CompEx-Atex course Manual 1210.pdf

ASET International Oil & Gas Training Academy

Comp Ex Hazardous Areas CourseMarch 2010 Revision

6th Edition, March 2010

Introduction

Ex Facility March 2010

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National Training and Certification of Personnel for Work on Electrical Apparatus for Use in Potentially Hazardous Atmospheres

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


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

a. Job Knowledge b. Competence Validation Testing (CVT)

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


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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.


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Course outline The training scheme The training scheme is arranged to prepare candidates for the assessment programme which comprises four discreet Competence Validation Tests (CVT’s) offered as complimentary pairs. The four CVT’s are as follows:

EX01 Preparation & Installation of Ex d, Ex e, Ex n and Ex p Systems EX02 Inspection & Maintenance of Ex d, Ex e, Ex n and Ex p Systems EX03 Preparation & Installation of Ex i Systems EX04 Inspection & Maintenance of Ex i Systems

Job knowledge The classroom (job knowledge) part of the training scheme consists of 12 Units which apply to the four CVT’s as illustrated below. Unit 1: General principles Unit 2: Standards,

Certification and Marking

Unit 3: Flameproof Ex d

EX01 & EX02 EX01 & EX02 EX01 & EX02 EX03 & EX04 EX03 & EX04

Unit 4: Increased Safety Ex e

Unit 5: Type ‘n’ protection

Unit 6: Pressurisation Ex p

EX01 & EX02 EX01 & EX02 EX01 & EX02 (Written Assessment) Unit 7: Intrinsic Safety Ex i Unit 8: Other methods of

protection Unit 9: Combined (Hybrid)

protection methods EX03 & EX04 (Written Assessment) EX01 & EX02

Unit 10: Wiring Systems Unit 11: Inspection &

Maintenance to BS EN60079-17

Unit 12: Sources of ignition

EX01 & EX02 EX01 & EX02 EX01 & EX02 EX03 & EX04 EX03 & EX04 EX03 & EX04

Unit 13: Induction to Competence Validation Testing

Unit 14: Permit to Work and Safe Isolation

EX01 & EX02 EX01 & EX02 EX03 & EX04 EX03 & EX04


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The CVT’s are a series of practical tests which you will undertake within the simulated work areas during the second half of the programme. On successful completion of these tests you will be awarded a Certificate of Core Competence which will indicate the areas the awarding body, Joint Training Ltd. (JTL), has deemed you are competent. During the final half-day of the programme you are required to sit written assessments in the form of multi-choice papers which are related to the practical CVT assessments. The staff who are involved in monitoring the various assessments are present only as observers and not to prompt or offer technical assistance. Their observations of your work is recorded on Nationally written checklists which are processed outwith the Centre and your results cannot be determined until this process is complete. Manual Units and applicable CVT’s

Unit 1: General Principles EX01, EX02, EX03 & EX04

Unit 2 : Standards, Certification & Marking EX01, EX02, EX03 & EX04

Unit 3: Flameproof Ex d EX01 & EX02

Unit 4: Increased Safety Ex e EX01 & EX02

Unit 5: Type ‘n’ Protection EX01 & EX02

Unit 6: Pressurisation Ex p EX01 & EX02 (Written Assessment)

Unit 7: Intrinsic Safety E x i EX03 & EX04

Unit 8: Other methods of Protection (Written Assessment)

Unit 9: Combined (Hybrid) Protection Methods EX01 & EX02

Unit 10: Wiring Systems EX01, EX02, EX03 & EX04

Unit 11: Inspection & Maintenance to BS EN60079-17 EX01, EX02, EX03 & EX04

Unit 12: Sources of Ignition EX01, EX02. EX03 & Ex04

Unit 13: Induction to Competence Validation Testing EX01, EX02. EX03 & Ex04

Unit 14: Permit to Work EX01, EX02. EX03 & Ex04

Course programme The following course programme is for illustration purposes only, particularly for the CVT assessments, and can change according to candidate numbers attending the course. A programme for the CVT assessments will be compiled during the week.

Ex Facility November 2008

7

Programme: Electrical Apparatus in Potentially Hazardous Areas 5 – Day Programme

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8:30

12:30

Course registration and induction

Unit 1: General Principles

Unit 10: Wiring systems & Demonstration of compound filled gland and diaphragm seal gland assembly

Unit 2: Standards: certification & marking

Unit 4: Increased Safety Ex e

Unit 5: Type ‘n’ Protection

Unit 6: Pressurisation Ex p

Unit 7: Intrinsic Safety E x i EX01 CVT Inspection & Maintenance of d, e & n apparatus

Candidates 7-12

EX02 CVT Preparation &Installationof d, e & n apparatus

Candidates 1-6

EX03 CVT Inspection & Maintenance of d, e & n apparatus

Candidates 7-12


Candidates 1-6

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17:00

Unit 3: Flameproof Ex d

Unit 10: Practical exercise: Assembly of compound filled and diaphragm seal type glands.

Unit 8: Other methods of protection

Unit 9: Combined (Hybrid) methods of protection

Unit 11: Inspection & Maintenance

Unit 13: Introduction to CVT’s

Unit 14: Work permit


Candidates 1-6


Candidates 7-12


Candidates 1-6


Candidates 7-12

Job Knowledge assessment

EX01, EX02, EX03 & EX04 Multi-choice examination

Unit 1:

General Principles

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Objectives: On completion of this unit, ‘General Principles’, you should know:

a. The nature of flammable materials with regard to ‘explosive limits’ (LEL/UEL), ‘flashpoint’, ‘ignition’ temperature’, the effect of ‘oxygen enrichment’ and ‘relative density’.

b. The basic principles of area classification. c. The Grouping of gases according to ‘minimum ignition energy’ (MIE) and ‘maximum

experimental safe gap’ (MESG). d. Appropriate T-ratings for apparatus relative to the ignition temperature of a given

flammable material. e. The levels of ‘ingress protection’.

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General Principles Nature of Flammable Materials Fire Triangle The fire triangle represents the three elements which must be present before combustion can take place. Each point of the triangle represents one of the essential elements which are:

1. Fuel: This can be in the form of a gas, vapour, mist or dust 2. Oxygen: Plentiful supply since there is approximately 21% by volume in air. 3. Source of Ignition: This can be an arc, spark, naked flame or hot surface.

Combustion will take place if all three elements, in one form or another, are present, the gas/air mixture is within certain limits and the source of ignition has sufficient energy. The removal of one element is sufficient to prevent combustion, as is the isolation or separation of the source of ignition from the gas/air mixture. These are two techniques used in explosion protected equipment. Other protection techniques allow the three elements to co-exist and either ensures that the energy of the source of ignition is maintained below specific values, or allows an explosion to take place and contains it within a robust enclosure. These techniques are addressed in the various sections of this manual.

Gas or vapour

Oxygen ( 21% in air )

Source of ignition

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Flammable (Explosive) Limits Combustion will only occur if the flammable mixture comprising fuel, in the form of a gas or vapour, and air are within certain limits. These limits are the ‘lower explosive limit’ (LEL), and the ‘upper explosive limit’ (UEL), and between these limits is known as the flammable range. An every day example of this is the carburettor of a petrol engine, which must be tuned to a particular point between these limits in order that the engine may function efficiently.

Lower Explosive Limit: When the percentage of gas, by volume, is below this limit the

mixture is too weak to burn, i.e. insufficient fuel and/or too much air.

Upper Explosive Limit: When the percentage of gas, by volume, is above this limit the

mixture is too rich to burn, i.e. insufficient air and/or too much fuel.

The flammable limits of some materials are given below.

Material

LEL

% by Volume

UEL

% by Volume

Propane 1.7 10.9

Methane 4.4 17

Ethylene 2.3 36

Hydrogen 4 77

Acetylene 2.3 100

Diethyl Ether 1.7 36

Kerosene 0.7 5

Carbon Disulphide 0.6 60

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Flammable (Explosive) Limits (continued) Different gases or vapours have different flammable limits and the greater the difference between the LEL and the UEL, known as the flammable range, the more dangerous the material. An explosive (flammable) atmosphere, therefore, only exists between these limits. Operational safety with flammable mixtures above the UEL is possible, but is not a practical proposition. It is more practical to operate below the LEL. Sources of Ignition Sources of ignition are many and varied and include:

a. Electrical arc/sparks b. Frictional sparks c. Hot surfaces d. Welding activities e. Cigarettes f. Static discharges g. Batteries h. Exhausts of combustion engines i. Thermite action j. Sodium exposed to water k. Pyrophoric reaction l. Chemical reactions m. Lightning strikes

The source of ignition as far as this text is concerned is primarily electrical equipment.

