa or 40 600 psi can developwhen liquid nitrogen is heated to ambient temperature in a confined space).

• Flammability (e.g. hydrogen, acetylene, methane), toxicity (e.g. carbon dioxide, fluorine), orchemical reactivity (fluorine, oxygen).

• Trace impurities in the feed streams can lead to combination of an oxidant with a flammablematerial (e.g. acetylene in liquid oxygen, solid oxygen in liquid hydrogen) and precautionsmust be taken to eliminate them.

• Several materials react with pure oxygen so care in selection of materials in contact withoxygen including cleaning agents is crucial.

Key precautions are given in Table 8.3.

The cryogens encountered in greatest volume include oxygen, nitrogen, argon and carbondioxide. Their physical properties are summarized in Table 8.4.

Liquid oxygen

Liquid oxygen is pale blue, slightly heavier than water, magnetic, non-flammable and does notproduce toxic or irritating vapours. On contact with reducing agents, liquid oxygen can causeexplosions.


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Gaseous oxygen is colourless, odourless and tasteless. It does not burn but supports combustionof most elements. Thus upon vaporization liquid oxygen can produce an atmosphere whichenhances fire risk; flammability limits of flammable gases and vapours are widened and fires burnwith greater vigour. It may cause certain substances normally considered to be non-combustible,e.g. carbon steel, to inflame. In addition to the general precautions set out in Table 8.3, thefollowing are also relevant to the prevention of fires and explosions:

• Prohibit smoking or other means of ignition in the area.• Avoid contact with flammable materials (including solvents, paper, oil, grease, wood, clothing)

and reducing agents. Thus oil or grease must not be used on oxygen equipment.• Purge oxygen equipment with oil-free nitrogen or oil-free air prior to repairs.• Post warning signs.• In the event of fire, evacuate the area and if possible shut off oxygen supply. Extinguish with

Table 8.3 General precautions with cryogenic materials

Obtain authoritative advice from the supplier.

Select storage/service materials and joints with care, allowing for the reduction in ductility at cryogenic temperatures.Provide special relief devices as appropriate.

Materials of construction must be scrupulously clean, free of grease etc.Use only labelled, insulated containers designed for cryogens, i.e. capable of withstanding rapid changes and extreme

differences in temperature, and fill them slowly to minimize thermal shock.Keep capped when not in use and check venting.Glass Dewar flasks for small-scale storage should be in metal containers, and any exposed glass taped to prevent glass

fragments flying in the event of fracture/implosion.Large-scale storage containers are usually of metal and equipped with pressure-relief systems.

In the event of faults developing (as indicated by high boil-off rates or external frost), cease using the equipment.

Provide a high level of general ventilation taking note of density and volume of gas likely to develop: initially gases willslump, while those less dense than air (e.g. hydrogen, helium) will eventually rise.

Do not dispose of liquid in a confined area.

Prevent contamination of fuel by oxidant gases/liquids.

With flammable gases, eliminate all ignition sources (refer to Chapter 6). Possibly provide additional high/low level ventilation;background gas detectors to alarm, e.g. at 40% of the LEL. With toxic gases, possibly provide additional local ventilation;monitors connected to alarms; appropriate air-fed respirators. (The flammable/toxic gas detectors may be linked toautomatic shutdown instrumentation.)

Limit access to storage areas to authorized staff knowledgeable in the hazards, position of valves and switches.Display emergency procedures.

Wear face shields and impervious dry gloves, preferably insulated and of loose fit.Wear protective clothing which avoids the possibility of cryogenic liquid becoming trapped near the skin: avoid turnups and

pockets and wear trousers over boots, not tucked in.Remove bracelets, rings, watches etc. to avoid potential traps of cryogen against skin.

Prior to entry into large tanks containing inert medium, ensure that pipes to the tank from cryogen storage are blanked offor positively closed off: purge with air and check oxygen levels.

If in doubt, provide air-fed respirators and follow the requirements for entry into confined spaces (Chapter 13).

First aid measures include:Move casualties becoming dizzy or losing consciousness into fresh air and provide artificial respiration if breathing stops.Obtain medical attention (Chapter 13).In the event of ‘frost-bite’ do not rub the affected area but immerse rapidly in warm water and maintain general bodywarmth.Seek medical aid.

Ensure that staff are trained in the hazards and precautions for both normal operation and emergencies.

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water spray unless electrical equipment is involved, when carbon dioxide extinguishers shouldbe used.

Liquid nitrogen and argon

Liquid nitrogen is colourless and odourless, slightly lighter than water and non-magnetic. It doesnot produce toxic or irritating vapours. Liquid argon is also colourless and odourless but significantlyheavier than water. Gaseous nitrogen is colourless, odourless and tasteless, slightly soluble inwater and a poor conductor of heat. It does not burn or support combustion, nor readily react withother elements. It does, however, combine with some of the more active metals, e.g. calcium,sodium and magnesium, to form nitrides. Gaseous argon is also colourless, odourless and tasteless,very inert and does not support combustion.

The main hazard from using these gases stems from their asphyxiant nature. In confined,unventilated spaces small leakages of liquid can generate sufficient volumes of gas to deplete theoxygen content to below life-supporting concentrations: personnel can become unconscious withoutwarning symptoms (Chapter 5). Gas build-up can occur when a room is closed overnight.

Also, because the boiling points of these cryogenic liquids are lower than that of oxygen, ifexposed to air they can cause oxygen to condense preferentially, resulting in hazards similar tothose of liquid oxygen.

Liquid carbon dioxide

Liquid carbon dioxide is usually stored under 20 bar pressure at –18°C. Compression and coolingof the gas between the temperature limits at the ‘triple point’and the ‘critical point’ will cause it

Table 8.4 Physical properties of selected cryogenic liquids

Property of liquid Oxygen Nitrogen Argon Carbondioxide

Molecular weight 32 28 40 44Boiling point

(at atmospheric pressure) °C –183 –196 –186 –78Freezing point °C –219 –210 –190 —Critical temperature K 154.8 126.1 150.7 —Density of liquid

(at atmospheric pressure) kg/m3 1141 807 1394 1562(solid)

Density of vapour(at NBP) kg/m3 4.43 4.59 5.70 2.90

Density of dry gas at 15°Cand at atmospheric pressure kg/m3 1.34 1.17 1.67 1.86

Latent heat of vaporization at NBPand atmospheric pressure kJ/kg 214 199 163 151

Expansion ratio (liquid to gas at15°C and atmospheric pressure) 842 682 822 538(1)

Volume per cent in dry air % 20.95 78.09 0.93 0.03

NBP Normal boiling point(1)From liquid CO2 at 21 bar –18°C.


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to liquefy. The triple point is the pressure temperature combination at which carbon dioxide canexist simultaneously as gas, liquid and solid. Above the critical temperature point of 31°C it isimpossible to liquefy the gas by increasing the pressure above the critical pressure of 73 bar.Reduction in the temperature and pressure of liquid below the triple point causes the liquid todisappear, leaving only gas and solid. (Solid carbon dioxide is also available for cryogenic workand at – 78°C the solid sublimes at atmospheric pressure.)

Liquid carbon dioxide produces a colourless, dense, non-flammable vapour with a slightlypungent odour and characteristic acid ‘taste’. Physical properties are given in Table 8.5 (see alsopage 277). Figure 8.1 demonstrates the effect of temperature on vapour pressure.

Table 8.5 Physical properties of carbon dioxide

Molecular weight 44.01Vapour pressure at 21°C 57.23 barSpecific volume at 21°C, 1 atm 547 ml/gSublimation point at 1 atm – 78.5°CTriple point at 5.11 atm – 56.6°CDensity, gas at 0°C, 1 atm 1.977 g/lSpecific gravity, gas at 0°C,

1 bar (air = 1) 1.521Critical temperature 31°CCritical pressure 73.9 barCritical density 0.468 g/mlLatent heat of vaporization

at triple point 83.2 cal/gat 0°C 56.2 cal/g

Specific heat, gas at 25°C, 1 atmCp 0.205 cal/g °CCv 0.1565 cal/g °Cratio Cp/Cv 1.310

Thermal conductivity at 0°C 3.5 " 10–5 cal/s cm2 °C/cmat 100°C 5.5 " 10–5 cal/s cm2 °C/cm

Viscosity, gas at 21°C, 1 atm 0.0148 cPEntropy, gas at 25°C, 1 atm 1.160 cal/g °CHeat of formation, gas at 25°C – 2137.1 cal/gSolubility in water at 25°C, 1 atm 0.759 vol/vol water

Inhalation of carbon dioxide causes the breathing rate to increase (Table 8.6): 10% CO2 in aircan only be endured for a few minutes; at 25% death can result after a few hours exposure.

The 8 hr TWA hygiene standard (see Chapter 5) for carbon dioxide is 0.5%; at higher levels lifemay be threatened by extended exposure. The following considerations therefore supplementthose listed in Table 8.3:

• Ensure that operator exposure is below the hygiene standard. (Note: For environmental monitoring,because of its toxicity, a CO2 analyser must be used as distinct from simply relying on checksof oxygen levels.)

• When arranging ventilation, remember that the density of carbon dioxide gas is greater thanthat of air.

• Ensure that pipework and control systems are adequate to cope with the pressures associatedwith storage and conveyance of carbon dioxide, which are higher than those encountered withmost other cryogenic liquids.

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Freezing point

Criticalpressure1071.6 p.s.i.a.at 31°C


















ur p





Figure 8.1 Carbon dioxide vapour pressure versus temperature

Liquefied natural gas

Liquefied natural gas is predominantly methane. The cryogenic properties of methane are:

Boiling point –162°CCritical temperature –82°CCritical pressure 45.7 atmLiquid-to-gas ratio 1 to 637

by volume


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The impurities in LNG result in slightly different properties, and there are significant variationsdepending upon its source of supply.

Natural gas is considered non-toxic but can produce an oxygen deficient atmosphere (p. 153).It is odourless (therefore an odorant is added for distribution by pipeline). Its physical propertiesare similar to those of methane, i.e.:

Ignition temperature 537°CFlammable limits 5% to 15%Vapour density 0.55

However, the safety considerations with LNG must account for:

• The tendency, for economic reasons, to store it in very large insulated containers.• The requirement for special materials of construction to cater for storage at –162°C, and for

design of plant to cope with thermal differences.• The prevention of leaks, since liquid may generate large quantities of flammable gas.• The addition of odorants after vaporization, i.e. the liquid is odour-free.• The gas generated by vaporization is cold and therefore denser than air, i.e. it tends to slump.

LPG and methane are discussed further in Chapter 9.

Table 8.6 Effect of carbon dioxide exposure on breathing rates

CO2 in air (vol. %) Increased lung ventilation

0.1–1 slight, unnoticeable2 50% increase3 100% increase5 300% increase; breathing becomes laborious

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Compressed gases

Whilst gases are sometimes prepared in situ for cost and safety reasons (e.g. to remove the riskassociated with their transport, storage and piping to point of use) they are more often stored onan industrial scale at low pressure, either under refrigerated conditions, e.g. cryogens (Chapter 8),or at ambient temperature in ‘gasholders’, which ‘telescope’ according to the quantity of gas andare fitted with water or oil seals to prevent gas escape. Smaller quantities of gas at high pressureare usually stored in bottle-shaped gas cylinders. They find widespread use in welding, fuel forgas burners, hospitals, laboratories etc. The construction of compressed gas cylinders ensuresthat, when first put into service, they are safe for their designated use. Serious accidents can,however, result from ignorance of the properties of the gases, or from misuse or abuse. Great careis needed during the transportation, handling, storage and disposal of such cylinders.

Compressed gases can often be more dangerous than chemicals in liquid or solid form becauseof the potential source of high energy, low boiling-point of some liquid contents resulting in thepotential for flashing (page 50), ease of diffusion of escaping gas, low flashpoint of some highlyflammable liquids, and the absence of visual and/or odour detection of some leaking materials.The containers also tend to be heavy and bulky.

Compressed gases, therefore, present a unique hazard from their potential physical and chemicaldangers. Unless cylinders are secured they may topple over, cause injury to operators, becomedamaged themselves and cause contents to leak. If the regulator shears off, the cylinder mayrocket like a projectile or ‘torpedo’ dangerously around the workplace. Other physical hazardsstem from the high pressure of a cylinder’s contents, e.g. accidental application of a compressedgas/air hose or jet into eyes or onto an open cut or wound, whereby the gas can enter the tissueor bloodstream, is particularly dangerous.

A further hazard exists when compressed air jets are used to clean machine components inworkplaces: flying particles have caused injury and blindness. Cylinders may fail if over-pressurizedor weakened by the application of heat. Liquefied gases, e.g. butane or propane, respond morerapidly to heat than the permanent gases such as nitrogen or oxygen. Cylinders are normallyprotected by pressure relief valves, fusible plugs or bursting discs.

Low boiling-point materials can cause frostbite on contact with living tissue. While this is anobvious hazard with cryogenics, e.g. liquid nitrogen or oxygen, cylinders of other liquefied gasesalso become extremely cold and covered in ‘frost’ as the contents are discharged (page 47).

Precautions also have to be instituted to protect against the inherent properties of the cylindercontents, e.g. toxic, corrosive, flammable (refer to Table 9.1). Most gases are denser than air;common exceptions include acetylene, ammonia, helium, hydrogen and methane. Even these mayon escape be much cooler than ambient air and therefore slump initially. Eventually the gas willrise and accumulate at high levels unless ventilated. Hydrogen and acetylene, which both havevery wide flammable limits (Table 6.1), can form explosive atmospheres in this way.

More dense gases will on discharge accumulate at low levels and may, if flammable, travel aconsiderable distance to a remote ignition source.

