Compex Manual July09

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Introduction



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 theauthors will not be held responsible for any inaccuracies found therein.

Acknowledgements:

The production of this document would not have been possible without the muchappreciated assistance from the following authorities and, therefore, the authors of thedocument wish to thank and gratefully acknowledge all those who provided material andadvice 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 AltensCentre.

The BASEEFA Crown mark shown in this document is the property of the Health and SafetyExecutive and should not be interpreted to convey certification. The marks have beenreproduced 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 inany form by any means. i.e. electronic, electrostatic, magnetic media, mechanical,photocopying, recording or otherwise without the permission in writing of the appointedrepresentative of Aberdeen College.

5th Edition, July 2009

Ex FacilityNovember 2008

2



Introduction

About the ‘Ex’ Faci li ty

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 beenin operation since August 1994 and has been designed and constructed specifically for theNational Training of personnel who work with electrical installations and plant in hazardousand/or potentially explosive environments. The facility includes both classroom andsimulated work areas, these being designed to give as realistic site conditions as is possibleto achieve.

The practical work candidates are required to carry out will take place in these simulatedareas and this is intended to make the candidates feel they are working under siteconditions.

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. Theremaining time will be spent on Competence Validation Testing in the simulatedhazardous areas. The tests are nationally set for Ex training.

The Outcome

The objective of the training is to introduce the candidate to operating procedures andtechniques and to give candidates and their employer’s confidence that the candidates arecompetent to work on electrical apparatus in hazardous or potentially explosiveenvironments. 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 ofelectrical equipment in hazardous areas is paramount. It is extremely important for allpersonnel who operate in these conditions to be competent in the correct techniques andoperational procedures. This can best be achieved by means of training by skilled staff in anenvironment as close to the ‘real thing’ as possible. In addition to this, the job knowledgedeveloped through the course must be put into operation in the actual working situation sothat the levels of expertise are increased through experience.

The Design of the Programme

The program is dived into two halves, namely:

a. Job Knowledgeb. Competence Validation Testing (CVT)

The ‘job knowledge’ component takes place during the first half of the week and provides theinformation and experience you need to tackle the CVT’S.


3



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.


4



Course outline

The training scheme

The training scheme is arranged to prepare candidates for the assessment programmewhich comprises four discreet Competence Validation Tests (CVT’s) offered ascomplimentary 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 applyto the four CVT’s as illustrated below.

Unit 1: General principles Unit 2: Standards,Certification andMarking

Unit 3: Flameproof Ex d

EX01 & EX02 EX01 & EX02 EX01 & EX02

EX03 & EX04 EX03 & EX04

Unit 4: Increased SafetyEx 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 ofprotection

Unit 9: Combined (Hybrid)protection methods

EX03 & EX04 (Written Assessment) EX01 & EX02

Unit 10: Wiring Systems Unit 11: Inspection &Maintenance toBS EN60079-17

Unit 12: Sources of ignition

EX01 & EX02 EX01 & EX02 EX01 & EX02

EX03 & EX04 EX03 & EX04 EX03 & EX04

Unit 13: Induction toCompetenceValidation Testing

Unit 14: Permit to Workand

Safe Isolation

EX01 & EX02 EX01 & EX02

EX03 & EX04 EX03 & EX04


5



Ex FacilitNo

yvember 2008

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.

Self-assessment pro ject

At the rear of this manual, you will find assessment material which you should completeduring the course. This exercise will enable you to determine your prior knowledge of thesubject, especially in the area of interpretation of apparatus labelling.

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 & EX02Unit 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



Programme: Electrical Apparatus in Potentially Hazardous Areas5 – Day Programme

Monday Tuesday Wednesday Thursday

Presenter

8:30

12:30

Courseregistration andinduction

Unit 1: GeneralPrinciples

Unit 10: Wiringsystems &Demonstration ofcompound filledgland anddiaphragm seal

gland assembly

Unit 2: Standards:certification &marking

Unit 4: IncreasedSafety Ex e

Unit 5: Type ‘n’Protection

Unit 6:Pressurisation Ex p

Unit 7: Intrinsic Safety E x i EX02 CVTInspection &Maintenanceof d, e & napparatus

Candidates7-12

EX01 Prepa&Instalof d, appar

Cand1-6

Break Break Break Break

13:00

17:00

Unit 3: FlameproofEx d

Unit 10: Practicalexercise: Assembly ofcompound filledand diaphragmseal type glands.

Unit 8: Othermethods ofprotection

Unit 9: Combined(Hybrid) methods ofprotection

Unit 11: Inspection &Maintenance

Unit 13: Introductionto CVT’s

Unit 14: Work permit

EX01 CVTPreparation&Installationof d, e & napparatus

Candidates1-6

EX02 CVTInspection &Maintenanceof d, e & napparatus

Candidates 7-12

EX01 CVTPreparation&Installationof d, e & napparatus

Candidates1-6

EX02 InspeMaintof d, eappar

Cand7-12


7



Unit 1:

General Principles



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 ‘relativedensity’.

b. The basic principles of area classification.

c. The Grouping of gases according to ‘minimum ignition energy’ (MIE) and ‘maximumexperimental safe gap’ (MESG).

d. Appropriate T-ratings for apparatus relative to the ignition temperature of a givenflammable material.

e. The levels of ‘ingress protection’.

2



General Principles

Nature of Flammable Materials

Fire Triangle

The fire triangle represents the three elements which must be present before combustioncan take place. Each point of the triangle represents one of the essential elements whichare:

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 inair.

3. Source of Ignition: This can be an arc , spark, naked flame or hot surface.

Source ofignitionOxygen

( 21% in air )

Gas or vapour

Combustion will take place if all three elements, in one form or another, are present, thegas/air mixture is within certain limits and the source of ignition has sufficient energy. Theremoval 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 inexplosion 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 specificvalues, or allows an explosion to take place and contains it within a robust enclosure. Thesetechniques are addressed in the various sections of this manual.

3



Flammable (Explosive) Limits

Combustion will only occur if the flammable mixture comprising fuel, in the form of a gas orvapour, 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 aparticular 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 themixture is too weak to burn, i.e. insufficient fuel and/or toomuch air.

Upper Explosive Limit : When the percentage of gas, by volume, is above this limit themixture is too rich to burn, i.e. insufficient air and/or too muchfuel.

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

4



Flammable (Explosive) Limits (continued)

Different gases or vapours have different flammable limits and the greater the differencebetween the LEL and the UEL, known as the flammable range, the more dangerous thematerial. An explosive (flammable) atmosphere, therefore, only exists between these limits.

Operational safety with flammable mixtures above the UEL is possible, but is not a practicalproposition. 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.

5



Flashpoint

By definition flashpoint is: ‘the lowest temperature at which sufficient vapour is given off aliquid, to form a flammable mixture with air that can be ignited by an arc, spark or nakedflame’. 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 innormal ambient temperatures. Reference to the tables of flammable materials from PDIEC60079-20 (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 aflammable material is discharged under pressure from a jet, its flashpoint may be reduced.

Amount of vapour released dependent

on temperature

6



Flashpoint (continued)

Kerosene: Flashpoint 38°C

At 38°C“Ignition”

At 37°C

Insufficient vapourgiven off

At 0°CNegligib le vapourgiven off

7



Ignition Temperature

Ignition temperature is defined as: ‘the minimum temperature at which a flammablematerial will spontaneously ignite’.

Ignition temperature, formerly known as auto-ignition temperature, is an importantparameter since many industrial processes generate heat. Careful selection of electricalequipment will ensure that the surface temperature produced by the equipment, indicated bythe T-rating, will not exceed the ignition temperature of the flammable atmosphere whichmay 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

8



Oxygen Enrichment

The normal oxygen content in the atmosphere is around 20.95%, and if a given location hasa value which exceeds this it is deemed to be oxygen enriched. Typical examples of whereoxygen 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 ignitiontemperature of flammable materials as shown in the table below.

Ai r Increased OxygenMaterial

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 themajority of gases and vapours, thereby widening their flammable range. This is illustrated inthe following table.

Ai r Increased OxygenMaterial

LEL%

UEL%

LEL%

UEL%

Methane 5 15 5.2 79

Propane 2.2 9.5 2.3 55

Hydrogen 4 75 4.7 94

* All values obtained from a source other than PD IEC60079-20

* All values obtained from a source other than PD IEC60079-20

Thirdly, oxygen enrichment of a flammable atmosphere can allow it to be ignited with muchlower 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 beassured because of the modified nature of the flammable mixture.

9



Density

If a flammable material is released, it is important to know whether the material will rise orfall in the atmosphere. The different flammable materials are compared with air andallocated 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 be2. 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, suchas butane or propane, can drift along at ground level and possibly into a non-hazardouslocation, or may collect in locations lower than ground level without ever dispersing. Suchlocations should be well ventilated in order to avoid ignition due to a stray spark or adiscarded cigarette.

Knowledge of where a flammable material will collect ensures that gas detectors when fittedwill be located at the correct level and ventilation is directed accordingly.

<1

>1

MaterialRelative vapour

density

1 Ai r

Propane 1.56

Methane 0.55

Ethylene 0.97

Hydrogen 0.07

Acetylene 0.9

Diethyl Ether 2.55

Kerosene 4.5*

CarbonDisulphide

2.64

* Value obtained from a sourceother than PD IEC60079-20

10



Area Classi ficat ion

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, installationand 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 quantitiessuch 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 everysource of release in the given areas of an installation. Zoning will have a bearing on, andsimplify 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 termsof the probability, frequency and duration of a release.

The three Zones, as defined in BS EN60079-10: Electrical apparatus for explosive gasatmospheres, Part 10. Classification of hazardous areas, are as follows:

Zone 0 - In this Zone, an explosive gas atmosphere is continuously present, orpresent for long periods.

Zone 1 - In this Zone, an explosive gas atmosphere is likely to occur in normaloperation.

Zone 2 - In this Zone, an explosive gas atmosphere is not likely to occur innormal operation and, if it does occur, is likely to do so onlyinfrequently and will exist for a short period only.

Although not specified in IEC 60079-10, but quoted in API RP 505**, the duration of a gasrelease, 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 Installationsat Petroleum Facilities Classified as Class I, Zone 0, Zone 1, and Zone 2.

11



Area Classi fi cat ion (continued)

Zone representation for ‘Area Classification Diagrams’ as recommended inBS EN60079-10

12




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 0

Zone 1

Sump:

Zone 1

13




Sources of Release

Welded pipe joint:( Non-hazardous )

Flanged joint :( Zone 2)

Pump gland:( Zone 2 or Zone 1

depending on thequality of the seal )

Space above liquidin a closed tank:( Zone 0)

14



Gas / Apparatus Grouping

In the IEC system, the group allocation for surface and underground (mining) industries areseparate. Group I is reserved for the mining industry, and Group II which is subdivided intoIIC, 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 degreeof risk they represent when ignited. One method involved determining the minimum ignitionenergy which would ignite the representative gases. The values obtained are relevant toIntrinsically Safe apparatus. In the table below it can be seen that for Group II, hydrogenand 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 theform of an 8 litre sphere which was situated inside a gas-tight enclosure. Both halves of thesphere had 25mm flanges and a mechanism enabled the gap dimension between theflanges 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 insidethe sphere was ignited. The maximum dimension between the flanges, which preventedignition 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 moredangerous a gas, the tighter the gap at the flanges has to be. It is important to note that theMESG values are not used for the design of Flameproof apparatus, only the maximumworking 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 leastrisk in terms of ‘minimum ignition energy’ and ‘MESG’.

Gas Group RepresentativeGas

MESG(mm)

MaximumWorking

Gap(mm)

MinimumIgnitionEnergy

(μJ)

I Methane(Firedamp)

1.14 0.5 260

IIA Propane 0.91 0.4 160

IIB Ethylene 0.65 0.2 95

Hydrogen 0.28IIC

Acetylene 0.370.1 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 aflammable material, and apparatus marked in this way mayonly be used in that hazard.

15



Gas / Apparatus Grouping (continued)

The sub-group marking is one of the important considerations during the selection processof explosion protected apparatus. For example, apparatus marked IIA can only be used inIIA 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 usedin all hazards.

Apparatus for determination of M.E.S.G

16



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 manufacturedto BS 229 has sub-group markings which are different to those of the IEC system and thecomparison is shown in the table below. The introduction of the ATEX Directives after 30June 2003 has caused manufacturers to discontinue the production of apparatus to thisstandard, 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

17



Temperature Classification

Approved electrical equipment must be selected with due regard to the ignition temperatureof the flammable gas or vapour which may be present in the hazardous location. Apparatuswill usually be marked with one of the temperature codes shown in the table below.

Temperature Codes

Temperature Code Maximum SurfaceTemperature

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 isbelow the ignition temperature of the flammable material. Moreover, the T-ratingtemperatures are based on a maximum ambient rating of 40°C as far as the UK isconcerned. 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 theapparatus certification, the ambient rating must be compatible with environmental ambienttemperatures, 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 andFar 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 ambienttemperature range which may be as low as -50°C.

Material IgnitionTemperature

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)

18



Temperature Classification (continued)

- 2

- 2

19



Ingress Protection

Enclosures of electrical equipment are classified according to their ability to resist theingress 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 theenclosure. 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 waterentering the enclosure, i.e. 0 indicates than no protection is afforded, and 8 that theapparatus can withstand continuous immersion in water at a specified pressure.

An abridged version of the full table is shown below.

Solid Objects Water

FirstNumeral

Level of ProtectionSecondNumeral

Level of Protection

0 No protection 0 No protection

1Protection against objectsgreater than 50 mm

1Protection against drops of waterfalling vertically

2Protection against objectsgreater than 12 mm

2Protection against drops of waterwhen tilted up to 15°

3Protection against objectsgreater than 2.5 mm

3Protection against sprayed waterup to 60°

4Protection against objectsgreater than 1.0 mm

4Protection against splashed waterfrom any direction

5 Dust-protected 5Protection against jets of waterfrom any direction

6 Dust-tight 6Protection against heavy seas- deck watertight

7Protection against immersion inwater 1m in depth and for aspecified time

8Protection against indefiniteimmersion in water at a specifieddepth

20



Unit 2:

Standards, Certification and

Marking



Objectives:

On completion of this unit, ‘Standards, Certif ication 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.


2



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 relyheavily on electrical energy to power, for example, lighting, heating and rotating electricalmachines.

The safe use of electrical energy in the hazardous locations of these industries can only beachieved if tried and tested methods of explosion protection are implemented and to thisend, the authorities involved in the writing of standards, testing and certification of equipmenthave a very important role to play.

Since the early 1920’s, many standards have evolved as a result of careful research, oftenprompted by incidents such as the Senghennydd colliery disaster in 1913 in which 439miners 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 inthe atmosphere. Other disasters include Abbeystead Water Pumping Station in which 16people lost their lives, once again due to the electrical ignition of methane gas, Flixboroughwhere an explosion killed 28 people due to ignition of a massive release of cyclohexane, andmore recently Piper Alpha in the North Sea in which 167 men lost their lives.

Construction of apparatus to relevant standards coupled with testing by an independentexpert test authority will ensure that the apparatus is suitable for its intended purpose.

Explosion protected apparatus may be constructed in accordance with relevant standards,but the integrity of such apparatus will only be preserved if such apparatus 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, butthis document has been superseded by a new series of five separate standards based onthe IEC 60079 series of International standards. These five documents apply to explosionprotected apparatus/systems in all countries in the EU and cover, (1) selection andinstallation of apparatus, (2) classification of hazardous areas, (3) inspection andmaintenance, (4) repair of explosion protected apparatus, and (5) data for flammable gasesprovided by an IEC document (See lower table on page 13). The BS EN60079 standardsare identical to the IEC60079 standards. Although BS 5345 has been withdrawn, itnevertheless remains a source of information for older installations, but applies to the UKonly with regard to the EU.

In the United Kingdom, manufacturing and testing standards are published by anorganisation known as the British Standards Institute (BSI). With regard to the EuropeanCommunity, the organisation which publishes harmonised standards for its member nationsis the European Committee for Electrotechnical Standardisation (CENELEC) and, withglobal harmonisation of standards the ultimate aim, the International ElectrotechnicalCommission (IEC) publishes standards for this purpose.

Historically, equipment designs are evaluated and prototypes tested by independentorganisations, one of which was formerly known as ‘British Approvals Service forElectrical Equipment in Flammable Atmospheres (BASEEFA), but was later known as‘Electrical Equipment Certification Service (EECS)’. The acronym BASEEFA, which hasbeen closely associated with explosion protected apparatus for many years, was retained by

EECS for certification marking purposes. EECS, which was part of the Health and SafetyExecutive (HSE), also published standards for special applications. EECS, however, closed


3



for business in September 2002, but encouraged by several major customers, former staffestablished an independent organisation known as Baseefa (2001) Ltd, and becomingsimply Baseefa two-years later.Having traded since March 2002, Baseefa (2001) Ltd. became an EU Notified Body (NB) inJune 2002 and was allocated the NB Number 1180. With the ATEX Directives becomingmandatory after 30 June 2003 the certification authorities in Europe are now known as

Notified Bodies with their own unique NB number , which will be marked on the certificationlabels of ATEX approved apparatus. Other Notified Bodies in the UK include SIRACertification Service, NB Number 0518, and ITS Testing and Certification Ltd., NBNumber 0359.

Some of the other overseas organisations involved in the publication of manufacturing andtesting standards, and also certification services are introduced later in this Unit.

Reasons for Product Certification

1. To demonstrate product quality with regard to the ability of the apparatus to functionsafely in a hazardous environment.

2. To enhance market acceptability by inspiring confidence in those involved in theselection, purchase, installation, operation and maintenance of approved/certifiedproducts.

3. To improve quality and safety control.

Certification Process

The ATEX Directives, ATEX 95 (formerly ATEX 100a) and ATEX 137, became mandatoryafter 30 June 2003. ATEX 95 is the product directive and ATEX 137 is the user directive. ATEX 95 requires all new equipment, which includes not only electrical equipment but alsomechanical equipment, e.g. pumps, gearboxes etc, and protective systems for use inpotentially explosive atmospheres, placed on the market of the European Community for thefirst time to be manufactured in compliance with the directive. Apparatus from out-with theEU, whether new or second hand, imported into the European Community and placed on themarket for the first time must also be in compliance with the directives.

In order to comply with ATEX 95, products must satisfy the Essential Safety Requirements(ESR’s) specified in the annexes of the Directives, with regard to the inherent risksassociated with the product for the protection of the public. This applies to both electrical andnon-electrical (mechanical) equipment. Subject to a successful Conformity Assessment, thiswill enable the product to display the CE mark.

The Conformity Assessment involves a series of Basic Modules which are listed in the tablebelow and their application in the subsequent simplified flow chart.


4



CE Conformity Assessment Modules

A Internal control of production Covers internal design and production control. Does notrequire the involvement of a notified body.

B EC type-examination Covers the design phase, the EC type-examination beingissued by a notified body. Has to be followed by a modulefor assessment during the production phase.

C Conformity to type Covers the production phase after module B. This moduleconfirms conformity of the product with that described inthe 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 ENISO 9002 and the involvement of a notified body who hasresponsibility for the approval and control of the qualitysystem regarding production, end product inspection andtesting implemented by the manufacturer.

E Product quality assurance Covers the production phase following module B.Production quality assurance is based on the standard ENISO 9003 and the involvement of a notified body who hasresponsibility for the approval and control of the qualitysystem regarding end product inspection and testingimplemented by the manufacturer.

F Product verification Covers the production phase following module B. The ECtype examination carried out by the notified body, toensure conformity to type in module B, is followed by theissue of a certificate of conformity.

G Unit verification Covers the design and production phases. A certificate ofconformity is issued after examination of every product bythe notified body.

H Full quality assurance Covers the design and production phases. Qualityassurance is based on the standard EN ISO 9003 and theinvolvement of a notified body who has responsibility forthe approval and control of the quality system for design,manufacture, final product inspection and testingimplemented by the manufacturer.


5



CE Conformity Assessment Modules (continued)

The illustration below shows how the modules listed on the previous page may beimplemented to obtain the CE marking for apparatus.

Design phase

Module A

Module C

Module D

Module E

Module F

Module G

Module B

Module H

Manufacturer

Production phase

ATEX 95

The ATEX Directive 94/9/EC ( ATEX 95 ) was adopted by the EC to enable free trade ofproducts between member states through alignment of technical and legal requirements.The directive applies not only to electrical equipment but also to mechanical equipment andprotective 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 ignitioncapable and requiring the inclusion of special design and installation techniques to preventignition 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 explosionprotection system. Protective systems include quenching systems, flame arrestors, fast-acting shut-off valves and pressure relief panels installed to limit damage due to anexplosion or prevent the spread of explosions.


6



ATEX 137

The ATEX Directive 99/92/EC ( ATEX 137 ), commonly known as the ‘use’ directive, isimplemented 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 presentinto hazardous or non-hazardous areas.

d. Have in place procedures/facilities to deal with accidents, incidents and emergenciesinvolving dangerous substances in the workplace.

e. Provide appropriate information and training of employees for their safety regardingprecautions 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 adangerous 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 amaintenance programme.

Marking of Hazardous Areas

All workplace hazardous areas must be indicated by a sign, as illustrated below, at the entrypoints to the hazardous areas. This applied to all new installations brought into service after30 June 2003. Existing installations were allowed an additional 3 years to meet thisrequirement. The directive specifies the exact requirements for the sign but generally it isrequired to be triangular with a yellow background, black border and marked ‘Ex’.

Ex


7



European Test Authorities

For the purpose of the ATEX Directives, the European test/certification authorities are nowknown as Notified Bodies, organisations which are registered with their respective

governments. Some examples are shown in the map of Europe below along with theirNotified Body (NB) number.

Finland: VTT Industrial Systems (0537)

Sweden: SP-Swedish National Testin 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

Bel ium: ISSeP (0539

France: LCIE (0081)

INERIS (0080)

S ain: LOM 0163

Italy: CESI (0722)

Germany: PTB (0102)


8



Evolution of BS – British Standards

SMRE: Safety in Mines Research Establishment

BASEEFA: British Approvals Service for Electrical Equipment in flammable Atmospheres


9



Ex FacilitNo

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10

Comparison of IEC, European (CENELEC) and Bri tish Standards

Prior to the closer ties between the UK and Europe, electrical equipment, such as flameproofor increased safety etc., was manufactured in accordance with the British Standard BS4683. 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 beconfused 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 theUK test house BASEEFA, later to become known as EECS. Other examples of marks areshown on page 14 of this Unit.

Because of the differences in standards, e.g. equipment manufactured in the UK could notbe used in the other European countries and vice-versa, and hence, equipment made to BS4683 could only be used in the UK, or in other countries outside Europe. Co-operationbetween 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 waspublished as BS 5501 and comprised nine separate parts as shown in the third column of

the table on page 11. The Euronorm equivalents, written in French or German, are shown onthe first column. Column four shows the second generation of the UK version of theharmonised standards which replaced BS5501.

