I l Elec trica I Installations in Hazard0 us Areas Electrical Installations in Hazardous Areas Eur Ing Alan McMillan C Eng FlEE FlnstMC c EINEMANN Butterworth-Heinemann Linacre House, Jordan Hill, Oxford OX2 8DP 225 Wildwood Avenue, Woburn, MA 01801-2041 A division of Reed Educational and Professional Publishing Ltd e A member of the Reed Elsevier plc group OXFORD BOSTON JOHANNESBURG MELBOURNE NEWDELHI SINGAPORE First published 1998 0 Reed Educational and Professional Publishing Ltd 1998 All rights reserved. No part of this publication may be reproduced in any material form (including photocopying or storing in any medium by electronic means and whether or not transiently or incidentally to some other use of this publication) without the written permission of the copyright holder except in accordance with the provisions of the Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London, England WlP 9HE. Applications for the copyright holder’s written permission to reproduce any part of this publication should be addressed to the publishers British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloguing in Publication Data A catalogue record for this book is available from the Library of Congress ISBN 0 7506 3768 4 Typeset by Laser Words, Madras, India Printed and bound in Great Britain by Biddles Ltd, Guildford and King’s Lynn Contents Preface xvii 1 Introduction 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Examples of historic incidents Technological approach History of development UK legislation European legislation Certification Certificate and labelling information The future of certification 2 Area classification Philosophy objectives and procedures Basic properties of flammable and combustible materials 2.1.1 Flammable gases 2.1.2 Flammable vapours 2.1.3 Flammable mists 2.1.4 Flammable liquids 2.1.5 Combustible dusts 2.2 Basis of area classification 2.3 General approach to area classification 2.4 Classification of sources of release 2.5 Hazardous zonal classification 2.5.1 Gases, vapours and mists 2.5.2 Dusts 2.5.3 2.1 Relationship between sources of release and Zones Information on fuels (gases, vapours and mists) 2.6 Collection of information 2.6.1 2.6.2 Information on fuels (dusts) 2.6.3 Information on process conditions 2.7 Procedures 2.8 Personnel involved 2.9 Results of area classification and frequency of repeats 1 1 2 4 6 8 10 15 18 22 22 22 22 23 23 24 24 24 25 26 27 27 28 30 30 30 32 34 34 39 41 vi Contents 3 Area classification practice for gases, vapours and mists in freely ventilated situations 3.1 3.2 3.3 3.4 Introduction Containment of flammable materials 3.1.1 Effects of storage conditions 3.1.2 3.1.3 Oxygen enrichment 3.1.4 General consideration of release Generalized method of area classification 3.2.1 Generalized zonal classification specification 3.2.2 Generalized extents of zones The source of hazard method of area classification 3.3.1 Types of release 3.3.2 Releases from pipe joints 3.3.3 3.3.4 Special pipe joint circumstances 3.3.5 Releases from moving seals Other practical well-ventilated situations Effect of sunlight on storage vessels Typical extents of Zone 2 from pipe joint releases 3.4.1 3.4.2 3.4.3 3.4.4 3.4.5 3.4.6 3.4.7 3.4.8 3.4.9 3.4.10 3.4.11 The fixed roof vented stock tank The floating roof tank Tanks containing gas, vapour or liquefied vapours Road and rail tanks for flammable liquids Oil/water separators Other open vessels Open drains Trenches Sampling points Walls and apertures Vents 4 Calculation of release rates and the extents of hazardous areas 4.1 4.2 Releases of gas and vapour 4.1.1 Examples of gas and vapour release Release of liquid below its atmospheric boiling point 4.2.1 Example of liquid release below its atmospheric boiling point Release of liquid above its atmospheric boiling point 4.3.1 Example of liquid release above its atmospheric boiling point Summary of use of equations 4.4.1 Gas and vapour releases 4.3 4.4 43 43 44 44 45 45 46 46 46 47 48 50 52 54 65 65 67 67 69 71 72 76 78 78 80 80 85 85 87 88 105 107 113 116 118 119 119 Contents vii 4.4.2 4.4.3 Releases in areas which are not well ventilated 4.5.1 4.6 Conclusion Liquid releases below boiling point Liquid releases above boiling point Example of gas release using BS/EN 10079-10 formulae 4.5 5 Area classification practice for gases, vapours and mists in areas which are not freely ventilated 5.1 Typical areas of restricted ventilation 5.1.1 Open areas surrounded by walls 5.1.2 Covered areas (dutch-barn type) 5.1.3 Above-ground rooms 5.1.4 Below-ground rooms Effect of walls on hazardous areas Roofs without walls or associated with one, two or three walls 5.3.1 Roofs without walls 5.3.2 5.3.2 5.3.4 5.4.1 5.4.2 5.4.3 High integrity ventilation 5.5 Rooms below ground 5.6 Rooms without any internal release but which abut external hazardous areas 5.7 Particular circumstances 5.7.1 The paint spray booth 5.7.2 The paint drying oven 5.2 5.3 Roofs associated with one wall Roofs associated with two walls Roofs associated with three walls The application of additional general ventilation The application of additional local ventilation 5.4 Rooms above ground 6 Area classification practice for dusts 6.1 Properties of dusts 6.1.1 6.1.2 6.1.3 6.1.4 Other important dust properties Area classification for dust releases 6.2.1 Sources of dust release 6.2.2 Definition of Zones 6.2.3 Extents of hazardous areas The ignition of dust clouds The ignition of dust layers Production of flammable gases and vapours by dusts 6.2 120 120 121 123 123 125 126 126 126 126 127 127 130 130 132 132 133 134 135 140 143 144 145 146 146 146 149 150 151 154 154 155 155 155 156 158 [...]