mcmillan, a. (1998). electrical installations in hazardous areas

viii Contents 6.3 Practical situations 6.3.1 Cyclones and bag filters 6.3.2 Loading hoppers within buildings 6.3.3 Loading hoppers outside buildings 7 Design philosophy for electrical a

I

l

Elec trica I Installations in Hazard0 us Areas

Electrical Installations in

Hazardous Areas

Eur Ing Alan McMillan C Eng FlEE FlnstMC

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

Certificate and labelling information

The future of certification

2 Area classification

Philosophy objectives and procedures

Basic properties of flammable and combustible

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

2.6.2 Information on fuels (dusts)

2.6.3 Information on process conditions

vi Contents

3 Area classification practice for gases, vapours and mists in

freely ventilated situations

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

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

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

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

viii Contents

6.3 Practical situations

6.3.1 Cyclones and bag filters

6.3.2 Loading hoppers within buildings

6.3.3 Loading hoppers outside buildings

7 Design philosophy for electrical apparatus for explosive

7.2.3 Containment of explosions (criterion c)

7.2.4 Energy limitation (criterion d)

7.2.5 Special situations

Situation in respect of Zone 2 apparatus

Protection of electrical apparatus for dust risks

7.5 Apparatus construction Standards

Zone 0 and/or Zone 1 compatible apparatus for gases, vapours and mists The marketing situation in respect of European Standards

Zone 2 compatible apparatus for gases, vapours and mists

Electrical apparatus for dust risks

8 General requirements for explosion protected apparatus

(gas, vapour and mist risks)

8.1

Apparatus to European Standards

BS/EN 50014 (1993) (including amendment 1 (1994))

8.1.1 Definitions

8.1.2 Division of apparatus into

8.1.3 Requirements for enclosures

Connection facilities and cable entries Additional requirements for particular types of apparatus

Contents ix

9 Apparatus using protection concepts encapsulation 'm', oil

immersion '0' and powder filling 'q'

9.1.4 Encapsulated circuits and components

9.1.5 The encapsulation process

9.1.6 Particular component problems

9.1.7 Type testing

Oil immersion - '0'

9.2.1 Construction of the apparatus

9.2.2 Containment of the oil

Requirements for the protective fluid (oil)

10 Apparatus using protection concept flameproof enclosure 'd'

10.1 Standards for flameproof apparatus

10.2 Construction and testing requirements for flamepaths

10.2.1 Joints between the interior of flameproof

enclosures and the external atmosphere 10.2.2 Joints for rotary or longitudinal shafts and

operating rods 10.2.3 Joints for shafts and rotating machines

10.2.4 Bearing greasing arrangements

10.2.5 Tests for flameproof joints

10.3 Construction of flameproof enclosures, entry

facilities and component parts

x Contents

11 Apparatus using protection concept pressurization 'p'

11.1 Standards for pressurization 'p'

11.2 Methods of pressurization

11.2.1 Static pressurization

11.2.2 Pressurization with leakage compensation

11.2.3 Pressurization with continuous dilution

11.3 Purge and dilution gases

11.4 Flammable materials imported into enclosures

and their containment

11.4.1 Flammable materials imported into enclosures

11.4.2 Containment of flammable materials within

enclosures 11.5 Enclosures, ducting and internal components

11.5.1 Enclosures

11.5.2 Ducting

11.5.3 Internal electrical components, etc

11.6 Safety provisions and devices

12 Apparatus using protection concept increased safety 'e'

12.1

12.2

12.3

The situation in regard to standardization

Basic construction requirements

12.2.1 Construction of enclosures

12.2.2 Terminals and connection facilities

12.2.3 Separation of conducting parts

12.3.8 Other types of apparatus

13 Apparatus and systems using protection concept intrinsic

safety 'i'