However, with the trend towards global harmonisation of standards continuing to makeprogress, a new series of standards have been gradually introduced having numbers basedon the International Standard numbers (second column), i.e. BS EN60079, as shown incolumn five of the following table.



Ex FacilitNo

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11

Comparison of IEC, European (CENELEC) and Bri tish Standards

CENELECEuronorm

(EN) Number

InternationalStandards

British Standard(BS) Number

Revised Standard(BS EN) Number

Latest RevisedStandard

(BS EN) Numbe

EN 50 014 IEC 60079-0 BS 5501: Pt. 1 BS EN50 014 BS EN60079-0









EN 50 021 IEC 60079-15 BS EN50 021 BS EN60079-15

IEC 60079-26 BS EN60079-26

IEC 60079-27 BS EN60079-27

IEC 60079-29-2 BS EN60079-29-2

IEC 60079-30-1 BS EN60079-30-1

IEC 60079-30-2 BS EN60079-30-2



Other (older) British Standards

The standards listed below are those which preceded the harmonised European standardslisted in the previous table. These standards, with the exception of BS 889, were not entirelyobsolete, 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, wherestill in use, must be maintained in accordance with these standards. It is, therefore, importantthat reference to the correct standard is made before maintenance is carried out on suchapparatus.

BS 229 Flameproof enclosure of electrical apparatus

BS 889 Flameproof electric fittings

BS 1259Intrinsically 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 ofelectrical 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


12



Standards for Selection, Installation and Maintenance

As previously stated, the UK Code of Practice BS 5345, which had for many years providedrecommendations for the selection, installation and maintenance of explosion protectedapparatus for use in potentially explosive atmospheres (other than mining applications or

explosives processing and manufacture), listed in the upper table below, was superseded bythe standards listed in the lower table. BS 5345, however, may be referred to forinstallations installed in accordance with its requirements. The table below illustrates thecomponent 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 andpressurised 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 tablebelow. Furthermore, the BS EN standards are identical to the IEC standards shown withinbrackets in the table below.

BS EN / IEC Nos .Electrical Apparatus for Explosive Gas Atmospheres:

BS EN60079-10: 2003(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 ofelectrical installations in hazardousareas (other than mines)

BS EN60079-19: 2007(IEC 60079-19: 2006)

Part 19: Repair and overhaul for apparatus usedin explosive atmospheres (other thanmines or explosives)

PD IEC60079-20: 2000(IEC 60079-20: 1996)

Data for flammable gases and vapours, relatingto the use of electrical apparatus


13



Certifi cation 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) This is the EECS (BASEEFA) symbol and

used to identify equipment for surface

industry use only.

4)

Equipment marked with this symbol, the

European Community mark, indicates that

the equipment has been constructed andtested in accordance with the

CENELEC/EURONORM standards.

5)

Symbol used by the German notified body

PTB

6)

The most commonly used symbol of theAmerican certification authority

Underwriters Laboratories (UL)

7)

The mark used by the Canadian Standards

Association

MEx


14



Apparatus Marking

Prior to the introduction of the ATEX Directives on 1 July 2003, apparatus for use inhazardous areas were marked as illustrated below. Apparatus complying with the ATEXDirectives, 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 areshown on page 18. Apparatus approved/certified as providing a method of protection for use in hazardouslocations are 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.

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 beused in the UK because it had been constructed to the British Standard BS 4683, which wasnot a harmonised European standard. Apparatus 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 20onwards for details of this scheme.

For apparatus marked EEx as in example ii. and iii., the additional letter ‘E’ indicates that theapparatus has been constructed to a harmonised European standard. Such apparatus wouldbe marked with the EECS certification authority symbol (fig 3) as well as the EuropeanCommunity mark (fig 4). Sample labels are shown below, and it should be noted that theconstruction standard to which the equipment has been manufactured to, i.e. BS 4683: Part2, BS 5501: Parts 1 & 5 and EN50 014 & EN50 018 are also given on the labels. For BS4683 equipment, the IEC equivalent standard, i.e. IEC 79-1 in example (a) below, is usuallyincluded.

(a) (b)


15



Apparatus Marking (cont inued)


16



Certifi cation Numbers

The certification number illustrated below was used by BASEEFA prior to the introduction of the ATEXdirectives, but the numbers used by other certification authorities will be different. Also,


17



Marking of ATEX Compliant Apparatus

ATEX represents the European Union’s Directive 94/9/EC, now known as ATEX 95, whichspecifies the new approach for the certification of explosion protected apparatus. Anintroduction 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 directivewill have on the marking of explosion protected apparatus. This will be the most obviousdifference to those involved in the selection, installation and maintenance of explosionprotected apparatus.

The marking required by ATEX 95 is illustrated below, which is additional to the markingrequirements already discussed.

0000

CE Mark

Notified body

ID number

EU Explosive

Atmosphere

Symbol

The Equipment Categories are defined overleaf


18



Category Definitions

Group II Category 1: Very high level of protection

Equipment with this category of protection may be used

where an explosive atmosphere is present continuouslyor for long periods, i.e. Zone 0 or Zone 20.

Category 2: High level of protection

Equipment with this category of protection may be usedwhere an explosive atmosphere is likely to occur innormal operation, i.e. Zone 1 or Zone 21.

Category 3: Normal level of protection

Equipment with this category of protection may be used

where an explosive atmosphere is unlikely to occur or beshort duration, i.e. Zone 2 or Zone 22.

Group I Category M1: Very high level of protection

Equipment can be operated in the presence of anexplosive atmosphere.

Category 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) enables a risk assessmentapproach 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 suitthe zone, which does not take into consideration the consequences of an explosion. Thetable below shows the zones where both ATEX Categories and EPL’s may be used from atraditional selection approach.

Zone ATEX Categories EPL’s

0 1 Ga

1 2 Gb

2 3 Gc


19



Equipment protection levels (EPL’s)

Equipment Protection Levels (EPL’s) are available for both gases and vapours and alsocombustible dusts as illustrated in the table below. Equipment marked ‘G’ is for use inflammable gases, vapours or mists, 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 subjectto rare faults.

Gb Equipment for explosive gas atmospheres, having a ‘high’ level of protection, whichis not a source of ignition in normal operation, or when subject to faults that may beexpected, 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 someadditional protection to ensure that it remains inactive as an ignition source in thecase 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 thatmay be expected, though not necessarily on a regular basis.

Dc Equipment for combustible dust atmospheres, having an ‘enhanced’ level ofprotection, which is not a source of ignition in normal operation and which may havesome additional protection to ensure that it remains inactive as an ignition source inthe case of regular expected occurrences.


20



EPL’s assigned to protection types (gases)

EPL Ga

EPL Protection type Marking

Intrinsic Safety Ex iaEncapsulation Ex ma

Ga

Two separate protection types eachmeeting EPL Gb

EPL Gb


Flameproof Ex d

Increased Safety Ex e

Intrinsic Safety Ex ib

EncapsulationEx mExmb

Oil immersion Ex o

PressurisationEx 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


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


21



EPL’s for combustible dusts


Intrinsic Safety Ex iD

Encapsulation Ex mDDa, 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, equipmentmanufactured 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 asillustrated 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 themarking illustrated on page 18.

Area for code indicatingthe Licensee Numberand the Certification

odyB


22



Examples of equipment certification


23




24




25



Baseefa Wallchart


26



UNIT 3

FLAMEPROOFEEx d / Ex d



OBJECTIVES

On completion of this unit, ‘flameproof EEx d / Ex d apparatus, you shouldknow:

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 andstopping devices, circuit protection, obstruction of flamepaths and additionalweatherproofing methods in accordance with BS EN60079-14.

d. The inspection requirements with regard to BS EN60079-17.


2



Flameproof EEx d / Ex d

Flameproof is one of the original methods of explosion protection developed for use in themining 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 componentssuch 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 anexplosion is permitted. This explosion, however, must be contained by the robustlyconstructed flameproof enclosure.


3



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 electricalapparatus (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 14Electrical installations in hazardous areas (other than mines)

BS EN60079-17: 2007 Electrical Apparatus for explosive gas atmospheres: Part 17Inspection and Maintenance of electrical installations in hazardousareas (other than mines)

BS 5345: Part 3: 1979(Withdrawn)

Code of Practice for the Selection, Installation and Maintenance offlameproof apparatus

Definition

The construction standard BS EN60079-1 defines flameproof as:

‘An enclosure in which the parts which can ignite an explosive atmosphere areplaced and which can withstand the pressure developed during an internal explosion

of an explosive mixture, and which prevents the transmission of the explosion to theexplosive atmosphere surrounding the enclosure’

Zone of Use: 1 & 2

Ambient Condi tions

Flameproof enclosures are normally designed for use in ambient temperatures in the range- 20°C to +40°C unless otherwise marked.


4



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 containcomponents 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 thegaps at the joints and threads of cable entries must be long and narrow to cool theflames/hot gases before they reach and cause ignition of a flammable atmosphere whichmay 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, phosphorbronze and stainless steel may be used. Plastic materials are also used but the free internalvolume must not exceed 10cm3. The latest standard specifies that for flanged joints ‘THERESHALL 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, SparksHot Surfaces

Contactors, Relaysetc

Ga


5



Gap Dimensions

Although the standards specify that there shall be no intentional gap at the joints offlameproof equipment, gaps will normally exist due to manufacturing methods, tolerancesand economics, but must not be in excess of the dimensions specified in the tables of the

relevant standards for a given hazard.

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


6



Flamepath Joints

he diagrams below illustrate examples of three joint types specified in the British standard

pigot joints will be used at junction box covers and motor enshields.

hreaded joints are used for cover joints, cable gland and conduit entries. An adequate

contrast to BS EN50019, the most recent standard, BS EN60079-1 permits the use of

TBS EN60079-1 for use in flameproof apparatus. In a flanged joint, the machined surface onthe 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 thestandard when the cover is properly bolted down. This type of joint will be used at the coversof, for example, junction boxes.

S Tflamepath length is normally achieved with a thread engagement of five full threads.

Inflanged 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

Interior

b) Spigot joint

Interior

c) Screwed joint

Interior


7



Flamepath Joints Types (Rotating Machines)

(d) cylindrical (shaft gland) joint

) labyrinth joint for shafts(d


8



Flamepath Joints (other examples)

lamepaths other than those at cover joints are also necessary where, for example, an

ush-button spindle

able (gland) entry

Factuator spindle passes through the wall of an enclosure, or where a cable gland or conduitenters an enclosure. Examples are shown below.

P

C


9



Entry by Cable Gland or Conduit

he thread engagement requirements for cable and conduit entries are specified in the

nly threaded entries are permitted for all cable glands or conduits entering flameproof

Volume

Tstandard BS EN60079-1 and apply to the three sub-groups IIA, IIB and IIC.

Oenclosures – clearance entries are not permitted.

≤ 100 cm3 > 100 cm3

ThreadEngagement

AxialL

ThreadEngagement

AxialLengthength

> 5 Full Threads > 5mm > 5 Full Threads > 8 mm

s already stated the above requirements for thread engagement are specified in the latest Astandard BS EN60079-1: 2007, but the previous standard BS EN50018: 2000 required atleast 6 full threads engagement in order to make sure that 5 full threads were actuallyengaged.


10



Ex FacilitNo

yvember 2008

11

Unused Cable or Conduit Entr ies

is important that unused cable/conduit entries in flameproof enclosures are closed using

Stoppers of the type illu C’ in the above diagram are available with

sed Cable or Conduit Entr ies

is important that unused cable/conduit entries in flameproof enclosures are closed using

Stoppers of the type illustrated by example C’ in the above diagram are available with

ItItappropriate 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.

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.

strated by example ‘‘

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 makeunauthorised removal more difficult, but may be fitted with the hexagon recess facing theexterior. Whichever way round they are fitted the certification markings must be visible forease of identification during ‘Visual’ inspection programmes. Also the thread engagementrequirements must be met. Stoppers of this type are tightened using an Allen Key.

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 makeunauthorised removal more difficult, but may be fitted with the hexagon recess facing theexterior. Whichever way round they are fitted the certification markings must be visible forease of identification during ‘Visual’ inspection programmes. Also the thread engagementrequirements 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



Flamepath Gap Dimensions – BS EN60079-1, Table 1

Maximum gap

mm

For a volumecm3

V ≤ 100

For a volumecm3

100 < V ≤ 500

For a vocm

500 < v ≤

Type of JointMinimum

width of jointL

mm

I IIA IIB I IIA IIB I IIA

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 0.3

Flanged, cylindrical orspigot joints

25 0.50 0.40 0.20 0.50 0.40 0.20 0.50 0.4

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 0.3

25 0.50 0.40 0.30 0.50 0.40 0.25 0.50 0.49

Sleevebearings

40 0.60 0.50 0.40 0.60 0.50 0.30 0.60 0.5

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 0.4

25 0.75 0.60 0.45 0.75 0.60 0.40 0.75 0.6

Cylindrical joints forshaftglands ofrotatingelectricalmachineswith:

Rolling-elementbearings

40 0.80 0.75 0.60 0.80 0.75 0.45 0.80 0.7

NOTE: Constructional values rounded according to ISO 31-0 should be taken when determining the maximu


12



yvember 2008

13

Flamepath Gap Dimensions – BS EN60079-1, Table 2

Maximum gapmm

Type of JointMinimum

width of jointL

mm

For a volumecm3 V ≤ 100

For a volumecm3 100 < V ≤ 500

For a volumecm3 500 < 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

12.5 0.15 0.15 0.15

25 0.18b 0.18b 0.18b

40 0.20c 0.20c 0.20c

Spigot joints(Figure 2a)

c ≤ 6mmd ≤ 0.5LL = c + df ≤ 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

Cylindrical jointsSpigot joints(Figure 2b)

40 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

Cylindrical joints forshaft glands of rotatingelectrical machines withrolling element bearings

40 0.30 0.30 0.30

a Flanged joints are permitted for explosive mixtures of acetylene and air only in accordance wi

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 detergap

Ex FacilitNo



Pressure Piling

If a flammable mixture us compressed prior to ignition, the resulting explosion will beconsiderably 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 otherside, resulting in a secondary explosion that can reach an explosion pressure around threetimes 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 totalcross-section) around any potential obstruction, which may be a large component or anumber of components. This will ensure that pressure piling is kept under control.


14



Pressure Piling in Flameproof Motors

Section 1 Section 2

Airgap

In rotating electrical machines, sections with appreciable free volume normally exist at eachend 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 theflammable mixture in section ‘2’ which will have been pressurised by the initial explosion.The airgap, therefore, also acts as a flamepath.


15



Obstruction of Flamepaths

The UK Code of Practise BS 5345 Part 3 recommended that obstruction of flameproofenclosures, particularly those with flanged joints, should be avoided. This recommendation isalso 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 otherelectrical apparatus etc., in close proximity to the opening at the joint can, in the event of aninternal explosion, reduce the efficiency of the flamepath to the extent that ignition of theexternal gas or vapour could occur.

The minimum distance between the flamepath opening and an obstruction, as specified inBS EN60079-14 (and BS 5345: Part 3) are:

Group Distance

IIA 10 mm

IIB 30 mm

IIC 40 mm


16



Ingress Protection Methods

The diagrams below illustrate the location of gaskets or rubber ‘O’ rings for ensuring a highlevel 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.


17



Weatherproofing

lameproof equipment must have a level of ingress protection to suit the environmental

here environmental conditions are extreme, consideration of additional measures may be

he use of non-setting grease on the machined surfaces of flamepaths has two advantages

ilicone based greases require careful consideration in order to avoid possible damage to

or Flameproof equipment, the limitations for the use of non-hardening tape as specified in

a. Non-hardening tape maybe applied around the flamepaths of apparatus with flanged

b. For group IIB apparatus, one layer with a short overlap may be applied around the

Note: The Code of Practise BS 5345: Part 3 (withdrawn but a relevant source of

Non-hardening tape must not be used on equipment marked IIC (or IIB + H2)

. The machined surfaces of flanged joints must not be painted prior to assembly.

Fconditions in which the equipment is installed. Equipment should have, as part of theirapproved design, seals or gaskets to prevent the ingress of water and/or dust. Additional

measures may be required, however, to comply with the requirement in BS EN60079-14 thatflameproof joints must be protected against corrosion and the ingress of water.

Wnecessary if this is permissible after consultation with relevant standards, or themanufacturer or other authority. These measures are specified in BS EN60079-14, theStandard which gives recommendations for the selection and installation of electricalequipment in hazardous areas. This standard specifies the limitations of use for non-hardening grease bearing textile tape (typically Denso tape) as detailed below and non-setting grease or compounds.

T

since, in addition to providing an additional level of ingress protection, it also inhibits theformation of rust on these surfaces.

Sthe elements of gas detectors.

FBS EN60079-14 are as follows:

joints allocated to group IIA applying one layer only with a short overlap.

flamepaths of apparatus with flanged joints, but only if the gap is less than 0.1mmregardless of the joint width.

information for older installations) recommended that expert advice be soughtwhen considering the use of non-hardening tape on group IIB or IICequipment installed in locations containing group IIB gases or vapours.

c.installed in locations containing group IIC gases or vapours.

dHowever, an enclosure may be painted after assembly.


18



Direct / Indirect Entry

he selection of cable glands for flameproof apparatus is influenced by several factors, one

irect entry comprises a single flameproof chamber within which components such as

Direct entry Indirect entry

Tof which is the method of entry into the apparatus. There are two entry methods, namelydirect and indirect, examples of which are shown below.

Dswitches, relays or contactors may be installed. Flameproof apparatus with indirect entry has two separate chambers, one of which contains only terminals for connection of theconductors of incoming cables or conduit. Connection to the arcing components in thesecond compartment is made via these flameproof terminals which pass through theflameproof interface between the two compartments.

EEx d

Enclosure

Flamepaths

EEx d

reEnclosu

Bushings

EEx d cable

glands


19



Electrical Protection

lameproof enclosures are tested for their ability to withstand internal gas explosions only,Fthey are not capable of withstanding the energy which may be released as a result of aninternal 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.


20



Modification of Flameproof Enclosures

lameproof enclosures are normally supplied complete with all internal components fitted

he certification, therefore, “seals” the design of the apparatus so that any unauthorised

a. Replacement components should always be exactly the same as the original

ote: Illustrations are for demonstration only and must not be carried out

Fand certified as a single entity by a recognised test authority. The testing procedure will takeinto consideration the free internal volume after all the components have been fitted, the

temperature rise (determined by the maximum power dissipation), creepage andclearance distances, and the rise in pressure as a result of an internal explosion using agas/air mixture in its most explosive proportions.

Tmodifications will effectively invalidate the approval/certification. Modifications willmodify the original test results recorded by the test/certification authority and, consequently,the following points should be observed.

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, andincreased volume will result if a smaller component is fitted.

N

Replacement o f ‘A’Originalarrangement

Replacement of ‘A’with a larger item with a smaller item


21



b. Adding components is also forbidden because of the possibility of increased

Addi tion of component ‘C’

c. The removal of components should also be avoided since an increase in the free

Removal of component ‘B’

explosion pressure as a result of pressure piling.

internal volume will result. The original test results, prior to certification, would becompromised as a result of a modification such as this.


22



Note: Illust rations are for demonstration only and must not be carried out

d. Drilling and tapping of cable gland/conduit entries should only be carried out

Correct alignment of the threaded entry is also important since the flamepath

he strength of a flameproof enclosure may be impaired if the number and size

e. Gaskets can only be replaced; they must not be added retrospectively if not included

The use of unauthorised sealants should also be avoided when it is required to

by the manufacturer of the enclosure, or his approved agent. The threads of theentries are required to be compatible with those of cable glands or conduit in terms oftype of thread, thread pitch and clearance tolerance since flamepaths exist at thesepoints.

length at one side will be reduced if the cable gland or conduit is not fittedperpendicular to the face of the enclosure.

Tof 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 andlocation of entries to ensure the enclosure will contain an internal explosion.

as part of the original design.

maintain or improve the IP rating.


23



BS EN 60079-17 Table 1: Inspection Schedule for Ex’d’, Ex’e’, and Ex ‘n’

Ch k that : x’n’

Installations (D = Detailed, C = Close, V = Visual) ec Ex’d’ Ex’e’ E

Grad pecte of Ins ion

D C VV D C V D C

A PPARATUS A

1 pparatus is appropriate to area classification A * * * * * * * * *

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 gasketsand/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 blankingelements are of the correct type and are complete and tight

- Physical check - Visual check

* **

* **

* **

10 ,Flange faces are clean and undamaged and gaskets, if anyare 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 STALLATIONIN

1 priateType of cable is appro * * *

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 ismaintained

* * *

6 Earthing connections, including any supplementary earthinghtbonding connections are satisfactory (e.g. connections are tig

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 satisfactory9 Automatic electrical protective devices operate within permitted

limits

* * *

10 * * * Automatic electrical protective devices are set correctly (auto resetnot 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 inaccordance with IEC 60079-14

* * *

14 stallation in accordance with * * * * * *Variable voltage/frequency indocumentation

C NVIRONMENTE

1 pparatus is adequately protected against corrosion, weather, A

vibration and other adverse factors

* * * * * * * * *

2 No undue accumulation of dust and dirt * * * * * * * * *

3 Electrical insulation is clean and dry * *


24



Note

pparatus using a combination of both ‘d’ and ‘e’ types of protection will require reference to

ote 2

he use of electrical test equipment, in accordance with items B7 and B8, should only be

1

Aboth columns during inspection.

N Tundertaken after appropriate steps are taken to ensure the surrounding area is free of aflammable gas or vapour


25



Unit 4:

Increased SafetyEEx e / Ex e




2

Objectives:

On completion of this unit, ‘Increased Safety EEx e / Ex e Apparatus’, youshould 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.




3

Increased Safety EEx e / Ex e

The explosion protection concept Increased Safety was invented in Germany where it hasbeen widely used for many years. It is has become popular in the UK mainly because it hasa number of advantages for certain applications over the traditional flameproof method of

explosion protection. America has traditionally relied on the use of explosion-proofenclosures 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 probablybeen viewed with a little trepidation.

This method of protection has a good safety record and comparable with the other methodsof protection. The letter ‘e’ which symbolises this method of protection is taken from theGerman 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 ofProtection “e”

BS EN60079-14: 2008 Electrical apparatus for explosive gas atmospheres: Part 14Electrical installations in hazardous areas (other thanmines)

BS EN60079-17: 2007 Electrical apparatus for explosive gas atmospheres: Part 17Inspection and maintenance of electrical installations inhazardous areas (other than mines)

BS 5345: Part 6: 1978

(Withdrawn)

Code of Practice for the Selection, Installation and

Maintenance of Increased Safety apparatus.