March 2010 ©6

Flashpoint By definition flashpoint is: ‘the lowest temperature at which sufficient vapour is given off a liquid, to form a flammable mixture with air that can be ignited by an arc, spark or naked flame’. Typical values are given below.

Material

Flashpoint

°C

Propane -104 Ethylene -120* Hydrogen -256* Acetylene -82* Diethyl Ether -45 Kerosene 38 Carbon Disulphide -95*

* Values obtained form a source other than PD IEC60079-20 The flashpoint of a material gives an indication of how readily that material will ignite in normal ambient temperatures. Reference to the tables of flammable materials from PD IEC60079-20 (see Appendix 1) reveals that different materials have different flashpoints, which vary from well below to well above 0°C. Materials with high flashpoints should not be overlooked as a potential hazard since exposure to hot surfaces can allow a flammable mixture to form locally. Furthermore, if a flammable material is discharged under pressure from a jet, its flashpoint may be reduced.

Amount of vapour released dependent on temperature

March 2010 ©7

Flashpoint (continued)

Kerosene: Flashpoint 38°C

At 38°C “Ignition”

At 37°C Insufficient vapour given off

At 0°C Negligible vapour given off

March 2010 ©8

Ignition Temperature Ignition temperature is defined as: ‘the minimum temperature at which a flammable material will spontaneously ignite’. Ignition temperature, formerly known as auto-ignition temperature, is an important parameter since many industrial processes generate heat. Careful selection of electrical equipment will ensure that the surface temperature produced by the equipment, indicated by the T-rating, will not exceed the ignition temperature of the flammable atmosphere which may be present around the equipment. Typical values of ignition temperature are:

Material

Ignition Temperature

°C

Propane 470 Methane 537 Ethylene 425 Hydrogen 560 Acetylene 305 Diethyl Ether 160 Kerosene 210 Carbon Disulphide 95

March 2010 ©9

Oxygen Enrichment The normal oxygen content in the atmosphere is around 20.95%, and if a given location has a value which exceeds this it is deemed to be oxygen enriched. Typical examples of where oxygen enrichment may occur are gas manufacturing plants, hospital operating theatres, and where oxy-acetylene equipment is used. Oxygen enrichment has three distinct disadvantages. First of all, it can lower the ignition temperature of flammable materials as shown in the table below.

Air

Increased Oxygen

Material

Ignition Temperature °C

Ignition Temperature °C

Hydrogen sulphide 260 220

Acetylene 305 296

Ethane 512 506 Secondly, oxygen enrichment significantly raises the upper explosive limit (UEL) of the majority of gases and vapours, thereby widening their flammable range. This is illustrated in the following table.

Air

Increased Oxygen

Material

LEL %

UEL %

LEL %

UEL %

Methane 5 15 5.2 79

Propane 2.2 9.5 2.3 55

Hydrogen 4 75 4.7 94

Thirdly, oxygen enrichment of a flammable atmosphere can allow it to be ignited with much lower values of electrical energy. Explosion protected equipment will have been tested in normal atmospheric conditions and, therefore, the safety of such equipment in an oxygen enriched atmosphere cannot be assured because of the modified nature of the flammable mixture.

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

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

March 2010 ©10

Density If a flammable material is released, it is important to know whether the material will rise or fall in the atmosphere. The different flammable materials are compared with air and allocated a number to denote their relative density with air. Since air is the reference, its relative density is 1 so that for a material twice as heavy as air, its relative density will be 2. Therefore, materials with a relative density less than unity will rise in the atmosphere, and those greater than unity will fall in the atmosphere. Materials which rise in the atmosphere can collect in roof spaces, and those which fall, such as butane or propane, can drift along at ground level and possibly into a non-hazardous location, or may collect in locations lower than ground level without ever dispersing. Such locations should be well ventilated in order to avoid ignition due to a stray spark or a discarded cigarette. Knowledge of where a flammable material will collect ensures that gas detectors when fitted will be located at the correct level and ventilation is directed accordingly.

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Material Relative vapour density

Air 1 Propane 1.56 Methane 0.55 Ethylene 0.97 Hydrogen 0.07 Acetylene 0.9 Diethyl Ether 2.55 Kerosene 4.5* Carbon

Disulphide 2.64

* Value obtained from a source other than PD IEC60079-20

March 2010 ©11

Area Classification An hazardous area is defined as: ‘An area in which an explosive gas atmosphere is present, or may be expected to be present, in quantities such as to require special precautions for the construction, installation and use of apparatus.’ A non-hazardous area is defined as: ‘An area in which an explosive gas atmosphere is not expected to be present in quantities such as to require special precautions for the construction, installation and use of apparatus.’ Zones Zoning is a means of representing the frequency of the occurrence and duration of an explosive gas atmosphere based on the identification and consideration of each and every source of release in the given areas of an installation. Zoning will have a bearing on, and simplify the selection of, the type of explosion protected equipment which may be used. Hazardous areas are, therefore, divided into three Zones which represent this risk in terms of the probability, frequency and duration of a release. The three Zones, as defined in BS EN60079-10-1: Electrical apparatus for explosive gas atmospheres, Part 10. Classification of hazardous areas, are as follows: Zone 0 - An area in which an explosive gas atmosphere is present continuously

or for long periods or frequently. Zone 1 - An area in which an explosive gas atmosphere is likely to occur in

normal operation occasionally. Zone 2 - An area in which an explosive gas atmosphere is not likely to occur in

normal operation but, if it does occur, will persist for a short period only.

Although not specified in IEC 60079-10-1, but quoted in API RP 505**, the duration of a gas release, or a number of gas releases, on an annual basis (one year comprises circa 8760 hours), for the different Zones is as follows.

Zone 2 - 0 – 10 hours

Zone 1 - 10 – 1000 hours

Zone 0 - over 1000 hours ** The above document, API RP 505, is published by the American Petroleum Institute and

entitled “Recommended Practice for Classification of Locations for Electrical Installations at Petroleum Facilities Classified as Class I, Zone 0, Zone 1, and Zone 2.

March 2010 ©12

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

March 2010 ©13

Area Classification (continued) Fixed Roof Storage Tank Distances: ‘a’ 3m from vent opening

‘b’ 3m above the roof

‘c’ 3m horizontally from the side of the tank

b

c a

Zone 2

Zone 1

Zone 0

Sump: Zone 1

March 2010 ©14

Area Classification (continued) Sources of Release

Welded pipe joint: ( Non-hazardous )

Flanged joint: ( Zone 2)

Pump gland: ( Zone 2 or Zone 1 depending on the quality of the seal )

Space above liquid in a closed tank: ( Zone 0)

March 2010 ©15

Gas / Apparatus Grouping In the IEC system, the group allocation for surface and underground (mining) industries are separate. Group I is reserved for the mining industry, and Group II which is subdivided into IIC, IIB and IIA for surface industries. The representative gases for the sub-groups are shown in the table below. Two methods have been used to ‘group’ these flammable materials according to the degree of risk they represent when ignited. One method involved determining the minimum ignition energy which would ignite the representative gases. The values obtained are relevant to Intrinsically Safe apparatus. In the table below it can be seen that for Group II, hydrogen and acetylene are the most easily ignited and propane the least easily ignited. The other method involved tests using, for example, a special flameproof enclosure in the form of an 8 litre sphere which was situated inside a gas-tight enclosure. Both halves of the sphere had 25mm flanges and a mechanism enabled the gap dimension between the flanges to be varied. During tests, the area inside and outside the sphere were occupied with a gas in its most explosive concentration in air and, by means of a spark-plug the gas inside the sphere was ignited. The maximum dimension between the flanges, which prevented ignition of the gas/air mixture, is known as the ‘maximum experimental safe gap’ (MESG), and the values for the representative gases are shown in the table below. The more dangerous a gas, the tighter the gap at the flanges has to be. It is important to note that the MESG values are not used for the design of Flameproof apparatus, only the maximum working gaps. The table also shows that these flammable materials fall into the same order for both tests, i.e. in a relative context, hydrogen and acetylene present the most risk and propane the least risk in terms of ‘minimum ignition energy’ and ‘MESG’.

Gas Group

Representative

Gas

MESG (mm)

Maximum Working

Gap (mm)

Minimum Ignition Energy

(μJ)

I Methane (Firedamp) 1.14 0.5 260

IIA Propane 0.91 0.4 160

IIB Ethylene 0.65 0.2 95

Hydrogen 0.28 IIC

Acetylene 0.37

0.1

20

Note: Apparatus other than flameproof or intrinsic safety, which has no sub-division letter (A, B or C) after the group II mark, may be used in all hazards. Apparatus marked IIxxxxx: xxxxx represents the chemical formula or name of a

flammable material, and apparatus marked in this way may only be used in that hazard.