13.1 The situation in respect of standardization

13.2 Basic application of the concept

13.2.1 Intrinsically safe apparatus

13.2.5 The intrinsically safe circuit

13.2.6 The intrinsically safe system

Levels of intrinsic safety

13.3.1 Intrinsic safety category ’ia’

13.3.2 Intrinsic safety category ‘ib’

Countable and non-countable faults

13.4.1 Non-countable faults

13.4.2 Countable faults

13.4.3 Effects of other faults

13.4.4 Infallible component, assembly or

Confirmation of intrinsic safety in respect of arc and

Basic component and construction requirements

13.7.1 Safety factors on component rating

13.7.2 Specific requirements for particular

components

Component and circuit failure modes

13.8.1 Wire and printed circuit tracks

13.10.5 Shunt safety assemblies

13.10.6 Internal wiring and connections

xii Contents

13.11 Diode safety barriers

13.12 Input and output specifications

13.13 Examples of fault counting in apparatus

13.14 Intrinsically safe systems

13.14.1 Interconnecting cable systems

13.14.2 Cable parameter measurement

14 Apparatus using protection concept ’ N (‘n’)

14.1 The situation in respect of standardization

14.2 Basic requirements of the protection concept

14.3 General constructional requirements

14.3.1 Environmental protection

14.3.2 Mechanical strength

14.3.3 Wiring and internal connections

14.3.4 External connection facilities

14.3.5 Conductor insulation and separation

14.4 Additional requirements for certain types of

non-sparking apparatus

14.4.1 Rotating electrical machines

14.4.2 Fuse links and fuseholders

14.4.3 Fixed luminaires

14.4.4 Portable luminaires and other light sources

14.4.5 Electronic and low power apparatus

14.5 Apparatus producing arcs, sparks and/or

ignition-capable hot surfaces

14.5.1 Enclosed break devices and non-incendive

components 14.5.2 Hermetically sealed devices

14.5.3 Sealed devices

14.5.4 Energy limited apparatus and circuits

14.5.5 Restricted breathing enclosures

15 Protection concepts for apparatus for dust risks

15.1 Situation in respect of standardization

15.2 Basic types of apparatus for use with combustible dusts

15.2.1 Degrees of enclosure

15.3 Operational requirements

15.4 Basic constructional requirements

15.4.1 Enclosure materials and mechanical strength

15.4.2 Joints intended to be opened in normal service

Contents xiii

15.5

15.6

Specific additional requirements for

particular types of electrical apparatus and connections

15.5.1 Connection facilities

15.5.2 Cable and conduit entries

15.5.3 Fuses and switchgear

15.5.4 Plugs and sockets

15.5.5 Luminaires and similar apparatus

Apparatus conforming to the protection concepts

appropriate to gas, vapour and mist risks

15.6.1 Spark ignition

15.6.2 Hot surface ignition

15.6.3 Basis of selection of apparatus with protection

concepts appropriate to gas/vapour/mist and air risks

16 Other methods of protection and future apparatus

16.2.3 General design and constructional

16.2.4 Specific requirements for particular

requirements types of apparatus and protective systems 16.3 Use of apparatus

17 Selection of power supply, apparatus and interconnecting

cabling system for both gas/vapour/mist risks and dust risks

17.1 Electrical supply systems

17.2 Electrical protection

17.3 Selection of apparatus

17.3.1 Selection in respect of gases, vapours

and mists 17.3.2 Selection of apparatus for dust risks

17.3.3 Selection on the basis of zone of risk

17.4 Selection of conduit or cable systems

17.4.1 Zone 0 and Zone 20

17.4.2 Zone 1 and Zone 21

17.4.3 Zone 2 and Zone 22

18 Installations in explosive atmospheres of gas, vapour, mist

xiv Contents

18.2 Legislation and enforcement

18.3 Basic installation requirements

18.3.8 Conduit and cable installation

18.4 Additional requirements or relaxations for particular

protection concepts

18.4.1 Hameproof electrical apparatus ‘d’

18.4.2 Increased safety apparatus ’e’

using inert gas 19.4.3 Pressurization with continuous dilution

using air 19.4.4 Pressurization with continuous dilution using

inert gas 19.5 Safety devices and procedures

19.5.1 Manufacturer provision of control devices and

systems

19.5.2 Manufacturer provision of control devices only

19.5.3 Manufacturer provision of control information

only 19.6 Purge gas and operation of control system (gas,

vapour and mist risks)

20 Installation of intrinsically safe apparatudassociated

apparatus and intrinsically safe systems 'i'

20.1 Standards and Codes

20.2 Basic installation requirements

20.3 Cables, conduits and conductors

20.3.1 Conductor temperature

20.3.2 Inductance and capacitance

20.3.3 Cable installation

20.3.4 Conduit installation

20.3.5 Marking of cables, cable bundles, cable trays,

or ducts and conduits 20.3.6 Additional requirements for Zone 0 (and

Zone 20 where appropriate) 20.4 Conductor terminations

20.4.1 Terminal construction

20.4.2 Assemblies of terminals

20.5.1

20.5 Earthing and bonding

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 and insulation of screens for

intrinsically safe circuits 20.5.5 Typical Zone 0 and Zone 20 intrinsically safe

circuits 20.5.6 Special circuits

21 Documentation, inspection, test and maintenance of

explosion protected apparatus, systems and installations

21.1 Documentation

21.2 Detailed inspection requirements

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

22.2 Static electricity including lightning

22.2.1 Dealing with static charge

22.2.2 Dealing with lightning

Ignition by radio frequency radiation

22.3.1 Basic safety assessment

22.3.2 Dealing with the hazard

The technology of application of electrical equipment in explosive atmo- spheres is very old, dating almost from the original application of electricity

to apparatus other than lighting From its origins it has been developed in most industrialized countries with the United Kingdom, Germany and the United Sates of America being in the vanguard As the world moves closer together this technology has, like all others, been coordinated so that its detail will be the same in all countries, principally to allow free marketing around the world This has led to more detailed standard requirements particularly in the case of apparatus construction

