The document outlines the Compex course for training personnel to work safely on electrical apparatus in hazardous environments, detailing both theoretical knowledge and practical assessments conducted in simulated conditions. The training focuses on competence validation testing and covers standards, installation, inspection, and maintenance procedures. It emphasizes the critical need for skilled training to ensure safety in environments with flammable materials.

1. ASET International Oil & Gas Training Academy
Comp Ex Hazardous Areas Course
March 2010 Revision

2. 6th
Edition, March 2010
Introduction

3. Ex Facility
March 2010
©
2
National Training and Certification of Personnel for Work on Electrical
Apparatus for Use in Potentially Hazardous Atmospheres
This package has been compiled with information gathered from current standards and the
authors will not be held responsible for any inaccuracies found therein.
Acknowledgements:
The production of this document would not have been possible without the much
appreciated assistance from the following authorities and, therefore, the authors of the
document wish to thank and gratefully acknowledge all those who provided material and
advice for the production of the package, particularly the following:
The British Standards Institute
James Scott Ltd, Aberdeen, Scotland
Weidmuller (Klippon Products) Ltd, Sheerness, Kent
Hawke Cable Glands Ltd, Ashton-under-Lyne, Lancashire
Hecagon Technology Ltd, Aylesbury, Buckinghamshire
Measurement Technology Ltd, Luton, Bedfordshire
Brook Hansen, Huddersfield, West Yorkshire
The Design and Presentation Team of Aberdeen College, including all staff at the Altens
Centre.
The BASEEFA Crown mark shown in this document is the property of the Health and Safety
Executive and should not be interpreted to convey certification. The marks have been
reproduced with the kind permission of the EECS (HSE).
Copyright of Document:
No part of this document may be reproduced, stored in a retrieval system or transmitted in
any form by any means. i.e. electronic, electrostatic, magnetic media, mechanical,
photocopying, recording or otherwise without the permission in writing of the appointed
representative of Aberdeen College.

4. Ex Facility
March 2010
©
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Introduction
About the ‘Ex’ Facility
Ex training courses have been run in Aberdeen College since 1990 and have developed to
the level of sophistication we have today. In its present form the CompEx course has been
in operation since August 1994 and has been designed and constructed specifically for the
National Training of personnel who work with electrical installations and plant in hazardous
and/or potentially explosive environments. The facility includes both classroom and
simulated work areas, these being designed to give as realistic site conditions as is possible
to achieve.
The practical work candidates are required to carry out will take place in these simulated
areas and this is intended to make the candidates feel they are working under site
conditions.
Approximately half of the week will be spent in the classroom where the ‘job knowledge’
elements of the course will be delivered by means of presentations incorporating lectures,
demonstrations, and photographic slides of good and bad practice on apparatus. The
remaining time will be spent on Competence Validation Testing in the simulated
hazardous areas. The tests are nationally set for Ex training.
The Outcome
The objective of the training is to introduce the candidate to operating procedures and
techniques and to give candidates and their employer’s confidence that the candidates are
competent to work on electrical apparatus in hazardous or potentially explosive
environments. The competence laid down nationally by industry and through this will help
make your industry a safer one.
About the Programme
The need for training in these areas of work is self evident in that the safe operation of
electrical equipment in hazardous areas is paramount. It is extremely important for all
personnel who operate in these conditions to be competent in the correct techniques and
operational procedures. This can best be achieved by means of training by skilled staff in an
environment as close to the ‘real thing’ as possible. In addition to this, the job knowledge
developed through the course must be put into operation in the actual working situation so
that the levels of expertise are increased through experience.
The Design of the Programme
The program is dived into two halves, namely:
a. Job Knowledge
b. Competence Validation Testing (CVT)
The ‘job knowledge’ component takes place during the first half of the week and provides the
information and experience you need to tackle the CVT’S.

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March 2010
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Selection, Installation, and Maintenance of Electrical Apparatus for use in Hazardous
Locations.
Units:
1) General principles
(a) Nature of flammable materials
(b) gas grouping
(c) basic principles of area classification
(d) temperature codes
(e) ingress protection
2) Standards, Certification and Marking
3) Flameproof Ex d
4) Increased Safety Ex e
5) Type ‘n’ protection
6) Pressurisation Ex p
7) Intrinsic Safety Ex i
8) Other methods of protection, Ex o, Ex q, Ex m & Ex s
9) Combined (Hybrid) methods of protection
10) Wiring Systems
11) Inspection & Maintenance to BS EN60079-17
12) Sources of ignition
13) Induction to Competence Validation Testing
14) Permit to Work System and Safe Isolation
Appendix 1 Data for flammable materials for use with electrical equipment, ref BS5345:
Part 1: General recommendations.
Appendix 2 Self assessment project and apparatus label reading.

6. Ex Facility
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Course outline
The training scheme
The training scheme is arranged to prepare candidates for the assessment programme
which comprises four discreet Competence Validation Tests (CVT’s) offered as
complimentary pairs. The four CVT’s are as follows:
EX01 Preparation & Installation of Ex d, Ex e, Ex n and Ex p Systems
EX02 Inspection & Maintenance of Ex d, Ex e, Ex n and Ex p Systems
EX03 Preparation & Installation of Ex i Systems
EX04 Inspection & Maintenance of Ex i Systems
Job knowledge
The classroom (job knowledge) part of the training scheme consists of 12 Units which apply
to the four CVT’s as illustrated below.
Unit 1: General principles Unit 2: Standards,
Certification and
Marking
Unit 3: Flameproof Ex d
EX01 & EX02 EX01 & EX02 EX01 & EX02
EX03 & EX04 EX03 & EX04
Unit 4: Increased Safety
Ex e
Unit 5: Type ‘n’
protection
Unit 6: Pressurisation
Ex p
EX01 & EX02 EX01 & EX02 EX01 & EX02
(Written Assessment)
Unit 7: Intrinsic Safety Ex i Unit 8: Other methods of
protection
Unit 9: Combined (Hybrid)
protection methods
EX03 & EX04 (Written Assessment) EX01 & EX02
Unit 10: Wiring Systems Unit 11: Inspection &
Maintenance to
BS EN60079-17
Unit 12: Sources of ignition
EX01 & EX02 EX01 & EX02 EX01 & EX02
EX03 & EX04 EX03 & EX04 EX03 & EX04
Unit 13: Induction to
Competence
Validation Testing
Unit 14: Permit to Work
and
Safe Isolation
EX01 & EX02 EX01 & EX02
EX03 & EX04 EX03 & EX04

7. Ex Facility
March 2010
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6
The CVT’s are a series of practical tests which you will undertake within the simulated work areas
during the second half of the programme. On successful completion of these tests you will be
awarded a Certificate of Core Competence which will indicate the areas the awarding body, Joint
Training Ltd. (JTL), has deemed you are competent.
During the final half-day of the programme you are required to sit written assessments in the form of
multi-choice papers which are related to the practical CVT assessments.
The staff who are involved in monitoring the various assessments are present only as observers and
not to prompt or offer technical assistance. Their observations of your work is recorded on Nationally
written checklists which are processed outwith the Centre and your results cannot be determined until
this process is complete.
Manual Units and applicable CVT’s
Unit 1: General Principles EX01, EX02, EX03 & EX04
Unit 2 : Standards, Certification & Marking EX01, EX02, EX03 & EX04
Unit 3: Flameproof Ex d EX01 & EX02
Unit 4: Increased Safety Ex e EX01 & EX02
Unit 5: Type ‘n’ Protection EX01 & EX02
Unit 6: Pressurisation Ex p EX01 & EX02 (Written Assessment)
Unit 7: Intrinsic Safety E x i EX03 & EX04
Unit 8: Other methods of Protection (Written Assessment)
Unit 9: Combined (Hybrid) Protection Methods EX01 & EX02
Unit 10: Wiring Systems EX01, EX02, EX03 & EX04
Unit 11: Inspection & Maintenance to BS EN60079-17 EX01, EX02, EX03 & EX04
Unit 12: Sources of Ignition EX01, EX02. EX03 & Ex04
Unit 13: Induction to Competence Validation Testing EX01, EX02. EX03 & Ex04
Unit 14: Permit to Work EX01, EX02. EX03 & Ex04
Course programme
The following course programme is for illustration purposes only, particularly for the CVT
assessments, and can change according to candidate numbers attending the course. A
programme for the CVT assessments will be compiled during the week.

8. Ex Facility
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Programme: Electrical Apparatus in Potentially Hazardous Areas
5 – Day Programme
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8:30
12:30
Course
registration and
induction
Unit 1: General
Principles
Unit 10: Wiring
systems &
Demonstration of
compound filled
gland and
diaphragm seal
gland assembly
Unit 2: Standards:
certification &
marking
Unit 4: Increased
Safety Ex e
Unit 5: Type ‘n’
Protection
Unit 6:
Pressurisation Ex p
Unit 7: Intrinsic Safety E x i EX01 CVT
Inspection &
Maintenance
of d, e & n
apparatus
Candidates
7-12
EX02 CVT
Preparation
&
Installation
of d, e & n
apparatus
Candidates
1-6
EX03 CVT
Inspection &
Maintenance
of d, e & n
apparatus
Candidates
7-12
EX04 CVT
Preparation
&
Installation
of d, e & n
apparatus
Candidates
1-6
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B
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B
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B
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13:00
17:00
Unit 3: Flameproof
Ex d
Unit 10: Practical
exercise:
Assembly of
compound filled
and diaphragm
seal type glands.
Unit 8: Other
methods of
protection
Unit 9: Combined
(Hybrid) methods of
protection
Unit 11: Inspection &
Maintenance
Unit 13: Introduction
to CVT’s
Unit 14: Work permit
EX01 CVT
Preparation
&
Installation
of d, e & n
apparatus
Candidates
1-6
EX02 CVT
Inspection &
Maintenance
of d, e & n
apparatus
Candidates 7-
12
EX03 CVT
Preparation
&
Installation
of d, e & n
apparatus
Candidates
1-6
EX04 CVT
Inspection &
Maintenance
of d, e & n
apparatus
Candidates
7-12
Job Knowledge
assessment
EX01, EX02, EX03 & EX04
Multi-choice examination

9. Unit 1:
General Principles

10. March 2010 ©
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Objectives:
On completion of this unit, ‘General Principles’, you should know:
a. The nature of flammable materials with regard to ‘explosive limits’ (LEL/UEL),
‘flashpoint’, ‘ignition’ temperature’, the effect of ‘oxygen enrichment’ and ‘relative
density’.
b. The basic principles of area classification.
c. The Grouping of gases according to ‘minimum ignition energy’ (MIE) and ‘maximum
experimental safe gap’ (MESG).
d. Appropriate T-ratings for apparatus relative to the ignition temperature of a given
flammable material.
e. The levels of ‘ingress protection’.

11. March 2010 ©
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General Principles
Nature of Flammable Materials
Fire Triangle
The fire triangle represents the three elements which must be present before combustion
can take place. Each point of the triangle represents one of the essential elements which
are:
1. Fuel: This can be in the form of a gas, vapour, mist or dust
2. Oxygen: Plentiful supply since there is approximately 21% by volume in
air.
3. Source of Ignition: This can be an arc, spark, naked flame or hot surface.
Combustion will take place if all three elements, in one form or another, are present, the
gas/air mixture is within certain limits and the source of ignition has sufficient energy. The
removal of one element is sufficient to prevent combustion, as is the isolation or separation
of the source of ignition from the gas/air mixture. These are two techniques used in
explosion protected equipment. Other protection techniques allow the three elements to co-
exist and either ensures that the energy of the source of ignition is maintained below specific
values, or allows an explosion to take place and contains it within a robust enclosure. These
techniques are addressed in the various sections of this manual.
Gas or vapour
Oxygen
( 21% in air )
Source of
ignition

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Flammable (Explosive) Limits
Combustion will only occur if the flammable mixture comprising fuel, in the form of a gas or
vapour, and air are within certain limits. These limits are the ‘lower explosive limit’ (LEL),
and the ‘upper explosive limit’ (UEL), and between these limits is known as the
flammable range.
An every day example of this is the carburettor of a petrol engine, which must be tuned to a
particular point between these limits in order that the engine may function efficiently.
Lower Explosive Limit: When the percentage of gas, by volume, is below this limit the
mixture is too weak to burn, i.e. insufficient fuel and/or too
much air.
Upper Explosive Limit: When the percentage of gas, by volume, is above this limit the
mixture is too rich to burn, i.e. insufficient air and/or too much
fuel.
The flammable limits of some materials are given below.
Material LEL
% by Volume
UEL
% by Volume
Propane 1.7 10.9
Methane 4.4 17
Ethylene 2.3 36
Hydrogen 4 77
Acetylene 2.3 100
Diethyl Ether 1.7 36
Kerosene 0.7 5
Carbon Disulphide 0.6 60

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Flammable (Explosive) Limits (continued)
Different gases or vapours have different flammable limits and the greater the difference
between the LEL and the UEL, known as the flammable range, the more dangerous the
material. An explosive (flammable) atmosphere, therefore, only exists between these limits.
Operational safety with flammable mixtures above the UEL is possible, but is not a practical
proposition. It is more practical to operate below the LEL.
Sources of Ignition
Sources of ignition are many and varied and include:
a. Electrical arc/sparks
b. Frictional sparks
c. Hot surfaces
d. Welding activities
e. Cigarettes
f. Static discharges
g. Batteries
h. Exhausts of combustion engines
i. Thermite action
j. Sodium exposed to water
k. Pyrophoric reaction
l. Chemical reactions
m. Lightning strikes
The source of ignition as far as this text is concerned is primarily electrical equipment.

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Flashpoint
By definition flashpoint is: ‘the lowest temperature at which sufficient vapour is given off a
liquid, to form a flammable mixture with air that can be ignited by an arc, spark or naked
flame’. Typical values are given below.
Material Flashpoint
°C
Propane -104
Ethylene -120*
Hydrogen -256*
Acetylene -82*
Diethyl Ether -45
Kerosene 38
Carbon Disulphide -95*
* Values obtained form a source other than PD IEC60079-20
The flashpoint of a material gives an indication of how readily that material will ignite in
normal ambient temperatures. Reference to the tables of flammable materials from PD
IEC60079-20 (see Appendix 1) reveals that different materials have different flashpoints,
which vary from well below to well above 0°C.
Materials with high flashpoints should not be overlooked as a potential hazard since
exposure to hot surfaces can allow a flammable mixture to form locally. Furthermore, if a
flammable material is discharged under pressure from a jet, its flashpoint may be reduced.
Amount of vapour released dependent
on temperature

15. March 2010 ©
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Flashpoint (continued)
Kerosene: Flashpoint 38°C
At 38°C
“Ignition”
At 37°C
Insufficient vapour
given off
At 0°C
Negligible vapour
given off

16. March 2010 ©
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Ignition Temperature
Ignition temperature is defined as: ‘the minimum temperature at which a flammable
material will spontaneously ignite’.
Ignition temperature, formerly known as auto-ignition temperature, is an important
parameter since many industrial processes generate heat. Careful selection of electrical
equipment will ensure that the surface temperature produced by the equipment, indicated by
the T-rating, will not exceed the ignition temperature of the flammable atmosphere which
may be present around the equipment. Typical values of ignition temperature are:
Material Ignition Temperature
°C
Propane 470
Methane 537
Ethylene 425
Hydrogen 560
Acetylene 305
Diethyl Ether 160
Kerosene 210
Carbon Disulphide 95

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Oxygen Enrichment
The normal oxygen content in the atmosphere is around 20.95%, and if a given location has
a value which exceeds this it is deemed to be oxygen enriched. Typical examples of where
oxygen enrichment may occur are gas manufacturing plants, hospital operating theatres,
and where oxy-acetylene equipment is used.
Oxygen enrichment has three distinct disadvantages. First of all, it can lower the ignition
temperature of flammable materials as shown in the table below.
Air Increased Oxygen
Material
Ignition Temperature
°C
Ignition Temperature
°C
Hydrogen sulphide 260 220
Acetylene 305 296
Ethane 512 506
Secondly, oxygen enrichment significantly raises the upper explosive limit (UEL) of the
majority of gases and vapours, thereby widening their flammable range. This is illustrated in
the following table.
Air Increased Oxygen
Material
LEL
%
UEL
%
LEL
%
UEL
%
Methane 5 15 5.2 79
Propane 2.2 9.5 2.3 55
Hydrogen 4 75 4.7 94
Thirdly, oxygen enrichment of a flammable atmosphere can allow it to be ignited with much
lower values of electrical energy.
Explosion protected equipment will have been tested in normal atmospheric conditions and,
therefore, the safety of such equipment in an oxygen enriched atmosphere cannot be
assured because of the modified nature of the flammable mixture.
* All values obtained from a source other than PD IEC60079-20
* All values obtained from a source other than PD IEC60079-20

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Density
If a flammable material is released, it is important to know whether the material will rise or
fall in the atmosphere. The different flammable materials are compared with air and
allocated a number to denote their relative density with air. Since air is the reference, its
relative density is 1 so that for a material twice as heavy as air, its relative density will be
2. Therefore, materials with a relative density less than unity will rise in the atmosphere,
and those greater than unity will fall in the atmosphere.
Materials which rise in the atmosphere can collect in roof spaces, and those which fall, such
as butane or propane, can drift along at ground level and possibly into a non-hazardous
location, or may collect in locations lower than ground level without ever dispersing. Such
locations should be well ventilated in order to avoid ignition due to a stray spark or a
discarded cigarette.
Knowledge of where a flammable material will collect ensures that gas detectors when fitted
will be located at the correct level and ventilation is directed accordingly.
<1
>1
Material
Relative vapour
density
Air 1
Propane 1.56
Methane 0.55
Ethylene 0.97
Hydrogen 0.07
Acetylene 0.9
Diethyl Ether 2.55
Kerosene 4.5*
Carbon
Disulphide
2.64
* Value obtained from a source
other than PD IEC60079-20

19. March 2010 ©
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Area Classification
An hazardous area is defined as:
‘An area in which an explosive gas atmosphere is present, or may be expected to be
present, in quantities such as to require special precautions for the construction, installation
and use of apparatus.’
A non-hazardous area is defined as:
‘An area in which an explosive gas atmosphere is not expected to be present in quantities
such as to require special precautions for the construction, installation and use of apparatus.’
Zones
Zoning is a means of representing the frequency of the occurrence and duration of an
explosive gas atmosphere based on the identification and consideration of each and every
source of release in the given areas of an installation. Zoning will have a bearing on, and
simplify the selection of, the type of explosion protected equipment which may be used.
Hazardous areas are, therefore, divided into three Zones which represent this risk in terms
of the probability, frequency and duration of a release.
The three Zones, as defined in BS EN60079-10-1: Electrical apparatus for explosive gas
atmospheres, Part 10. Classification of hazardous areas, are as follows:
Zone 0 - An area in which an explosive gas atmosphere is present continuously
or for long periods or frequently.
Zone 1 - An area in which an explosive gas atmosphere is likely to occur in
normal operation occasionally.
Zone 2 - An area in which an explosive gas atmosphere is not likely to occur in
normal operation but, if it does occur, will persist for a short period
only.
Although not specified in IEC 60079-10-1, but quoted in API RP 505**, the duration of a gas
release, or a number of gas releases, on an annual basis (one year comprises circa 8760
hours), for the different Zones is as follows.
Zone 2 - 0 – 10 hours
Zone 1 - 10 – 1000 hours
Zone 0 - over 1000 hours
** The above document, API RP 505, is published by the American Petroleum Institute and
entitled “Recommended Practice for Classification of Locations for Electrical Installations
at Petroleum Facilities Classified as Class I, Zone 0, Zone 1, and Zone 2.

20. March 2010 ©
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Area Classification (continued)
Zone representation for ‘Area Classification Diagrams’
In accordance with BS EN60079-10, the illustrations below are the preferred method for
representing the various zones in an hazardous area.

21. March 2010 ©
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Area Classification (continued)
Fixed Roof Storage Tank
Distances: ‘a’ 3m from vent opening
‘b’ 3m above the roof
‘c’ 3m horizontally from the side of the tank
b
c
a
Zone 2
Zone 1
Zone 0
Sump:
Zone 1

22. March 2010 ©
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Area Classification (continued)
Sources of Release
Welded pipe joint:
( Non-hazardous )
Flanged joint:
( Zone 2)
Pump gland:
( Zone 2 or Zone 1
depending on the
quality of the seal )
Space above liquid
in a closed tank:
( Zone 0)

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Gas / Apparatus Grouping
In the IEC system, the group allocation for surface and underground (mining) industries are
separate. Group I is reserved for the mining industry, and Group II which is subdivided into
IIC, IIB and IIA for surface industries. The representative gases for the sub-groups are
shown in the table below.
Two methods have been used to ‘group’ these flammable materials according to the degree
of risk they represent when ignited. One method involved determining the minimum ignition
energy which would ignite the representative gases. The values obtained are relevant to
Intrinsically Safe apparatus. In the table below it can be seen that for Group II, hydrogen
and acetylene are the most easily ignited and propane the least easily ignited.
The other method involved tests using, for example, a special flameproof enclosure in the
form of an 8 litre sphere which was situated inside a gas-tight enclosure. Both halves of the
sphere had 25mm flanges and a mechanism enabled the gap dimension between the
flanges to be varied. During tests, the area inside and outside the sphere were occupied with
a gas in its most explosive concentration in air and, by means of a spark-plug the gas inside
the sphere was ignited. The maximum dimension between the flanges, which prevented
ignition of the gas/air mixture, is known as the ‘maximum experimental safe gap’ (MESG),
and the values for the representative gases are shown in the table below. The more
dangerous a gas, the tighter the gap at the flanges has to be. It is important to note that the
MESG values are not used for the design of Flameproof apparatus, only the maximum
working gaps.
The table also shows that these flammable materials fall into the same order for both tests,
i.e. in a relative context, hydrogen and acetylene present the most risk and propane the least
risk in terms of ‘minimum ignition energy’ and ‘MESG’.
Gas Group Representative
Gas
MESG
(mm)
Maximum
Working
Gap
(mm)
Minimum
Ignition
Energy
(μJ)
I
Methane
(Firedamp)
1.14 0.5 260
IIA Propane 0.91 0.4 160
IIB Ethylene 0.65 0.2 95
Hydrogen 0.28
IIC
Acetylene 0.37
0.1 20
Note: Apparatus other than flameproof or intrinsic safety, which has no sub-division letter
(A, B or C) after the group II mark, may be used in all hazards.
Apparatus marked IIxxxxx: xxxxx represents the chemical formula or name of a
flammable material, and apparatus marked in this way may
only be used in that hazard.

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Gas / Apparatus Grouping (continued)
The sub-group marking is one of the important considerations during the selection process
of explosion protected apparatus. For example, apparatus marked IIA can only be used in
IIA hazards such as propane, it cannot be used in IIB or IIC hazards. Apparatus marked IIB
can be used in IIB and IIA hazards but not IIC hazards. Apparatus marked IIC can be used
in all hazards.
Apparatus for determination of M.E.S.G

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Gas / Apparatus Grouping (continued)
Comparison of BS 229 and IEC
BS 229 is an old British Standard, which has now been withdrawn, but electrical apparatus
was still manufactured to this standard up until several years ago. Apparatus manufactured
to BS 229 has sub-group markings which are different to those of the IEC system and the
comparison is shown in the table below. The introduction of the ATEX Directives after 30
June 2003 has caused manufacturers to discontinue the production of apparatus to this
standard, but apparatus already in use will be unaffected.
BS 229 Representative Gas IEC
1 Methane I
2 Propane IIA
3a Ethylene
3b Coal Gas
IIB
4 Hydrogen & Acetylene IIC

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Temperature Classification
Approved electrical equipment must be selected with due regard to the ignition temperature
of the flammable gas or vapour which may be present in the hazardous location. Apparatus
will usually be marked with one of the temperature classes shown in the table below. The
temperature class indicates the maximum temperature the surfaces of an enclosure, which
are exposed to a flammable gas, must not exceed during normal or specified fault
conditions.
Temperature Classes
T - Class
Maximum Surface
Temperature
T1 450°C
T2 300°C
T3 200°C
T4 135°C
T5 100°C
T6 85°C
In the table below, it will be observed that for each material, the T-rating temperature is
below the ignition temperature of the flammable material. Moreover, the T-rating
temperatures are based on a maximum ambient rating of 40°C as far as the UK is
concerned. For example, apparatus classified T5, based on a 40°C ambient rating, will have
a maximum permitted temperature rise of 60°C. In order to avoid infringement of the
apparatus certification, the ambient rating must be compatible with environmental ambient
temperatures, and the temperature rise not exceeded. This is demonstrated on page 20.
A further consideration is apparatus for use in hotter climates, typically found in Middle and
Far Eastern countries, which will usually require ambient ratings greater than 40°C.
Apparatus for use in colder (arctic) climates will require a much lower limit to the ambient
temperature range which may be as low as -50°C.
Material
Ignition
Temperature
T-Rating
Methane 537°C T1 (450°C)
Ethylene 425°C T2 (300°C)
Cyclohexane 259°C T3 (200°C)
Diethyl Ether 160°C T4 (135°C)
T5 (100°C)
Carbon Disulphide 95°C T6 (85°C)

27. March 2010 ©
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Temperature Classification (continued)
-2
-2

28. March 2010 ©
20
Ingress Protection
Enclosures of electrical equipment are classified according to their ability to resist the
ingress of solid objects and water by means of a system of numbers known as the
‘International Protection (IP) Code’. This code, which is not always marked on apparatus,
consists of the letters IP followed by two numbers, e.g. IP56.
The first number, in the range 0-6, indicates the degree of protection against solid objects,
and the higher the number the smaller the solid object that is prevented from entering the
enclosure. Zero (0) indicates no protection and 6 indicate the apparatus is dust-tight.
The second number, ranging from 0-8, identifies the level of protection against water
entering the enclosure, i.e. 0 indicates than no protection is afforded, and 8 that the
apparatus can withstand continuous immersion in water at a specified pressure.
An abridged version of the full table is shown below.
Solid Objects Water
First
Numeral
Level of Protection
Second
Numeral
Level of Protection
0 No protection 0 No protection
1
Protection against objects
greater than 50 mm
1
Protection against drops of water
falling vertically
2
Protection against objects
greater than 12 mm
2
Protection against drops of water
when tilted up to 15°
3
Protection against objects
greater than 2.5 mm
3
Protection against sprayed water
up to 60°
4
Protection against objects
greater than 1.0 mm
4
Protection against splashed water
from any direction
5 Dust-protected 5
Protection against jets of water
from any direction
6 Dust-tight 6
Protection against heavy seas
- deck watertight
7
Protection against immersion in
water 1m in depth and for a
specified time
8
Protection against indefinite
immersion in water at a specified
depth

29. Unit 2:
Standards, Certification and
Marking

30. March 2010 ©
2
Objectives:
On completion of this unit, ‘Standards, Certification and Marking’, you should know:
a. Current British, European and International Standards and also relevant older British
Standards and Codes of Practice.
b. The certification process for explosion protected apparatus.
c. The methods of marking explosion protected apparatus.
d. The basic requirements of the ATEX Directives.
e. The correlation between the ATEX categories and Equipment Protection Levels
(EPL’s)

31. March 2010 ©
3
Standards, Certification and Marking
Introduction
There are many industries involved in the process of hazardous materials, and these include
chemical plants, oil refineries, gas terminals and offshore installations. These industries rely
heavily on electrical energy to power, for example, lighting, heating and rotating electrical
machines.
The safe use of electrical energy in the hazardous locations of these industries can only be
achieved if tried and tested methods of explosion protection are implemented and to this
end, the organisations involved in the writing of standards, testing and certification of
equipment have a very important role to play.
Since the early 1920’s, many standards have evolved as a result of careful research, often
prompted by incidents such as the Senghennydd colliery disaster in 1913 in which 439
miners lost their lives. The cause at that time was not fully understood but after investigation,
was thought to have been due to an electrical spark igniting methane (firedamp) present in
the atmosphere. Other disasters include Abbeystead Water Pumping Station in which 16
people lost their lives, once again due to the electrical ignition of methane gas, Flixborough
where an explosion killed 28 people due to ignition of a massive release of cyclohexane, and
more recently Piper Alpha in the North Sea in which 167 men lost their lives.
Construction of equipment to relevant standards coupled with testing by an independent
certification body will ensure that the equipment is suitable for its intended purpose.
Explosion protected equipment may be constructed in accordance with relevant standards,
but the integrity of such equipment will only be preserved if it is selected, installed and
maintained in accordance with the manufacturers recommendations. Guidance in this
respect has been provided for many years by the UK Code of Practice BS 5345, but this
document has been superseded by a new series of five separate standards based on the
IEC 60079 series of International standards. These five documents apply to explosion
protected equipment/systems in all countries in the EU and cover, (1) selection and
installation of equipment, (2) classification of hazardous areas, (3) inspection and
maintenance, (4) repair of explosion protected equipment, and (5) data for flammable gases
provided by an IEC document (See lower table on page 13). The BS EN60079 standards
are identical to the IEC60079 standards. Although BS 5345 has been withdrawn, it
nevertheless remains a source of information for older installations, but applies to the UK
only with regard to the EU.
In the United Kingdom, manufacturing and testing standards are published by an
organisation known as the British Standards Institute (BSI). With regard to the European
Community, the organisation which publishes harmonised standards for its member nations
is the European Committee for Electrotechnical Standardisation (CENELEC) and, with
global harmonisation of standards the ultimate aim, the International Electrotechnical
Commission (IEC) publishes standards for this purpose.
Historically, equipment designs are evaluated and prototypes tested by independent
organisations, one of which was formerly known as ‘British Approvals Service for
Electrical Equipment in Flammable Atmospheres (BASEEFA), but was later known as
‘Electrical Equipment Certification Service (EECS)’. The acronym BASEEFA, which has
been closely associated with explosion protected equipment for many years, was retained by
EECS for certification marking purposes. EECS, which was part of the Health and Safety
Executive (HSE), also published standards for special applications. EECS, however, closed

32. March 2010 ©
4
for business in September 2002, but encouraged by several major customers, former staff
established an independent organisation known as Baseefa (2001) Ltd, and became simply
Baseefa Ltd. two-years later. Having traded since March 2002, Baseefa Ltd. became an EU
Notified Body (NB) in June 2002 and was allocated the NB Number 1180.
With the introduction of the ATEX Directives, which become mandatory after 30 June 2003,
a procedure for the evaluation of equipment for compliance with the ATEX directives was
implemented. This procedure involves a series of modules, listed on page 5, covering the
design, quality control and production phases for equipment, which are audited by a Notified
Body. A Notified Body is an independent organisation that has been assessed and
accredited by a national body (United Kingdom Accreditation Service, UKAS, in the UK) as
having the expertise to operate as a Notified Body in accordance with the directives with
regard to conformity assessment of products. A Notified Body has been notified to the
European Commission by its member state
Notified Bodies have their own unique NB number, which will be marked on the certification
labels of ATEX compliant apparatus. Other Notified Bodies in the UK include SIRA
Certification Service, NB Number 0518, and ITS Testing and Certification Ltd., NB
Number 0359 and many others throughout the EU. Notified bodies may require the services
of other organisations for testing product prototypes.
ATEX Directives
On the 12 June 1989 a Framework Directive 89/391/EEC was adopted by the European
Commission the objective being to establish a basis for improving the safety of employees in
the workplace. Supplementary directives namely, 94/9/EC, introduced under Article 100a of
the Treaty of Rome and now known as ATEX 95, and 99/92/EC, now ATEX 137, address
equipment use and safety in hazardous areas. ATEX 95 is the product directive and ATEX
137 is the workplace directive. Both these directives, unlike previous directives, establish a
New Approach in that they are mandatory by law rather than advisory. ATEX 95, the
product directive, mandatory from 01 July 2003, requires all new equipment, which
includes not only electrical equipment but also mechanical (non-electrical) equipment, e.g.
pumps, gearboxes etc, and protective systems for use in potentially explosive atmospheres,
placed on the market of the European Community for the first time to be manufactured in
compliance with the directive. Equipment from out-with the EU, whether new or second
hand, imported into the European Community and placed on the market for the first time
must also be in compliance with the directive.
ATEX 95 applies to the design requirements of equipment and hence concerns mainly the
manufacturer and supplier but availability of spare parts and items held in stock would be of
concern to equipment users. Therefore, in order to comply with ATEX 95, products must
satisfy the Essential Health & Safety Requirements (EHSR’s) specified in the annexes of
the Directives, with regard to the inherent risks associated with the product for the protection
of the public. This is usually achieved by compliance with relevant harmonised standards,
and although it is possible to achieve compliance by means other than the harmonised
standards, difficulty would arise installing, inspecting and repairing such equipment to the BS
EN60079 standards 14, 17 & 19. Subject to a successful Conformity Assessment, the
product can display the CE mark which indicates compliance with the ATEX Directive.
ATEX 137, the user directive, became fully mandatory from 01 July 2006 and places
responsibilities on employers to provide a safe working environment for employees.

33. March 2010 ©
5
CE Conformity Assessment Modules
The Conformity Assessment involves a series of Basic Modules which are listed in the table
below and their application in the subsequent simplified flow chart.
A Internal control of production Covers internal design and production control. Does not
require the involvement of a notified body.
B EC type-examination Covers the design phase, the EC type-examination being
issued by a notified body. Has to be followed by a module
for assessment during the production phase.
C Conformity to type Covers the production phase after module B. This module
confirms conformity of the product with that described in
the EC examination certificate as issued during module B.
D Production quality assurance Covers the production phase following module B.
Production quality assurance is based on the standard EN
ISO 9002 and the involvement of a notified body who has
responsibility for the approval and control of the quality
system regarding production, end product inspection and
testing implemented by the manufacturer.
E Product quality assurance Covers the production phase following module B.
Production quality assurance is based on the standard EN
ISO 9003 and the involvement of a notified body who has
responsibility for the approval and control of the quality
system regarding end product inspection and testing
implemented by the manufacturer.
F Product verification Covers the production phase following module B. The EC
type examination carried out by the notified body, to
ensure conformity to type in module B, is followed by the
issue of a certificate of conformity.
G Unit verification Covers the design and production phases. A certificate of
conformity is issued after examination of every product by
the notified body.
H Full quality assurance Covers the design and production phases. Quality
assurance is based on the standard EN ISO 9003 and the
involvement of a notified body who has responsibility for
the approval and control of the quality system for design,
manufacture, final product inspection and testing
implemented by the manufacturer.

