Electrical Installations in Hazardous Areas

678 Pages·1998·33.91 MB·English

by  Alan McMillan Eur Ing Alan McMillan CEng FIEE FInst MC

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Elec tricaI Installations in Hazard0 us Areas

Electrical Installations in
Hazardous Areas
Eur Ing Alan McMillan C Eng FlEE FlnstMC
c
E I N E M A N N
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
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other use of this publication) without the written permission of the
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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 Examples of historic incidents 1
1.2 Technological approach 2
1.3 History of development 4
1.4 UK legislation 6
1.5 European legislation 8
1.6 Certification 10
1.7 Certificate and labelling information 15
1.8 The future of certification 18
2 Area classification 22
Philosophy objectives and procedures 22
2.1 Basic properties of flammable and combustible
materials 22
2.1.1 Flammable gases 22
2.1.2 Flammable vapours 23
2.1.3 Flammable mists 23
2.1.4 Flammable liquids 24
2.1.5 Combustible dusts 24
2.2 Basis of area classification 24
2.3 General approach to area classification 25
2.4 Classification of sources of release 26
2.5 Hazardous zonal classification 27
2.5.1 Gases, vapours and mists 27
2.5.2 Dusts 28
2.5.3 Relationship between sources of release
and Zones 30
2.6 Collection of information 30
2.6.1 Information on fuels (gases, vapours
and mists) 30
2.6.2 Information on fuels (dusts) 32
2.6.3 Information on process conditions 34
2.7 Procedures 34
2.8 Personnel involved 39
2.9 Results of area classification and frequency of repeats 41
vi Contents
3 Area classification practice for gases, vapours and mists in
freely ventilated situations 43
Introduction 43
3.1 Containment of flammable materials 44
3.1.1 Effects of storage conditions 44
3.1.2 Effect of sunlight on storage vessels 45
3.1.3 Oxygen enrichment 45
3.1.4 General consideration of release 46
3.2 Generalized method of area classification 46
3.2.1 Generalized zonal classification specification 46
3.2.2 Generalized extents of zones 47
3.3 The source of hazard method of area classification 48
3.3.1 Types of release 50
3.3.2 Releases from pipe joints 52
3.3.3 Typical extents of Zone 2 from pipe joint
releases 54
3.3.4 Special pipe joint circumstances 65
3.3.5 Releases from moving seals 65
3.4 Other practical well-ventilated situations 67
3.4.1 The fixed roof vented stock tank 67
3.4.2 The floating roof tank 69
3.4.3 Tanks containing gas, vapour or liquefied
vapours 71
3.4.4 Road and rail tanks for flammable liquids 72
3.4.5 Oil/water separators 76
3.4.6 Other open vessels 78
3.4.7 Open drains 78
3.4.8 Trenches 80
3.4.9 Sampling points 80
3.4.10 Walls and apertures 85
3.4.11 Vents 85
4 Calculation of release rates and the extents of
hazardous areas 87
4.1 Releases of gas and vapour 88
4.1.1 Examples of gas and vapour release 105
4.2 Release of liquid below its atmospheric boiling point 107
4.2.1 Example of liquid release below its
atmospheric boiling point 113
4.3 Release of liquid above its atmospheric boiling point 116
4.3.1 Example of liquid release above its
atmospheric boiling point 118
4.4 Summary of use of equations 119
4.4.1 Gas and vapour releases 119
Contents vii
4.4.2 Liquid releases below boiling point 120
4.4.3 Liquid releases above boiling point 120
4.5 Releases in areas which are not well ventilated 121
4.5.1 Example of gas release using BS/EN 10079-10
formulae 123
4.6 Conclusion 123
5 Area classification practice for gases, vapours and mists in
areas which are not freely ventilated 125
5.1 Typical areas of restricted ventilation 126
5.1.1 Open areas surrounded by walls 126
5.1.2 Covered areas (dutch-barn type) 126
5.1.3 Above-ground rooms 126
5.1.4 Below-ground rooms 127
5.2 Effect of walls on hazardous areas 127
5.3 Roofs without walls or associated with one, two or
three walls 130
5.3.1 Roofs without walls 130
5.3.2 Roofs associated with one wall 132
5.3.2 Roofs associated with two walls 132
5.3.4 Roofs associated with three walls 133
5.4 Rooms above ground 134
5.4.1 The application of additional general
ventilation 135
5.4.2 The application of additional local ventilation 140
5.4.3 High integrity ventilation 143
5.5 Rooms below ground 144
5.6 Rooms without any internal release but which abut
external hazardous areas 145
5.7 Particular circumstances 146
5.7.1 The paint spray booth 146
5.7.2 The paint drying oven 146
6 Area classification practice for dusts 149
6.1 Properties of dusts 150
6.1.1 The ignition of dust clouds 151
6.1.2 The ignition of dust layers 154
6.1.3 Production of flammable gases and vapours
by dusts 154
6.1.4 Other important dust properties 155
6.2 Area classification for dust releases 155
6.2.1 Sources of dust release 155
6.2.2 Definition of Zones 156
6.2.3 Extents of hazardous areas 158