March 2010 ©16

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

March 2010 ©17

Gas / Apparatus Grouping (continued) Comparison of BS 229 and IEC BS 229 is an old British Standard, which has now been withdrawn, but electrical apparatus was still manufactured to this standard up until several years ago. Apparatus manufactured to BS 229 has sub-group markings which are different to those of the IEC system and the comparison is shown in the table below. The introduction of the ATEX Directives after 30 June 2003 has caused manufacturers to discontinue the production of apparatus to this standard, but apparatus already in use will be unaffected.

BS 229 Representative Gas IEC

1 Methane I

2 Propane IIA

3a Ethylene

3b Coal Gas

IIB

4 Hydrogen & Acetylene IIC

March 2010 ©18

Temperature Classification Approved electrical equipment must be selected with due regard to the ignition temperature of the flammable gas or vapour which may be present in the hazardous location. Apparatus will usually be marked with one of the temperature classes shown in the table below. The temperature class indicates the maximum temperature the surfaces of an enclosure, which are exposed to a flammable gas, must not exceed during normal or specified fault conditions. Temperature Classes

T - Class Maximum Surface Temperature

T1 450°C

T2 300°C

T3 200°C

T4 135°C

T5 100°C

T6 85°C

In the table below, it will be observed that for each material, the T-rating temperature is below the ignition temperature of the flammable material. Moreover, the T-rating temperatures are based on a maximum ambient rating of 40°C as far as the UK is concerned. For example, apparatus classified T5, based on a 40°C ambient rating, will have a maximum permitted temperature rise of 60°C. In order to avoid infringement of the apparatus certification, the ambient rating must be compatible with environmental ambient temperatures, and the temperature rise not exceeded. This is demonstrated on page 20. A further consideration is apparatus for use in hotter climates, typically found in Middle and Far Eastern countries, which will usually require ambient ratings greater than 40°C. Apparatus for use in colder (arctic) climates will require a much lower limit to the ambient temperature range which may be as low as -50°C.

Material Ignition Temperature T-Rating

Methane 537°C T1 (450°C)

Ethylene 425°C T2 (300°C)

Cyclohexane 259°C T3 (200°C)

Diethyl Ether 160°C T4 (135°C)

T5 (100°C)

Carbon Disulphide 95°C T6 (85°C)

March 2010 ©19

Temperature Classification (continued)

-2

-2

March 2010 ©20

Ingress Protection Enclosures of electrical equipment are classified according to their ability to resist the ingress of solid objects and water by means of a system of numbers known as the ‘International Protection (IP) Code’. This code, which is not always marked on apparatus, consists of the letters IP followed by two numbers, e.g. IP56. The first number, in the range 0-6, indicates the degree of protection against solid objects, and the higher the number the smaller the solid object that is prevented from entering the enclosure. Zero (0) indicates no protection and 6 indicate the apparatus is dust-tight. The second number, ranging from 0-8, identifies the level of protection against water entering the enclosure, i.e. 0 indicates than no protection is afforded, and 8 that the apparatus can withstand continuous immersion in water at a specified pressure. An abridged version of the full table is shown below.

Solid Objects Water

First Numeral Level of Protection Second

Numeral Level of Protection

0 No protection 0 No protection

1 Protection against objects greater than 50 mm 1 Protection against drops of water

falling vertically

2 Protection against objects greater than 12 mm 2 Protection against drops of water

when tilted up to 15°

3 Protection against objects greater than 2.5 mm 3 Protection against sprayed water

up to 60°

4 Protection against objects greater than 1.0 mm 4 Protection against splashed water

from any direction

5 Dust-protected 5 Protection against jets of water from any direction

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

7 Protection against immersion in water 1m in depth and for a specified time

8 Protection against indefinite immersion in water at a specified depth

Unit 2:

Standards, Certification and Marking

March 2010 © 2

Objectives: On completion of this unit, ‘Standards, Certification and Marking’, you should know:

a. Current British, European and International Standards and also relevant older British Standards and Codes of Practice.

b. The certification process for explosion protected apparatus.

c. The methods of marking explosion protected apparatus.

d. The basic requirements of the ATEX Directives.

e. The correlation between the ATEX categories and Equipment Protection Levels (EPL’s)

March 2010 © 3

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

March 2010 © 4

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

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

A

Internal control of production

Covers internal design and production control. Does not require the involvement of a notified body.

B

EC type-examination

Covers the design phase, the EC type-examination being issued by a notified body. Has to be followed by a module for assessment during the production phase.

C

Conformity to type

Covers the production phase after module B. This module confirms conformity of the product with that described in the EC examination certificate as issued during module B.

D

Production quality assurance

Covers the production phase following module B. Production quality assurance is based on the standard EN ISO 9002 and the involvement of a notified body who has responsibility for the approval and control of the quality system regarding production, end product inspection and testing implemented by the manufacturer.

E

Product quality assurance

Covers the production phase following module B. Production quality assurance is based on the standard EN ISO 9003 and the involvement of a notified body who has responsibility for the approval and control of the quality system regarding end product inspection and testing implemented by the manufacturer.

F

Product verification

Covers the production phase following module B. The EC type examination carried out by the notified body, to ensure conformity to type in module B, is followed by the issue of a certificate of conformity.

G

Unit verification

Covers the design and production phases. A certificate of conformity is issued after examination of every product by the notified body.

H

Full quality assurance

Covers the design and production phases. Quality assurance is based on the standard EN ISO 9003 and the involvement of a notified body who has responsibility for the approval and control of the quality system for design, manufacture, final product inspection and testing implemented by the manufacturer.

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CE Conformity Assessment Modules (continued) The illustration below shows how the modules listed on the previous page may be implemented to obtain the CE marking for apparatus.

ATEX 95 The ATEX Directive 94/9/EC ( ATEX 95 ) was adopted by the EC to enable free trade of products between member states through alignment of technical and legal requirements and concerns the design of explosion protected equipment. The directive applies not only to electrical equipment but also to mechanical equipment and protective systems used in the presence of potentially explosive atmospheres containing gases/vapours or combustible dusts. Equipment is defined as any item which is inherently ignition capable or is potentially ignition capable and requiring the inclusion of special design and installation techniques to prevent ignition of any surrounding flammable atmosphere which may be present. The ‘equipment’ may also be interfaces located in the non-hazardous area which are part of an explosion protection system. Protective systems include quenching systems, flame arrestors, fast-acting shut-off valves and pressure relief panels installed to limit damage due to an explosion or prevent the spread of explosions.

Design phase Production phase

Module A

Module C

Module D

Module E

Module F

Module G

Module BManufacturer

Module H

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ATEX 137 The ATEX Directive 99/92/EC ( ATEX 137 ), commonly known as the ‘use’ directive, is implemented in the UK via the Dangerous Substances and Explosives Atmosphere Regulations 2002 (DSEARs). Employers are obliged to implement the following minimum requirements in the workplace with regard to DSEARs.

a. Carry out a risk assessment where dangerous substances are or may be present. b. Eliminate or reduce risk as far as is reasonably practicable. c. Classify locations in the workplace where explosive atmospheres may be present

into hazardous or non-hazardous areas. d. Have in place procedures/facilities to deal with accidents, incidents and emergencies

involving dangerous substances in the workplace. e. Provide appropriate information and training of employees for their safety regarding

precautions to be taken when dangerous substances are present in the workplace, written instruction for tasks undertaken by employees and operation of a permit-to-work system.

f. Clearly identify the contents of containers and pipes. g. Co-ordinate operations where two or more employees share a workplace in which a

dangerous substance may be present. h. Posting of warning signs for locations where explosive atmospheres may occur. i. Selection of equipment in accordance with ATEX 95 and establishment of a

maintenance programme. Marking of Hazardous Areas Article 7 in the Directive ATEX 137 states:

‘Where necessary, places where explosive atmospheres may occur in such quantities as to endanger the health and safety of workers shall be marked with signs at their points of entry in accordance with Annex III.’

Annex III of the directive specifies the exact requirements for the sign but generally it is required to be triangular with a yellow background, black border and marked ‘Ex’.

Ex

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European Notified Bodies The illustration below shows some of the Notified Bodies along with their unique Notified Body (NB) number. There are around sixty Notified bodies in the EU at the time of writing.