34. March 2010 ©
6
CE Conformity Assessment Modules (continued)
The illustration below shows how the modules listed on the previous page may be
implemented to obtain the CE marking for apparatus.
ATEX 95
The ATEX Directive 94/9/EC ( ATEX 95 ) was adopted by the EC to enable free trade of
products between member states through alignment of technical and legal requirements and
concerns the design of explosion protected equipment. The directive applies not only to
electrical equipment but also to mechanical equipment and protective systems used in the
presence of potentially explosive atmospheres containing gases/vapours or combustible
dusts.
Equipment is defined as any item which is inherently ignition capable or is potentially ignition
capable and requiring the inclusion of special design and installation techniques to prevent
ignition of any surrounding flammable atmosphere which may be present. The ‘equipment’
may also be interfaces located in the non-hazardous area which are part of an explosion
protection system. Protective systems include quenching systems, flame arrestors, fast-
acting shut-off valves and pressure relief panels installed to limit damage due to an
explosion or prevent the spread of explosions.
Design phase Production phase
Module A
Module C
Module D
Module E
Module F
Module G
Module B
Manufacturer
Module H

35. March 2010 ©
7
ATEX 137
The ATEX Directive 99/92/EC ( ATEX 137 ), commonly known as the ‘use’ directive, is
implemented in the UK via the Dangerous Substances and Explosives Atmosphere
Regulations 2002 (DSEARs). Employers are obliged to implement the following minimum
requirements in the workplace with regard to DSEARs.
a. Carry out a risk assessment where dangerous substances are or may be present.
b. Eliminate or reduce risk as far as is reasonably practicable.
c. Classify locations in the workplace where explosive atmospheres may be present
into hazardous or non-hazardous areas.
d. Have in place procedures/facilities to deal with accidents, incidents and emergencies
involving dangerous substances in the workplace.
e. Provide appropriate information and training of employees for their safety regarding
precautions to be taken when dangerous substances are present in the workplace,
written instruction for tasks undertaken by employees and operation of a permit-to-
work system.
f. Clearly identify the contents of containers and pipes.
g. Co-ordinate operations where two or more employees share a workplace in which a
dangerous substance may be present.
h. Posting of warning signs for locations where explosive atmospheres may occur.
i. Selection of equipment in accordance with ATEX 95 and establishment of a
maintenance programme.
Marking of Hazardous Areas
Article 7 in the Directive ATEX 137 states:
‘Where necessary, places where explosive atmospheres may occur in such
quantities as to endanger the health and safety of workers shall be marked
with signs at their points of entry in accordance with Annex III.’
Annex III of the directive specifies the exact requirements for the sign but generally it is
required to be triangular with a yellow background, black border and marked ‘Ex’.
Ex

36. March 2010 ©
8
European Notified Bodies
The illustration below shows some of the Notified Bodies along with their unique Notified
Body (NB) number. There are around sixty Notified bodies in the EU at the time of writing.
Finland: VTT Industrial Systems (0537)
Sweden: SP-Swedish National Testing (402)
Norway: NEMKO AS (0470)
DNV AS (0575)
Denmark: UL Int DEMKO A/S (0539)
UK: Baseefa (1180)
SIRA (0518)
BSI Product Services (0086)
ITS Testing & Cert. Ltd (0359)
Lloyd’s Reg Ver Ltd (0038)
Netherlands: KEMA (0344)
Belgium: ISSeP (0539)
France: LCIE (0081)
INERIS (0080)
Spain: LOM (0163)
Italy: CESI (0722)
Germany: PTB (0102)

37. March 2010 ©
9
Comparison of IEC, European (CENELEC) and British Standards
Prior to the closer ties between the UK and Europe, electrical equipment, such as flameproof
or increased safety etc., was manufactured in accordance with the British Standard BS 4683
(see table in page 11). Equipment built and certified to this standard was entitled to display
the mark Ex on its label, which indicated that the apparatus was explosion protected. This
term should not be confused with term explosion-proof as they are entirely different. In
addition to the ‘Ex’ mark, the label was also marked with a ‘crown’ symbol, which is the
distinctive mark for the UK test house BASEEFA, later to become known as EECS. Other
examples of marks are shown on page 14 of this Unit.
Because of the differences in standards, e.g. equipment manufactured in the UK could not
be used in the other European countries and vice-versa, and hence, equipment made to BS
4683 could only be used in the UK, or in other countries outside Europe. Co-operation
between the standards writing bodies in the UK and Europe resulted in the development of
‘Harmonised’ standards, also known as ‘Euronorms’, for which the English version was
published as BS 5501 and comprised nine separate parts as shown in the third column of
the table on page 10. The Euronorm equivalents, written in French or German, are shown on
the first column. Column four shows the second generation of the UK version of the
harmonised standards which replaced BS5501.
However, with the trend towards global harmonisation of standards continuing to make
progress, a new series of standards have been gradually introduced having numbers based
on the International Standard numbers (second column), i.e. BS EN60079, as shown in
column five of the following table.

38. March 2010 ©
10
Comparison of IEC, European (CENELEC) and British Standards
CENELEC
Euronorm
(EN) Number
International
Standards
British Standard
(BS) Number
Revised Standard
(BS EN) Number
Latest Revised
Standard
(BS EN) Number
Type of Protection
EN 50 014 IEC 60079-0 BS 5501: Pt. 1 BS EN50 014 BS EN60079-0 General Requirements
EN 50 015 IEC 60079-6 BS 5501: Pt. 2 BS EN50 015 BS EN60079-6 Oil Immersion ‘o’
EN 50 016 IEC 60079-2 BS 5501: Pt. 3 BS EN50 016 BS EN60079-2 Pressurised Apparatus ‘p’
EN 50 017 IEC 60079-5 BS 5501: Pt. 4 BS EN50 017 BS EN60079-5 Power Filling ‘q’
EN 50 018 IEC 60079-1 BS 5501: Pt. 5 BS EN50 018 BS EN60079-1 Flameproof Enclosure ‘d’
EN 50 019 IEC 60079-7 BS 5501: Pt. 6 BS EN50 019 BS EN60079-7 Increased Safety ’e’
EN 50 020 IEC 60079-11 BS 5501: Pt. 7 BS EN50 020 BS EN60079-11 Intrinsic Safety ‘i’
EN 50 028 IEC 60079-18 BS 5501: Pt. 8 BS EN50 028 BS EN60079-18 Encapsulation ‘m’
EN 50 039 IEC 60079-25 BS 5501: Pt. 9 BS EN50 039 BS EN60079-25 Intrinsic Safety Systems ‘i’
EN 50 021 IEC 60079-15 BS EN50 021 BS EN60079-15 Type of Protection ‘n’
IEC 60079-26 BS EN60079-26
Equipment with Equipment Protection
Level Ga
IEC 60079-27 BS EN60079-27
Fieldbus intrinsically safe concept
(FISCO)
IEC 60079-29-2 BS EN60079-29-2
Gas detector selection, installation,
use and maintenance
IEC 60079-30-1 BS EN60079-30-1
Electrical resistance trace heating –
General & testing requirements
IEC 60079-30-2 BS EN60079-30-2
Electrical resistance trace heating –
Application guide

39. March 2010
11
Other (older) British Standards
The standards listed below are those which preceded the harmonised European standards
listed in the previous table. These standards, with the exception of BS 889, were not entirely
obsolete, and older designs of equipment were still manufactured to these standards and
available on the market prior to 30 June 2003, the date after which implementation of the
ATEX Directives became mandatory. Apparatus manufactured to these standards, where
still in use, must be maintained in accordance with these standards. It is, therefore, important
that reference to the correct standard is made before maintenance is carried out on such
apparatus.
BS 229 Flameproof enclosure of electrical apparatus
BS 889 Flameproof electric fittings
BS 1259
Intrinsically safe electric apparatus and circuits for use in
explosive atmospheres
BS 4683: Part 1 Classification of maximum surface temperature
BS 4683: Part 2 The construction and testing of flameproof enclosures of
electrical apparatus
BS 4683: Part 3 Type of protection ‘N’
BS 4683: Part 4 Type of protection ‘e’
BS 6941 Type of Protection ‘N’
BS 5000: Part 15 Machines with type of protections ‘e’
BS 5000: Part 16 Type ‘N’ electric motors

40. March 2010 ©
12
Standards for Selection, Installation, Inspection and Maintenance
As previously stated, the UK Code of Practice BS 5345, which had for many years provided
recommendations for the selection, installation and maintenance of explosion protected
equipment for use in potentially explosive atmospheres (other than mining applications or
explosives processing and manufacture), listed in the upper table below, was superseded by
the standards listed in the lower table. BS 5345, however, may be referred to for
installations installed in accordance with its requirements. The table below illustrates the
component parts of BS 5345.
UK Code of Practice Type of Protection
BS 5345: Part 1 General Recommendations
BS 5345: Part 2 Classification of Hazardous Areas
BS 5345: Part 3 ‘d’ Flameproof enclosure
BS 5345: Part 4 ‘i’ Intrinsically safe apparatus and systems
BS 5345: Part 5
‘p’ Pressurisation, continuous dilution and
pressurised rooms
BS 5345: Part 6 ‘e’ Increased safety
BS 5345: Part 7 ‘N’ (Non - incendive)
BS 5345: Part 8 ‘s’ Special protection
BS 5345: Part 9
‘o’ Oil immersion
‘q’ Powder filling
The standards which supersede the Code of Practice BS 5345 are illustrated in the table
below. Furthermore, the BS EN standards are identical to the IEC standards shown within
brackets in the table below apart from a few informative annexes.
BS EN / IEC Nos.
Electrical Apparatus for Explosive Gas
Atmospheres:
BS EN60079-10: 2009
(IEC 60079-10-1: 2008)
Part 10: Classification of hazardous areas
BS EN60079-14: 2008
(IEC 60079-14: 2007)
Part 14: Electrical installations in hazardous
areas (other than mines)
BS EN60079-17: 2007
(IEC 60079-17: 2007)
Part 17: Inspection and maintenance of
electrical installations in hazardous
areas (other than mines)
BS EN60079-19: 2007
(IEC 60079-19: 2006)
Part 19: Repair and overhaul for apparatus used
in explosive atmospheres (other than
mines or explosives)
BS EN60079-20-1: 2010
(IEC 60079-20-1: 2010)
Material characteristics for gas and vapour
classification – Test methods and data

41. March 2010 ©
13
Certification body symbols
1) Equipment marked with this symbol may
only be used for underground (mining)
applications in the UK.
2)
Equipment marked with this symbol has
been constructed to the old British Standard
BS229
3) Symbol formerly used by EECS
(BASEEFA) to identify equipment for
surface industry use only.
4)
Equipment marked with this symbol, the
European Ex mark, indicates that the
equipment has been constructed and tested
in accordance with the CENELEC/
EURONORM standards. This mark only
will be used on ATEX compliant equipment.
5)
Symbol formerly used by the German
notified body PTB
6)
The most commonly used symbol of the
American certification authority
Underwriters Laboratories (UL)
7)
The mark used by the Canadian Standards
Association
MEx

42. March 2010 ©
14
Equipment Marking
Prior to the introduction of the ATEX Directives on 1 July 2003, equipment for use in
hazardous areas were marked as illustrated below. Equipment complying with the ATEX
Directives, however, will still be marked in this way but will have additional markings to
indicate that the apparatus conforms with the ATEX Directives. The ATEX markings are
shown on page 18. Equipment approved/certified as providing a method of protection for
use in hazardous locations is required to display the following markings.
a. The symbols Ex, and
b. The type of protection used, e.g. ‘d’, ‘e’, ‘N’, and
c. The gas group, e.g. IIA, IIB or IIC, and
d. The T-rating, e.g. T1, T2 etc.
e. The ambient rating, e.g. -200
C to +400
C (normal range for UK but may not be marked
on equipment.)
Note: For higher ambient ratings the marking may be either Tamb +500
C, or
-200
C < Tamb < +500
C
Examples:
(i) Ex d IIB T3
(ii) EEx d IIC T4
(iii) EEx e II T6
In example (i), equipment marked thus (Ex), as far as Europe was concerned, could only be
used in the UK because it had been constructed to the British Standard BS 4683, which was
not a harmonised European standard. Equipment constructed to this standard, however,
was used in other countries out-with the European Community. Such equipment would also
be marked with the EECS certification authority symbol (fig 3) on the previous page.
Equipment certified in accordance with the IEC Ex scheme will be marked Ex. See page 20
onwards for details of this scheme.
For equipment marked EEx as in example ii. and iii., the additional letter ‘E’ indicates that the
equipment has been constructed to a harmonised European standard. Such equipment
would be marked with the EECS certification authority symbol (fig 3) as well as the European
Community mark (fig 4). Sample labels are shown below, and it should be noted that the
construction standard to which the equipment has been manufactured to, i.e. BS 4683: Part
2, BS 5501: Parts 1 & 5 and EN50 014 & EN50 018 are also given on the labels. For BS
4683 equipment, the IEC equivalent standard, i.e. IEC 79-1 in example (a) below, is usually
included.
(a) (b)

43. March 2010 ©
15
Equipment marking (continued)
The certification labels attached to explosion protected equipment will display markings to
enable their correct selection for use in hazardous areas. For example, equipment
manufactured to the old UK standard BS4683 and the subsequent CENELEC EN500 series
of harmonised standards will be marked Ex and EEx respectively. However, with the
CENELEC and IEC standards becoming technically identical, i.e. the EN60079 standards
are identical to the IEC60079 standards, the marking has reverted to Ex.
The illustration below shows the marking on equipment constructed to the harmonised
standard BS EN50018.
Equipment manufactured to the latest standards, the BS EN60079 series, will be marked as
follows along with the ATEX markings shown on page 17. The main differences are the
removal of the letter ‘E’ compared to the illustration above and the introduction of the EPL
‘Gb’. EPL’s are explained on pages 18 to 21.
Ex d IIC T6 Gb

44. March 2010 ©
16
Certification Numbers
The certification number illustrated below was used by BASEEFA prior to the introduction of
the ATEX directives, but the numbers used by other certification authorities will be different.
Components typically displaying a suffix ‘U’ include Ex e terminals, Ex d stoppers for
flamepoof enclosures, and small volume plastic flameproof switches which have exposed
terminals.
ATEX compliant equipment will have standardised certification numbers which will include
the abbreviation of the notified body’s name followed by the year of certification, the acronym
ATEX, the serial number and either of the suffix’s ‘X’ or ‘U’ where applicable, as shown
below.
BAS 08 ATEX 1234 X

45. March 2010 ©
17
Marking of ATEX Compliant Equipment
The ATEX Directive 94/9/EC, now known as ATEX 95, specifies the new approach for the
certification of explosion protected equipment. An introduction to the ATEX approach has
been considered in pages 4-7 but its wider issues are beyond the scope of this Unit. What is
relevant, however, is the influence the directive will have on the marking of explosion
protected equipment. This will be the most obvious difference to those involved in the
selection, installation and maintenance of explosion protected apparatus.
The marking required by ATEX 95 is illustrated below, which is additional to the marking
requirements already discussed. Also, the hexagonal symbol below will replace the
individual symbols used by the different certification bodies, and the CE mark indicates
compliance with the ATEX Directive.
The Equipment Categories are defined overleaf
0000
CE Mark
Notified body
ID number
EU Explosive
Atmosphere
Symbol

46. March 2010 ©
18
Category (Cat) Definitions
The ATEX Categories were introduced to ‘break’ the traditional link between the protection
types and zones, i.e. the selection of equipment suitable for the zone. This approach
enables, for example, Cat 3 equipment, typically Ex n, to be used in zone 1 if a risk
assessment revealed that the consequences of ignition of a flammable atmosphere was low.
The Categories below, however, show the traditional link with the zones. Conversely, if the
consequences of ignition were greater then a better Category of protection may be required.
Group II Cat 1: Very high level of protection
Equipment with this category of protection may be used where an
explosive atmosphere is present continuously or for long periods, i.e.
Zone 0 or Zone 20.
Cat 2: High level of protection
Equipment with this category of protection may be used where an
explosive atmosphere is likely to occur in normal operation, i.e. Zone
1 or Zone 21.
Cat 3: Normal level of protection
Equipment with this category of protection may be used where an
explosive atmosphere is unlikely to occur or be short duration, i.e.
Zone 2 or Zone 22.
Group I Cat M1: Very high level of protection
Equipment can be operated in the presence of an explosive
atmosphere.
Cat M2: High level of protection
Equipment to be de-energised in the presence of an explosive
atmosphere.
Note: Zones 20, 21 and 22 are the corresponding zones for combustible dusts.
Equipment protection levels (EPL’s)
The introduction of Equipment Protection Levels (EPL’s), which are used internationally,
enables a risk assessment approach to be implemented for the selection of explosion
protected equipment in hazardous areas. This provides an alternative to the traditional
method of selecting equipment to suit the zone, which does not take into consideration the
consequences of an explosion. The table below shows the zones where both ATEX
Categories and EPL’s may be used from a traditional selection approach. Selection of
equipment according to the EPL will in future be according to the EPL’s specified for the
zones in area classification diagrams so that where the consequences of an explosion are
likely to be greater, a higher EPL will be specified. Alternatively, if the consequences of an
explosion are lower, a lesser EPL may be specified.
Zone ATEX Categories EPL’s
0 1 Ga
1 2 Gb
2 3 Gc

47. March 2010 ©
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Equipment protection levels (EPL’s)
Equipment Protection Levels (EPL’s) are available for both gases and vapours and also
combustible dusts as illustrated in the table below. Equipment marked ‘G’ is for use in
flammable gases and vapours, and for use in combustible dusts when marked ‘D’.
Zone
Equipment protection levels
( EPL’s )
0 Ga
1 Ga or Gb
2 Ga, Gb or Gc
20 Da
21 Da or Db
22 Da, Db or Dc
EPL Definitions
Group II gases
Ga Equipment for explosive gas atmospheres, having a ‘very high’ level of protection,
which is not a source of ignition in normal operation, expected faults, or when subject
to rare faults.
Gb Equipment for explosive gas atmospheres, having a ‘high’ level of protection, which
is not a source of ignition in normal operation, or when subject to faults that may be
expected, though not necessarily on a regular basis.
Gc Equipment for explosive gas atmospheres, having an ‘enhanced’ level of protection,
which is not a source of ignition in normal operation and which may have some
additional protection to ensure that it remains inactive as an ignition source in the
case of regular expected occurrences, for example, failure of a lamp.
Group III Dusts
Da Equipment for combustible dust atmospheres, having a ‘very high’ level of protection,
which is not a source of ignition in normal operation, or when subject to rare faults.
Db Equipment for combustible dust atmospheres, having a ‘high’ level of protection,
which is not a source of ignition in normal operation, or when subject to faults that
may be expected, though not necessarily on a regular basis.
Dc Equipment for combustible dust atmospheres, having an ‘enhanced’ level of
protection, which is not a source of ignition in normal operation and which may have
some additional protection to ensure that it remains inactive as an ignition source in
the case of regular expected occurrences.

48. March 2010 ©
20
EPL’s assigned to protection types (gases)
EPL Ga
EPL Protection type Marking
Intrinsic Safety Ex ia
Ga
Encapsulation Ex ma
EPL Gb
EPL Protection type Marking
Flameproof Ex d
Increased Safety Ex e
Intrinsic Safety Ex ib
Encapsulation
Ex m
Exmb
Oil immersion Ex o
Pressurisation
Ex p, Ex px,
Ex py
Powder filled Ex q
Gb
Fieldbus Intrinsic Safety Concept
(FISCO)
**
** No designated marking code at the time of writing
EPL Gc
EPL Protection type Marking
Intrinsic Safety Ex ic
Encapsulation Ex mc
Non-sparking Ex n, Ex nA
Restricted breathing Ex nR
Energy limitation Ex nL
Sparking equipment Ex nC
Pressurisation Ex pz
Gc
Fieldbus non-incendive Concept
(FNICO)
**
** No designated marking code at the time of writing

49. March 2010 ©
21
EPL’s for combustible dusts
EPL Protection type Marking
Intrinsic Safety Ex iD
Encapsulation Ex mD
Da, Db, or Dc
Protection by enclosure tD
Db or Dc Pressurisation pD
Equipment marking
Since there is now technical alignment of the CENELEC and IEC standards, equipment
manufactured in Europe will no longer be marked EEx, and instead will be marked Ex.
Where equipment is certified under the IECEx scheme the IECEx Conformity Mark as
illustrated below will be displayed on the equipment. For the foreseeable future, however,
acceptance in the EU will require the equipment to comply with ATEX and display the
marking illustrated on page 18.
Area for code indicating
the Licensee Number
and the Certification
Body

50. March 2010 ©
22
Example of an EC – Type Examination Certificate

51. March 2010 ©
23

52. March 2010 ©
24

53. March 2010 ©
25
Baseefa Wallchart

54. UNIT 3
FLAMEPROOF
EEx d / Ex d

55. March 2010 ©
2
OBJECTIVES
On completion of this unit, ‘flameproof EEx d / Ex d apparatus, you should
know:
a. The principle of operation and causes of pressure piling.
b. The general constructional requirements including types of joints.
c. The installation requirements with regard to thread engagement of cable entries and
stopping devices, circuit protection, obstruction of flamepaths and additional
weatherproofing methods in accordance with BS EN60079-14.
d. The inspection requirements with regard to BS EN60079-17.

56. March 2010 ©
3
Flameproof EEx d / Ex d
Flameproof is one of the original methods of explosion protection developed for use in the
mining industry. It has a wide range of applications, typically junction boxes, lighting fittings,
electric motors etc.
The letter ‘d’, which symbolises this type of protection, is from the German word ‘druckfeste’
(kapselung), which roughly translated means ‘pressure tight’ (enclosure).
Flameproof apparatus, when properly installed in the intended location, enables components
such as switches, contractors and relays etc. to be safely used in hazardous areas.
Flameproof is the only one of the nine different methods of explosion protection in which an
explosion is permitted. This explosion, however, must be contained by the robustly
constructed flameproof enclosure so that ignition of the surrounding flammable atmosphere
cannot occur.

57. March 2010 ©
4
Standards
BS EN60079-1: 2007 Flameproof enclosures ‘d’
BS EN50 018: 2000 Flameproof enclosures ‘d’
BS 5501: Part 5: 1977 Flameproof enclosures ‘d’
BS 4683: Part 2: 1971
The construction and testing of flameproof enclosures of electrical
apparatus (Ex d)
BS 229: 1957 Flameproof enclosures of electrical apparatus
IEC 60079-1: 2007
Electrical Apparatus for explosive gas atmospheres –
Part 1: Flameproof enclosures ‘d’
BS EN60079-14: 2008
Electrical Apparatus for explosive gas atmospheres: Part 14
Electrical installations in hazardous areas (other than mines)
BS EN60079-17: 2007
Electrical Apparatus for explosive gas atmospheres: Part 17
Inspection and Maintenance of electrical installations in hazardous
areas (other than mines)
BS 5345: Part 3: 1979
(Withdrawn)
Code of Practice for the Selection, Installation and Maintenance of
flameproof apparatus
Definition
The construction standard BS EN60079-1 defines flameproof as:
‘An enclosure in which the parts which can ignite an explosive atmosphere are
placed and which can withstand the pressure developed during an internal explosion
of an explosive mixture, and which prevents the transmission of the explosion to the
explosive atmosphere surrounding the enclosure’
EPL: Gb
Zone of Use: 1 & 2
Ambient Conditions
Flameproof enclosures are normally designed for use in ambient temperatures in the range
- 20°C to +40°C unless otherwise marked.

58. March 2010 ©
5
Principle of Operation
Flameproof enclosures are not gas tight and a gas or vapour will enter the enclosure where,
for example, joints or cable entries exist. Since these enclosures are designed to contain
components which are an ignition source, ignition of the gas or vapour may occur, and the
resulting explosion pressure can reach a peak value of around 150 p.s.i.
The enclosure must, therefore, be strong enough to contain this explosion pressure, and the
gaps at the joints and threads of cable entries must be long and narrow to cool the
flames/hot gases before they reach and cause ignition of a flammable atmosphere which
may exist out with the enclosure.
Typical materials used for the construction of flameproof apparatus include cast iron,
aluminium alloys, and where corrosion resistance is required, gun metal bronze, phosphor
bronze and stainless steel may be used. Plastic materials are also used but the free internal
volume must not exceed 10cm3
. The latest standard specifies that for flanged joints ‘THERE
SHALL BE NO INTENTIONAL GAP AT THE JOINTS’ and infers the same for other joint
types. The average roughness Ra of the flamepath surfaces must not exceed 6.3μm.
Flammable MIxture
Arcs, Sparks
Hot Surfaces
Contactors, Relays
etc
Gap

59. March 2010 ©
6
Gap Dimensions
It is not necessary for a gap to exist at the flamepaths of a flameproof enclosure. The latest
standard BS EN60079-1 states there shall be no intentional gap between the surfaces of
enclosures with flanged joints.
This said, however, a gap will be necessary at the cylindrical joints of rotating machines, i.e.
where the rotor shaft exits the end-shield and also where push-button spindles pass through
flameproof enclosures to operate the internal switches.
Flameproof enclosures with spigot or screwed joints, however, require some clearance to
enable covers to be removed relatively easily for installation and maintenance purposes.
These clearance/gap dimensions, and also those for rotating machines and push-button
stations, must be within the dimensions specified in the tables for gap dimensions in the
construction standard for flameproof equipment, e.g. BS EN60079-1.
Factors which influence the dimension of the gap are:
a. The width of the joint
b. The gas group
c. The internal volume of the enclosure
d. The type of joint

60. March 2010 ©
7
Flamepath Joints
The diagrams below illustrate examples of three joint types specified in the British standard
BS EN60079-1 for use in flameproof apparatus. In a flanged joint, the machined surface on
the cover makes face-to-face contact with the corresponding surface on the base to give a
gap dimension normally less than that specified in the tables of gap dimensions in the
standard when the cover is properly bolted down. This type of joint will be used at the covers
of, for example, junction boxes.
Spigot joints will be used at junction box covers and motor enshields.
Threaded joints are used for cover joints, cable gland and conduit entries. An adequate
flamepath length is normally achieved with a thread engagement of five full threads.
In contrast to BS EN50019, the most recent standard, BS EN60079-1 permits the use of
flanged joints when a IIC gas such as acetylene is the hazard only if the gap is ≤ 0.04mm,
has a length L ≥ 9.5mm and the free internal volume does not exceed 500 cm3
.
a) Flanged joint
b) Spigot joint
c) Screwed joint
Interior
Interior
Interior

61. March 2010 ©
8
Flamepath Joints Types (Rotating Machines)
(d) cylindrical (shaft gland) joint
(d) labyrinth joint for shafts

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9
Flamepath Joints (other examples)
Flamepaths other than those at cover joints are also necessary where, for example, an
actuator spindle passes through the wall of an enclosure, or where a cable gland or conduit
enters an enclosure. Examples are shown below.
Push-button spindle
Cable (gland) entry

63. March 2010 ©
10
Entry by Cable Gland or Conduit
The thread engagement requirements for cable and conduit entries are specified in the
standard BS EN60079-1 and apply to the three sub-groups IIA, IIB and IIC.
Only threaded entries are permitted for all cable glands or conduits entering flameproof
enclosures – clearance entries are not permitted.
Volume
≤ 100 cm3
> 100 cm3
Thread
Engagement
Axial
Length
Thread
Engagement
Axial
Length
> 5 Full Threads > 5mm > 5 Full Threads > 8 mm
As already stated the above requirements for thread engagement are specified in the latest
standard BS EN60079-1: 2007, but the previous standard BS EN50018: 2000 required at
least 6 full threads engagement in order to make sure that 5 full threads were actually
engaged.
Note: Flameproof equipment manufactured to the old British standard BS229 may have
different non-metric thread forms at cable gland entries. This difficulty can be
overcome by the use of certified Ex d adaptors which have compatible thread forms
to suit both the entry in the enclosure and the cable gland.

64. March 2010 ©
11
Unused Cable or Conduit Entries
It is important that unused cable/conduit entries in flameproof enclosures are closed using
appropriate stoppers, as specified in the standards, or those supplied by the manufacturer.
These must be ‘component certified’ metal stoppers – plastic stoppers are unacceptable –
which are fully engaged by 5 full threads. The construction standard specifies suitable types,
examples of which are illustrated below.
Stoppers of the type illustrated by example ‘C’ in the above diagram are available with
certification markings on either the plain side or the same side as the hexagon recess.
Ideally, stoppers of this type should be fitted with the plain side facing the exterior to make
unauthorised removal more difficult, but may be fitted with the hexagon recess facing the
exterior. Whichever way round they are fitted the certification markings must be visible for
ease of identification during ‘Visual’ inspection programmes. Also the thread engagement
requirements must be met. Stoppers of this type are tightened using an Allen Key.
Split pin
A
B
C
D
Interior
Screwdriver slot
Special fastener
Hexagon recess
Hexagon head
Shearable neck
Exterior

65. March 2010
12
Flamepath Gap Dimensions – BS EN60079-1, Table 1
Maximum gap
mm
For a volume
cm3
V ≤ 100
For a volume
cm3
100 < V ≤ 500
For a volume
cm3
500 < v ≤ 2 000
For a volume
cm3
V > 2 000
Type of Joint
Minimum
width of joint
L
mm
I IIA IIB I IIA IIB I IIA IIB I IIA IIB
6 0.30 0.30 0.20 - - - - - - - - -
9.5 0.35 0.30 0.20 0.35 0.30 0.20 - - - - - -
12.5 0.40 0.30 0.20 0.40 0.30 0.20 0.40 0.30 0.20 0.40 0.20 0.15
Flanged, cylindrical or
spigot joints
25 0.50 0.40 0.20 0.50 0.40 0.20 0.50 0.40 0.20 0.50 0.40 0.20
6 0.30 0.30 0.20 - - - - - - - - -
9.5 0.35 0.30 0.20 0.35 0.30 0.20 - - - - - -
12.5 0.40 0.35 0.25 0.40 0.30 0.20 0.40 0.30 0.20 0.40 0.20 -
25 0.50 0.40 0.30 0.50 0.40 0.25 0.50 0.490 0.25 0.50 0.40 0.20
Sleeve
bearings
40 0.60 0.50 0.40 0.60 0.50 0.30 0.60 0.50 0.30 0.60 0.50 0.25
6 0.45 0.45 0.30 - - - - - - - - -
9.5 0.50 0.45 0.35 0.50 0.40 0.25 - - - - - -
12.5 0.60 0.50 0.40 0.60 0.45 0.30 0.60 0.45 0.30 0.60 0.30 0.20
25 0.75 0.60 0.45 0.75 0.60 0.40 0.75 0.60 0.40 0.75 0.60 0.30
Cylindrical
joints for
shaft
glands of
rotating
electrical
machines
with:
Rolling-
element
bearings
40 0.80 0.75 0.60 0.80 0.75 0.45 0.80 0.75 0.45 0.80 0.75 0.40
NOTE: Constructional values rounded according to ISO 31-0 should be taken when determining the maximum gap.

66. March 2010 ©
13
Flamepath Gap Dimensions – BS EN60079-1, Table 2
Maximum gap
mm
Type of Joint
Minimum
width of joint
L
mm
For a volume
cm3
V ≤ 100
For a volume
cm3
100 < V ≤ 500
For a volume
cm3
500 < v ≤ 2 000
For a volume
cm3
V > 2 000
5 0.10 - - -
9.5 0.10 0.10 - -
15.8 0.10 0.10 0.4 -
Flanged joints
25 0.10 0.10 0.4 0.4
12.5 0.15 0.15 0.15 -
25 0.18b
0.18b
0.18b
0.18b
40 0.20c
0.20c
0.20c
0.20c
Spigot
joints
(Figure 2a)
c ≤ 6mm
d ≤ 0.5L
L = c + d
f ≤ 1mm
6 0.10 - - -
9.5 0.10 0.10 - -
12.5 0.15 0.15 0.15 -
25 0.l5 0.15 0.15 0.15
Cylindrical joints
Spigot joints
(Figure 2b)
40 0.20 0.20 0.20 0.20
6 0.15 - - -
9.5 0.15 0.15 - -
12.5 0.25 0.25 0.25 -
25 0.25 0.25 0.25 0.25
Cylindrical joints for
shaft glands of rotating
electrical machines with
rolling element bearings
40 0.30 0.30 0.30 0.30
a
Flanged joints are permitted for explosive mixtures of acetylene and air only in accordance with 5.2.7
b
Maximum gap of cylindrical part increased to 0.20 mm if f < 0.5 mm
c
Maximum gap of cylindrical part increased to 0.25 mm if f < 0.5 mm
NOTE: The constructional values rounded according to ISO 21 –D should be taken when determining the maximum
gap

67. March 2010 ©
14
Pressure Piling
If a flammable mixture us compressed prior to ignition, the resulting explosion will be
considerably higher than if the same mixture was ignited at normal atmospheric pressure.
Pressure piling can materialise as a result of sub-division of the interior of a flameproof
enclosure, which prevents the natural development of an explosion.
An explosion at one side of an obstacle pre-compresses the flammable mixture at the other
side, resulting in a secondary explosion that can reach an explosion pressure around three
times that of the first or normal explosion pressure.
Manufacturers, guided by relevant construction standards, must ensure that, in any cross-
section within an enclosure, there is adequate free space (typically 20 – 25% of the total
cross-section) around any potential obstruction, which may be a large component or a
number of components. This will ensure that pressure piling is kept under control.