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Table 9.1 Compressed gases: hazards and construction materials for services

Gas Hazard (1) Materials of construction for ancillary services(2)

Compatible Incompatible

Acetylene F Stainless steel, aluminium, Unalloyed copper, alloyswrought iron containing >70% copper,

silver, mercury, and cast ironAir O Any common metal or plasticAllene F Mild steel, aluminium, brass, Copper, silver and their alloys,

or stainless steel PVC and neopreneAmmonia C F T Iron and steel Copper, zinc, tin and their alloys

(e.g. brass), and mercuryArgon Any common metalArsine F T Stainless steel and ironBoron trichloride C T Any common metal for dry Any metal incompatible with

gas hydrochloric acid when moistCopper, Monel, Hastelloy B, gas is used

PVC, polythene and PTFE ifmoist gas is used

Boron trifluoride C T Stainless steel, copper, Rubber, nylon, phenolic resins,nickel, Monel, brass, cellulose and commercialaluminium for dry gas PVC!200°C. Borosilicate glassfor low pressures. For moistgas, copper and polyvinylidenechloride plastics

Bromine pentafluoride C T O Monel and nickelBromine trifluoride C T O Monel and nickelBromotrifluoroethylene F T Most common metals so long Magnesium alloys and

as gas is dry aluminium containing >2%magnesium

Bromotrifluoromethane Most common metals1,3-Butadiene F T Mild steel, aluminium, brass, PVC and Neoprene plastic

copper or stainless steelButane F Any common metal1, Butene F Any common metalCarbon dioxide T Iron, steel, copper, brass, For moist gas avoid materials

plastic for dry gas. For attacked by acidsmoist gas use stainlesssteel or certain plastics

Carbon monoxide F T Copper-lined metals for Iron, nickel and certain otherpressures <34 bar. Certain metals at high pressureshighly alloyed chrome steels

Carbon tetrafluoride Any common metalCarbonyl fluoride C F T Steel, stainless steel, copper

or brass for dry gas.Monel, copper or nickelfor moist gas

Carbonyl sulphide F T Aluminium and stainless steelChlorine C T O Extra heavy black iron or Rubber (e.g. gaskets)

steel for dry gas. Dropforged steel, PTFE tape.Moist gas requires glass,stoneware (for lowpressures) and noblemetals. High silica, iron,Monel and Hastelloy showsome resistance

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Chlorine trifluoride C T O Monel and nickel, PTFE andKel-F, soft copper, 2Saluminium and lead aresuitable for gaskets

Chlorodifluoromethane Steel, cast iron, brass, Silver, brass, aluminium, steel,copper, tin, lead, copper, nickel can causealuminium at normal decomposition at elevatedconditions temperatures. Magnesium

Neoprene or chloroprene alloys and aluminiumrubber and pressed fabrics containing >2% magnesium.are suitable for gaskets Natural rubber

Chloropentafluoroethane Neoprene or chloroprene Silver, brass, aluminium, steel,rubber and pressed fabrics copper, nickel can causeare suitable for gaskets decomposition at elevated

temperatures. Magnesiumalloys and aluminiumcontaining >2% magnesium.Natural rubber

Chlorotrifluoroethane F T Most common metalsChlorotrifluoromethane As for chlorodifluoromethaneCyanogen F T Stainless steel, Monel and

Inconel !65°C. Glass-linedequipment. Iron and steel atordinary temperatures

Cyanogen chloride C T Common metals for dry gas.Monel, tantalum. Glass formoist gas

Cyclobutane F Most common metalsCyclopropane F Most common metalsDeuterium F Most common metalsDiborane F T Most common metals. Rubber and certain

Polyvinylidene chloride, hydrocarbon lubricantspolyethylene, Kel-F PTFEgraphite and siliconevacuum grease

Dibromodifluoromethane Copper or stainless steel Aluminium for wet gas1,2-Dibromotetra- C Most common metals for dry Zinc

fluoroethane gas. Stainless steel, titaniumand nickel for moist gas

Dichlorodifluoromethane As for chlorodifluoromethaneDichlorofluoromethane As for chlorodifluoromethaneDichlorosilane C F T Nickel and nickel steels and Stainless steel for moist gas

PTFE1,2-Dichlorotetra- As for chlorodifluoromethane

fluoroethane1,1-Difluoro-1- F Most common metals under Hot metals can cause degradation

chloroethane normal conditions to toxic corrosive products1,1-Difluoroethane F Most common metals under Hot metals can cause degradation

normal conditions to toxic corrosive products1,1-Difluoroethylene F Most common metalsDimethylamine C F T Iron and steel Copper, tin, zinc, and their alloysDimethyl ether F T Most common metals2,2-Dimethyl propane F Most common metalsEthane F Most common metalsEthyl acetylene F Steel and stainless steel Copper, other metals capable of

forming explosive acetylides


Table 9.1 Cont’d

Gas Hazard(1) Materials of construction for ancillary services(2)

Compatible Incompatible

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Ethyl chloride F T Most materials for dry gasesEthylene F Any common metalEthylamine C F T Iron and steel. Reinforced Copper, tin, zinc and their

neoprene hose alloysEthylene oxide F T Properly grounded steel Copper, silver, magnesium and

their alloysFluorine C T O Brass, iron, aluminium,

magnesium and copper atnormal temperatures.Nickel and Monel athigher temperatures

Fluoroform Any common metalGermane F T Iron and steelHelium Any common metalHexafluoroacetone C T For dry gas Monel, nickel,

Inconel, stainless steel,copper and glass –Hastelloy C-line equipment

Hexafluoroethane Any common metal fornormal temperatures.Copper, stainless steel andaluminium !150°C

Hexafluoropropylene Any common metal for dry gasHydrogen F Most common metals for At elevated temperature and

normal use pressure hydrogenembrittlement can result

Hydrogen bromide C T Most common metals when dry. Most metals when gas is moist.Silver, platinum and tantalum Galvanized pipe or brass orfor moist gas. Heavy black bronze fittingsiron for high-pressure work.High-pressure steel,Monel or aluminium pipe.

Hydrogen chloride C T Stainless steel, mild steel for Galvanized pipes or brass ornormal conditions of bronze fittingstemperature and pressure.When moist use silver,platinum or tantalum.Moist or dry gas usebacked carbon, graphite.High pressure work in heavyblack iron pipework. Highpressure Monel or aluminiumiron bronze valves

Hydrogen cyanide F T Low-carbon steel at normaltemp. and stainless steelfor higher temperatures

Hydrogen fluoride C T Steel in the absence of sulphur Cast iron or malleable fittingsdioxide contaminants in thegas and at temperatures<65°C. Monel, Inconel,nickel and copper forliquid or gas at elevatedtemperature

Hydrogen iodide C T Stainless steel, mild steel Moist gas corrodes most metalsunder normal temperatureand pressure

Table 9.1 Cont’d

Gas Hazard(1) Materials of construction for ancillary services(2)

Compatible Incompatible

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Silver, platinum and Galvanized pipe or brass ortantalum, carbon, graphite bronze fittingsfor wet gas. At higherpressures use extra heavyblack iron pipe. High-pressure steel, Monel oraluminium-iron-bronze valves

Hydrogen selenide F T Aluminium and stainlesssteel are preferred but iron,steel or brass are acceptable

Hydrogen sulphide F T Aluminium preferred. Iron and steel Many metals in the presence ofare satisfactory. Brass, though moist gastarnished, is acceptable

Isobutane F Most common metalsIsobutylene F Most common metalsKrypton Most common metalsMethane F Most common metalsMethyl acetylene F Most common metals Copper, silver, mercury and

their alloysMethylamine C F T Iron and steel Copper, tin, zinc and their

alloys. Avoid mercuryMethyl bromide C F T Most common metals when dry Aluminium and its alloys3-Methyl-1-butane F Most common metalsMethyl chloride F T Most common metals when Zinc, magnesium rubber and

dry neoprene particularly whenmoist. Aluminium is forbidden

Methyl fluoride F T Most common metalsMethyl mercaptan F T Stainless steel and copper-free

steel alloys and aluminium.Iron and steel for dry gas

Methyl vinyl ether F Most common metals Copper and its alloysNeon Most common metalsNickel carbonyl F T Most common metals for pure gas.

Copper or glass-lined equipmentfor carbonyl in the presenceof carbon monoxide

Nitric oxide T O Most common metals for drygas. For moist gas use18:8 stainless steel, PTFE

Nitrogen Any common metalNitrogen dioxide C T O Most common metals for dry

gas. For moist gas use18:8 stainless steel

Nitrogen trifluoride T O Nickel and Monel are Plasticspreferred. Steel, copperand glass are acceptable atordinary temperatures

Nitrogen trioxide C T O Steel for dry gas otherwiseuse 18:8 stainless steel

Nitrosyl chloride C T O Nickel, Monel and Inconel. Formoist gas tantalum is suitable

Nitrous oxide O Most common metalsOctofluorocyclobutane T Cast iron and stainless steel <120°C, Avoid the metals opposite

steel !175°C, Inconel, nickel >500°Cand platinum !400°C

Oxygen O Most common metals On grease or combustible


Table 9.1 Cont’d

Gas Hazard (1) Materials of construction for ancillary services(2)

Compatible Incompatible

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Oxygen difluoride T O Glass, stainless steel, copper, materialsMonel or nickel !200°C. Athigher temperatures onlynickel and Monel arerecommended

Ozone F T O Glass, stainless steel, Teflon, Copper and its alloys, rubber orHypalon, aluminium, any composition thereof, oil,Tygon, PVC and polythene grease or readily combustible

materialPerchloryl fluoride T Most metals and glass for dry Many gasket materials are

gas at ordinary embrittledtemperatures At higher temperatures many

organic materials and somemetals can be ignited

Some metals such as titaniumshow deflagration in contactwith the gas under severe shock

Perfluorobutane Most common materialsPerfluorobutene T Most common materials when dryPerfluoropropane Most common metalsPhosgene C T Common metals for dry gas.

Monel, tantalum or glasslined equipment for moist gas

Phosphine F T Iron or steelPhosphorus pentafluoride F T Steel, nickel, Monel and Pyrex for

dry gas. For moist gas hardrubber and paraffin wax

Phosphorus trifluoride Steel, nickel, Monel and themore noble metals andPyrex for dry gas

Propane F Most common metalsPropylene F Most common metalsPropylene oxide F T Steel or stainless steel Rubber

preferred though copperand brass are suitable foracetylene-free gas. PTFE gaskets

Silane F T Iron, steel, copper, brassSilicone tetrafluoride C T Most common metals for the

dry gas. Steel, Monel andcopper for moist gas

Sulphur dioxide C T O Most common metals for dry gas. ZincLead, carbon, aluminium andstainless steel for moist gas

Sulphur hexafluoride Most common metals.Copper, stainless steel andaluminium are resistant tothe decompositionproducts at 150°C

Sulphur tetrafluoride C T Stainless steel or ‘Hastelloy Glass for moist gasC’ lined containers. Glasssuitable for short exposuresif dry. ‘Tygon’ for low-pressureconnections

Sulphuryl fluoride T Any common metal at normal Some metals at elevatedtemperatures and pressures temperatures

Tetrafluoroethylene F Most common metals

Table 9.1 Cont’d

Gas Hazard (1) Materials of construction for ancillary services(2)

Compatible Incompatible

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Tetrafluorohydrazine T O Glass, stainless steel, copper ornickel to temperatures of 200°C.For higher temperatures usenickel and Monel

Trichlorofluoromethane T Steel, cast iron, brass, Some of the opposite at highcopper, tin, lead, temperatures magnesiumaluminium under normal, alloys and aluminium coatingdry conditions >2% magnesium. Natural rubber

1,1,2-Trichloro-1,2,2- As above As abovetrifluoroethane

Trimethylamine C F T Iron, steel, stainless steel and Copper, tin, zinc and most ofMonel. Rigid steel piping their alloys

Vinyl bromide F T Steel Copper and its alloysVinyl chloride C F T Steel Copper and its alloysVinyl fluoride F Steel Copper and its alloysXenon Most common materials

C CorrosiveF FlammableT ToxicO Oxidizing(1) Even non-toxic gases are potentially hazardous owing to asphyxiation (oxygen deficiency). Irrespective of material, all

equipment must be adequately designed to withstand process pressures.(2) This is a guide and is no substitute for detailed literature.

To prevent interchange of fittings between cylinders of combustible and non-combustiblegases, the valve outlets are screwed left-hand and right-hand thread, respectively (Table 9.2).Primary identification is by means of labelling with the name and chemical formula on theshoulder of the cylinder. Secondary identification is by use of ground colours on the cylinderbody. Unless specified in Table 9.2, gas and gas mixtures shall be identified by a colour classificationindicating gas properties in accordance with the risk diamond on the cylinder label e.g.

Toxic and/or corrosive YellowFlammable RedOxidizing Light blueInert (non-toxic, non-corrosive, Bright green

non-flammable, non-oxidizing

The full scheme is given in BS EN 1089–3: 1997.This should be consulted for the colour coding of gas mixtures used for inhalation e.g. medical

and breathing apparatus mixtures containing oxygen.


Table 9.1 Cont’d

Gas Hazard (1) Materials of construction for ancillary services(2)

Compatible Incompatible

Table 9.2 Specific colour codes for selected compressed gases

Gas Colour

Acetylene MaroonArgon Dark greenCarbon dioxide GreyHelium BrownOxygen WhiteNitrogen BlackNitrous oxide Blue

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Table 9.3 General precautions for handling compressed gases

Consult the supplier for data on the specification, properties, handling advice and on suitable service materials for individualgases.

StorageSegregate according to hazard.Stores should be adequately ventilated and, ideally, located outside and protected from the weather.Store away from sources of heat and ignition.Cylinders within workplaces should be restricted to those gases in use. Specially designed compartments with partitions may

be required to protect people in the event of explosion. Take into account emergency exits, steam or hot water systems,the proximity of other processes etc. Consider the possibility of dense gases accumulating in drains, basem*nts, cableducts, lift shafts etc.

Where necessary, provide fireproof partitions/barriers to separate/protect cylinders.Protect from mechanical damage.All cylinders must be properly labelled and colour coded (BS 349).Store full and empty cylinders separately.Use in rotation: first in, first out.Restrict access to the stores to authorized staff.Display ‘No smoking’ and other relevant warning signs.Ensure that all staff are fully conversant with the correct procedures when using pressure regulators. (For cylinders without

handwheel valves, the correct cylinder valve keys should be kept readily available, e.g. on the valve. Only use such keys.Do not extend handles or keys to permit greater leverage; do not use excessive force, e.g. hammering, when opening/closing valves or connecting/disconnecting fittings. The pressure regulator must be fully closed before opening thecylinder valve. This valve can then be opened slowly until the regulator gauge indicates the cylinder pressure but shouldnot be opened wider than necessary. The pressure regulator can then be opened to give the required delivery pressure.When a cylinder is not in use, or is being moved, the cylinder valve must be shut. When a cylinder has been connected,the valve should be opened with the regulator closed; joints should then be tested with soap/detergent solution.)

Clearly and permanently mark pressure gauges for use on oxygen. Do not contaminate them with oil or grease or use themfor other duties.

Cylinders that cannot be properly identified should not be used; do not rely on colour code alone.Never try to refill cylinders.Never use compressed gas to blow away dust or dirt.Provide permanent brazed or welded pipelines from the cylinders to near the points of gas use. Select pipe materials suitable

for the gas and its application. Any flexible piping used should be protected against physical damage. Never use rubberor plastic connections from cylinders containing toxic gases.

On acetylene service, use only approved fittings and regulators. Avoid any possibility of it coming into contact with copper,copper-rich alloys or silver-rich alloys. (In the UK use at a pressure greater than 600 mbar g must be notified to HMExplosives Inspectorate for advice on appropriate standards.)

On carbon dioxide service, rapid withdrawal of gas may result in plugging by solid CO2. Close the valve, if possible, to allowthe metal to warm up; this will prevent a sudden gas discharge.

Replace the correct caps or guards on cylinder valves when not in use and for return to the supplier.Test and inspect cylinders and pressure regulators regularly in accordance with current legislation.Design and manage cylinder stores in accordance with suppliers’ recommendations.Wear appropriate personal protection when entering any store.Inspect condition of cylinders regularly, especially those containing hazardous gases (e.g. corrosive).

UseTransport gases in specially designed trolleys and use eye protection, stout gloves (preferably textile or leather) and protective

footwear.Do not roll or drop cylinders off the backs of wagons; never lift cylinders by the cap.Ideally, depending on the length of pipe run, locate cylinders outside (for hazardous gases, valves installed within the

workplace can be used for remote control of the main supply from the cylinder in the event of an emergency). Sitecylinders so that they cannot become part of an electrical circuit.