In the UK the considerable standardization of technology is defined in

more than 30 published standards (some national, some European and some

international) While this is basically good, in that it details what is neces- sary and thus makes the achievement of safety easier in principle, it has drawbacks in that there is considerable complication which can cause confu- sion Despite the longevity of the technology I can find no serious attempt

in the UK to produce a freely published volume, such as this, which brings together the entire technology under one roof, as it were This fact, together with the pivotal role played by the UK in development through the British Standards Institution, which brought together all the necessary expertise

to produce the necessary technical standards, the Safety in Mines Research Establishment (now the Health and Safety Laboratory of the Health and Safety Executive) and the Electrical Research Association (now ERA Tech- nology), organizations that carried out much of the research work necessary

to permit the current standards to exist and the large contribution made by

UK industry, led me to write this volume

1 The determination of the likelihood and the areas contaminated or likely

to be contaminated by explosive atmospheres produced by fuels such

as gas, vapour, mist, dust or a combination of these This is still the least researched of the areas of this technology, principally because there are so many variations, in particular circumstances occurring in practical locations

2 The construction of electrical equipment so that it is unlikely to become

an ignition source This has been heavily researched in many countries because, unlike area classification, it is relatively specific and lends itself more readily to specification

3 The installation, operation, maintenance and inspection of electrical equipment This again is heavily influenced by the circumstances The field can be divided into three facets:

by provision of the background reasoning, make those documents more understandable In addition, by developing practical examples of their use,

it will assist in their application

This field is not one for inexperienced engineers and technologists and thus must be approached with care In addition there are many local condi- tions which can vary the advice given here and those involved need to be aware of this and have sufficient expertise to determine conditions under

which additional requirements are necessary and those, much less common,

where relaxations are possible The onus is, of course, always on the occu- pier of a location to be able to jus* what is done on safety grounds and

it is hoped that this book will assist in this activity

The contents here relate to the situation in the UK but differences in Europe and other counties are not great and its content should be useful elsewhere

Finally, unlike the situation historically existing, where this technology was often applied in isolation, it is now important to recognize that it can only be applied as a part of an overall safety strategy That is not to say that its requirements can be ignored if they adversely affect other safety features but rather that, if such is the case, an alternative approach to achievement

of its requirements should be sought It should always be remembered that electrical installations in explosive atmospheres should only exist where necessary (i.e., where they can be fully justified)

Alan McMillan

7

ln traduction

Where combustible or flammable materials are stored or processed there is,

in most circumstances, a possibility of their leaking or otherwise having the ability to produce what may be described as an explosive atmosphere in conjunction with the oxygen present in air This is true for gases, vapours, mists and dusts and, as electricity is widely used in industries and other places where such explosive atmospheres can occur, the propensity of elec- trical energy to create sparking or hot surfaces presents a possibility that the explosive atmospheres may be ignited with resultant fire or explosion

This hazard has been recognized for many decades - almost since the use

of electricity was introduced into mining and other industries - and the precautions taken to overcome this problem date back, in their basic incep- tion, to the turn of the twentieth century and before

There is no way in which explosions can be totally prevented in indus- tries where explosive atmospheres can occur as all human endeavour is fallible but it is necessary to develop our operations to a degree where such explosions are so rare that their risk is far outweighed by the benefits

of the processes in which they may occur Such balance is evident in the coalmining industry where the overall risks associated with working under- ground, where explosions are one constituent, have been seen as justifiable

on the basis of society’s need for fuel It is true that the risks are minimized

as far as possible but only to a level consistent with the need to win coal and accidents still occur It remains true, however, that the risk of these accidents has been reduced to a level acceptable to our society and partic- ularly those working in the industry That is not to say that when a risk is identified by an incident nothing is done We always learn from these and invariably they result in changes to our operating systems and equipment

in order to minimize the risk of a repeat Notwithstanding all of our efforts, however, accidents of significant proportion still occur with a degree of regularity which causes us all concern

1 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,

a s has already been indicated, is seen as an obvious igniting agent

2 Electrical installations in hazardous areas

Piper Alpha - 1988

This oil platform was effectively destroyed by a gas explosion which resulted from a major release of gas suggested to be due to erroneous process operation The initial and subsequent explosions and fire effectively prevented controlled evacuation of the platform and heavy loss of life was caused

Texaco Pembroke refinery - 1994

A major vapour explosion occurred leading to a major fire which was extremely difficult to extinguish The refinery burned for a considerable time with consequent adverse effects on the local environment Casualties were light but the refinery suffered considerable damage