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Pressure Piling in Flameproof Motors
In rotating electrical machines, sections with appreciable free volume normally exist at each
end within the main frame of the machine. These sections are linked by the airgap between
the stator and rotor cores. In the illustration of a flameproof machine in the diagram above,
an explosion in section ‘1’ must be prevented from migrating to, and causing ignition of the
flammable mixture in section ‘2’ which will have been pressurised by the initial explosion.
The airgap, therefore, also acts as a flamepath.
Section 1 Section 2

69. March 2010 ©
16
Obstruction of Flamepaths
The UK Code of Practise BS 5345 Part 3 recommended that obstruction of flameproof
enclosures, particularly those with flanged joints, should be avoided. This recommendation is
also given in BS EN60079-14: Electrical installation in hazardous areas (other then mines).
A solid obstruction such as a wall, steelwork, conduit, brackets, weather guards or other
electrical apparatus etc., in close proximity to the opening at the joint can, in the event of an
internal explosion, reduce the efficiency of the flamepath to the extent that ignition of the
external gas or vapour could occur.
The minimum distance between the flamepath opening and an obstruction, as specified in
BS EN60079-14 (and BS 5345: Part 3) are:
Group Distance
IIA 10 mm
IIB 30 mm
IIC 40 mm

70. March 2010 ©
17
Ingress Protection Methods
The diagrams below illustrate the location of gaskets or rubber ‘O’ rings for ensuring a high
level of ingress protection. The gaskets etc. must be an integral part of the original design,
i.e. they cannot be added at a later date to an enclosure manufactured without gaskets.
Typical examples for outdoor use are illustrated below.

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18
Weatherproofing / protection of flamepaths
Flameproof equipment must have a level of ingress protection to suit the environmental
conditions of the location in which the equipment is installed and hence equipment should
have, as part of their certified design, seals or gaskets to prevent the ingress of water and/or
dust. Flamepaths must also be protected in accordance with manufacturer’s instructions
and the requirements of BS EN60079-14 which will involve additional measures as detailed
below. This is particularly important where environmental conditions are extreme.
Protection of flamepaths
The following measures are not permissible:
a) painting of flamepath surfaces - enclosures may be painted after assembly;
b) fitting of unauthorised seals/gaskets – replacement seals/gaskets may only be
fitted where the originals, which are part of the certified design, are degraded or
damaged.
Permitted measures:
c) application of non-setting grease or anti-corrosive agents having no evaporating
solvents;
d) non-hardening grease-bearing (Denso) tape – see application/limitations of use
below.
Note: The use of non-setting grease on the machined surfaces of flamepaths has
two advantages since, in addition to providing an additional level of ingress
protection; it also inhibits the formation of rust on these surfaces.
Silicone based greases require careful consideration in order to avoid
possible damage to the elements of gas detectors.
For Flameproof equipment, the limitations for the use of non-hardening tape as specified in
BS EN60079-14 are as follows:
a. Non-hardening tape maybe applied around the flamepaths of apparatus with flanged
joints allocated to group IIA applying one layer only with a short overlap.
b. For group IIB apparatus, one layer with a short overlap may be applied around the
flamepaths of apparatus with flanged joints, but only if the gap is less than 0.1mm
regardless of the joint width.
Note: The Code of Practise BS 5345: Part 3 (withdrawn but a relevant source of
information for older installations) recommended that expert advice be sought
when considering the use of non-hardening tape on group IIB or IIC
equipment installed in locations containing group IIB gases or vapours.
c. Non-hardening tape must not be used on equipment marked IIC (or IIB + H2)
installed in locations containing group IIC gases or vapours.

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19
Direct / Indirect Entry
The selection of cable glands for flameproof apparatus is influenced by several factors, one
of which is the method of entry into the apparatus. There are two entry methods, namely
direct and indirect, examples of which are shown below.
Direct entry comprises a single flameproof chamber within which components such as
switches, relays or contactors may be installed. Flameproof apparatus with indirect entry
has two separate chambers, one of which contains only terminals for connection of the
conductors of incoming cables or conduit. Connection to the arcing components in the
second compartment is made via these flameproof terminals which pass through the
flameproof interface between the two compartments.
Direct entry Indirect entry
EEx d
Enclosure
EEx d
Enclosure
Flamepaths
Bushings
EEx d cable
glands

73. March 2010 ©
20
Electrical Protection
Flameproof enclosures are tested for their ability to withstand internal gas explosions only;
they are not capable of withstanding the energy which may be released as a result of an
internal short-circuit. In order to avoid invalidation of the certification, it is important that
properly rated/calibrated electrical protection, e.g. fuses and/or circuit breakers, are utilised.
Cover bolt (fastener) requirements
Should the requirement arise where it is necessary to replace the cover bolts etc of a
flameproof enclosure, only steel bolts having the correct length, type of thread, type of head
and tensile strength should be used.
Regarding cover bolt tightness the torque values specified by the manufacturer should be
observed. In the absence of manufacturer’s torque values the minimum requirement is
spanner tight, however, care must be exercised to avoid under-tightening as this can allow
an increase in the flamepath gap. Also, over-tightening of the bolts can result in them
stretching and hence reducing their strength with the consequence that an internal explosion
may not be contained within the enclosure.
It is important that all cover bolts are in place and correctly tightened prior to energising a
flameproof enclosure.

74. March 2010 ©
21
Modification of Flameproof Enclosures
Flameproof enclosures are normally supplied complete with all internal components fitted
and certified as a single entity by a recognised test authority. The testing procedure will take
into consideration the free internal volume after all the components have been fitted, the
temperature rise (determined by the maximum power dissipation), creepage and
clearance distances, and the rise in pressure as a result of an internal explosion using a
gas/air mixture in its most explosive proportions.
The certification, therefore, “seals” the design of the apparatus so that any unauthorised
modifications will effectively invalidate the approval/certification. Modifications will
modify the original test results recorded by the test/certification authority and, consequently,
the following points should be observed.
a. Replacement components should always be exactly the same as the original
specified components in order to avoid infringement of the certification. For example,
a component larger or smaller than the original will affect the internal geometry of the
enclosure. Pressure piling is a possibility if a larger component is fitted, and
increased volume will result if a smaller component is fitted.
Note: Illustrations are for demonstration only and must not be carried out
Original
arrangement
Replacement of ‘A’
with a larger item
Replacement of ‘A’
with a smaller item

75. March 2010 ©
22
b. Adding components is also forbidden because of the possibility of increased
explosion pressure as a result of pressure piling.
Addition of component ‘C’
c. The removal of components should also be avoided since an increase in the free
internal volume will result. The original test results, prior to certification, would be
compromised as a result of a modification such as this.
Removal of component ‘B’

76. March 2010 ©
23
Note: Illustrations are for demonstration only and must not be carried out
d. Drilling and tapping of cable gland/conduit entries should only be carried out
by the manufacturer of the enclosure, or his approved agent. The threads of the
entries are required to be compatible with those of cable glands or conduit in terms of
type of thread, thread pitch and clearance tolerance since flamepaths exist at these
points.
Correct alignment of the threaded entry is also important since the flamepath
length at one side will be reduced if the cable gland or conduit is not fitted
perpendicular to the face of the enclosure.
The strength of a flameproof enclosure may be impaired if the number and size
of entries exceeds that permitted in the original design certified by the test authority.
Compliance with the original design is paramount with regard to number, size and
location of entries to ensure the enclosure will contain an internal explosion.
e. Gaskets can only be replaced; they must not be added retrospectively if not included
as part of the original design.
The use of unauthorised sealants should also be avoided when it is required to
maintain or improve the IP rating.

77. March 2010 ©
24
BS EN 60079-17 Table 1: Inspection Schedule for Ex’d’, Ex’e’, and Ex ‘n’
Installations (D = Detailed, C = Close, V = Visual)
Check that: Ex’d’ Ex’e’ Ex’n’
Grade of Inspection
D C V D C V D C V
A APPARATUS
1 Apparatus is appropriate to area classification * * * * * * * * *
2 Apparatus group is correct * * * * * *
3 Apparatus temperature class is correct * * * * * *
4 Apparatus circuit identification is correct * * *
5 Apparatus circuit identification is available * * * * * * * * *
6 Enclosure, glass parts and glass-to-metal sealing gaskets
and/or compounds are satisfactory
* * * * * * * * *
7 There are no unauthorised modifications * * *
8 There are no visible unauthorised modifications * * * * * *
9 Bolts, cable entry devices (direct and indirect) and blanking
elements are of the correct type and are complete and tight
- Physical check
- Visual check
* *
*
* *
*
* *
*
10 Flange faces are clean and undamaged and gaskets, if any,
are satisfactory
*
11 Flange gap dimensions are within maximal permitted values * *
12 Lamp rating, type and position are correct * * *
13 Electrical connections are tight * *
14 Condition of enclosure gaskets is satisfactory * *
15 Enclosed-break and hermetically sealed devices are undamaged *
16 Restricted breathing enclosure is satisfactory *
17 Motor fans have sufficient clearance to enclosure and/or covers * * *
18 Breathing and draining devices are satisfactory * * * * * *
B INSTALLATION
1 Type of cable is appropriate * * *
2 There is no obvious damage to cables * * * * * * * * *
3 Sealing of trunking, ducts, pipes and/or conduits is satisfactory * * * * * * * * *
4 Stopping boxes and cable boxes are correctly filled *
5 Integrity of conduit system and interface with mixed system is
maintained
* * *
6 Earthing connections, including any supplementary earthing
bonding connections are satisfactory (e.g. connections are tight
and conductors are of sufficient cross section)
- Physical check
- Visual check
*
* *
*
* *
*
* *
7 Fault loop impedance (TN system) or earthing resistance
(IT systems is satisfactory)
* * *
8 Insulation resistance is satisfactory * * *
9 Automatic electrical protective devices operate within permitted
limits
* * *
10 Automatic electrical protective devices are set correctly (auto reset
not possible)
* * *
11 Special conditions of use (if applicable) are complied with * * *
12 Cables not in use are correctly terminated * * *
13 Obstructions adjacent to flameproof flanged joints are in
accordance with IEC 60079-14
* * *
14 Variable voltage/frequency installation in accordance with
documentation
* * * * * *
C ENVIRONMENT
1 Apparatus is adequately protected against corrosion, weather,
vibration and other adverse factors
* * * * * * * * *
2 No undue accumulation of dust and dirt * * * * * * * * *
3 Electrical insulation is clean and dry * *

78. March 2010 ©
25
Note 1
Apparatus using a combination of both ‘d’ and ‘e’ types of protection will require reference to
both columns during inspection.
Note 2
The use of electrical test equipment, in accordance with items B7 and B8, should only be
undertaken after appropriate steps are taken to ensure the surrounding area is free of a
flammable gas or vapour

79. Unit 4:
Increased Safety
EEx e / Ex e

80. March 2010 ©
2
Objectives:
On completion of this unit, ‘Increased Safety EEx e / Ex e Apparatus’, you
should know:
a. The principle of operation.
b. The principle design features.
c. The methods for estimating terminal content of enclosures.
d. The installation requirements according to BS EN 60079-14.
e. The inspection requirements according to BS EN 60079-17.

81. March 2010 ©
3
Increased Safety EEx e / Ex e
The explosion protection concept Increased Safety was invented in Germany where it has
been widely used for many years. It is has become popular in the UK mainly because it has
a number of advantages for certain applications over the traditional flameproof method of
explosion protection. America has traditionally relied on the use of explosion-proof
enclosures in hazardous locations, and the prospect of using an Increased Safety enclosure,
which is not designed to withstand an internal explosion, as an alternative, has probably
been viewed with a little trepidation.
This method of protection has a good safety record and comparable with the other methods
of protection. The letter ‘e’ which symbolises this method of protection is taken from the
German phrase ‘Erhohte Sicherheit’, which roughly translated means ‘increased security’.
Typical applications are induction motors, lighting fittings and junction boxes.
Standards
BS EN60079-7: 2007
Electrical apparatus for explosive gas atmospheres.
Increased Safety ‘e’
BS EN50 019: 2000 Increased Safety enclosure ‘e’
BS 5501: Part 6: 1977 Increased Safety enclosure ‘e’
BS 4683: Part 4: 1973 Type of protection ‘e’
IEC 60079-7: 2001-11
Construction and Test of Electrical Apparatus, Type of
Protection “e”
BS EN60079-14: 2008
Electrical apparatus for explosive gas atmospheres: Part 14
Electrical installations in hazardous areas (other than
mines)
BS EN60079-17: 2007
Electrical apparatus for explosive gas atmospheres: Part 17
Inspection and maintenance of electrical installations in
hazardous areas (other than mines)
BS 5345: Part 6: 1978
(Withdrawn)
Code of Practice for the Selection, Installation and
Maintenance of Increased Safety apparatus.

82. March 2010 ©
4
Definition
‘A protection method in which increased measures are taken to prevent the possibility of
excessive HEAT, ARCS or SPARKS occurring on internal or external parts of the apparatus
in normal operation’.
EPL: Gb
Zones of use: 1 & 2
Ambient Temperatures
Increased Safety enclosures are normally designed for use in ambient temperatures in the
range -20 °C to +40 °C unless otherwise marked.
Increased Safety light fittings
Increased safety light fittings usually have other methods of protection, e.g powder filled Ex q
protected capacitors and flameproof protected lampholders, and hence the marking on the
certification label will be Ex edq. The following, however, note is important.
Note: Lamps for Ex e, luminaries, which have mono-pin, bi-pin or screw connections where
the caps are made from non-conductive material with a conductive coating, are not
permitted unless tested with the equipment.

83. March 2010 ©
5
Principle
The safe operation of Increased Safety apparatus is dependent on the prevention of any
source of ignition, i.e. excessive surface temperatures, arcs or sparks, which might
otherwise be produced by internal or external parts of the apparatus. Special design features
are, therefore, incorporated in the apparatus by the manufacturer and are as follows.
1. Mechanically strong enclosure resistant to impact - tested to 4 or 7 joules impact
energy depending on application.
2. Ingress protection against solid objects and water - at least IP 54.
3. Terminals manufactured from high quality insulation material.
4. Specified creepage and clearances incorporated in the design of terminals.
5. Terminal locking devices to ensure conductors remain secure in service.
6. Certified de-rating of terminals.
7. Terminal population of enclosure limited by circuit design.
8. Close excess current circuit protection.
Increased Safety Terminals
The terminals installed in an Increased Safety enclosure must be ‘component certified’
terminals. They will be manufactured from good quality materials such as Melamine,
Polyamide and, for special applications, Ceramic. These materials, which have good thermal
stability, have been subjected to a ‘Comparative Tracking Index (CTI)’ test to determine their
resistance to tracking.
The following definitions are relevant:
Clearance distance: The shortest distance through air between two conductors.
Creepage distance: The shortest distance between two conductors along the
surface of an insulator.
Tracking: The leakage current which passes across the
contaminated surface of an insulator between live
terminals, or live terminals and earth.
Comparative Tracking Index: The numerical value of maximum voltage, in volts at which
an insulation material withstands e.g., 100 drops of
electrolyte (usually ammonium chloride solution in distilled
water) without tracking.

84. March 2010 ©
6
Increased Safety Terminals
Test Criteria - Comparative Tracking Index (CTI)
The Comparative Tracking Index (CTI) test criteria are given in the table below. Four grades
of materials ‘a’, ‘b’, ‘c’ and ‘d’ are considered, the highest quality material being ‘a’ which is
subjected to the greatest number of drops of electrolyte falling between the test electrodes,
and the highest voltage applied across the electrodes from the variable voltage source. Each
material must withstand the specified number of drops of the electrolyte at the specified
voltage for it to be acceptable.
Thus, the combination of high quality materials and good design, which incorporates
specified creepage and clearance distances, ensures that Increased Safety terminals have a
greater resistance to tracking to prevent arcing or sparking.
Grade of Material C.T.I. Test Voltage Number of Drops
a - 600 > 100
b 500 500 > 50
c 380 380 > 50
d 175 175 > 50
The International Standard IEC 60112 groups insulating materials according to their tracking
resistance as illustrated in the following table.
Material group Comparative tracking index ( CTI )
I 600 < CTI
II 400 < CTI < 600
IIIa 175 < CTI < 400
Creepage and Clearance Distances

85. March 2010 ©
7
Increased Safety Terminals
Creepage and Clearance Distances
Terminals
Partition
Screw heads
Clearance
29 75
Creepage
path
30 6
Clearance & creepage
path 26.4mm
Clearance and creepage paths
to extend to adjacent clamping
screw
Clearance and
creepage paths
14.0mm
Creepage path runs
between locating rivet and
assembly rail 27.8 mm
Clearance path extends
from end of bolt to
assembly rail 20.5mm

86. March 2010 ©
8
Increased Safety Terminals
Creepage Distances Relative to Voltage and Grade of Insulation
The following table from BS EN60079-7 shows the creepage distances relative to the grade
of material and applied voltage.
Minimum creepage distance
(mm)
Material group
Voltage (see note 1)
U r.m.s a.c. or d.c.
(V)
I II IIIa
Minimum clearance
(mm)
10 ( see note 3 ) 1.6 1.6 1.6 1.6
12.5 1.6 1.6 1.6 1.6
16 1.6 1.6 1.6 1.6
20 1.6 1.6 1.6 1.6
25 1.7 1.7 1.7 1.7
32 1.8 1.8 1.8 1.8
40 1.9 2.4 3.0 1.9
50 2.1 2.6 3.4 2.1
63 2.1 2.6 3.4 2.1
80 2.2 2.8 3.6 2.2
100 2.4 3.0 3.8 2.4
125 2.5 3.2 4.0 2.5
160 3.2 4.0 5 3.2
200 4.0 5.0 6.3 4.0
250 5.0 6.3 8.0 5.0
320 6.3 8.0 10.0 6.0
400 8.0 10.0 12.5 6.0
500 10.0 12.5 16.0 8.0
630 12.0 16.0 20.0 10.0
800 16.0 20.0 25.0 12.0
1000 20.0 25.0 32.0 14.0
1250 22.0 26.0 32.0 18.0
1600 23.0 27.0 32.0 20.0
2000 25.0 28.0 32.0 23.0
2500 32.0 36.0 40.0 29.0
3200 40.0 45.0 50.0 36.0
4000 50.0 56.0 63.0 44.0
5000 63.0 71.0 80.0 50.0
6300 80.0 90.0 100.0 60
8000 100.0 110.0 125.0 80.0
10000 125.0 140.0 160.0 100.0
Note 1: Voltages shown are derived from IEC 60664-1. The working voltage may exceed
the voltages given in the table by 10%. This is based on the rationalisation of
supply voltages given in table 3b of IEC 60664-1
Note 2: The creepage distance and clearance values shown are based on a maximum
supply voltage tolerance of +10%.
Note 3: At 10 V and below, the value of CTI is not relevant and materials not meeting the
requirement for material group IIIa may be acceptable.

87. March 2010 ©
9
Increased Safety Terminal Types and Ratings
The terminals are de-rated so that the maximum current for Increased Safety applications is
nearly half that for standard industrial applications as illustrated in the following table for
enclosures manufactured to BS 5501 Part 6. This de-rating, along with other considerations,
ensures that internal and external surface temperatures are kept within prescribed limits.
The table below also shows the maximum conductor size for each terminal type.
Terminal
Type
Conductor
Size
Increased Safety
Maximum Current
(amps)
Industrial Maximum
Current
(amps)
SAK 2.5 2.5 15 27
SAK 4 4 21 36
SAK 6 6 26 47
SAK 10 10 37 65
SAK 16 16 47 87
SAK 35 35 75 145
SAK 70 70 114 220
Increased Safety Terminals
Terminal Locking Device
It is essential that conductors are securely connected in the terminals to prevent sparks
occurring as a result of loose connections. The illustration below shows how this is achieved.

88. March 2010 ©
10
Estimation of Terminal Population
The number of terminals which can be installed in a given size of enclosure is limited.
Several methods have been developed by manufacturers for this purpose. These are:
Enclosure Factor: A method used in apparatus manufactured to BS 4683 Part 4
in which the terminal content is assessed by dividing the
‘enclosure factor’ by the certified current rating of a given
terminal.
Load Limit: Similar to ‘enclosure factor’ but used only on apparatus
manufactured to BS 5501 Part 6.
Kelvin Rating: Normally used for high current applications and apparatus
manufactured to BS 4683 Part 4 and BS 5501 Part 6. In this
method, enclosures and terminals are assigned a temperature
rating. Enclosures will normally be limited to a temperature rise
of 40K for a T6 temperature rating, but the temperature for the
terminals will be dependent on their type, rated current, size of
associated conductor, and the size of enclosure in which they
are installed. This involves the use of tables which are
provided by the manufacturer. Once the terminal ‘K’ rating has
been established, it is divided into the ‘K’ rating for the
enclosure to give the number of terminals of one type which
may be installed.
Max Dissipated Power: This is a method which will replace the current ‘load limit’
method and applies to apparatus manufactured to BS 5501
Part 6 and BS EN50019. In this method, enclosures are
assigned a ‘watts dissipation’ rating, but the rating of the
terminals is determined by use of a unique table (provided by
the manufacturer) for the enclosure. This table provides the
‘watts dissipation’ of the terminal through consideration of
conductor size and load current. The terminal content is
determined by dividing the ‘watts dissipation’ value for the
terminal into that for the enclosure.
Another method used by manufacturers is to specify the maximum current per pole and
also the maximum current per mm2
.
Examples of labels with the above information are shown overleaf.

89. March 2010 ©
11
Examples of labels
(a) Enclosure factor (b) Load limit
(c) Enclosure factor (d) Maximum dissipated power
(e) Maximum current per pole and per sq. mm
Klippon
TYPE TB11EX S/No. 9364
EEx e II T6
BASEEFA CERT. No. EX84B1333X
BS5501 Pt.6 (EN50 019)
LOAD LIMIT 600A
Klippon
ENCLOSURE TYPE TB11
BS 4683 Pt.4 Ex e II T6
BASEEFA No. Ex 77152/B
MAX. CIRCUIT VOLTAGE 726
ENCLOSURE FACTOR 416
SERIAL NUMBER 1334
Klippon
TYPE TB12 S/No.867594
EEx e II T6
BASEEFA CERT. No. Ex84B3290X
BS5501 Pt.6 (EN50 019)
LOAD LIMIT 40K
Klippon
TYPE STB2 EEx II T6 S/No. T499
BASEEFA CERT. No. 86B 2138X
BS5501 Pt.6 (EN50 019)
MAX. DISSIPATED POWER 7 WATTS
HAWKE CABLE GLANDS Ltd.
BS5501: Pt.6: 1977
(EN50 019) EEx e II T6
BASEEFA No. Ex 8142BX
TYPE REF PL639 SERIAL No. 9960/89
PHASE-TO-PHASE 726
MAX VOLTS
PHASE-TO-EARTH
MAX.CURRENT DENSITY
AMPS PER SQ. MM 4
MAX AMPS PER POLE 10

90. March 2010 ©
12
Sample Calculation using ‘Load limit’
The ‘Load Limit’ will be specified on the certification label of an Increased Safety enclosure,
as illustrated below, and represents the sum of all the circuit currents the enclosure is able to
carry without exceeding the temperature classification.
Thus, the number of terminals of one type which can be installed in a given enclosure is
simply the ‘Load Limit’ divided by the Increased Safety current rating of the terminal type to
be used, as demonstrated in the following calculation.
TYPE TB11 S/No D779
EEx e II T6
BASEEFA CERT No Ex 84B3299X
BS 5501 Pt 6 (EN50 019)
LOAD LIMIT 600
Enclosure Load Limit = 600
SAK 2.5 Ex e terminal rating = 15 A
Number of SAK 2.5 terminals =
rating
terminal
2.5
SAK
Limit
Load
=
15
600
= 40 SAK 2.5 terminals
Where the circuit current is below the certified current rating of the terminals, it may be
possible to base the terminal population on the circuit current provided it will not exceed the
assigned value. Assuming a circuit current of 10 A, the calculation is as follows.
Enclosure Load Limit = 600
Circuit current = 10 A
Number of SAK 2.5 terminals =
current
Circuit
Limit
Load
=
10
600
= 60 SAK 2.5 terminals

91. March 2010 ©
13
Terminal Assemblies
Component Approved Terminal Group
1. Mounting rail;
2. Terminals - certified components;
3. End plate;
4. End bracket;
5. Distance sleeve;
6. Partition;
7. Copper cross-connection;
8. Zinc plated screw;
9. Copper cross-connection;
10. Copper cross-connection.
Insulated comb
alternative for
linking terminals

92. March 2010 ©
14
Terminal Assemblies
Cable gland selection
The use of uncertified equipment in hazardous areas was an option available, in IEC 60079-
14: 2003, to installers via self-assessment of equipment intended for use in zone 2. This
option also applied to cable glands for use with Ex e and Ex n equipment providing the
glands maintained the IP rating and withstood the impact test requirements for the
equipment protection types.
The introduction of the latest standards, however, has effectively removed this option by
virtue of the requirement for revised ‘seal aging’ tests involving repeated heating and cooling
cycles, which is now a requirement for all cable glands as detailed in IEC 60079-0 The
latest issue of IEC 60079-14: 2007 now requires all cable glands to be certified or approved
by the manufacturer.

93. March 2010 ©
15
Installation of cable glands & accessories
The illustrations below show the minimum requirements for the installation of cable glands
and accessories, i.e. earth tags, IP washers, serrated washers and locknuts, depending on
whether the enclosure is metal, or plastic with or without an internal continuity plate and the
entries are threaded, or unthreaded.
Note: Minimum requirements infer maintaining IP54 which a threaded entry 6mm in
length will achieve.
Metal enclosure
without
removable gland
plate and has
unthreaded
entry
Metal enclosure
with threaded
entry 6mm long
Plastic enclosure
with clearance
entry and no
internal continuity
plate Metal enclosure
with removable
gland plate and
clearance entries
Enclosure wall
or gland plate
Enclosure wall
or gland plate

94. March 2010 ©
16
Installation, Inspection and Maintenance
It is essential that Increased Safety enclosures are installed and maintained in accordance
with the relevant Standards and Codes of Practice in order to comply with the Certification.
The following list specifies the main points.
1. Enclosure content should not be modified without consulting the
manufacturer.
2. Only components specifically approved should be fitted in the enclosure.
3. All terminal screws, used and unused, should be tightened down.
4. Conductor insulation should extend to within 1 mm from the metal throat of the
terminal.
5. Partitions should be fitted at either side of terminal linking assemblies.
6. Only one conductor should be fitted to each terminal side (unless more than one is
permitted in the equipment certificate).
7. An additional single conductor, min 1.0 mm2
, may be connected within the same
terminal way when an insulated comb is used.
8. Only the conductors from each cable entry shall be loomed together.
9. The insulation of cables shall be suitable for use at least 80°C for a T5 temperature
class.
10. The individual earth continuity plates within plastic enclosures must be bonded
together and locknuts used to secure glands to the continuity plates. For clearance
holes, serrated metal washers must be used between locknuts and the glandplate.
11. When Intrinsic and Increased Safety circuits occupy the same enclosure the two
types of circuit must have at least 50 mm clearance between them.
12. There must be adequate clearance between adjacent enclosures to allow proper
installation of cables and glands.
13. All unused cable entries should be closed using suitable plugs.
14. The schedule of the appropriate certificate should be consulted before cable entry
holes are drilled.
15. Cable glands or conduit entries must maintain the minimum ingress protection of
IP 54.
16. All lid and gland plate bolts must be fully tightened after installation.

95. March 2010 ©
17
Increased Safety EEx e / Ex e Motors
These motors are similar in appearance to standard industrial motors and inspection of the
certification/rating plate is usually necessary to identify them. These motors are not designed
to withstand an internal explosion and hence have special design features to prevent arcs,
sparks and excessive surface temperatures occurring both internally and externally. The
principal design features are:
1. Special attention to airgap concentricity and clearance of all rotating parts.
2. Impact testing of motor frame.
3. Temperature rise 10 °C lower than normal.
4. T2 or T3 surface temperature limitation.
5. Compliance with tE characteristic.
6. Special terminal block with specific creepage/clearance distances and locking
devices on terminals.
7. Minimum ingress protection to IP54.
Under stall (locked rotor) conditions, the rotor surface temperature will normally increase
faster than that of the stator windings, and hence, the T-rating applies to both internal and
external surface temperatures.
Under fault conditions, the motor must trip within the tE time specified on the motor data
plate.
tE time
Defined as: ‘the time taken to reach the limiting temperature from the temperature reached in
normal service (i.e. hot) when carrying the starting current IA at maximum ambient
temperature.
In the graph shown on page 17, ‘OA’ represents the maximum ambient temperature and
‘OB’ the temperature reached at maximum rated current. If the rotor locks as a result of a
fault, the temperature will rise rapidly towards ‘C’ as shown in part 2 of the graph, which is
less than the T rating of the motor. The time taken to reach ‘C’ from ‘B’ is known as the tE
time, and during fault conditions the thermal overload device in the motor starter must trip
the motor within this time.
Increased safety motors are intended for continuous duty only, i.e. they are unsuitable for
applications which require frequent stopping and starting and/or long run-up times.

96. March 2010 ©
18
Determination of tE Time
Limiting Temperature
Temperature limited either by selected T-Rating
or Limit for Class of Winding Insulating Material
A = Maximum ambient temperature.
B = Maximum temperature at rated current.
C = Limiting temperature.
θ = Temperature.
(1) = Temperature rise at rated current.
(2) = Temperature rise during locked rotor test.
tE = Time from maximum temperature (B) at rated current to limiting
temperature (C).
Max limiting temperature
Temperature
C
0
θ
Hours Secs
Rotor locked
A
B
C
Time
0

97. March 2010 ©
19
Tripping Characteristic of Thermal Overload device
The thermal overload device will be selected for suitability according to its tripping
characteristic. The tE time and IA/IN current ratio are influential in the selection of the device
and are marked on the motor nameplate.
IN = rated current of motor.
IA = locked rotor current of motor.
Example 1: IA/IN = 5 and tE time = 10 secs
The above characteristic would trip the motor after 8 secs, which is
within the tE time and therefore acceptable.
Example2: IA/IN = 4.5 and tE time = 8 secs
For these values the tripping time is 10 secs, which is outwith the tE
time assigned to the motor, therefore an overload device with this
characteristic would not be suitable for the values specified.
40
20
10
1
2
5
3 4 5 6 7 8 9 10
t
time
E
I / I current ratio
A N

98. March 2010 ©
20
BS EN 60079-17 Table 1: Inspection Schedule for Ex’d’, Ex’e’, and Ex ‘n’
Installations (D = Detailed, C = Close, V = Visual)
Check that: Ex’d’ Ex’e’ Ex’n’
Grade of Inspection
D C V D C V D C V
A APPARATUS
1 Apparatus is appropriate to area classification * * * * * * * * *
2 Apparatus group is correct * * * * * *
3 Apparatus temperature class is correct * * * * * *
4 Apparatus circuit identification is correct * * *
5 Apparatus circuit identification is available * * * * * * * * *
6 Enclosure, glass parts and glass-to-metal sealing gaskets
and/or compounds are satisfactory
* * * * * * * * *
7 There are no unauthorised modifications * * *
8 There are no visible unauthorised modifications * * * * * *
9 Bolts, cable entry devices (direct and indirect) and blanking
elements are of the correct type and are complete and tight
- Physical check
- Visual check
* *
*
* *
*
* *
*
10 Flange faces are clean and undamaged and gaskets, if any,
are satisfactory
*
11 Flange gap dimensions are within maximal permitted values * *
12 Lamp rating, type and position are correct * * *
13 Electrical connections are tight * *
14 Condition of enclosure gaskets is satisfactory * *
15 Enclosed-break and hermetically sealed devices are undamaged *
16 Restricted breathing enclosure is satisfactory *
17 Motor fans have sufficient clearance to enclosure and/or covers * * *
18 Breathing and draining devices are satisfactory * * * * * *
B INSTALLATION
1 Type of cable is appropriate * * *
2 There is no obvious damage to cables * * * * * * * * *
3 Sealing of trunking, ducts, pipes and/or conduits is satisfactory * * * * * * * * *
4 Stopping boxes and cable boxes are correctly filled *
5 Integrity of conduit system and interface with mixed system is
maintained
* * *
6 Earthing connections, including any supplementary earthing
bonding connections are satisfactory (e.g. connections are tight
and conductors are of sufficient cross section)
- Physical check
- Visual check
*
* *
*
* *
*
* *
7 Fault loop impedance (TN system) or earthing resistance
(IT systems is satisfactory)
* * *
8 Insulation resistance is satisfactory * * *
9 Automatic electrical protective devices operate within permitted
limits
* * *
10 Automatic electrical protective devices are set correctly (auto reset
not possible)
* * *
11 Special conditions of use (if applicable) are complied with * * *
12 Cables not in use are correctly terminated * * *
13 Obstructions adjacent to flameproof flanged joints are in
accordance with IEC 60079-14
* * *
14 Variable voltage/frequency installation in accordance with
documentation
* * * * * *
C ENVIRONMENT
1 Apparatus is adequately protected against corrosion, weather,
vibration and other adverse factors
* * * * * * * * *
2 No undue accumulation of dust and dirt * * * * * * * * *
3 Electrical insulation is clean and dry * *

99. March 2010 ©
21
Note 1: Apparatus using a combination of both ‘d’ and ‘e’ types of protection will require
reference to both columns during inspection.
Note 2: The use of electrical test equipment, in accordance with items B7 and B8, should
only be undertaken after appropriate steps are taken to ensure the surrounding area
is free of a flammable gas or vapour.