... terminations 20.4.1 Terminal construction 20.4.2 Assemblies of terminals 20.5 Earthing and bonding 20.5.1 Typical Zone 1 and Zone 21 intrinsically safe circuits with bonding in the non -hazardous area 20.5.2 Typical Zone 1 and Zone 21 intrinsically safe circuits with bonding in the hazardous area 20.5.3 Typical Zone 1 and Zone 21 circuits with bonding connection at more than one point 20.5.4 Bonding... I Examples of historic incidents The following are examples of the more significant incidents occurring in the UK and, although they were not necessarily caused by electricity, there is in at least one of the cases a suspicion of electrical initiation and electricity, as has already been indicated, is seen as an obvious igniting agent 2 Electrical installations in hazardous areas Senghennyd colliery... done by 8 Electrical installations in hazardous areas industry in general and organizations such as The Institute of Petroleum i which produced a model code of safe practice6 for the ol industry Industry, unlike the govenunental organizations, concentrated much of its work on the matters associated with how hazardous areas were formed and matters associated with installation and maintenance Individual... normally from installed equipment 6 Electrical installations in hazardous areas and more predictable in quantity and frequency, and second the recognition that far from dealing with one gas and one dust, as in mining, surface industry was dealing with a myriad of different materials each with its own characteristics This recognition led to development of the technique of area classification to define the... selective in discussing most of the principal requirements therein, while at the same time trying to explain the reasoning which led to their inclusion Therefore, when applying the technology it will be necessary to address the appropriate standards and codes in all cases but this book will, by provision of the background reasoning, make those documents more understandable In addition, by developing practical... 13.2 Basic application of the concept 13.2.1 Intrinsically safe apparatus 13.2.2 Associated apparatus 297 297 297 298 300 305 309 332 333 333 334 Contents xi 13.2.3 Interconnections 13.2.4 Simple apparatus 13.2.5 The intrinsically safe circuit 13.2.6 The intrinsically safe system 13.3 Levels of intrinsic safety 13.3.1 Intrinsic safety category ’ia’ 13.3.2 Intrinsic safety category ‘ib’ 13.4 Countable... that of inspection by a body expert in hazardous area technology, such as the Safety in Mines Research Establishment and its associates, against not very specific standards, to inspection by a competent test laboratory against very detailed standards not requiring anything like the previous level of expertise Within the EU there are now some 17 approved bodies for such certification, including the... intended to be a body for the deciding of the meaning of unclear parts of the Standards although it, of necessity becomes involved in such activity The clarification and interpretation of Standards is for the Standards' writing bodies (CENELEC in this case) but such bodies are by their nature cumbersome and thus queries on Standards 14 Electrical installations in hazardous areas Certiflcade o Conformity... those electrical installations which really need to be present rather than those which convenience would make desirable, and ensure that these are protected in a way which makes the overall risk of an explosion sufficiently low 1.3 History of development The use of electrical equipment in explosive atmospheres was originally the province of the mining industry and, although the technology was used in. .. 21.2.1 Initial inspection 21.2.2 Inspection after apparatus repair 21.2.3 Inspection after change in area classification, sub-group or surface temperature classification 21.2.4 Routine inspection 598 599 599 604 604 604 xvi Contents 21.2.5 Visual inspection 21.2.6 Inspection procedures 21.3 Testing 21.3.1 Necessary testing 21.4 Maintenance of explosion protected apparatus 21.4.1 General maintenance 607 . Elec trica I Installations in Hazard0 us Areas Electrical Installations in Hazardous Areas Eur Ing Alan McMillan C Eng FlEE FlnstMC c EINEMANN Butterworth-Heinemann Linacre House,. Trenches Sampling points Walls and apertures Vents 4 Calculation of release rates and the extents of hazardous areas 4.1 4.2 Releases of gas and vapour 4.1.1 Examples of gas and vapour. Typical Zone 1 and Zone 21 intrinsically safe circuits with bonding in the non -hazardous area 20.5.2 Typical Zone 1 and Zone 21 intrinsically safe circuits with bonding in the hazardous area