4

Definition

‘A protection method in which increased measures are taken to prevent the possibility ofexcessive HEAT, ARCS or SPARKS occurring on internal or external parts of the apparatusin normal operation’.

Zones of use: 1 & 2

Ambient Temperatures

Increased Safety enclosures are normally designed for use in ambient temperatures in therange -20 °C to +40 °C unless otherwise marked.




5

Principle

The safe operation of Increased Safety apparatus is dependent on the prevention of anysource of ignition, i.e. excessive surface temperatures, arcs or sparks, which mightotherwise 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 impactenergy 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 thermalstability, have been subjected to a ‘Comparative Tracking Index (CTI)’ test to determine theirresistance 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 thesurface of an insulator.

Tracking: The leakage current which passes across thecontaminated surface of an insulator between liveterminals, or live terminals and earth.

Comparative Tracking Index: The numerical value of maximum voltage, in volts at whichan insulation material withstands e.g., 100 drops ofelectrolyte (usually ammonium chloride solution in distilledwater) without tracking.




6


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 issubjected 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. Eachmaterial must withstand the specified number of drops of the electrolyte at the specifiedvoltage for it to be acceptable.

Thus, the combination of high quality materials and good design, which incorporatesspecified creepage and clearance distances, ensures that Increased Safety terminals have agreater 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 trackingresistance 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




7


Creepage and Clearance Distances

Terminals

Partition

Screw heads

Clearance

Creepagepath

Clearance & creepagepath 26.4mm

Clearance and creepage pathsto extend to adjacent clampingscrew

Clearance andcreepage paths14.0mm

Creepage path runs

between locating rivet andassembly rail 27.8 mm

Clearance path extendsfrom end of bolt to

assembly rail 20.5mm




8


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 10.0800 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 125.0 140.0 160.0 100.0Note 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 ofsupply voltages given in table 3b of IEC 60664-1

Note 2: The creepage distance and clearance values shown are based on a maximumsupply voltage tolerance of +10%.

Note 3: At 10 V and below, the value of CTI is not relevant and materials not meeting therequirement for material group IIIa may be acceptable.




9

Increased Safety Terminal Types and Ratings

The terminals are de-rated so that the maximum current for Increased Safety applications isnearly half that for standard industrial applications as illustrated in the following table forenclosures 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.

TerminalType

ConductorSize

Increased SafetyMaximum Current

(amps)

Industrial MaximumCurrent(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


Terminal Locking Device

It is essential that conductors are securely connected in the terminals to prevent sparksoccurring as a result of loose connections. The illustration below shows how this is achieved.




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 4in which the terminal content is assessed by dividing the‘enclosure factor’ by the certified current rating of a giventerminal.

Load Limit: Similar to ‘enclosure factor’ but used only on apparatusmanufactured to BS 5501 Part 6.

Kelvin Rating: Normally used for high current applications and apparatusmanufactured to BS 4683 Part 4 and BS 5501 Part 6. In this

method, enclosures and terminals are assigned a temperaturerating. Enclosures will normally be limited to a temperature riseof 40K for a T6 temperature rating, but the temperature for theterminals will be dependent on their type, rated current, size ofassociated conductor, and the size of enclosure in which theyare installed. This involves the use of tables which areprovided by the manufacturer. Once the terminal ‘K’ rating hasbeen established, it is divided into the ‘K’ rating for theenclosure to give the number of terminals of one type whichmay be installed.

Max Dissipated Power: This is a method which will replace the current ‘load limit’method and applies to apparatus manufactured to BS 5501Part 6 and BS EN50019. In this method, enclosures areassigned a ‘watts dissipation’ rating, but the rating of theterminals is determined by use of a unique table (provided bythe manufacturer) for the enclosure. This table provides the‘watts dissipation’ of the terminal through consideration ofconductor size and load current. The terminal content isdetermined by dividing the ‘watts dissipation’ value for theterminal into that for the enclosure.

Another method used by manufacturer’s is to specify the maximum current per pole andalso the maximum current per mm2.

Examples of labels with the above information are shown overleaf.




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. 9364EEx e II T6

BASEEFA CERT. No. EX84B1333XBS5501 Pt.6 (EN50 019)

LOAD LIMIT 600A

Klippon

ENCLOSURE TYPE TB11BS 4683 Pt.4 Ex e II T6BASEEFA No. Ex 77152/BMAX. CIRCUIT VOLTAGE 726ENCLOSURE FACTOR 416SERIAL NUMBER 1334

Klippon

TYPE TB12 S/No.867594EEx e II T6

BASEEFA CERT. No. Ex84B3290XBS5501 Pt.6 (EN50 019)

LOAD LIMIT 40K

Klippon

TYPE STB2 EEx II T6 S/No. T499BASEEFA CERT. No. 86B 2138XBS5501 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 8142BXTYPE REF PL639 SERIAL No. 9960/89

PHASE-TO-PHASE 726MAX VOLTS

PHASE-TO-EARTHMAX.CURRENT DENSITY

AMPS PER SQ. MM 4MAX AMPS PER POLE 10




12

Sample Calculation us ing ‘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 tocarry without exceeding the temperature classification.

Thus, the number of terminals of one type which can be installed in a given enclosure issimply the ‘Load Limit’ divided by the Increased Safety current rating of the terminal type tobe 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 =ratingterminal2.5SAK

LimitLoad

=15600

= 40 SAK 2.5 terminals

Where the circuit current is below the certified current rating of the terminals, it may bepossible to base the terminal population on the circuit current provided it will not exceed theassigned 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 =currentCircuit

LimitLoad

=10

600

= 60 SAK 2.5 terminals




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-connect ion.

Insulated combalternative forlinking terminals




14

Terminal Assemblies




15

Installation, Inspect ion and Maintenance

It is essential that Increased Safety enclosures are installed and maintained in accordancewith 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 themanufacturer .

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 theterminal.

5. Partitions should be fitted at either side of terminal linking assemblies.

6. Only one conductor should be fitted to each terminal side.

7. An additional single conductor, min 1.0 mm2, may be connected within the sameterminal 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 temperatureclass.

10. The individual earth continuity plates within plastic enclosures must be bondedtogether and locknuts used to secure glands to the continuity plates. For clearanceholes, serrated metal washers must be used between locknuts and the glandplate.

11. When Intrinsic and Increased Safety circuits occupy the same enclosure the twotypes of circuit must have at least 50 mm clearance between them.

12. There must be adequate clearance between adjacent enclosures to allow properinstallation 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 entryholes are drilled.

15. Cable glands or conduit entries must maintain the minimum ingress protection ofIP 54.

16. All lid and gland plate bolts must be fully tightened after installation.




16

Increased Safety EEx e / Ex e Motors

These motors are similar in appearance to standard industrial motors and inspection of thecertification/rating plate is usually necessary to identify them. These motors are not designedto withstand an internal explosion and hence have special design features to prevent arcs,

sparks and excessive surface temperatures occurring both internally and externally. Theprincipal 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 lockingdevices on terminals.

7. Minimum ingress protection to IP54.

Under stall (locked rotor) conditions, the rotor surface temperature will normally increasefaster than that of the stator windings, and hence, the T-rating applies to both internal andexternal surface temperatures.

Under fault conditions, the motor must trip within the tE time specified on the motor dataplate.

tE time

Defined as: ‘the time taken to reach the limiting temperature from the temperature reached innormal service when carrying the starting current I A 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 afault, the temperature will rise rapidly towards ‘C’ as shown in part 2 of the graph, which isless than the T rating of the motor. The time taken to reach ‘C’ from ‘B’ is known as the t E 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 forapplications which require frequent stopping and starting and/or long run-up times.




17

Determination of tE Time

Limit ing Temperature

Temperature limited either by selected T-Ratingor 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 limitingtemperature (C).

Max limiting temperature

T e m p e

r a t u r e

C

0

Hours Secs

Rotor locked

A

B

C

Time

0




18

Tripping Characteristic of Thermal Overload device

The thermal overload device will be selected for suitability according to its tripping

characteristic. The tE time and I A/IN current ratio are influential in the selection of the deviceand are marked on the motor nameplate.

IN = rated current of motor.

I A = locked rotor current of motor.

Example 1: I A/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: I A/IN = 4.5 and tE time = 8 secs

For these values the tripping time is 10 secs, which is outwith the t E time assigned to the motor, therefore an overload device with thischaracteristic would not be suitable for the values specified.

40

20

10

1

2

5

3 4 5 6 7 8 9 10

t

t i m e

E

I / I current ratio A N




19

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 * * * * * * * * *






* * * * * * * * *




- Physical check- Visual check

* **

* **

* **

10 Flange faces are clean and undamaged and gaskets, if any,are satisfactory

*









B INSTALLATION

1 Type of cable is appropriate * * *




* * *

6 Earthing connections, including any supplementary earthingbonding connections are satisfactory (e.g. connections are tightand conductors are of sufficient cross section)


** *

** *

** *


* * *

8 Insulation resistance is satisfactory * * *

9 Automatic electrical protective devices operate within permitted

limits

* * *

10 Automatic electrical protective devices are set correctly (auto resetnot possible)

* * *




* * *

14 Variable voltage/frequency installation in accordance withdocumentation

* * * * * *

C ENVIRONMENT

1 Apparatus is adequately protected against corrosion, weather,vibration and other adverse factors

* * * * * * * * *






20

Note 1: Apparatus using a combination of both ‘d’ and ‘e’ types of protection will requirereference 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 areais free of a flammable gas or vapour.



Objectives:

On completion of this unit, ‘Type ‘n’ Apparatus’, you should know:


b. The principle design features.

c. The protection methods applied to arcing/sparking components to enable their use inenclosures etc.

d. The installation requirements according to BS EN 60079-14.



2



Type ‘n’ Protection

Since the presence of a flammable gas or vapour is less likely in Zone 2, the constructionalrequirements for electrical equipment used in these hazardous locations are not as strict asthose 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 exceptthat there is a relaxation in the constructional requirements.

Type ‘n’ protection, a UK innovation, became an accepted method of explosion protection byCENELEC around the year 1999 through the publication of the standard EN50021. Prior tothe issue of this standard by CENELEC, this type of protection was symbolised by the (uppercase) letter ‘N’ when constructed to UK standards and, as far as Europe is concerned, wasonly 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 enablingwider 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 withtype of protection N

BS 4683: Part 3: 1972 Type of protection ‘N’

IEC 60079-15: 2005-03 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 electricalinstallations in hazardous areas (other than mines)

BS 5345: Part 7: 1979(Withdrawn)

Code of Practice for the Selection, Installation andMaintenance of apparatus with type ‘N’ protection.

Definition

The definition for Electrical apparatus with type of protection “n” as given in the BritishStandard BS EN60079-15: 2005 is:

‘A type of protection applied to electrical apparatus such that, in normal operationand in certain specified abnormal conditions, it is not capable of igniting a

surrounding explosive atmosphere’.


3



Zone of use: 2

Ambient condit ions

Type ‘n’ apparatus is normally designed for use in ambient temperatures in the range -20 °Cto + 40 °C unless otherwise marked.

Principle

In Zone 2 hazardous locations, the presence of a flammable gas or vapour is not likely to bepresent, or if it is present it’s duration will be for a short time only. This fact allows the use ofless expensive methods of protection, i.e. non-incendive or type ‘n’ protection. As previouslystated, type ‘n’ protection is similar in concept to increased safety type ‘e’ protection. Thedesign 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 fromoccurring either internally or externally. Since the design requirements are not as strict asthose for increased safety type ‘e’ protection, it is possible for the manufacturer to installwithin type ‘n’ apparatus, components which produce hot surfaces, arcs or sparks, providingthese components have incorporated in them additional methods of protection. Theseadditional 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, arerequired to be impact tested to 7J where the risk of impact is high, or 4J where therisk of impact is low;

2) Minimum ingress protection IP54 where an enclosure has exposed live partsinternally, 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.

Gland entries mustmaintain enclosure

integrity

Material must be suitable

for the environment andmust withstand impact


4



Addi tional protect ion measures

As previously mentioned, components which produce arcs/sparks or hot surfaces may beinstalled in type ‘n’ apparatus provided additional protection measures are included. Theseare explained below.

Energy limited apparatus and circui ts

The technique of energy limitation applies the principles of intrinsic safety by the use ofcomponents, which are part of the apparatus circuits, or outwith the apparatus, to preventignition of a flammable gas. Energy limitation will involve the use of Associated energy-limited apparatus and Energy limited apparatus where both are separate entities, butwhen both are contained in the same item of equipment, the equipment is known as Selfprotected energy-limited apparatus.

Associated energy-limited apparatus

Apparatus of this type will use zener diodes and series resistors to limit thevoltage and current available to sparking contacts and energy storingcomponents within the energy-limited apparatus, or at the output terminals ofthe associated energy-limited apparatus.

Where the supply to the apparatus is mains voltage via a transformer, an upwardtolerance of 10% must be assumed unless alternative measures allowdispensation of this requirement.

Energy limited circuits:

In order that this type of apparatus may be correctly installed, manufacturers arerequired to specify the maximum values of voltage, current, power, inductanceand capacitance including cable inductance and capacitance that may beconnected.

Limitedoutput

energy

Sealed device

A device containing normally sparking components or hot surfaces constructed in such away that opening is prevented in normal operation and in which the sealing effectivelyprevents access by a flammable gas or vapour. The free internal volume must be less than

100 cm

3

.


5



Enclosed break device

This technique is used in, for example, the lamp holders of type ‘n’ apparatus. The examplebelow shows a typical lamp holder in which there are two sets of contacts. One set ofcontacts is enclosed in what is effectively a flameproof enclosure in which the free internalvolume must not exceed 20 cm3. This enclosure is designed to withstand an internalexplosion and the voltage and current limitations are 690 V and 16 A respectively.

Hermetically sealed device

A device which prevents an external gas or vapour gaining access to the interior by sealingof joints by fusion, e.g. welding, soldering, brazing, or the fusion of glass to metal. Theexample of hermetic sealing shown below is a reed switch which comprises a set of contactshermetically sealed within a glass envelope.


6



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) 200k greaterthan the marked maximum temperature and be free of intentional voids. The encapsulantshould have a minimum thickness of 3mm, or not less than 1mm if the free surface area isless than 200mm2.

Restricted breathing

A technique mainly used in type ‘n’ lighting fittings whereby entry to the interior of theapparatus by a flammable gas or vapour is restricted by virtue of good sealing at all jointsand cable entries. For apparatus fitted with a device for routine testing of it’s restrictivebreathing properties the manufacturer will have tested to ensure that an internal pressure of300Pa (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 testingthen the internal pressure must not change from 3kPa (300mm water gauge) belowatmospheric to 1.5kPa (150mm water gauge) in less than 3 minutes. This type of protectionis suitable for use in Zone 2 only.

n-pressurisation

This method involves pressurising the interior of an enclosure using a combination ofpurging with leakage compensation, or purging with static pressurisation.

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

Marking

The above table shows the marking on Type ‘n’ apparatus to indicate the method applied toeither eliminate or control spark energy and/or hot surfaces.

The following is an example of marking applied to type-n apparatus containing sparkingcontacts protected by another method.

EEx nC IIB T5


7





Grade of Inspection

D C V D C V D C V

A APPARATUS







* * * * * * * * *





* **

* **

* **


*








18 Breathing and drainage devices are satisfactory * * * * * *

B INSTALLATION





* * *



** *

** *

** *


* * *


9 Automatic electrical protective devices operate within permitted

limits

* * *


* * *




* * *


C ENVIRONMENT


* * * * * * * * *




8




Note 2: The use of electrical test equipment, in accordance with items B7 and B8, shouldonly be undertaken after appropriate steps are taken to ensure the surrounding areais free of a flammable gas or vapour.


9



Unit 6:

PressurisationEEx p / Ex p



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 andsystems.

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.


2



Pressur ised Equipment

Introduction

Pressurisation is a simple technique for providing explosion protection. If the interior of an enclosureis at a pressure above that externally, any flammable gases around the enclosure will be preventedfrom entering the enclosure. Components which are a source of ignition, i.e. they producearcs/sparks or hot surfaces, are permitted within the enclosure and, clearly, safety is dependent onthe maintenance of the safe gas. The safe gas is the medium which ‘segregates’ the flammable gasfrom 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 safeoperation.

The latest standard for this type of protection, BS EN60079-2, has introduced three types ofpressurisation, 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: 2008Electrical apparatus for explosive gasatmospheres: Part 14. Electrical installations inhazardous areas (other than mines)

BS EN60079-17: 2007

Electrical apparatus for explosive gasatmospheres: Part 17. Inspection andmaintenance of electrical installations inhazardous areas (other than mines)


3



Definition

Pressurisation is defined as:

‘The technique of guarding against the ingress of the external atmosphere into an enclosureor room by maintaining a protective gas therein at a pressure above that of the external

atmosphere.

’

Zones of use: 1 & 2

Appl ications

Pressurisation has a wide range of applications, i.e. it can provide explosion protection for adiverse range of instrument or electrical apparatus, there being no limit to size, withinreason, which can be accommodated. Typical examples are transformer/rectifier cabinets,oil drilling control consoles, visual display units (VDU’s), gas analysis equipment, controlrooms, switch rooms and workshops. With regard to flameproof apparatus, and in particularrotating machines, there is a maximum practical limit above which handling becomes difficultand manufacturers may overcome this difficulty by the use of a pressurised enclosure. Apressurised machine would be significantly lighter than a flameproof machine of the samerating.

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 internalrelease 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 inZone 1, or Group 1 for mining applications. Type py establishes a Zone 2 classificationwithin 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. Thetable 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.


4



Principle

The basic principle of operation involves raising and maintaining the internal pressure of theenclosure to a level slightly above the atmospheric pressure out with the enclosure. Thisensures that any flammable gases or vapours out with the enclosure cannot enter theenclosure. The minimum over-pressure specified in the latest standard BS EN60079-2 is0.5 mBar or 50 Pa for types px and py , and 0.25 mBar or 25 Pa for type pz. Previousstandards specified 0.5 mBar or 50 Pa. The safe gas used to provide the over-pressure willnormally 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 overpressurefor enclosures and the maximum rate of leakage which occurs at maximumoverpressure.

Purging

When a pressurised system has not been in use for some time it is important that electrical apparatusinside the enclosure is not energised prior to what is known as the ‘purge’ cycle. Purging, which mustoccur automatically, involves passing a quantity of the safe gas through the enclosure for a specifiedtime in order to remove any flammable gases which may have entered the enclosure. The standardsspecify that the minimum quantity of the safe gas required to achieve adequate purging is equivalentto 5 times the internal volume of the enclosure and associated ducting. The purge duration will becontrolled 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 onsite, will require on-site tests to establish the purge duration necessary for safe operation. If loss ofpressure occurs during operation, the control system must automatically purge the enclosure again.


5



Enclosures

The European and IEC standards require a minimum level of ingress protection forpressurised enclosures to IP 4X but, not all enclosures are suitable for pressurisation. Anenclosure may have ingress protection to IP54 but, it’s lid seal, for example, is designed toprevent 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 withstandimpact tests and the internal over-pressure with regard to the strength of the walls, and haveeffective and correctly orientated door seals. The enclosure and its associated ducts mustbe capable of withstanding, in normal operation, an over-pressure equivalent to 1.5 times themaximum working over-pressure declared by the manufacturer. Alternatively, the enclosuremust be capable of withstanding the maximum over-pressure obtained when all outlet ductsare 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 gassuch as nitrogen or another suitable gas. When air is the protective gas, it may be providedby either a motor driven fan, a compressor, or from storage cylinders. The protective gasmust be non-toxic and free from contaminants such as moisture, oil, dust, fibres andchemicals, 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 willbe marked with this temperature. When air is used as the safe gas its oxygen content mustnot 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 wouldbe 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 gainaccess to enclosures, it is essential that doors/covers are fitted with warning labels sincethere 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 theelectrical supply when the door/cover is opened, and restore the electrical supply only whenthe doors/covers are closed. Doors/covers requiring the use of a tool or key for openingmust display the warning: “ Do not open when energised” .

When a pressurised enclosure contains components which have hot surfaces, or arecapable of storing energy, e.g. capacitors, doors/covers should be fitted with a warningnotice which states the time delay after isolation of the electrical supply to the componentsbefore opening the doors/covers.


6



Control circuit/safety devices

The level of overpressure will be monitored by an overpressure sensor or switch and locatedat a point in the enclosure which has been found by test or experience to be the most difficultto maintain the overpressure, e.g. the internal circulation fan in a pressurised machine. Theexact point must be specified either on the enclosure or on the certificate. The rate of flowthrough the enclosure will be monitored by a flow-rate sensor or switch. A pressure gauge isalso desirable and should be located where it can be easily read. The table below, from thelatest standard BS EN60079-2, specifies the safety devices required according to theprotection type.

1. Over-pressure monitoring device.2. Protective gas flow-rate monitoring device.3. Pressure gauge.

4. Pressure relief valve: setting 75% of maximum declaredsafe over-pressure

When the safe gas is provided from compressed-air cylinders, failure of the regulator couldresult in distortion of the pressurised enclosure due to excessive overpressure, and toovercome this risk it is recommended that a pressure relief valve is installed. The setting ofthe relief valve is required to be 75% of the maximum safe overpressure declared by themanufacturer.


7



Safety device requirements for protection types

Design criteria Type px Type py Type pz

Safety device to detectloss of minimumoverpressure

Pressure sensor(see 7.9)

Pressure sensor(see 7.9)

Indicator orpressure sensor

Safety device(s) toverify purge period

Timing device,pressure sensor,and flow sensor atoutlet; (see 7.6)

Time and flowmarked

(see 7.7c)

Time and flowmarked

(see 7.7c)

Safety device for a dooror cover that requires atool to open

Warning

(see 6.2b)

Warning

(see 6.2b)No requirement

Safety device for a dooror cover that does notrequire a tool to open

Interlock, (see 7.12)

(no internal hotparts)

Warning

See 6.2b

(no internal hotparts)

Warning

(see 6.2b)

Safety device for hotinternal parts whenthere is a containmentsystem (see clause 15)

Alarm and stop flowof flammablesubstance

Not applicable forprotection typesince internal hotparts not permitted

Alarm

(normal releasenot permitted)

Ducts

The entry of the inlet duct must be positioned in a non-hazardous location (except wherecylinders provide the protective gas) and this location must be periodically reviewed in caseplant modifications have altered its classification. The exhaust duct, ideally, should have itsoutlet situated in a non-hazardous location in which there are no sources of ignition, but maybe located in a hazardous location if a spark/particle arrestor is fitted. The table below offersguidance in this respect.

Ducts should be located in non-hazardous areas as far as possible. Where inlet or outletducts 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 requirementspecified 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 cannotbe obstructed causing restriction of the flow of the protective gas. The ducts should alsohave adequate mechanical strength, be located where accidental damage is unlikely andhave adequate protection against corrosion.