100. Unit 5:
Type ‘n’ Apparatus
Ex N / EEx n / Ex n

101. March 2010 ©
2
Objectives:
On completion of this unit, ‘Type ‘n’ Apparatus’, you should know:
a. The principle of operation.
b. The principle design features.
c. The protection methods applied to arcing/sparking components to enable their use in
enclosures etc.
d. The installation requirements according to BS EN 60079-14.
e. The inspection requirements according to BS EN 60079-17.

102. March 2010 ©
3
Type ‘n’ Protection
Since the presence of a flammable gas or vapour is less likely in Zone 2, the constructional
requirements for electrical equipment used in these hazardous locations are not as strict as
those for equipment used in Zone 1. A method of protection which falls into this category is
type ‘n’ apparatus, which is basically similar to increased safety type “e” apparatus except
that there is a relaxation in the constructional requirements.
Type ‘n’ protection, a UK innovation, became an accepted method of explosion protection by
CENELEC around the year 1999 through the publication of the standard EN50021. Prior to
the issue of this standard by CENELEC, this type of protection was symbolised by the (upper
case) letter ‘N’ when constructed to UK standards and, as far as Europe is concerned, was
only acceptable for use in the UK.
Now that EN50 021 has been approved, this type of apparatus will be symbolised by the
(lower case) letter ‘n’ and will also display the European Community mark thus enabling
wider use of this type of protection in the EC.
Standards
BS EN60079-15: 2005 Electrical apparatus for explosive gas atmospheres.
Type of protection “n”
BS EN50 021: 1999 Type of protection “n”
BS 6941: 1988 Electrical apparatus for explosive atmospheres with
type of protection N
BS 4683: Part 3: 1972 Type of protection ‘N’
IEC 60079-15: 2010 Construction, test and marking of type of protection
“n” electrical apparatus
BS EN60079-14: 2008 Electrical apparatus for explosive gas atmospheres:
Part 14. Electrical installations in hazardous areas
(other than mines)
BS EN60079-17: 2007 Electrical apparatus for explosive gas atmospheres:
Part 17. Inspection and maintenance of electrical
installations in hazardous areas (other than mines)
BS 5345: Part 7: 1979
(Withdrawn)
Code of Practice for the Selection, Installation and
Maintenance of apparatus with type ‘N’ protection.
Definition
The definition for Electrical apparatus with type of protection “n” as given in the British
Standard BS EN60079-15: 2005 is:
‘A type of protection applied to electrical apparatus such that, in normal operation
and in certain specified abnormal conditions, it is not capable of igniting a
surrounding explosive atmosphere’.

103. March 2010 ©
4
EPL: Gc
Zone of use: 2
Ambient conditions
Type ‘n’ apparatus is normally designed for use in ambient temperatures in the range -20 °C
to + 40 °C unless otherwise marked.
Principle
In Zone 2 hazardous locations, the presence of a flammable gas or vapour is not likely to be
present, or if it is present it’s duration will be for a short time only. This fact allows the use of
less expensive methods of protection, i.e. non-incendive or type ‘n’ protection. As previously
stated, type ‘n’ protection is similar in concept to increased safety type ‘e’ protection. The
design features for this type of protection ensure that, in normal operation, sources of
ignition in the form of excessive surface temperatures, arcs or sparks are prevented from
occurring either internally or externally. Since the design requirements are not as strict as
those for increased safety type ‘e’ protection, it is possible for the manufacturer to install
within type ‘n’ apparatus, components which produce hot surfaces, arcs or sparks, providing
these components have incorporated in them additional methods of protection. These
additional methods are described later in this unit. The principal design features for type ‘n’
apparatus are as follows.
1) Enclosures, guards, protective covers, motor fan guards and cable glands, are
required to be impact tested to 7J where the risk of impact is high, or 4J where the
risk of impact is low;
2) Minimum ingress protection IP54 where an enclosure has exposed live parts
internally, or IP44 where insulated live parts are used internally;
3) Use of certified terminals;
4) Terminals manufactured form high quality insulation material;
5) Specified creepage and clearance distances incorporated into the design of the
terminals;
6) Terminal locking devices to ensure conductors remain secure in service.
7) Cable glands to comply with the requirements of IEC 60079-0.
Gland entries must
maintain enclosure
integrity
Material must be suitable
for the environment and
must withstand impact

104. March 2010 ©
5
Cable gland selection
The requirements for cable glands entering Ex e equipment, as specified in BS EN60079-14:
2003 states that they maintain the type of protection and ingress protection of the
equipment, and meet the impact test requirements. The inference here would appear to
suggest that provided uncertified cable glands were manufactured to BS6121 their use
would be acceptable with Ex e equipment. This of course does not apply to uncertified
plastic cable glands.
The introduction of the latest standards, however, has effectively removed this option by
virtue of the requirement for revised ‘seal aging’ tests involving repeated heating and cooling
cycles, which is now a requirement for all cable glands as detailed in IEC 60079-0 The
latest issue of IEC 60079-14: 2007 now requires all cable glands to be certified or approved
by the manufacturer.
Additional protection measures
As previously mentioned, components which produce arcs/sparks or hot surfaces may be
installed in type ‘n’ apparatus provided additional protection measures are included. These
are explained below.
Energy limited apparatus and circuits
The technique of energy limitation applies the principles of intrinsic safety by the use of
components, which are part of the apparatus circuits, or out-with the apparatus, to prevent
ignition of a flammable gas. Energy limitation will involve the use of Associated energy-
limited apparatus and Energy limited apparatus where both are separate entities, but
when both are contained in the same item of equipment, the equipment is known as Self
protected energy-limited apparatus.
Associated energy-limited apparatus
Apparatus of this type will use zener diodes and series resistors to limit the
voltage and current available to sparking contacts and energy storing
components within the energy-limited apparatus, or at the output terminals of
the associated energy-limited apparatus.
Where the supply to the apparatus is mains voltage via a transformer, an upward
tolerance of 10% must be assumed unless alternative measures allow
dispensation of this requirement.
Energy limited circuits:
In order that this type of apparatus may be correctly installed, manufacturers are
required to specify the maximum values of voltage, current, power, inductance
and capacitance including cable inductance and capacitance that may be
connected.
Limited
output
energy

105. March 2010 ©
6
Sealed device
A device containing normally sparking components or hot surfaces constructed in such a
way that opening is prevented in normal operation and in which the sealing effectively
prevents access by a flammable gas or vapour. The free internal volume must be less than
100 cm3
.
Enclosed break device
This technique is used in, for example, the lamp holders of type ‘n’ apparatus. The example
below shows a typical lamp holder in which there are two sets of contacts. One set of
contacts is enclosed in what is effectively a flameproof enclosure in which the free internal
volume must not exceed 20 cm3
. This enclosure is designed to withstand an internal
explosion and the voltage and current limitations are 690 V and 16 A respectively.
Note: Lamps for Ex n, luminaries, which have mono-pin, bi-pin or screw connections where
the caps are made from non-conductive material with a conductive coating, are not
permitted unless tested with the equipment.
Hermetically sealed device
A device which prevents an external gas or vapour gaining access to the interior by sealing
of joints by fusion, e.g. welding, soldering, brazing, or the fusion of glass to metal. The
example of hermetic sealing shown below is a reed switch which comprises a set of contacts
hermetically sealed within a glass envelope.

106. March 2010 ©
7
Encapsulated device
The device in this instance will be totally sealed by an encapsulating material, typically
‘epoxy resin’, to prevent access of a flammable gas or vapour to an ignition source within.
The encapsulant is required to have a continuous operating temperature (COT) 200
k greater
than the marked maximum temperature and be free of intentional voids. The encapsulant
should have a minimum thickness of 3mm, or not less than 1mm if the free surface area is
less than 200mm2
.
Restricted breathing
A technique mainly used in type ‘n’ lighting fittings whereby entry to the interior of the
apparatus by a flammable gas or vapour is restricted by virtue of good sealing at all joints
and cable entries. For apparatus fitted with a device for routine testing of it’s restrictive
breathing properties the manufacturer will have tested to ensure that an internal pressure of
300Pa (30mm water gauge) below atmospheric will not change to 150Pa (15mm water
gauge) in less than 80 seconds. If the apparatus does not have a device for routine testing
then the internal pressure must not change from 3kPa (300mm water gauge) below
atmospheric to 1.5kPa (150mm water gauge) in less than 3 minutes. This type of protection
is suitable for use in Zone 2 only.
Type ‘n’ apparatus variations
Type ‘n’ apparatus variations Marking
Restricted breathing enclosures R
Energy limited apparatus L
Includes devices protected by: sealing,
encapsulation, hermetic-sealing, enclosed-
break and non-incendive methods
C
Non-sparking apparatus A
Note: It is intended that Ex nL equipment will be replaced by
Ex ic equipment as described in page 7 of Unit 7 since
they are of similar design.
Marking
The above table shows the marking on Type ‘n’ apparatus to indicate the method applied to
either eliminate or control spark energy and/or hot surfaces.
The following is an example of marking applied to type-n apparatus containing sparking
contacts protected by another method.
EEx nC IIB T5

107. March 2010 ©
8
BS EN 60079-17 Table 1: Inspection Schedule for Ex’d’, Ex’e’, and Ex ‘n’
Installations (D = Detailed, C = Close, V = Visual)
Check that: Ex’d’ Ex’e’ Ex’n’
Grade of Inspection
D C V D C V D C V
A APPARATUS
1 Apparatus is appropriate to area classification * * * * * * * * *
2 Apparatus group is correct * * * * * *
3 Apparatus temperature class is correct * * * * * *
4 Apparatus circuit identification is correct * * *
5 Apparatus circuit identification is available * * * * * * * * *
6 Enclosure, glass parts and glass-to-metal sealing gaskets
and/or compounds are satisfactory
* * * * * * * * *
7 There are no unauthorised modifications * * *
8 There are no visible unauthorised modifications * * * * * *
9 Bolts, cable entry devices (direct and indirect) and blanking
elements are of the correct type and are complete and tight
- Physical check
- Visual check
* *
*
* *
*
* *
*
10 Flange faces are clean and undamaged and gaskets, if any,
are satisfactory
*
11 Flange gap dimensions are within maximal permitted values * *
12 Lamp rating, type and position are correct * * *
13 Electrical connections are tight * *
14 Condition of enclosure gaskets is satisfactory * *
15 Enclosed-break and hermetically sealed devices are undamaged *
16 Restricted breathing enclosure is satisfactory *
17 Motor fans have sufficient clearance to enclosure and/or covers * * *
18 Breathing and drainage devices are satisfactory * * * * * *
B INSTALLATION
1 Type of cable is appropriate * * *
2 There is no obvious damage to cables * * * * * * * * *
3 Sealing of trunking, ducts, pipes and/or conduits is satisfactory * * * * * * * * *
4 Stopping boxes and cable boxes are correctly filled *
5 Integrity of conduit system and interface with mixed system is
maintained
* * *
6 Earthing connections, including any supplementary earthing
bonding connections are satisfactory (e.g. connections are tight
and conductors are of sufficient cross section)
- Physical check
- Visual check
*
* *
*
* *
*
* *
7 Fault loop impedance (TN system) or earthing resistance
(IT systems is satisfactory)
* * *
8 Insulation resistance is satisfactory * * *
9 Automatic electrical protective devices operate within permitted
limits
* * *
10 Automatic electrical protective devices are set correctly (auto reset
not possible)
* * *
11 Special conditions of use (if applicable) are complied with * * *
12 Cables not in use are correctly terminated * * *
13 Obstructions adjacent to flameproof flanged joints are in
accordance with IEC 60079-14
* * *
14 Variable voltage/frequency installation in accordance with
documentation
C ENVIRONMENT
1 Apparatus is adequately protected against corrosion, weather,
vibration and other adverse factors
* * * * * * * * *
2 No undue accumulation of dust and dirt * * * * * * * * *
3 Electrical insulation is clean and dry * *

108. March 2010 ©
9
Note 1: Apparatus using a combination of both ‘d’ and ‘e’ types of protection will require
reference to both columns during inspection.
Note 2: The use of electrical test equipment, in accordance with items B7 and B8, should
only be undertaken after appropriate steps are taken to ensure the surrounding area
is free of a flammable gas or vapour.

109. Unit 6:
Pressurisation
EEx p / Ex p

110. March 2010 ©
2
Objectives:
On completion of this unit, ‘Pressurised EEx p / Ex p apparatus, you should know:
a. The principle of operation and the importance of purging.
b. The control measures required to ensure the safe operation of apparatus and
systems.
c. The variations of pressurisation methods.
d. The action required on loss of overpressure.
e. The installation requirements according to BS EN 60079-14.
f. The inspection requirements according to BS EN 60079-17.

111. March 2010 ©
3
Pressurised Equipment
Introduction
Pressurisation is a simple technique for providing explosion protection. If the interior of an enclosure
is at a pressure above that externally, any flammable gases around the enclosure will be prevented
from entering the enclosure. Components which are a source of ignition, i.e. they produce
arcs/sparks or hot surfaces, are permitted within the enclosure and, clearly, safety is dependent on
the maintenance of the safe gas. The safe gas, which is taken from a known non-hazardous area via
the inlet duct, is the medium which ‘segregates’ the flammable gas from the source of ignition, and its
continued presence will be confirmed by an approved/certified ‘fail-safe’ control/monitoring system. A
slight over-pressure is usually adequate to maintain safe operation.
The latest standard for this type of protection, BS EN60079-2, has introduced three types of
pressurisation, namely px, py and pz, around which the requirements of the standard are based.
Some of these requirements are considered in this Unit.
Standards
BS EN60079-2: 2007 Pressurised enclosures ‘p’
BS EN50 016: 2002 Pressurised Apparatus ‘p’
BS 5501-3: 1977 Pressurised Apparatus ‘p’
IEC 60079-2: 2007 Pressurised enclosures ‘p’
BS EN60079-14: 2008
Electrical apparatus for explosive gas
atmospheres: Part 14. Electrical installations in
hazardous areas (other than mines)
BS EN60079-17: 2007
Electrical apparatus for explosive gas
atmospheres: Part 17. Inspection and
maintenance of electrical installations in
hazardous areas (other than mines)

112. March 2010 ©
4
Definition
Pressurisation is defined as:
‘The technique of guarding against the ingress of the external atmosphere into an enclosure
or room by maintaining a protective gas therein at a pressure above that of the external
atmosphere.
EPL’s: Type px - Gb ( See explanation for types below )
Type py - Gb
Type pz - Gc
Zones of use: 1 & 2
Applications
Pressurisation has a wide range of applications, i.e. it can provide explosion protection for a
diverse range of instrument or electrical apparatus, there being no limit to size, within
reason, which can be accommodated. Typical examples are transformer/rectifier cabinets,
oil drilling control consoles, visual display units (VDU’s), gas analysis equipment, control
rooms, switch rooms and workshops. With regard to flameproof apparatus, and in particular
rotating machines, there is a maximum practical limit above which handling becomes difficult
and manufacturers may overcome this difficulty by the use of a pressurised enclosure. A
pressurised machine would be significantly lighter than a flameproof machine of the same
rating.
Types of pressurisation
The latest construction standard, BS EN60079-2, identifies three types of pressurisation (px,
py and pz), their selection being dependent on the zone of use, the likelihood of an internal
release of gas, and the presence/absence of an internal source of ignition. Type px
establishes non-hazardous conditions within an enclosure when the enclosure is located in
Zone 1, or Group 1 for mining applications. Type py establishes a Zone 2 classification
within the enclosure when the enclosure is located in Zone 1. Type pz establishes a non-
hazardous classification within the enclosure when the enclosure is located in Zone 2. The
table on page 16 illustrates how the protection type is determined based on the Zone of use,
and whether or not there are flammable materials and sources of ignition in the enclosure.

113. March 2010 ©
5
Principle
The basic principle of operation involves raising and maintaining the internal pressure of the
enclosure to a level slightly above the atmospheric pressure out with the enclosure. This
ensures that any flammable gases or vapours out with the enclosure cannot enter the
enclosure. The minimum over-pressure specified in the latest standard BS EN60079-2 is
0.5 mBar or 50 Pa for types px and py, and 0.25 mBar or 25 Pa for type pz. Previous
standards specified 0.5 mBar or 50 Pa. The safe gas used to provide the over-pressure will
normally be air but an inert gas such as nitrogen may also be used in certain instances.
Note: Manufacturers must indicate the operational maximum and minimum overpressure
for enclosures and the maximum rate of leakage which occurs at maximum
overpressure.
Purging
When a pressurised system has not been in use for some time it is important that electrical apparatus
inside the enclosure is not energised prior to what is known as the ‘purge’ cycle. Purging, which must
occur automatically, involves passing a quantity of the safe gas through the enclosure for a specified
time in order to remove any flammable gases which may have entered the enclosure. The standards
specify that the minimum quantity of the safe gas required to achieve adequate purging is equivalent
to 5 times the internal volume of the enclosure and associated ducting. The purge duration will be
controlled by a timer in association with a flow-rate sensor in the control circuit. Manufacturers may,
however, recommend a greater number of air changes. Very large systems, which are installed on
site, will require on-site tests to establish the purge duration necessary for safe operation. If loss of
pressure occurs during operation, the control system must automatically purge the enclosure again.

114. March 2010 ©
6
Enclosures
The European and IEC standards require a minimum level of ingress protection for
pressurised enclosures to IP 4X but, not all enclosures are suitable for pressurisation. An
enclosure may have ingress protection to IP54 but, it’s lid seal, for example, is designed to
prevent entry of contaminants and not to maintain an over-pressure within the enclosure.
Enclosures must, therefore, be appropriately designed, i.e. be strong enough to withstand
impact tests and the internal over-pressure with regard to the strength of the walls, and have
effective and correctly orientated door seals. The enclosure and its associated ducts must
be capable of withstanding, in normal operation, an over-pressure equivalent to 1.5 times the
maximum working over-pressure declared by the manufacturer. Alternatively, the enclosure
must be capable of withstanding the maximum over-pressure obtained when all outlet ducts
are closed. In either instance the minimum overpressure will be 2 mBar (200 Pa).
Protective gas
The protective gas, which is normally air except for certain applications, may be an inert gas
such as nitrogen or another suitable gas. When air is the protective gas, it may be provided
by either a motor driven fan, a compressor, or from storage cylinders. The protective gas
must be non-toxic and free from contaminants such as moisture, oil, dust, fibres and
chemicals, and other contaminants which could jeopardise the safe operation of the system.
Normally, the temperature of the safe gas entering the inlet duct should not exceed 40°C.
Where temperatures above or below this value are required, the pressurised enclosure will
be marked with this temperature. When air is used as the safe gas its oxygen content must
not be greater than that normally present in the atmosphere, i.e. 20.9%.
A duplicate supply of the protective gas is also desirable when, on loss of pressure, it would
be more dangerous to de-energise the electrical apparatus within the enclosure.
When an inert gas such as nitrogen is used as the protective gas and personnel can gain
access to enclosures, it is essential that doors/covers are fitted with warning labels since
there is a danger of asphyxiation. Doors should also be fitted with suitable locks.
Enclosure covers/doors
Where the interior of a type px pressurised enclosure can be accessed via doors/covers
without the use of tools or keys, an interlock is required to automatically de-energise the
electrical supply when the door/cover is opened, and restore the electrical supply only when
the doors/covers are closed. Doors/covers requiring the use of a tool or key for opening
must display the warning: “Do not open when energised”.
When a pressurised enclosure contains components which have hot surfaces, or are
capable of storing energy, e.g. capacitors, doors/covers should be fitted with a warning
notice which states the time delay after isolation of the electrical supply to the components
before opening the doors/covers.

115. March 2010 ©
7
Control circuit/safety devices
The level of overpressure will be monitored by an overpressure sensor or switch and located
at a point in the enclosure which has been found by test or experience to be the most difficult
to maintain the overpressure, e.g. the internal circulation fan in a pressurised machine. The
exact point must be specified either on the enclosure or on the certificate. The rate of flow
through the enclosure will be monitored by a flow-rate sensor or switch. A pressure gauge is
also desirable and should be located where it can be easily read. The table below, from the
latest standard BS EN60079-2, specifies the safety devices required according to the
protection type.
1. Over-pressure monitoring device.
2. Protective gas flow-rate monitoring device.
3. Pressure gauge.
4. Pressure relief valve: setting 75% of maximum declared
safe over-pressure
When the safe gas is provided from compressed-air cylinders, failure of the regulator could
result in distortion of the pressurised enclosure due to excessive overpressure, and to
overcome this risk it is recommended that a pressure relief valve is installed. The setting of
the relief valve is required to be 75% of the maximum safe overpressure declared by the
manufacturer.

116. March 2010 ©
8
Safety device requirements for protection types
Design criteria Type px Type py Type pz
Safety device to detect
loss of minimum
overpressure
Pressure sensor
(see 7.9)
Pressure sensor
(see 7.9)
Indicator or
pressure sensor
Safety device(s) to
verify purge period
Timing device,
pressure sensor,
and flow sensor at
outlet; (see 7.6)
Time and flow
marked
(see 7.7c)
Time and flow
marked
(see 7.7c)
Safety device for a door
or cover that requires a
tool to open
Warning
(see 6.2b)
Warning
(see 6.2b)
No requirement
Safety device for a door
or cover that does not
require a tool to open
Interlock, (see 7.12)
(no internal hot
parts)
Warning
See 6.2b
(no internal hot
parts)
Warning
(see 6.2b)
Safety device for hot
internal parts when
there is a containment
system (see clause 15)
Alarm and stop flow
of flammable
substance
Not applicable for
protection type
since internal hot
parts not permitted
Alarm
(normal release
not permitted)
Ducts
The entry of the inlet duct must be positioned in a non-hazardous location (except where
cylinders provide the protective gas) and this location must be periodically reviewed in case
plant modifications have altered its classification. The exhaust duct, ideally, should have its
outlet situated in a non-hazardous location in which there are no sources of ignition, but may
be located in a hazardous location if a spark/particle arrestor is fitted. The table below offers
guidance in this respect.
Ducts should be located in non-hazardous areas as far as possible. Where inlet or outlet
ducts pass through hazardous areas, they are required to be free of leakage if there is a
possibility that the pressure of the protective gas is below the minimum requirement
specified in the standards or that specified by the manufacturer.
It is essential that both the inlet and outlet ducts are arranged in such a way that they cannot
be obstructed causing restriction of the flow of the protective gas. The ducts should also
have adequate mechanical strength, be located where accidental damage is unlikely and
have adequate protection against corrosion.

117. March 2010 ©
9
Spark particle barriers:
Type of apparatus within enclosure
Zone in which
exhaust duct is
located A B
Zone 2 Required Not required
Zone 1 Required * Required *
A: apparatus which may produce ignition-capable sparks or particles in
normal operation.
B: apparatus which does not produce ignition-capable sparks or particles
in normal operation.
* A device to prevent rapid entry of a flammable gas into the enclosure upon
loss of pressure should be fitted if the surface temperature of apparatus
within the enclosure is likely to be a source of ignition.
Duct arrangements
The density of the safe gas relative to the flammable gas has an influence on the position of
the inlet and outlet ducts on the enclosure. This will speed up the rate of displacement of the
flammable gas and so ensure efficient purging of the system. If the safe gas is heavier than
the flammable gas the inlet duct will be positioned at the bottom of the enclosure and the
exhaust duct at the top. If the safe gas is lighter than the flammable gas the positions of the
ducts will be reversed.
1. When the safe gas is more dense
than the flammable gas:
2. When the safe gas is less dense
than the flammable gas:

118. March 2010 ©
10
Variations of Pressurisation
Several variations of pressurised systems are available. These are:
a. Static pressurisation.
b. Pressurisation with continuous flow;
c. Pressurisation with leakage compensation;
d. Pressurisation with continuous dilution;
a. Static pressurisation
This form of pressurisation has limited applications and, therefore, is not widely used.
The technique involves pressurising and sealing the enclosure in a non-hazardous area
prior to transportation into a hazardous area. Clearly the seals of the enclosure must be
very good to minimise leakage once the source of the safe gas is disconnected.
b. Pressurisation with continuous flow
In this variant the internal over-pressure is maintained as a result of continual flow of
the safe gas through the enclosure. The safe gas in this instance has a dual purpose. In
addition to maintaining the over-pressure, it may also be used to cool hot parts within
the enclosure such as thyristors, or the windings of a pressurised rotating machine. The
rate of flow of the safe gas is set at a level which will prevent the temperature of the hot
parts exceeding their temperature limit, thereby ensuring that the pressurised enclosure
operates within it’s T-rating.

119. March 2010 ©
11
c, Pressurisation with leakage compensation
This method of pressurisation is used when enclosures are poorly sealed at their joints.
The system is purged in the usual manner with the damper at the exhaust duct open
but, on completion, the damper is closed and the flow of protective gas reduced to a
level sufficient to compensate for leakages occurring at the seals/joints of the
enclosure.
d. Continuous dilution
The analysis of flammable gases on, for example, an offshore platform may take place
in pressurised enclosures. A sample of gas will be drawn into a gas analyser and, after
analysis, will be expelled into the interior of the pressurised enclosure. The safe gas
therefore has two functions. In addition to maintaining over-pressure during and after
the initial purge, the rate of flow of the safe gas will be adjusted to ensure that the
concentration of the gas/air mixture within the enclosure is well below the lower
explosive limit (LEL).
Purging may be disregarded in Zone 2 if the concentration of the flammable gas
released within the enclosure is considerably below the lower-explosive limit, e.g. 25%
LEL. Gas detectors may be installed to verify that the atmosphere within the enclosure
remains non-hazardous.

120. March 2010 ©
12
d. Continuous dilution (continued)
Types and Magnitude of Internal Release
The recommended action when loss of pressure occurs in pressurised apparatus using
continuous dilution is addressed in BS EN60079-2 by consideration of the types of release
given in the tables below.
1. Normal release
None No release of flammable gas or vapour.
Limited
A release of flammable gas or vapour which
is limited to a value which can be diluted to
well below the lower explosive limit (LEL).
2. Abnormal release
Limited
A release of flammable gas or vapour which is
limited to a value which can be diluted to well
below the lower explosive limit (LEL).
Unlimited
A release of flammable gas or vapour which is
not limited to a value which can be diluted to well
below the lower explosive limit (LEL).

121. March 2010 ©
13
Combination of Release
Combination 1 No normal release, limited abnormal release
Combination 2 No normal release, unlimited abnormal release
Combination 3 Limited normal release, limited abnormal release
Combination 4 Limited normal release, unlimited abnormal release
The above combinations of release are applied in the table on page 14 which specifies the
action necessary on loss of pressure within an enclosure using the technique of continuous
dilution.
Action on Loss of Pressure
1. No internal source of release
The over-pressure within the enclosure is monitored by a pressure switch/sensor, and a
flow-rate switch/sensor, located at the exhaust duct, is used to monitor the rate of flow of the
safe gas through the enclosure. Loss of over-pressure or rate of flow will activate either an
alarm or shutdown of the internal electrical components, the action taken being dependent
on:
a. The Zone in which the system is located;
b. The type of apparatus/components within the enclosure.
For a system which does not have an internal source of release and contains electrical
equipment, BS EN60079-14 specifies the action to be taken on loss of pressure as follows.
Area classification
Enclosure contains
ignition-capable apparatus
Enclosure contains apparatus
which does not produce a
source of ignition in normal
operation
Zone 1 Alarm and switch off
b
Alarm
a
Zone 2 Alarm
a
No action
a) Operation of the alarm requires immediate action to restore the integrity of the
system.
b) An alternative protective gas supply should be available if a more dangerous
condition is likely as a result of automatic switch-off.

122. March 2010 ©
14
Action on Loss of Pressure (continued)
3. With an internal source of release
Internal release
Combination
Normal Abnormal
Area
classification
Ignition-capable
apparatus
Apparatus with no
sources of ignition
Zone 1
Alarm and
switch off
Alarm
1 None Limited Zone 2
or non-
hazardous
Alarm
No protective
measures
required
Zone 1
Alarm and
switch off
Alarm
2 None Unlimited Zone 2
or non-
hazardous
Alarm
No protective
measures
required
3 Limited Limited
Zone 1
or
Zone 2
Alarm and
switch off Alarm
4 Limited Unlimited
Zone 1
or
Zone2
Alarm and
switch off Alarm
Externally Mounted Electrical Apparatus
Electrical apparatus mounted on the exterior of a pressurised enclosure must be explosion
protected in accordance with the Zone in which the enclosure is situated. Typical examples
are pressure/flow rate sensors or switches which may use Ex i apparatus, junction boxes
may use Ex d, Ex e or Ex n methods of protection. This requirement also applies to the
motor and its starter, of the fan which provides the flow of air, unless they are situated in a
non-hazardous area. It is preferable that the motor and its starter are located in a
non-hazardous area.
Apparatus Energised During Absence of Overpressure
An anti-condensation heater may be used in a rotating electrical machine to prevent the
internal surfaces and atmosphere becoming cold, thereby preventing the formation of
moisture in the windings. Because the heater will be energised when the machine is without
over-pressure, it is essential that it is explosion protected. Emergency lighting will normally
be installed in pressurised control rooms, cabins etc. and energised when there is loss of
over-pressure, hence, these fittings must also be explosion protected, typically Ex e.
Solenoids for fire dampers will be Ex d protected. Alarms, over-pressure and flow-rate
sensors may use IS protection. Ex d enclosures will be used for control panels.

123. March 2010 ©
15

124. March 2010 ©
16
Determination of protection type
Enclosure
does
not
contain
ignition-capable
apparatus
Type
py
No
pressurisation
required
Type
py
Type
py
b
Type
py
No
pressurisation
required
d
Enclosure
contains
ignition-capable
apparatus
Type
px
a
Type
pz
Type
px
a
Type
px
(and
ignition-capable
apparatus
is
not
located
in
the
dilution
area)
Type
px
a
(inert)
c
Type
pz
(inert)
c
External
Zone
classification
1
2
1
2
1
2
Flammable
substance
in
the
containment
system
No
containment
system
No
containment
system
Gas
/
vapour
Gas
/
vapour
Liquid
Liquid
NOTE:
If
the
flammable
substance
is
a
liquid,
normal
release
is
never
permitted
a)
Protection
type
px
also
applies
to
Group
I
b)
If
no
normal
release,
see
annex
E
c)
The
protective
gas
shall
be
inert
if
“(inert)”
is
shown
after
the
pressurisation
type;
see
clause
13.
d)
Protection
by
pressurisation
is
not
required
since
it
is
considered
unlikely
that
a
fault
causing
a
release
of
liquid
will
simultaneously
occur
with
a
fault
in
the
equipment
that
would
provide
an
ignition
source

125. March 2010 ©
17
Design requirements relevant to protection type
Type
pz
with
alarm
IP3X
minimum
IEC
60079-0,
half
the
value
in
table
4
Time
and
flow
marked
Spark
and
particle
barrier
required,
see
5.8
unless
incandescent
particles
not
normally
produced
No
requirement
(
Note
2
)
Spark
and
particle
barrier
required,
see
5.8
Spark
and
particle
barrier
required,
see
5.8
unless
incandescent
particles
not
normally
produced
Warning,
see
5.3
and
6.2
b)
ii)
No
requirement
(
Note
3
)
Warning,
see
5.3
and
6.2
b)
ii)
Type
pz
with
indicator
IP4X
minimum
IEC
60079-0,
table
4
Time
and
flow
marked
Spark
and
particle
barrier
required,
see
5.8
unless
incandescent
particles
not
normally
produced
No
requirement
(
Note
2
)
Spark
and
particle
barrier
required,
see
5.8
Spark
and
particle
barrier
required,
see
5.8
unless
incandescent
particles
not
normally
produced
Warning,
see
5.3
and
6.2
b)
ii)
No
requirement
(
Note
3
)
Warning,
see
5.3
and
6.2
b)
ii)
Type
py
IP4X
minimum
IEC
60079-0,
table
4
Time
and
flow
marked
No
requirement
(
Note
1
)
No
requirement
(
Note
2
)
Spark
and
particle
barrier
required,
see
5.8
No
requirement
(
Note
1
)
Warning,
see
5.3
(note
1)
Warning,
see
5.3
(note
1)
Not
applicable
Type
px
IP4X
minimum
IEC
60079-0,
table
4
Requires
a
timing
device
and
monitoring
of
pressure
&
flow
Spark
and
particle
barrier
required,
see
5.8
unless
incandescent
particles
not
normally
produced
No
requirement
(
Note
2
)
Spark
and
particle
barrier
required,
see
5.8
Spark
and
particle
barrier
required,
see
5.8
unless
incandescent
particles
not
normally
produced
Warning,
see
5.3
and
6.2
b)
ii)
Interlock,
see
7.12
(
No
internal
hot
parts
)
Comply
with
6.2
b)
ii)
Design
criteria
Degree
of
enclosure
protection
according
to
IEC
60529
or
IEC
60034-5
Resistance
of
enclosure
to
impact
Verifying
purge
period
Preventing
incandescent
particles
from
exiting
a
normally
closed
relief
vent
into
a
Zone
1
area
Preventing
incandescent
particles
from
exiting
a
normally
closed
relief
vent
into
a
Zone
2
area
Preventing
incandescent
particles
from
exiting
a
vent
open
to
a
Zone
1
area
in
normal
operation
Preventing
incandescent
particles
from
exiting
a
vent
open
to
a
Zone
2
area
in
normal
operation
Door
/
cover
requiring
a
tool
to
remove
Door
/
cover
not
requiring
a
tool
to
remove
Internal
hot
parts
that
require
a
cool-
down
period
before
opening
enclosure
See
Notes
on
following
page

126. March 2010 ©
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Design requirements relevant to protection type ( continued )
The following notes are relevant to the table on the previous page.
Note 1: Sub clause 6.2b) ii) is not applicable for type py since neither hot internal parts nor
normally created incandescent particles are permitted.
Note 2: There is no requirement for spark and particle barriers since in abnormal operation,
where the relief vent opens, it is unlikely that the external atmosphere is within
explosive limits.
Note 3: There is no requirement for marking or tool accessibility on a pz enclosure since in
normal operation the enclosure is pressurised with all covers and doors in place.
If a cover or door is removed, it is unlikely that the atmosphere is within the
explosive limits.
Temperature classification
Type px or type py pressurisation
The temperature classification allocated to pressurised apparatus is required to be in
accordance with IEC 60079-0 and determined from the higher of either:
a) the hottest point of the enclosure external surface; or
b) the internal component with the hottest surface.
With regard to (b), however, the surface temperature of an internal component may exceed
the temperature class of the pressurised enclosure if the component complies with 5.3 of
IEC 60079-0, or the pressurised enclosure is marked with the time required for the
component to cool to the marked temperature class. This may be achieved by the following
methods.
c) The joints of the enclosure and its ducts are designed to prevent the ingress
of a flammable gas coming into contact with the hot surfaces before they
have cooled to below the T rating.
d) By the introduction of a secondary ventilation system.
e) By encapsulating the hot surfaces or enclosing them in gas-tight containers.
Type pz pressurisation
For this type of pressurisation, the hottest external surface will be used to determine the
temperature class of the enclosure but, internal explosion protected apparatus remaining
energised in the absence of over-pressure will also have to be taken into consideration for
determining the temperature classification.