Securely clamp, or otherwise firmly hold in position, cylinders on installation. (Unless otherwise specified, cylinders containingliquefied or dissolved gases must be used upright.)

Avoid subjecting cylinders containing liquid to excessive heat.

Table 9.3 provides general guidance for handling compressed gases.

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The hazards and safety precautions for selected common compressed gases are discussedbelow to illustrate the general approach. More details should be sought from suppliers. Somemethods for their preparation in situ are noted; full experimental details must be obtained fromthe literature.


Acetylene is manufactured by the controlled reaction between water and calcium carbide:

CaC2 + 2H2O " Ca (OH)2 + C2H2

Alternatively it is obtained from cracking low molecular-weight aliphatic hydrocarbons, or by thepartial oxidation of natural gas.

Because of its high chemical reactivity, acetylene has found wide use in synthesis of vinylchloride, vinyl acetate, acrylonitrile, vinyl ethers, vinyl acetylene, trichloro- and tetrachloro-ethylene etc., in oxyacetylene cutting and welding, and as a fuel for atomic absorption instruments.

Acetylene is a simple asphyxiant and anaesthetic. Pure acetylene is a colourless, highly flammablegas with an ethereal odour. Material of commercial purity has an odour of garlic due to thepresence of impurities such as phosphine. Its physical properties are shown in Table 9.4. Acetylene,which condenses to a white solid subliming at –83oC, is soluble in its own volume of water buthighly soluble in acetone.

Under certain conditions acetylene can explode when mixed with air, hydrogen or ethylene.Accidental heating of a small area of cylinder wall to 185oC or above may promote an extremely

dangerous condition. Violent reactions have occurred between acetylene and oxidants such asoxides of nitrogen (see later), nitric acid, calcium hypochlorite, ozone and halogens. In the freestate acetylene can decompose violently, e.g. above 9 psig (0.62 bar) undissolved (free) acetylenewill begin to dissociate and revert to its constituent elements. This is an exothermic process whichcan result in explosions of great violence. For this reason acetylene is transported in acetonecontained in a porous material inside the cylinder. Voids in the porous substance can result fromsettling, e.g. if the cylinder is stored horizontally or through damage to the cylinder in the formof denting. Voids may enable acetylene to decompose, e.g. on initiation by mechanical shock ifthe cylinder is dropped.

Fit approved cylinder pressure regulators, selected to give a maximum pressure on the reduced side commensurate with therequired delivery pressure. (The regulator and all fittings upstream of it must be able to withstand at least the maximumcylinder pressure.)

Fit in-line flame arresters for flammable gases and eliminate ignition sources.Use compatible pipe fittings. (Flammable gas cylinders have valves with left-hand threads; cylinders for oxygen and non-

flammable gases, except occasionally helium, have valves with right-hand threads. Certain liquefied gas cylinders havetwo supply lines, one for gas and one for liquid, dependent on cylinder position.)

Do not use oil, grease or joining compounds on any fittings for compressed gas cylinders.Fit an excess flow valve to the outlet of a regulator, selected to allow the maximum required gas flow.Use respirators and face protection etc. when changing regulators on cylinders of toxic gases.Turn off gas supply at the cylinder at the end of each day’s use.Consider the need for gas detection/alarms, e.g. for hazardous gases left in use out of normal hours.Periodic checks:

Ensure no gas discharge when gauge reading is zeroEnsure reading on gauge does not increase as the regulator valve is closedCheck for ‘crawl’ due to wear on the regulator valve and seat assemblyEnsure no leak between cylinder and regulatorOverhaul regulators on a 3–6 month basis for corrosive gases, annually for others

Train staff in hazards and correct handling procedures.


Table 9.3 Cont’d

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Table 9.4 Physical properties of acetylene

Molecular weight 26.038Vapour pressure of pure liquid at 21°C (not cylinder pressure) 43.8 barSpecific volume at 15.6°C, 1 atm 902.9 ml/gBoiling point at 1.22 atm –75°CSublimation point at 1 atm –84.0°CTriple point at saturation pressure –80.8°CSpecific gravity, gas at 15.6°C, 1 atm (air = 1) 0.9057Density, gas at 0°C, 1 atm 1.1709 g/lCritical temperature 36.3°CCritical pressure 62.4 barCritical density 0.231 g/mlLatent heat of sublimation at –84°C 193.46 cal/gLatent heat of fusion at triple point 23.04 cal/gFlammable limits in air 2.5–81.0% by volumeAuto-ignition temperature 335°CGross heat of combustion at 15.6°C, 1 atm 13.2 cal/ccSpecific heat, gas at 25°C, 1 atm

Cp 0.4047 cal/g°CCv 0.3212 cal/g °Cratio Cp/Cv 1.26

Thermal conductivity, gas at 0°C 4.8 # 10–5 cal/s cm2 °C/cmViscosity, gas at 25°C, 1 atm 0.00943 cPEntropy, gas at 25°C, 1 atm 1.843 cal/g °CSolubility in water at 0°C, 1 atm 1.7 vol/vol H2O

Figure 9.1 illustrates the rise in cylinder pressure with temperature. Normally, acetylene cylindersare fitted with a fusible metal plug which melts at about 100°C.

Acetylene can form metal acetylides, such as copper or silver acetylide, which on dryingbecome highly explosive: service materials require careful selection.

In addition to the general precautions for compressed gases in Table 9.3, the following controlmeasures should be considered for acetylene:

• Never use free acetylene at pressures above 9 psig (0.62 bar) unless special safety features areemployed.

• Store and use cylinders only in an upright position.• Store reserves separate from oxygen cylinders.• Ensure that no means of accidental ignition are in the area and provide adequate ventilation.• Consult local regulations for use of this gas.• Ensure that ‘empty’ cylinders have the valve closed to prevent evaporation of acetone.• Close cylinder valve before shutting off regulator, to permit gas to bleed from regulator.• When used e.g. for welding, avoid the careless use of flame which could fuse the metal safety

plug in the cylinder.• In the event of fire issuing from the cylinder, close the gas supply if it is safe to do so and

evacuate the area.• Consider the need for detection/alarm systems and in any event check periodically for leaks

with e.g. soap solution, never with a naked flame.


The physical properties of air are given in Table 9.5. Air is a mixture of nitrogen, oxygen, argon,

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10030 40 50 60 70 80 90 100 110 120

–1 4 10 16 21 27 32 38 43 49






e (p


carbon dioxide, water vapour, rare gases and trace quantities of ozone, oxides of nitrogen, acetylene,methane and other hydrocarbons. Its composition varies with altitude. Dry air is inert in its effecton metals and plastics. The hazards associated with compressed air, in addition to those associatedwith any pressure system (i.e. the potential for rupture of equipment or pipework), are:

• From inhalation at pressures above atmospheric, used in tunnelling or diving, or from breathingapparatus or resuscitation equipment, if the pressure is too high or exposure is prolonged. Thismay cause symptoms from pain to dyspnoea, disorientation and unconsciousness; it may befatal.

• From particulate matter blown from orifices or surfaces, e.g. into the eyes.• From entry into any of the body orifices, which can result in serious internal damage.• From penetration of unbroken skin, or cuts. Foreign matter, e.g. grease, metal, concrete, may

also be injected into subcutaneous tissues.• From whipping of an unsecured hose on rapid gas release.

Figure 9.1 Acetylene (in acetone): full cylinder pressure versus temperature

Table 9.5 Physical properties of air

Density @ 20°C, 1 atm 0.0012046 g/lCritical temperature –140.6°CCritical pressure 546.8 psia (37.2 atm) (38.4 kg/cm2 absolute)Critical density 0.313 g/mlViscosity @ 0°C, 1 atm 170.9 micropoises

AIR 275

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The precautions include:

• Prohibition on playing around with compressed air hoses, e.g. aiming directly at any individual.• Avoidance of blowing away dust or dirt from equipment, the floors, or clothing etc. (which

may also produce a dust inhalation or explosion hazard).• Direction of the exhaust air from tools away from the operator.• Proper training and instruction for anyone required to use air-fed breathing apparatus. Restriction

of exposures to compressed air to safe levels.


Ammonia can be made on a small scale by heating an intimate mixture of ammonium chlorideand dry slaked lime in a ratio of 1:3, respectively:

Ca(OH)2 + 2NH4Cl " CaCl2 + 2NH3 + 2H2O

Industrially, production is either from the Haber process at high pressure:

N2 + 3H2 " 2NH3

or the cyanamide process

CaC2 + N2 " CaCN2 + C

CaCN2 + 3H2O " 2NH3 + CaCO3

At room temperature and atmospheric pressure ammonia is a colourless, alkaline gas with apungent smell. It dissolves readily in water. Physical properties are summarized in Table 9.6. Theeffect of temperature on vapour pressure of anhydrous ammonia is shown in Figure 9.2.

Ammonia is shipped as a liquefied gas under its own vapour pressure of 114 psig (7.9 bar) at21°C. Uses are to be found in refrigeration, fertilizer production, metal industries, the petroleum,chemical and rubber industries, domestic cleaning agents and water purification. Aqueous solutionsof ammonia are common alkaline laboratory reagents; ca 0.88 solution is the strongest available.Ammonia gas is expelled on warming.

Ammonia gas is irritating to the eyes, mucous membranes and respiratory tract. Because of itsodour few individuals are likely to be unwittingly over-exposed for prolonged periods. Table 9.7summarizes the physiological effects of human exposure. Clearly at high concentrations the gasbecomes corrosive and capable of causing extensive injuries. Thus 1% in air is mildly irritating,2% has a more pronounced effect and 3% produces stinging sensations.

On contact with the skin, liquid ammonia produces severe burns compounded by frostbite dueto the freezing effect from rapid evaporation from the skin.

Moist ammonia attacks copper, tin, zinc and their alloys. Ammonia is also flammable withflammability limits of 15–28%.

Ammonia can also react violently with a large selection of chemicals including ethylene oxide,halogens, heavy metals, and oxidants such as chromium trioxide, dichlorine oxide, dinitrogentetroxide, hydrogen peroxide, nitric acid, liquid oxygen, and potassium chlorate.

Besides the control measures given in Table 9.3, the following precautions are appropriate:

• Wear rubber gloves, chemical goggles and, depending upon scale, a rubber apron or fullchemical suit.

• Never heat ammonia cylinders directly with steam or flames to speed up gas discharge.

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• Use under well-ventilated conditions and provide convenient safety showers and eye-washfacilities.

• Ensure that gas cannot be accidentally ignited.• Check for leaks, e.g. with moist litmus paper or concentrated hydrochloric acid (which forms

dense white fumes of ammonium chloride).• In the event of accident, administer first aid (see Table 9.9).

Carbon dioxide

Carbon dioxide is present in air and is a constituent of natural gas escaping from mineral springsand fissures in the earth’s surface. It is also the ultimate product of combustion of carbon and itscompounds. Laboratory scale preparation usually entails reaction between dilute hydrochloricacid and marble (calcium carbonate):

2HCl + CaCO3 " CaCl2 + H2O + CO2

Industrially, it is obtained as a by-product of fermentation of sugar to alcohol:

C6H12O2 " 2C2H5OH + 2CO2

or by burning co*ke/limestone mixture in a kiln:

CaCO3 " CO2 + CaO

Table 9.6 Physical properties of ammonia

Molecular weight 17.031Vapour pressure at 21°C (cylinder pressure) 7.87 barSpecific volume at 21°C, 1 atm 1.411 ml/gBoiling point at 1 atm – 33.35°CTriple point at 1 atm – 77.7°CTriple point pressure 1.33 mbarSpecific gravity, gas at 0°C, 1 atm (air = 1) 0.5970Density, gas at boiling point 0.000 89 g/mlDensity, liquid at boiling point 0.674 g/mlCritical temperature 132.44°CCritical pressure 113 barCritical density 0.235 g/mlFlammable limits in air 15–28% by volumeLatent heat of vaporization at boiling point 327.4 cal/gSpecific heat, liquid at –20°C 1.126 cal/g KSpecific heat, gas at 25°C, 1 atm

Cp 0.5160 cal/g°CCv 0.4065 cal/g °Cratio, Cp/Cv 1.269

Thermal conductivity, gas at 25°C, 1 atm 5.22 # 10–5 cal/s cm2 °C/cmEntropy, gas at 25°C, 1 atm 2.7 cal/g °CHeat of formation, gas at 25°C –648.3 cal/gSolubility at 0°C, 1 atm

in water 42.8% by weightin methanol, absolute 29.3% by weightin ethanol, absolute 20. 95% by weight

Viscosity, gas at 0°C, 1 atm 0.009 18 cPViscosity, liquid at –33.5°C 0.266 cP


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Boiling point




















ur p





Liquid carbon dioxide is discussed on page 261. Carbon dioxide gas is commonly used forcarbonating drinks, in fire extinguishers, for gas-shielding of welding and in shell moulding infoundries. Its physical and toxicological properties are summarized in Tables 8.5, 8.6 and 5.29.

The gas is non-flammable, and is used for inert gas purging. Because it is 1.5 timesheavier than air it may accumulate at low level. The general handling precautions are those inTable 9.3.

Figure 9.2 Ammonia vapour pressure versus temperature

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Carbon monoxide

Carbon monoxide is produced by incomplete combustion of carbon and its compounds. In thelaboratory it can be prepared by careful dehydration of formic or oxalic acid with sulphuric acid:

HCO2H " CO + H2O

Traditionally, pure CO is not used industrially; water gas or producer gas are used instead.However, pure CO is made by thermal decomposition of nickel carbonyl:

Ni(CO)4 " Ni + 4CO

Carbon monoxide is a toxic, flammable, colourless and odourless gas which is slightly lighterthan air and slightly soluble in water. Some physical constants are given in Table 9.8. Corrosionby pure carbon monoxide is considered negligible. It is shipped as a non-liquefied gas in high-pressure steel containers. Its main uses include fuel gas mixtures with hydrogen and for reductionof ores. Its main hazards are its extreme toxic effects which stem from its ability to complex withhaemoglobin (with which it has an affinity 300 times that of oxygen) resulting in chemicalasphyxiation (see Table 5.31). It burns in air with a characteristic blue flame. It combines directlywith chlorine in sunlight to produce highly toxic phosgene:

Table 9.7 Physiological effects of ammonia

Atmospheric concentration Effects(ppm)

20 First perceptible odour40 A few individuals may suffer slight eye irritation

100 Noticeable irritation of eyes and nasal passages after few minutes’ exposure400 Severe irritation of the throat, nasal passages and upper respiratory tract700 Severe eye irritation

No permanent effect if exposure <30 min1700 Serious coughing, bronchial spasms, <30 min exposure may be fatal5000 Serious oedema, strangulation, asphyxia

Fatal almost immediately

Table 9.8 Physical properties of carbon monoxide

Molecular weight 28.01Specific volume @ 21°C, 1 atm 13.8 cu.ft/lb (861.5 ml/g)Boiling point @ 1 atm –191.5°CTriple point –205.01°CSpecific gravity @ 21°C, 1 atm 115.14 mm HgDensity (liquid) @ bp 0.9678Latent heat of vaporization @ bp 1444 cal/moleLatent heat of fusion @ tp 200.9 cal/moleFlammable limits in air 12.5–74%Autoignition temperature 650°CSpecific heat (gas) @ 25°C, 1 atm

Cp 0.2491 cal/g °CCv 0.1774 cal/g °Cratio Cp/Cv 1.4

Viscosity (gas) @ 0°C, 1 atm 0.0166 centipoiseEntropy (gas) @ 25°C 47.266 cal/mole °CHeat of formation (gas) @ 25°C –26.417 kcal/mole


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CO + Cl2 " COCl2

Liquid carbon monoxide in the presence of nitrous oxide poses blast hazards.Precautions for handling carbon monoxide in compressed gas cylinders in addition to those

given in Table 9.3 include:

• Handle in well-ventilated conditions.• Consider the need for respiratory equipment.• Use CO gas detection system if used indoors or in confined spaces.• Check the system periodically for leaks.• Avoid accidental contact with ignition sources.• Segregate stocks from oxygen cylinders or other oxidizing or flammable substances.