8



Spark partic le barriers:

Type of apparatus within enclosureZone in whichexhaust duct is

located A B

Zone 2 Required Not required

Zone 1 Required * Required *

A: apparatus which may produce ignition-capable sparks or particles innormal operation.

B: apparatus which does not produce ignition-capable sparks or particlesin normal operation.

* A device to prevent rapid entry of a flammable gas into the enclosure uponloss 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 ofthe inlet and outlet ducts on the enclosure. This will speed up the rate of displacement of theflammable gas and so ensure efficient purging of the system. If the safe gas is heavier thanthe flammable gas the inlet duct will be positioned at the bottom of the enclosure and theexhaust duct at the top. If the safe gas is lighter than the flammable gas the positions of theducts will be reversed.

1. When the safe gas is more densethan the flammable gas:

2. When the safe gas is less densethan the flammable gas:


9



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 bevery 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 ofthe safe gas through the enclosure. The safe gas in this instance has a dual purpose. Inaddition to maintaining the over-pressure, it may also be used to cool hot parts withinthe enclosure such as thyristors, or the windings of a pressurised rotating machine. Therate of flow of the safe gas is set at a level which will prevent the temperature of the hotparts exceeding their temperature limit, thereby ensuring that the pressurised enclosure

operates within it’s T-rating.


10



c, Pressurisation wi th 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 openbut, on completion, the damper is closed and the flow of protective gas reduced to alevel sufficient to compensate for leakages occurring at the seals/joints of theenclosure.

d. Continuous dilution

The analysis of flammable gases on, for example, an offshore platform may take placein pressurised enclosures. A sample of gas will be drawn into a gas analyser and, afteranalysis, will be expelled into the interior of the pressurised enclosure. The safe gastherefore has two functions. In addition to maintaining over-pressure during and afterthe initial purge, the rate of flow of the safe gas will be adjusted to ensure that theconcentration of the gas/air mixture within the enclosure is well below the lowerexplosive limit (LEL).

Purging may be disregarded in Zone 2 if the concentration of the flammable gasreleased 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 enclosureremains non-hazardous.


11



d. Continuous dilut ion (continued)

Types and Magnitude of Internal Release

The recommended action when loss of pressure occurs in pressurised apparatus usingcontinuous dilution is addressed in BS EN60079-2 by consideration of the types of releasegiven in the tables below.

1. Normal release

None No release of flammable gas or vapour.

Limited A release of flammable gas or vapour whichis limited to a value which can be diluted towell below the lower explosive limit (LEL).

2. Abnormal release

Limited A release of flammable gas or vapour which islimited to a value which can be diluted to wellbelow the lower explosive limit (LEL).

Unlimited A release of flammable gas or vapour which isnot limited to a value which can be diluted to wellbelow the lower explosive limit (LEL).


12



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 theaction necessary on loss of pressure within an enclosure using the technique of continuousdilution.

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 aflow-rate switch/sensor, located at the exhaust duct, is used to monitor the rate of flow of thesafe gas through the enclosure. Loss of over-pressure or rate of flow will activate either analarm or shutdown of the internal electrical components, the action taken being dependenton:

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 electricalequipment, BS EN60079-14 specifies the action to be taken on loss of pressure as follows.

Area classificationEnclosure contains

ignition-capable apparatus

Enclosure contains apparatuswhich does not produce asource of ignition in normal

operation

Zone 1 Alarm and switch offb

Alarma

Zone 2 Alarma No action

a) Operation of the alarm requires immediate action to restore the integrity of thesystem.

b) An alternative protective gas supply should be available if a more dangerouscondition is likely as a result of automatic switch-off.


13



Ex FacilitNo

yvember 2008

14

Action on Loss of Pressure (continued)

3. With an internal source of release

Internal releaseCombination

Normal Abnormal

Areaclassification

Ignition-capableapparatus

Apparatus with nosources of ignition

Zone 1 Alarm andswitch off

Alarm

1 None Limited Zone 2

or non-

hazardous

Alarm

No protectivemeasures

required

Zone 1 Alarm andswitch off

Alarm

2 None Unlimited Zone 2or non-

hazardous

AlarmNo protective

measures

required

3 Limited Limited

Zone 1

or

Zone 2

Alarm andswitch off Alarm

4 Limited Unlimited

Zone 1

or

Zone2

Alarm andswitch off Alarm

Externally Mounted Electrical Apparatus

Electrical apparatus mounted on the exterior of a pressurised enclosure must be explosionprotected in accordance with the Zone in which the enclosure is situated. Typical examplesare pressure/flow rate sensors or switches which may use Ex i apparatus, junction boxesmay use Ex d, Ex e or Ex n methods of protection. This requirement also applies to themotor and its starter, of the fan which provides the flow of air, unless they are situated in anon-hazardous area. It is preferable that the motor and its starter are located in anon-hazardous area.

Apparatus Energised During Absence of Overpressure

An anti-condensation heater may be used in a rotating electrical machine to prevent theinternal surfaces and atmosphere becoming cold, thereby preventing the formation ofmoisture in the windings. Because the heater will be energised when the machine is withoutover-pressure, it is essential that it is explosion protected. Emergency lighting will normallybe installed in pressurised control rooms, cabins etc. and energised when there is loss ofover-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-ratesensors may use IS protection. Ex d enclosures will be used for control panels.




15



Determination of protection type

E n c l o s u r e d o e s n o t c o n t a i n

i g n i t i o n - c a p a b l e a p p a r a t u s

T y p e p y

N o p r e s s u r i s a t i o n r e q u i r e d

T y p e p y

T y p e p y

b

T y p e p y

N o p r e s s u r i s a t i o n r e q u i r e d

d

E n c l o s u r e c o n t a i n s i g n i t i o n - c a p a b l e

a p p a r a t u s

T y p e p x a

T y p e p z

T y p e p x a

T y p e p x ( a n d i g n i t i o n - c a p a b l e

a p p a r a t u s i s n o t l o c a t e d i n t h e

d i l u t i o n a r e a )

T y p e p x a

( i n e r t ) c

T y p e p z ( i n e r t ) c

E x t e r n a l Z o n e c l a s s i f i c a t i o n

1 2 1 2 1 2

F l a m m a b l e s u b s t a n c e i n t h e

c o

n t a i n m e n t s y s t e m

N o c o n t a i n m e n t s y s t e m

N o c o n t a i n m e n t s y s t e m

G

a s / v a p o u r

G

a s / v a p o u r

L i q u i d

L i q u i d

N O T E : I f t h e f l a m m a b l e s u b s t a n c e

i s a l i q u i d , n o r m a l r e l e a s e i s n e v e

r p e r m i t t e d

a )

P r o t e c t i o n t y p e p x a l s o a p p l i e s

t o G r o u p I

b )

I f n o n o r m a l r e l e a s e , s e e a n n e

x E

c )

T h e p r o t e c t i v e g a s s h a l l b e i n

e r t i f “ ( i n e r t ) ” i s s h o w n a f t e r t h e

p r e s s u r i s a t i o n t y p e ; s e e c l a u s e 1 3 .

d )

P r o t e c t i o n

b y

p r e s s u r i s a t i o n

i s

n o t r e q u i r e d

s i n c e

i t i s

c o n s i d e r e d u n l i k e l y

t h a t a f a u

l t c a u s i n g a r e l e a s e o f l i q u i d w i l l

s i m u l t a n e o u s l y o c c u r w i t h a f a u l t i n t h e e q u i p m e n t t h a t w o u l d

p r o v i d e a n i g n i t i o n s o u r c e


16



Design requirements relevant to protection type

T y p e

p z

w i t h

a l a r m

I P 3 X m i n i m u m

I E C 6 0 0 7 9 - 0 , h a l f t h e v

a l u e i n

t a b l e 4

T i m e a n d f l o w m a r k e d

S p a r k

a n d

p a r t i c l e

b a r r i e r

r e q u i r e d ,

s e e

5 . 8

u n l e s s

i n c a n d e s c e n t

p a r t i c l e s

n o t

n o r m a l l y p r o d u c e d

N o r e q u i r e m e n t

( N o t e 2 )

S p a r k

a n d

p a r t i c l e

b a r r i e r

r e q u i r e d , s e e 5 . 8

S p a r k

a n d

p a r t i c l e

b a r r i e r

r e q u i r e d ,

s e e

5 . 8

u n l e s s


p a r t i c l e s

n o t


W a r n i n g , s e e 5 . 3 a n d 6 .

2 b ) i i )


( N o t e 3 )

W a r n i n g , s e e 5 . 3 a n d 6 .

2 b ) i i )

T y p e

p z

w i t h i n d

i c a t o r


I E C 6 0 0 7 9 - 0 , t a b l e 4

T i m e a n d f l o w m a r k e d

S p a r k

a n d

p a r t i c l e

b a r r i e r

r e q u i r e d ,

s e e

5 . 8

u n l e s s


p a r t i c l e s

n o t



( N o t e 2 )

S p a r k

a n d

p a r t i c l e

b a r r i e r

i r e d ,

r e q u

s e e 5 . 8

S p a r k

a n d

p a r t i c l e

b a r r i e r

r e q u i r e d ,

s e e

5 . 8

u n l e s s


p a r t i c l e s

n o t


W a r n i n g , s e e 5 . 3 a n d 6

. 2 b ) i i )


( N o t e 3 )

W a r n i n g , s e e 5 . 3 a n d 6

. 2 b ) i i )

T y

p e

p y


I E C

6 0 0 7 9 - 0 ,

t a b l e 4

T i m e

a n d

f l o w

m a r k e

d


( N o t e

1 )


( N o t e

2 )

S p a r k

a n d

p a r t i c l e

b a r r i e r

r e q u i r e d ,

s e e 5 . 8


( N o t e

1 )

W a r n i n g ,

s e e

5 . 3 ( n o t e 1 )

W a r n i n g ,

s e e

5 . 3 ( n o t e 1 )

N o t a p p l i c a b l e

T y p e

p x


I E C 6 0 0 7 9 - 0 , t a b l e 4

R e q u i r e s a t i m i n g d e v i c e

a n d

m o n i t o r i n g

o f

p r e s s u r e & f l o w

S p a r k a n d p a r t i c l e b a r r i e r

r e q u i r e d , s e e 5 . 8 u n l e s s


p a r t i c l e s

n o t n o r m a l l y p r o d u c e d


( N o t e 2 )


r e q u i r e d , s e e 5 . 8


r e q u i r e d , s e e 5 . 8 u n l e s s


p a r t i c l e s

n o t n o r m a l l y p r o d u c e d

W a r n i n g , s e e 5 . 3 a n d 6 . 2

b ) i i )

I n t e r l o c k , s e e 7 . 1 2

( N o i n t e r n a l h o t p a r t s )

C o m p l y w i t h 6 . 2 b ) i i )

D e s i g n c r i t e r i a

D

e g r e e

o f

e n c l o s u r e

p r o t e c t i o n

a

c c o r d i n g

t o

I E C

6 0 5 2 9

o r

I E C

6

0 0 3 4 - 5

R

e s i s t a n c e o f e n c l o s u r e t o i m p a c t

V

e r i f y i n g p u r g e p e r i o d

P

r e v e n t i n g


p a r t i c l e s

f r o m

e x i t i n g a n o r m a l l y c l o s e d r e l i e f

v

e n t i n t o a Z o n e 1 a r e a

P

r e v e n t i n g


p a r t i c l e s

f r o m

e x i t i n g a n o r m a l l y c l o s e d r e l i e f

v

e n t i n t o a Z o n e 2 a r e a

P

r e v e n t i n g


p a r t i c l e s

f r o m e x i t i n g a v e n t o p e n t o a Z o n e 1

a

r e a i n n o r m a l o p e r a t i o n

P

r e v e n t i n g


p a r t i c l e s

f r o m e x i t i n g a v e n t o p e n t o a Z o n e 2

a

r e a i n n o r m a l o p e r a t i o n

D

o o r / c o v e r r e q u i r i n g

a

t o o l t o

r e m o v e

D

o o r / c o v e r n o t r e q u i r i n g a t o o l t o

r e m o v e

I n t e r n a l h o t p a r t s t h a t r e q u i r e a c o o l -

d

o w n

p e r i o d

b e f o r e

o p e n i n g

e

n c l o s u r e

S

e e N o t e s o n f o l l o w i n g p a g e


17



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 nornormally 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 withinexplosive limits.

Note 3: There is no requirement for marking or tool accessibility on a pz enclosure since innormal 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 theexplosive limits.

Temperature classification

Type px or type py pressurisation

The temperature classification allocated to pressurised apparatus is required to be inaccordance 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 exceedthe temperature class of the pressurised enclosure if the component complies with 5.3 ofIEC 60079-0, or the pressurised enclosure is marked with the time required for thecomponent to cool to the marked temperature class. This may be achieved by the followingmethods.

c) The joints of the enclosure and its ducts are designed to prevent the ingressof a flammable gas coming into contact with the hot surfaces before theyhave 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 thetemperature class of the enclosure but, internal explosion protected apparatus remainingenergised in the absence of over-pressure will also have to be taken into consideration for

determining the temperature classification.


18



Marking

The construction standard BS EN60079-2 specifies that pressurised enclosures must bemarked as detailed in IEC 60079-0. The apparatus marking must be visible and contain thefollowing 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 basedon the minimum purge flow rate and the minimum purge duration, and theminimum 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 mustincrease the volume of the safe gas to compensate for the additionalvolume of the ducts.


19



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 areaclassification

* * *

2 Apparatus installed is that specified in the documentation – Fixedapparatus 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 ofthe 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 andconductors 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 relaycubicles

*

10 As applicable, short-circuit protection of the power supply is inaccordance with the documentation

*

11 Special conditions of use (if applicable) are complied with *

12 Cables not in use are correctly terminated *

C ENVIRONMENT


* * *

2 No undue accumulation of dust and dirt * * *


20



Unit 7:

Intrinsic Safety

EEx I / Ex i



Objectives:

On completion of this uni t, ‘Intrinsic Safety EEx I / Ex i apparatus, you should know:


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.



2



Intrins ic Safety EEx / Ex i

Intrinsic Safety is a widely used method of explosion protection. It is used for very low powerapplications 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 25Intrinsically 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 inexplosive atmospheres

IEC 60079-11: 2006 Electrical apparatus for explosive gas atmospheres – Part 11:Intrinsic safety ‘i’

IEC 60079-25: 2008 Electrical apparatus for explosive gas atmospheres: – Part 25Intrinsically safe systems

IEC 60079-27: 2008 Explosive atmospheres: – Part 28: Protection of equipmentand 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 inhazardous 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’.


3



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 thatwhich can cause ignition by either sparking or heating effects.’

Zones of use: 0, 1 & 2 (Ex i ‘a’)1 & 2 (Ex i ‘b’)

2 (Ex i ‘c’)

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 insufficientenergy to ignite the most easily ignitable concentration of a flammable mixture. This isachieved 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 arenot exceeded under normal, or even fault conditions.

The circuit parameters, i.e. voltage, current, resistance, inductance and capacitance arefactors which have to be considered in the design of an IS circuit. Consultation with thecharacteristic ignition curves given in the construction standard (shown in this unit on pages9, 12 and 13), and the application of appropriate safety factors, will ensure that safe valuesare established for these parameters during the design stage.

An IS system, which usually comprises a safe to hazardous area interface, cables, junctionboxes and field (hazardous) area apparatus, must also be designed in such a way as toguard against the possibility of particular faults occurring. In contrast to other methods ofexplosion protection, intrinsic safety is a system concept which applies to the wholesystem and not to any one item only. Apparatus in the safe area connected to apparatusin the hazardous area is known as ‘associated apparatus’, and each item making up thesystem will have a Certificate of Conformity. Associated apparatus may be used in thehazardous area if installation is within another method of explosion protection, e.g.flameproof. In addition, an overall system certificate may cover the system.


4



The voltage supply to electrical apparatus, which is connected to the non-IS terminals ofassociated apparatus, must not be greater than the voltage Um marked on the associatedapparatus label. The Code of Practice BS5345 recommended this value should not exceed250Vrms. The electrical supply prospective short-circuit current must not be in excess of1500A.

Advantages of IS are:

a. Live maintenance is possibleb. Cost effective – certified enclosures not required and ordinary

wiring may be usedc. Safe – low voltage not harmful to personneld. Can be used in Zone 0

The Zener Barr ier

The faults which can jeopardise the security of IS systems are either overvoltage orovercurrent, 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 individualcomponents.

The interface, which is connected between the safe area and hazardous area apparatus, isnormally located in the safe area and situated as close as possible to the boundary with thehazardous area, but may be located in the hazardous area if installed in a flameproofenclosure.

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.

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 lowerresistance value or short-circuit would allow more current to flow in the IS circuit, which iscontrary to the concept of this type of protection. Infallibility will be satisfied by the use of aquality wire-wound or metal film resistor which should not operate at more than 2/3 of itsrated current, voltage and power for a specified temperature range. The next component forconsideration is the zener diode, the purpose of which is to limit the voltage available to theapparatus 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 andpower.


5



For infallibility to be satisfied, the zener diode is required to fail to a short-circuit. Failure to ahigher resistance or open-circuit could allow voltage levels beyond safe limits to “invade” thehazardous area.

Note: Tests by manufacturers have shown that diodes virtually always fail to a short-circuitstate, but there can be no guarantee of this. Diodes can only be considered infalliblewhen 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, itspurpose 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-filledceramic type capable of operating properly even when exposed to a prospective fault-currentof up to 4000 A. A fuse of this type avoids the problem which can occur with other types offuses when they rupture, namely vaporisation which can allow the fuse to continue toconduct.

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 themanufacturer.

Note: Categories (levels of protection), ‘ia’, ‘ib’ and ‘ic’, are described on the following pagebut with regard to the infallibility of components, this applies to ‘ia’ and ‘ib’, but is notapplicable to ‘ic’. Furthermore, for level of protection ‘ic’ the 2/3 safety factor appliesonly to the power rating; it does not apply to the voltage and current provided therated values are not exceeded.

Zener Barrier Operation

In the event of a short-circuit developing in the apparatus in the hazardous area, or acrossthe IS wiring, the series resistor in the zener barrier will limit the short-circuit current to a safelevel so that the integrity of the system is maintained.

If a voltage greater than the normal maximum voltage of the IS system invades the circuit atthe input terminals of the zener barrier, this will trigger the zener diode, and the resultingfault current will be shunted to earth. The excessive voltage is, therefore, prevented fromreaching the apparatus in the hazardous area as illustrated in the diagram on the followingpage.


6



Zener Barrier Operation (continued)

Levels of protection for IS

Previously referred to as categories of intrinsic safety, these are now called levels ofprotection of which there are three, namely ‘ia’, ‘ib’ and ‘ic’, the level of safety provided byeach being dependant on the number component faults which are considered. For the firstlevel of protection, ‘ic’, no faults are considered in order to maintain safety. The secondlevel of protection will maintain safety in the event of one fault occurring. The third level ofprotection, ‘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, additionalzener 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 forthe 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 usedin type ‘n’ equipment, i.e. ‘nL’

Therefore, the addition of a second zener diode, connected in parallel with the first, willsatisfy the requirements of category ‘ib’ intrinsic safety in which safety is assured with onefault. 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.


7



Levels of protection for IS (continued)

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.

Minimum Ignition Current Curves

Since it is necessary to limit the voltage and current in an IS circuit to ensure operationalsafety, the design of the circuit will be based on the minimum ignition current curves given inthe construction standard and reproduced on page 9. Pages 12 and 13 also illustrate thecurves 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 bedetermined 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 ofthis device since a rise in its temperature may raise the triggering voltage of the zenerdiodes. 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 thepoint of contact with the curve towards the vertical (current) axis, gives a safe current of140 mA. A safety factor of 1.5 must be applied to this value, i.e. 2/3 of 140mA is equal to93.33 mA. By applying ohm’s law, 28V/93.33 mA = 300 Ω, the same resistance as the zenerbarrier, it has been verified that the 28V, 300 Ω interface is suitable for maintaining theintegrity of the IS circuit in a IIC hazard.


8



Minimum Ignition Current Curves: Resistive Circuits


9



Simple Apparatus

The spark energy of an IS circuit, during normal or fault conditions, will be insufficient tocause ignition of a surrounding hazard. The introduction of a switch, which in normaloperation produces sparks and does not dissipate power, will not alter the situation, and infact, any device which is resistive by nature and non-energy storing may be added to thecircuit without jeopardising the integrity of intrinsic safety.

Devices such as these are referred to as simple apparatus and do not need to be certifiedor marked. Such passive devices include switches, junction boxes, terminals, potentiometersand simple semiconductor devices. Simple apparatus may also include sources of storedenergy, for example, capacitors and inductors having well defined parameters, the value ofwhich must be considered during the design stage of an IS installation. Sources ofgenerated energy, typically thermocouples and photocells, may also be described as simpleapparatus providing they do not generate more than 1.5 V, 100mA and 25 mW. Anycapacitance or inductance in these devices must also be considered during the design stageof an installation.

Since simple apparatus is not required to be certified, justification for its use must beincluded in the system documentation.

Enclosures

The minimum ingress protection for enclosures if IS circuits is IP20, but environmentalconditions may require a higher rating.

Energy Storage

Energy storing devices such as inductors and capacitors have the potential to upset thesecurity of an IS system. Energy can be stored in these devices over a period of time andthen released in a surge of greater amplitude at, for example, a break in the IS sables due toa fault or live disconnection at terminals. This could occur regardless of the designconstraints 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. Fieldapparatus which have energy storing capability, i.e. they have some internal inductance, aretermed ‘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 atthe design stage. Energy will be stored under normal operating conditions, but will be greaterunder fault conditions. The voltage will influence which parameter is predominant, i.e. for avoltage of around 5 V, the inductance will be predominant, but at 28V, the capacitance willbe predominant.


10



Where simple apparatus only is used in the field, the inductance and capacitance presentwill be due to the cables only, and if the cable runs are short these parameters will benegligible. The electrical parameters Cc, Lc and Lc/Rc for typical instrument cables withtwisted or adjacent cores must be determined by:

a. Obtaining the worst case parameters from the cable manufacturer, orb. Measurement of the parameters using a sample of the cable, orc. Adoption of the following values –

Inductance, (L) 1 μH/mCapacitance, (C) 200 pF/mInductance/resistance ratio 30 μ H/Ω

Where field apparatus has both appreciable inductance and capacitance, it is important thatthe 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 theinductive circuit curves after first of all evaluating the maximum source current. Assuming aninterface with a maximum output of 28 V and 300 Ω resistance, the maximum source currentis:

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 beapproximately 4.0 mH. This value is found by projecting vertically form 140 mA on thecurrent axis, and then horizontally towards the inductance axis form the point of contact onthe IIC curve.