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Marking
The construction standard BS EN60079-2 specifies that pressurised enclosures must be
marked as detailed in IEC 60079-0. The apparatus marking must be visible and contain the
following information:
a) the manufacturers name;
b) the manufacturers type number;
c) the manufacturers serial number;
d) the symbol Ex p, followed by the pressurisation category, i.e. px, py, or pz;
e) the gas group symbol II;
f) the temperature class, or the maximum surface temperature, or both, e.g. T3,
or 200 °C, or 200 °C (T3);
g) the name or acronym of the testing station;
h) the test station certificate number;
i) the internal free volume excluding the ducts;
j) the protective gas (when a gas other than air is used);
k) the minimum quantity of the safe gas necessary to purge the enclosure based
on the minimum purge flow rate and the minimum purge duration, and the
minimum additional purge duration per unit volume of additional ducting**;
l) the minimum and maximum permissible over-pressure;
m) the minimum flow of protective gas;
n) the minimum and maximum supply pressure to the pressurised system;
o) the maximum leakage rate from the pressurised enclosure;
p) the temperature or temperature range of the safe gas at the inlet duct;
q) the point(s) where the pressurisation must be monitored
**Note: In order to ensure adequate purging of the system the user must
increase the volume of the safe gas to compensate for the additional
volume of the ducts.

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BS EN60079-17: Table 3: Inspection Schedule for Ex ’p’ Installations
Check that: Grade of inspection
Visual
APPARATUS
1 Circuit and/or apparatus documentation is appropriate to area
classification
* * *
2 Apparatus installed is that specified in the documentation – Fixed
apparatus only
* *
3 Circuit and/or apparatus category and group correct * *
4 Apparatus temperature class is correct * *
5 Installation is clearly labelled * *
6 There are no unauthorised modifications *
7 There are no visible unauthorised modifications * *
8 Safety barrier units, relays and other energy limiting devices are of
the approved type, installed in accordance with the certification
requirements and securely earthed where required
* * *
9 Electrical connections are tight *
10 Printed circuit boards are clean and undamaged *
B INSTALLATION
1 Cables are installed in accordance with the documentation *
2 Cables screens are earthed in accordance with the documentation *
3 There is no obvious damage to cables * * *
4 Sealing of trunking, ducts, pipes and/or conduits is satisfactory * * *
5 Point-to-point connections are all correct *
6 Earth continuity is satisfactory (e.g. connections are tight and
conductors are of sufficient cross-section
*
7 Earth connections maintain the integrity of the type of protection * * *
8 The intrinsically safe circuit is isolated from earth or earthed at one
point only ( refer to documentation )
*
9 Separation is maintained between intrinsically safe and non-
intrinsically safe circuits in common distribution boxes or relay
cubicles
*
10 As applicable, short-circuit protection of the power supply is in
accordance with the documentation
*
11 Special conditions of use (if applicable) are complied with *
12 Cables not in use are correctly terminated *
C ENVIRONMENT
1 Apparatus is adequately protected against corrosion, weather,
vibration and other adverse factors
* * *
2 No undue accumulation of dust and dirt * * *

129. Unit 7:
Intrinsic Safety
EEx i / Ex i

130. March 2010 ©
2
Objectives:
On completion of this unit, ‘Intrinsic Safety EEx I / Ex i apparatus, you should know:
a. The principle of operation.
b. The difference between ‘ia’, ‘ib’ and ‘ic’ categories of IS.
c. The importance of zener and galvanic interfaces.
d. The installation of requirements according to BS EN 60079-14.
e. The inspection requirements according to BS EN 60079-17.

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Intrinsic Safety EEx / Ex i
Intrinsic Safety is a widely used method of explosion protection. It is used for very low power
applications only, and typical examples are control and instrumentation circuits.
Standards
BS EN60079-11: 2007 Equipment protection by intrinsic safety ‘i’
BS EN50020: 2002 intrinsic safety ‘i’
BS 5501: Part 7. 1977
(EN50 020)
Intrinsic safety ‘i’
BS EN60079-25: 2004 Electrical apparatus for explosive gas atmospheres: – Part 25
Intrinsically safe systems
BS 5501: Part 9 1982
(EN50 039)
Intrinsically safe electrical systems ‘i’
BS 1259: 1958 Intrinsically safe electrical apparatus and circuits for use in
explosive atmospheres
IEC 60079-11: 2006 Electrical apparatus for explosive gas atmospheres – Part 11:
Intrinsic safety ‘i’
IEC 60079-25: 2010 Electrical apparatus for explosive gas atmospheres: – Part 25
Intrinsically safe systems
IEC 60079-27: 2008 Explosive atmospheres: – Part 28: Protection of equipment
and transmission systems using optical radiation
BS EN60079-14: 2008 Electrical apparatus for explosive gas atmospheres: Part 14.
Electrical installations in hazardous areas (other than mines)
BS EN60079-17: 2007 Electrical apparatus for explosive gas atmospheres: Part 17.
Inspection and maintenance of electrical installations in
hazardous areas (other than mines)
BS 5345: Part 4 1977
(Withdrawn)
Code of Practice for the selection, installation and
maintenance of electrical apparatus with a type of protection ‘i’.

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Definition
BS EN60079-11 defines an intrinsically safe circuit as:
‘A type of protection based on the restriction of electrical energy within apparatus and of
interconnecting wiring exposed to the potentially explosive atmosphere to a level below that
which can cause ignition by either sparking or heating effects.’
EPL’s: ia - Ga
Ib - Gb
Ic - Gc
Zones of use: 0, 1 & 2 (Ex ia) ( based on traditional approach )
1 & 2 (Ex ib)
2 (Ex ic)
Basic Principles of IS
Intrinsically Safe circuits achieve safety by maintaining very low energy levels such that hot
surfaces will not be produced, and electrical sparks, if they occur, will have insufficient
energy to ignite the most easily ignitable concentration of a flammable mixture. This is
achieved by limiting the voltage and current supplied to the apparatus in the hazardous area.
To maintain safety, it is of paramount importance that these levels of voltage and current are
not exceeded under normal, or even fault conditions.
The circuit parameters, i.e. voltage, current, resistance, inductance and capacitance are
factors which have to be considered in the design of an IS circuit. Consultation with the
characteristic ignition curves given in the construction standard (shown in this unit on pages
9, 12 and 13), and the application of appropriate safety factors, will ensure that safe values
are established for these parameters during the design stage.
An IS system, which usually comprises a safe to hazardous area interface, cables, junction
boxes and field (hazardous) area apparatus, must also be designed in such a way as to
guard against the possibility of particular faults occurring. In contrast to other methods of
explosion protection, intrinsic safety is a system concept which applies to the whole
system and not to any one item only. Apparatus in the safe area, namely the interface,
connected to apparatus in the hazardous area is known as ‘associated apparatus’, and
each item making up the system, other than ‘simple apparatus’, will have a Certificate of
Conformity. Associated apparatus, such as the interface is typically marked with square
[Ex ib] IIC Ex ib IIC

133. March 2010 ©
5
brackets [Ex ia]IIC, may be used in the hazardous area if installation is within another
method of explosion protection, e.g. flameproof. Also, power supply modules supplying the
system may be installed in flameproof or pressurised Ex p enclosures if installed in the
hazardous area. An overall system certificate may cover the installation. Only the
equipment specified in the system documentation may be installed in the system.
The voltage supply to electrical apparatus, which is connected to the non-IS terminals of
associated apparatus, must not be greater than the voltage Um marked on the associated
apparatus label or specified in the system documentation. The Code of Practice BS5345
recommended this value should not exceed 250Vrms. The electrical supply prospective
short-circuit current must not be in excess of 1500A.
Advantages of IS are:
a. Live maintenance is possible
b. Cost effective – certified enclosures not required and ordinary
wiring may be used
c. Safe – low voltage not harmful to personnel
d. Can be used in Zone 0
Interface types
Interface types include the zener shunt diode barrier, described below, and the galvanic
isolator described on page 18. The purpose of the interface is to prevent high energy levels
entering the hazardous area and not to protect the hazardous area equipment to which it is
connected.
The Zener Barrier
The faults which can jeopardise the security of IS systems are either overvoltage or
overcurrent, and protection against these conditions is afforded by the use of an interface,
typically a Zener barrier, the construction of which will be considered in terms of its individual
components.
The interface, which is connected between the safe area and hazardous area apparatus, is
normally located in the safe area and situated as close as possible to the boundary with the
hazardous area, but may be located in the hazardous area if installed in a flameproof
enclosure.
A simple zener barrier has three principal components, (1) a resistor, (2) a zener diode, and
(3) a fuse, all of which must have infallible properties.

134. March 2010 ©
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Infallibility, with regard to the current limiting resistor, means that in the event of it failing,
failure will be to a higher resistance value or open-circuit. Clearly, failure to a lower
resistance value or short-circuit would allow more current to flow in the IS circuit, which is
contrary to the concept of this type of protection. Infallibility will be satisfied by the use of a
quality wire-wound or metal film resistor which should not operate at more than 2/3 of its
rated current, voltage and power for a specified temperature range. The next component for
consideration is the zener diode, the purpose of which is to limit the voltage available to the
apparatus in the hazardous area. The zener diode, as a single item, is not considered to be
an infallible component, must also be operated at only 2/3 of its rated current, voltage and
power.
For infallibility to be satisfied, the zener diode is required to fail to a short-circuit. Failure to a
higher resistance or open-circuit could allow voltage levels beyond safe limits to “invade” the
hazardous area.
Note: Tests by manufacturers have shown that diodes virtually always fail to a short-circuit
state, but there can be no guarantee of this. Diodes can only be considered infallible
when two or more are connected in parallel as discussed later.
The third component, a fuse, is located at the input (safe) end of the zener barrier, its
purpose being to protect the zener diodes, and not to protect against, for example, a short-
circuit in the field apparatus. Infallibility of the fuse is assured by the use of a sand-filled
ceramic type capable of operating properly even when exposed to a prospective fault-current
of up to 4000 A. A fuse of this type avoids the problem which can occur with other types of
fuses when they rupture, namely vaporisation which can allow the fuse to continue to
conduct.
As required by the standards, the fuse is encapsulated along with the other components of
the barrier to deter replacement. The repair of Zener barriers is not permissible, even by the
manufacturer.
Note: Categories (levels of protection), ‘ia’, ‘ib’ and ‘ic’, are described on the following page
but with regard to the infallibility of components, this applies to ‘ia’ and ‘ib’, but is not
applicable to ‘ic’. Furthermore, for level of protection ‘ic’ the 2/3 safety factor applies
only to the power rating; it does not apply to the voltage and current provided the
rated values are not exceeded.
Zener Barrier Operation
In the event of a short-circuit developing in the apparatus in the hazardous area, or across
the IS wiring, the series resistor in the zener barrier will limit the short-circuit current to a safe
level so that the integrity of the system is maintained.

135. March 2010 ©
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If a voltage greater than the normal maximum voltage of the IS system invades the circuit at
the input terminals of the zener barrier, this will trigger the zener diode, and the resulting
fault current will be shunted to earth. The excessive voltage is, therefore, prevented from
reaching the apparatus in the hazardous area as illustrated in the diagram on the following
page.
Levels of protection for IS
Previously referred to as categories of intrinsic safety, these are now called levels of
protection of which there are three, namely ‘ia’, ‘ib’ and ‘ic’, the level of safety provided by
each being dependant on the number component faults which are considered. For the first
level of protection, ‘ic’, no faults are considered in order to maintain safety. The second
level of protection, ‘b’ will maintain safety in the event of one fault occurring. The third level
of protection, ‘ia’, is required to maintain safety should two simultaneous faults occur.
Clearly, for the zener barrier (interface) to maintain safety with one or two faults, additional
zener diodes are necessary since they are the components most likely to fail.
Since the use of infallible components, or the occurrence of faults are not a consideration for
the level of protection ‘ic’, equipment marked in this way is suitable for use only in zone 2.
Also, it is intended that the level of protection ‘ic’ will replace the energy limited method used
in type ‘n’ equipment, i.e. ‘nL’
Therefore, the addition of a second zener diode, connected in parallel with the first, will
satisfy the requirements of category ‘ib’ intrinsic safety in which safety is assured with one

136. March 2010 ©
8
fault. A third zener diode connected in parallel with the other two will satisfy the conditions
for category ‘ia’ intrinsic safety in which safety is assured with two faults.
Category ‘ib’ intrinsic safety may be used in Zones 1 & 2, but not Zone 0, and category ‘ia’
intrinsic safety is permitted in Zones 0, 1 and 2.
Note 1: A simple test to verify if the fuse of a zener barrier has blown is to disconnect both
the input and output and measure the resistance between the input and output
terminals.
Note 2: Equipment in the hazardous area connected to Associated equipment in the non-
hazardous area must be compatible, e.g. the same group and level of protection.
If, for example, a zener barrier was marked [Ex ib] IIC and the equipment in the
hazardous area marked Ex ia IIC, the level of protection would be reduced to ib.
Minimum Ignition Current Curves
Since it is necessary to limit the voltage and current in an IS circuit to ensure operational
safety, the design of the circuit will be based on the minimum ignition current curves given in
the construction standard and reproduced on page 9. Pages 12 and 13 also illustrate the
curves for determining the maximum circuit inductance and capacitance respectively.
Resistive Circuits
For a purely resistive circuit, if the voltage is known, the maximum circuit current can be
determined from the graph, which enables selection of the correct interface.
Thus, for a purely resistive circuit for operation in a IIC hazard, it is intended that a 28 V,
300 Ω zener barrier will be used. A safety factor of 10% must be applied to the voltage of
this device since a rise in its temperature may raise the triggering voltage of the zener
diodes. Applying the safety factors of 10% (1.1 x 28 V = 30.8 V) produces a value of 30.8 V,
which is then located on the horizontal (voltage) axis of the graph.
Moving vertically from this point towards the IIC curve, and then moving horizontally from the
point of contact with the curve towards the vertical (current) axis, gives a safe current of
140 mA. A safety factor of 1.5 must be applied to this value, i.e. 2/3 of 140mA is equal to
93.33 mA. By applying ohm’s law, 28V/93.33 mA = 300 Ω, the same resistance as the zener
barrier, it has been verified that the 28V, 300 Ω interface is suitable for maintaining the
integrity of the IS circuit in a IIC hazard.

137. March 2010 ©
9
Minimum Ignition Current Curves: Resistive Circuits

138. March 2010 ©
10
Simple Apparatus
The spark energy of an IS circuit, during normal or fault conditions, will be insufficient to
cause ignition of a surrounding hazard. The introduction of a switch, which in normal
operation produces sparks and does not dissipate power, will not alter the situation, and in
fact, any device which is resistive by nature and non-energy storing may, theoretically, be
added to the circuit without jeopardising the integrity of intrinsic safety.
Devices such as these are referred to as simple apparatus and do not need to be certified
or marked. Such passive devices include switches, junction boxes, terminals, potentiometers
and simple semiconductor devices. Simple apparatus may also include sources of stored
energy, for example, capacitors and inductors having well defined parameters, the value of
which must be considered during the design stage of an IS installation. Sources of
generated energy, typically thermocouples and photocells, may also be described as simple
apparatus providing they do not generate more than 1.5 V, 100mA and 25 mW. Any
capacitance or inductance in these devices must also be considered during the design stage
of an installation.
Since simple apparatus is not required to be certified, justification for its use must be
included in the system documentation.
Enclosures
The minimum ingress protection for enclosures if IS circuits is IP20, but environmental
conditions may require a higher rating. As indicated in ‘simple apparatus’ above, enclosures
used as junction boxes are not required to be certified for use in hazardous areas but must
be marked that they contain IS circuits as illustrated below.
Enclosures, however, containing components with, for example, a non-IS input/IS output,
typically a zener barrier, may be installed in a flameproof enclosure for use in an hazardous
area. The marking on such an enclosure would be, for example, Ex d [ia].
Energy Storage
Energy storing devices such as inductors and capacitors have the potential to upset the
security of an IS system. Energy can be stored in these devices over a period of time and
then released in a surge of greater amplitude at, for example, a break in the IS sables due to
a fault or live disconnection at terminals. This could occur regardless of the design
constraints on voltage and current, and cause ignition of a surrounding flammable gas.
Measures must, therefore, be applied to counteract this problem at the design stage. Field
apparatus which have energy storing capability, i.e. they have some internal inductance, are
termed ‘non-simple’ and are required to be certified.
Cables, especially long runs between the interface and the apparatus in the hazardous area,
will have appreciable inductance and capacitance which must be taken into consideration at
the design stage. Energy will be stored under normal operating conditions, but will be greater
under fault conditions. The voltage will influence which parameter is predominant, i.e. for a
voltage of around 5 V, the inductance will be predominant, but at 28V, the capacitance will
be predominant.
THIS ENCLOSURE
CONTAINS IS CIRCUITS

139. March 2010 ©
11
Where simple apparatus only is used in the field, the inductance and capacitance present
will be due to the cables only, and if the cable runs are short these parameters will be
negligible. The electrical parameters Cc, Lc and Lc/Rc for typical instrument cables with
twisted or adjacent cores must be determined by:
a. Obtaining the worst case parameters from the cable manufacturer, or
b. Measurement of the parameters using a sample of the cable, or
c. Adoption of the following values –
Inductance, (L) 1 μH/m
Capacitance, (C) 200 pF/m
Inductance/resistance ratio 30 μ H/Ω
Where field apparatus has both appreciable inductance and capacitance, it is important that
the combined inductance and capacitance of the field apparatus and cables does not
exceed the values specified by the manufacturer of the interface.
Evaluation of Cable Parameters
Inductance
The maximum inductance of the interconnecting cables can be established from the
inductive circuit curves after first of all evaluating the maximum source current. Assuming an
interface with a maximum output of 28 V and 300 Ω resistance, the maximum source current
is:
28 V/ 300 Ω = 93.33 mA
Applying a safety factor of 1.5:
1.5 x 93.33 mA = 140 mA
From the graph on page 13, the maximum safe inductance for the interconnecting cables,
assuming connection to simple apparatus in the hazardous area, is found to be
approximately 4.0 mH. This value is found by projecting vertically form 140 mA on the
current axis, and then horizontally towards the inductance axis form the point of contact on
the IIC curve.
Capacitance
For capacitance circuits, the procedure is exactly the same. A safety factor of 1.5 is applied
to the zener barrier voltage of 28 V.
i.e. 1.5 x 28 V = 42 V
Using the IIC curve in the graph on page 13, the maximum safe capacitance for the
interconnecting cables, assuming that connection is to ‘simple apparatus’ in the hazardous
area, is found to be 0.08 μF approximately.
Comparison of the above values with the data provided by the cable manufacturer will
establish of the interconnecting cable run is satisfactory.

140. March 2010 ©
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Inductive Circuit Curves for Group II

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Capacitive Circuit Curves for Group II

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14
Earthing
A dedicated high-integrity earth is a vital factor in maintaining the security of IS circuits,
particularly when zener barriers are used. Galvanic isolators, however, operate on a
different principle (discussed later in this section) and, therefore, a high-integrity earth is not
required, but earthing may be used for interference suppression.
The earth bars on which zener barriers are mounted are insulated from the surrounding
metalwork and connected directly to the main earth point via separate earthing conductors.
Two cables, each secured at separate points at either end, are normally used to connect the
barrier earth bar to the main earth point to facilitate earth resistance tests which must be
periodically carried out. The resistance between the barrier earth bar and the main earth
point should not be greater than 1 Ω. A value of 0.1 Ω is not unrealistic.
The earth cable must be insulated, and the insulation undamaged, along its entire length so
that contact with the plant metalwork is avoided: Where the risk of damage is high,
mechanical protection for the cables should be provided.
The earth conductors must have a rating capable of carrying the maximum fault current and
have an appropriate cross-sectional area (csa) by means of:
a. At least two separate 1.5mm2
(minimum) copper conductors, or
b. At least one 4mm2
(minimum) copper conductor.
Note: The IS circuit in the hazardous area must be able to withstand a 500V insulation
resistance test to earth.

143. March 2010 ©
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Earthing and Bonding

144. March 2010 ©
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Earthing and Bonding

145. March 2010 ©
17
Galvanic Isolation
Although zener barriers have been, and continue to be, widely used in industry, they have
particular limitations which are:
a. A dedicated high-integrity earth is necessary to divert fault currents away from the
hazardous area.
b. A direct connection exists between the hazardous and safe area circuits and earth,
which tends to apply constraints on the rest of the system.
c. Hazardous area apparatus must withstand a 500 V insulation resistance test to earth.
Devices which overcome these difficulties are isolation interfaces typically relays, opto
isolators and transformers. Since there is no direct connection between the hazardous and
non-hazardous areas when these interfaces are used an IS earth is not required and
earthing of, for example, cable screens may be carried out at the plant/enclosure earth.
Relay/Transformer Isolation
In the example below, isolation between the hazardous and safe areas is achieved by
means of an high integrity component approved transformer and component approved relay.
The design of these devices ensures that high voltage invasion of the IS circuit will be
prevented from reaching the hazardous area apparatus.
Opto-coupler/Transformer Isolation
This method comprises a component certified opto-isolator and a component approved
transformer. Light (or infrared) emitted from the LED when it is forward biased falls onto the
phototransistor which is shielded from external light.

146. March 2010 ©
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Installation of IS Apparatus
The apparatus which make up an IS installation, i.e. field apparatus, associated
apparatus/interfaces, are required to be certified items which have been manufactured in
accordance with relevant standards (see page 3). Such apparatus, including interconnecting
cables, must be installed in accordance with the manufacturer’s instructions, system
documentation and with regard to the recommendations in BS EN60079-14. Existing
installations, however, may have been installed in accordance with the Code of Practice
BS5345.
Installation Requirements for Cables
The conductors of IS cables are required to be insulated with elastomeric or thermoplastic
insulation which has a minimum thickness of 0.3mm. The cables must be capable of
withstanding 500Va.c. or 750Vd.c. test voltages between conductors and earth, conductors
and screens and screens and earth. Alternatively, mineral insulated cable may be used. The
conductors of cables in the hazardous area, and this includes the individual strands of finely
stranded cables, must have a diameter not less than 0.1mm. Separation of the individual
strands of cables must be prevented by, for example, the use of core-end ferrules. Though
not a mandatory requirement, the colour of IS cables (and terminals) is light blue.
Minimum Conductor Sizes
Although the Code of Practice BS5345 has been withdrawn it is still relevant to existing plant
and installations installed in accordance with its recommendations. The following table,
taken from BS5345, specifies the maximum current and minimum cross-sectional area for
copper conductors for temperature classifications within the range T1-T4 so that the cables
may operate within the temperature class established for the IS system when carrying
maximum current during fault conditions.
Maximum Current (A) 1.0 1.65 3.3 5.0 6.6 8.3
Minimum csa (mm2
) 0.017 0.03 0.09 0.19 0.28 0.44
Mechanical Protection
The interconnecting cables of an IS circuit are required to have an overall sheath in order to
maintain the integrity of the system, i.e. to prevent contact with cables of other circuits, or
earth, as a result of damage, and to ensure the circuit parameters in terms of inductance and
capacitance are not exceeded.
Armouring or screening of cables for mechanical protection is not required except for IS
circuits with multi-core cables in Zone 0.

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Segregation of IS and Non-IS Circuits
Segregation of IS and non-IS circuits in both hazardous and non-hazardous areas is
important to avoid the possibility of higher voltages from non-IS circuits invading IS circuits.
This may be achieved by any one of the following methods.
a. Adequate separation between IS circuit cables and non-IS circuit cables, or
b. Positioning of the IS circuit cables such as to guard against the risk of mechanical
damage, or
c. The use of armoured, metal sheathed, or screened cables for either the IS or non-IS
cables.
In addition to the above requirements, cables must not carry the conductors of both IS
circuits and non-IS circuits.
Where IS cables and the cables of other circuits share the same duct, bundle or tray, both
types of circuit must be segregated by means of an insulated or earthed metal partition.
Separation is not necessary of either the IS cables or the cables of the other circuit are
armoured, screened or metal sheathed.
The armouring of cables should be securely bonded to the plant earth.
Unused Cable Cores
Where multi-core cables have one or more unused cores, either of the following termination
methods may be used to maintain the integrity of the installation.
a. Connected to separate terminals at both ends so that the cores are insulated from
one another and earth, or
b. Connected to the same earth point, if applicable, as used by the IS circuits in the
cable, typically a zener barrier earth-bar. The unused cores at the other end of the
cable, however, must be insulated from each other and earth by means of suitable
terminals.
Cable Screens
Where the interconnecting cables of IS circuits have overall screens, or groups of
conductors with individual screens, the screens are required to be earthed at one point
only, as specified in the loop diagram for the installation, which is usually the zener barrier
earth bar. If, however, the IS circuit is isolated from earth, connection of the screen to the
equipotential bonding system should be made at one point only.
The Code of Practice BS5345 specified that, prior to connection of the screens to the barrier
earth bar, an insulation resistance (IR) test should be carried out between each pair of
screens. The test readings should be not less than 1MΩ/km when measured at 500V at
20°C for 1 minute.
Overall screens are required to be insulated from the external metalwork, i.e. cable tray etc.

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Induced Voltage
IS circuits must be installed using methods that avoid external electric or magnetic fields
affecting them. Generally, induced voltage in IS interconnecting cables is not likely but may
occur if the IS cables are placed parallel to and in close proximity to single-core cables
carrying heavy current, or overhead power lines. Adequate segregation between the
different circuits will overcome this difficulty as will the use of screens and/or twisted cores.
Marking of Cables
The sheath or core insulation of IS circuit cables may be coloured light blue in order that they
may be easily identified as part of an IS circuit. Hence, to avoid confusion, light blue cables
must not be used for other types of circuits.
Marking of IS cables is not deemed necessary if either the IS or non-IS cables are armoured,
screened, or metal sheathed.
Where IS circuits and non-IS circuits share the same enclosure, e.g. measuring and control
cabinets, switchgear, distribution apparatus, etc., appropriate measures must be
implemented to distinguish between the two types of circuit, and avoid confusion where a
blue neutral conductor may be present. These measures are:
a. Combining the IS cores in a common light blue harness,
b. Labelling,
c. Clear arrangement and spatial separation.
Multi-core Cables
More than one IS circuit may be run in a multi-core cable, but it is NOT permissible for IS
and non-IS circuits to be run in the same multi-core cable. The conductor insulation must
have adequate radial thickness but not less than 0.2mm and be capable of withstanding an
rms a.c. test voltage equal to twice the nominal voltage of the IS circuit but not less than
500V. For each IS circuit in a multi-core cable the cores are required to be adjacent to one
another for the entire length of a cable. If, however, a cable has, for example, individually
screened pairs, then ideally each circuit should be connected to cores from the same screen
and not to cores within other screens. An exception to this applies where an IS circuit
requires a triple screened cable, i.e. three cores within a screen, but a cable with screened
pairs only is available. This screened pair cable may be used where two adjacent screened
pairs are utilised, with the spare unused core dealt with as specified in ‘Unused cores’ on the
previous page. Connection to earth of this core, if required, should be at the same point as
other earthed cores in the circuit as detailed in the hook-up diagram.

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Test Requirements (multi-core cables)
Multi-core cables must be capable of withstanding the following dielectric tests.
a. 500Vr.m.s (or 750Vd.c.) applied across the cores connected together and the cable
screens and/or armouring connected together.
b. For multi-core cables not having screens for individual circuits, 1000Vr.m.s (or
1500Vd.c.) applied across half the cores which are connected together and the
remaining cores which are also connected together.
The methods used for the above tests are required to be carried out as specified in a
relevant cable standard, but where no method is specified, tests must comply with 10.6 of
IEC 60079-11.
Fault Conditions (multi-core cables)
The type of multi-core cable used in IS installations will have an influence on faults, if any,
which may be taken into consideration.
Type A cable: If the IS circuits are individually screened with a minimum surface area
coverage of 60%, no faults between circuits are taken into consideration.
Type B cable: If the cable is fixed and protected against mechanical damage and none of its
circuits has a maximum voltage greater than 60V, no faults between circuits
are taken into consideration.
Type C cable: For this cable type, but without the requirements specified for Type A and
Type B cables, two short-circuits between conductors and up to four
simultaneous open-circuits of conductors have to be considered. No faults
need be considered if all the circuits in the cable are identical and have a
safety factor of four times that required for categories ‘ia’ or ‘ib’.
Where multi-core cables do not comply with the requirements specified in page 20, the
number of short-circuits between conductors and simultaneous open-circuits of conductors
has no limit.
As previously stated, BS5345 has been withdrawn but is still relevant to existing plant and
installations, and includes the following recommendations for multi-core cables.
Where a multi-core cable, which is located in Zone 0, has more than one IS circuit, it is
essential that no combination of faults between the IS circuits within the cable will cause an
unsafe condition. An exemption to this requirement applies if:
a. The risk of mechanical damage to the cable is minimal or, where the risk of damage
is high, additional protection is provided, and
b. The cables are firmly secured along their length, and
c. Each IS circuit uses adjacent cores in the cable throughout it’s length, and
d. None of the IS circuits can operate during normal or fault conditions at more than
60V peak, or
e. The cores of each IS circuit are within a screen which is insulated and earthed as
previously discussed.

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Clearance Distances
The clearance distance between the bare parts of cable conductors, connected to terminals,
and earth or other conducting parts should not be less than 3mm.
The clearance between the bare parts of cable conductors of separate IS circuits connected
to terminals should not be less than 6mm.
Where IS and non-IS circuits occupy the same enclosure there must be adequate separation
between the two circuit types. This may be achieved by either:
a. 50mm clearance between the IS and non-IS terminals. The terminals and wiring
should be positioned such that contact between the circuits is not likely should a wire
from either circuit become detached.
b. An insulated partition or earth metal partition located between the IS and non-IS
terminals. The partition must reach to within 1.5mm of the enclosure walls, or
maintain at least 50mm creepage between the terminals in all directions around the
partition.
With regard to existing plant or installations, clearance distances may be in accordance with
the Code of Practice BS5345 as detailed in the table below.
Peak Voltage
(V)
Minimum clearance in air between
terminals of separate circuits
(mm)
Minimum clearance in air
between terminals and earth
(mm)
0-90 6 4
90-375 6 6
Test Instruments
IS electrical test instruments are available for testing installations in the presence of
flammable gases. Such instruments will have output parameters not in excess of 1.2V, 0.1A,
25mW and not capable of storing more than 20μJ of energy. It must be remembered,
however, there exists the possibility that the parameters, inductance and capacitance, of the
circuits under test may be large enough to modify the spark energy produced at the test
probes of the instruments and cause ignition of the surrounding flammable gases. Testing in
the presence of flammable gases, therefore, requires careful consideration of the circuits to
be tested.