The above examples clearly demonstrate the dangers present, particu- larly in locations where escape of personnel is difficult and it is essential, therefore, that all involved have an understanding of the technology used

to minimize the risk of explosion

Fig 1.1 The explosion triangle

the basis for technology since the turn of the twentieth century when the problem was first identified in the mining industry While in other areas of risk the approach is often based much more heavily on statistical analysis than is the case here, the approach in respect of explosive atmospheres is well established and accepted, having been in use since the early 1900s The presence of many subjective areas which make statistical analysis difficult have also limited the statistical approach although there have been many attempts to apply such an approach Thus current and foreseeable future technology is based upon that currently used, and there is no indication

of a radical change to readdress the technology on a statistical basis as is done, for example, in the nuclear industry

A typical attempt to analyse the statistical level of security achieved in relation to gas, vapour and mist releases is that in a paper by W.A Hicks and K.J Brown at the 1971 Institution of Electrical Engineers Conference' which identified the risk of ignition as between and Many others however have produced different figures as the assumptions made

in respect of the subjective elements of the technology vary

The technology is currently based upon the identification of the risk of an explosive atmosphere being present in a particular place coupled with the identification of the likelihood of electrical equipment within the explosive atmosphere malfunctioning in a way which would cause it to become a source of ignition coincident with the presence of that explosive atmosphere The objectives are not just to identify these coincidences but to utilize the information so obtained to influence the design of particular process plants and similar operational situations in a way so as to minimize the risk of creation of an explosive atmosphere, and hence the risk of an explosion due to electrical installations To this end, the generality of the approach is

to seek out situations where an explosive atmosphere is normally present

of necessity due to the process involved, situations where the likelihood of its presence is high and situations where the likelihood is of its presence is

4 Electrical installations in hazardous areas

low but identifiable In this scenario catastrophe does not play a part and although it is necessary to plan for catastrophe such plans are by and large outside the scope of this technology In addition this technology should not

be used in isolation but as part of an overall safety strategy for a location where the problem occurs

Having identified the possible presence of an Explosive Atmosphere it is then the part of technology to identify 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

of the use of ventilation to restrict the possibility of explosive atmospheres forming and the employment of a safety lamp (Fig 1.2) to minimize the risk of ignition

The introduction of electricity in the latter part of the nineteenth century and the early part of the twentieth century led to significant other risks being identified Initially electricity was utilized for lighting and motive force The lighting was typically provided by incandescent filament lamps, none of the more sophisticated lamps having been developed at the time, and the motive force usually by either dc or wound rotor ac machines which were initially typical of the motors available Both lighting and machines required control equipment (often as simple as a switch) but this equipment also introduced risks associated with hot surfaces and sparks, together with the possibility of the presence of both methane and coal dust

The solutions to these problems in relation to gas, vapour and mist releases were developed in both the UK and Germany along very similar lines and in very similar time scales In Germany the organization prin- cipally involved was what is now known as the Berggewerkschaftlichen

Introduction 5

Flame (candle or oil/wick)

\

Gauze (flame trap) (does not prevent access of methane but prevents ignition of methane/ai r

k / outside lamp)

oil reservoir

Fig 1.2 Principle of Davy Lamp

Versuchsstrecke (BVS) and Dr Ing Carl Beyling of that organization was awarded the Gold Medal of the UK Institution of Mining Engineers in 1938 for his work in this area In the UK a similar but governmental organiza- tion had significant involvement in similar developments This is now as the Health and Safety Laboratory of the Health and Safety Executive but

is better known by its earlier title of the Safety in Mines Research Estab- lishment

The initial technique for protection of electrical equipment was what we now know as flameproof enclosure and intended for high-power electrical equipment where the level of electrical energy necessary for equipment operation was always sufficient to initiate ignition if released in a spark or as heat This was well developed as early as 1905 and was rapidly followed by

a second technique, now known as the intrinsically safe circuit This second technique was developed for mine signalling systems and relied upon the fact that intelligence could be transmitted by very small amounts of elec- trical energy which, if released, was not sufficient to ignite any expected explosive atmosphere The advantage of this latter technique was in the flexibility which it offered as large heavy protective enclosures were not necessary

Initially these two techniques were developed for the mining industry where methane was the most sensitive flammable material present but as the techniques began to be applied to surface industry two significant differ- ences in approach became rapidly apparent First it was recognized that releases of flammable material were normally from installed equipment

6 Electrical installations in hazardous areas

and more predictable in quantity and frequency, and second the recogni- tion 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 risks of explosive atmospheres occurring

in specific locations and the development of additional types of protection

to more readily reflect the varying levels of hazard which could be iden- tified It is these two factors that led to the current UK and international industrial practice which this book seeks to describe