Capacitance

For capacitance circuits, the procedure is exactly the same. A safety factor of 1.5 is appliedto 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 theinterconnecting cables, assuming that connection is to ‘simple apparatus’ in the hazardous

area, is found to be 0.08 μF approximately.


11



Comparison of the above values with the data provided by the cable manufacturer willestablish of the interconnecting cable run is satisfactory.

Inductive Circuit Curves for Group II


12



Capacitive Circuit Curves for Group II


13



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 adifferent 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 surroundingmetalwork 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 thebarrier earth bar to the main earth point to facilitate earth resistance tests which must beperiodically carried out. The resistance between the barrier earth bar and the main earthpoint 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 sothat 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 andhave an appropriate cross-sectional area (csa) by means of:

a. At least two separate 1.5mm2 (minimum) copper conductors, orb. At least one 4mm2 (minimum) copper conductor.

Note: The IS circuit in the hazardous area must be able to withstand a 500V insulationresistance test to earth.


14



Earthing and Bonding


15



Earthing and Bonding


16



Galvanic Isolation

Although zener barriers have been, and continue to be, widely used in industry, they haveparticular limitations which are:

a. A dedicated high-integrity earth is necessary to divert fault currents away from thehazardous 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, optoisolators and transformers.

Relay/Transformer Isolation

In the example below, isolation between the hazardous and safe areas is achieved bymeans 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 beprevented from reaching the hazardous area apparatus.

Opto-coupler/Transformer Isolation

This method comprises a component certified opto-isolator and a component approvedtransformer. Light (or infrared) emitted from the LED when it is forward biased falls onto thephototransistor which is shielded from external light.


17



Installation of IS Apparatus

The apparatus which make up an IS installation, i.e. field apparatus, associated apparatusand interface units, are required to be certified items which have been manufactured inaccordance with relevant standards (see page 3). Such apparatus, including interconnectingcables, must be installed in accordance with the manufacturer’s instructions, systemdocumentation and with regard to the recommendations in BS EN60079-14. Existinginstallations, however, may have been installed in accordance with the Code of PracticeBS5345.

Installation Requirements for Cables

The conductors of IS cables are required to be insulated with elastomeric or thermoplasticinsulation which has a minimum thickness of 0.3mm. The cables must be capable ofwithstanding 500Va.c. or 750Vd.c. test voltages between conductors and earth, conductorsand 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 finelystranded cables, must have a diameter not less than 0.1mm. Separation of the individualstrands of cables must be prevented by, for example, the use of core-end ferrules. Thoughnot 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 plantand installations installed in accordance with its recommendations. The following table,taken from BS5345, specifies the maximum current and minimum cross-sectional area forcopper 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 carryingmaximum 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 tomaintain the integrity of the system, i.e. to prevent contact with cables of other circuits, orearth, as a result of damage, and to ensure the circuit parameters in terms of inductance andcapacitance are not exceeded.

Armouring or screening of cables for mechanical protection is not required except for IScircuits with multi-core cables in Zone 0.


18



Segregation of IS and Non-IS Circuits

Segregation of IS and non-IS circuits in both hazardous and non-hazardous areas isimportant 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, orb. Positioning of the IS circuit cables such as to guard against the risk of mechanical

damage, orc. 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 IScircuits and non-IS circuits.

Where IS cables and the cables of other circuits share the same duct, bundle or tray, bothtypes 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 arearmoured, 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 terminationmethods 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, orb. 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 thecable, however, must be insulated from each other and earth by means of suitableterminals.

Cable Screens

Where the interconnecting cables of IS circuits have overall screens, or groups ofconductors with individual screens, the screens are required to be earthed at one pointonly, 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 theequipotential bonding system should be made at one point only.

The Code of Practice BS5345 specified that, prior to connection of the screens to the barrierearth bar, an insulation resistance (IR) test should be carried out between each pair ofscreens. The test readings should be not less than 1MΩ/km when measured at 500V at20°C for 1 minute.

Overall screens are required to be insulated from the external metalwork, i.e. cable tray etc.


19



Induced Voltage

IS circuits must be installed using methods that avoid external electric or magnetic fieldsaffecting them. Generally, induced voltage in IS interconnecting cables is not likely but mayoccur if the IS cables are placed parallel to and in close proximity to single-core cablescarrying heavy current, or overhead power lines. Adequate segregation between thedifferent 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 theymay be easily identified as part of an IS circuit. Hence, to avoid confusion, light blue cablesmust 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 controlcabinets, switchgear, distribution apparatus, etc., appropriate measures must beimplemented to distinguish between the two types of circuit, and avoid confusion where ablue 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. The conductor insulation musthave adequate radial thickness but not less than 0.2mm and be capable of withstanding anrms a.c. test voltage equal to twice the nominal voltage of the IS circuit but not less than500V.

Test Requirements

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 cablescreens and/or armouring connected together.

b. For multi-core cables not having screens for individual circuits, 1000Vr.m.s (or1500Vd.c.) applied across half the cores which are connected together and theremaining cores which are also connected together.

The methods used for the above tests are required to be carried out as specified in arelevant cable standard, but where no method is specified, tests must comply with 10.6 ofIEC 60079-11.


20



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 areacoverage 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 itscircuits has a maximum voltage greater than 60V, no faults between circuitsare taken into consideration.

Type C cable: For this cable type, but without the requirements specified for Type A andType B cables, two short-circuits between conductors and up to foursimultaneous open-circuits of conductors have to be considered. No faultsneed be considered if all the circuits in the cable are identical and have asafety 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, thenumber of short-circuits between conductors and simultaneous open-circuits of conductorshas no limit.

As previously stated, BS5345 has been withdrawn but is still relevant to existing plant andinstallations, 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 isessential that no combination of faults between the IS circuits within the cable will cause anunsafe condition. An exemption to this requirement applies if:

a. The risk of mechanical damage to the cable is minimal or, where the risk of damageis 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 than60V peak, or

e. The cores of each IS circuit are within a screen which is insulated and earthed aspreviously discussed.


21



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 connectedto terminals should not be less than 6mm.

Where IS and non-IS circuits occupy the same enclosure there must be adequate separationbetween the two circuit types. This may be achieved by either:

a. 50mm clearance between the IS and non-IS terminals. The terminals and wiringshould be positioned such that contact between the circuits is not likely should a wirefrom either circuit become detached.

b. An insulated partition or earth metal partition located between the IS and non-ISterminals. 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 thepartition.

With regard to existing plant or installations, clearance distances may be in accordance withthe Code of Practice BS5345 as detailed in the table below.

Peak Voltage

(V)

Minimum clearance in air betweenterminals of separate circuits

(mm)

Minimum clearance in airbetween 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 offlammable 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 thecircuits 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 inthe presence of flammable gases, therefore, requires careful consideration of the circuits tobe tested.


22



Ex FacilitNo

yvember 2008

23

BS EN60079-17: Table 2: Inspection Schedule for Ex ’i’ Installations

Grade InspectionCheck That:

Detailed Close Visual A Apparatus


* * *


* *






8 Safety barrier units, replays and other energy limiting devices are ofthe approved type, installed in accordance with the certificationrequirements and securely earthed where required

* * *



B Installation





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 onepoint only (refer to documentation)

*


*


*



C Environment


* * *




IS Inspection Record No: A Safe Area A

Apparatus Location

Cable Connection Drawing No.

Junction Box No.

Instrument Loop Drawing No.

Tag No.

Correctly labelled

No damage

Barrier or Replay orSafe Area Apparatus

Securely mounted on earth bar

Correctly labelled

Connected to correct unit andterminals

Cable Cores

Crimped OK and tight in terminalblocks

No damageTerminal Blocks

Creepage and clearance OK

Date

Inspectors Initials

Comments


24



yvember 2008

25

IS Inspection Record B IS Cab

Ex FacilitNo

Location

Junction Box No.

Junction Box Connection Drawing No.


Cable No.

Segregated f rom Non-IS Cables

No damageIS Cables in Hazardous Areas

Properly supported

Date

Inspector’s Initials

Correctly labelled

No damageIS Cables in Safe Area

Segregated f rom Non-IS Cables

Cable Screen

Unused Cores

Date




IS Inspection RecordNo:

CJunction Boxes in Hazardous

Area

Location

Junction Box 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


Date


Comments:


26



IS Inspection Record No: D Hazardous Area Apparatus

Location

Junction Box 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 terminalsCable Cores

Crimped OK and tight in terminal blocks

No damageTerminal Blocks


Date


Comments:


27



Unit 8:

Other Methods of Protection

EEx o / Ex o, EEx q / Ex q,EEx m / Ex m & Ex s



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.


2



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 forelectrical 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: Part9 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 areimmersed in protective liquid in such a way that an explosive atmosphere, which may beabove the liquid or outside the enclosure, cannot be ignited.’

Breathingdevice

Oil-filling

pointOil-level

indicator

Drain plug


3



Zones of Use: 1 & 2

Principle

The oil level is used to completely cover the components within the apparatus whicharc/spark or produce hot surfaces during normal operation, thereby effectively establishing abarrier between the components below the oil and any flammable gases which may bepresent above the oil or outside the enclosure. A particular advantage of this method ofprotection 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 isused, a by-product of this process is the production of hydrogen and acetylene. Thiscondition was considered to be undesirable for apparatus intended for use in hazardouslocations, which may explain why, until recently, its use was limited to Zone 2 in the UK. Therevised standards, however, have stricter specifications and this type of protection is nowpermitted in Zone 1.

Construction

The construction standard requires a breather to be fitted to the apparatus to allow releaseof the flammable gases produced during arc quenching, and thereby preventing the build-upof these gases in the space above the oil, whilst simultaneously preventing the ingress ofdust or moisture, and hence, contamination of the oil. The enclosure ingress protection willbe IP66.

It is also a requirement that the apparatus is fitted with a gauge which can display thehighest 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 thegauge, even at it’s lowest point, the minimum depth of oil remaining above the arc/heatproducing 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 protectiveliquid, but other types may be used, e.g. unused silicone insulating liquids. Silicone liquidsare required to have specific properties, which include:

a) a minimum fire point of 3000C in accordance with the test method given in HD565 S1 (IEC 60836);

b) a minimum flash point (closed) 2000C in accordance with ISO 2719;c) a maximum kinematic viscosity of 100 cSt at 250C 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 -300C in accordance with ISO 3016;

g) a maximum neutralisation value of acidity of 0.03mg KOH/g in accordance withIEC 60588-2 (Note: reference to this standard is for the test method only andnot to permit the use of materials banned by legislation.)

h) causing no degradation to the characteristics of materials it makes contact

with.


4



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 liquidover the entire ambient temperature range.

The free surface temperature of the protective liquid is required to be 25 K less than thespecified minimum flashpoint for the protective liquid.

Internal and external fasteners, fluid level indicators and parts for filling and draining theprotective liquid including plugs must have measures applied to prevent them becomingloose. 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-sealedenclosures with an expansion device which incorporates a mechanism for automatic trippingof the electrical supply on detection of gas evolution from the protective liquid as a result of afault within the enclosure. The trip mechanism may only be manually reset.


5



Powder Filling EEx q / Ex q

The explosion protection concept powder filling is not widely used and typical applicationsare, for example, capacitors in Increased Safety Ex ‘edq’ lighting fittings, andtelecommunications 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 forelectrical 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


‘A type of protection in which the parts capable of igniting an explosive atmosphere are fixedin position and completely surrounded by a filling material to prevent the ignition of anexternal explosive atmosphere.’

Source ofignition , e.g.(capacitor)

Powder filling

Zone of Use: 1 & 2


6



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 maypermeate 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 inertpowder. The depth of granules is influenced by the level and duration of the of the arccurrent produced by the components within the filling material, and tests specified in theconstruction standard enable a safe correlation between these two parameters to beestablished. 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 constructedto 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 theapparatus to be marked with the suffix ‘X’.

The size of granules for the filling material must be in accordance with the sieve limitsspecified in the standard ISO 565. The upper limit for the granules may be achieved using asieve manufactured from metal wire cloth or a perforated metal plate with a nominalperforation size of 1 mm. For the lower limit, metal wire cloth with a nominal perforation size0.5 mm may be used. The filling material is required to withstand an electric strength testwhere the leakage current must not be in excess of 10-6 A.

The minimum clearance distances between electrically conducting parts and insulatedcomponents or the inner surface of the enclosure wall are given below.

Operating voltage U a.c. r.m.s or d.c.

Minimum distancemm

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 aresurrounded by the filling material, must have minimum clearance distances between thecomponent and the inner wall of the enclosure in accordance with the table above. For freevolumes in the range 3 cm3 - 30 cm3 the above distances apply but should not be less than

15 mm.


7



Encapsulation EEx / Ex m

The method of protection, encapsulation, is used mainly for smaller items of equipmentsuch 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: 2004 Encapsulated apparatus

Definition


‘A type of protection whereby parts that are capable of igniting an explosive atmosphere byeither sparking or heating are enclosed in a compound in such a way that the explosiveatmosphere cannot be ignited under operating or installation conditions.’


8



Levels of protection:

ma Encapsulated apparatus having a level of protection ‘ma’ must not be capable ofcausing 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 ofcausing ignition during the following situations:

i) in normal operation and installation conditions;ii) in defined failure conditions.

Zone of Use: ma 0, 1 & 2

mb 1 & 2

mc 2

Principle

With this type of protection, the encapsulant, typically a thermosetting, thermoplastic, epoxyresin or elastomeric material, establishes a complete barrier between any surroundingflammable 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. Verysmall components which have enclosed moving parts, e.g. a reed relay, may be protected byencapsulation.

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’. Encapsulationwith the level of protection ‘ma’ must not have an operating voltage in excess of 1 kV and beincapable of causing ignition during:

a) normal operation and installation conditions;b) any specified abnormal conditions;c) defined failure conditions.

Encapsulation with the level of protection ‘mb’ must be incapable of causing ignition during:

a) normal operation and installation conditions;b) defined failure conditions.


9



The encapsulant must be capable of remaining intact during electrical input variations in therange 90% - 110% of the specified rating, adverse load conditions and any internal electricalfault. The apparatus is required to remain safe with one internal fault for the level ofprotection ’mb’ and two faults for the level of protection ‘ma’. This applies to a short-circuitoccurring 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 constructionof the apparatus, i.e. within a metallic enclosure which is either closed or unclosed on allsides, or has 100% free surface area. As these requirements are extensive, the table belowshows some of the applicable distances for apparatus with 100% free surface area.

Protection level

ma mb

Free surface < 2 cm3 > 1 mm *

> 3 mmFree surface > 2 cm3 > 3 mm *

* The depth of encapsulant will also be influenced by the ratedvoltage as given in Table 1 of the standard.


10



Special Protection Ex s

Apparatus which has not quite met the requirements of a particular construction standard willhave 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 harmonisedconstruction standards, or in the installation, inspection and maintenance series ofstandards, 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 consideredfor 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 quitemeeting the requirements of a given standard, nor is this type of protection inferior to othermore popular methods of explosion protection. Indeed the tests on apparatus presented forcertification under Special Protection are likely to be more onerous than the tests for othertypes 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 specifiedimpact 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 possiblewith 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 kVpoly-phase cage induction pump motor in which the method of explosion protection isbasically dependent on the interior of the motor being completely filled with water. Any freespace within the motor is occupied by water, and hence, the entry of a flammable gas isprevented. 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 tothermo-cycling. The motor, which drives a pump, is intended for use in Zone 1.


11



Unit 9:

Combined (Hybrid) Methods

of Protection



Objectives:

On completion of this unit, ‘Combined (Hybrid) Methods of Protection’ , you shouldknow:

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.


2



Combined (Hybrid) Methods of Protection

Electrical equipment may be manufactured with more than one method of explosionprotection. Equipment of this type has combined methods of protection but may also beknown 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.

Ignition by sparkingcomponents contained within

flameproof enclosure

EEx d

A traditional push-button station for use in an hazardous location comprises a flameproofEEx d or Ex d enclosure, in which a standard industrial switch is fitted. An alternative to thisarrangement is an Increased Safety EEx e or Ex e enclosure with a small flameproof EEx dor 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 conceptof protection. Such equipment will be marked EEx ed, Ex ed, EEx de or Ex de.

Ignition by sparking contactscontained within the ‘smallvolume’ EEx d or Ex d switchEEx e / Ex e

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


3



Standards

Hybrid apparatus may be constructed using any combination of the various methods ofexplosion protection and, therefore, the apparatus will be marked with the symbolic lettersand construction standard numbers relative to the types of explosion protection used.

Probably the most commonly used combination involves ‘d’ and ‘e’ types of apparatus, andso the table below shows these standards only. The full list of standards can be found in Unit2. Hybrid apparatus must also be installed and maintained in accordance with relevantstandards.

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 gasatmospheres: Part 14. Electrical installations inhazardous areas (other than mines)

BS EN60079-17: 2007 Electrical apparatus for explosive gasatmospheres: Part 17. Inspection andmaintenance of electrical installations inhazardous areas (other than mines)

Motors – EEx de / Ex de


4



Motors – EEx de / Ex de

Manufacturers also produce electric motors in which there are combined methods ofprotection. The main body of the motor will be flameproof EEx d or Ex d and the terminal boxincreased 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 arehybrid terminals, i.e. they employ both flameproof and increased safety features in theirconstruction.

1. Terminal box cover andscrews

2. Gasket3. Certified cable glands4. Gland plate5. Increased Safety

terminals

6. Terminal plate7. Terminal box and screws

EEx de / Ex de Motor Terminal Box

To achieve the required level of ingress protection, gaskets are fitted between the terminalbox and its cover, between the terminal plate and box, and between the gland plate andterminal box. On no account, however, should a gasket be fitted between the terminal plateand 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 verymuch like a flameproof box in terms of its construction. This likeness means that there is apossibility that personnel unaware of this concept may remove the gaskets and, therefore, itis important that certification labels are studied before any work is carried out. Removal ofthe gaskets in an attempt to return the box to its assumed status, i.e. flameproof, would bean unauthorised modification which would invalidate the certification.


5



EEx de – Sample Certi fication Label

Ex de – Sample Certi fication Label

0081 II 2 G

Ex de IIB T4

Duty S1 No. E956732

Ins. cl F IP55

V Hz kW r/m cos

440 60 37 1760 0.8

LCIE 07ATEX599X

IEC 60034-1


6



Lighting Fittings – EEx edq / Ex edq

The lighting fitting illustrated below employs three protection concepts, i.e. increased safetytype ‘e’, flameproof type ‘d’ and powder filing type ’q’. This type of fitting is widely used in thepetro-chemical industry.

The constructional features are:

1. Flameproof lampholders;

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 ofprotection, powder filling type ‘q’. Switches will be flameproof type ‘d’ construction andterminals will be increased safety type ‘e’.


7



EEx e m ib / Ex e m ib

An enclosure may have an encapsulated component inside. A typical example is atelephone for use in an hazardous location. The casing of the telephone would useincreased 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 encapsulationtype ‘m’ would be used to protect that part of the circuit. Terminals would be increased safetytype ‘e’.

EEx e enclosure


8



EEx pde / Ex pde

Enclosures using the protection concept, pressurisation type ‘p’, may have internalapparatus which have to remain energised in the absence of overpressure. Such apparatusmust 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 beenergised when the machine is idle.

Apparatus out with the machine, e.g. junction boxes, pressure sensors etc., will also have tobe protected in accordance with the Zone.

Note: Since anti-condensation heaters are normally ‘live’ when a machine is idle, a noticewarning 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 anon-hazardous area may be used in a hazardous area if installed in, for example, apressurised enclosure as illustrated below.


9



Unit 10:

Wiring Systems



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’ offlameproof enclosures.

c. The correct assembly techniques for various types of cable glands.

d. Recognised practices for terminating single and multiple pair cables with or withoutscreens.

e. Recognised practices for maintaining ingress protection, earth continuity andtermination of unused conductor cores and screens.

f. Earthing requirements in hazardous areas.

g. The installation requirements according to BS EN 60079-14.

h. The inspection requirements according to BS EN 60079-17.

2



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 and one reason is it’sease of installation compared to conduit.

With regard to conduit, one of it’s disadvantages, particularly on offshore installations, is it’ssusceptibility to corrosion as a result of exposure to sea-spray. Deterioration due tocorrosion can occur relatively quickly and, as a consequence, can reduce the strength of theconduit. This is undesirable particularly where conduit is the method of entry to a flameproofenclosure because of the possible inability of the conduit to contain an internal explosion inthe run of conduit between the enclosure and the sealing device. Furthermore, corrodedconduit may not meet the impact resistance requirements essential for use with IncreasedSafety apparatus.

Standards

BS EN60079-14: 2008 Electrical apparatus for explosive gasatmospheres: Part 14. Electrical installationsin hazardous areas (other than mines).

BS EN50262: 1999 Metric cable glands for electrical installations

BS 6121-5: 2005 Mechanical cable glands. Code of practicefor selection, installation and inspection ofcable glands and armour glands.

BS 5345 (withdrawn) Code of practice for the selection, installationand maintenance of electrical apparatus foruse in potentially explosive atmospheres.

3



Cables

Cables for use in hazardous areas are not certified but are required to be constructed frommaterials 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 importantconsiderations include fire survival, fire resistance, fire retardancy, fire propagation, toxicityand smoke emission. Thus in circuits essential for safety the cables installed are required tooperate in a fire for a specified time.

Cables may also be manufactured from materials, typically polymer compounds that producelower smoke and fume emissions during a fire. Cables with this capability will be identifiedas halogen free, low smoke & fume (LSF), low smoke zero halogen (LSZH), or zerohalogen low smoke (ZHLS).

Fixed apparatus in zones 1 and 2

Cables manufactured from thermoplastic, thermosetting, elastomeric or mineral insulatingmaterials may be used in fixed wiring installations. Cables commonly used in the industryare of the EPR/CSP type. Mineral insulated metal sheathed (MIMS) cable is also suitable foruse in hazardous areas, but it’s aluminium variation requires careful consideration beforeuse. Aluminium conductors 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 typesare 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 heavypolychloroprene or alternative equivalent synthetic elastomeric sheath, or a heavy toughrubber sheath, or manufactured from materials providing equally robust construction. The

minimum cross-sectional area for such cables is 1.0mm

2

.

4



Where the voltage to earth and current of portable electrical apparatus does not exceed250V and 6A respectively, cables having an ordinary polychloroprene or alternativeequivalent synthetic elastomeric sheath, or a heavy tough rubber sheath, or manufacturedfrom materials providing equally robust construction may be used.

The sheath of flexible cables may be manufactured from ordinary tough rubber , ordinarypolychloroprene, heavy tough rubber , heavy polychloroprene, or plastics providing theequivalent 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 range30 °C - 90 °C.

Cable specified as ‘low smoke and fume’ (LSF) has insulation which does not containhalogens, so that smoke and acid emission are minimised in the event of a fire.

5



Cables (cont inued)

Cables may also be selected with consideration to their fire resistant and/or flameretardant properties, and two standards are relevant in this respect.