Table 9.9 First aid measures following exposure to a compressed gas

Obtain medical help immediatelyInhalation Remove victim to uncontaminated area and carry out artificial respiration

In the case of hydrogen sulphide, ensure that the patient remains rested and refrainsfrom exercise for 24 hr

For chlorine gassing, lay victim on stomach with head and shoulders slightly lowered;discourage from coughing

Skin contact Use emergency shower, removing contaminated clothing and shoes at the sametime

Eye contact Wash promptly with copious amounts of water for $15 min


Chlorine can be made on a small scale by oxidation of hydrogen chloride with, e.g., manganesedioxide:

MnO2 + 4HCl " MnCl2 + Cl2 + 2H2O

Industrially, chlorine is obtained as a by-product in the electrolytic conversion of salt to sodiumhydroxide. Hazardous reactions have occurred between chlorine and a variety of chemicals includingacetylene, alcohols, aluminium, ammonia, benzene, carbon disulphide, diethyl ether, diethyl zinc,fluorine, hydrocarbons, hydrogen, ferric chloride, metal hydrides, non-metals such as boron andphosphorus, rubber, and steel.

Chlorine is very reactive and finds wide use, e.g. in water purification, sanitation, as a bleachingagent, as a versatile raw material in synthetic chemistry etc. In liquid form, chlorine is a clearamber dense liquid. The gas is greenish-yellow, about 2.5 times as dense as air. Although non-flammable, it will support combustion. Liquid chlorine causes severe irritation and blistering ofskin. The gas has a pungent suffocating odour and is irritant to the nose and throat. It is anextremely powerful blistering agent and respiratory irritant. Persons exposed to chlorine becomerestless, sneeze, develop sore throat and salivate copiously. Effects on the body are summarizedin Table 9.10 and physical characteristics are given in Table 9.11.

Moist chlorine is corrosive to skin and to most common materials of construction. Wet chlorineat low pressure can be handled in chemical stonewear, glass or porcelain and in certain alloys andplastics.

The effect of temperature on vapour pressure is shown in Figure 9.3. Cylinders are normallyprotected from over-pressurization by a fusible metal plug melting at about 85°C.

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The following safety measures supplement the general precautions listed in Table 9.3:

• Provide convenient showers, eye-wash facilities and appropriate respiratory protection foremergencies.

• Work in well-ventilated area wearing appropriate skin protection and respiratory equipment.• Check for leaks (e.g. with aqueous ammonia) and consider the need for detection/alarm systems.

Leaks should be dealt with immediately after evacuating the area.• Never connect the cylinder directly to vessels of liquid since suck-back into the cylinder may

result in violent reaction. Insert a trap in the line between the chlorine supply and the receiverof sufficient capacity to accommodate all the liquid.

• Never supply heat directly to the cylinder.• Segregate stocks of chlorine from acetylene, hydrogen, ammonia and fuel gases and ensure no

accidental contact with ethers, hydrocarbons and other organics and finely divided metals.Never mix chlorine with another gas in the cylinder.

• In the event of exposure, apply first aid as in Table 9.9 (refer also to Table 13.17).

Table 9.10 Physiological effects of chlorine

Atmospheric Effectsconcentration(ppm)

1 Minimum concentration causing slight symptoms after several hours3.5 Minimum concentration detectable by odour4 Maximum concentration that can be breathed for 1 hr without damage

15 Minimum concentration causing throat irritation30 Minimum concentration causing coughing

40–60 Concentration dangerous within 30 min1000 Concentration likely to be fatal after a few deep breaths

Table 9.11 Physical properties of chlorine

Molecular weight 70.906Vapour pressure at 21°C 5.88 barSpecific volume at 21°C, 1 atm 337.1 ml/gBoiling point at 1 atm –34.05°CFreezing point at 1 atm –100.98°CSpecific gravity, gas at 0°C, 1 atm (air = 1) 2.49Specific gravity, liquid at 20°C 1.41Density, gas at 0°C, 1 atm 3.214 g/lDensity, liquid at 0°C, 3.65 atm 1.468 g/lCritical temperature 144°CCritical pressure 77.1 barCritical density 0.573 g/mlLatent heat of vaporization at boiling point 68.8 cal/gHeat of fusion at flash point 22.9 cal/gSpecific heat, liquid at 0–24°C 0.226 cal/g °CSpecific heat, gas at 15°C, 1 atm

Cp 0.115 cal/g °CCv 0.085 cal/g °Cratio Cp/Cv 1.355

Thermal conductivity, gas at 0°C 1.8 # 10–5 cal/s cm2 °C/cmViscosity, gas at 20°C, 1 atm 0.0147 cPViscosity, liquid at 20°C 0.325 cPSolubility in water at 20°C, 1 atm 7.30 g/l


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Criticalpressure1118.7 psiaat 144°C


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Boiling point


Hydrogen does not appear free in the atmosphere except at levels below 1 ppm, since rapiddiffusivity enables molecules to escape the earth’s gravitational field and it is continuously lostfrom the atmosphere. It is present in the earth’s crust at about 0.87% in combination with oxygenin water and with carbon and other elements in organic substances. It is prepared commerciallyon a small scale by action of sulphuric acid on zinc:

Figure 9.3 Chlorine vapour pressure versus temperature

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Zn + H2SO4 " ZnSO4 + H2

and industrially by electrolysis of sodium chloride, or sodium hydroxide, or by reduction of steamby carbon monoxide:

C + H2O " CO + H2O (water gas)

H2 + CO + H2O " CO2 + 2H2

Hydrogen is used for the hydrogenation of oils and fats, in metallurgy, metal welding/cutting,ammonia synthesis and petroleum refining. It is the lightest gas known. It is colourless andodourless, only slightly soluble in water but readily soluble in hydrocarbons. Hydrogen is non-toxic but can act as an asphyxiant. It is usually shipped in containers at 2000 psig (137.9 bar) at21°C, often protected by frangible discs backed up by a fusible metal plug melting at 100°C.Physical properties are given in Table 9.12.

Table 9.12 Physical properties of hydrogen

Molecular weight 2.016Specific volume at 21°C, 1 atm 11 967 ml/gBoiling point at 1 atm –252.9°CTriple point at 0.0695 atm –259.3°CSpecific gravity, gas at 23.9°C, 1 atm (air = 1) 0.06952Density, gas at 0°C, 1 atm 0.0899 g/lDensity, liquid at –253°C, 1 atm 0.0708 g/mlCritical temperature –240.2°CCritical pressure 12.98 barCritical density 0.03136 g/mlLatent heat of vaporization at boiling point 106.5 cal/gLatent heat of fusion at triple point 13.875 cal/gFlammable limits in air 4.0–75% by volumeAuto-ignition temperature 585°CSpecific heat, gas at 0–200°C, 1 atm

Cp 3.44 cal/g °CCv 2.46 cal/g °Cratio Cp/Cv 1.40

Thermal conductivity at 0°C 0.00040 cal/s cm2 °C/cmViscosity, gas at 15°C, 1 atm 0.0087 cPSolubility in water at 15.6°C, 1 atm 0.019 vol/vol H2O

The main danger with hydrogen is of fire or explosion. Hydrogen burns in chlorine to yieldhydrogen chloride. Although relatively inactive at ambient temperature it reacts with many elementseither at high temperatures or in the presence of catalysts and can react dangerously with air,acetylene, aromatics, unsaturated organic matter, halogens, metals such as lithium, calcium,barium, strontium and potassium, and with oxidants such as chlorine dioxide, oxides of nitrogenand palladium oxides. The following precautions are important to supplement those in Table 9.3:

• Use only in well-ventilated conditions to avoid accumulation at high levels.• Eliminate means of accidental ignition.• Use only explosion-proof electrical equipment and spark-proof tools.• Ground all equipment and lines used with hydrogen.• Check for leaks with soapy water and consider the need for automatic detection/alarms.


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Hydrogen chloride

Hydrogen chloride may be conveniently prepared by heating sodium chloride with sulphuric acid:

NaCl + H2SO4 " NaHSO4 + HCl

When this reaction has occurred accidentally sufficient hydrogen chloride has been liberated toexplosively burst the vessel. The purest form of hydrogen chloride is made by the action of wateron silicon tetrachloride:

2H2O + SiCl4 " SiO2 + 4HCl

Commercially, hydrogen chloride is obtained either as a by-product in the manufacture of saltcake from sodium chloride, or by allowing chlorine produced as a by-product in electrolyticprocesses to react with hydrogen in the presence of activated charcoal. It is also formed as a by-product in the manufacture of phenol.

Anhydrous hydrogen chloride is a colourless, pungent, heavy, corrosive, thermally-stable gaswith a suffocating odour. It is heavier than air and fumes strongly in moist air and is highlysoluble in water with evolution of much heat. Physical properties are given in Table 9.13 and itspressure vs temperature profile in Figure 9.4. It is shipped as a liquefied gas with a cylinderpressure of about 613 psig at 21°C and platinum coated frangible bursting discs and fusible metalplugs. Its main uses are as a chemical intermediate and in hydrochlorinations. Its toxicity resultsfrom its severe irritating effects to the upper respiratory tract and corrosivity towards skin, eyesand mucous membranes. Neutralization of alkalis in tissues can result in death from oedema orspasm of the larynx. At exposures of 50–100 ppm work is impossible, and difficult at 10–50 ppm;the TLV is a short-term exposure limit of 5 ppm ceiling.

Table 9.13 Physical properties of hydrogen chloride

Molecular weight 36.46Vapour pressure @ 21°C 613 psigSpecific volume @ 21°C, 1 atm 661.7 ml/gBoiling point @ 1 atm –85.03°CFreezing point @ 1 atm –114.19°CSpecific gravity (gas) @ 0°C, 1 atm 1.268Density (gas) @ 0°C, 1 atm 1.639 g/lDensity (liquid) @ –36°C 1.194 g/lCritical temperature 51.4°CCritical pressure 1198 psia (81.5 atm)Critical density 0.42 g/mlLatent heat of vaporization @ bp 103.12 cal/gSpecific heat (gas) @ 15°C, 1 atm

Cp 0.1939 cal/g °CCv 0.1375 cal/g °Cratio Cp/Cv 1.41

Viscosity (gas) @ 20°C, 1 atm 0.0156 cPSolubility in water @ 0°C, 1 atm 82.31 g/100 g water

The gas is essentially inert to common materials of construction such as stainless steel undernormal conditions of use. Platinum and gold are also not attacked by pure hydrogen chloride.

In the presence of moisture, however, most metals are corroded and it is advised that theproposed use and pressures are discussed with the supplier so that suitable construction materialsare established prior to installation. Hydrogen chloride neither burns nor supports combustion,

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Figure 9.4 Hydrogen chloride vapour pressure vs temperature

although burning sodium will continue to burn in it forming hydrogen and sodium chloride.Hydrogen chloride gas has produced runaway reactions with dinitrotoluene, fluorine (with ignition),sodium, and alcoholic hydrogen cyanide.

Liquid hydrogen chloride does not conduct electricity and is without action on zinc, iron,magnesium, calcium oxide and certain carbonates. However, it does dissolve aluminium.

Some special precautions for use of compressed hydrogen chloride gas include:

• Store and use under ventilated conditions.


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• Avoid galvanized pipe and brass or bronze fittings.• Wear protective clothing such as rubber or plastic aprons, rubber gloves, gas-tight goggles and

respiratory equipment as appropriate.• Ensure fast-acting showers are available close to site of use/storage plus eye-wash fountains or

similar facilities for eye irrigation.• Prevent suck-back of foreign material into the cylinder by use of check valves or vacuum break

traps.• Switch off gas lines from use backwards to the cylinder.

Hydrogen sulphide

Hydrogen sulphide is usually prepared on a small scale by the action of hydrochloric acid onferrous sulphide:

FeS + 2HCl " FeCl2 + H2S

The purest form is obtained by passing a mixture of sulphur vapour and hydrogen over finelydivided nickel at 450°C.

Hydrogen sulphide is used in the preparation of metal sulphides, oil additives etc., in thepurification and separation of metals, as an analytical reagent and as raw material in organicsynthesis. It burns in air with a blue flame:

2H2S + 3O2 " 2SO2 + 2H2O

or if oxygen is depleted:

2H2S + O2 " 2H2O + S

Hydrogen sulphide occurs naturally, e.g. in natural gas and petroleum, volcanic gases, and fromdecaying organic matter. It may be present near oil wells and where petroleum is processed.Commercially it is obtained as a by-product from many chemical reactions including off-gas inthe production of some synthetic polymers (e.g. rayon, nylon) from petroleum products, and bythe action of dilute mineral acids on metal sulphides. Physical properties are summarized in Table9.14 and effects of temperature on vapour pressure are shown in Figure 9.5.

Hydrogen sulphide is a dense, colourless, highly flammable water-soluble gas with an offensiveodour of rotten eggs. It is highly toxic; its effects on the body are given in Table 5.32. Acutepoisoning may result from exposures at or above 700 ppm due to systemic effects, includingattack on the nervous system and respiratory collapse. Hydrogen sulphide may become rapidlyoxidized on contact with a range of metal oxides and in certain cases may ignite or explode. It canalso react dangerously with a host of oxidants, rust and soda lime.

Cylinders are typically protected from over-pressurization by frangible gold-plated discs andfusible plugs.

Important precautions include:

• Use in well-ventilated conditions and eliminate sources of ignition.• Operators should work in pairs.• Do not rely on the sense of smell to detect hydrogen sulphide leaks. Strips of wet lead acetate

paper turn black on exposure to hydrogen sulphide and offer a simple indicator, as do colourindicator tubes. For plant-scale operations, instrumental multi-point detectors and alarms arelikely to be more appropriate.

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• Segregate cylinders of hydrogen sulphide from oxygen or other highly-oxidizing or combustiblematerials.

• Ground all lines and equipment used with hydrogen sulphide.• Insert traps in the line to prevent suck-back of liquid into the cylinder.• Provide respiratory protection for emergencies.• In the event of exposure, apply first aid as indicated in Table 9.9.

Liquefied petroleum gases (LPG)

LPG is a mixture of propane and n- and iso-butanes, plus small amounts of their olefinic counterparts.The main sources are natural gas wells, gas from crude oil wells and the cracking of crude oil. Therequirements for commercial LPG are defined in national standards and a stenching agent isadded for some uses.