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BS EN60079-17: Table 2: Inspection Schedule for Ex ’i’ Installations
Grade Inspection
Check That:
Detailed Close Visual
A Apparatus
1 Circuit and/or apparatus documentation is appropriate to area
classification
* * *
2 Apparatus installed is that specified in the documentation – Fixed
apparatus only
* *
3 Circuit and/or apparatus category and group correct * *
4 Apparatus temperature class is correct * *
5 Installation is clearly labelled * *
6 There are no unauthorised modifications *
7 There are no visible unauthorised modifications * *
8 Safety barrier units, replays and other energy limiting devices are of
the approved type, installed in accordance with the certification
requirements and securely earthed where required
* * *
9 Electrical connections are tight *
10 Printed circuit boards are clean and undamaged *
B Installation
1 Cables are installed in accordance with the documentation *
2 Cables screens are earthed in accordance with the documentation *
3 There is no obvious damage to cables * * *
4 Sealing of trunking, ducts, pipes and/or conduits is satisfactory * * *
5 Point-to-point connections are all correct *
6 Earth continuity is satisfactory (e.g. connections are tight and
conductors are of sufficient cross-section)
*
7 Earth connections maintain the integrity of the type of protection * * *
8 The intrinsically safe circuit is isolated from earth or earthed at one
point only (refer to documentation)
*
9 Separation is maintained between intrinsically safe and non-
intrinsically safe circuits in common distribution boxes or relay
cubicles
*
10 As applicable, short-circuit protection of the power supply is in
accordance with the documentation
*
11 Special conditions of use (if applicable) are complied with *
12 Cables not in use are correctly terminated *
C Environment
1 Apparatus is adequately protected against corrosion, weather,
vibration and other adverse factors
* * *
2 No undue accumulation of dust and dirt * * *

152. March 2010
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IS Inspection Record No: A Safe Area Apparatus
Apparatus Location
Cable Connection Drawing No.
Junction Box No.
Instrument Loop Drawing No.
Tag No.
Correctly labelled
No damage
Barrier or Replay or
Safe Area Apparatus
Securely mounted on earth bar
Correctly labelled
Connected to correct unit and
terminals
Cable Cores
Crimped OK and tight in terminal
blocks
No damage
Terminal Blocks
Creepage and clearance OK
Date
Inspectors Initials
Comments

153. March 2010 ©
25
IS Inspection Record B IS Cables
Location
Junction Box No.
Junction Box Connection Drawing No.
Instrument Loop Drawing No.
Cable No.
Segregated from Non-IS Cables
No damage
IS Cables in Hazardous Areas
Properly supported
Date
Inspector’s Initials
Correctly labelled
No damage
IS Cables in Safe Area
Segregated from Non-IS Cables
Cable Screen
Unused Cores
Date
Inspector’s Initials

154. March 2010
26
IS Inspection Record
No:
C
Junction Boxes in Hazardous
Area
Location
Junction Box No.
Junction Box Connection Drawing No.
Instrument Loop Drawing Numbers
Correctly labelled
No damage
Weather sealing OK
Clean and dry inside
Box and Lid
Unused holes plugged
Cable gland Securing cable OK
Correctly labelled
No damage
Screens correctly connected
Cable
No unspecified cables
Correctly labelled
Connected to correct terminals
Cable Cores
Crimped OK and tight in terminal blocks
Terminal blocks No damage
Creepage and clearance OK
Date
Inspector’s Initials
Comments:

155. March 2010 ©
27
IS Inspection Record No: D Hazardous Area Apparatus
Location
Junction Box No.
Junction Box Connection Drawing No.
Instrument Loop Drawing No.
Tag No.
Correctly labelled
Securely mounted
Apparatus
(External)
No damage
Weather sealing OK
Apparatus
(Internal)
Clean and dry inside
Cable Gland
Securing cable OK
Correctly labelled
No damage
Cable
Screen insulated from earth
Correctly labelled
Connected to correct terminals
Cable Cores
Crimped OK and tight in terminal blocks
No damage
Terminal Blocks
Creepage and clearance OK
Date
Inspector’s Initials
Comments:

156. March 2010 ©
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Inspection of IS earth system
IS Inspection Record No:
1 Check that the IS bars are correctly mounted on insulating blocks.
2 Check that the IS earth bars are firmly supported.
3 Check that the IS earth bars are protected against accidental
connection to any non-IS earth (e.g. supporting rack or cubicle).
4 Check that the IS cable bars are labelled ‘IS EARTH’.
5 Check that the IS earth bars are connected together in accordance
with the approved drawing.
6 Check that the cables connecting IS earth bars have the correct
conductor size (refer to drawing) and an insulating sheath which is
undamaged.
7 Check that the cable connections to the IS earth bars are clean and
tight.
8 Check that the main IS earth bar is connected back to the sub-station
or switchroom earth bar in accordance with the approved drawing.
9 Check that the cables (there should be two) connecting the main IS
earth bar to the sub-station or switchroom earth bar have the correct
conductor size (refer to drawing) and an insulating sheath which is
undamaged along its full length and not in contact with unarmoured
cables. These cables should be inspected along their entire route.
10 Check that the cable connections to the main IS earth bar and the
substation or switchroom earth bar are clean and tight.
Date:
Inspector’s Initials
Comments:

157. Unit 8:
Other Methods of Protection
EEx o / Ex o, EEx q / Ex q,
EEx m / Ex m & Ex s

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Objectives:
On completion of this unit, ‘Other Methods of Protection EEx o / Ex o, EEx q / Ex q,
EEx m / Ex m & Ex s’ Apparatus, you should know:
a. The principle of operation of each type of protection.
b. Typical applications for each type of protection.

159. March 2010 ©
3
Other Methods of Protection
Oil-immersion EEx / Ex o
Oil-immersion is not a popular method of explosion protection but is typically used for
heavy duty transformers and switchgear.
Standards
BS EN50 015: 2005 Oil immersion ‘o’
BS 5501-2: 1977 Oil immersion ‘o’
IEC 60079-6: 2007 Oil-immersed apparatus
BS 5345: Part 9 *
Installation and maintenance requirements for
electrical apparatus with type of protection ‘o’
oil-immersed apparatus
* Since BS EN60079-14 and BS EN60079-17 do not provide selection, installation,
inspection and maintenance requirements for oil-immersed apparatus, BS 5345: Part
9 remains the only reference for guidance in these areas for the present.
Definition
The definition for this type of protection is:
‘A type of protection in which the electrical apparatus or parts of the electrical apparatus are
immersed in protective liquid in such a way that an explosive atmosphere, which may be
above the liquid or outside the enclosure, cannot be ignited.’
Breathing
device
Oil-level
indicator
Drain plug
Oil-filling
point

160. March 2010 ©
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EPL: Gb
Zones of Use: 1 & 2
Principle
The oil level is used to completely cover the components within the apparatus which
arc/spark or produce hot surfaces during normal operation, thereby effectively establishing a
barrier between the components below the oil and any flammable gases which may be
present above the oil or outside the enclosure. A particular advantage of this method of
protection is that circulation of the oil, by convection, enables hot-spots to be dispersed.
One function of the oil is to quench arcs occurring at the contacts and, where mineral oil is
used, a by-product of this process is the production of hydrogen and acetylene. This
condition was considered to be undesirable for apparatus intended for use in hazardous
locations, which may explain why, until recently, its use was limited to Zone 2 in the UK. The
revised standards, however, have stricter specifications and this type of protection is now
permitted in Zone 1.
Construction
The construction standard requires a breather to be fitted to the apparatus to allow release
of the flammable gases produced during arc quenching, and thereby preventing the build-up
of these gases in the space above the oil, whilst simultaneously preventing the ingress of
dust or moisture, and hence, contamination of the oil. The enclosure ingress protection will
be IP66.
It is also a requirement that the apparatus is fitted with a gauge which can display the
highest and lowest levels of oil, and that the apparatus is installed in such a way that the
gauge can be easily read while the apparatus is in service. In the event of breakage of the
gauge, even at it’s lowest point, the minimum depth of oil remaining above the arc/heat
producing components, after leakage of oil at this point, should be not less than 25 mm.
The standard specifies unused mineral oil which complies with IEC 60296 for the protective
liquid, but other types may be used, e.g. unused silicone insulating liquids. Silicone liquids
are required to have specific properties, which include:
a) a minimum fire point of 3000
C in accordance with the test method given in HD
565 S1 (IEC 60836);
b) a minimum flash point (closed) 2000
C in accordance with ISO 2719;
c) a maximum kinematic viscosity of 100 cSt at 250
C in accordance with ISO
3104;
d) a minimum electrical breakdown strength of 27 kV in accordance with EN
60156;
e) a minimum volume resistivity of 1014
ohm.cm in accordance with IEC
60247;
f) a pour point maximum of -300
C in accordance with ISO 3016;
g) a maximum neutralisation value of acidity of 0.03mg KOH/g in accordance with
IEC 60588-2 (Note: reference to this standard is for the test method only and
not to permit the use of materials banned by legislation.)
h) causing no degradation to the characteristics of materials it makes contact
with.

161. March 2010 ©
5
Construction (continued)
A label indicating the maximum and minimum levels of the protective liquid must be visible,
which take into account level variations due to expansion/contraction of the protective liquid
over the entire ambient temperature range.
The free surface temperature of the protective liquid is required to be 25 K less than the
specified minimum flashpoint for the protective liquid.
Internal and external fasteners, fluid level indicators and parts for filling and draining the
protective liquid including plugs must have measures applied to prevent them becoming
loose. Such measures include:
a) locking washers;
b) cementing of threads;
c) wiring of bolt heads.
Sealed enclosures are required to be fitted with a pressure-relief device, and non-sealed
enclosures with an expansion device which incorporates a mechanism for automatic tripping
of the electrical supply on detection of gas evolution from the protective liquid as a result of a
fault within the enclosure. The trip mechanism may only be manually reset.

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Powder Filling EEx q / Ex q
The explosion protection concept powder filling is not widely used and typical applications
are, for example, capacitors in Increased Safety Ex ‘edq’ lighting fittings, and
telecommunications equipment in some European countries.
Standards
BS EN60079-5: 2007 Powder filling ‘q’
BS EN50017: 1998 Powder filling ‘q’
BS 5501-4: 1977 Powder filling ‘q’
IEC 60079-5: 2007 Sand-filled apparatus
BS 5345: Part 9 *
Installation and maintenance requirements for
electrical apparatus with type of protection ‘q’
sand filled apparatus
* Since BS EN60079-14 and BS EN60079-17 do not provide selection, installation,
inspection and maintenance requirements for powder-filled apparatus, BS 5345:
Part 9 remains the only reference for guidance in these areas for the present.
Definition
The definition for this type of protection is:
‘A type of protection in which the parts capable of igniting an explosive atmosphere are fixed
in position and completely surrounded by a filling material to prevent the ignition of an
external explosive atmosphere.’
EPL: Gb
Zone of Use: 1 & 2
Source of
ignition , e.g.
(capacitor)
Powder filling

163. March 2010 ©
7
Principle
The filling, which may be quartz or glass particles, achieves safety by what is known as
“suppression of flame propagation”. It is inevitable that a flammable gas or vapour may
permeate the granules and reach the parts producing arcs/sparks or hot surfaces. The
quantity of gas or vapour, however, will be too small to support an explosion within the inert
powder. The depth of granules is influenced by the level and duration of the of the arc
current produced by the components within the filling material, and tests specified in the
construction standard enable a safe correlation between these two parameters to be
established. This method of protection is suitable for use in all group II gases or vapours.
Construction
The minimum ingress protection for this type of protection is IP54, but apparatus constructed
to provide IP55 must be fitted with a breathing device. Where use is in clean, dry
environments only, the ingress protection must be at least IP43, which requires the
apparatus to be marked with the suffix ‘X’.
The size of granules for the filling material must be in accordance with the sieve limits
specified in the standard ISO 565. The upper limit for the granules may be achieved using a
sieve manufactured from metal wire cloth or a perforated metal plate with a nominal
perforation size of 1 mm. For the lower limit, metal wire cloth with a nominal perforation size
0.5 mm may be used. The filling material is required to withstand an electric strength test
where the leakage current must not be in excess of 10-6
A.
The minimum clearance distances between electrically conducting parts and insulated
components or the inner surface of the enclosure wall are given below.
Operating voltage U
a.c. r.m.s or d.c.
Minimum distance
mm
U < 275 5
275 < U < 420 6
420 < U < 550 8
550 < U < 750 10
750 < U < 1000 14
1000 < U < 3000 36
3000 < U < 6000 60
6000 < U < 10000 100
Components having a free volume less than 3 cm3
, for example relays, which are
surrounded by the filling material, must have minimum clearance distances between the
component and the inner wall of the enclosure in accordance with the table above. For free
volumes in the range 3 cm3
- 30 cm3
the above distances apply but should not be less than
15 mm.

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8
Encapsulation EEx / Ex m
The method of protection, encapsulation, is used mainly for smaller items of equipment
such as solenoid coils and electronic components.
Standards
BS EN60079-18: 2004 Encapsulation ‘m’
EN50 028: 1987 Encapsulation ‘m’
BS 5501-8: 1987 Encapsulation ‘m’
IEC 60079-18: 2009 Encapsulated apparatus
Definition
The definition for this type of protection is:
‘A type of protection whereby parts that are capable of igniting an explosive atmosphere by
either sparking or heating are enclosed in a compound in such a way that the explosive
atmosphere cannot be ignited under operating or installation conditions.’

165. March 2010 ©
9
Levels of protection:
ma Encapsulated apparatus having a level of protection ‘ma’ must not be capable of
causing ignition during the following situations:
i) in normal operation and installation conditions;
ii) any specified abnormal conditions;
iii) in defined failure conditions.
mb Encapsulated apparatus having a level of protection ‘mb’ must not be capable of
causing ignition during the following situations:
i) in normal operation and installation conditions;
ii) in defined failure conditions.
mc No information at time of writing.
EPL’s: ma - Ga
mb - Gb
mc - Gc
Zone of Use: ma 0, 1 & 2
mb 1 & 2
mc 2
Principle
With this type of protection, the encapsulant, typically a thermosetting, thermoplastic, epoxy
resin or elastomeric material, establishes a complete barrier between any surrounding
flammable gas or vapour and the source of ignition within the compound.
Construction
The construction standards state that the encapsulant must be free of voids and, therefore,
this method of protection is unsuitable where components have exposed moving parts. Very
small components which have enclosed moving parts, e.g. a reed relay, may be protected by
encapsulation.
Encapsulated apparatus may be manufactured with one of two protection levels, i.e. ‘ma’ or
‘mb’. Switching contacts, however, are not permitted in protection level ‘ma’. Encapsulation
with the level of protection ‘ma’ must not have an operating voltage in excess of 1 kV and be
incapable of causing ignition during:
a) normal operation and installation conditions;
b) any specified abnormal conditions;
c) defined failure conditions.

166. March 2010 ©
10
Encapsulation with the level of protection ‘mb’ must be incapable of causing ignition during:
a) normal operation and installation conditions;
b) defined failure conditions.
The encapsulant must be capable of remaining intact during electrical input variations in the
range 90% - 110% of the specified rating, adverse load conditions and any internal electrical
fault. The apparatus is required to remain safe with one internal fault for the level of
protection ’mb’ and two faults for the level of protection ‘ma’. This applies to a short-circuit
occurring in any component, failure of any component, or a fault in the printed circuit boards.
Minimum clearance distances within the encapsulant will be dependent on the construction
of the apparatus, i.e. within a metallic enclosure which is either closed or unclosed on all
sides, or has 100% free surface area. As these requirements are extensive, the table below
shows some of the applicable distances for apparatus with 100% free surface area.
Protection level
ma mb
Free surface < 2 cm3 > 1 mm *
> 3 mm
Free surface > 2 cm3 > 3 mm *
* The depth of encapsulant will also be influenced by the rated
voltage as given in Table 1 of the standard.

167. March 2010 ©
11
Special Protection Ex s
Apparatus which has not quite met the requirements of a particular construction standard will
have been additionally certified under the BASEEFA Standard ‘Special Protection Ex s’
provided it had been established that, after close scrutiny of the design and testing of the
apparatus, it was capable of operating safely in the hazard for which it was designed.
Special Protection is not included in the BS EN500 or BS EN600 series of harmonised
construction standards, or in the installation, inspection and maintenance series of
standards, BS EN60079-14 and BS EN60079- 17 respectively.
Standards
SFA 3009 Special protection
BS 5345: Part 8
Installation and maintenance requirements for
electrical apparatus with type of protection ‘s’
special protection
Zones of Use: 0, 1 & 2
Principle
The constructional requirements of this standard, in terms of test and acceptance criteria,
were intended to be unspecific in order to allow a broad range of designs to be considered
for certification. Because apparatus may be of unorthodox design, the experience of test-
house staff plays an important part in contriving appropriate tests and acceptance criteria.
Special protection is not an easy option for obtaining certification for apparatus not quite
meeting the requirements of a given standard, nor is this type of protection inferior to other
more popular methods of explosion protection. Indeed the tests on apparatus presented for
certification under Special Protection are likely to be more onerous than the tests for other
types of explosion protection.
A hand torch is a typical example of apparatus certified under Special Protection. Thorough
testing will have established that the construction is robust enough to withstand a specified
impact without causing, for example, a short-circuit of the battery, and breakage of the bulb,
its holder and the glass cover are unlikely.
A further requirement is that opening of the torch, i.e. to replace the battery, is only possible
with the aid of a special tool, which is required to be kept in a non-hazardous area.
Another known example of apparatus certified under Special Protection Ex s is a 6.6 kV
poly-phase cage induction pump motor in which the method of explosion protection is
basically dependent on the interior of the motor being completely filled with water. Any free
space within the motor is occupied by water, and hence, the entry of a flammable gas is
prevented. Clearly, it is imperative that the interior of the motor remains completely full of
water at all times, and this is ensured by a header tank to compensate for expansion due to
thermo-cycling. The motor, which drives a pump, is intended for use in Zone 1.

168. Unit 9:
Combined (Hybrid) Methods
of Protection

169. March 2010 ©
2
Objectives:
On completion of this unit, ‘Combined (Hybrid) Methods of Protection’, you should
know:
a. The advantages of combining two or more methods of protection in apparatus.
b. The installation requirements according to BS EN 60079-14.
c. The inspection requirements according to BS EN 60079-17.

170. March 2010 ©
3
Combined (Hybrid) Methods of Protection
Electrical equipment may be manufactured with more than one method of explosion
protection. Equipment of this type has combined methods of protection but may also be
known as a hybrid. Such an approach combines the best features of each type of protection
into one piece of equipment for both economic and practical purposes.
A traditional push-button station for use in an hazardous location comprises a flameproof
EEx d or Ex d enclosure, in which a standard industrial switch is fitted. An alternative to this
arrangement is an Increased Safety EEx e or Ex e enclosure with a small flameproof EEx d
or Ex d component certified switch fitted inside. Because the switch produces sparks in
normal operation, clearly it has to be flameproof to comply with the Increased Safety concept
of protection. Such equipment will be marked EEx ed, Ex ed, EEx de or Ex de.
The advantages of the hybrid arrangement over the traditional flameproof method are:
a. Lower cost and weight,
b. Glanding arrangements are simplified,
c. Minimum ingress protection IP54 but may be as high as IP66
Ignition by sparking
components contained within
flameproof enclosure
EEx d
Ignition by sparking contacts
contained within the ‘small
volume’ EEx d or Ex d switch
EEx e / Ex e
l

171. March 2010 ©
4
Standards
Hybrid apparatus may be constructed using any combination of the various methods of
explosion protection and, therefore, the apparatus will be marked with the symbolic letters
and construction standard numbers relative to the types of explosion protection used.
Probably the most commonly used combination involves ‘d’ and ‘e’ types of apparatus, and
so the table below shows these standards only. The full list of standards can be found in Unit
2. Hybrid apparatus must also be installed and maintained in accordance with relevant
standards.
BS EN60079-1: 2007 Flameproof enclosures ‘d’
BS EN50 018: 2000 Flameproof enclosure ‘d’
BS 5501-5: 1977 Flameproof enclosure ‘d’
BS EN60079-7: 2007 Increased safety enclosure ‘e’
BS EN50 019: 2000 Increased safety enclosure ‘e’
BS 5501-6: 1977 Increased safety enclosure ‘e’
BS EN60079-14: 2008 Electrical apparatus for explosive gas
atmospheres: Part 14. Electrical installations in
hazardous areas (other than mines)
BS EN60079-17: 2007 Electrical apparatus for explosive gas
atmospheres: Part 17. Inspection and
maintenance of electrical installations in
hazardous areas (other than mines)
Motors – EEx de / Ex de

172. March 2010 ©
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Motors – EEx de / Ex de
Manufacturers also produce electric motors in which there are combined methods of
protection. The main body of the motor will be flameproof EEx d or Ex d and the terminal box
increased safety EEx e or Ex e. An alternative terminal plate is fitted to a motor of this type
to accommodate special terminals which are screwed into the terminal plate. These are
hybrid terminals, i.e. they employ both flameproof and increased safety features in their
construction.
EEx de / Ex de Motor Terminal Box
To achieve the required level of ingress protection, gaskets are fitted between the terminal
box and its cover, between the terminal plate and box, and between the gland plate and
terminal box. On no account, however, should a gasket be fitted between the terminal plate
and the frame of the motor as this joint is a flamepath.
It must be emphasised that, on some motors, the increased safety terminal box looks very
much like a flameproof box in terms of its construction. This likeness means that there is a
possibility that personnel unaware of this concept may remove the gaskets and, therefore, it
is important that certification labels are studied before any work is carried out. Removal of
the gaskets in an attempt to return the box to its assumed status, i.e. flameproof, would be
an unauthorised modification which would invalidate the certification.
Cable gland selection
As already mentioned in unit 4, the requirements for cable glands entering Ex e equipment,
and in this instance the Ex e terminal box of a type de motor, as specified in BS EN60079-
14: 2003, states that cable glands must maintain the type of protection and ingress
1. Terminal box cover and
screws
2. Gasket
3. Certified cable glands
4. Gland plate
5. Increased Safety
terminals
6. Terminal plate
7. Terminal box and screws

173. March 2010 ©
6
protection of the equipment, and meet the impact test requirements. The inference here
would appear to suggest that provided uncertified cable glands were manufactured to
BS6121 their use would be acceptable with Ex e equipment. This of course does not apply
to uncertified plastic cable glands.
The introduction of the latest standards, however, has effectively removed this option by
virtue of the requirement for revised ‘seal aging’ tests involving repeated heating and cooling
cycles, which is now a requirement for all cable glands as detailed in IEC 60079-0 The
latest issue of IEC 60079-14: 2007 now requires all cable glands to be certified or approved
by the manufacturer.
EEx de – Sample Certification Label – ( pre ATEX )
Ex de – Sample Certification Label – ( ATEX )
II 2 G
Ex de IIB T4
Duty S1 No. E956732
Ins. cl F IP55
V Hz kW r/m cosφ
440 60 37 1760 0.8
LCIE 07ATEX599X
0081
IEC 60034-1

174. March 2010 ©
7
Lighting Fittings – EEx edq / Ex edq
The lighting fitting illustrated below employs three protection concepts, i.e. increased safety
type ‘e’, flameproof type ‘d’ and powder filing type ’q’. This type of fitting is widely used in the
petro-chemical industry.
The constructional features are:
1. Flameproof mono-pin lamp holder’s;
2. Increased safety choke designed not to overheat if the lamp fails;
3. Temperature rating based on internal and external surface temperatures;
4. Enclosure sealing providing high ingress protection;
5. Increased safety enclosure including glands designed to withstand specified impact.
In this lighting fitting, the circuits include capacitors which are protected by a method of
protection, powder filling type ‘q’. Switches will be flameproof type ‘d’ construction and
terminals will be increased safety type ‘e’.
Lamps for Ex e, (and also Ex n), luminaries, which have mono-pin, bi-pin or screw
connections where the caps are made from non-conductive material with a conductive
coating, are not permitted unless tested with the equipment.

175. March 2010 ©
8
EEx e m ib / Ex e m ib
An enclosure may have an encapsulated component inside. A typical example is a
telephone for use in an hazardous location. The casing of the telephone would use
increased safety type ‘e’ protection, most of the internal circuits would be intrinsically safe,
type ‘i’, but part of the circuitry would operate at a higher voltage and therefore encapsulation
type ‘m’ would be used to protect that part of the circuit. Terminals would be increased safety
type ‘e’.
EEx e enclosure

176. March 2010 ©
9
EEx pde / Ex pde
Enclosures using the protection concept, pressurisation type ‘p’, may have internal
apparatus which have to remain energised in the absence of overpressure. Such apparatus
must be protected in accordance with the Zone in which the enclosure is located. A typical
example is an anti-condensation heater within a pressurised machine which will be
energised when the machine is idle.
Apparatus out with the machine, e.g. junction boxes, pressure sensors etc., will also have to
be protected in accordance with the Zone.
Note: Since anti-condensation heaters are normally ‘live’ when a machine is idle, a notice
warning of this danger should be displayed.
EEx pi / Ex pi
The part(s) of an IS system which are marked to indicate that they should be installed in a
non-hazardous area may be used in a hazardous area if installed in, for example, a
pressurised enclosure as illustrated below.

177. Unit 10:
Wiring Systems

178. March 2010 ©
2
Objectives:
On completion of this unit, ‘Wiring systems’, you should know:
a. Appropriate cable types for use with explosion protected apparatus.
b. The selection procedure for cable glands by consideration of ‘Zone’, ‘Gas Group’,
‘volume’, ‘method of entry’, ‘cable construction’ and’ ‘internal components’ of
flameproof enclosures.
c. The correct assembly techniques for various types of cable glands.
d. Recognised practices for terminating single and multiple pair cables with or without
screens.
e. Recognised practices for maintaining ingress protection, earth continuity and
termination of unused conductor cores and screens.
f. Earthing requirements in hazardous areas.
g. The installation requirements according to BS EN 60079-14.
h. The knowledge and skills requirements for technicians (operatives) undertaking the
selection and erection of explosion protected equipment in hazardous areas.

179. March 2010 ©
3
Wiring Systems
Electrical equipment in hazardous areas may be wired using cable having metallic or non-
metallic sheath, or conduit. The use of cable is generally predominant mainly for it’s ease of
installation compared to conduit.
With regard to conduit, one of it’s disadvantages, particularly on offshore installations, is it’s
susceptibility to corrosion as a result of exposure to a salt-laden atmosphere. Deterioration
due to corrosion can occur relatively quickly and, as a consequence, can reduce the strength
of the conduit. This is undesirable particularly where conduit is the method of entry to a
flameproof enclosure because of the possible inability of the conduit to contain an internal
explosion in the run of conduit between the enclosure and the sealing device. Furthermore,
corroded conduit may not meet the impact resistance requirements essential for use with
Increased Safety apparatus.
Standards
BS EN60079-14: 2008 Electrical apparatus for explosive gas
atmospheres - Part 14: Electrical installations
in hazardous areas (other than mines).
IEC 60079-14: 2007 Explosive atmospheres - Part 14: Electrical
installations design, selection and erection
BS EN50262: 1999 Metric cable glands for electrical installations
BS 6121-5: 2005 Mechanical cable glands. Code of practice
for selection, installation and inspection of
cable glands and armour glands.
BS 5345 (withdrawn) Code of practice for the selection, installation
and maintenance of electrical apparatus for
use in potentially explosive atmospheres.

180. March 2010 ©
4
Cables
Cables for use in hazardous areas are not certified but are required to be constructed from
materials as specified in BS EN60079-14 and constructed to relevant standards so that,
providing the cable has been correctly installed, failure is unlikely. A typical standard for the
manufacture of cables for marine, offshore mobile and fixed platforms is BS 6883.
The selection of cables is important with regard to their performance in a fire and important
considerations include fire survival, fire resistance, fire retardancy, fire propagation, toxicity
and smoke emission. Thus, in circuits essential for safety the cables installed are required
to operate in a fire for a specified time.
Cables may also be manufactured from materials, typically polymer compounds that produce
lower smoke and fume emissions during a fire. Cables with this capability will be identified
as halogen free, low smoke & fume (LSF), low smoke zero halogen (LSZH), or zero
halogen low smoke (ZHLS).
Fixed apparatus in zones 1 and 2
Cables for fixed apparatus in hazardous areas are required to be manufactured from
thermoplastic, thermosetting, elastomeric or mineral insulating materials. The cables should
be suitable for the ambient conditions where used, be circular, compact, have extruded
bedding and any fillers should be non-hygroscopic. Cables commonly used in the industry
are of the EPR/CSP type (see diagrams on page 5). Mineral insulated metal sheathed
(MIMS) cable is also suitable for use in hazardous areas, but it’s aluminium variation
requires careful consideration before use.
Aluminium conductors, except those for IS or energy-limited installations, must only be
connected to suitable terminals and have a cross-sectional area (c.s.a.) not less than
16 mm2
. Examples of the various cable insulation types are given in the table below.
chlorosulphonated polyethylene CSP
cross-linked polyethylene XLPE
ethylene propylene rubber EPR
ethylene vinyl acetate EVA
natural rubber NR
polychloroprene PCP
Elastomeric
silicone rubber SR
polyethylene PE
polypropoline PP
Thermoplastic
polyvinyl chloride PVC
Portable and transportable apparatus in zones 1 and 2
Portable and transportable electrical apparatus may be wired using cables having a heavy
polychloroprene or alternative equivalent synthetic elastomeric sheath, or a heavy tough

181. March 2010 ©
5
rubber sheath, or manufactured from materials providing equally robust construction. The
minimum cross-sectional area for such cables is 1.0mm2
.
Where the voltage to earth and current of portable electrical apparatus does not exceed
250V and 6A respectively, cables having an ordinary polychloroprene or alternative
equivalent synthetic elastomeric sheath, or a heavy tough rubber sheath, or manufactured
from materials providing equally robust construction may be used.
The sheath of flexible cables may be manufactured from ordinary tough rubber, ordinary
polychloroprene, heavy tough rubber, heavy polychloroprene, or plastics providing the
equivalent strength to heavy tough rubber.
Elastomeric Cables
Elastomeric cables comprising EPR insulated conductors, CSP inner and outer sheath,
which are heat and oil resistant and flame retardant (HOFR). Operating temperature range
30 °C - 90 °C.
Cable specified as ‘low smoke and fume’ (LSF) has insulation which does not contain
halogens, so that smoke and acid emission are minimised in the event of a fire.

182. March 2010 ©
6
Cables (continued)
Cables may also be selected with consideration to their fire resistant and/or flame
retardant properties, and two standards are relevant in this respect.
IEC 60331 (Fire resistant): A cable manufactured in compliance with this standard will
continue to operate in a fire without disruption of essential
circuits and emergency circuits.
IEC 60332 (Flame retardant): A cable manufactured in compliance with this standard is
self-extinguishing and will not propagate the fire.
Cold Flow
Certain materials used in the manufacture of cables are susceptible to a condition commonly
known as ‘cold flow’, which could have a detrimental effect on the type of explosion
protection concerned. This condition can occur at ambient temperature, and the use of cable
entry devices which have compression seals should be avoided since the part of the cable
acted on by the seal can “flow” away from the pressure of the seal resulting in an ineffective
seal. Recent developments by cable gland manufacturers have resulted in new designs of
cable glands which can reduce, if not eliminate, the effects of ‘cold flow’ by the use of seals
which apply less pressure on the cable insulation but still maintain the integrity of the type of
explosion protection in apparatus.
Jointing of Cables
In hazardous areas, cable runs should, ideally, be continuous and without interruption where
possible. Joints may only be made using appropriate methods, for example, in an enclosure
having a type of explosion protection suitable for the Zone, or by epoxy or compound filled
devices, or heat shrink sleeving in accordance with the manufacturers instructions.
Whichever method is used, the joints must be mechanically, electrically and environmentally
appropriate. Conductor connections are required to be made by any of the following
methods: compression connectors, secured screw connectors, welding or brazing. Soldering
is permissible if the conductors being connected are held together by suitable mechanical
means and then soldered.
Termination of conductors
The cores of cables with multi-stranded conductors, especially those with fine strands, are
required to be installed in a manner which ensures all the strands are terminated, i.e. no
separation. This may be achieved by; cable lugs, or; core end sleeves (bootlace ferrules),
or; the type of terminal. Soldering alone, however, is not permitted. Whichever method is
used it is important that creepage / clearance distances are maintained in accordance with
the type of protection and the manufacturer’s installation instructions.
Unused cable cores
In the hazardous area, unused cable cores may either be connected to earth or insulated
from earth by means of terminals appropriate to the type of protection. Insulating tape alone
must not be used for this purpose.

183. March 2010 ©
7
Requirements for Cables and Glands
Cable glands must be selected with due regard to the methods of explosion protection
employed and also environmental conditions. The requirements for cable glands include:
(a) to firmly secure the cable entering the apparatus;
(b) to maintain the ingress protection of the apparatus;
(c) to maintain earth continuity between the apparatus and any armouring in the
cable;
(d) to ensure containment of an internal explosion in flameproof apparatus;
(e) to maintain the integrity of ‘restricted breathing’ apparatus.
Glands for Mineral Insulated Cables
Cable glands for use with MICC (Mineral Insulated Copper Cable) or MIMS (Mineral
Insulated Metal Sheath) cable for use in hazardous areas will be marked Ex d. This gland,
however, may be used as a means of entry to Increased Safety apparatus providing an
alternative Ex e seal is used. This seal is specially constructed to comply with the
requirements for Increased Safety apparatus as illustrated by the diagrams below.
Seal Assemblies
It will be observed from the Ex e seal assembly illustrated in the lower diagram that the
‘headed PTFE sleeving’ passes through the holes in the stub cap. This arrangement
ensures that creepage/clearance distances are maintained within the seal.
The compound used within the Ex e seal assembly was previously required to be
doublebond non-metallic black epoxy putty 1536, with the Component Certificate for this
seal containing a ‘schedule for conditions of use’. Current specifications, however, allow use
of the same compound for both Ex d and Ex e applications.
Difficulty may be experienced in achieving the desired level of ingress protection with
MICC/MIMS cable glands due to the very small shoulder on the gland body, and may be
overcome by the use of hard plastic washers manufactured for this purpose.
Ex d type seal
Ex e type seal

184. March 2010 ©
8
Selection of Cable Glands
The correct selection of cables and glands, particularly for flameproof apparatus, is very
important since there are a number of factors which can jeopardise the integrity of this type
apparatus. As previously discussed the cable construction, ingress protection, earth
continuity and secureness of the cable entering the apparatus must be maintained. An
additional consideration is electrolytic action caused by contact between dissimilar metals,
which results in increased corrosion and premature degradation of glands and cable entries.
Cable glands with a suffix ‘X’ in the certificate number may only be used in fixed installations
and not on portable or transportable equipment. The ‘special installation conditions’
specified in the certificate for the cable gland may require that a clamp is fitted within 300mm
from the end of the gland to avoid twisting or pulling of the cable and hence unnecessary
stress on the terminals inside the equipment.
For portable and transportable equipment cable glands without the suffix ‘X’ should be used.
Flameproof equipment
Since an explosion is permitted within flameproof equipment it follows that the cable glands
used must be capable of maintaining the integrity of the equipment. Such glands will be
capable of resisting the force of an internal explosion by virtue of their strong construction,
flamepaths where applicable and also compression, diaphragm, or compound filled seals.
The type of cable gland used will be selected from consideration of the six points listed
below which take into consideration the strength of an internal explosion.
1. Does the cable have filled interstices?
2. Is the enclosure direct or indirect entry?
3. Does the enclosure contain a source of ignition?
4. What is the gas group of the apparatus?
5. In what zone is the apparatus is installed?
6. What is the internal volume of the enclosure?
These considerations are addressed in the flowchart on page 10.
Note: The standard specifying the constructional requirements for cable glands, BS6121,
now replaced by BS EN50262, uses certain references numbers to identify their
function. For example, a cable gland for use with unarmoured cable is allocated the
reference ‘A2’. The reference ‘E1’ is used to identify a cable gland for use with
armoured cable. Wire armour will be identified by a ‘W’ and ‘F’ indicates flameproof.
So the reference for a flameproof gland for use with wire-armoured cable will be
E1FW.