IEC 60331 (Fire resistant): A cable manufactured in compliance with this standard willcontinue to operate in a fire without disruption of essentialcircuits and emergency circuits.

IEC 60332 (Flame retardant): A cable manufactured in compliance with this standard isself-extinguishing and will not propagate the fire.

Cold Flow

Certain materials used in the manufacture of cables are susceptible to a condition commonlyknown 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 cableentry devices which have compression seals should be avoided since the part of the cableacted on by the seal can “flow” away from the pressure of the seal resulting in an ineffectiveseal. Recent developments by cable gland manufacturers have resulted in new designs ofcable glands which can reduce, if not eliminate, the effects of ‘cold flow’ by the use of sealswhich apply less pressure on the cable insulation but still maintain the integrity of the type ofexplosion 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 enclosurehaving a type of explosion protection suitable for the Zone, or by epoxy or compound filleddevices, or heat shrink sleeving in accordance with the manufacturers instructions.Whichever method is used, the joints must be mechanically, electrically and environmentallyappropriate. Conductor connections are required to be made by any of the followingmethods: compression connectors, secured screw connectors, welding or brazing. Solderingis permissible if the conductors being connected are held together by suitable mechanicalmeans and then soldered.

Requirements for Cables and Glands

Cable glands must be selected with due regard to the methods of explosion protectionemployed 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 thecable;

(d) to ensure containment of an internal explosion in flameproof apparatus;

(e) to maintain the integrity of ‘restricted breathing’ apparatus.

6



Glands for Mineral Insulated Cables

Cable glands for use with MICC (Mineral Insulated Copper Cable) or MIMS (MineralInsulated 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 therequirements for Increased Safety apparatus as illustrated by the diagrams below.

Seal Assembl ies

Ex e type seal

Ex d type seal

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 arrangementensures that creepage/clearance distances are maintained within the seal.

The compound used within the Ex e seal assembly was previously required to bedoublebond non-metallic black epoxy putty 1536, with the Component Certificate for thisseal containing a ‘schedule for conditions of use’. Current specifications, however, allow useof the same compound for both Ex d and Ex e applications.

Difficulty may be experienced in achieving the desired level of ingress protection withMICC/MIMS cable glands due to the very small shoulder on the gland body, and may beovercome by the use of hard plastic washers manufactured for this purpose.

7



Selection of Cable Glands

The correct selection of cables and glands, particularly for flameproof apparatus, is veryimportant since there are a number of factors which can jeopardise the integrity of this typeapparatus. As previously discussed the cable construction, ingress protection, earth

continuity and secureness of the cable entering the apparatus must be maintained. Anadditional consideration is electrolytic action caused by contact between dissimilar metals,which results in increased corrosion and premature degradation of glands and cable entries.

Flameproof apparatus, however, introduces other considerations which are as follows.

1. Is the enclosure direct or indirect entry?2. Does the enclosure contain a source of ignition?3. Gas group of the apparatus.4. Zone in which the apparatus is installed;5. 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 theirfunction. For example, a cable gland for use with unarmoured cable is allocated thereference ‘A2’. The reference ‘E1’ is used to identify a cable gland for use witharmoured 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 beE1FW.

Direct Entry Method (Flameproof Ex d)

a) Flameproof Ex d / EEx d

8



Indirect Entry Methods

b. Flameproof EEx d / Ex d c. Flameproof I Increased Safety EEx de / Ex de

Maintaining Ingress Protection at Cable Gland Entr ies

The cable gland selected, as the means of entry to an enclosure, must suit the cable usedand, for type ‘e’ or type ‘n’ enclosures, where the ingress protection will be at least IP54 orgreater, the cable gland must maintain the ingress protection of the enclosure. Where suchenclosures have unthreaded entries IP sealing washers will be necessary. Whereenclosures 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 than6mm, an IP sealing washer (or thread sealant) is necessary to maintain IP54, but if the wallthickness is 6mm or greater an IP washer (or thread sealant) is deemed not necessary tomaintain IP54 unless a greater ingress protection level is required.

For flameproof enclosures, a sealing washer may be fitted between the cable gland and thewall of the enclosure to improve the ingress protection providing the thread engagement ismaintained, i.e. five full threads or 8mm, whichever gives the greater engagement.

9



Cable Gland Selection for Flameproof Apparatus

Cable glands for use with flameproof enclosures may be selected by following the procedurerecommended 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 partof the flameproof enclosure when tested with a section of the cable intended to beused.

(b) A flameproof cable entry device in which a sealing ring is an integral part of theconstruction and used with cables manufactured from thermoplastic, thermoseting orelastomeric materials. The cable must be compact and circular, have extrudedbedding and have non-hygroscopic fillers in the case of a filled cable. Selection ofthe 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 theapparatus certification document or have component approval, having cable entrydevices suitable for the cables intended for use. The compound or seals in thesedevices are required to provide sealing around the individual cable cores. Thestopping 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 orsimilar arrangements which seal around the individual cores of the cable;

(f) Alternative methods designed to maintain the integrity of the flameproof apparatus.

10



Cable gland selection for flameproof apparatus (continued)

The flowchart below, taken from BS EN60079-14, may be used to determine the mostsuitable type of cable gland for entry to flameproof apparatus.

Does thisenclosurecontain aninternalsource ofignition?

Does thehazardousgas requireIICapparatus?

Is the areaofinstallationZone 1?

Is thevolume oftheenclosuregreater than2 dm

3?

Apply10.4.2

(d) or (e)

NoYes

Ye

Yes

Yes

No

No

Use a suitablecable entrydevice with asealing ring

Start

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 aflameproof gland where ‘stopping’ around the individual cores of the cable is achieved byeither compound or elastomeric seals.

11



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 sealswhen other cable gland types are used.

The cable gland selection table below represents part of the data available for this type ofcable gland. Refer to the Hawke catalogue for the complete specification for this cablegland.

12



Assembly of gland


13



Assembly of gland (cont inued)


14



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 fordirect entry enclosures where the connecting cables are not circular, compact/filled, or wherean enclosure is located in a IIC area and contains a source of ignition, or where an enclosurehas an internal volume greater than 2 litres, contains a source of ignition and is located in aZone 1, IIA or IIB area.

As previously, the cable gland selection table below represents part of the data available forthis type of cable gland. Refer to the Hawke catalogue for the complete specification for thiscable gland.

15



Assembly of gland


16





17





18





19



Conduit

The use of conduit in hazardous areas requires particular care, especially when used withflameproof enclosures. In addition to maintaining the ingress protection (IP) rating of anenclosure - this applies to all types of protection - the integrity of the enclosure must bemaintained, i.e. the conduit in the run between the enclosure wall and the conduit sealingdevice must also be able to withstand the force of an explosion within the enclosure so thatthe flames/hot gases are prevented from reaching the external atmosphere. Where twoflameproof enclosures are connected by means of conduit, seals must be fitted to avoidpressure piling occurring during an internal explosion.

Sealing devices are also used to prevent the migration of gases from one hazardous locationto another. Although not entirely gas-tight, they will limit, to an acceptable level, the quantityof gas which will pass at normal atmospheric pressure. Where positive or negativepressures 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 BSEN60079-14.

Selection of conduit

Conduit used with explosion protected apparatus will be that recommended by themanufacturer 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 mechanicalstrength 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 andIEC 60614-2-5 are unsuitable for protecting cables connected to flameproofapparatus. Reference to national or other standards should be sought in thisinstance.

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, stoppingboxes are required to be fitted as close to the enclosure wall as possible, or not more than50mm from the enclosure wall to limit pressure piling. Alternatively, the manufacturer may fita stopping box in the enclosure as part of the certified design of the enclosure

20



General installation requirements

The installation of equipment in hazardous areas may involve the use of metallic mountingbrackets, cable tray, weather protection etc. It is important that the light metal content ofsuch 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 canbecome 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 electrici ty

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 staticelectricity if measures are not implemented to control this. Static electricity is more thancapable 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-metallicparts may be limited in accordance with the table below, the surface area limit beingdependent 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-metallicmaterial is surrounded by a conductive earthed frame.

21



Technicians / operatives

Technicians, or operatives as they are called in the standard, are required to have sufficientknowledge to achieve the correct selection and erection of explosion protected equipment inhazardous areas. This knowledge includes:

(a) an understanding of the general principles of explosion protection;

(b) an understanding of the general principles of the various types of explosionprotection and their marking;

(c) an understanding of the design features of the different types of explosionprotected equipment upon which their safe operation is dependent;

(d) an understanding of the content of equipment certificates, including theinformation for correct installation, and the related sections of BS EN60079-14.

(e) a broad understanding of the inspection and maintenance requirements of thedifferent methods of explosion protection as given in BS EN60079-17.

(f) familiarity with the particular techniques to be used for the selection and erectionof equipment as given in BS EN60079-14;

(g) an understanding of the additional importance of permit-to-work systems andsafe isolation for safe work on explosion protected equipment.

Assessment

The 2008 issue of BS EN60079-14 specifies that those persons, i.e. Responsible Persons,Operatives and Designers, involved in work in, or associated with, hazardous locations arerequired 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.

22



IS Cable Requirements

HazardousNon-hazardous

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 thatwhich is necessary to ignite a flammable mixture, even if a spark is produced at a break inthe cables.

23




Non-hazardous Hazardous

3 2 1 4

1. Insulation between screen and SWA or braid.

2. Screen (optional) - normally earthed at one point only, which is usually the barrierearth 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.

24





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

25





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.

26



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 effectiveearthing 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 areproduced.

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 goodcondition’ (see inspection schedules table 1, item B6; table 2, items B6 and B7 and table 3,item B3).

Explanation of terms

Electrical earthing or c ircui t protective conductors (CPC)

Conductors installed to provide a low impedance path for the current which flows under faultconditions to the general mass of earth. Normally the CPC is connected directly to anyassociated metal work of the equipment.

Electrical bonding

Conductors installed to establish continuity between adjoining metal work and the armouringof separate cables to ensure that, under fault conditions, all metal work and cable armouringare 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 atthe same time as a metal switch board cover or motor frame, will be deemed extraneousconductive parts.

27



Types of systems

(a) TN-S The system has separate neutral and protective conductorsthroughout.

(b) TT A system in which one point of the source of energy is directlyearthed but which is electrically independent of the electrodesused to earth the exposed conductive parts of the electricalinstallation.

(c) TN-C A system in which a single conductor serves as both neutraland protective conductor throughout the system.

(d) TN-C-S A system in which a single conductor serves as both neutraland protective conductor in part of the system.

(e) IT A system in which there is no direct connection between liveparts 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 earthedthrough a fault-limiting impedance.

The second letter indicates the installation earthing arrangements where:

3) T represents the exposed conductive parts of the installation connecteddirectly to earth;

4) N represents the exposed conductive parts of the installation which areconnected 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 singleconductor.

28



System earthing configurations

(a) TN-S

Generally, this method will be used when the electrical supply is provided viaunderground cables having metal sheaths and armour. The consumer’s earthterminal will be connected to the supply authorities protective conductor, that is themetal sheath and armour of the underground cable, thereby establishing acontinuous 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 viaoverhead cables but with no earth terminal provided by the supply authority. Theconsumer may have to provide an earth electrode for connection of the circuitprotective conductors. With this system, it is recommended that consumers useresidual current devices because of the difficulty in obtaining an effective earthconnection.

29



(c) TN-C

In this system the same conductor, perhaps the outer conductor of a concentriccable, 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 electricalconnection between the consumer and the supply authority, or where the supply isprovided by a private generator.

(d) TN-C-S

The supply authorities installation will use a TN-C system where both the neutral andcircuit protective conductor are served by a single (PEN) conductor. If theconsumers installation, which is connected to the TN-C supply system, employs aTN-S system where the neutral and circuit protective conductors are separate, thenthe overall system is known as a TN-C-S system. The majority of new installationsuse this arrangement which is termed a PME system by the supply authorities.

30



(e) IT

In this arrangement the system may have no connection to earth, or be connected toearth via a relatively high impedance, the ohmic value of which will depend on thelevel at which fault currents will be limited. Protection in this method is afforded by arelay which monitors any earth-leakage current as a result of an earth-fault. This willactivate 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 followingdocuments.

BS EN60079-14: 2008Electrical apparatus for explosive gas atmospheres: Part 14Electrical installations in hazardous areas (other thanmines)

BS 5345( withdrawn )

Code of practice for: Selection, installation andmaintenance of electrical apparatus for use in potentiallyexplosive atmospheres (other than mining applications orexplosive 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: 2003Electrostatics – Code pf practice for the avoidance ofhazards due to static electricity

BS 5958: Pts 1 & 2: 1991 Control of Undesirable Static Electricity

31



Earthing systems in hazardous areas

BS EN60079-14 specifies the conditions of use for the following earthing systems inhazardous areas. The conditions apply to electrical installations, except IS circuits, in zones1 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 andprotective conductor PE) in the hazardous area, i.e. the neutral and the protective conductorshall 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 beconnected 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 conductiveparts) 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) isused, 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 assupplementary equipotential bonding. Further information may be obtained by referenceto 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 ITsystems where all exposed and extraneous conductive parts are required to be connected tothe 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.

32



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 followingformula from the 16th Edition of the I.E.E. Wiring Regulations, BS7671.

k

t2IS =

Where: S = nominal cross-sectional area of earthing conductor mm2

I = fault-current for a negligible impedance fault that will flowthrough the associated protective device (the current-limitingeffect of circuit impedance’s and limiting capacity (I2t) ofprotective device will be taken into account. A furtherconsideration is the increase in resistance of the conductors asa result of the temperature rise during clearance of the fault.

(A)

t = operating time of protective device when clearing thefault-current I.

(secs)

k = factor which takes into account resistivity, temperaturecoefficient and heat capacity of conductor material, and theappropriate initial and final temperatures.

Values for k are given in tables 54B, 54C, 54D, 54E, & 54F in the I.E.E. Wiring Regulations.

33



CSA of CPC in relation to phase conductor

Alternatively, the minimum cross-sectional area of the protective conductor, in relation to thecross-sectional area of the associated phase conductor, may be determined byconsideration 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 phaseconductor If the protective conductor is

of the same material as thephase conductor

If the protective conductor is

not the same material as thephase conductor

mm2

S ≤ 16

16 ≤ S ≤ 35

S > 35

mm2

S

16

S2

mm2

k1Sk2

k116k2

k1Sk22

Note: The values of ‘k’ in the above table are given in the IEE Wiring Regulations, BS 7671as 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.

34



Main equipotential bonding conductors

The IEE Wiring Regulations, BS 7671, specify that the main equipotential bondingconductor in an installation, other than a PME system, is required to have a cross-sectionalarea 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 mainequipotential bonding conductor in relation to the neutral conductor of the supply.

Table 54H

Copper equivalent cross-sectional areaof the supply neutral conductor Minimum copper equivalentcross-sectional area of the mainequipotential bonding conductor

35 mm2 or less 10 mm

2

over 35 mm2 up to 50 mm

216 mm

2


2 25 mm

2


2 35 mm

2

over 150 mm2 50 mm

2

Practical example with and without earth bonding

The diagram on page 29 shows a simple installation comprising a motor, distributiontransformer, fuses and connecting cable. The fuses are necessary to provide protectionagainst 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 furtherdamage 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 thecircuit parameters, e.g. the resistance of the fault path - the earth-loop impedance - andthe fault current magnitude. The lower the earth-loop impedance, the higher the fault-currentwill be and the faster the fuse will rupture. The 16th edition of the I.E.E. Regulationsspecifies the requirements for earth-loop impedance.

Normally the star-point of the distribution transformer secondary winding is connected to anearth mat buried in the soil, but this alone will not provide a low enough earth-loopimpedance, and so an earthing bond is required between the motor frame and the star-pointof the transformer secondary winding. Let us now investigate the situation with and withoutthe bonding conductor between the/

35



main earth conductor and the motor frame when a fault occurs between one phase andearth within the motor. It will also be assumed that the motor is bolted securely to thebedplate 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 f rame.

Consider the circuit on page 35 which comprises a motor, transformer andinterconnecting 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 motorR = the resistance between the motor feet and bedplate;Vph = the phase voltage.

Voltage across motor frame and bedplate, V = VphxR RmRg

R ++

V = 240x10.010.05

1

++

V = 208 V

Thus, anyone standing next to the motor and touching it’s frame would receive a severeshock 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 thebonding 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 theeffective resistance at this point is significantly reduced. Similarly, a bondingconductor 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 ofshort 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 ofdangerous voltage levels. In order to avoid this difficulty, the earth-loop

impedance should be significantly lower than 0.1 Ω.

36



Practical example with and wi thout earth bonding (continued)

No earth bond connectedbetween motor frame and

Earth bond connectedbetween motor frameand main earth conductormain earth conductor

37



Static electrici ty

Static electricity is more than capable of igniting flammable materials and its presence in thepetro-chemical industry represents a very high risk which must be countered by theapplication 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 StandardBS 5958: Code of Practice for the control of undesirable static electricity, although the latterremains current.

The passage of oil, gases or dusts through process pipework and containment vesselscauses an internal build-up of static charges, which emerge on the exterior of the pipes andtanks to establish potentials the magnitude of which can be many thousands of volts. This isunacceptable 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 bystatic 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.

38



Static electrici ty (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 Codeof Practice BS 5345. For new installations guidance for the control of static electricity maybe found in PD CLC/TR 50404. A summary of the recommendations in this document isgiven in page 38.

Type of installation Areaclassification

Recommendedmaximum resistance

to earth

(Ω)

Comments

Main metal plantstructure,

Zones 0, 1 & 2 10 Ω Earthing normally inherentin 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 bemounted on non-conductingsupports and specialearthing connections maythen be required.

Metal pipelines. Zones 0, 1 & 2 10 Ω Earthing normally inherentin the structure. Specialearthing connections may berequired across joints if

there is doubt that the 10 Ω criterion will be satisfied.

Transportable metal

items: drums tanksetc.

Zones 0, 1 & 2 10 Ω Special earthing connections

are normally required.

Metal plant withsome non-conductingelements: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 satisfieda special earthingconnection should be usedto obtain a resistance of less

than 10 Ω to earth.

Higher resistivitynon-conducting

items with or withoutisolated metalcomponents: e.g.bolts in a plasticpipeline

Zones 0, 1 & 2 10 Ω The general electrostaticignition risk and the fire

hazard normally precludethe use of suchnon-conducting materialsunless it can be shown thatsignificant chargeaccumulation will not occur.In the absence of chargeaccumulation, earthing is notrequired in Zone 2 areas

Items fabricatedfrom conductive orantistatic materials

Zones 0, 1 & 2 1MΩ - 10MΩ

39



Static electricity (continued)

PD CLC/TR 50404: summary of maximum earthing resistances for the control of staticelectricity.

Sub clause Type of installation Maximumresistance to

earth

( Ω )

Comments

11.3.1.1 Main plantstructure

106

Earthing normally inherent in thestructure

11.3.1.1 Large fixed metalplant (reactionvessels, powdersilos, etc.)

106

Earthing normally inherent in thestructure. Special earthing could berequired for items mounted on non-conducting supports

11.3.1.1 Metal pipelines10

6

Earthing normally inherent in thestructure. Special earthing connectionrequired across joints if resistance

could exceed the 106

Ω criterion11.3.1.2 Movable metal

items (drums, roadand rail tankers,etc.)

106

Earthing connections are normallyrequired during filling and emptying

11.3.2 Metal plant withsome non-conductiveelements (valves,etc.)

106*

In special cases a limit of 100// Ω couldbe acceptable, but in general if a

106 Ω criterion cannot be satisfied, a

special earthing connection should beused

11.3.3 Non-conductiveitems with orwithout isolated

metal components(e.g. bolts in aplastic pipeline)

No generallyapplicablevalue*

The general electrostatic ignition riskand the fire hazard normally precludethe use of such materials unless it can

be shown that significant chargeaccumulation will not occur. In theabsence of charge accumulationearthing is not required in zone 2 and inzone 22.

11.3.4 Items fabricatedfrom non-conductive ordissipativematerials

106 to 10

8

* Very small conductive items need not be earthed, see 4.4.2.

Note 1: The above recommendations should be read in conjunction with the paragraphsindicated in the first column above.

Note 2: In zone 2 and in zone 22 earthing is required only when charge accumulation iscontinuous.

Note 3: In order to provide protection against lightning or to meet the electricity powersupply earthing requirements a lower value of resistance to earth is normallyrequired.

40



Unit 11:

Inspection & Maintenance

to BS EN 60079-17



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.


2



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 thatdegradation of the apparatus, due to environmental conditions and other factors, could affectthe integrity of the apparatus and allow ignition of any flammable gas or vapour in anhazardous area.

Inspection of equipment should be carried out on a regular basis to enable detection ofpotential faults early enough to prevent major breakdowns occurring, minimise downtimeand loss of production, and also possible injury to personnel. A maintenance programmebased on the results of inspection surveys can then be implemented, which will allowcontinued reliability and safe operation of the equipment.

Apparatus will only remain approved/certified if it is maintained in accordance with therecommendations provided by manufacturers and relevant standards.

Standards

BS EN60079-17: 2007Electrical apparatus for explosive gas atmospheres:Part 17. Inspection and maintenance of electrical installationsin 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 andmaintenance of electrical apparatus for use in potentiallyexplosive 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 clearunderstanding of the various types of explosion protection, installation practices, rules andregulations, and the general principles of area classification. Manufacturers have gone togreat lengths to design and build apparatus in accordance with relevant standards and haveit tested and certified by a third party test house to ensure the apparatus is safe for use inhazardous areas. All this effort will have been in vain if the technician in the field does nothave the necessary knowledge to install and/or maintain apparatus in accordance with themanufacturer’s requirements, relevant standards and Codes of Practice. Personneloperating in this field must, therefore, have appropriate training, and thereafter, regularrefresher training. Records detailing the experience and training of personnel must bemaintained.


3



Apparatus may be explosion protected at the time of leaving the manufacturer’s premisesbut, the way the apparatus is subsequently handled, selected, installed and maintained, willhave an influence on whether the apparatus will be safe for use in an hazardous area and/orremain certified. Personnel need to be aware of, for example, the consequences of a brokenfoot 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, flameproofapparatus will affect the integrity of such apparatus.

Principal causes of apparatus deterioration

BS EN60079-17 lists factors which have a significant effect on the deterioration of equipmentin 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 withmanufacturer’s recommendations.

Apparatus withdrawn f rom service

Where it is required to withdraw apparatus during maintenance, any exposed conductorsfrom 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 beisolated from all sources of power supply and terminated in a suitable enclosure, orcompletely removed.


4



IEC Standards

The International Electrotechnical Commission (IEC) Standards relative to explosionprotected apparatus have been available since the late nineteen-sixties when they werepublished 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 theEuropean Standards. Attempts to remedy this situation were implemented by the variouscommittees within IEC to effect a complete revision of their Standards. There has also beengreater co-operation between IEC and CENELEC to achieve technical alignment of theirrespective Standards.