The common LPGs in general use are commercial propane, comprising predominantly propaneand/or propylene, and commercial butane. The physico-chemical properties of propane and thebutanes are given in Table 9.15. These compounds are gaseous at normal ambient temperatureand pressure but are readily liquefied by the application of moderate pressure. They are stored anddistributed as liquids in low pressure cylinders or bulk containers at ambient temperature andallowed to revert to gas at the point of use. Large-scale storage and shipment by sea is inrefrigerated vessels at close to atmospheric pressure.

Butane itself is considered to be insoluble in water. Exposures of up to 5% for 2 hours appearnot to present problems. The TLV is 800 ppm. The relationship between pressure and temperatureis given by Figure 9.6.

Propane has a characteristic natural gas odour and is basically insoluble in water. It is a simpleasphyxiant but at high concentrations has an anaesthetic effect. The TLV is 2500 ppm. It is usuallyshipped in low-pressure cylinders as liquefied gas under its own vapour pressure of ca 109 psigat 21°C. Its pressure/temperature profile is given in Figure 9.7.

Table 9.14 Physical properties of hydrogen sulphide

Molecular weight 34.08Vapour pressure at 21°C 17.4 barSpecific volume at 21°C, 1 atm 701 ml/gBoiling point at 1 atm –60.33°CFreezing point at 1 atm –85.49°CSpecific gravity, gas at 15°C, 1 atm (air = 1) 1.1895Density, gas at 0°C, 1 atm 1.5392 g/lDensity, liquid at boiling point 0.993 g/mlCritical temperature 100.4°CCritical pressure 90.23 barCritical density 0.349 g/mlLatent heat of vaporization at boiling point 131 cal/gLatent heat of fusion at melting point 16.7 cal/gSpecific heat, gas at 25°C, 1 atm

Cp 0.240 cal/g °CCv 0.181 cal/g °Cratio Cp/Cv 1.32

Thermal conductivity at 0°C 3.05 # 10–5 cal/s cm2 °C/cmFlammable limits in air 4.3–45% by volumeAuto-ignition temperature 260°CSolubility in water at 20°C, 1 atm 0.672 g/100 ml waterViscosity, gas at 0°C, 1 atm 0.01166 cP


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Criticalpressure1309 psiaat 100.4°C

Boiling point

LPG is considered to be non-toxic with no chronic effects, but the vapour is slightly anaesthetic.In sufficiently high concentrations, resulting in oxygen deficiency, it will result in physicalasphyxiation. The gases are colourless and odourless but an odorant or stenching agent (e.g.methyl mercaptan or dimethyl sulphide) is normally added to facilitate detection by smell downto approximately 0.4% by volume in air, i.e. one-fifth of the lower flammable limit. The odorantis not added for specific applications, e.g. cosmetic aerosol propellant.

The main danger with LPG arises from its flammability. Fire or explosion may be fuelled bygas escape from leaking cylinders, from an appliance which has not been turned off properly, or

Figure 9.5 Hydrogen sulphide vapour pressure vs temperature

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from an appliance in which the flame has been extinguished. Any fire near an LPG cylinder maycause it to overheat and catch fire, or result in a BLEVE with missiles projected over longdistances.

The following safety measures supplement the general precautions listed in Table 9.3:

• Do not store or use a cylinder on its side, but upright with the valve uppermost.• Do not store or leave full or empty cylinders below ground level.• Never change a cylinder without first closing the cylinder valve and extinguishing naked lights

in the vicinity.

Table 9.15 Properties of LPGs

Propane Butane isoButane

Molecular weight 44.1 58.1 58.1Vapour pressure at 21°C, i.e. cylinder 7.7 1.15 21.6

pressure (kg/cm2 gauge)Specific volume at 21°C/l atm (ml/g) 530.6 399.5 405.8Bp at 1 atm (°C) –42.07 –0.5 –11.73Mp at 1 atm (°C) –187.69 –138.3 –159.6SG, gas at 16°C/l atm (air = 1) 1.5503 2.076 2.01Density, liquid at sat. pressure (g/ml) 0.5505 0.5788 0.563

(20°C) (20°C) (15°C)Density, gas at 0°C/l atm (kg/m3) 2.02 2.70 –Critical temperature (°C) 96.8 152 135Critical pressure (atm) 42 37.5 37.2Critical density (g/ml) 0.220 0.225 0.221Latent heat of vap. at bp (cal/g) 101.76 92.0 87.56Latent heat of fusion at mp (cal/g) 19.10 19.17 18.67Specific heat, liquid at 16°C (cal/g°C) – 0.5636 0.5695Specific heat, gas at 16°C:

Cp (cal/g°C) 0.3885 0.3908 0.3872Cv (cal/g°C) 0.3434 0.3566 0.3530ratio CP/Cv 1.13 1.1 1.1

Specific heat ratio at 16°C/l atm, CP/Cv 1.131 1.096 1.097Gross heat of combustion at 16°C/l atm 22.8 30.0 29.8

(cal/ml)Viscosity, gas at 1 atm (centipoise) 0.00803 0.0084 0.00755

(16°C) (15°C) (23°C)Coefficient of cubical expansion at 15°C 0.0016 0.0011 –

(per °C)Surface tension (dynes/cm) 16.49 16.02 15.28

(–50°C) (–10°C) (–20°C)Solubility in water at 1 atm (volumes/100 6.5 – 1.7

volumes water) (18°C) – (17°C)Flammable limits in air (% by volume) 2.2–9.5 1.9–8.5 1.8–8.4Autoignition temp. (°C) 467.8 405 543Max. explosion pressure (MPa) 0.86 0.86 –Min. ignition energy (MJ) 0.25 0.25 –Max. flame temperature (°C) 2155 2130 –Max. burning velocity (m/s) 0.45 0.38 –Necessary min. inert gas conc. for explosion

prevention in case of emergent outflow of gasin closed volumes (% v/v):

Nitrogen 45 41 –Carbon dioxide 32 29 –


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°F 25




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• Store cylinders, both full and empty, in a cool location away from flammable, toxic, or corrosivematerials and preferably at least 6.1 m from any source of ignition or heat.

• Replace any valve-protecting covers on empty cylinders, or those not in use. Handle cylinderswith care.

• Unless the installation is designed to be permanent, always disconnect a cylinder after use.• Always wear appropriate protective equipment, including gloves and goggles, when filling an

LPG cylinder.

Figure 9.6 n-Butane vapour pressure vs temperature

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The general requirements for the storage of LPG cylinders are given in Tables 9.16 to 9.18.Considerations in the transport of cylinders by road are given in Chapter 15.


Methane is obtained commercially from natural gas wells and from cracking of petroleum fractions.

Figure 9.7 Propane vapour pressure vs temperature








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Table 9.16 General requirements for storage of LPG cylinders

• Store in the open in a well-ventilated area at ground level.• Avoid other materials stacked near restricting natural ventilation.

Flammable liquid and combustible, corrosive, oxidizing or toxic substances and compressed gases should be keptseparately.

• Avoid cylinders impeding or endangering means of escape from premises or from adjoining premises.• The store floor should be level. A load-bearing surface (concrete, paved or compacted) is required where cylinders are

to be stacked.• Security arrangements should be such as to prevent tampering or vandals. Fencing should be of robust wire mesh which

does not obstruct ventilation.• The area should be at the separation distance from the property boundary, any building or fixed source of ignition quoted

in Table 9.17. This may only be reduced if suitable fire-resisting separation is provided.• To give additional protection from thermal radiation from any cylinder stack fire the minimum separation distance to any

nearby building housing a vulnerable population should, for quantities >400 kg, be 8 m or as in Table 9.17, column 3,whichever is the greater. This may be reduced to those in Table 9.17, column 4, by the installation of fire-resistingseparation or a fire wall.

• Prohibit all sources of ignition, including smoking, within a store or within the separation distance (exclude motorvehicles other than fork-lift trucks and those for delivery/collection from open-air stores).

• Avoid openings into buildings, cellars, or pits within 2 m or the separation distances, whichever is greater. (Any gully ordrain unavoidably within 2 m should have the opening securely covered or fitted with a water seal to prevent vapouringress.)

• Electrical equipment suitable for a Zone 2 area (e.g. to BS 5345) and constructed to a recognized standard should beinstalled within the store and separation distance. Zone 2 areas are summarized in Table 9.18.

• Clearly mark the area with notices indicating an LPG storage area, flammable contents, prohibition of ignition sourcesand procedures to follow in case of fire.

• Avoid accumulation of rubbish, small bushes, dry leaves etc. within the separation distance. Remove weeds and longgrass within the separation distance and up to 3 m from cylinders.

• Cylinders should be stored upright with the valves closed with any protective cover, cap or plug in place. Cartridgeswithout valves may be stored on their sides.

• Cylinders on a vehicle or trailer parked overnight rate as a single stack so that the separation distance in Table 9.17,column 3, is applicable.

• Cylinders received into store and taken out for delivery should be checked for damage or leakage. Stacks should beinspected daily for stability and that they contain no damaged/leaking cylinders.

• Cylinders should be handled carefully to avoid personal injury or damage to them.

The physical properties of methane are given in Table 9.19 and the relationship between pressureand temperature in Figure 9.8. It is considered to be non-toxic but is an asphyxiant at highconcentrations. Coalminers have inhaled air containing up to 9% methane with no apparentuntoward effect but higher concentrations of at least 10% in air result in a feeling of pressure onthe eyes and forehead which will disappear after breathing fresh air. Characteristic symptoms ofasphyxiation occur at higher concentrations (i.e. rapid respiration, fatigue, nausea, vomitingpossibly leading to loss of consciousness and anoxia). At low concentrations the odour of methaneis undetectable; at exposures of >5000 ppm there is a sweet oil-type odour. Selected gradescontain an odorizer, e.g. natural gas for commercial and domestic full.

It is considered to be chemically inert at room temperature and atmospheric pressure but it doesreact under more forcing conditions and vigorous reactions have occurred with halogens, interhalogencompounds, and oxidizing agents such as liquid oxygen and dioxygen difluoride.

The main hazard is that of flammability. The following precautions supplement those in Table9.3 for the storage of methane gas cylinders:

• Store in a purpose-built compound preferably in the open air and well ventilated.• Locate free from fire risk and away from sources of heat and ignition.• Maintain clear access, and restrict access to the compound. Mark with hazard warning signs.• Prohibit the use of naked flames or smoking in the vicinity of, or inside, the compound.

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• Store separately from oxygen and oxidants, using a fire-resistant partition where necessary.• Store the minimum quantity practicable.• Check periodically for general condition and leakage.


Nitrogen is an odourless, colourless gas which comprises ca 79% by volume of air and is anessential constituent of all living organisms, e.g. as protein. It is made in the laboratory by gently

Table 9.17 Recommended minimum separation distances for total storage of LPG in cylinders or size of maximumstack (the greater of the two distances is advised)

(1) (2) (3) (4)Total quantity LPG store Size of largest stack Minimum separation Minimum separation

distance to boundary, distance to boundary,building or fixed building or fixed ignitionignition sources from the source from fire wallnearest cylinder (where (where provided)* **no fire wall provided)

(kg) (kg) (m) (m)

From 15 to 400 1*** Nil,, 400 to 1000 Up to 1000 3 1,, 1000 to 4000 4 1,, 4000 to 6000 From 1000 to 3000 5 1.5,, 6000 to 12 000 6 2,, 12 000 to 20 000 ,, 3000 to 5000 7 2.5,, 20 000 to 30 000 ,, 5000 to 7000 8 3,, 30 000 to 50 000 ,, 7000 to 9000 9 3.5,, 50 000 to 60 000 ,, 9000 to 10 000 10 4,, 60 000 to 100 000 11 4.5,, 100 000 to 150 000 ,, 10 000 to 20 000 12 5,, 150 000 to 250 000 ,, 20 000 to 30 000 15 6

Above 250 000 20 7

*The distance from the nearest cylinder to a boundary, building etc. should be not less than in column 3 when measuredaround the fire wall.**Minimum distance from nearest cylinder to fire wall should normally be 1.5 m except as qualified.***No separation distance is required for these quantities where boundary walls and buildings are of suitable construction.

Table 9.18 Areas classified as requiring Zone 2 electrical equipment

Location Extent of classified area

Storage in open air In the storage area up to a height of 1.5 m above the top of thestack or beneath any roof over the storage place.Outside the storage area or the space covered by any roof up to1.5 m above ground level and within the distance set out for afixed source of ignition in Table 9.17, column 3.

Storage within a specially designed building or in The entire space within the building or storage area and outsidea specially designed storage area within a building any doorway, low level ventilator or other opening into the

store within the separation distance set out in Table 9.17,column 3, up to a height of 1.5 m above ground level.


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warming a concentrated solution of equimolar proportions of ammonium chloride and sodiumnitrite:

NH4Cl + NaNO2 " NaCl + NH4NO2 " N2 + 2H2O

On the industrial scale nitrogen is obtained by the fractional distillation of liquid air (see page261). It will neither burn nor support combustion. Nitrogen is distributed as a pressurized gas ingrey cylinders with black shoulders. (Oxygen-free nitrogen has opposed white spots on thecylinder shoulder.) It finds wide use in its inert capacity, e.g. in electrical equipment and in thechemical and food industries. Large volumes of atmospheric nitrogen are converted into ammoniumsulphate for fertilizer and into nitric acid.

Figure 9.8 Methane vapour pressure vs temperature

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Since it is chemically inert no special materials of construction are required. Selected physicalproperties are listed in Table 9.20.

Nitrogen is non-toxic but will cause asphyxiation through oxygen depletion of air and is themost common cause of gassing accidents in industry. There are no warning signs beforeunconsciousness occurs, and at high concentrations almost instant unconsciousness may occurand prove fatal (page 77). Table 5.7 summarizes the health effects of oxygen-deficient atmospheres.

Nitrogen oxides

The various oxides of nitrogen are given in Chapter 5.Nitrous oxide is a colourless, non-flammable, non-corrosive gas with a sweetish odour and

taste. It is prepared both in the laboratory and on a commercial scale by heating ammoniumnitrate:

NH4NO3 " N2O + 2H2O

Heating must be terminated when two-thirds of the nitrate has decomposed since explosivenitrogen trichloride may be formed from traces of ammonium chloride impurity.

Nitrous oxide may also be obtained by the controlled reduction of nitrates or nitrites, decompositionof hyponitrites, or thermal decomposition of hydroxylamine.

It is generally considered not to be toxic and non-irritating. One of its main applications is, incombination with air or oxygen, as a weak anaesthetic in medicine and dentistry. At low concentrationsit produces hysteria (hence the term laughing gas). At high concentrations in the absence of air itis a simple asphyxiant. It is also used as a dispersing agent in whipping cream.