185. March 2010 ©
9
Direct Entry Method (Flameproof Ex d)
a) Flameproof Ex d / EEx d
Indirect Entry Methods
b. Flameproof EEx d / Ex d c. Flameproof I Increased Safety EEx de / Ex de

186. March 2010 ©
10
Maintaining Ingress Protection at Cable Gland Entries
The cable gland selected, as the means of entry to an enclosure, must suit the cable used
and, for type ‘e’ or type ‘n’ enclosures, where the ingress protection will be at least IP54 or
greater, the cable gland must maintain the ingress protection of the enclosure. Where such
enclosures have unthreaded entries IP sealing washers will be necessary. Where
enclosures have threaded entries the requirement for an IP sealing washer will depend on
the wall thickness in order to maintain a minimum of IP54. If the wall thickness is less than
6mm, an IP sealing washer (or thread sealant) is necessary to maintain IP54, but if the wall
thickness is 6mm or greater an IP washer (or thread sealant) is deemed not necessary to
maintain IP54 unless a greater ingress protection level is required.
For flameproof enclosures, a sealing washer may be fitted between the cable gland and the
wall of the enclosure to improve the ingress protection providing the thread engagement is
maintained, i.e. five full threads or 8mm, whichever gives the greater engagement.
Cable Gland Selection for Flameproof Apparatus
Cable glands for use with flameproof enclosures may be selected by following the procedure
recommended in BS EN60079-14 as detailed below.
The method of entry must be in compliance with one of the following:
(a) A cable entry device, which meets the requirements of IEC 60079-1, certified as part
of the flameproof enclosure when tested with a section of the cable intended to be
used.
(b) A flameproof cable entry device in which a sealing ring is an integral part of the
construction and used with cables manufactured from thermoplastic, thermoseting or
elastomeric materials. The cable must be compact and circular, have extruded
bedding and have non-hygroscopic fillers in the case of a filled cable. Selection of
the cable entry device to be in accordance with the flow chart illustrated on page 11.
(c) Mineral insulated cable and a suitable flameproof cable entry device.
(d) Flameproof stopping box or sealing chamber, which are either specified in the
apparatus certification document or have component approval, having cable entry
devices suitable for the cables intended for use. The compound or seals in these
devices are required to provide sealing around the individual cable cores. The
stopping box or sealing chamber must be fitted to the apparatus at the cable entry.
(e) Flameproof entry devices, typically barrier glands, with compound filled seals or
similar arrangements which seal around the individual cores of the cable;
(f) Alternative methods designed to maintain the integrity of the flameproof apparatus.

187. March 2010 ©
11
Cable gland selection for flameproof apparatus (continued)
The flowchart below, taken from BS EN60079-14, may be used to determine the most
suitable type of cable gland for entry to flameproof apparatus.
Application of 10.4.2 requires the use of either a flameproof compound filled sealing device
in which the compound provides ‘stopping’ around the individual cores of the cable, or a
flameproof gland where ‘stopping’ around the individual cores of the cable is achieved by
either compound or elastomeric seals.
Start
Does this
enclosure
contain an
internal
source of
ignition?
Does the
hazardous
gas require
IIC
apparatus?
Is the area
of
installation
Zone 1?
Use a suitable
cable entry
device with a
sealing ring
Is the
volume of
the
enclosure
greater than
2 dm
3
?
Apply
10.4.2
(d) or (e)
Ye
Yes
Yes
Yes
No
No
No

188. March 2010 ©
12
Cable glands
Hawke 501/453/Universal gland: EEx d IIC / EEx e II
The gland illustrated below, as previously explained, may be used with cables susceptible to
‘cold flow’ to avoid indentations in the cable insulation due to the force of compression seals
when other cable gland types are used.
The cable gland selection table below represents part of the data available for this type of
cable gland. Refer to the Hawke catalogue for the complete specification for this cable
gland.

189. March 2010 ©
13
Assembly of gland
Hawke 501/453/Universal gland: EEx d IIC / EEx e II

190. March 2010 ©
14
Assembly of gland (continued)
Hawke 501/453/Universal gland: EEx d IIC / EEx e II

191. March 2010 ©
15
Cable glands
Hawke ICG 653 Universal Barrier gland: EEx d IIC / EEx e II
The compound filled barrier seal in the cable gland illustrated below prevents the effects of
an internal explosion from reaching the cable. Generally, barrier glands are required for
direct entry enclosures where the connecting cables are not circular, compact/filled, or where
an enclosure is located in a IIC area and contains a source of ignition, or where an enclosure
has an internal volume greater than 2 litres, contains a source of ignition and is located in a
Zone 1, IIA or IIB area.
As previously, the cable gland selection table below represents part of the data available for
this type of cable gland. Refer to the Hawke catalogue for the complete specification for this
cable gland.

192. March 2010 ©
16
Assembly of gland
Hawke ICG 653 Universal Barrier gland: EEx d IIC / EEx e II

193. March 2010 ©
17
Assembly of gland (continued)
Hawke ICG 653 Universal Barrier gland: EEx d IIC / EEx e II

194. March 2010 ©
18
Assembly of gland (continued)
Hawke ICG 653 Universal Barrier gland: EEx d IIC / EEx e II

195. March 2010 ©
19
Assembly of gland (continued)
Hawke ICG 653 Universal Barrier gland: EEx d IIC / EEx e II

196. March 2010 ©
20
Conduit
The use of conduit in hazardous areas requires particular care, especially when used with
flameproof enclosures. In addition to maintaining the ingress protection (IP) rating of an
enclosure - this applies to all types of protection - the integrity of the enclosure must be
maintained, i.e. the conduit in the run between the enclosure wall and the conduit sealing
device must also be able to withstand the force of an explosion within the enclosure so that
the flames/hot gases are prevented from reaching the external atmosphere. Where two
flameproof enclosures are connected by means of conduit, seals must be fitted to avoid
pressure piling occurring during an internal explosion.
Sealing devices are also used to prevent the migration of gases from one hazardous location
to another. Although not entirely gas-tight, they will limit, to an acceptable level, the quantity
of gas which will pass at normal atmospheric pressure. Where positive or negative
pressures are likely, appropriate measures must be implemented.
Appropriate installation practices must, therefore, be observed and this requires observation
of the manufacturer’s installation specification and the recommendations given in BS
EN60079-14.
Selection of conduit
Conduit used with explosion protected apparatus will be that recommended by the
manufacturer and selected from either:
(a) screwed, heavy gauge steel, solid drawn or seam welded conduit; or
(b) flexible conduit of metal or composite material construction, for example metal
conduit with a plastic or elastomer jacket, of heavy or very heavy mechanical
strength classification manufactured in accordance with ISO 10807.
Note: The current issue of BS EN60079-14: 2003, in contrast to the 1997 issue,
specifies that conduits as detailed above manufactured to IEC 60614-2-1 and
IEC 60614-2-5 are unsuitable for protecting cables connected to flameproof
apparatus. Reference to national or other standards should be sought in this
instance.
Conduit entering flameproof enclosures is required to be engaged by 5 full threads.
Sealing of conduit
Stopper boxes must be fitted where conduit leaves or enters an hazardous area.
Where conduit is used with flameproof enclosures containing a source of ignition, stopping
boxes are required to be fitted as close to the enclosure wall as possible, or not more than
50mm from the enclosure wall to limit pressure piling. Alternatively, the manufacturer may fit
a stopping box in the enclosure as part of the certified design of the enclosure

197. March 2010 ©
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General installation requirements
The installation of equipment in hazardous areas may involve the use of metallic mounting
brackets, cable tray, weather protection etc. It is important that the light metal content of
such items does not exceed the following limits relative to the EPL requirements for different
locations. If the light metal content exceeds the limits specified, frictional sparking can
become stronger.
EPL Ga locations
Total content of aluminium, magnesium, titanium and zirconium - 10%, or
Total content of magnesium, titanium and zirconium - 7.5%
EPL Gb locations
Total content of magnesium and titanium - 7.5%
EPL Gc locations
No limitations.
Static electricity
The use of non-metallic installation materials, such as plastic covered cable tray, plastic
mounting brackets and plastic weather protection, can create an unacceptable level of static
electricity if measures are not implemented to control this. Static electricity is more than
capable of igniting flammable gases/vapours and therefore has to be controlled
The initial approach to the control of static electricity is the selection of material having an
insulation resistance not exceeding 1 GΩ. Alternatively, the surface area of non-metallic
parts may be limited in accordance with the table below, the surface area limit being
dependent on the EPL requirement for the location.
Maximum surface area mm2
Location EPL requirement IIA location IIB location IIC location
Ga 5000 2500 400
Gb 10000 10000 2000
Gc 10000 10000 2000
The dimensions in the above table may be increased by a multiple of 4 if the non-metallic
material is surrounded by a conductive earthed frame.

198. March 2010 ©
22
The knowledge and skills of technicians (operatives)
Selection and erection
Technicians, or operatives as they are called in the standard, are required to have sufficient
knowledge to achieve the correct selection and erection of explosion protected equipment in
hazardous areas. This knowledge, which includes the basic requirements for safe work in
hazardous areas, also includes:
(a) an understanding of the general principles of explosion protection;
(b) an understanding of the general principles of the various types of explosion
protection and their marking;
(c) an understanding of the design features of the different types of explosion
protected equipment upon which their safe operation is dependent;
(d) an understanding of the content of equipment certificates, including the
information for correct installation, and the related sections of BS EN60079-14.
(e) a broad understanding of the inspection and maintenance requirements of the
different methods of explosion protection as given in BS EN60079-17.
(f) familiarity with the particular techniques to be used for the selection and erection
of equipment as given in BS EN60079-14;
(g) an understanding of the additional importance of permit-to-work systems and
safe isolation for safe work on explosion protected equipment.
Competency
Furthermore technicians (operatives) are required to provide evidence of their competency in
the areas specified immediately above. In addition, documentary evidence of competency in
respect of the following:
(a) the use and availability of documentation;
(b) the compilation of job reports to the user/operator;
(c) the practical skills required for the preparation and installation of the various
types of explosion protection;
(d) use and compilation of installation records.
Assessment
The 2008 issue of BS EN60079-14 specifies that those persons, i.e. Responsible Persons,
Operatives (Technicians) and Designers, involved in work in, or associated with, hazardous
locations are required to provide evidence of competence in accordance with national
regulations, standards, or user requirements.
The person is required to provide evidence that he/she:
(a) has the necessary skills required for the scope of work;
(b) can act competently across the specified range of activities;
(c) has the relevant knowledge and understanding underpinning competency.

199. March 2010 ©
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Electrical Isolation
Safe work on electrical equipment can only be achieved by ensuring the equipment is
properly isolated by means of isolators, fuses or links. The means of isolation applies to the
circuit and neutral conductors of each circuit or group of circuits.
In order to enable speedy identification, clear labelling should be positioned in close
proximity to the means of isolation.
Fault finding
The tracing of electrical faults in explosion protected equipment, which involves the use of
test instruments, may be possible when gas-free conditions are verified through continual
monitoring or the issue of a gas-free certificate.
IS Cable Requirements
The requirements for IS cables will be specified in the system documentation.
Cables need not be mechanically protected since the energy in an IS circuit is below that
which is necessary to ignite a flammable mixture, even if a spark is produced at a break in
the cables.
Non-hazardous Hazardous

200. March 2010 ©
24
IS Cable Requirements
1. Insulation between screen and SWA or braid.
2. Screen (optional) - normally earthed at one point only, which is usually the barrier
earth bar.
3. Individual insulated conductors.
4. SWA or braid (optional) - normally earthed at each end, and at any intervening
junction boxes through the cable glands.
1
2
3 4
Non-hazardous Hazardous

201. March 2010 ©
25
IS Cable Requirements
1. Zener safety barrier;
2. Barrier mounting rail/earth bar;
3. SWA/braid connected (earthed) to enclosure via gland;
4. Screen connected to barrier mounting rail/earth bar;
5. Dedicated earth conductors connected to main earth point using either:
a. two separate 1.5 mm2
minimum conductors (BS EN60079-14), or
b. a single copper conductor 4 mm2
minimum (BS 5345 Part 4
& BS EN60079-14)
Note: Longer runs may require conductors of larger cross-sectional area, e.g. 6mm2
or 10 mm2
Non-hazardous Hazardous

202. March 2010 ©
26
IS Cable Requirements
6. Junction box;
7. Cable glands;
8. Junction box bonded locally to structure;
9. Screen through connected;
10. Screen terminated but not isolated at field apparatus.
Non-hazardous Hazardous

203. March 2010 ©
27
Earthing and bonding
The principal reasons for earthing and bonding in electrical installations are:
1) to eliminate the possibility of electric shock to personnel;
2) to enable protection devices to operate correctly so that the duration of fault
currents are kept to a minimum;
3) to equalise the voltage potential of normally non-current carrying metalwork;
4) to prevent electrostatic charge of process plant due to fluid movement.
In hazardous areas, the elimination of sources of ignition is very important and effective
earthing and bonding will play an important role here. Electrical faults, if allowed to persist,
can develop to a point where excessive surface temperatures and/or arcs/sparks are
produced.
BS EN60079-17 clause 4.9 states: ‘Care shall be taken to ensure that the earthing and
potential equalisation bonding provisions in hazardous areas are maintained in good
condition’ (see inspection schedules table 1, item B6; table 2, items B6 and B7 and table 3,
item B3).
Explanation of terms
Electrical earthing or circuit protective conductors (CPC)
Conductors installed to provide a low impedance path for the current which flows under fault
conditions to the general mass of earth. Normally the CPC is connected directly to any
associated metal work of the equipment.
Electrical bonding
Conductors installed to establish continuity between adjoining metal work and the armouring
of separate cables to ensure that, under fault conditions, all metal work and cable armouring
are maintained at the same potential.
Exposed conductive parts
Exposed conductive parts include the metal work of switchboards, enclosures, motor
frames and transformer tanks.
Extraneous conductive parts
Any metal work associated with the plant, for example pipe work which can be touched at
the same time as a metal switch board cover or motor frame, will be deemed extraneous
conductive parts.

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Types of systems
(a) TN-S The system has separate neutral and protective conductors
throughout.
(b) TT A system in which one point of the source of energy is directly
earthed but which is electrically independent of the electrodes
used to earth the exposed conductive parts of the electrical
installation.
(c) TN-C A system in which a single conductor serves as both neutral
and protective conductor throughout the system.
(d) TN-C-S A system in which a single conductor serves as both neutral
and protective conductor in part of the system.
(e) IT A system in which there is no direct connection between live
parts and earth but exposed conductive parts of the electrical
installation are earthed.
Classification of systems
A system comprises an electrical supply to which an electrical installation is connected.
The first letter indicates the supply earthing arrangements where:
1) T represents a system having one or more points of the supply directly
connected to earth;
2) I represents a system in which the supply is not earthed, but may be earthed
through a fault-limiting impedance.
The second letter indicates the installation earthing arrangements where:
3) T represents the exposed conductive parts of the installation connected
directly to earth;
4) N represents the exposed conductive parts of the installation which are
connected directly to the earthed point of the supply.
The third letter indicates the earthed supply conductor where:
5) S represents separate neutral and protective conductors;
6) C represents neutral and protective conductors combined in a single
conductor.

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System earthing configurations
(a) TN-S
Generally, this method will be used when the electrical supply is provided via
underground cables having metal sheaths and armour. The consumer’s earth
terminal will be connected to the supply authorities protective conductor, that is the
metal sheath and armour of the underground cable, thereby establishing a
continuous path back to the supply transformer star-point which is earthed.
(b) TT
Generally, this method will be used when the electrical supply is provided via
overhead cables but with no earth terminal provided by the supply authority. The
consumer may have to provide an earth electrode for connection of the circuit
protective conductors. With this system, it is recommended that consumers use
residual current devices because of the difficulty in obtaining an effective earth
connection.

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(c) TN-C
In this system the same conductor, perhaps the outer conductor of a concentric
cable, is used for both the neutral and circuit protective conductor (PEN conductor)
throughout the system. It is typically used where the electrical supply is provided by
a privately owned transformer or converter, i.e. where there is no electrical
connection between the consumer and the supply authority, or where the supply is
provided by a private generator.
(d) TN-C-S
The supply authorities installation will use a TN-C system where both the neutral and
circuit protective conductor are served by a single (PEN) conductor. If the
consumers installation, which is connected to the TN-C supply system, employs a
TN-S system where the neutral and circuit protective conductors are separate, then
the overall system is known as a TN-C-S system. The majority of new installations
use this arrangement which is termed a PME system by the supply authorities.

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(e) IT
In this arrangement the system may have no connection to earth, or be connected to
earth via a relatively high impedance, the ohmic value of which will depend on the
level at which fault currents will be limited. Protection in this method is afforded by a
relay which monitors any earth-leakage current as a result of an earth-fault. This will
activate an audio or visual alarm, or disconnect the electrical supply.
Regulations and standards
The requirements for earthing practice within the UK may be found in the following
documents.
BS EN60079-14: 2008
Electrical apparatus for explosive gas atmospheres: Part 14
Electrical installations in hazardous areas (other than
mines)
BS 5345
( withdrawn )
Code of practice for: Selection, installation and
maintenance of electrical apparatus for use in potentially
explosive atmospheres (other than mining applications or
explosive processing and manufacture)
BS 7671: 2008 IEE Wiring Regulations
IEE Recommendations for the Electrical and Electronic
Equipment of Mobile and Fixed Offshore Installations
Electricity Supply Regulations 1988
Electricity at Work Regulations 1989
BS 7430: 1998 Code of Practice for Earthing
BS 6651: 1999 Protection of Structures against Lightning
PD CLC/TR 50404: 2003
Electrostatics – Code pf practice for the avoidance of
hazards due to static electricity
BS 5958: Pts 1 & 2: 1991 Control of Undesirable Static Electricity

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Earthing systems in hazardous areas
BS EN60079-14 specifies the conditions of use for the following earthing systems in
hazardous areas. The conditions apply to electrical installations, except IS circuits, in zones
1 and 2 up to 1000Vac(rms) / 1500Vdc. In the absence of harmonised requirements for
installations operating above these voltages, national requirements should be observed.
Type TN systems
If a type TN earthing system is used, it shall be type TN-S (with separate neutral N and
protective conductor PE) in the hazardous area, i.e. the neutral and the protective conductor
shall not be connected together, or combined in a single conductor, in the hazardous area.
At any point of the transition from type TN-C to type TN-S, the protective conductor shall be
connected to the equipotential bonding system in the non-hazardous area.
The monitoring of leakage between the neutral and PE conductors in the hazardous area is
also recommended in the standard.
Type TT system
If a type TT earthing system (separate earth’s for power system and exposed conductive
parts) is used in zone 1, then it shall be protected by a residual current device.
This system may not be acceptable where the earth resistivity is high.
Type IT system
If a type IT earthing system (neutral isolated from earth or earthed through an impedance) is
used, an insulation monitoring device shall be provided to indicate the first earth fault.
With this system, there may be a requirement for local bonding which is also known as
supplementary equipotential bonding. Further information may be obtained by reference
to IEC 60364-4-41.
Potential equalisation
In order to prevent different voltage potentials occurring in the metal work of plant in
hazardous areas, potential equalisation will be necessary. This applies to TN, TT and IT
systems where all exposed and extraneous conductive parts are required to be connected to
the equipotential bonding system. The bonding system may comprise protective conductors,
metal conduits, metal cable sheaths, steel wire armouring and metallic parts of structures,
but not neutral conductors. The security of connections must be assured by non-
loosening devices.

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Maximum Disconnection Times for TN Systems
Table 41A
U0 (volts) t (seconds)
120 0.8
220 to 277 0.4
400 0.2
greater than 400 0.1
Where U0 = Nominal voltage
Earthing conductor cross-sectional area
Calculation of csa
The cross-sectional area of earthing conductors may be calculated using the following
formula from the 16th Edition of the I.E.E. Wiring Regulations, BS7671.
k
t
2
I
S =
Where: S = nominal cross-sectional area of earthing conductor mm
2
I = fault-current for a negligible impedance fault that will flow
through the associated protective device (the current-limiting
effect of circuit impedance’s and limiting capacity (I2
t) of
protective device will be taken into account. A further
consideration is the increase in resistance of the conductors as
a result of the temperature rise during clearance of the fault.
(A)
t = operating time of protective device when clearing the
fault-current I.
(secs)
k = factor which takes into account resistivity, temperature
coefficient and heat capacity of conductor material, and the
appropriate initial and final temperatures.
Values for k are given in tables 54B, 54C, 54D, 54E, & 54F in the I.E.E. Wiring Regulations.

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CSA of CPC in relation to phase conductor
Alternatively, the minimum cross-sectional area of the protective conductor, in relation to the
cross-sectional area of the associated phase conductor, may be determined by
consideration of table 54G shown below.
Table 54G
Minimum CSA of protective conductor in relation to the CSA of associated phase conductor.
Minimum CSA of corresponding protective conductor (Sp)
CSA of phase
conductor If the protective conductor is
of the same material as the
phase conductor
If the protective conductor is
not the same material as the
phase conductor
mm2
S ≤ 16
16 ≤ S ≤ 35
S > 35
mm2
S
16
S
2
mm2
k1S
k2
k116
k2
k1S
k22
Note: The values of ‘k’ in the above table are given in the IEE Wiring Regulations, BS 7671
as follows where:
k1 is the value of k for the phase conductor, selected from table 43A in
Chapter 43 according to the materials of both conductor and insulation.
k2 is the value of k for the protective conductor, selected from Tables 54B,
54C, 54D, 54E or 54F as applicable.

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Main equipotential bonding conductors
The IEE Wiring Regulations, BS 7671, specify that the main equipotential bonding
conductor in an installation, other than a PME system, is required to have a cross-sectional
area not less than half the cross-sectional area specified for the installation earthing
conductor and not less than 6 mm2
. If a copper bonding conductor is used, the cross-
sectional need not be greater than 25 mm2
or, where other metals are used, the cross-
sectional area which provides equivalent conductance will apply.
With regard to a PME system, Table 54H below details the requirements for the main
equipotential bonding conductor in relation to the neutral conductor of the supply.
Table 54H
Copper equivalent cross-sectional area
of the supply neutral conductor
Minimum copper equivalent
cross-sectional area of the main
equipotential bonding conductor
35 mm2
or less 10 mm2
over 35 mm2
up to 50 mm2
16 mm2
over 50 mm2
up to 95 mm2
25 mm2
over 95 mm2
up to 150 mm2
35 mm2
over 150 mm2
50 mm2
Practical example with and without earth bonding
The diagram on page 29 shows a simple installation comprising a motor, distribution
transformer, fuses and connecting cable. The fuses are necessary to provide protection
against short-circuits which may occur between phases or between phase and earth.
Electrical faults such as these must be disconnected as quickly as possible to prevent further
damage to equipment and, more importantly, to prevent injury to personnel.
The speed at which a fuse ruptures is dependent not only on the type of fuse, but also the
circuit parameters, e.g. the resistance of the fault path - the earth-loop impedance - and
the fault current magnitude. The lower the earth-loop impedance, the higher the fault-current
will be and the faster the fuse will rupture. The 16th edition of the I.E.E. Regulations
specifies the requirements for earth-loop impedance.
Normally the star-point of the distribution transformer secondary winding is connected to an
earth mat buried in the soil, but this alone will not provide a low enough earth-loop
impedance, and so an earthing bond is required between the motor frame and the star-point
of the transformer secondary winding. Let us now investigate the situation with and without
the bonding conductor between the/

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main earth conductor and the motor frame when a fault occurs between one phase and
earth within the motor. It will also be assumed that the motor is bolted securely to the
bedplate but, due to dirt, rust or paint, the resistance between the feet of the motor and the
bedplate is l Ω.
Case 1: No earth connection between main earth conductor and motor frame.
Consider the circuit on page 35 which comprises a motor, transformer and
interconnecting cable. For simplicity resistive values only are used.
Rg = the resistance of one phase of the generator;
Rm = the resistance of one phase of the motor
R = the resistance between the motor feet and bedplate;
Vph = the phase voltage.
Voltage across motor frame and bedplate, V = Vph
x
R
Rm
Rg
R
+
+
V = 240
x
1
0.01
0.05
1
+
+
V = 208 V
Thus, anyone standing next to the motor and touching it’s frame would receive a severe
shock particularly if the deck was wet.
Case 2: Earth connection between main earth conductor and motor frame.
The above situation is avoided with appropriate earthing and bonding. If the
bonding conductor is connected between the motor frame and the main earth, the
resistance of 1 Ω between the motor feet and bedplate is shunted and the
effective resistance at this point is significantly reduced. Similarly, a bonding
conductor connected between the motor feet and bedplate would achieve a similar
result.
It is, therefore, essential that earth conductors have sufficient cross-sectional area
(csa) to carry prospective fault-currents, which can be very high but usually of
short duration, until they are interrupted by the electrical protection. It has been
demonstrated that a contact resistance of 1 Ω can result in the presence of
dangerous voltage levels. In order to avoid this difficulty, the earth-loop
impedance should be significantly lower than 0.1 Ω.

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Practical example with and without earth bonding (continued)
No earth bond connected
between motor frame and
main earth conductor
Earth bond connected
between motor frame
and main earth conductor

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Static electricity
Static electricity is more than capable of igniting flammable materials and its presence in the
petro-chemical industry represents a very high risk which must be countered by the
application of appropriate measures. Recommendations for the avoidance of hazards due to
static electricity are given in PD CLC/TR 50404: 2003 which replaces the British Standard
BS 5958: Code of Practice for the control of undesirable static electricity, although the latter
remains current.
The passage of oil, gases or dusts through process pipework and containment vessels
causes an internal build-up of static charges, which emerge on the exterior of the pipes and
tanks to establish potentials the magnitude of which can be many thousands of volts. This is
unacceptable in hazardous locations and can be eliminated by ensuring that all pipes, tanks,
etc., are solidly bonded together and bonded to the main earth.
Bonding across pipe flanges and joints can also reduce the problem of corrosion caused by
static charges.
Static electrical charges can be reduced in many instances by:
1) slowing the flow rate of fluids through pipes;
2) adding compounds to liquids;
3) the use of pipes manufactured from materials with high carbon content.

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Static electricity (continued)
BS 5958 recommendations for earthing resistances
BS 5958 is termed at the time of writing – current, superseded – which infers that it applies
only to existing installations, for example, installations installed in accordance with the Code
of Practice BS 5345. For new installations guidance for the control of static electricity may
be found in PD CLC/TR 50404. A summary of the recommendations in this document is
given in page 38.
Type of installation Area
classification
Recommended
maximum resistance
to earth
(Ω)
Comments
Main metal plant
structure,
Zones 0, 1 & 2 10 Ω Earthing normally inherent
in the structure.
Large fixed metal
plant items.
Reaction vessels
+ powder silos etc.
Zones 0, 1 & 2 10 Ω Earthing normally inherent
in the structure.
Occasionally items may be
mounted on non-conducting
supports and special
earthing connections may
then be required.
Metal pipelines. Zones 0, 1 & 2 10 Ω Earthing normally inherent
in the structure. Special
earthing connections may be
required across joints if
there is doubt that the 10 Ω
criterion will be satisfied.
Transportable metal
items: drums tanks
etc.
Zones 0, 1 & 2 10 Ω Special earthing connections
are normally required.
Metal plant with
some non-
conducting
elements:
Rotating shafts,
stirrers etc.
Zones 0, 1 & 2 10 Ω In special cases a limit of
100/ 1Ω may be acceptable,
but in general if 1MΩ
criterion cannot be satisfied
a special earthing
connection should be used
to obtain a resistance of less
than 10 Ω
to earth.
Higher resistivity
non-conducting
items with or without
isolated metal
components: e.g.
bolts in a plastic
pipeline
Zones 0, 1 & 2 10 Ω The general electrostatic
ignition risk and the fire
hazard normally preclude
the use of such
non-conducting materials
unless it can be shown that
significant charge
accumulation will not occur.
In the absence of charge
accumulation, earthing is not
required in Zone 2 areas
Items fabricated
from conductive or
antistatic materials
Zones 0, 1 & 2 1MΩ - 10MΩ

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Static electricity (continued)
PD CLC/TR 50404: summary of maximum earthing resistances for the control of static
electricity.
Sub clause Type of installation Maximum
resistance to
earth
( Ω )
Comments
11.3.1.1 Main plant
structure
106
Earthing normally inherent in the
structure
11.3.1.1 Large fixed metal
plant (reaction
vessels, powder
silos, etc.)
106
Earthing normally inherent in the
structure. Special earthing could be
required for items mounted on non-
conducting supports
11.3.1.1 Metal pipelines
106
Earthing normally inherent in the
structure. Special earthing connection
required across joints if resistance
could exceed the 106
Ω criterion
11.3.1.2 Movable metal
items (drums, road
and rail tankers,
etc.)
106
Earthing connections are normally
required during filling and emptying
11.3.2 Metal plant with
some non-
conductive
elements (valves,
etc.)
106
*
In special cases a limit of 100// Ω could
be acceptable, but in general if a
106
Ω criterion cannot be satisfied, a
special earthing connection should be
used
11.3.3 Non-conductive
items with or
without isolated
metal components
(e.g. bolts in a
plastic pipeline)
No generally
applicable
value*
The general electrostatic ignition risk
and the fire hazard normally preclude
the use of such materials unless it can
be shown that significant charge
accumulation will not occur. In the
absence of charge accumulation
earthing is not required in zone 2 and in
zone 22.
11.3.4 Items fabricated
from non-
conductive or
dissipative
materials
106
to 108
* Very small conductive items need not be earthed, see 4.4.2.
Note 1: The above recommendations should be read in conjunction with the paragraphs
indicated in the first column above.
Note 2: In zone 2 and in zone 22 earthing is required only when charge accumulation is
continuous.
Note 3: In order to provide protection against lightning or to meet the electricity power
supply earthing requirements a lower value of resistance to earth is normally
required.

217. Unit 11:
Inspection & Maintenance
to BS EN 60079-17

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Objectives:
On completion of this unit ‘Inspection & Maintenance’, you should know:
a. The importance of appropriate and regular inspection and maintenance.
b. The requirements of types of inspection ‘initial’, ‘periodic’ and ‘sample’.
c. How to apply inspection schedules, Tables 1, 2 & 3 form BS EN60079-17 for ‘visual’,
‘close’ and ‘detailed’ grades of inspection.
d. The knowledge and skills requirements for technicians (operatives) undertaking
inspection and maintenance of explosion protected equipment in hazardous areas.

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Inspection and Maintenance
Introduction
This unit is concerned with the inspection and maintenance of electrical apparatus used in
hazardous locations in accordance with relevant standards. This is very important because,
in addition to the risk of mechanical damage to apparatus, there is also the risk that
degradation of the apparatus, due to environmental conditions and other factors, could affect
the integrity of the apparatus and allow ignition of any flammable gas or vapour in an
hazardous area.
Inspection of equipment should be carried out on a regular basis to enable detection of
potential faults early enough to prevent major breakdowns occurring, minimise downtime
and loss of production, and also possible injury to personnel. A maintenance programme
based on the results of inspection surveys can then be implemented, which will allow
continued reliability and safe operation of the equipment.
Apparatus will only remain approved/certified if it is maintained in accordance with the
recommendations provided by manufacturers and relevant standards.
Standards
BS EN60079-17: 2007
Electrical apparatus for explosive gas atmospheres:
Part 17. Inspection and maintenance of electrical installations
in hazardous areas (other than mines).
IEC 60079-17: 2007
Explosive atmospheres –
Part 17: Electrical installations inspection and maintenance
BS 5345 (Withdrawn)
Code of practice for the selection, installation and
maintenance of electrical apparatus for use in potentially
explosive atmospheres.
Qualifications of Personnel
It is essential that personnel involved in the selection, installation, inspection and
maintenance of explosion protected apparatus in hazardous areas have a clear
understanding of the various types of explosion protection, installation practices, rules and
regulations, and the general principles of area classification. Manufacturers have gone to
great lengths to design and build apparatus in accordance with relevant standards and have
it tested and certified by a third party test house to ensure the apparatus is safe for use in
hazardous areas. All this effort will have been in vain if the technician in the field does not
have the necessary knowledge to install and/or maintain apparatus in accordance with the
manufacturer’s requirements, relevant standards and Codes of Practice. Personnel
operating in this field must, therefore, have appropriate training, and thereafter, regular
refresher training. Records detailing the experience and training of personnel must be
maintained. Apparatus may be explosion protected at the time of leaving the manufacturer’s
premises but, the way the apparatus is subsequently handled, selected, installed and
maintained, will have an influence on whether the apparatus will be safe for use in an
hazardous area and/or remain certified. Personnel need to be aware of, for example, the

220. March 2010 ©
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consequences of a broken foot on a flameproof motor. Increased Safety apparatus may
have ‘special conditions of use’ and failure to observe these will reduce margins of safety
and invalidate the certification. Furthermore, the incorrect selection of cable glands with
regard to, for example, flameproof apparatus will affect the integrity of such apparatus.
Knowledge and skills of technicians (operatives)
Inspection and maintenance
Technicians, or operatives as they are called in the standard, are required to have sufficient
knowledge to enable proper inspection and maintenance of explosion protected equipment
in hazardous areas. This knowledge includes:
(a) an understanding of the general principles of explosion protection;
(b) an understanding of the general principles of types of protection and marking;
(c) an understanding of those aspects of equipment design which affect the protection
concept;
(d) an understanding of certification and relevant parts of IEC60079-17;
(e) an understanding of the additional importance of Permit to Work systems and safe
isolation in relation to Explosion Protection;
(f) familiarity with the particular techniques to be employed in the inspection and
maintenance of equipment referred to in IEC60079-17;
(g) a comprehensive understanding of the selection and erection requirements of
IEC60079-14:
(h) a general understanding of the repair and reclamation requirements of
IEC60079-19.
Competency
Furthermore technicians (operatives) are required to provide evidence of their competency in
the areas specified immediately above and, in addition, documentary evidence of
competency in respect of the following:
(a) the use and availability of documentation;
(b) the practical skills required for the inspection and maintenance of the various
types of explosion protection.
Assessment
The competency of technicians (operatives) shall be verified and approved at intervals not
exceeding 5 years from sufficient evidence that the person:
(a) has the necessary skills required for the scope of work;
(b) can act competently across the specified range of activities; and
(c) has the relevant knowledge and understanding underpinning the competency.