With regard to the EU, explosion protected apparatus is normally constructed in accordancewith national and harmonised standards. IEC standards, however, have tended not to beused 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 therehave been instances where manufacturers have been requested by larger users of explosionprotected 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 oneinstance, has led to the manufacturer issuing a ‘self declaration’ for apparatus they havemanufactured to a particular IEC Standard.

An IEC Standard which has become more widely accepted is IEC 60079-17, which is now aBritish Standard, BS EN60079-l7. This Standard comprises a series of Tables for theinspection of the various methods of explosion protection. Table 1 is an inspection schedulewhich lists the areas to be inspected for the types of apparatus Ex d, Ex e and Ex n. Table 2and Table 3 are schedules for the inspection of IS apparatus and Pressurised Ex papparatus respectively. These Tables are illustrated at the end of this section. For eachtype 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 willbe apparent only by the use of access equipment, e.g. step ladders (wherenecessary), and tools. Close inspections do not normally require theenclosure 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, wherenecessary, tools and test equipment.

Inspection schedules are, therefore, a means by which electrical installations may besystematically assessed for the correct installation of apparatus and also the effects ofenvironmental conditions such as water, ambient temperature, vibration etc.


5



Documentation

Prior to the implementation of an inspection / maintenance programme it is essential that allnecessary documentation is available. These will include hazardous area drawings of theplant, apparatus group and temperature class, list and location of apparatus spares,

technical information, manufacturer’s instructions, and a complete inventory of all hazardousarea equipment installed in the plant including their location in the plant and up-to-daterecords of all previous inspections and maintenance tasks carried out. It is also vitallyimportant that the certification documents for each item of explosion protected apparatus areavailable so that, for example, clarification of any ‘Special Installation Conditions’ may beverified at a later date.

The maintenance of comprehensive records is thus an essential requirement for the safeoperation of electrical equipment in hazardous areas. Experience has shown thatmodifications to existing hazardous area equipment and also the installation of additionalhazardous area equipment, has occurred in hazardous areas installations without theseactions 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 ‘initialinspection’ 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.

Thereafter, ‘periodic inspections’ should be implemented to verify that the installation isbeing maintained in an appropriate condition for continued use in the hazardous area. Thegrade of inspection for ‘periodic inspections’ may be ‘visual’ or ‘close’ and should becarried 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 theoutcome of a ‘visual/close inspection’, it may be necessary to carry out a further ‘detailedinspection’. Experience gained in similar situations with regard to apparatus, plants andenvironments 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 notexceed three years. Interim ‘sample inspections’ may be implemented to either


6



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 beestablished and how the various grades of inspection, i.e. ‘visual’ , ‘close’ or ‘detailed’, maybe 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 containscomponents which are ignition capable in normal operation. Typical componentsare switches, contactors, relays etc. where ignition capable arcs or sparks areproduced at their contacts, and, for example, resistors which may produceexcessive surface temperatures.


7



Typical inspection procedure for periodic inspections


8



BS EN 60079-17 Table 1: Inspect ion 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



3 Apparatus temperature class is correct * * * * * *4 Apparatus circuit identification is correct * * *



* * * * * * * * *





* **

* **

* **

10 Flange faces are clean and undamaged and gaskets, if any,are satisfactory *









B INSTALLATION


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 *


* * *



** *

** *

** *


* * *


9 Automatic electrical protective devices operate within permittedlimits

* * *


* * *

11 Special conditions of use (if applicable) are complied with * * *12 Cables not in use are correctly terminated * * *


* * *


* * * * * *


9




Grade of Inspection

D C V D C V D C V

C ENVIRONMENT


* * * * * * * * *

2 No undue accumulation of dust and dirt * * * * * * * * *3 Electrical insulation is clean and dry * *


Note 2: The use of electrical test equipment, in accordance with items B7 and B8, shouldonly be undertaken after appropriate steps are taken to ensure the surrounding areais free of a flammable gas or vapour.


10





Detailed Close Visual

A Apparatus


* * *


* *







* * *

9 Electrical connections are tight *10 Printed circuit boards are clean and undamaged *

B Installation






6 Earth continuity is satisfactory (e.g. connections are tight andconductors are of sufficient cross-section)

*


8 The intrinsically safe circuit is isolated from earth to earthed at onepoint only (refer to documentation)

*


*


*



C Environment

1 Apparatus is adequately protected against corrosion, weather,


* * *



11



BS EN60079-17: Table 3: Inspection Schedule for Ex ’p’ Installations



A Apparatus

1 Apparatus is appropriate to area classification * * *

2 Apparatus group 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/orcompounds are satisfactory

* * *



9 Lamp rating, type and position are correct *

B Installation

1 Type of cable is appropriate *


3 Earthing connections, including any supplementary earthingbonding connections are satisfactory (e.g. connections are tight andconductors are of sufficient cross section


** *

4 Fault loop impedance (TN systems) or earthing resistance (ITsystems) is satisfactory

*

5 Automatic electrical protective devices operate within permittedlimits

*

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 functioncorrectly

*

12 Pre-energising purge period is adequate *

13 Conditions of spark and particular barriers of ducts for exhaustingthe gas in hazardous area satisfactory

*


C Environment


* * *



12



Unit 12:

Sources of Ignition




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


2



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 mSduration in a circuit carrying 20 mA at 10 V. From this perspective, it is clear that for devicessuch as these to operate safely in a hazardous area require them to be installed in, forexample, a flameproof enclosure.

The voltage level has an influence on how incendive a spark will be. Flammable gases andvapours are more readily ignited at high voltages than low voltages, and is basically why IScircuits are seldom designed for use above 30 V.

The use of electrical test instruments, typically voltmeters and insulation resistance testersetc., are a potential source of electrical sparks. These instruments should only be usedunder controlled circumstances, i.e. under the control of a work permit and tests to ensuregas free conditions.

Hot Surfaces

The flow of current through, for example, the windings of an electric motor invariablyproduces heat which will raise the surface temperature of the motor. If the motor isexcessively overloaded and the thermal overload device in the starter is incorrectly set, thesurface temperature of the motor may well exceed it’s T-rating. Overheating can also becaused by blockage of the cooling fan intake, damaged cooling fan, or collapse of bearingdue 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 capableof igniting a flammable gas or vapour.

Other sources of heat are process pipes and machinery, combustion engine manifolds andexhaust pipes, and light bulbs.

Batteries

Batteries, whatever their size, are a potential source of ignition as they will produceincendive sparks if their terminals are short-circuited. Current of the order 1000 A can begenerated 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 ifpowered by low-power batteries. High-power batteries must not be used unless permitted bythe manufacturer. Replacement of batteries must only be carried out in a non-hazardousarea.


3



Friction

The abrasive wheels of portable grinding machines are more than capable of producingincendive 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 Electrici ty

Static electricity is normally caused by two insulating materials rubbing together. The looselyheld electrons in the atoms of one material are detached and transferred to the othermaterials, so that the material which loses electrons becomes positively charged. Thiscondition may remain for some time because the materials are insulators and do not offer aconductive 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 becleaned 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 begenerated at the nozzle of an aerosol canister. Similarly, 10000 V or more can be generatedat the nozzle of high-pressure steam cleaning equipment. Bonding and earthing of aircraftduring refuelling prevents the build up of electrostatic charges which might otherwise causethe aviation fuel vapour to ignite.

Lightning

Lightning is a type of static electricity caused by the movement of clouds. Air between cloudsor between clouds and earth, acts as an insulator allowing the charges to build up and theresult 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 lightingstrike. Lightning strikes will be readily discharged to earth by the normal metal constructionof 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 likelysource of ignition, known as thermite action, which can produce sparks capable of ignitinga flammable gas or vapour. The use of aluminium ladders in hazardous areas shouldtherefore 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, reactswith the iron of the pipe to produce iron sulphide. Iron sulphide when exposed to air veryquickly 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 theiron sulphide with water or prevent its contact with air.


4



Radio frequency

The increase in the use of mobile telephones, which operate at high frequencies, hascaused some concern. Such concern was expressed by a major oil company in 1993 aboutthe risk of using mobile telephones in petrol stations. Petrol stations have Zone 1 areasaround 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 radarinstallations.

With regard to radar installations, concern was expressed about the possible ignition offlammable gases at the St. Fergus Gas Terminal in the North East of Scotland by radartransmissions from the nearby radar installation at Crimond.

Vibration

Vibration is undesirable since it causes premature deterioration of equipment if allowed topersist. Typical examples are increased wear in bearings, loosening of electricalconnections, etc. Vibration has also been known to cause metal fatigue of the coppersheath and conductors of MICC cable due to work hardening.


5



Unit 13:

Induction to CompetenceValidation Testing




Objectives:

On completion of this unit, ‘Induction to Competence Validation Testing ’, you shouldknow:

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 andinstallation of an Ex i system and associated apparatus.

d. The procedures and competence requirements for EX04: the inspection andmaintenance of an Ex i system and associated apparatus.


2



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 includeselection of materials, apparatus, equipment andtools. Safe working practices to be adhered to atall times and include the mandatory use ofPersonal Protective Equipment in thedesignated areas.

Permit-to-work and safe electricalisolation:

Complete relevant section of permit-to-work inaccordance with procedures detailed in Unit 14.

On-site preparation: Implement, with reference to AssessmentWorkpacks, all on-site procedures to achieve thecompetence standard required for Installation,Inspection and Maintenance relative to UnitsEX01, EX02, EX03 and EX04.

EX01 Preparation and Installation of EEx d, e & n Apparatus

Section A

Preparation and Safe

Isolation of the electricalCircuit:

Correctly locate electrical supply source and

safely isolate installation under the control of apermit-to-work system

Section B

Installation comprisingEx d, Ex e and Ex napparatus:

a) Inspect suitability of pre-fixed apparatus, cablesand glands.

b) Install appropriate cables and glands in amanner which will maintain the integrity of thepre-fixed apparatus.

c) Carry out appropriate electrical (instrument)tests after ensuring appropriate safeguards areimplemented.

d) Fit apparatus covers and live-test installation.


3



EX02 Inspection of EEx d, e & n Apparatus

Sections A, B & C

Inspection of apparatusand 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 specifythe remedial action necessary to return theinstallation to specification.

Section D

Safe Isolation of theelectrical circuit.(Prior to Section C):

Correctly locate electrical supply source and safelyisolate installation under the control of a permit-to-worksystem.

EX03 Preparation and Installation of EEx i Apparatus

Section A

Installation comprisingEx i apparatus:

a) Inspect suitability of pre-fixed apparatus, cablesand glands.

b) Install appropriate cables, glands and safetyinterfaces in a manner which will maintainapparatus integrity.

c) Carry out appropriate electrical (instrument)tests after ensuring appropriate safeguards areimplemented.


4



EX04 Inspection of EEx i Apparatus

Sections A, B & C

Inspection of apparatusand 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 andspecify the remedial action necessary to returnthe installation to specification.

Section D

Safe Isolation of theelectrical circuit.(Prior to Section C):

Correctly locate electrical supply source and safelyisolate installation under the control of a permit-to-work system.


5





Grade of Inspection

D C V D C V D C V

A APPARATUS







* * * * * * * * *





* **

* **

* **


*




14 Condition of enclosure gaskets is satisfactory * *15 Enclosed-break and hermetically sealed devices are undamaged *




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 * * * * * * * * *



* * *



** *

** *

** *


* * *


9 Automatic electrical protective devices operate within permittedlimits * * *


* * *




* * *


* * * * * *


6




Grade of Inspection

D C V D C V D C V

C ENVIRONMENT

1 Apparatus is adequately protected against corrosion, weather,


* * * * * * * * *




Note 2: The use of electrical test equipment, in accordance with items B7 and B8, shouldonly be undertaken after appropriate steps are taken to ensure the surroundingarea is free of a flammable gas or vapour.

`


7






A Apparatus


* * *


* *







* * *



B Installation






6 Earth continuity is satisfactory (e.g. connections are tight andconductors are of sufficient cross-section)

*


8 The intrinsically safe circuit is isolated from earth to earthed at onepoint only (refer to documentation)

*


*


*



C Environment


* * *



8



Unit 14:

Permit to Work Systemand Safe Isolation



Objectives:

On completion of this uni t, ‘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 controldevices for tests EX01, EX02, EX03 and EX04;

c. the procedure to safely isolate and secure isolation of electrical circuits andapparatus for tests EX01, EX02, EX03 and EX04.



Permit-to-work and safe isolation

Candidates attending the 5-day CompEx course are required to carry out four practicalassessments in the simulated hazardous areas. During these assessments, candidatesmust 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 assumedmay be present at any time.

Work permit

In order to ensure that safety is maintained, candidates must operate within the control of awork 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 likelyto produce a source of ignition. Such situations occur when electrical test instrumentsand/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 toIsolate’ 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 vol tage 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 confirmresult 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 switchingoff and removal of keys in the fire and gas panel.



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

Authorisation to isolate (Authorised person)

Equipment has been isolated at

and checked for zero voltage at

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

I herby declare the above work has been completed and work site cleared(Candidate)

I herby authorise de-isolation (Authorised person)

De-isolation complete (Candidate)

7. Cancellation

All work detailed above is completed and ‘Permit-to-Work’ is cancelled(Authorised person)



GAS TEST CERTIFICATE

This certificate confirms that the work bay nominated below in the Ex TrainingFacility 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 Author ised person(signed)

Zero voltage test (isolation)

Use of portable heat gun

Final ‘inst rument’ circuit testing



Appendix 1:

Data forflammable materials



PD IEC 60079-20 -TABLE 1: DATA FOR FLAMMABLE MATERIALS

Ref Gaz ou vapeurGas or vapour

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°C vol pour centvol per cent

mg/1

1 Aldéhyde acétique Acetaldehyde

CH2CHO 1.52 -38 4.00 80.0 74 1108

2 Acida acétique Acetic acid

CH3COOH 2.07 40 4.00 17.0 100 428

3 Anhydride acétoque Acetic anhydibe

(CH3CO)2O 3.52 49 2.00 10.0 85 428

4 Acétone Acetone

(Ch3)2CO 2.00 <-20 2.50 13.0 60 316

5 Acétonitrile Acetoniltrile

CH3CH 1.42 2 3.00 16.0 51 275

6 Chlorure d’acétyle Acatyl chloride

CH3COCI 2.70 -4 5.00 19.0 157 620

7 Acétyléne (voir 4.3) Acatyl chloride

CH=CH 0.90 2.30 100.0 24 1092

8 Acétylé flouride Acetyl fluoride

CH3COF 2.14 <-17 5.60 19.9 142 505

9 Acrylaldehyde CH2=CHCHO 1.93 -18 2.85 31.8 65 728

10 Acide acrylique Acrylic acid

CH2=CHCOOH 2.48 56 2.90 85

11 Acrylonitrille Acrylonitrille

CH2=CHCN 1.83 -5 2.80 28.0 64 620

12 Acryloyl chlordide Ch2CHCOCI 3.12 -8 2.06 18.0 220 662





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13 Acétate d’allyle Allyl acetate

CH2=CHCH2OOCCH2 3.45 13 1.70 9.3 69 3800

14 Alcool d’allyle Allyl alcohol

CH2=CHCH2CH 2.00 21 2.50 18.0 61 438

15 Chlorure d’allyle Allyl chloride

CH2=CHCH2CI 2.64 -32 2.90 11.2 92 357

16 Ally 2. 3-epoxypropl ather CH2=CH-CH°O CHCH2-CH20 3.94 45

17 2-Aminoelhanol NH2-CH2CH2OH 2.10 85

18 Ammonic Ammonia

NH3 0.59 15.0 33.6 107 240

19 Amphétamine Amphetamina (INN)

C6H5CH2-CH(NH2)CH3 4.67 <100

20 Anlline Anlline

C6H5NH2 3.22 75 1.20 11.0 47 425

21 Azepane CH2(CH2)5NH 3.41 23

22 BenzaldéhydeBenzaklehyde

C6H3CHO 3.65 64 1.40 62

23 BenzéneBenzene

C6H6 2.70 -11 1.20 8.6 30 280

24 1-Brombutane1-Bromobulane

CH3(CH2)2CH2Br 4.72 13 2.60 6.6 143 380





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25 2 Bromo-1.1-diethoxyethane (CH3CH2O)2CHCH2Br 7.34 57

26 BrométhaneBromoethane

CH3CH2Br 3.75 <-20 6.70 11.3 306 517

27 Buts-1.3-diéneButa-1.3-

diene

CH2=CHCH=CH2 1.87 -85gaz/gas

1.40 16.3 31 385

28 ButaneButane

C4H

10 2.05 -60

gaz/gas

1.40 9.3 33 225

29 IsoButaneIsobutane

(CH3)2CHCH3 2.00gaz/gas

1.3 9.8 31 236

30 Butan-1-ol CH3(CH2)2CH2OH 2.55 29 1.70 12.0 62 372

31 Butanone CH3CH2COCH3 2.48 -9 1.80 10.0 50 302

32 But-l-ane CH2=CHCH2CH3 1.95 -80gaz/gas

1.60 10.0 38 235

33 (Isomére non mentionnéBut-2enes (isomer notstated)

CH3CH=CHCH2 1.94gaz/gas

1.60 10.0 40 228

34 But-3-en-3-olide CH2=CCHO(O)O 2.90 33

35 2-(2-Butoxyethoxy)ethanol CH3(CH2)OCH2CH2OCH2CH2OH 5.59 78

36 Acétate da butyleButyl acetate

CH3COOCH2(CH2)CH3 4.01 22 1.3 7.5 64 390





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37 n-Butyl acrylate CH2=CHCOOC4Hg 4.41 38 1.2 8.0 63 425

38 ButylamineButylamine

CH3(CH2)3NH2 2.52 -12 1.7 9.8 49 286

39 IsoButylaminIsoButylamin

(CH3)2CHCH2NH2 2.52 -20 1.47 10.8 44 330

40 Butyl 2m 3-epoxyprophylether

CH3(CH2)3OCH2CHCH20 4.48 44

41 Ester butylique de l’acidehydroxyacélique

Butyl glycolate

HOCH2COOC4H9 4.45 61

42 IsoButylisobutyrate (CH2)2CHCOOCH2CH(CH3)2 4.93 34 0.80 47

43 Butylmethacrylate CH2=C(CH3)COO(CH)3CH3 4.90 53 1.00 6.8 58 395

44 tart-Butyl methyl ether CH3OC(CH3)2 3.03 -27 1.50 8.4 54 310

45 n-Butylpropionate C2H5COOC4H9 4.48 40 1.10 7.7 58 409

46 But-l-yne CH3CH2C=CH

47 Aldéhyde de butyleButyraldehyde

CH3CH2CH2CHO 2.48 -22 1.6 11.0 47 320

48 IsoButyraldeydeisoButyraldehyde

(CH3)2CHCH0 2.48 -22 1.6 11.0 47 320





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49 Isobutyric acid (CH3)2CHCOOH 3.03 5.8

50 Butyrul fluoride C3H7COF 3.10 <-14 2.60 95

51 Sulfure de carbone (voir4.4) Carbon disulphide (see 4.4)

C82 2.64 -30 0.60 60.0 19 1900

52 Monoxyde de carbone(voir4.5) Carbon monoxide(saturated at 18°C) (see4.5)

CO 0.97 10.90 74.0 126 870

53 Carbonyl sulphide COS 2.07 6.5 28.5 160 700

54 ChlorobenzéneChlorobenzene

C5H5CI 3.88 28 1.40 11.0 66 520

55 1-Chlorobutane1-Chlorobutane

CH3(CH2)2CH2CI 3.20 -12 1.60 10.0 69 386

56 2- Chlorobutane2- Chlorobutane

CH3CHCIC2H5 3.19 <-18 2.20 8.8 82 339

57 1-Chlore-2. 3-epoxpropane OCH2CHCH2CI 3.30 28 2.30 34.4 86 1325

58 ChloréthanolChlorethane

CH3CH2CI 2.22 3.60 15.4 95 413

59 Chloréthanlol2-Chloroethanol

CH2CICH2OH 2.76 55 5.00 16.0 160 540

60 ChloréthyaneChloroethylane

CH2=CHCI 2.15 -78gaz/gas

3.60 33.0 94 610





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61 ChlorométhaneChloromethane

CH3CI 1.78 -24gaz/gas

7.60 19.0 160 410

62 Ether clordiméthyliqueClormethyl methyl ether

CH3OCH2CI 2.78 -6

63 1-Chloro-2-methylpropane (CH3)2CHCH2CI 3.19 <-14 2.00 8.8 75 340

64 2-Chloro-2-methylprpane (CH3)3CCI 3.19 <-18

65 3-Chloro-2-methylprop-l-ane CH2=C(CH3)CH2CI 3.12 -16 2.10 77

66 5-Chloropentan-2-one CH3CO(CH2)3CI 4.16 61 2.00 98

67 1-Chloropropane1-Chloropropane

CH3CH2CH2CI 2.70 -32 240 11.1 78 365

68 2- Chloropropane2- Chloropropane

(CH3)2CHCI 2.70 <-20 2.80 10.7 92 350

69 Chlorotrifluoroethylane CF2CFCI 4.01 gaz/gas 4.6 64.3 220 3117

70 1-Chloro-2.2.2-triflouroethylmethyl ether

CF3CHCIOCH3 5.12 4 8.00 484

71 a-Chlorotoleuene C6H5CH2CI 4.36 60 1.20 63

72 Naohte de houilleCoal tar naphtha





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73 Gaz de cokarle (voir 4.1) Coke oven das (see 4.1)