It does not react with oxygen, ozone, hydrogen, chlorine, potassium, phosphine or aqua regia.However, whilst stable at ordinary temperatures, it decomposes readily to oxygen and nitrogen at600°C and therefore supports combustion of burning substances. When nitrous oxide is transferredfrom a stock cylinder to smaller cylinders the gas expansion results in cooling and a reduction inpressure. On heating the stock container to increase pressure and thereby facilitate transfer the gas

Table 9.19 Physical properties of methane

Molecular weight 16.04Specific volume @ 21°C 1479.5 ml/gBoiling point @ 1 atm –161.5oCFreezing point @ 1 atm –182.6°CTriple point –182.5°CTriple point pressure 0.115 atmSpecific gravity (gas) @ 16°C, 1 atm 0.5549Density (gas) @ 0°C, 1 atm 0.72 g/lDensity (liquid) @ bp 0.4256 g/lCritical temperature –82.1°CCritical pressure 673.3 psia (45.8 atm)Critical density 0.162 g/mlLatent heat of vaporization @ bp 121.54 cal/gSpecific heat (gas) @ 16°C, 1 atm Cp/Cv 1.307Flammable limits in air 5.3–14%Autoignition temperature 540°CMinimum ignition energy 0.28 mJFlame temperature 1880°CLimiting oxygen index 11.5%Viscosity (gas) @ 1 atm, 4.4°C 0.0106 cP


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decomposes causing explosive rupture of the stock cylinder. This emphasizes the importance ofkeeping cylinders away from heat sources, e.g. oxyacetylene welding operations. Explosive reactionhas also occurred between nitrous oxide and a variety of chemicals including amorphous boron,ammonia, carbon monoxide, hydrogen, hydrogen sulphide, and phosphine. Because the oxygencontent of 36.4% is higher than the 21% in air, combustion or oxidation in nitrous oxide is muchfaster than in air.

It is transported in high pressure steel cylinders equipped with brass valves.Physical properties are summarized in Table 9.21 and the vapour pressure/temperature relationship

is depicted by Figure 9.9. The general precautions in Table 9.3 apply.

Nitric oxide is made commercially by oxidation of ammonia above 500°C in the presence ofplatinum, or by reduction of nitrous acid with ferrous sulphate or ferrous halides. The physical

Table 9.20 Physical properties of nitrogen

Molecular weight 28.0134Specific volume @ 21°C 861.5 ml/gBoiling point @ 1 atm –195.8°CTriple point –210.0°CTriple point pressure 94.24 mm HgDensity (gas) @ 20°C 1.250 g/lDensity (liquid) @ bp 0.8064 g/mlCritical temperature –147.1oCCritical pressure 33.5 atmCritical density 0.311 g/mlLatent heat of vaporization @ bp 47.51 cal/gSpecific heat (gas) @ 16°C, 1 atm

Cp 0.2477 cal/g °CCv 0.1765 cal/g °Cratio Cp /Cv 1.4

Viscosity (gas) @ 15°C, 1 atm 0.01744 centipoisesDielectric constant (liquid) @ bp 1.433Solubility in water @ 0°C 2.3 ml/100 ml water

Table 9.21 Physical properties of nitrous oxide

Molecular weight 44.013Vapour pressure @ 21°C 745 psigSpecific volume @ 21°C, 1 atm 543 ml/gBoiling point @ 1 atm –89.5°CFreezing point @ 1 atm –90.84°CSpecific gravity (gas) @ 15°C, 1 atm 1.530Density (gas) @ 0°C, 1 atm 1.907 g/lDensity (liquid) @ bp 1.266 g/lCritical temperature 36.5°CCritical pressure 1054 psia (71.7 atm)Critical density 0.457 g/lLatent heat of vaporization @ bp 89.9 cal/gSpecific heat gas @ 25°C, 1 atm

Cp 0.2098 cal/g °CCv 0.1610 cal/g °Cratio Cp/Cv 1.3

Viscosity (gas) @ 0°C, 1 atm 0.01362 centipoiseSolubility in water @ 0°C, 1 atm 1.3 volumes/volume of water

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1000–60–80°F 6038–18–51–62°C 16



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properties of nitric oxide are given in Table 9.22. This is also a colourless, non-flammable gaswhich is basically non-corrosive to standard materials of construction. Liquid nitric oxide likeother cryogenic oxidizers (e.g. ozone) is very sensitive to detonation in the absence of fuel. It isthe simplest molecule that is capable of detonation in all three phases: the liquid oxide mayexplode during distillation. Nitric oxide is more toxic than nitrous oxide. It decomposes into itselements only when heated to 1000°C and therefore it is not a ready supporter of combustion.Vigorously burning phosphorus continues to burn in the gas but burning sulphur or charcoal isextinguished.

Figure 9.9 Nitrous oxide vapour pressure vs temperature


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Nitric oxide combines readily with atmospheric oxygen at ambient temperature to producebrown fumes of pungent nitrogen dioxide, and in the presence of charcoal with chlorine to formnitrosyl chloride:

2NO + O2 " NO2

2NO + Cl2 " 2NOCl

It is shipped in cylinders as a non-liquefied gas at a pressure of about 500 psig at 21°C and isprimarily used as a chemical intermediate (e.g. in production of nitric acid). It is somewhatsoluble in water producing nitric acid, making the gas slightly irritating to the lower reaches ofthe respiratory system and mucous membranes causing congestion to the throat, bronchi andoedema of the lungs with little warning. The acids neutralize alkali in tissue with subsequentadverse effect on blood pressure, producing headaches and dizziness. The OEL is 25 ppm (8 hrTWA) and 35 ppm (15 min STEL), but generation of the more toxic dioxide on release to air isalways a major consideration.

Some special safety measures include:

• Handle only in well-ventilated areas, preferable with a hood equipped with forced ventilation.• Provide adequate number of exits from the work area.• Use approved personal protection as appropriate, including self-contained breathing apparatus

and associated training.• Provide suitable first-aid cover.• Prevent air contamination in high-pressure reactions since the nitrogen dioxide which could

form may pose ignition and detonation hazards.

Gaseous nitrogen dioxide is a brown, paramagnetic, non-flammable, toxic, strongly oxidizing,corrosive substance shipped in approved, low-pressure steel cylinders. It is prepared in situ byheating lead nitrate:

2Pb(NO3)2 " 2PbO + 4NO2 + O2

It is available commercially from several routes including as a product from the manufacture ofsodium nitrate from sodium chloride and nitric acid, and from a process involving the passage ofammonia and air over heated platinum and treating the nitric oxide so formed with oxygen.

Table 9.22 Physical properties of nitric oxide

Molecular weight 30.006Specific volume @ 21°C, 1 atm 811 ml/gBoiling point @ 1 atm –151.7°CFreezing point @ 1 atm –163.6°CDensity (gas) @ 0°C, 1 atm 1.3402 g/lDensity (liquid) @ bp 1.269 g/lCritical temperature –93°CCritical pressure 940.8 psia (64 atm)Critical density 0.52 g/mlLatent heat of vaporization @ bp 110.2 cal/gSpecific heat (gas) @ 15°C, 1 atm

Cp 0.2328 cal/g °CCv 0.1664 cal/g °Cratio Cp/Cv 1.4

Viscosity (gas) @ 15°C 1 atm 0.0178 cPSolubility in water @ 0°C, 1 atm 7.34 ml/100 g water

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The brown nitrogen dioxide gas condenses to a yellow liquid which freezes to colourlesscrystals of dinitrogen tetroxide. Below 150°C the gas consists of molecules of dinitrogen tetroxideand nitrogen dioxide in equilibrium and the proportion of dinitrogen tetroxide increases as thetemperature falls. Above 150°C nitrogen dioxide dissociates into nitric oxide and oxygen.

Nitrogen dioxide is an oxidizing agent; it gives up all, or part, of its oxygen to reducing agents,leaving a residue of nitrogen and nitric oxide. It reacts with potassium, hydrogen sulphide,mercury, burning phosphorus or carbon, heated iron and copper. Explosions have been reportedbetween nitrogen dioxide and a host of materials including alcohols (to produce alkyl nitrates),boron compounds, carbonyl metals, propyl nitrite, nitroaniline dust, sodium amide, triethylamine,and vinyl chloride.

Nitrogen dioxide reacts with water, giving first a mixture of nitrous and nitric acids, andultimately nitric acid and nitric oxide:

H2O + 2NO2 " HNO3 + HNO2

H2O + 3NO2 " 2HNO3 + NO

When dry the gas is not corrosive to mild steel at normal temperatures and pressures. Metals andalloys such as carbon steel, stainless steel, aluminium, nickel and Inconel are satisfactory. For wetusage stainless steels resistant to 60% nitric acid are suitable. Important uses include use as ableaching agent, an oxidation catalyst, polymerization inhibitor, a nitrating agent, oxidizing agent,rocket fuel, and in explosives manufacture. Its physical properties are summarized in Table 9.23and its vapour pressure/temperature relationship is shown in Figure 9.10.

Table 9.23 Physical properties of nitrogen dioxide

Molecular weight 46.005 (or 92.01 for the tetroxide)Vapour pressure @ 21°C 14.7 psiaSpecific volume @ 21°C, 1 atm 293.4 ml/gBoiling point @ 1 atm 21.25°CFreezing point @ 1 atm –9.3°CSpecific gravity (gas) @ 20°C, 1 atm 1.58Density (gas) @ 21°C, 1 atm 3.3 g/lDensity (liquid) @ 20°C 1.448 g/mlCritical temperature 158.0°CCritical pressure 1470 psia (100 atm)Critical density 0.56 g/mlLatent heat of vaporization @ bp 99.0 cal/gSpecific heat (gas) @ 25°C, 1 atm Cp 0.1986 cal/g °CViscosity (liquid) @ 20°C 4.275 millipoises

A key feature of its toxicity (page 154) at low concentrations is the delay between exposure andonset of symptoms. The OES is 3 ppm (8 hr TWA) and 5 ppm (15 min STEL). Effects of exposureare summarized in Table 5.33. Chronic exposures to low concentrations may cause chronicirritation of the respiratory tract with cough, headache, loss of weight, loss of appetite, dyspepsia,corrosion of the teeth and gradual loss of strength. Concentrations above 60 ppm produce immediateirritation of the nose and throat with coughing, choking, headache, shortness of breath andrestlessness. Even brief exposures above 200 ppm may prove fatal. Liquid nitrogen dioxide(dinitrogen tetroxide) is corrosive to skin.

First-aid measures include removal from the contaminated atmosphere, rest and administrationof pure oxygen. Skin or eyes in contact with liquid should be thoroughly irrigated. Medicalattention should be sought. Other special precautions include:


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• Handle in well-ventilated area, preferably with hood equipped with forced extract ventilation.• Ensure adequate number of emergency exits.• Consider the need for personal protection such as skin, eye (goggles/face shield) and respiratory

protection including self-contained breathing apparatus.• Provide instant-acting safety showers and eye-wash facilities in the location of the work

area.• Train staff in appropriate first-aid measures including how to seek immediate medical assistance.

Figure 9.10 Nitrogen dioxide vapour pressure vs temperature

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Oxygen occurs free in air in which it forms 21% by volume. It is also found combined withhydrogen in water and constitutes 86% of the oceans, and with other elements such as mineralsconstituting ca 50% of the earth’s crust. In the laboratory it is usually prepared by the thermaldecomposition of potassium chlorate in the presence of manganese dioxide catalyst:

2KClO3 " 2KCl + 3O2

Industrially, it is manufactured either by fractional distillation of air, or by electrolysis of sodiumhydroxide and it is distributed as a non-liquefied gas in pressurized black cylinders at ca 2200 psigat 21°C. Since it is non-corrosive no special materials of construction are required.

Selected physical properties of oxygen are included in Table 9.24. It is a colourless, odourlessand tasteless gas which is essential for life and considered to be non-toxic at atmospheric pressure.It is somewhat soluble in water and is slightly heavier than air. Important uses are in the steel andglass industries, oxyacetylene welding, as a chemical intermediate, waste-water treatment, fuelcells, underwater operations and medical applications.

Table 9.24 Physical properties of oxygen

Molecular weight 32.00Specific volume @ 21°C, 1 atm 755.4 ml/gBoiling point @ 1 atm –183.0oCTriple point –218.8°CDensity (gas) @ 0°C, 1 atm 1.4291 g/lDensity (liquid) @ bp 1.141 g/lCritical temperature 1118.4°CCritical pressure 737 psia (50.14 atm)Critical density 0.427 g/lLatent heat of vaporization @ bp 50.94 cal/gSpecific heat (gas) @ 15°C, 1 atm

Cp 0.2200 cal/g °CCv 0.1554 cal/g °Cratio Cp/Cv 1.42

Viscosity (gas) @ 25°C, 1 atm 0.02064 centipoiseSolubility in water @ 0°C, 1 atm 1 volume/21 volumes water

Explosive reactions can occur between oxygen and a wide range of chemicals including organiccompounds (such as acetone, acetylene, secondary alcohols, hydrocarbons), alkali and alkalineearth metals, ammonia, biological specimens previously anaesthetized with ether, hydrogen andfoam rubber.

Oxygen supports combustion and the hazard is increased if the concentration in air exceeds21% (page 199) or at pressures above atmospheric pressure. Substances ignite more readily, burnat a faster rate, generate higher temperatures and may be extremely difficult to extinguish. Substances,e.g. plastics, clothing or metals, which may not normally burn easily can burn vigorously inoxygen-enriched air. Oxygen may become trapped within clothing; this can then be ignited andcause serious burn injuries. Because some substances, e.g. oil and grease, may react explosivelywith pressurized oxygen it is important never to use lubricants on oxygen equipment and to freepipelines from deposits of them.

Enrichment of the atmosphere in any workplace to about 25% oxygen can be hazardous; thisis particularly so in a confined space. Inhalation of 100% oxygen at atmospheric pressure for


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16 hr per day for several days poses no undue problems but longer periods of exposure to highpressures can adversely affect neuromuscular coordination and the power of concentration.

In addition to the control measures given in Table 9.3, the following precautions are appropriatewhen using industrial and medical oxygen, or mixtures of oxygen with other gases.Never:

• Use oxygen to sweeten the air of a workplace.• Use oxygen instead of fresh air to ventilate or cool a confined space.• Use oxygen instead of compressed air or as a source of pressure, e.g. to clear blockages in

pipelines or to power air-driven tools.• Use oxygen to blow down clothing, benches or machinery.• Use oxygen to inflate vehicle tyres, rubber boats etc.• Use oxygen to start a diesel engine.• Use oxygen to cool the person.• Use oil or grease on oxygen equipment.• Use jointing compound or tape to cure leaks in oxygen equipment, e.g. at cylinder connections.• Cut off the supply of oxygen by nipping or kinking flexible hose when changing equipment.


• Only use materials and equipment which are suitable for oxygen service and to a recognizedstandard.

• Regularly check equipment for signs of leaks, e.g., at hose connections; replace damaged orworn items. Usually the system is pre-tested with, e.g., nitrogen.

• Ensure that equipment, e.g. pipework for oxygen service, is kept clean and free from oil, greaseor dust.

• Ensure that the rated maximum inlet pressure of the regulator is not less than the cylindersupply pressure. (For cylinder pressures up to 200 bar, pressure regulators should comply withBS 5741. For higher cylinder pressures check with the manufacturer that the pressure regulatorhas been shown to be suitable by appropriate testing.)

• Ensure that the pressure adjusting screw of a pressure regulator is fully unwound, so that theregulator outlet valve is closed before opening the oxygen cylinder valve.