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Principal causes of apparatus deterioration
BS EN60079-17 lists factors which have a significant effect on the deterioration of equipment
in hazardous locations. These factors are listed below.
1) Susceptibility to corrosion;
2) Exposure to chemicals or solvents;
3) Likelihood of accumulation of dust or dirt;
4) Likelihood of water ingress;
5) Exposure to excessive ambient temperatures;
6) Ultraviolet radiation;
7) Risk of mechanical damage;
8) Exposure to undue vibration;
9) Training and experience of personnel;
10) Likelihood of unauthorised modifications or adjustments;
11) Likelihood of inappropriate maintenance, for example not in accordance with
manufacturer’s recommendations.
Apparatus withdrawn from service
Where it is required to withdraw apparatus during maintenance, any exposed conductors
from the apparatus must be made safe by:
(a) termination in a suitable enclosure, or
(b) isolated from all sources of power supply and insulated, or
(c) isolated from all sources of power supply and earthed.
Where the intention is to permanently remove apparatus, the associated wiring must be
isolated from all sources of power supply and terminated in a suitable enclosure, or
completely removed.
IEC Standards
The International Electrotechnical Commission (IEC) Standards relative to explosion
protected apparatus have been available since the late nineteen-sixties when they were
published under the IEC 79-xx series, which subsequently evolved into the IEC 60079-xx
series. These Standards, however, had not kept pace with the advances in made by the
European Standards. Attempts to remedy this situation were implemented by the various
committees within IEC to effect a complete revision of their Standards. There has also been
greater co-operation between IEC and CENELEC to achieve technical alignment of their
respective Standards.

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With regard to the EU, explosion protected apparatus is normally constructed in accordance
with national and harmonised standards. IEC standards, however, have tended not to be
used for this purpose but, because of the trend towards global harmonisation of standards,
in which the IEC has an important role, this situation has changed. To fuel this change there
have been instances where manufacturers have been requested by larger users of explosion
protected apparatus to have such apparatus constructed and certified to the IEC Standards.
The certification of such apparatus has created difficulties for the manufacturers and, in one
instance, has led to the manufacturer issuing a ‘self declaration’ for apparatus they have
manufactured to a particular IEC Standard.
An IEC Standard which has become more widely accepted is IEC 60079-17, which is now a
British Standard, BS EN60079-l7. This Standard comprises a series of Tables for the
inspection of the various methods of explosion protection. Table 1 is an inspection schedule
which lists the areas to be inspected for the types of apparatus Ex d, Ex e and Ex n. Table 2
and Table 3 are schedules for the inspection of IS apparatus and Pressurised Ex p
apparatus respectively. These Tables are illustrated at the end of this section. For each
type of explosion protection, three grades of inspection are specified which are ‘visual’,
‘close’ and ‘detailed’ and defined as follows:
Visual: An inspection which identifies, without the use of access equipment or tools,
those defects, e.g. missing bolts, which will be apparent to the eye.
Close: An inspection which encompasses those aspects covered by a Visual
Inspection and, in addition, identifies those defects, e.g. loose bolts, which will
be apparent only by the use of access equipment, e.g. step ladders (where
necessary), and tools. Close inspections do not normally require the
enclosure to be opened, or the equipment to be de-energised.
Detailed: An inspection which encompasses those aspects covered by a Close
Inspection and, in addition, identifies those defects, e.g. loose termination’s,
which will only be apparent by opening the enclosure, and/or using, where
necessary, tools and test equipment.
Inspection schedules are, therefore, a means by which electrical installations may be
systematically assessed for the correct installation of apparatus and also the effects of
environmental conditions such as water, ambient temperature, vibration etc.
Documentation
Prior to the implementation of an inspection / maintenance programme it is essential that all
necessary documentation is available. These will include hazardous area drawings of the
plant, apparatus group and temperature class, list and location of apparatus spares,
technical information, manufacturer’s instructions, and a complete inventory of all hazardous
area equipment installed in the plant including their location in the plant and up-to-date
records of all previous inspections and maintenance tasks carried out. It is also vitally
important that the certification documents for each item of explosion protected apparatus are
available so that, for example, clarification of any ‘Special Installation Conditions’ may be
verified at a later date.
The maintenance of comprehensive records is thus an essential requirement for the safe
operation of electrical equipment in hazardous areas. Experience has shown that

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modifications to existing hazardous area equipment and also the installation of additional
hazardous area equipment, has occurred in hazardous areas installations without these
actions being recorded in the relevant documentation.
Inspections types
Three types of inspection are specified in BS EN60079-17. These are:
a) initial inspection;
b) periodic inspection;
c) sample inspection.
An installation, including its systems and apparatus, should be subjected to an ‘initial
inspection’ before being brought into service to establish that the types of protection
selected, and their method of installation are suitable. The grade of inspection shall be
‘detailed’ in accordance with Tables 1, 2 and 3 of BS EN60079-17. No faults are
permissible on handover.
Thereafter, ‘periodic inspections’ should be implemented to verify that the installation is
being maintained in an appropriate condition for continued use in the hazardous area. The
grade of inspection for ‘periodic inspections’ may be ‘visual’ or ‘close’ and should be
carried out at regular intervals, the interval being influenced by the environmental conditions,
but should not be greater than 3 years unless expert advice is sought. Depending on the
outcome of a ‘visual/close inspection’, it may be necessary to carry out a further ‘detailed
inspection’. Experience gained in similar situations with regard to apparatus, plants and
environments may be used to establish the inspection programme.
Factors having an influence on the frequency and grade of ‘periodic inspections’ are:
a) type of apparatus;
b) manufacturers recommendations;
c) environmental conditions;
d) Zone of use;
e) results of previous inspections
It is recommended that, however, the interval between ‘periodic inspections’ does not
exceed three years. Interim ‘sample inspections’ may be implemented to either support or
modify the frequency of ‘periodic inspections’ and may be of a grade ‘Visual’, ‘Close’ or
Detailed.
The flowchart on page 8 illustrates how a typical maintenance programme may be
established and how the various grades of inspection, i.e. ‘visual’, ‘close’ or ‘detailed’, may
be applied during the various types of inspection, i.e. ‘initial’, ‘periodic’ or ‘sample’.
Consideration is also given to frequency of periodic inspections.
Note: I.C. appearing in the flowchart on page 8 infers that electrical equipment contains
components which are ignition capable in normal operation. Typical components
are switches, contactors, relays etc. where ignition capable arcs or sparks are
produced at their contacts, and, for example, resistors which may produce
excessive surface temperatures.

224. March 2010 ©
8
Typical inspection procedure for periodic inspections

225. March 2010 ©
9
BS EN 60079-17 Table 1: Inspection Schedule for Ex’d’, Ex’e’, and Ex ‘n’
Installations (D = Detailed, C = Close, V = Visual)
Check that: Ex’d’ Ex’e’ Ex’n’
Grade of Inspection
D C V D C V D C V
A APPARATUS
1 Apparatus is appropriate to area classification * * * * * * * * *
2 Apparatus group is correct * * * * * *
3 Apparatus temperature class is correct * * * * * *
4 Apparatus circuit identification is correct * * *
5 Apparatus circuit identification is available * * * * * * * * *
6 Enclosure, glass parts and glass-to-metal sealing gaskets
and/or compounds are satisfactory
* * * * * * * * *
7 There are no unauthorised modifications * * *
8 There are no visible unauthorised modifications * * * * * *
9 Bolts, cable entry devices (direct and indirect) and blanking
elements are of the correct type and are complete and tight
- Physical check
- Visual check
* *
*
* *
*
* *
*
10 Flange faces are clean and undamaged and gaskets, if any,
are satisfactory
*
11 Flange gap dimensions are within maximal permitted values * *
12 Lamp rating, type and position are correct * * *
13 Electrical connections are tight * *
14 Condition of enclosure gaskets is satisfactory * *
15 Enclosed-break and hermetically sealed devices are undamaged *
16 Restricted breathing enclosure is satisfactory *
17 Motor fans have sufficient clearance to enclosure and/or covers * * *
18 Breathing and draining devices are satisfactory * * * * * *
B INSTALLATION
1 Type of cable is appropriate * * *
2 There is no obvious damage to cables * * * * * * * * *
3 Sealing of trunking, ducts, pipes and/or conduits is satisfactory * * * * * * * * *
4 Stopping boxes and cable boxes are correctly filled *
5 Integrity of conduit system and interface with mixed system is
maintained
* * *
6 Earthing connections, including any supplementary earthing
bonding connections are satisfactory (e.g. connections are tight
and conductors are of sufficient cross section)
- Physical check
- Visual check
*
* *
*
* *
*
* *
7 Fault loop impedance (TN system) or earthing resistance
(IT systems is satisfactory)
* * *
8 Insulation resistance is satisfactory * * *
9 Automatic electrical protective devices operate within permitted
limits
* * *
10 Automatic electrical protective devices are set correctly (auto reset
not possible)
* * *
11 Special conditions of use (if applicable) are complied with * * *
12 Cables not in use are correctly terminated * * *
13 Obstructions adjacent to flameproof flanged joints are in
accordance with IEC 60079-14
* * *
14 Variable voltage/frequency installation in accordance with
documentation
* * * * * *
Note: table continued on following page

226. March 2010 ©
10
Check that: Ex’d’ Ex’e’ Ex’n’
Grade of Inspection
D C V D C V D C V
C ENVIRONMENT
1 Apparatus is adequately protected against corrosion, weather,
vibration and other adverse factors
* * * * * * * * *
2 No undue accumulation of dust and dirt * * * * * * * * *
3 Electrical insulation is clean and dry * *
Note 1: Apparatus using a combination of both ‘d’ and ‘e’ types of protection will require
reference to both columns during inspection.
Note 2: The use of electrical test equipment, in accordance with items B7 and B8, should
only be undertaken after appropriate steps are taken to ensure the surrounding area
is free of a flammable gas or vapour.
Moveable equipment
The movement of electrical equipment, i.e, portable, hand-held and transportable, can result
in damage due to incorrect handling and hence there may be a need for a shorter interval
between periodic inspections. The recommendation is that a close inspection is carried out
every 12 months.
Where equipment is frequently opened, typically battery compartments, the recommendation
is a detailed inspection every 6 months.
Furthermore, it is the responsibility of the user to visually inspect equipment prior to use to
ensure freedom from apparent damage.

227. March 2010 ©
11
BS EN60079-17: Table 2: Inspection Schedule for Ex ’i’ Installations
Grade Inspection
Check That:
Detailed Close Visual
A Apparatus
1 Circuit and/or apparatus documentation is appropriate to area
classification
* * *
2 Apparatus installed is that specified in the documentation – Fixed
apparatus only
* *
3 Circuit and/or apparatus category and group correct * *
4 Apparatus temperature class is correct * *
5 Installation is clearly labelled * *
6 There are no unauthorised modifications *
7 There are no visible unauthorised modifications * *
8 Safety barrier units, replays and other energy limiting devices are of
the approved type, installed in accordance with the certification
requirements and securely earthed where required
* * *
9 Electrical connections are tight *
10 Printed circuit boards are clean and undamaged *
B Installation
1 Cables are installed in accordance with the documentation *
2 Cables screens are earthed in accordance with the documentation *
3 There is no obvious damage to cables * * *
4 Sealing of trunking, ducts, pipes and/or conduits is satisfactory * * *
5 Point-to-point connections are all correct *
6 Earth continuity is satisfactory (e.g. connections are tight and
conductors are of sufficient cross-section)
*
7 Earth connections maintain the integrity of the type of protection * * *
8 The intrinsically safe circuit is isolated from earth to earthed at one
point only (refer to documentation)
*
9 Separation is maintained between intrinsically safe and non-
intrinsically safe circuits in common distribution boxes or relay
cubicles
*
10 As applicable, short-circuit protection of the power supply is in
accordance with the documentation
*
11 Special conditions of use (if applicable) are complied with *
12 Cables not in use are correctly terminated * * *
C Environment
1 Apparatus is adequately protected against corrosion, weather,
vibration and other adverse factors
* * *
2 No undue accumulation of dust and dirt * * *

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BS EN60079-17: Table 3: Inspection Schedule for Ex ’p’ Installations
Grade Inspection
Check That:
Detailed Close Visual
A Apparatus
1 Apparatus is appropriate to area classification * * *
2 Apparatus group is correct * *
3 Apparatus temperature class is correct * *
4 Apparatus circuit identification is correct *
5 Apparatus circuit identification is available * * *
6 Enclosures, glass parts and glass-to-metal sealing gaskets and/or
compounds are satisfactory
* * *
7 There are no unauthorised modifications *
8 There are no visible unauthorised modifications * *
9 Lamp rating, type and position are correct *
B Installation
1 Type of cable is appropriate *
2 There is no obvious damage to cables * * *
3 Earthing connections, including any supplementary earthing
bonding connections are satisfactory (e.g. connections are tight and
conductors are of sufficient cross section
- Physical check
- Visual check
*
* *
4 Fault loop impedance (TN systems) or earthing resistance (IT
systems) is satisfactory
*
5 Automatic electrical protective devices operate within permitted
limits
*
6 Automatic electrical protective devices are set correctly *
7 Protective gas inlet temperature is below maximum specified *
8 Ducts, pipes and enclosures are in good condition * * *
9 Protective gas is substantially free form contaminants * * *
10 Protective gas pressure and/or flow is adequate * * *
11 Pressure and/or flow indicators, alarms and interlocks function
correctly
*
12 Pre-energising purge period is adequate *
13 Conditions of spark and particular barriers of ducts for exhausting
the gas in hazardous area satisfactory
*
14 Special conditions of use (if applicable) are complied with *
C Environment
1 Apparatus is adequately protected against corrosion, weather,
vibration and other adverse factors
* * *
2 No undue accumulation of dust and dirt * * *

229. Unit 12:
Sources of Ignition

230. March 2010 ©
2
Objectives:
On completion of this unit, ‘Sources of Ignition’, you should know:
a. typical everyday sources of ignition in the workplace
b. lesser known sources of ignition

231. March 2010 ©
3
Sources of Ignition
Electrical Sparks
Electrical sparks are caused primarily by the opening and closing of contacts, for example,
electrical switches, contactors and relays. To ignite a flammable mixture consisting of
hydrogen and air requires only 20 μJ, the energy produced as a result of a break of 0.1 mS
duration in a circuit carrying 20 mA at 10 V. From this perspective, it is clear that for devices
such as these to operate safely in a hazardous area require them to be installed in, for
example, a flameproof enclosure.
The voltage level has an influence on how incendive a spark will be. Flammable gases and
vapours are more readily ignited at high voltages than low voltages, and is basically why IS
circuits are seldom designed for use above 30 V.
The use of electrical test instruments, typically voltmeters and insulation resistance testers
etc., are a potential source of electrical sparks. These instruments should only be used
under controlled circumstances, i.e. under the control of a work permit and tests to ensure
gas free conditions.
Hot Surfaces
The flow of current through, for example, the windings of an electric motor invariably
produces heat which will raise the surface temperature of the motor. If the motor is
excessively overloaded and the thermal overload device in the starter is incorrectly set, the
surface temperature of the motor may well exceed it’s T-rating. Overheating can also be
caused by blockage of the cooling fan intake, damaged cooling fan, or collapse of bearing
due to lack of lubrication. The latter can dramatically raise the surface temperature locally to
a ‘blue heat’ state which equates to a temperature around 430°C which is more than capable
of igniting a flammable gas or vapour.
Other sources of heat are process pipes and machinery, combustion engine manifolds and
exhaust pipes, and light bulbs.
Batteries
Batteries, whatever their size, are a potential source of ignition as they will produce
incendive sparks if their terminals are short-circuited. Current of the order 1000 A can be
generated if the terminals of automotive batteries are short-circuited. There is also the added
complication that during charging of lead-acid batteries, hydrogen and oxygen are released.
This requires well ventilated battery rooms.
The certification of portable instruments may only allow their use in hazardous areas if
powered by low-power batteries. High-power batteries must not be used unless permitted by
the manufacturer. Replacement of batteries must only be carried out in a non-hazardous
area.

232. March 2010 ©
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Friction
The abrasive wheels of portable grinding machines are more than capable of producing
incendive sparks and hot surfaces locally at the point of contact by the abrasive wheel.
Drilling using portable tools can also generate heat between the drill bit and the work piece.
Power tools, of course, must not be used in hazardous areas, unless used under strictly
controlled conditions, because they are sources of ignition.
Static Electricity
Static electricity is normally caused by two insulating materials rubbing together. The loosely
held electrons in the atoms of one material are detached and transferred to the other
materials, so that the material which loses electrons becomes positively charged. This
condition may remain for some time because the materials are insulators and do not offer a
conductive return path for the electrons.
Nylon clothing removed from the body can generate enough static electricity to ignite a
flammable gas or vapour, and there are instances on record of this occurring.
Plastic explosion protected enclosures normally carry the warning that they should be
cleaned using a damp cloth to avoid generation of static electricity.
The movement of fluids can also generate electrostatic charges, and up to 5000 V can be
generated at the nozzle of an aerosol canister. Similarly, 10000 V or more can be generated
at the nozzle of high-pressure steam cleaning equipment. Bonding and earthing of aircraft
during refuelling prevents the build up of electrostatic charges which might otherwise cause
the aviation fuel vapour to ignite.
Lightning
Lightning is a type of static electricity caused by the movement of clouds. Air between clouds
or between clouds and earth, acts as an insulator allowing the charges to build up and the
result is that very high voltages are generated. Once the voltage reaches a critical point,
breakdown of the air occurs and the energy is released suddenly in the form of a lighting
strike. Lightning strikes will be readily discharged to earth by the normal metal construction
of an installation, but flammable gases or vapours can be ignited by lightning.
Impact
The combination of rusty iron or steel, aluminium and impact between the two is a likely
source of ignition, known as thermite action, which can produce sparks capable of igniting
a flammable gas or vapour. The use of aluminium ladders in hazardous areas should
therefore be avoided. The use of aluminium paint in hazardous areas also requires caution.
Pyrophoric Reaction
Hydrogen sulphide (H2S), or other sulphide compounds passing through iron pipes, reacts
with the iron of the pipe to produce iron sulphide. Iron sulphide when exposed to air very
quickly oxidises and will reach temperatures capable of igniting a flammable gas or vapour.
This phenomenon is known as pyrophoric reaction and can be prevented by soaking the
iron sulphide with water or prevent its contact with air.

233. March 2010 ©
5
Radio frequency
The increase in the use of mobile telephones, which operate at high frequencies, has
caused some concern. Such concern was expressed by a major oil company in 1993 about
the risk of using mobile telephones in petrol stations. Petrol stations have Zone 1 areas
around the pumps due to the presence of petrol vapour, and the energy transmitted by a
mobile phone, if used in these areas, could be picked up by metalwork in the area which,
acting as an aerial, could produce a spark of sufficient energy to ignite the petrol vapour.
Other sources of radio frequency are of course radio and television transmitters and radar
installations.
With regard to radar installations, concern was expressed about the possible ignition of
flammable gases at the St. Fergus Gas Terminal in the North East of Scotland by radar
transmissions from the nearby radar installation at Crimond.
Vibration
Vibration is undesirable since it causes premature deterioration of equipment if allowed to
persist. Typical examples are increased wear in bearings, loosening of electrical
connections, etc. Vibration has also been known to cause metal fatigue of the copper
sheath and conductors of MICC cable due to work hardening.

234. Unit 13:
Induction to Competence
Validation Testing

235. March 2010 ©
2
Objectives:
On completion of this unit, ‘Induction to Competence Validation Testing’, you should
know:
a. The procedures and competence requirements for EX01: the preparation and
installation of Ex d, Ex e and Ex n apparatus.
b. The procedures and competence requirements for EX02: the inspection and of Ex d,
Ex e and Ex n apparatus.
c. The procedures and competence requirements fro EX03: the preparation and
installation of an Ex i system and associated apparatus.
d. The procedures and competence requirements for EX04: the inspection and
maintenance of an Ex i system and associated apparatus.

236. March 2010 ©
3
Induction to Competence Validation Testing
Competence Validation Tests EX01, EX02, EX03 and EX04
Off-site preparation: Implement, with reference to Assessment
Workpacks, all off-site procedures to include
selection of materials, apparatus, equipment and
tools. Safe working practices to be adhered to at
all times and include the mandatory use of
Personal Protective Equipment in the
designated areas.
Permit-to-work and safe electrical
isolation:
Complete relevant section of permit-to-work in
accordance with procedures detailed in Unit 14.
On-site preparation: Implement, with reference to Assessment
Workpacks, all on-site procedures to achieve the
competence standard required for Installation,
Inspection and Maintenance relative to Units
EX01, EX02, EX03 and EX04.
EX01 Preparation and Installation of EEx d, e & n Apparatus
Section A
Preparation and Safe
Isolation of the electrical
Circuit:
Correctly locate electrical supply source and
safely isolate installation under the control of a
permit-to-work system
Section B
Installation comprising
Ex d, Ex e and Ex n
apparatus:
a) Inspect suitability of pre-fixed apparatus, cables
and glands.
b) Install appropriate cables and glands in a
manner which will maintain the integrity of the
pre-fixed apparatus.
c) Carry out appropriate electrical (instrument)
tests after ensuring appropriate safeguards are
implemented.
d) Fit apparatus covers and live-test installation.

237. March 2010 ©
4
EX02 Inspection of EEx d, e & n Apparatus
Sections A, B & C
Inspection of apparatus
and environment:
With reference to Table 1 of BS EN60079-17:
a) Identify and record five Visual faults.
b) Identify and record five Close faults.
c) Identify and record five Detailed faults.
d) Compile a report of the faults found and specify
the remedial action necessary to return the
installation to specification.
Section D
Safe Isolation of the
electrical circuit.
(Prior to Section C):
Correctly locate electrical supply source and safely
isolate installation under the control of a permit-to-work
system.
EX03 Preparation and Installation of EEx i Apparatus
Section A
Installation comprising
Ex i apparatus:
a) Inspect suitability of pre-fixed apparatus, cables
and glands.
b) Install appropriate cables, glands and safety
interfaces in a manner which will maintain
apparatus integrity.
c) Carry out appropriate electrical (instrument)
tests after ensuring appropriate safeguards are
implemented.

238. March 2010 ©
5
EX04 Inspection of EEx i Apparatus
Sections A, B & C
Inspection of apparatus
and environment:
With reference to Table 2 of BS EN60079-17:
a) Identify and record five Visual faults.
b) Identify and record five Close faults.
c) Identify and record five Detailed faults.
d) Compile a report of the faults found and
specify the remedial action necessary to return
the installation to specification.
Section D
Safe Isolation of the
electrical circuit.
(Prior to Section C):
Correctly locate electrical supply source and safely
isolate installation under the control of a permit-to-
work system.

239. March 2010 ©
6
BS EN 60079-17 Table 1: Inspection Schedule for Ex’d’, Ex’e’, and Ex ‘n’
Installations (D = Detailed, C = Close, V = Visual)
Check that: Ex’d’ Ex’e’ Ex’n’
Grade of Inspection
D C V D C V D C V
A APPARATUS
1 Apparatus is appropriate to area classification * * * * * * * * *
2 Apparatus group is correct * * * * * *
3 Apparatus temperature class is correct * * * * * *
4 Apparatus circuit identification is correct * * *
5 Apparatus circuit identification is available * * * * * * * * *
6 Enclosure, glass parts and glass-to-metal sealing gaskets
and/or compounds are satisfactory
* * * * * * * * *
7 There are no unauthorised modifications * * *
8 There are no visible unauthorised modifications * * * * * *
9 Bolts, cable entry devices (direct and indirect) and blanking
elements are of the correct type and are complete and tight
- Physical check
- Visual check
* *
*
* *
*
* *
*
10 Flange faces are clean and undamaged and gaskets, if any,
are satisfactory
*
11 Flange gap dimensions are within maximal permitted values * *
12 Lamp rating, type and position are correct * * *
13 Electrical connections are tight * *
14 Condition of enclosure gaskets is satisfactory * *
15 Enclosed-break and hermetically sealed devices are undamaged *
16 Restricted breathing enclosure is satisfactory *
17 Motor fans have sufficient clearance to enclosure and/or covers * * *
18 Breathing and draining devices are satisfactory * * * * * *
B INSTALLATION
1 Type of cable is appropriate * * *
2 There is no obvious damage to cables * * * * * * * * *
3 Sealing of trunking, ducts, pipes and/or conduits is satisfactory * * * * * * * * *
4 Stopping boxes and cable boxes are correctly filled *
5 Integrity of conduit system and interface with mixed system is
maintained
* * *
6 Earthing connections, including any supplementary earthing
bonding connections are satisfactory (e.g. connections are tight
and conductors are of sufficient cross section)
- Physical check
- Visual check
*
* *
*
* *
*
* *
7 Fault loop impedance (TN system) or earthing resistance
(IT systems is satisfactory)
* * *
8 Insulation resistance is satisfactory * * *
9 Automatic electrical protective devices operate within permitted
limits
* * *
10 Automatic electrical protective devices are set correctly (auto reset
not possible)
* * *
11 Special conditions of use (if applicable) are complied with * * *
12 Cables not in use are correctly terminated * * *
13 Obstructions adjacent to flameproof flanged joints are in
accordance with IEC 60079-14
* * *
14 Variable voltage/frequency installation in accordance with
documentation
* * * * * *
Note: table continued overleaf

240. March 2010 ©
7
Check that: Ex’d’ Ex’e’ Ex’n’
Grade of Inspection
D C V D C V D C V
C ENVIRONMENT
1 Apparatus is adequately protected against corrosion, weather,
vibration and other adverse factors
* * * * * * * * *
2 No undue accumulation of dust and dirt * * * * * * * * *
3 Electrical insulation is clean and dry * *
Note 1: Apparatus using a combination of both ‘d’ and ‘e’ types of protection will require
reference to both columns during inspection.
Note 2: The use of electrical test equipment, in accordance with items B7 and B8, should
only be undertaken after appropriate steps are taken to ensure the surrounding
area is free of a flammable gas or vapour.
`

241. March 2010 ©
8
BS EN60079-17: Table 2: Inspection Schedule for Ex ’i’ Installations
Grade Inspection
Check That:
Detailed Close Visual
A Apparatus
1 Circuit and/or apparatus documentation is appropriate to area
classification
* * *
2 Apparatus installed is that specified in the documentation – Fixed
apparatus only
* *
3 Circuit and/or apparatus category and group correct * *
4 Apparatus temperature class is correct * *
5 Installation is clearly labelled * *
6 There are no unauthorised modifications *
7 There are no visible unauthorised modifications * *
8 Safety barrier units, replays and other energy limiting devices are of
the approved type, installed in accordance with the certification
requirements and securely earthed where required
* * *
9 Electrical connections are tight *
10 Printed circuit boards are clean and undamaged *
B Installation
1 Cables are installed in accordance with the documentation *
2 Cables screens are earthed in accordance with the documentation *
3 There is no obvious damage to cables * * *
4 Sealing of trunking, ducts, pipes and/or conduits is satisfactory * * *
5 Point-to-point connections are all correct *
6 Earth continuity is satisfactory (e.g. connections are tight and
conductors are of sufficient cross-section)
*
7 Earth connections maintain the integrity of the type of protection * * *
8 The intrinsically safe circuit is isolated from earth to earthed at one
point only (refer to documentation)
*
9 Separation is maintained between intrinsically safe and non-
intrinsically safe circuits in common distribution boxes or relay
cubicles
*
10 As applicable, short-circuit protection of the power supply is in
accordance with the documentation
*
11 Special conditions of use (if applicable) are complied with *
12 Cables not in use are correctly terminated *
C Environment
1 Apparatus is adequately protected against corrosion, weather,
vibration and other adverse factors
* * *
2 No undue accumulation of dust and dirt * * *

242. Unit 14:
Permit to Work System
and Safe Isolation

243. March 2010 ©
2
Objectives:
On completion of this unit, ‘Permit to Work and Safe Isolation’, you should know:
a. the procedure to complete a ‘permit to work’ to enable safe completion of tests EX01,
EX02, EX03 and EX04;
b. the procedures to identify, from drawings, the location of protection and control
devices for tests EX01, EX02, EX03 and EX04;
c. the procedure to safely isolate and secure isolation of electrical circuits and
apparatus for tests EX01, EX02, EX03 and EX04.

244. March 2010 ©
3
Permit-to-work and safe isolation
Candidates attending the 5-day CompEx course are required to carry out four practical
assessments in the simulated hazardous areas. During these assessments, candidates
must demonstrate their ability to work safely by ensuring that all precautions are taken to
prevent ignition of a flammable gas which, for the purpose of the assessments, it is assumed
may be present at any time.
Work permit
In order to ensure that safety is maintained, candidates must operate within the control of a
work permit - a sample is shown overleaf - which must be requested from the
Assessor/Authorised Person.
In association with the work permit, a gas-free certificate must be endorsed by the
Assessor/Authorised Person at all instances when, for example, a particular action is likely
to produce a source of ignition. Such situations occur when electrical test instruments
and/or portable electric tools are used.
Procedures for CVT’s EX01, EX02, EX03 & EX04
Isolation
Candidates are required to:
a) Request a ‘work permit’.
b) Complete parts 1, 2 and 3 of the ‘Work Permit’ and obtain ‘Authorisation to
Isolate’ the electrical circuit for the respective workbay.
Note: PPE in the designated areas is mandatory
c) Identify the ‘point of isolation’ plant reference No. and apparatus ID for
‘zero voltage testing’.
d) Isolate the electrical circuit and secure using two locks (candidate +
assessor’s locks) and warning label.
e) Request ‘gas-free certificate’.
f) Select appropriate test instrument, carry out ‘zero voltage test’ and confirm
result on part 3 of ‘work permit’.
(Note: instrument must be proved before and after use)
g) Obtain approval to proceed with work (part 4 of work permit).
Note: Step ‘d’ does not apply to EX03 since isolation is achieved by switching
off and removal of keys in the fire and gas panel.

245. March 2010 ©
4
Final instrument testing
h) Request endorsement of ‘gas-free certificate’ prior to final instrument
testing (part 5 of work permit).
i) Prepare installation for live testing and clear worksite (part 6 of work permit).
De-isolation
j) Obtain authorisation to de-isolate (part 6 of work permit).
k) Confirm de-isolation is complete (part 6 of work permit).
l) Obtain cancellation of work permit (part 7 of work permit).

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PERMIT TO WORK
1. Work details
EX01 EX02 EX03 EX04 Date:
Job description:
2. Safety requirements – Personal Protective Equipment – (Tick items)
Coveralls Footwear Eye protection
Hard hat Gloves
3. Isolation
Gas free test required Yes No
Gas free certificate endorsed Yes
ƒ Authorisation to isolate (Authorised person)
ƒ Equipment has been isolated at
and checked for zero voltage at
ƒ Isolation complete & zero voltage confirmed by candidate
(Candidate)
4. Authorisation/acceptance
I herby authorise to proceed with work
(Candidate) (Authorised person)
I understand and accept responsibility for the work (Candidate)
5. Final Instrument testing (EX01 & EX03 only)
Gas free test required Yes No
Gas free certificate endorsed Yes
6. Clearance/de-isolation
ƒ I herby declare the above work has been completed and work site cleared
(Candidate)
ƒ I herby authorise de-isolation (Authorised person)
ƒ De-isolation complete (Candidate)
7. Cancellation
All work detailed above is completed and ‘Permit-to-Work’ is cancelled
(Authorised person)

247. March 2010 ©
6
GAS TEST CERTIFICATE
ƒ This certificate confirms that the work bay nominated below in the Ex Training
Facility has been tested and deemed to be free of flammable gases for only the
specific task(s) authorised below.
Work Details (tick box)
EX01 EX02 EX03 EX04
Location
Workbay No.
Authorised by_________________(signed) Date____________
Action to be authorised Authorised person
(signed)
Zero voltage test (isolation)
Use of portable heat gun
Final ‘instrument’ circuit testing