The basic historic UK legislation covering the use of electrical equipment

in explosive atmospheres is that included in the Electricity Regulations' of

the Factories Acts3 Regulation 27 of these regulations states:

All conductors and apparatus exposed to the weather, wet, corrosion, inflammable surroundings or explosive atmosphere, or used in any process or for any special purpose other than for lighting or power, shall be so constructed or protected, and such special precautions shall

be taken as may be necessary adequately to prevent danger in view

of such exposure or use

This regulation clearly states the objective to be achieved but does not define the method of its achievement While one may be concerned at this, its intent

is to allow the widest possible range of approaches to the achievement of the required level of security and thus to give the maximum freedom of operation to industry, while at the same time, laying upon that industry the requirement to achieve an adequate level of security in its operation

Regulation 27 remained in force, even after the enactment of the Health and Safety at Work Act 1974*, until replaced by Regulation 6 of the 1989

Electricity at Work Regulations5 Regulation 6 states:

Electrical equipment which may reasonably foreseeably be exposed to:- (a) mechanical damage;

@) the effects of weather, natural hazards, temperature or pressure; (c) the effects of wet, dirty, dusty or corrosive conditions; or

(d) any flammable or explosive substance, including dusts, vapours

or gases,

shall be of such construction or as necessary protected as to prevent,

so far as is reasonably practible, danger arising from such exposure The tenor of this new regulation, now current, is very much the same as its predecessor The objective to be achieved is specified and within that objec- tive maximum freedom is given to industry in methods of its achievement

Introduction 7

The above method of legislating, while common in the UK, contrasts significantly with legislation in countries such as Germany where legislation tends to be more specific, giving much more detail in respect of the precautions to be adopted There is, however, little or no evidence available

to suggest that one or the other approach produces a better result as far

as safety is concerned Thus, the UK approach has much to commend it providing as it does maximum flexibility but, conversely, practitioners in the UK must be fully competent to deal with the flexibility permitted

In respect of dusts, a further regulation exists in the Factories Acts3 which reflects the different nature of such materials, in that when a dust is released

it does not disperse as is the case with gases, vapours and mists but settles and forms a layer which can be re-formed as a cloud at any time by any

sort of physical intervention The regulation in question is Regulation 31(1)

While not specifically referring to electrical equipment, this regulation includes it as a possible source of ignition and identifies the method of protection as effective enclosure This is possible as dust is nothing like as penetrative as gas, vapour or mist and can effectively be excluded with much less difficulty

To underpin these regulations and give guidance, many British Standards and Codes containing details of acceptable methods of compliance and third-party certification facilities have been developed to give purchasers

of electrical equipment confidence These certification schemes do not, however, extend to installation and use

In the past, when equipment construction Standards were limited and lacked detail, a great deal of expertise was necessary within the certification bodies as it was they who had to interpret what general statements within Standards actually meant Thus, it was not surprising that the certification body in the UK was associated with the Health and Safety Executive and the Safety in Mines Research Establishment organizations which made great contributions to the more detailed technological base currently available Now, with much more detailed requirements, this relationship, while remaining useful, is no longer necessary The contribution of organizations such as the Safety in Mines Research Establishment, and the Electrical Research Association (now ERA Technology Ltd), the latter through its industry sponsored project work, to the detail existing in current Standards and Codes cannot however be overstated

In addition to the above organizations, which were principally associated with the construction of equipment, a great deal of work was done by

8 Electrical installations in hazardous areas

industry in general and organizations such as The Institute of Petroleum

which produced a model code of safe practice6 for the oil 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 companies also made significant contributions and, as an example of this, the RoSPA/ICI Code of Practice7 covering use of electrical equipment in explosive atmospheres in the chemical industry is probably one of the finest documents of its type ever produced

1.5 European legislation

With the accession of the UK to the EU it became subject to EU legislation

in this field The first such legislation produced was the Explosive Atmo- spheres Directive 1975' This Directive was limited to equipment for gas, vapour and mist risks and was what is described as an optional Direc- tive, solely concerned with barriers to trade It did not dictate what must

be used in explosive atmospheres but merely identified equipment which could not be defined by individual member states as unsuitable for use

in their country The Directive referred to all constituent parts of electrical installations capable of use in potentially explosive atmospheres, other than mines and its Article 4 set the scene as follows:

Member States may not, on grounds of safety requirements for the design and manufacture of electrical equipment for use in Potentially Explosive Atmosphere, prohibit the sale or free movement or the use, for its proper purpose of the electrical equipment (covered by the Directive)

While this clearly prevented individual member countries from insisting that all equipment used must comply with individual national require- ments, it did not prevent equipment complying with national requirements from use in addition to that complying with the Directive even though these could differ