74 Crésols (Ensemble d’isoméres)Cresols (Mixed Isomers)

CH3C6H4OH 3.73 81 1.10 50

75 Aldéhyde crotoniqueCrotonaldehyde

CH3CH=CHCHO 2.41 13 2.10 16.0 62 470

76 CuméneCumene

C6H5CH(CH3)2 4.13 31 0.80 6.5 40 328

77 CyclobutaneCyclobutane

CH2(CH2)2CH2 1.93 1.80 42

78 CycloheptaneCycloheptane

CH2(CH2)5CH2 3.39 <10 1.10 6.7 44 275

79 CyclohexaneCyclohexane

CH2(CH2)4CH2 2.90 -15 1.20 8.3 40 290

80 CyclohexanolCyclohexanol

CH2(CH2)4CHOH 3.45 61 1.20 11.1 50 460

81 CyclohexanoneCyclohexanone

CH2(CH2)4CO 3.38 43 1.00 9.4 42 386

82 CyclohexéneCyclohexene

CH2(CH2)3CH=CH 2.83 -17 1.20 41

83 CyclohexylamineCyclohexylamine

CH2(CH2)4CHNH2 3.42 32 1.60 9.4 63 372

84 1.3-Cyclopentadlene CH2CHCHCHCH 2.30 -50





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85 CyclopentaneCyclopentane

CH2(CH2)3CH2 2.40 -37 1.4 41

86 CyclopentaéneCyclopentene

CH=CHCH2CH2CH 2.30 <-22 1.48 41

87 CyclopropaneCyclopropane

CH2CH2CH2 1.45 240 10.4 42 183

88 Cyclopropyl methyl ketone CH3COCHCH2CH2 2.90 15 1.70 58

89 p-Cymére p-Cymene CH3C6H4CH(CH3)2 4.62 47 0.70 6.5 39 366

90 2.2.3.3.4.4.5.5.6.6.7.7 –Dodecafluroheptylmethacrylate

CH2=C(CH3)COOCH2(CF2)6H 9.93 49 1.60 195

91 DecahydronaphthaléneDecahydronaphthelene trans

CH2(CH2)3CHCH(CH2)3CH2 4.76 54 0.70 4.9 40 284

92 Decane (Ensemble d’isoméres)Decane (Mixed Isomers)

C10H22 4.90 46 0.70 5.6 41 433

93 Ether butyliqueDibutyl ether

(CH3(CH2)3)2O 4.48 25 0.90 8.5 48 460

94 Paroxide de butyle di-tertiare

Di-tetr-butyl peroxide

(CH3)3COOC(CH3)3 5.0 18

95 Dichlorobenzéne (isomére not

mentioned)

s

Dichlorobenzenes (isomer notstated)

C5H4CI2 5.07 66 2.20 9.2 134 564

96 3.4-Dichlorobut-1-ene CH2=CHCHCICH2CI 4.31 31 1.30 7.2 68 368





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mg/1

97 1.3-Dichlorobut-2-ene CH3CCI=CHCH2CI 4.31 27

98 Dichlorosllane de diéthyleDichlorodlethylsllane

(C2H5)2SICI2 24 3.40 223

99 1.1-Dichloréthane11.-Dichloroethane

CH3CHCI2 3.42 -10 5.60 16.0 230 660

100 1.2-Dichloréthane1.2-Dichloroethane

CH2CICH2CI 3.42 13 6.20 16.0 255 654

101 DichloréthyléneDichloroethylene

CICH=CHCI 3.55 -10 9.70 12.8 391 518

102 1.2-Dichloropropane1.2-Dichloropropane

CH3CHCICH2CI 3.90 15 3.40 14.5 160 682

103 Dicylopentadiene (technical) C10H12 4.56 36 0.60 43

104 1.2-Diathoxyethane C2H5O(CH2)2OC2H5 4.07 16

105 DiéthylamineDiethylamine

(C3H5)2NH 2.53 -23 1.70 10.0 50 306

106 Diethyl carbonata (CH3CH20)2CO 407 24 1.4 11.7 69 570

107 Ether éthyliqueDiathyl ether

(CH3CH2)2O 2.55 -45 1.70 38.0 50 1118

108 Oxalate de dléthyleDiethyl oxalate

(COOCH2CH3)2 5.04 76





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109 Sulfate de diéthyleDiethyl sulphate

(CH3CH2)2SO4 5.31 104

110 1.1-Difluoroethylene CH2=CF2 2.21 3.90 25.1 102 665

111 DihexylétherDlhexyl ether

(CH3(CH2)6)2O 6.43 75

112 Di-idobutylamineDilsobutyamine

((CH3)2CHCH2)2NH 4.45 26 0.80 3.6 42 190

113 Disobutyl carbionl ((CH3)2CHCH2)2CHOH 4.97 75 0.70 6.1 42 370

114 Di-isopentylétherDilisopantyl ether

(CH3)2CH(CH2)20(CH2)2CH(CH3)2 5.45 44 1.27 104

115 Di-isopropylaimeDisopropylaime

((CH3)2CH)2NH 3.48 -20 1.20 6.3 49 260

116 Di-isopropylétherDisopropyl ether

((CH3)2CH)2O 3.52 -28 1.00 21.0 45 900

117 DiaméthylaimeDiamthylaime

(CH3)2NH 1.55 -18gaz/gas

2.80 14.4 53 272

118 1.2-Dimethoxyethane CH3O(CH2)2OCH3 3.10 -6 1.6 10.4 60 390

119 Diamethoxymethane CH2(OCH3)2 2.60 -21 3.00 16.9 93 535

120 2-Diméthylaminoéthanol2-

Dimthylaminoethanol

(CH3)2NC2H4OH 3.03 39





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121 3-(Dimethylamino)propiononitrille

(CH3)2NHCH2CH2CN 3.38 60 1.57 62

122 Ether méthyliqueDimethyl ether

(CH3)2O 1.59 -42gaz/gas

2.70 32.0 51 610

123 Formamide de diméthyleN.N-Dimethylformamide

HCON(CH3)2 2.51 58 1.80 16.0 55 500

124 3.4-Dimethyl hexane CH3CH2CH(CH2)CH(CH3)CH2CH3 3.87 2 0.80 6.5 38 310

125 N.N-Diamrthylhydrazine (CH3)2NNH2 2.07 -18 2.4 20 60 490

126 1.4-Diamrthylhydrazine NH(CH3)CH2CH2NH(CH3)CH2CH2 3.98 9

127 N.N-Dimethylpropane-1.3-diamine

(CH3)2N(CH2)3NH2 3.52 26 1.20 50

128 Sulfate de diméthyleDimathyl

sulphate

(CH3O)2SO2 4.34 39

129 1.4-Dioxane1.4-Dioxane

OCH2CH2OCH2CH2 3.03 11 1.90 28.6 74 813

130 1.3-Dioxolane

1.3-Dioxolane

OCH2CH2OCH2 2.55 -5 2.3 30.5 70 935

131 Dipenténe. brutDipentene. crude

C10H16 4.66 42 0.75 6.1 43 346

132 DipentylétherDipentyl ether

(CH3(CH2)4)2O 5.45 57





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133 DipropylamineDipropylamine

(CH3CH2CH2)2NH 3.48 4 1.60 9.1 66 376

134 DipropylétherDipropyl ether

(C3H7)2O 3.53 <-5

135 1.2-Epoxypropane CH3CHCH2O 2.00 -37 1.90 37.0 49 901

136 EthaneEthane

CH3CH2 1.04 2.50 15.5 31 194

137 Ethanethlol CH3CH2SH 2.11 <-20 2.80 18.0 73 468

138 EthanolEthanol

CH3CH2OH 1.59 12 3.1 19.0 59 359

139 Ethanol éthoxylé2-Ethoxyethanol

CH3CH2OCH2CH2OH 3.10 40 1.80 15.7 68 593

140 Acétate d’éthanol éthoxylé2-Ethoxyethyl acetate

CH3COOCH2CH2OCH2CH3 4.72 47 1.20 12.7 65 642

141 2- (2-Ethoxyethoxy) ethanol CH3CH2OCH2CH2OCH2CH2OH 4.62 94

142 Acéthate d’éthyleEthyl acetate

CH3COOCH2CH3 3.04 -4 2.20 11.0 81 406

143 Acétylacétate d’éthyleEthyl acetoacetate

CH3COCH2COOCH2CH3 4.50 65 1.00 9.5 54 519

144 Acrylate d’éthyleEthyl acrylate

CH2=CHCOOCH2CH3 3.45 9 1.40 14.0 59 588





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145 EthylamineEthylamine

C2H5NH2 1.50 <-20 2.65 14.0 49 260

146 EthylbenzéneEthlbenzene

CH2CH3C8H5 3.66 23 1.00 7.8 44 340

147 Ethyl butyrateEthyl butrate

CH3CH2CH2COOC2H5 4.00 21 1.40 65

148 EthylcyclobutaneEthylcyclobutane

CH3CH2CHCH2CH2CH2 2.90 <-16 1.20 7.7 42 272

149 EthylocychexaneEthylcyclohexane

CH3CH2CH(CH2)4CH2 3.87 <24 0.90 6.6 42 310

150 EthycyclopantaneEthylcyclopantane

CH2CH2CH(CH2)3CH2 3.40 <5 1.05 6.8 42 280

151 EthyléneEthylene

CH2=CH2 0.97 2.3 35.0 26 423

152 Ethylenediamine NH2CH2CH2NH2 2.07 34 2.7 16.5 84 396

153 Oxyde d’éthéneEthylene oxide

CH2CH2O 1.52 <-18 2.60 100.0 47 1848

154 Formiate d’éthyleEthyl formate

HCOOCH2CH3 2.55 -20 2.70 16.5 87 497

155 2-Ethythéxyl acetate CH3COOCH2CH(C2H5)C4H9 5.94 44 0.75 6.2 63 439

156 Ethyl isobutyrate (CH3)2CHCOOC2H5 4.00 10 1.60 75





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157 Méthacrylate d’éthyleEthyl methacrylate

CH2=CCH3COOCH2CH3 3.90 (20) 1.50 70

158 Ethyl methyl ether CH3OCH2CH3 2.10 2.00 10.1 50 255

159 Nitrite d’éthyle (voir 4.2)

Ethyl nitrite (see 4.2) CH3CH2ONO 2.60 -35 3.00 50.0 94 155

160 O-Ethylphosphorodichloridothioate

C2H5OPSCI2 7.27 75

161 (Isomére non mentionné)Ethylpropylacrolein(Isomer notstated)

C3H14O 4.34 40

162 FormaldéhydeFormaldehyde

HCH0 1.03 7.00 73.0 88 920

163 acide formiqueFormic acid

HCOOH 1.60 42 10.0 57.0 190 104

164 2-Furaldehda OCH=CHCH=CHCHO 3.30 60 2.10 19.3 85 768

165 FuraneFuran

CH=CHCH=CHO 2.30 <-20 2.30 14.3 66 408

166 Furfuryl alcohol OC(CH2OH)CHCHCH 3.38 61 1.8 16.3 70 670

167 1.2.3-Trimethylbenzene CHCHCHC(CH2)C(CH3)C(CH3) 4.15 61 0.80 7.0

168 Heptane (ensemble d’isoméres)Heptane (mixed isomers)

C7H16 3.46 -4 1.10 6.7 48 281





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169 Heptan-1-ol CH2(CH2)5CH2CH 4.03 60

170 Heptan-2-one CH3CO(CH2)4CH3 3.94 39 1.10 7.9 5.2 378

171 Hept-2-ene CH3(CH2)3CH=CHCH3 3.40 <0

172 Hexane (ensembled’isomérs)Hexane (mixed Isomers)

CH3(CH2)3CH3 2.97 -21 1.00 8.4 35 290

173 1-Hexanol1-Hexanol

C5H13OH 3.60 63 1.20 51

174 Hexan-2-one CH3CO(CH2)3CH3 3.46 23 1.20 8.0 50 336

175 HydrogéneHydrogen

H2 0.07 4.00 77.0 3.4 63

176 CyanogéneHydrogen cyanide

HCN 0.90 <-20 5.40 46.0 60 520

177 Sulfure d’hydrogéneHydrogen cyanide

H2S 1.19 4.00 45.6 57 650

178 4-Hydroxy-4-methylpenta-2-

one

CH3COCH2C(CH3)2OH 4.00 68 1.80 6.9 86 336

179 KéroséneKerosene

38 0.70 5.0

180 1.3.5-Trimethylbenzene (CHCCH2)CHC(CH2)CHC(CH3) 4.15 44 0.8 7.3 40 365





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181 MétaldéhyhdeMetaldehyde

(C2H4O)4 6.10 36

182 Methacryloyl chloride CH2CCH3=COCI 3.60 17 2.50 106

183 Méthane (grisou)Methane (firedamp)

CH4 0.55 4.40 17.0 29 113

184 Méthane (voir 4.6)Methane (see 4.6)

CH4 4.40 17.0 29 113

185 MéthanolMethanol

CH3OH 1.11 11 5.50 36.0 73 484

186 Methanethiol CH3SH 1.60 4.1 21.0 80 420

187 Méthoxyéthanol2-Methoxyethanol

CH3OCH2CH2OH 2.63 39 2.40 20.6 76 650

188 Acétate de méthyleMethyl acetate

CH3COOCH3 2.56 -10 3.20 16.0 99 475

189 Acétylacétate de méthyleMethyl acetoacetate

CH3COOCH2COCH3 4.00 62 1.30 14.2 82 685

190 Acrylate de méthyleMethyl acrylate

CH2=CHOOCH3 3.00 -3 2.40 25.0 85 903

191 MéthylamineMethylamine

CH3NH2 1.00 -18gaz/gas

4.20 20.7 55 270

192 Méthy butane2-Methylbutane

(CH3)2CHCH2CH3 2.50 <-51 1.30 8.0 38 242





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193 2-Methylbutane-2-ol CH3CH2C(OH)(CH3)2 3.03 18 1.40 10.2 50 374

194 2-Methaylbutane-1-ol (CH3)2CH(CH2)2OH 3.03 42 1.30 10.5 47 385

195 2-Methylbutane-2-ene (CH3)2C=CHCH3 2.40 -63 1.30 6.6 37 189

196 Methyl chloroformate CH3OOCC 3.30 10 7.5 26 293 1020

197 Méthyl cyclobutaneMethylcyclobutane

CH3CH2CH2CH2

198 Méthyl cyclohexaneMethalcyclohexane

CH3CH(CH2)4CH2 3.38 -4 1.15 6.7 47 275

199 Méthyl cyclohexaneMethylcyclohexanois

CH3C6H10OH 3.93 68

200 (isomers non mentionné)Methylcyclopentadienes(isomernot stated)

C6H8 2.76 <-18 1.30 7.6 43 249

201 Méthyln cyclopantaneMethylcyclopentane

CH3CH(CH2)2CH2 2.90 <-10 1.00 8.4 35 296

202 Méthyléne cyclobutane

Methylanecyclobutane

C(=CH2)CH2CH2CH2 2.35 <0 1.25 8.6 35 239

203 4-Methylenetetrahydropyran OCH2CH2C(=CH2)CH2CH2 3.78 2 1.50 60

204 2-Methy-1-butane-3-yne HC=CC(CH3)CH2 2.28 -54 1.40 38





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205 Formiate de méthyleMethyl formate

HCOOCH3 2.07 -20 5.00 23.0 125 580

206 2-Methylfuran OC(CH3)CHCHCH 2.83 <-15 1.40 9.7 47 325

207 2-Methythexe-3. 5-dien-2-ol CH2=CHC=CC(OH)(CH3)2 3.79 24

208 Methylisocyanate CH3NCO 1.96 -7 5.30 26.0 123 605

209 Méthacrylate de méthyleMethyl methacrylate

CH3=CCH3COOCH3 3.45 10 1.70 12.5 71 520

210 Methyl 2-methoxypropionate CH3CH(CH3O)COOCH3 4.06 48 1.20 58

211 4-Methylpantan-2-ol (CH3)2CHCH2CHOHCH3 3.50 37 1.14 5.5 47 235

212 4-Methylpantan-2-one (CH3)2CHCH2COCH3 3.45 16 1.20 8.0 50 336

213 2-Methylpent-2-enal CH3CH2CHC(CH3)COH 3.76 30 1.46 58

214 4-Methylpent-3-en-2-one (CH3)2(CCHCOCH)3 3.78 24 1.60 7.2 64 289

215 2-Methylpropan-1-ol (CH3)2CHCH2OH 2.55 28 1.70 9.8 52 305

216 2-Methylprop-l-ane (CH3)2C=CH2 1.93 gaz/gas 1.6 10 37 235





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217 2-Methylpyridine NCH(CH3)CHCHCHCH 3.21 27 1.20 45

218 3-Methylpyridine NCHCH(CH3)CHCHCH 3.21 43 1.40 8.1 53 308

219 4-methylpyridine NCHCHCH(CH3)CHCH 3.21 43 1.10 7.8 42 296

220 a-Styréne de méthylea-Methyl styrene

C6H5C(CH3)=CH2 4.08 40 0.90 6.6 44 330

221 Methyl tert-pentyl ether (CH3)2COCH3)CH2CH3 3.50 <-14 1.50 62

222 2-Methytlophane SC(CH3)CHCHCH 3.40 -1 1.30 6.5 52 261

223 2-Methylthlophane NC(CH3)CHCHC(CH2=CH)CH 4.10 61

224 MorpholineMorpholine

OCH2CH2NHCH2CH2 3.00 31 1.80 15.2 65 550

225 NaphtaNapphta

2.50 <-18 0.90 6.0

226 NaphtaléneNaphthalene

C10H8 4.42 77 0.90 6.0

227 NitrobenzéneNitrobenzene

CH3CH2N02 4.25 88 1.70 40.0 87 2067

228 NitroéthaneNitroethane

C2H5NO2 2.58 27 3.40 107





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229 NitrométhaneNitromethane

CH3NO2 2.11 36 7.30 63.0 187 1613

230 I-NitropropaneI-Nitropropane

CH3CH2CH2NO2 3.10 36 2.20 82

231 NonaneNonane

CH3(CH2)7CH2 4.43 30 0.70 5.6 37 301

232 2.2.3.3.4.4.5.5-Octafluono 1.1-dimethyloantan-l-ol

H(CF2CF2)2C(CH3)2OH 8.97 61

233 OctaidéhydeOctalehyde

CH3(CH2)6CHO 4.42 52

234 OctaneOctane

CH3(CH2)6CH3 3.93 13 0.80 6.5 38 311

235 l-Octanoll-Octanol

CH3(CH2)6CH2OH 4.50 81 0.9 7.4 49 385

236 (ensemble d’isomérs)Octane (mixed isomers)

C8H16 3.66 -18 1.10 6.9 50 270

237 ParaformaldéhydeParaformaldehyde

poly(CH20) 70 7.00 73.0

238 Penta-1.3-diene CH2=CH-CH=CH-CH3 2.34 <-31 1.2 9.4 35 261

239 Pentanes (ensemble d’isomérs)Pentanes (mixed isomers)

C5H12 2.48 -40 1.40 7.8 42 236

240 Pentant-2.4-dione CH3COCH2COCH3 3.50 34 1.70 71





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241 Pentan-l-ol CH3(CH2)2CH2OH 3.03 38 1.06 10.5 38 385

242 Pentanols (ensemble d’isomérs)Pentanols (mixed isomers)

C5H11OH 3.04 34 1.20 10.5 44 388

243 Pentan-3-one (CH3CH2)2CO 3.00 12 1.60 58

244 Pentyl acetate CH3COO-(CH2)4-CH3 4.48 25 1.00 7.1 55 387

245 PétrolePetroleum

2.8 <-20 1.2 8.0

246 PhénolPhenol

C6H5OH 3.24 75 1.3 9.5 50 370

247 Phenytacetylene C6H5C=CH 3.52 41

248 PropanePropane

CH3CH2CH3 1.56 -104 1.70 10.9 31 200

249 Propan-1-ol CH3CH2CH2OH 2.07 22 2.20 17.5 55 353

250 Propan-2-ol (CH2)2CHOH 2.07 12 2.00 12.7 50 320

251 Propane CH2=CHCH3 1.50 2.00 11.0 35 194

252 Propionic acid CH3CH2COOH 2.55 52 2.1 12.0 64 370





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253 Proplonic aldehyde C2H5CHO 2.00 <-26 2.00 47

254 Acétate de propylePropoyl acetate

CH3COOCH2CH2CH3 3.50 10 1.70 8.0 70 343

255 Iso Propyl acetate CH3COOCH(CH3)2 3.51 4 1.8 8.1 75 340

256 PropylaminePropylamine

CH3(CH2)2NH2 2.04 -37 2.00 10.4 49 258

257 Iso Propylamine (CH3)2CHNH2 2.03 <-24 2.30 8.6 55 208

258 Iso Propyl chloroacetate CICH2COOCH(CH3)2 4.71 42 1.60 89

259 Iso Propyl formate HCOOCH(CH3)2 3.03 <-8

260 2-iso Propyl-5-methylhex-2-enal

(CH3)2CH-C(CHO)CHCH2CH(CH3)2 5.31 41 3.05 192

261 Nitrate d’isopropyleIso Propyl nitrate

(CH3)2CHONO2 11 2.00 100.0 75 3738

262 Propyne CH3C=CH 1.38 1.70 16.8 28 280

263 Prop-2-yn-l-ol HC=CCH2OH 1.89 33 2.40 55

264 PyridinePyridine

C5H5N 2.73 17 1.70 12.0 56 398





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277 ToluéneToluene

C6H5CH3 3.20 4 1.1 7.8 42 300

278 1.1.3-Triethoxybutane (CH3CH2O)2CHCH2CH(CH3CH2O)CH3 6.56 33 0.78 5.8 60 451

279 TriéthylamineTriethylamine

(CH3CH2)3N 3.50 -7 1.20 8.0 51 339

280 1.1.1-Trifluorethane CF3CH3 290 680 17.6 234 605

281 2.2.2-Trifluoroethanol CF3CH2OH 345 30 8.4 28.8 350 119

282 Trifluoroethylene CF2=CFH 2.83 15.30 27.0 502 904

283 3.3.3-Trifluroprop-l-ane CF3CH=CH2 3.31 4.70 184

284 TriméthylamineTrimethylamine

(CH3)3N 2.04 2.00 12.0 50 297

285 4.4.5-Trimethyl-1.3-dioxane

OCH2OCH(CH3)C(CH3)2CH2 4.48 35

286 2.2.4-Trimethylpentane (CH3)2CHCH2C(CH3)3 309 -12 1.0 6.0 47 284

287 2.4.6-Trimethyl-1.3.5-trioxane

OCH(CH3)OCH(CH3)OCH(CH3) 4.56 27 1.30 72

288 1.3.5-Trioxane1.3.5-trioxane

OCH2OCH2OCH2 3.11 45 3.20 29.0 121 109





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289 TérébenthineTurpentine

35 0.80

290 Iso Valeraldehyde (CH3)2CHCH2CHO 2.97 -12 0.70 60

291 Acétate de vinyleVinyl acetate

CH3COOCH=CH2 3.00 -8 2.60 13.4 93 478

292 (isomére non mentionné)Vinyl cyclohexanenes (isomernot stated)

CH2CHC6H9 3.72 15 0.80 35

293 Vinlidene chloride CH2=CCI2 3.40 -18 7.30 15.0 2.94 645

294 2-Vinyloxyethanol CH2=CH-OCH2CH2OH 3.04 52

295 2-Vinylpyrine NC(CH2=CH)CHCHCHCH 3.62 35 1.20 51

296 4-Vinylpyridine NCHCHC(CH2=CH)CHCH 3.62 43 1.10 47

297 Gaz de l’eau 1.2

298 Xylénes

Xylenes

C6H4(CH3)2 3.66 30 1.00 7.6 44 336

299 Xylidenes C6H3(CH3)2NH2 4.17 96 1.00 7.0 50 355

Compex Manual July09

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Transcript of Compex Manual July09