Finland: VTT Industrial Systems (0537)

Sweden: SP-Swedish National Testing (402)

Norway: NEMKO AS (0470) DNV AS (0575)

Denmark: UL Int DEMKO A/S (0539)

UK: Baseefa (1180)

SIRA (0518) BSI Product Services (0086) ITS Testing & Cert. Ltd (0359) Lloyd’s Reg Ver Ltd (0038)

Netherlands: KEMA (0344)

Belgium: ISSeP (0539)

France: LCIE (0081) INERIS (0080)

Spain: LOM (0163)

Italy: CESI (0722)

Germany: PTB (0102)

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

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10

Comparison of IEC, European (CENELEC) and British Standards

CENELEC Euronorm

(EN) Number

International Standards

British Standard

(BS) Number

Revised Standard (BS EN) Number

Latest Revised

Standard (BS EN) Number

Type of Protection

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

EN 50 015 IEC 60079-6 BS 5501: Pt. 2 BS EN50 015 BS EN60079-6 Oil Immersion ‘o’

EN 50 016 IEC 60079-2 BS 5501: Pt. 3 BS EN50 016 BS EN60079-2 Pressurised Apparatus ‘p’

EN 50 017 IEC 60079-5 BS 5501: Pt. 4 BS EN50 017 BS EN60079-5 Power Filling ‘q’

EN 50 018 IEC 60079-1 BS 5501: Pt. 5 BS EN50 018 BS EN60079-1 Flameproof Enclosure ‘d’

EN 50 019 IEC 60079-7 BS 5501: Pt. 6 BS EN50 019 BS EN60079-7 Increased Safety ’e’

EN 50 020 IEC 60079-11 BS 5501: Pt. 7 BS EN50 020 BS EN60079-11 Intrinsic Safety ‘i’

EN 50 028 IEC 60079-18 BS 5501: Pt. 8 BS EN50 028 BS EN60079-18 Encapsulation ‘m’

EN 50 039 IEC 60079-25 BS 5501: Pt. 9 BS EN50 039 BS EN60079-25 Intrinsic Safety Systems ‘i’

EN 50 021 IEC 60079-15 BS EN50 021 BS EN60079-15 Type of Protection ‘n’

IEC 60079-26

BS EN60079-26 Equipment with Equipment Protection Level Ga

IEC 60079-27 BS EN60079-27 Fieldbus intrinsically safe concept (FISCO)

IEC 60079-29-2 BS EN60079-29-2 Gas detector selection, installation, use and maintenance

IEC 60079-30-1 BS EN60079-30-1 Electrical resistance trace heating – General & testing requirements

IEC 60079-30-2 BS EN60079-30-2 Electrical resistance trace heating – Application guide

March 2010 11

Other (older) British Standards The standards listed below are those which preceded the harmonised European standards listed in the previous table. These standards, with the exception of BS 889, were not entirely obsolete, and older designs of equipment were still manufactured to these standards and available on the market prior to 30 June 2003, the date after which implementation of the ATEX Directives became mandatory. Apparatus manufactured to these standards, where still in use, must be maintained in accordance with these standards. It is, therefore, important that reference to the correct standard is made before maintenance is carried out on such apparatus.

BS 229 Flameproof enclosure of electrical apparatus

BS 889 Flameproof electric fittings

BS 1259 Intrinsically safe electric apparatus and circuits for use in explosive atmospheres

BS 4683: Part 1 Classification of maximum surface temperature

BS 4683: Part 2

The construction and testing of flameproof enclosures of electrical apparatus

BS 4683: Part 3 Type of protection ‘N’

BS 4683: Part 4 Type of protection ‘e’

BS 6941 Type of Protection ‘N’

BS 5000: Part 15 Machines with type of protections ‘e’

BS 5000: Part 16 Type ‘N’ electric motors

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Standards for Selection, Installation, Inspection and Maintenance As previously stated, the UK Code of Practice BS 5345, which had for many years provided recommendations for the selection, installation and maintenance of explosion protected equipment for use in potentially explosive atmospheres (other than mining applications or explosives processing and manufacture), listed in the upper table below, was superseded by the standards listed in the lower table. BS 5345, however, may be referred to for installations installed in accordance with its requirements. The table below illustrates the component parts of BS 5345.

UK Code of Practice Type of Protection BS 5345: Part 1 General Recommendations BS 5345: Part 2 Classification of Hazardous Areas BS 5345: Part 3 ‘d’ Flameproof enclosure BS 5345: Part 4 ‘i’ Intrinsically safe apparatus and systems

BS 5345: Part 5 ‘p’ Pressurisation, continuous dilution and pressurised rooms

BS 5345: Part 6 ‘e’ Increased safety BS 5345: Part 7 ‘N’ (Non - incendive) BS 5345: Part 8 ‘s’ Special protection

BS 5345: Part 9 ‘o’ Oil immersion ‘q’ Powder filling

The standards which supersede the Code of Practice BS 5345 are illustrated in the table below. Furthermore, the BS EN standards are identical to the IEC standards shown within brackets in the table below apart from a few informative annexes.

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

BS EN60079-10: 2009 (IEC 60079-10-1: 2008) Part 10: Classification of hazardous areas

BS EN60079-14: 2008 (IEC 60079-14: 2007)

Part 14: Electrical installations in hazardous areas (other than mines)

BS EN60079-17: 2007 (IEC 60079-17: 2007)

Part 17: Inspection and maintenance of electrical installations in hazardous areas (other than mines)

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

Part 19: Repair and overhaul for apparatus used in explosive atmospheres (other than mines or explosives)

BS EN60079-20-1: 2010 (IEC 60079-20-1: 2010)

Material characteristics for gas and vapour classification – Test methods and data

March 2010 © 13

Certification body symbols

1)

Equipment marked with this symbol may only be used for underground (mining) applications in the UK.

2)

Equipment marked with this symbol has been constructed to the old British Standard BS229

3)

Symbol formerly used by EECS (BASEEFA) to identify equipment for surface industry use only.

4)

Equipment marked with this symbol, the European Ex mark, indicates that the equipment has been constructed and tested in accordance with the CENELEC/ EURONORM standards. This mark only will be used on ATEX compliant equipment.

5)

Symbol formerly used by the German notified body PTB

6)

The most commonly used symbol of the American certification authority Underwriters Laboratories (UL)

7)

The mark used by the Canadian Standards Association

MEx

March 2010 © 14

Equipment Marking Prior to the introduction of the ATEX Directives on 1 July 2003, equipment for use in hazardous areas were marked as illustrated below. Equipment complying with the ATEX Directives, however, will still be marked in this way but will have additional markings to indicate that the apparatus conforms with the ATEX Directives. The ATEX markings are shown on page 18. Equipment approved/certified as providing a method of protection for use in hazardous locations is required to display the following markings.

a. The symbols Ex, and b. The type of protection used, e.g. ‘d’, ‘e’, ‘N’, and c. The gas group, e.g. IIA, IIB or IIC, and d. The T-rating, e.g. T1, T2 etc. e. The ambient rating, e.g. -200C to +400C (normal range for UK but may not be marked

on equipment.)

Note: For higher ambient ratings the marking may be either Tamb +500C, or

-200C < Tamb < +500C Examples:

(i) Ex d IIB T3 (ii) EEx d IIC T4

(iii) EEx e II T6 In example (i), equipment marked thus (Ex), as far as Europe was concerned, could only be used in the UK because it had been constructed to the British Standard BS 4683, which was not a harmonised European standard. Equipment constructed to this standard, however, was used in other countries out-with the European Community. Such equipment would also be marked with the EECS certification authority symbol (fig 3) on the previous page. Equipment certified in accordance with the IEC Ex scheme will be marked Ex. See page 20 onwards for details of this scheme. For equipment marked EEx as in example ii. and iii., the additional letter ‘E’ indicates that the equipment has been constructed to a harmonised European standard. Such equipment would be marked with the EECS certification authority symbol (fig 3) as well as the European Community mark (fig 4). Sample labels are shown below, and it should be noted that the construction standard to which the equipment has been manufactured to, i.e. BS 4683: Part 2, BS 5501: Parts 1 & 5 and EN50 014 & EN50 018 are also given on the labels. For BS 4683 equipment, the IEC equivalent standard, i.e. IEC 79-1 in example (a) below, is usually included.

(a) (b)

March 2010 © 15

Equipment marking (continued) The certification labels attached to explosion protected equipment will display markings to enable their correct selection for use in hazardous areas. For example, equipment manufactured to the old UK standard BS4683 and the subsequent CENELEC EN500 series of harmonised standards will be marked Ex and EEx respectively. However, with the CENELEC and IEC standards becoming technically identical, i.e. the EN60079 standards are identical to the IEC60079 standards, the marking has reverted to Ex. The illustration below shows the marking on equipment constructed to the harmonised standard BS EN50018.