The 1975 Directive also had to define what was required of equipment

to comply with it, and this led to considerable emphasis on the work of the European Committee for Electrical Standardization (CENELEC)9 which produced a range of very detailed Standards describing the construction

of suitable electrical equipment (the EN 50 - - - range of European Stan- dards) These Standards were then given legal status by being referred to in Supplementary Directives'O or the EU JournaP2 To ensure that equipment did indeed comply the basic Directive recognized the Distinctive Commu- nity Mark (Fig 1.3) which could only be affixed to equipment in compliance with the Standards referred to in the Supplementary arrangements and required that this compliance be attested by a Certificate of Conformity

or Inspection Certificate issued by an approved body The Certificate of Conformity was for equipment which complied with one of the recognized

Introduction 9

Fig 1.3 The Distinctive Community Mark

CENELEC Standards referred to in the Supplementary Directives, and the Inspection Certificate for equipment which did not comply but was consid- ered by the approved body to be of at least equivalent safety In this latter case, however, all of the approved bodies in all member states had to agree

on equivalence and thus, although this route allowed some flexibility, it was seldom used due to its expensive and time consuming nature

The Explosive Atmospheres Directive 19758 remained in force until 1996

when it was superseded by a new Directive on the subject1’ The new Direc- tive followed the EU ’new approach’ in which the technical requirements were included within the Directive, rather than by reference to Standards Unlike its predecessor, in this Directive there was a mandatory requirement that after a certain cut-off date all equipment put into use must of necessity comply with it and, unlike its predecessor, included dusts - bringing equip- ment for use in dust risks into the certification net set up by its predecessor Article 2 of this Directive states:

Member States shall take all appropriate measures to ensure that the equipment, protective systems and devices to which this Directive applies may be placed on the market and put into service only if, when properly installed and maintained and used for their intended purpose, they do not endanger the health and safety of persons and, where appropriate, domestic animals or property

As the essential requirements for health and safety are included in this Directive it effectively excludes all other equipment The exclusion of non-

complying equipment (including that complying with the 1976 Directive)

will come into force in on 30 June 2003 European Standards are no longer referred to in the new Directive but will be identified in the EU Journal” as acceptable as a means of compliance with the Directive (but not, as before,

10 Electrical installations in hazardous areas

the only means of compliance) In addition non-electrical equipment and systems have been brought into the scope of the new Directive

Both of the Directives are brought into effect in Great Britain by the Explosive Atmosphere (Certification) Regulations13 and in Northern Ireland

by similar legislation

The EU Directives and National Implementation legislation referred to above refer only to the construction of equipment and not to its installation and use which is still a matter for National Law A Directive14 is in discus- sion within the EU, however, which will address matters of installation and use This Directive is still at a relatively early stage but its implications are far reaching It formalizes the requirements on employers to identify hazardous areas (with notices), to class@ such areas and to consult with and inform employees It also formalizes the requirement for the use of experts (properly trained and experienced personnel) in the workplace to oversee installations While much of what is included is correct and is commonsense, it adds a degree of formality not hitherto seen in the UK and thus, when promulgated, may have a significant effect on UK industry Having said that, much of what is in the proposed Directive is in accordance with the recommendations and guidance in this book and other guides

As has been stated there is no specific requirement for certification in respect

of equipment used in hazardous areas in the UK, other than that associ- ated with the EU Directives associated with construction and marketing of equipment and ensuing National Law Certification has, however, become accepted as the norm, at least in the more hazardous of the affected areas and is an important aspect of the technology It must be noted however that over the years the vision of certification has changed from 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 stan- dards, 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 certi- fication, including the non-EU European and Scandinavian countries with whom the EU has agreements As far as EU legislation is concerned, these are all equivalent and a certificate from any one of them is sufficient to demonstrate that the equipment satisfies the requirements of the appro- priate European Standard Equipment which is certified by any one of these

17 approved bodies is normally identified by the manufacturer by marking the apparatus with the Distinctive Community Mark in addition to any marking associated with the certification

The 17 approved bodies are:

Belgium (EU)

Institut Scientifique de Service Public (ISSEP)

Division de colfontaine

Laboratoire Central des Industries l?lectriques(LCIE)

Boite Postale NO8

Great Britain (EU)

Electrical Equipment Certification Service (EECS)

Health & Safety Executive

12 Electrical installations in hazardous areas

Northern Ireland (EU)

Industrial Science Centre

Department of Economic Development

A-1030 Wein Austria

Technischer merwachungs-Verein Ostereich ( m - A )

in this area does not apply to Northern Ireland, which results in the need for an approved body in Northern Ireland even though that organization has no plans to issue any certificates and it certainly does not at present