• Open cylinder valves slowly.• Ensure that the cylinder valves are closed and piped supplies isolated whenever work is stopped.• Ensure that flexible oxygen hose for welding etc. complies with BS 5120. The correct colour

for oxygen is blue.• Ensure that proper fresh air ventilation is provided in oxy-fuel gas welding and cutting operations.• Ensure that high-pressure oxygen systems are designed, constructed, installed and commissioned

by competent people with specialized knowledge of the subject.• When working on ships, remove pipes or hoses when work stops, other than for short intervals.• Store oxygen cylinders in a well-ventilated area or compound away from combustible materials

and separated from cylinders of flammable gases.• Handle oxygen cylinders carefully, preferably using a purpose-built trolley and keep secured to

prevent cylinders from falling.• Wear protective clothing appropriate to the work, e.g. leather gloves, fire-retardant overalls,

safety shoes or boots and eye protection.• If applicable, locate oxygen cylinders outside any confined space and in an area of good


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Ozone is an allotrope of oxygen containing three oxygen atoms. It occurs naturally in the upperatmosphere and is formed in small quantities during electrical discharges from electrical machinesor when white phosphorus smoulders in air. In the laboratory it is most conveniently obtained bysubjecting air to electrical discharges in ‘ozonizers’ when some of the oxygen molecules dissociateinto oxygen atoms which then combine with other oxygen molecules. However, the yield ofozone is only 10% even when pure oxygen is used. It may also be prepared by electrolysis of ice-cold dilute sulphuric acid using a high current density. Here the concentration of ozone liberatedat the platinum-in-glass anode is about 14%.

Pure ozone is made by fractional distillation of the blue liquid resulting from the cooling ofozonized oxygen in liquid air. Commercially it is often supplied dissolved in chlorofluorocarbonsin stainless steel cylinders at ca 475 psig cylinder pressure at 20°C often transported chilled withdry ice. These solutions can be handled safely at vapour concentrations of ca 20% by volume ofozone.

The physical properties of ozone are summarized in Table 9.25.

Table 9.25 Physical properties of ozone

Molecular weight 47.998Boiling point @ 1 atm –111.9°CFreezing point @ 1 atm –192°CDensity (gas) @ 0°C, 1 atm 2.143 g/lDensity (liquid) @ –183°C 1.571 g/lCritical temperature –12.1°CCritical pressure 802.6 psia (54.6 atm)Viscosity (liquid) @ –183°C 1.57 cPLatent heat of vaporization @ bp 3410 cal/moleDielectric constant (liquid) @ –183°C 4.79Dipole moment 0.55DSolubility in water @ 0°C, 1 atm 0.494 volume/volume of water

Ozone is strongly exothermic in its reactions and neat solid or liquid phases are highly explosive.Pure ozone is a toxic, slightly bluish, unstable, non-flammable but potentially explosive gas

with a smell akin to that of much-diluted chlorine. It is used mainly because of its extremeoxidizing ability (second only to fluorine in oxidizing power) in chemical syntheses or becauseof its powerful germicidal activity on many bacterial organisms, e.g. as a water purification agent(e.g. swimming pools) although it may leave an unpleasant taste, as a bleach, in treatment ofindustrial waste, sterilization of air (e.g. in the ventilation of premises of underground railwayswith limited access to fresh air), deodorizing sewage and stack gases, and in food preservation.Indeed, algae and certain fungi resistant to chlorine are highly susceptible to ozone. It decomposesslowly at room temperature and rapidly at 200°C and is decomposed by many finely-dividedmetals. It reacts readily with unsaturated organic moieties to form ozonides:

R1—CH ==CH—R2 + O3 " R1—CH CH—R2





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where R1 and R2 are univalent organic groups.Violent reactions have occurred between ozone and many chemicals, a small selection being

acetylene, alkenes, dialkyl zincs, benzene/rubber solution, bromine, carbon monoxide and ethylene,diethyl ether, hydrogen bromide, and nitrogen oxide.

Ozone is an irritant to eyes and mucous membranes. Inhalation can cause pulmonary oedemaand bleeding at ‘high’ concentrations, whilst at lower exposures symptoms include headache,shortness of breath, or drowsiness. Long-term effects may include chronic pulmonary effects,ageing, and possibly lung cancer. The ACGIH classify ozone as one of those ‘Agents which causeconcern that they could be carcinogenic for humans but which cannot be assessed conclusivelybecause of the lack of data. In vitro or animal studies do not provide indications of carcinogenicitywhich are sufficient to classify the agent into one of the other categories.’ The TLV is set as asliding scale for exposures during different workloads, thus:

• 0.05 ppm for heavy work.• 0.08 ppm for moderate work.• 0.10 ppm for light work.• 0.20 ppm for heavy, moderate, or light workloads for up to a maximum exposure of 2 hours.

Because of the odour threshold of ca 0.015 ppm, exposure to ozone below the TLV can usuallybe detected by smell.

Precautions in addition to those in Table 9.3 include:

• Keep cylinders chilled (to help prevent decomposition rather than as a safety measure).• Avoid copper and copper alloys since these can catalyse the decomposition, and rubber components

are unsuitable.• Pre-test systems for leaks with inert gas.• Prevent contact with grease, oil or other combustible material.• Clean all equipment for oxygen service.• Handle in a ventilated hood to protect surrounding atmosphere from leaks.• Consider the need for appropriate personal protection including eye, skin and respiratory

equipment.• Consider the need for leak detection systems.• Where possible avoid explosions by working with dilute solutions at low temperatures in

suitable solvents.

Sulphur dioxide

Sulphur dioxide is used as a preservative for beer, wine and meats; in the production of sulphitesand hydrosulphites; in solvent extraction of lubricating oils; as a general bleaching agent for oilsand foods; in sulphite pulp manufacture; in the cellulose and paper industries; and for disinfectionand fumigation.

It is a non-flammable colourless gas which is twice as dense as air, and slightly soluble in waterforming sulphurous acid. It is readily liquefied as a gas under its own vapour pressure of about35 psig (2.4 bar) at 21°C. Figure 9.11 depicts the effect of temperature on vapour pressure; Table9.26 lists the physical properties. Cylinders tend to be protected against over–pressurization bymetal plugs melting at about 85°C.

Gaseous sulphur dioxide is highly irritant and practically irrespirable. Effects on the body aresummarized in Table 5.3. It can be detected at about 3.5 ppm and the irritating effects would

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Boiling point

Figure 9.11 Sulphur dioxide vapour pressure vs temperature

preclude anyone from suffering prolonged exposure at high concentrations unless unconscious, ortrapped.

Liquid sulphur dioxide may cause eye and skin burns resulting from the freezing effects uponevaporation. Dry sulphur dioxide is non-corrosive to common materials of construction exceptzinc. The presence of moisture renders the environment corrosive.

In addition to the precautions listed in Table 9.3, the following controls are appropriate:

• Use in well-ventilated areas.


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Table 9.26 Physical properties of sulphur dioxide

Molecular weight 64.063Vapour pressure at 21°C 2.37 barSpecific volume at 21°C, 1 atm 368.3 ml/gBoiling point at 1 atm –10.0°CFreezing point at 1 atm –75.5°CSpecific gravity, gas at 0°C, 1 atm (air = 1) 2.264Density, gas at 0°C, 1 atm 2.927 g/lDensity, liquid at –10°C 1.46 g/mlCritical temperature 157.5°CCritical pressure 78.8 barCritical density 0.524 g/mlLatent heat of vaporization at boiling point 92.8 cal/gLatent heat of fusion at melting point 27.6 cal/gSpecific heat, liquid at 0°C 0.318 cal/g °CSpecific heat, gas at 25°C, 1 atm

Cp 0.1488 cal/g °CCv 0.1154 cal/g °Cratio Cp/Cv 1.29

Thermal conductivity at 0°C 2.06 # 10–5 cal/s cm2 °C/cmViscosity, gas at 18°C, 1 atm 124.2 mPSolubility in water at 0°C, 1 atm 18.59% by weight

at 20°C, 1 atm 10.14% by weight

• Wear eye/face protection, approved footwear and rubber gloves.• Showers and eye-wash facilities and respiratory protection should be conveniently located for

emergencies.• Insert traps in the line to avoid liquid suck-back into the cylinder.• Check for leaks with soap solution, aqueous ammonia or colour indicator tubes.• First aid measures include those in Table 9.9.

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Monitoring techniques

As mentioned in Chapters 4, 5 and 16 chemicals can be a nuisance or pose safety, health andenvironmental risks, or become wasteful of expensive resources if allowed to escape excessivelyand uncontrollably into the general or workplace environment. Escapes can result from inadequateprocess control, errors in operation or maintenance, incomplete understanding of the process, etc.Such problems can arise from both: periodic emissions of chemicals due to the need to open, orenter, the ‘system’ occasionally (e.g. during sampling, cleaning, line-breaking) including bothplanned and unplanned releases (e.g. due to accidents, human error) and, continuous low-levelfugitive emissions from normally-closed points, e.g. valve seals, flange gaskets, pump seals, drainvalves.

The need to monitor the impact of activities involving chemicals on the environment may stemfrom sound management practice or to satisfy a host of specific legal requirements. Thus, in theUK under the Environmental Protection (Prescribed Substances and Processes) Regulations 1991,operators must apply BATNEEC to prevent or minimize the release of prescribed substances intothe environment, or to render harmless any emissions. The prescribed substances for release intothe air are given in Table 10.1. No prescribed process may be operated without an authorizationfrom the Environment Agency and air pollutants which must be measured and the frequency ofmonitoring are set out in the authorization. Compliance with emission limits for municipal wasteincineration plants (Table 10.2) also requires monitoring.

Table 10.1 Prescribed substances for release into the air

Oxides of sulphur and other sulphur compoundsOxides of nitrogen and other nitrogen compoundsOxides of carbonOrganic compounds and partial oxidation compoundsMetals, metalloids and their compoundsAsbestos, glass fibres and mineral fibresHalogens and their compoundsPhosphorus and its compoundsParticulate matter

In addition to pollution episodes, risks may arise due to atmospheric oxygen concentrationsfluctuating beyond its normal level of 21% posing health (page 72) or fire hazards. Fire andexplosion dangers may also arise from the presence of flammable gases, vapours, or dusts in theatmosphere (Chapter 6).

Thus, as illustrated by Table 17.13 monitoring emissions of hazardous chemicals into theenvironment may be required for a variety of reasons such as:


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• Assessing fire or explosion risks from atmospheres containing flammable gas, vapour or dust.• Determining oxygen content of the working atmosphere.• Determining sources of leaks of toxic, flammable, or nuisance pollutants.• Identifying unknown pollutants.• Assessing process efficiency and control.• Assessing environmental risk from effluent discharges or for formal environmental impact

assessment.• Determining employee exposure to known toxic substances.• Providing data for internal company environmental audits.• Investigation of the causes of accidents.• Investigation of the cause and nature of problems (e.g. local complaints of odour) or pollution


Selected general analytical techniques formonitoring environmental pollution

Stages in environmental monitoring include obtaining representative samples of the environmentin question and subsequent analysis of physical, chemical or microbiological attributes. Monitoringtechniques range from sophisticated in-line, continuous sampling and instantaneous analysislinked to audible/visual alarms or features to control the pollution; samplers running continuously,e.g. throughout a normal day for subsequent analysis; to grab samples (i.e. samples collected overa short time span of, e.g., a few minutes). Continuous monitoring is common in personal dosimetrystudies where an appropriate collection device samples air wherever a worker is throughout aspecified period, e.g. 15 minutes or 8 hours (page 111). A selection of common analytical techniquesinclude the following.

Gases and vapours

Atomic absorption/emission spectrometry

Metal ions are most commonly measured using atomic absorption spectrometry. In this technique

Table 10.2 Selected emission limits for municipal waste incineration (units: mg/m3)

Country EU EU EU UK UK

Plant capacity 3 1–3 <1 >1 <1(tonne per hour)

Particulates 30 100 200 30 200CO 100 100 100 100 100SO2 300 300 – 300 300Volatile organic 20 20 20 20 20

compoundsHF 2 4 – 2 –NOx as NO2 – – – 350 –Cr, Cu, Mn, Pb 5 5 –Ni, As 1 1 – 1 (incl Sn) 5Cd, Hg 0.2 0.2 – 0.1 eachDioxins – – – 1


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the test sample is aspirated into a flame where chemical reduction of metal ions to metal atomsoccurs. Light is emitted at the discrete absorption wavelength for the metal. A disadvantage is theneed for a separate lamp for each element. Emission spectrometry is therefore preferred. Here testmaterial is heated and vaporized using a DC or inductively-coupled plasma generator, after whichan optical emission spectrum as a function of wavelength is recorded. An advantage of thistechnique is that a range of metals or metalloids can be analysed simultaneously.


Here a chemical reaction produces a molecule with electrons in an excited state. Upon decay tothe ground state the liberated radiation is detected. One such example is the reaction betweenozone and nitric oxide to form nitrogen dioxide emitting radiation in the near infra-red in the0.5–3µ region. The technique finds use for measuring nitric oxide in ambient air or stack emissions.


This technique permits the separation of a mixture of compounds by their partition between twoimmiscible heterogeneous phases, one of which is stationary. It detects substances qualitativelyand quantitatively. The chromatogram retention time is compound-specific, and peak-height indicatesthe concentration of pollutant in the sample. Detection systems include flame ionization, thermalconductivity and electron capture. With gas chromatography the mixtures to be separated are inthe vapour phase under the operating conditions of the equipment. A gas is used as the mobilephase to carry the sample over a column of stationary phase. Flame ionization detection operatesby ionisation of molecules in a hydrogen flame and detection of the current change using a pairof biased electrodes. The current signal is directly related to the number of carbon atoms in thesample. Thermal conductivity detectors measure the change in electrical resistance of a heatedfilament as gas flows over it. It is most suitable for gases with very high, or very low, conductivity.Traditionally gas chromatography is a laboratory analysis but portable versions are now availablefor field work.

In classical liquid chromatography a solution of solute percolates under gravity through acolumn packed with finely-divided solid when different compounds elute at different rates. Inhigh-performance liquid chromatography (HPLC) the liquid is eluted from a packed columnunder high pressure using solvent. Detection systems include differential refractive index, diodearray, electrochemical and ultra-violet-visible absorption. HPLC is used for analysis of lessvolatile compounds in liquid samples than those in gas chromatography.

Because of its sensitivity (<1 ppm), ion chromatography has become extremely popular foranalysis of ions in solution. It is a column-based method for separating ions similar to HPLC butusing ion exchange columns and either high- or low-conductivity eluent. The most commondetectors are electrical conductivity and ultra-violet absorption. It finds wide use in air pollutionmonitoring of rain waters, impinger solutions and filter extracts for anions such as sulphate,nitrate, chloride, and cations, including ammonia and metals.


Use is made of colour changes resulting from reaction of pollutant and chemical reagents: colourintensity indicates concentration of pollutant in the sample. Reaction can take place in solution oron solid supports in tubes or on paper strips, e.g. litmus or indicator paper. Quantitative assessmentof colour formation can also be determined using visible spectroscopy. Instruments are calibrated


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such that colour intensity is directly related to concentration of contaminant in the test sample.Arguably the technique could also embrace simple acid-base titrations which utilize colour indicatorsto determine the end-point.