Equipment manufactured to the latest standards, the BS EN60079 series, will be marked as follows along with the ATEX markings shown on page 17. The main differences are the removal of the letter ‘E’ compared to the illustration above and the introduction of the EPL ‘Gb’. EPL’s are explained on pages 18 to 21.

Ex d IIC T6 Gb

March 2010 © 16

Certification Numbers The certification number illustrated below was used by BASEEFA prior to the introduction of the ATEX directives, but the numbers used by other certification authorities will be different.

Components typically displaying a suffix ‘U’ include Ex e terminals, Ex d stoppers for flamepoof enclosures, and small volume plastic flameproof switches which have exposed terminals. ATEX compliant equipment will have standardised certification numbers which will include the abbreviation of the notified body’s name followed by the year of certification, the acronym ATEX, the serial number and either of the suffix’s ‘X’ or ‘U’ where applicable, as shown below.

BAS 08 ATEX 1234 X

March 2010 © 17

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

The Equipment Categories are defined overleaf

0000

CE Mark

Notified body ID number

EU Explosive Atmosphere Symbol

March 2010 © 18

Category (Cat) Definitions The ATEX Categories were introduced to ‘break’ the traditional link between the protection types and zones, i.e. the selection of equipment suitable for the zone. This approach enables, for example, Cat 3 equipment, typically Ex n, to be used in zone 1 if a risk assessment revealed that the consequences of ignition of a flammable atmosphere was low. The Categories below, however, show the traditional link with the zones. Conversely, if the consequences of ignition were greater then a better Category of protection may be required. Group II Cat 1: Very high level of protection

Equipment with this category of protection may be used where an explosive atmosphere is present continuously or for long periods, i.e. Zone 0 or Zone 20.

Cat 2: High level of protection Equipment with this category of protection may be used where an explosive atmosphere is likely to occur in normal operation, i.e. Zone 1 or Zone 21.

Cat 3: Normal level of protection Equipment with this category of protection may be used where an explosive atmosphere is unlikely to occur or be short duration, i.e. Zone 2 or Zone 22.

Group I Cat M1: Very high level of protection Equipment can be operated in the presence of an explosive atmosphere.

Cat M2: High level of protection Equipment to be de-energised in the presence of an explosive atmosphere.

Note: Zones 20, 21 and 22 are the corresponding zones for combustible dusts.

Equipment protection levels (EPL’s) The introduction of Equipment Protection Levels (EPL’s), which are used internationally, enables a risk assessment approach to be implemented for the selection of explosion protected equipment in hazardous areas. This provides an alternative to the traditional method of selecting equipment to suit the zone, which does not take into consideration the consequences of an explosion. The table below shows the zones where both ATEX Categories and EPL’s may be used from a traditional selection approach. Selection of equipment according to the EPL will in future be according to the EPL’s specified for the zones in area classification diagrams so that where the consequences of an explosion are likely to be greater, a higher EPL will be specified. Alternatively, if the consequences of an explosion are lower, a lesser EPL may be specified.

Zone ATEX Categories EPL’s

0 1 Ga 1 2 Gb 2 3 Gc

March 2010 © 19

Equipment protection levels (EPL’s) Equipment Protection Levels (EPL’s) are available for both gases and vapours and also combustible dusts as illustrated in the table below. Equipment marked ‘G’ is for use in flammable gases and vapours, and for use in combustible dusts when marked ‘D’.

Zone Equipment protection levels ( EPL’s )

0 Ga

1 Ga or Gb

2 Ga, Gb or Gc

20 Da

21 Da or Db

22 Da, Db or Dc

EPL Definitions Group II gases Ga Equipment for explosive gas atmospheres, having a ‘very high’ level of protection,

which is not a source of ignition in normal operation, expected faults, or when subject to rare faults.

Gb Equipment for explosive gas atmospheres, having a ‘high’ level of protection, which

is not a source of ignition in normal operation, or when subject to faults that may be expected, though not necessarily on a regular basis.

Gc Equipment for explosive gas atmospheres, having an ‘enhanced’ level of protection,

which is not a source of ignition in normal operation and which may have some additional protection to ensure that it remains inactive as an ignition source in the case of regular expected occurrences, for example, failure of a lamp.

Group III Dusts Da Equipment for combustible dust atmospheres, having a ‘very high’ level of protection,

which is not a source of ignition in normal operation, or when subject to rare faults. Db Equipment for combustible dust atmospheres, having a ‘high’ level of protection,

which is not a source of ignition in normal operation, or when subject to faults that may be expected, though not necessarily on a regular basis.

Dc Equipment for combustible dust atmospheres, having an ‘enhanced’ level of

protection, which is not a source of ignition in normal operation and which may have some additional protection to ensure that it remains inactive as an ignition source in the case of regular expected occurrences.

March 2010 © 20

EPL’s assigned to protection types (gases) EPL Ga

EPL Protection type Marking

Intrinsic Safety Ex ia Ga

Encapsulation Ex ma

EPL Gb


Flameproof Ex d

Increased Safety Ex e

Intrinsic Safety Ex ib

Encapsulation Ex m Exmb

Oil immersion Ex o

Pressurisation Ex p, Ex px, Ex py

Powder filled Ex q

Gb

Fieldbus Intrinsic Safety Concept (FISCO) **

** No designated marking code at the time of writing EPL Gc


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

March 2010 © 21

EPL’s for combustible dusts


Intrinsic Safety Ex iD

Encapsulation Ex mD Da, Db, or Dc

Protection by enclosure tD

Db or Dc Pressurisation pD

Equipment marking Since there is now technical alignment of the CENELEC and IEC standards, equipment manufactured in Europe will no longer be marked EEx, and instead will be marked Ex. Where equipment is certified under the IECEx scheme the IECEx Conformity Mark as illustrated below will be displayed on the equipment. For the foreseeable future, however, acceptance in the EU will require the equipment to comply with ATEX and display the marking illustrated on page 18.

Area for code indicating the Licensee Number and the Certification Body

March 2010 © 22

Example of an EC – Type Examination Certificate

March 2010 © 23

March 2010 © 24

March 2010 © 25

Baseefa Wallchart

UNIT 3

FLAMEPROOF EEx d / Ex d

March 2010 ©

2

OBJECTIVES On completion of this unit, ‘flameproof EEx d / Ex d apparatus, you should know:

a. The principle of operation and causes of pressure piling. b. The general constructional requirements including types of joints. c. The installation requirements with regard to thread engagement of cable entries and

stopping devices, circuit protection, obstruction of flamepaths and additional weatherproofing methods in accordance with BS EN60079-14.

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

March 2010 ©

3

Flameproof EEx d / Ex d Flameproof is one of the original methods of explosion protection developed for use in the mining industry. It has a wide range of applications, typically junction boxes, lighting fittings, electric motors etc. The letter ‘d’, which symbolises this type of protection, is from the German word ‘druckfeste’ (kapselung), which roughly translated means ‘pressure tight’ (enclosure).

Flameproof apparatus, when properly installed in the intended location, enables components such as switches, contractors and relays etc. to be safely used in hazardous areas. Flameproof is the only one of the nine different methods of explosion protection in which an explosion is permitted. This explosion, however, must be contained by the robustly constructed flameproof enclosure so that ignition of the surrounding flammable atmosphere cannot occur.

March 2010 ©

4

Standards

BS EN60079-1: 2007 Flameproof enclosures ‘d’

BS EN50 018: 2000 Flameproof enclosures ‘d’

BS 5501: Part 5: 1977 Flameproof enclosures ‘d’

BS 4683: Part 2: 1971 The construction and testing of flameproof enclosures of electrical apparatus (Ex d)

BS 229: 1957 Flameproof enclosures of electrical apparatus

IEC 60079-1: 2007 Electrical Apparatus for explosive gas atmospheres – Part 1: Flameproof enclosures ‘d’

BS EN60079-14: 2008 Electrical Apparatus for explosive gas atmospheres: Part 14 Electrical installations in hazardous areas (other than mines)

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

BS 5345: Part 3: 1979 (Withdrawn)

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

Definition The construction standard BS EN60079-1 defines flameproof as:

‘An enclosure in which the parts which can ignite an explosive atmosphere are placed and which can withstand the pressure developed during an internal explosion of an explosive mixture, and which prevents the transmission of the explosion to the explosive atmosphere surrounding the enclosure’

EPL: Gb Zone of Use: 1 & 2 Ambient Conditions Flameproof enclosures are normally designed for use in ambient temperatures in the range - 20°C to +40°C unless otherwise marked.