It might also be thought odd that the Safety in Mines Research Estab- lishment or its successor, the Health and Safety Laboratory, is not present despite its long history of expertise in this area This is because it was part of the British Civil Service (Government Service) The current Govern- ment associated body is the Electrical Equipment Certification Service which comes from the same roots and has access to the same expertise as did the Safety in Mines Research Establishment Some of the listed bodies have logos and these are shown in Fig 1.4 to assist in their recognition

The certificates issued by all of these approved bodies have exactly the same forrnat which assists in their usage whatever their source They identify the equipment certified, together with its certification code

Introduction 13

Electrical Equipment Certification Service

EECS I BASEEFA &

PTB

Fig 1.4 Typical certification logos

(described later) and the manufacturer An example of a typical certificate

is given in Fig 1.5 What should be noted is the limit of the certificate

It only specifies the equipment as being in accordance with the detailed construction requirements in the specified Standard and does not address installation which will vary depending upon the country of installation Therefore care needs to be taken in careful consideration of the way in which equipment is installed, so as to ensure that the safety elements included in its construction are not negated by its method of installation

The listed approved bodies meet regularly in a working group titled Heads of Test Houses Liaison Committee (HOTL)I5 which was set up by the Commission of the EU The object of this group is to ensure that all approved bodies use the Standards in the same way and present their certificates in the same way It is not 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

3 This certiticate is issued for the electrical apparatus:

CONTROL CONSOLE TYPE ABC.123

4 Manufactured and submitted for d a t i o n A MANUFACTURERLTD by: I

of 123 Fore Street, Buxton, SK17 9JK

5 This electrical apparatus and any acceptable variation thereto is specified in the Schedule to this Certificate and the docnments therein referred do

6 BASEEFA being an Approved Certification Body in accordance with Article 14 of the cooncil Directive

O f ~ E u r O p e a n - ' 'cs of 18 Decemk 1975 (76/117/EEC) certifies that the appamus has baen found to comply with harmonised European Standards:

8 The manufaclurer of the electrical apparatus r d d to in this &ate, hac the responsibility to ensure that the apparatus conforms to the specifcation laid down in the Schedule to this certificate and has satisfied routine verifications and tests specified thcrcin

This appamus may be marked with the Distinctive Community Mark specified in Annex I1 to the Council D i d v e of 16 January 1984 (Doc 84/47/EEC) A facsimile ofthis mark is printed on sheet 1 of this cerWtcate

introduction 1 5

can take considerable time to resolve Because of the commercial nature of the use of certification HOTL performs a valuable role in providing speedy temporary clarification pending the decision of the Standards writing body and to this end HOTL members notify that body of all temporary clarifi- cations which they have adopted The Standards writing body may then endorse or override them as it wishes, in its own good time This does not normally represent any problem for the holder of a certificate based

on an HOTL clarification later overturned by the Standards writing body because, unless a prima-facie danger is identified in relation to the HOTL decision, the certificate would be allowed to stand, although members of HOTL would automatically adopt the official clarification as soon as it was available for future certification

Many of the approved bodies issue certificates to equipment complying with their own or national Standards in addition to equipment complying with the European Standards referred to in the Directive These are not covered by the Directive and their acceptance is a matter for the individual user This is likewise true of certificates issued by bodies not approved by the EU even though they may be national bodies and likewise acceptance

is a matter for the individual Where these latter certificates are in relation

to the European Standards then it is only the expertise of the non-approved certification body which must be considered but in other cases (e.g, Factory

Mutual Research Corporation and Underwriters Laboratories in the USA)

the Standards to which the equipment is certified (or listed which is what the activity is called in the USA) differ significantly, and the effect of this must also be considered

1.7 Certificate and labelling information

There is no real short cut to identification of suitable equipment as the schedules issued with certificates of conformity and inspection certificates contain information which is necessary to the user These should always be made available to the purchasers of certified equipment and there is a legal obligation upon suppliers to do this insofar as safety is dependent upon such information There is, however, a standard coding which appears on both certificate and label usually and this is as follows

Certifying body reference

This appears usually as a set of initials and these are those shown in brackets

in Section 1.5 of this chapter (e.g., PTB, LCIE, etc.)

16 Electrical installations in hazardous areas

Ex - explosion protected equipment

96 - the last two digits of the year of issue

D - amendment status of the Standard used for certification

2 - principal method of protection

1 = flameproof or pressurized (see Chapters 10 and 11)

2 = intrinsic safety (see Chapter 13)

3 = increased safety (see Chapter 12)

4 = type N (n) apparatus (see Chapter 14)

5 = special protection (apparatus which does not wholly comply with one of the Standards but is considered as suitable)

6 = battery operated vehicles (usually using more than one type

of protection)

7 = oil immersed or powder filled (see Chapter 9)

X = indicates that there are special (unusual) installation condi- tions associated with the equipment and these will be speci- fied on the certificate If U appears instead of X or no suffix,

it means that the equipment is considered to be a component and cannot be used unless incorporated in other equipment and further certified