Electrochemical techniques

In electrochemical cells sample oxidation produces an electric current proportional to theconcentration of test substance. Sometimes interferences by other contaminants can be problematicand in general the method is poorer than IR. Portable and static instruments based on this methodare available for specific chemicals, e.g. carbon monoxide, chlorine, hydrogen sulphide.

Coulometry measures the amount of current flowing through a solution in an electrochemicaloxidation or reduction reaction and is capable of measuring at ppm or even ppb levels of reactivegases. Thus a sample of ambient air is drawn through an electrolyte in a cell and the requiredamount of reactant is generated at the electrode. This technique tends to be non-specific, butselectivity can be enhanced by adjustment of pH and electrolyte composition, and by incorporationof filters to remove interfering species.

Ion-selective electrodes are a relatively cheap approach to analysis of many ions in solution.The emf of the selective electrode is measured relative to a reference electrode. The electrodepotential varies with the logarithm of the activity of the ion. The electrodes are calibrated usingstandards of the ion under investigation. Application is limited to those ions not subject to thesame interference as ion chromatography (the preferred technique), e.g. fluoride, hydrogen chloride(see Table 10.3).

Table 10.3 Examples of applications of ion-selective electrodes

Electrode Measurement range (ppm) Major interference

Ammonia 0.01–17 000 Ionic – noneBromide 0.08–80 000 CN–, I–, S– –

Chloride 0.35–3500 CN–, I–, Br–, S– –

Cyanide 0.003–2600 I–, S– –

Fluoride 0.02–1900 OH–

Iodide 0.013–127 000 CN–, S– –

Nitrate 0.6–62 000 I–, Br–, SCN–, ClO4–

Sulphide 0.32–32 100 Ag+, Hg+

Infra-red spectroscopy

The basis of this technique is absorption of IR radiation by molecules over a wide spectrum ofwavelengths to give a characteristic ‘fingerprint’ spectrum providing both qualitative and quantitativedata on the substance. This versatile technique owes its success in occupational hygiene to thedevelopment of a portable spectrometer of the non-dispersive type which focuses on specific partsof the spectrum in which the pollutant shows peak absorption as opposed to scanning the entirespectrum. Table 10.4 identifies principal absorption peaks for selected gases. One advantage of IRis that the detector does not ‘react’ with the gases and the major functional components areprotected and easily removed for maintenance. Since IR detection is potentially sensitive totemperature, the instrument requires approximately 15 minutes to equilibrate prior to use. Watervapour can seriously affect performance.

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Table 10.4 Main IR absorption peaks for selected gases

Chemical Wavelength (micron)

Carbon dioxide 4.35Carbon monoxide 4.60Methane 3.30Nitric oxide 5.30Nitrogen dioxide 3.70Nitrous oxide 4.50Sulphur dioxide 4.00

Table 10.5 UV wavelengths for selected gases

Gas Wavelength (nm)

Ammonia 200Chlorine 280–380Hydrogen sulphide 200–230Nitrogen dioxide 380–420Oxygen/ozone 170Sulphur dioxide 285

Compound specific analysers

Several instruments are available that are designed to monitor a specific compound rather than awide range of substances. The detection system varies according to the pollutant. A selection isgiven in Table 10.6.

Mass spectrometry

This technique relies on the formation of ions by various means in a high-vacuum chamber, theiracceleration by an electrical field and subsequent separation by mass/charge ratio in a magneticfield and the detection of each species. It can be used for both inorganic and organic substances,be very sensitive, and be of value in examining mixtures of compounds especially if linked to glc.Usually this is a laboratory technique but portable or ‘transportable’ models are now available.

Ultra-violet spectrometry

Outermost valency electrons in atoms are excited by ultra-violet radiation. The excited electronsreturn to the ground state liberating energy by disassociation, re-emission, fluorescence, orphosphorescence. The level of UV radiation absorbed follows the Beer–Lambert law (page 312).The peak wavelength for selected gases is given in Table 10.5. Photo ionization detectors (PIDs)use ultraviolet light to ionize gas molecules such as volatile organic compounds; the free electronscollected at electrodes result in a current flow proportional to the gas concentration. The lamprequires constant cleaning and hence may have limited life expectancy.


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Samples of particulate matter can be subjected to many of the above analytical techniques inchemical characterization. The following methods are, however, particularly applicable to analysisof physical characteristics of particulate matter isolated from air sampling.

Mass concentration

Simple gravimetry of the sample is likely to be an integral component of the determination of,e.g., the concentration of, or exposures to, airborne dust. Care is required to avoid errors arisingfrom absorption of atmospheric moisture. This can be avoided by using blank filters, by conditioningthe filters in an atmospherically-controlled room, or use of a desiccator.

Automatic aerosol mass concentration can be achieved directly by collecting particles on asurface followed by use of a piezoelectric or oscillation microbalance, or by !-attenuation sensingtechniques, or indirectly using light scattering. The piezoelectric microbalance contains anelectrostatic precipitator to deposit particles onto a vibrating silica crystal. The change in resonancefrequency is converted into mass concentration using a microprocessor. Oscillating balancesoperate on the principle that air at 50°C (to avoid condensation) passes through a filter attachedto the top of a tapered glass tube which vibrates at its natural frequency. As material is depositedon the filter the oscillation frequency changes directly in proportion to the increased mass. Betagauges rely on the principle that when low-energy ! particles pass through a material the intensityof the beam is attenuated according to Beer–Lambert law:

Table 10.6 Selected examples of compound specific instruments

Compound Detection system

Ammonia Coulometry (e.g. Nessler method)Ion selective electrodeOxidation to NOx and chemiluminescence

Carbon monoxide PolarographyInfra-red

Chlorine Ultraviolet spectroscopyHydrogen chloride Polarography

Ion-selective electrodeHydrogen fluoride Polarography

ColorimetryInorganic cyanides Colorimetry

Ion-selective electrodeOxides of nitrogen Chemiluminescence

CoulometryOxygen Polarography

Paramagnetic susceptibilityFluorescence

Ozone Ultraviolet spectroscopyChemiluminescenceCoulometry

Phosgene Ultraviolet spectroscopyPhosphorus and its compounds Flame photometryToluene Ion-mobility spectroscopyTotal hydrocarbons Flame ionizationSulphur compounds Flame photometry

CoulometryUV fluorescence

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I = Io–ux

where I and Io are the initial and attenuated beam intensities, u is the mass absorption coefficientand x is the absorber thickness.

Light scattering

Optical particle counters provide information on the particles present in different size ranges. Abeam of light is collimated and focused onto a measurement cell. Light impinging on a particleis scattered and reaches a photomultiplier tube and converted to an output proportional to particlesize. Particle size distributions are computed by appropriate software.

Electrostatic sampling

Particles become positively charged by a corona discharge and travel out of the charging chamberand collect on a substrate such as a microscope slide. Thus, the method is useful for particleswhich are to be examined by optical or electron microscopy.

Optical microscopy

This technique is invaluable for measurement of particle size, for counting the number of particlesand for identification of particles by:

• morphology, e.g. by comparison with standard particles, and• refractive index using polarized light microscopy.

Electron microscopy

With a resolution of 0.01 µm this technique outperforms optical light microscopy (0.1 µm) andis used, e.g., to examine fine particles such as metal fume. When linked to other facilities such asdispersive X-ray analysis, quantitative data can be obtained.

X-ray techniques

Crystals produce different diffraction patterns when subjected to bombardment of monochromaticX-ray sources and thereby provide unequivocal identification of crystalline materials.

In X-ray fluorescence incident radiation induces electronic fluorescent emission in most atoms.The effects can be used both qualitatively and quantitatively for metals, alloys etc.

Monitoring water quality

Water is essential to man both directly and indirectly through agriculture and industry in whichvast quantities are used for cooling, energy production, irrigation, refrigeration, washing, solventsetc. Risk of contamination can render water dangerous, unpleasant, or unusable. Point sources ofwater pollution include domestic and industrial waste whilst non-point sources include agriculturaland urban run-offs. Analysis of water is important for estimating the nature and concentration ofcontaminants and hence fitness for use. Artificial contaminants are mainly of domestic and


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industrial origin, and are increasing in similarity because of the expanding domestic use ofchemicals (cosmetics, detergents, paints, garden insecticides and fertilizers). Water quality can beassessed by direct analysis of chemical substances or by indirect effects, e.g. pH, colour, turbidity,odour, impact on dissolved oxygen content.

Chemical pollutants are classified as inorganic or organic. The former include metals (e.g. Mn,Fe, Cu, Zn, Hg, Cd, As, Cr), anions (e.g. Cl–, SiO3

2–, CN–, F–, NO3–, NO2

–, PO4– – –, SO3


––, S––), and gases (Cl2, NH3, O2, O3). Methods for the examination of waters and associatedmaterials published by the UK Department of the Environment are listed in Table 10.7. Selectedmethods for metal analysis are summarized in Table 10.8. Sampling protocols are described in,e.g., BS 6068 and BS EN 2567. Examples of BS methods for analysis of chemical contaminantsin water are illustrated by Table 10.9. Biological methods are also given in BS 6068.

Monitoring land pollution

Sources of land pollution include transport accidents, spillage during chemical handling, loss ofcontainment from storage tanks, leakage and landfill of waste effluent. An appreciation of theprocesses governing retention, degradation and removal of pollutants and the behaviour of specificpollutants in soil are essential in devising correct sampling and analytical strategies for assessingland contamination. Even soil itself varies in dynamics and composition from one site to another.Constituents include solid phase materials (such as complex mixtures of clays, minerals, organicmatter), liquid aqueous phase of solutions (e.g. natural minerals, fertilizers, pesticides and industrialwastes) and gaseous phase components (e.g. oxygen, nitrogen, carbon dioxide, oxides of nitrogen,ammonia, hydrogen sulphide). The determination of toxic elements and organic substances insoils is a requisite of some EC directives as a means of controlling environmental pollution.Analyses are important when certain types of waste are recycled, e.g. by spreading sludge fromwater purification units on land, composting from household refuse. The choice of analyticalmethod will be dictated by accuracy, sensitivity etc. Some key techniques are summarized inTable 10.10 and selected BS methods for monitoring soil quality are listed in Table 10.11.

Monitoring air pollution


Differences exist between the monitoring of pollution levels in ambient and workplace air. Thesereflect the differences in levels of contaminant, environmental standards, purposes for which dataare used, etc. (see also Table 16.8). Thus, although similarities may exist in detection techniques,the sampling regimes, analytical details and hardware specifications may differ for assessment ofthe two environments. In general, atmospheric levels of contaminants are much lower in ambientair than those encountered in the workplace. As a result larger volumes of sample are often neededfor ambient air analyses. This can be achieved using pumps of larger flow rate capacities, or bylonger sampling times.

Atmospheric monitoring involves first obtaining samples of the air with subsequent analysis ofthe samples collected. Examples of sampling techniques for gases and vapours are given in Table10.12. Air samples can be pumped into instruments for direct analysis and data readout. Alternatively,they are collected in air-tight bags, or absorbed in liquids, or onto solid sorbents, for subsequentlaboratory analysis using techniques such as those described on page 308. Common solid sorbents

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Table 10.7 Methods for the examination of water and associated materials published by the UK Department of theEnvironment

A review and methods for the use of epilithic diatoms for detecting and monitoring changes in river water quality, 1993

Chlorphenylid, Flucofuron and Sulcofuron Waters (Tentative Methods based on methylation and GC-ECD, ion-pair HPLC andhydrolysis of Sulcofuron to 4-chloro-3-trifluoromethylaniline by GC-ECD), 1993

Cyanide in Waters etc. (by Reflux Distillation followed by either Potentiometry using a Cyanide Selective Electrode orColorimetry, or Continuous Flow Determination of Cyanide or Determination by Microdiffusion), 1988

Determination of Aldicarb and other N-methyl carbamates in Waters (by HPLC or Confirmation of total Aldicarb residues andother N-methyl carbamates in waters by GC), 1994

Determination of the pH Value of Sludge, Soil, Mud and Sediment; and the Lime Requirement of Soil (Second Edition) (byDetermination of the pH Value of Sludge, Soil, Mud and Sediment or by Determination of the Lime Requirement of Soil),1992

Flow Injection Analysis, An Essay Review and Analytical Methods

Information on Concentration and Determination Procedures in Atomic Spectrophotometry, 1992

Isolation and Identification of Giardia Cysts, Cryptosporidium Oocysts and Free Living Pathogenic Amoebae in Water etc.,1989

Kjeldahl Nitrogen in Waters [including Mercury Catalysed Method, Semi-automated Determination of Kjeldahl Nitrogen(Copper Catalysed, Multiple Tube, Block Digestion Method followed by Air Segmented Continuous Flow Colorimetry)Determination of Kjeldahl Nitrogen in Raw and Potable Water (Hydrogen Peroxide, Multiple tube, Block DigestionMethod followed by Manual or Air-Segmented Continuous Flow Colorimetry) Semi-automated Determination of KjeldahlNitrogen (Copper/Titanium Catalysed, Multiple Tube, Block Digestion Method followed by Distillation and Air SegmentedContinuous Flow Colorimetry), Air-segmented Continuous Flow Colorimetric Analysis of Digest Solutions for Ammonia],1987

Linear Alkylbenzene Sulphonates (LAS) and Alkylphenol Ethoxylates (APE) in Waters, Wastewaters and Sludges by HighPerformance Liquid Chromatography, 1993

Phenylurea herbicides (urons), Dinocap, Dinoseb, Benomyl, Carbendazim and Metamitron in Waters [e.g. determination ofphenylurea herbicides by reverse phase HPLC, phenylurea herbicides by dichloromethane extraction, determination byGC/NPD, phenylurea herbicides by thermospray LC-MS, Dinocap by HPLC, Dinoseb water by HPLC, Carbendazim andBenomyl (as Carbendazim) by HPLC], 1994

Phosphorus and Silicon in Waters, Effluents and Sludges [e.g. Phosphorus in Waters, Effluents and Sludges by Spectrophotometry-phosphom*olybdenum blue method, Phosphorus in Waters and Acidic Digests by Spectrophotometry-phosphovanadomolybdate method, Ion Chromatographic Methods for the Determination of Phosphorus Compound,Pretreatment Methods for Phosphorus Determinations, Determination of silicon by Spectrophotometric Determination ofMolybdate Reactive Silicon-1-amino-2-naphthol-4, sulphonic acid (ANSA) or Metol reduction methods or ascorbic acidreduction method, Pretreatment Methods to Convert Other Forms of Silicon to Soluble Molybdate Reactive Silicon,Determination of Phosphorus and Silicon Emission Spectrophotometry], 1992

Sulphate in Waters, Effluents and Solids (2nd Edition) [including Sulphate in Waters, Effluents and Some Solids by BariumSulphate Gravimetry, Sulphate in waters and effluents by direct Barium Titrimetry, Sulphate in waters by InductivelyCoupled Plasma Emission Spectrometry, Sulphate in waters and effluents by a Continuous Flow Indirect SpectrophotometricMethod Using 2-Aminoperimidine, Sulphate in waters by Flow Injection Analysis Using a Turbidimetric Method, Sulphatein waters by Ion Chromatography, Sulphate in waters by Air-Segmented Continuous Flow Colorimetry using MethylthymolBlue], 1988

Temperature Measurement for Natural, Waste and Potable Waters and other items of interes