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5

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

Flammable MIxture

Arcs, Sparks Hot Surfaces

Contactors, Relays etc

Gap

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

a. The width of the joint b. The gas group c. The internal volume of the enclosure d. The type of joint

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

a) Flanged joint

b) Spigot joint

c) Screwed joint Interior

Interior

Interior

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8

Flamepath Joints Types (Rotating Machines)

(d) cylindrical (shaft gland) joint (d) labyrinth joint for shafts

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

Cable (gland) entry

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10

Entry by Cable Gland or Conduit The thread engagement requirements for cable and conduit entries are specified in the standard BS EN60079-1 and apply to the three sub-groups IIA, IIB and IIC. Only threaded entries are permitted for all cable glands or conduits entering flameproof enclosures – clearance entries are not permitted.

Volume

≤ 100 cm3 > 100 cm3

Thread Engagement

Axial Length

Thread Engagement

Axial Length

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

As already stated the above requirements for thread engagement are specified in the latest standard BS EN60079-1: 2007, but the previous standard BS EN50018: 2000 required at least 6 full threads engagement in order to make sure that 5 full threads were actually engaged. Note: Flameproof equipment manufactured to the old British standard BS229 may have

different non-metric thread forms at cable gland entries. This difficulty can be overcome by the use of certified Ex d adaptors which have compatible thread forms to suit both the entry in the enclosure and the cable gland.

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Unused Cable or Conduit Entries It is important that unused cable/conduit entries in flameproof enclosures are closed using appropriate stoppers, as specified in the standards, or those supplied by the manufacturer. These must be ‘component certified’ metal stoppers – plastic stoppers are unacceptable – which are fully engaged by 5 full threads. The construction standard specifies suitable types, examples of which are illustrated below.

Stoppers of the type illustrated by example ‘C’ in the above diagram are available with certification markings on either the plain side or the same side as the hexagon recess. Ideally, stoppers of this type should be fitted with the plain side facing the exterior to make unauthorised removal more difficult, but may be fitted with the hexagon recess facing the exterior. Whichever way round they are fitted the certification markings must be visible for ease of identification during ‘Visual’ inspection programmes. Also the thread engagement requirements must be met. Stoppers of this type are tightened using an Allen Key.

Split pinA

B

C

D

Interior

Screwdriver slot

Special fastener

Hexagon recess

Hexagon head

Shearable neck

Exterior

March 2010 12

Flamepath Gap Dimensions – BS EN60079-1, Table 1

Maximum gap

mm

For a volume

cm3 V ≤ 100

For a volume

cm3 100 < V ≤ 500

For a volume

cm3 500 < v ≤ 2 000

For a volume

cm3 V > 2 000

Type of Joint

Minimum width of joint

L mm

I IIA IIB I IIA IIB I IIA IIB I IIA IIB 6 0.30 0.30 0.20 - - - - - - - - -

9.5 0.35 0.30 0.20 0.35 0.30 0.20 - - - - - - 12.5 0.40 0.30 0.20 0.40 0.30 0.20 0.40 0.30 0.20 0.40 0.20 0.15

Flanged, cylindrical or spigot joints

25 0.50 0.40 0.20 0.50 0.40 0.20 0.50 0.40 0.20 0.50 0.40 0.20 6 0.30 0.30 0.20 - - - - - - - - -

9.5 0.35 0.30 0.20 0.35 0.30 0.20 - - - - - - 12.5 0.40 0.35 0.25 0.40 0.30 0.20 0.40 0.30 0.20 0.40 0.20 - 25 0.50 0.40 0.30 0.50 0.40 0.25 0.50 0.490 0.25 0.50 0.40 0.20

Sleeve bearings

40 0.60 0.50 0.40 0.60 0.50 0.30 0.60 0.50 0.30 0.60 0.50 0.25 6 0.45 0.45 0.30 - - - - - - - - -

9.5 0.50 0.45 0.35 0.50 0.40 0.25 - - - - - - 12.5 0.60 0.50 0.40 0.60 0.45 0.30 0.60 0.45 0.30 0.60 0.30 0.20 25 0.75 0.60 0.45 0.75 0.60 0.40 0.75 0.60 0.40 0.75 0.60 0.30

Cylindrical joints for shaft glands of rotating electrical machines with:

Rolling-element bearings

40 0.80 0.75 0.60 0.80 0.75 0.45 0.80 0.75 0.45 0.80 0.75 0.40

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

March 2010 ©

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Flamepath Gap Dimensions – BS EN60079-1, Table 2

Maximum gap mm

Type of Joint

Minimum width of joint

L mm

For a volume cm3

V ≤ 100

For a volume cm3

100 < V ≤ 500

For a volume cm3

500 < v ≤ 2 000

For a volume cm3

V > 2 000

5 0.10 - - - 9.5 0.10 0.10 - -

15.8 0.10 0.10 0.4 -

Flanged joints

25 0.10 0.10 0.4 0.4 12.5 0.15 0.15 0.15 - 25 0.18b 0.18b 0.18b 0.18b 40 0.20c 0.20c 0.20c 0.20c

Spigot joints (Figure 2a)

c ≤ 6mm d ≤ 0.5L L = c + d f ≤ 1mm

6 0.10 - - - 9.5 0.10 0.10 - -

12.5 0.15 0.15 0.15 - 25 0.l5 0.15 0.15 0.15

Cylindrical joints Spigot joints (Figure 2b)

40 0.20 0.20 0.20 0.20 6 0.15 - - -

9.5 0.15 0.15 - - 12.5 0.25 0.25 0.25 - 25 0.25 0.25 0.25 0.25

Cylindrical joints for shaft glands of rotating electrical machines with rolling element bearings

40 0.30 0.30 0.30 0.30

a Flanged joints are permitted for explosive mixtures of acetylene and air only in accordance with 5.2.7 b Maximum gap of cylindrical part increased to 0.20 mm if f < 0.5 mm c Maximum gap of cylindrical part increased to 0.25 mm if f < 0.5 mm

NOTE: The constructional values rounded according to ISO 21 –D should be taken when determining the maximum gap

March 2010 © 14

Pressure Piling

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

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Pressure Piling in Flameproof Motors

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

Section 1 Section 2

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

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

Group Distance

IIA 10 mm

IIB 30 mm

IIC 40 mm

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Ingress Protection Methods

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

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Weatherproofing / protection of flamepaths Flameproof equipment must have a level of ingress protection to suit the environmental conditions of the location in which the equipment is installed and hence equipment should have, as part of their certified design, seals or gaskets to prevent the ingress of water and/or dust. Flamepaths must also be protected in accordance with manufacturer’s instructions and the requirements of BS EN60079-14 which will involve additional measures as detailed below. This is particularly important where environmental conditions are extreme. Protection of flamepaths The following measures are not permissible:

a) painting of flamepath surfaces - enclosures may be painted after assembly; b) fitting of unauthorised seals/gaskets – replacement seals/gaskets may only be

fitted where the originals, which are part of the certified design, are degraded or damaged.

Permitted measures:

c) application of non-setting grease or anti-corrosive agents having no evaporating solvents;

d) non-hardening grease-bearing (Denso) tape – see application/limitations of use below.

Note: The use of non-setting grease on the machined surfaces of flamepaths has

two advantages since, in addition to providing an additional level of ingress protection; it also inhibits the formation of rust on these surfaces.

Silicone based greases require careful consideration in order to avoid possible damage to the elements of gas detectors.

For Flameproof equipment, the limitations for the use of non-hardening tape as specified in BS EN60079-14 are as follows:

a. Non-hardening tape maybe applied around the flamepaths of apparatus with flanged joints allocated to group IIA applying one layer only with a short overlap.

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

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

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

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

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

installed in locations containing group IIC gases or vapours.

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

Direct entry Indirect entry

EEx d Enclosure EEx d

Enclosure

Flamepaths

Bushings

EEx d cable glands

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Electrical Protection Flameproof enclosures are tested for their ability to withstand internal gas explosions only; they are not capable of withstanding the energy which may be released as a result of an internal short-circuit. In order to avoid invalidation of the certification, it is important that properly rated/calibrated electrical protection, e.g. fuses and/or circuit breakers, are utilised.

Cover bolt (fastener) requirements Should the requirement arise where it is necessary to replace the cover bolts etc of a flameproof enclosure, only steel bolts having the correct length, type of thread, type of head and tensile strength should be used. Regarding cover bolt tightness the torque values specified by the manufacturer should be observed. In the absence of manufacturer’s torque values the minimum requirement is spanner tight, however, care must be exercised to avoid under-tightening as this can allow an increase in the flamepath gap. Also, over-tightening of the bolts can result in them stretching and hence reducing their strength with the consequence that an internal explosion may not be contained within the enclosure. It is important that all cover bolts are in place and correctly tightened prior to energising a flameproof enclosure.