123 = serial number of certificate within year

Protection coding

This normally appears in the following form:

EEx d IIC T4

The meaning of these symbols is as follows:

E - indicates that the equipment complies with a European Standard The symbol will not be present if such is not the case

Ex - indicates explosion protected equipment

d - indicates the type of protection used

o = oil immersion (see Chapter 9)

p = pressurization (see Chapter 11)

q = powder filling (see Chapter 9)

d = flameproof enclosure (see Chapter 10)

e = increased safety (see Chapter 12)

i = intrinsic safety (see Chapter 13) (Intrinsic safety usually

appears with a further suffix, for example ia or ib)

m = encapsulation (see Chapter 9)

n = type n equipment (See Chapter 14); (n sometimes appears as

IIA - equipment is tested in an ideal mixture of propane and air

IIB - equipment is tested in an ideal mixture of ethylene and air

IIC - equipment is tested in an ideal mixture of hydrogen and air (where the equipment is to a type of protection where sparking is prevented the letter will be omitted and only 11 will appear as sub-grouping

is not necessary)

T4 - indicates the maximum temperature achieved by any ignition capable part of the equipment and indicates that no part of the equipment will exceed

An ambient temperature of 40 "C is assumed unless otherwise stated

on the label and certificate

Historically, there have been other methods of coding in Europe and remain different methods in the USA These are shown in Tables 1.1 and 1.2 It must however be noted that because of slightly differing information forming the basis for these that the relationship is only approximate

Table 1.1 Relationship of grouping and classification systems

Current

European

~~~

Flame proof Intrinsic Safety sub-group IIA Group I1 class 2c class 1 Group D sub-group IIB Group I11 class 2d class 2 Group C sub-group IIC Group IV class 2e and 2f class 3a and 3n Group Band A Notes :

1 UK Flameproof Group IV excludes acetylene which was treated separately

2 UK intrinsic safety class 2e did not include acetylene, but 2f did

3 German class 3a excludes acetylene as does USA Group B and UK Class 2e Acetylene is included in German class 3n, USA Group A and UK Class 2

4 In the USA the following Groups are also present: E - Conducting dusts; F - nonCon- ducting dusts; G - Flour and Grain dust

5 To add further complexity, USA apparatus is classed as to its intended use Class A is for gases and vapous, Class B is for dusts and class C is for fibres and flyings

18 Electrical installations in hazardous areas

Table 1.2 Relationship of temperature classi-

Note: Prior to the introduction of a separate temperature

classification system in the USA temperature classifica-

tion was associated with the grouping system as follows:

Groups A, B and D were given a maximum temperature

of 280°C; Group C was given a maximum temperature

of 180°C; Groups E and F were given a temperature of

200 "C; and Group G a temperature of 165°C

1.8 The future of certification

As has been stated, the situation in regard to certification is significantly

affected by the 1990 Directive" which came into force early in 1996

While this will initially rely on European Standards referred to in the European Journal12 it is certain that the breadth of the essential requirements contained within the Directive" will ultimately be used As these essential

requirements are couched in much more general terms than the Standards, then the approved bodies will have to revert to the expert interpretation of more general requirements much as they did before the advent of the more

detailed Standards The level of expertise of the certification bodies will once

again, therefore, become of paramount importance To this end the HOTL

grouping will assume a much greater sigruficance and it is unlikely that it will contain sufficient expertise without introducing industrial expertise into

it How this can be done without making it as cumbersome as a Standards- making body will no doubt become a matter for considerable debate in the not too distant future

The inclusion of non-electrical equipment for which the level of detailed

standardization in this area is much lower will mean that the problem of

certification to the requirements contained in the new Directive" will be apparent much sooner Not only will the currently approved bodies not

Introduction 19

have any detailed Standards but they will probably have only limited exper-

tise in the non-electrical areas covered As a result of this it is likely that

a new set of approved bodies will appear separately from those in the

electrical sphere

Another inclusion in this new Directive is the requirement for a manufac-

turer or supplier to have a quality management system in most cases and

to have that also certified to a set of requirements similar to BS/EN/ISO

900216 (although the requirements are again enshrined in the Directive)

Manufacturer designs and constructs prototype equipment in accordance with appropriate EN Standard

I

Manufacturer applies to approved (notified) body for certificate of conformity

I

Approved body examines equipment for compliance with documentation supplied and against appropriate EN Standard (including testing)

I

Approved (notified) body advises detail of any non compliances Manufacturer corrects

Approved (notified) body issues certificate

Note: In the U K both approved (notified) bodies require a

quality system to be in place at the manufacturers which is certified by a certification body acceptable

to them to BSIENIISO 9002 (they issue such certificates)

Fig 1.6(a) Route to certification Directive 76/117/EEC