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Modification of Flameproof Enclosures Flameproof enclosures are normally supplied complete with all internal components fitted and certified as a single entity by a recognised test authority. The testing procedure will take into consideration the free internal volume after all the components have been fitted, the temperature rise (determined by the maximum power dissipation), creepage and clearance distances, and the rise in pressure as a result of an internal explosion using a gas/air mixture in its most explosive proportions. The certification, therefore, “seals” the design of the apparatus so that any unauthorised modifications will effectively invalidate the approval/certification. Modifications will modify the original test results recorded by the test/certification authority and, consequently, the following points should be observed.

a. Replacement components should always be exactly the same as the original specified components in order to avoid infringement of the certification. For example, a component larger or smaller than the original will affect the internal geometry of the enclosure. Pressure piling is a possibility if a larger component is fitted, and increased volume will result if a smaller component is fitted.

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

Original arrangement

Replacement of ‘A’ with a larger item

Replacement of ‘A’ with a smaller item

March 2010 ©

22

b. Adding components is also forbidden because of the possibility of increased explosion pressure as a result of pressure piling.

Addition of component ‘C’

c. The removal of components should also be avoided since an increase in the free internal volume will result. The original test results, prior to certification, would be compromised as a result of a modification such as this.

Removal of component ‘B’

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

d. Drilling and tapping of cable gland/conduit entries should only be carried out by the manufacturer of the enclosure, or his approved agent. The threads of the entries are required to be compatible with those of cable glands or conduit in terms of type of thread, thread pitch and clearance tolerance since flamepaths exist at these points.

Correct alignment of the threaded entry is also important since the flamepath length at one side will be reduced if the cable gland or conduit is not fitted perpendicular to the face of the enclosure.

The strength of a flameproof enclosure may be impaired if the number and size of entries exceeds that permitted in the original design certified by the test authority. Compliance with the original design is paramount with regard to number, size and location of entries to ensure the enclosure will contain an internal explosion.

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

as part of the original design.

The use of unauthorised sealants should also be avoided when it is required to maintain or improve the IP rating.

March 2010 ©

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BS EN 60079-17 Table 1: Inspection Schedule for Ex’d’, Ex’e’, and Ex ‘n’ Installations (D = Detailed, C = Close, V = Visual) Check that: Ex’d’ Ex’e’ Ex’n’ Grade of Inspection D C V D C V D C V A APPARATUS 1 Apparatus is appropriate to area classification * * * * * * * * * 2 Apparatus group is correct * * * * * * 3 Apparatus temperature class is correct * * * * * * 4 Apparatus circuit identification is correct * * * 5 Apparatus circuit identification is available * * * * * * * * * 6 Enclosure, glass parts and glass-to-metal sealing gaskets

and/or compounds are satisfactory * * * * * * * * *

7 There are no unauthorised modifications * * * 8 There are no visible unauthorised modifications * * * * * * 9 Bolts, cable entry devices (direct and indirect) and blanking

elements are of the correct type and are complete and tight - Physical check - Visual check

*

*

*

*

*

*

*

*

*

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

11 Flange gap dimensions are within maximal permitted values * * 12 Lamp rating, type and position are correct * * * 13 Electrical connections are tight * * 14 Condition of enclosure gaskets is satisfactory * * 15 Enclosed-break and hermetically sealed devices are undamaged * 16 Restricted breathing enclosure is satisfactory * 17 Motor fans have sufficient clearance to enclosure and/or covers * * * 18 Breathing and draining devices are satisfactory * * * * * * B INSTALLATION 1 Type of cable is appropriate * * * 2 There is no obvious damage to cables * * * * * * * * * 3 Sealing of trunking, ducts, pipes and/or conduits is satisfactory * * * * * * * * * 4 Stopping boxes and cable boxes are correctly filled * 5 Integrity of conduit system and interface with mixed system is

maintained * * *

6 Earthing connections, including any supplementary earthing bonding connections are satisfactory (e.g. connections are tight and conductors are of sufficient cross section) - Physical check - Visual check

*

*

*

*

*

*

*

*

*

7 Fault loop impedance (TN system) or earthing resistance (IT systems is satisfactory) * * *

8 Insulation resistance is satisfactory * * * 9 Automatic electrical protective devices operate within permitted

limits * * *

10 Automatic electrical protective devices are set correctly (auto reset not possible) * * *

11 Special conditions of use (if applicable) are complied with * * * 12 Cables not in use are correctly terminated * * * 13 Obstructions adjacent to flameproof flanged joints are in

accordance with IEC 60079-14 * * *

14 Variable voltage/frequency installation in accordance with documentation * * * * * *

C ENVIRONMENT 1 Apparatus is adequately protected against corrosion, weather,

vibration and other adverse factors * * * * * * * * *

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

March 2010 ©

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

Unit 4:

Increased Safety EEx e / Ex e

March 2010 © 2

Objectives: On completion of this unit, ‘Increased Safety EEx e / Ex e Apparatus’, you should know:

a. The principle of operation.

b. The principle design features.

c. The methods for estimating terminal content of enclosures.

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

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

March 2010 © 3

Increased Safety EEx e / Ex e The explosion protection concept Increased Safety was invented in Germany where it has been widely used for many years. It is has become popular in the UK mainly because it has a number of advantages for certain applications over the traditional flameproof method of explosion protection. America has traditionally relied on the use of explosion-proof enclosures in hazardous locations, and the prospect of using an Increased Safety enclosure, which is not designed to withstand an internal explosion, as an alternative, has probably been viewed with a little trepidation. This method of protection has a good safety record and comparable with the other methods of protection. The letter ‘e’ which symbolises this method of protection is taken from the German phrase ‘Erhohte Sicherheit’, which roughly translated means ‘increased security’. Typical applications are induction motors, lighting fittings and junction boxes.

Standards

BS EN60079-7: 2007 Electrical apparatus for explosive gas atmospheres. Increased Safety ‘e’

BS EN50 019: 2000 Increased Safety enclosure ‘e’ BS 5501: Part 6: 1977 Increased Safety enclosure ‘e’ BS 4683: Part 4: 1973 Type of protection ‘e’

IEC 60079-7: 2001-11 Construction and Test of Electrical Apparatus, Type of Protection “e”

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

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


Code of Practice for the Selection, Installation and Maintenance of Increased Safety apparatus.

March 2010 © 4

Definition ‘A protection method in which increased measures are taken to prevent the possibility of excessive HEAT, ARCS or SPARKS occurring on internal or external parts of the apparatus in normal operation’. EPL: Gb Zones of use: 1 & 2 Ambient Temperatures Increased Safety enclosures are normally designed for use in ambient temperatures in the range -20 °C to +40 °C unless otherwise marked. Increased Safety light fittings Increased safety light fittings usually have other methods of protection, e.g powder filled Ex q protected capacitors and flameproof protected lampholders, and hence the marking on the certification label will be Ex edq. The following, however, note is important. Note: Lamps for Ex e, luminaries, which have mono-pin, bi-pin or screw connections where

the caps are made from non-conductive material with a conductive coating, are not permitted unless tested with the equipment.

March 2010 © 5

Principle The safe operation of Increased Safety apparatus is dependent on the prevention of any source of ignition, i.e. excessive surface temperatures, arcs or sparks, which might otherwise be produced by internal or external parts of the apparatus. Special design features are, therefore, incorporated in the apparatus by the manufacturer and are as follows.

1. Mechanically strong enclosure resistant to impact - tested to 4 or 7 joules impact energy depending on application.

2. Ingress protection against solid objects and water - at least IP 54.

3. Terminals manufactured from high quality insulation material.

4. Specified creepage and clearances incorporated in the design of terminals.

5. Terminal locking devices to ensure conductors remain secure in service.

6. Certified de-rating of terminals.

7. Terminal population of enclosure limited by circuit design.

8. Close excess current circuit protection.

Increased Safety Terminals The terminals installed in an Increased Safety enclosure must be ‘component certified’ terminals. They will be manufactured from good quality materials such as Melamine, Polyamide and, for special applications, Ceramic. These materials, which have good thermal stability, have been subjected to a ‘Comparative Tracking Index (CTI)’ test to determine their resistance to tracking. The following definitions are relevant: Clearance distance: The shortest distance through air between two conductors. Creepage distance: The shortest distance between two conductors along the

surface of an insulator. Tracking: The leakage current which passes across the

contaminated surface of an insulator between live terminals, or live terminals and earth.

Comparative Tracking Index: The numerical value of maximum voltage, in volts at which

an insulation material withstands e.g., 100 drops of electrolyte (usually ammonium chloride solution in distilled water) without tracking.

March 2010 © 6

Increased Safety Terminals Test Criteria - Comparative Tracking Index (CTI) The Comparative Tracking Index (CTI) test criteria are given in the table below. Four grades of materials ‘a’, ‘b’, ‘c’ and ‘d’ are considered, the highest quality material being ‘a’ which is subjected to the greatest number of drops of electrolyte falling between the test electrodes, and the highest voltage applied across the electrodes from the variable voltage source. Each material must withstand the specified number of drops of the electrolyte at the specified voltage for it to be acceptable. Thus, the combination of high quality materials and good design, which incorporates specified creepage and clearance distances, ensures that Increased Safety terminals have a greater resistance to tracking to prevent arcing or sparking.

Grade of Material C.T.I. Test Voltage Number of Drops a - 600 > 100 b 500 500 > 50 c 380 380 > 50 d 175 175 > 50

The International Standard IEC 60112 groups insulating materials according to their tracking resistance as illustrated in the following table.

Material group Comparative tracking index ( CTI ) I 600 < CTI II 400 < CTI < 600

IIIa 175 < CTI < 400 Creepage and Clearance Distances

March 2010 © 7

Increased Safety Terminals Creepage and Clearance Distances

Terminals

Partition

Screw heads

Clearance 29 75Creepage

path 30 6

Clearance & creepage path 26.4mm

Clearance and creepage paths to extend to adjacent clamping screw

Clearance and creepage paths 14.0mm

Creepage path runs between locating rivet and assembly rail 27.8 mm

Clearance path extends from end of bolt to assembly rail 20.5mm

March 2010 © 8

Increased Safety Terminals Creepage Distances Relative to Voltage and Grade of Insulation The following table from BS EN60079-7 shows the creepage distances relative to the grade of material and applied voltage.

Minimum creepage distance (mm)

Material group

Voltage (see note 1) U r.m.s a.c. or d.c.

(V) I II IIIa

Minimum clearance (mm)

10 ( see note 3 ) 1.6 1.6 1.6 1.6 12.5 1.6 1.6 1.6 1.6 16 1.6 1.6 1.6 1.6 20 1.6 1.6 1.6 1.6 25 1.7 1.7 1.7 1.7 32 1.8 1.8 1.8 1.8 40 1.9 2.4 3.0 1.9 50 2.1 2.6 3.4 2.1 63 2.1 2.6 3.4 2.1 80 2.2 2.8 3.6 2.2 100 2.4 3.0 3.8 2.4 125 2.5 3.2 4.0 2.5 160 3.2 4.0 5 3.2 200 4.0 5.0 6.3 4.0 250 5.0 6.3 8.0 5.0 320 6.3 8.0 10.0 6.0 400 8.0 10.0 12.5 6.0 500 10.0 12.5 16.0 8.0 630 12.0 16.0 20.0 10.0 800 16.0 20.0 25.0 12.0

1000 20.0 25.0 32.0 14.0 1250 22.0 26.0 32.0 18.0 1600 23.0 27.0 32.0 20.0 2000 25.0 28.0 32.0 23.0 2500 32.0 36.0 40.0 29.0 3200 40.0 45.0 50.0 36.0 4000 50.0 56.0 63.0 44.0 5000 63.0 71.0 80.0 50.0 6300 80.0 90.0 100.0 60 8000 100.0 110.0 125.0 80.0 10000 125.0 140.0 160.0 100.0

Note 1: Voltages shown are derived from IEC 60664-1. The working voltage may exceed the voltages given in the table by 10%. This is based on the rationalisation of supply voltages given in table 3b of IEC 60664-1

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

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

March 2010 © 9

Increased Safety Terminal Types and Ratings The terminals are de-rated so that the maximum current for Increased Safety applications is nearly half that for standard industrial applications as illustrated in the following table for enclosures manufactured to BS 5501 Part 6. This de-rating, along with other considerations, ensures that internal and external surface temperatures are kept within prescribed limits. The table below also shows the maximum conductor size for each terminal type.

Terminal Type

Conductor Size

Increased Safety Maximum Current

(amps)

Industrial Maximum Current (amps)

SAK 2.5 2.5 15 27

SAK 4 4 21 36

SAK 6 6 26 47

SAK 10 10 37 65

SAK 16 16 47 87

SAK 35 35 75 145

SAK 70 70 114 220

Increased Safety Terminals Terminal Locking Device It is essential that conductors are securely connected in the terminals to prevent sparks occurring as a result of loose connections. The illustration below shows how this is achieved.

March 2010 © 10

Estimation of Terminal Population The number of terminals which can be installed in a given size of enclosure is limited. Several methods have been developed by manufacturers for this purpose. These are: Enclosure Factor: A method used in apparatus manufactured to BS 4683 Part 4

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

Load Limit: Similar to ‘enclosure factor’ but used only on apparatus

manufactured to BS 5501 Part 6. Kelvin Rating: Normally used for high current applications and apparatus

manufactured to BS 4683 Part 4 and BS 5501 Part 6. In this method, enclosures and terminals are assigned a temperature rating. Enclosures will normally be limited to a temperature rise of 40K for a T6 temperature rating, but the temperature for the terminals will be dependent on their type, rated current, size of associated conductor, and the size of enclosure in which they are installed. This involves the use of tables which are provided by the manufacturer. Once the terminal ‘K’ rating has been established, it is divided into the ‘K’ rating for the enclosure to give the number of terminals of one type which may be installed.

Max Dissipated Power: This is a method which will replace the current ‘load limit’

method and applies to apparatus manufactured to BS 5501 Part 6 and BS EN50019. In this method, enclosures are assigned a ‘watts dissipation’ rating, but the rating of the terminals is determined by use of a unique table (provided by the manufacturer) for the enclosure. This table provides the ‘watts dissipation’ of the terminal through consideration of conductor size and load current. The terminal content is determined by dividing the ‘watts dissipation’ value for the terminal into that for the enclosure.

Another method used by manufacturers is to specify the maximum current per pole and also the maximum current per mm2. Examples of labels with the above information are shown overleaf.

March 2010 © 11

Examples of labels (a) Enclosure factor (b) Load limit (c) Enclosure factor (d) Maximum dissipated power

(e) Maximum current per pole and per sq. mm

Klippon TYPE TB11EX S/No. 9364

EEx e II T6 BASEEFA CERT. No. EX84B1333X BS5501 Pt.6 (EN50 019)

LOAD LIMIT 600A

Klippon ENCLOSURE TYPE TB11 BS 4683 Pt.4 Ex e II T6 BASEEFA No. Ex 77152/B MAX. CIRCUIT VOLTAGE 726 ENCLOSURE FACTOR 416 SERIAL NUMBER 1334

Klippon

TYPE TB12 S/No.867594 EEx e II T6

BASEEFA CERT. No. Ex84B3290X BS5501 Pt.6 (EN50 019)

LOAD LIMIT 40K

Klippon TYPE STB2 EEx II T6 S/No. T499 BASEEFA CERT. No. 86B 2138X BS5501 Pt.6 (EN50 019) MAX. DISSIPATED POWER 7 WATTS

HAWKE CABLE GLANDS Ltd. BS5501: Pt.6: 1977 (EN50 019) EEx e II T6 BASEEFA No. Ex 8142BX TYPE REF PL639 SERIAL No. 9960/89 PHASE-TO-PHASE 726 MAX VOLTS PHASE-TO-EARTH MAX.CURRENT DENSITY AMPS PER SQ. MM 4 MAX AMPS PER POLE 10

March 2010 © 12

Sample Calculation using ‘Load limit’ The ‘Load Limit’ will be specified on the certification label of an Increased Safety enclosure, as illustrated below, and represents the sum of all the circuit currents the enclosure is able to carry without exceeding the temperature classification. Thus, the number of terminals of one type which can be installed in a given enclosure is simply the ‘Load Limit’ divided by the Increased Safety current rating of the terminal type to be used, as demonstrated in the following calculation.

TYPE TB11 S/No D779

EEx e II T6

BASEEFA CERT No Ex 84B3299X

BS 5501 Pt 6 (EN50 019)

LOAD LIMIT 600

Enclosure Load Limit = 600

SAK 2.5 Ex e terminal rating = 15 A

Number of SAK 2.5 terminals = ratingterminal2.5SAK

LimitLoad

= 15600

= 40 SAK 2.5 terminals

Where the circuit current is below the certified current rating of the terminals, it may be possible to base the terminal population on the circuit current provided it will not exceed the assigned value. Assuming a circuit current of 10 A, the calculation is as follows.

Enclosure Load Limit = 600

Circuit current = 10 A

Number of SAK 2.5 terminals = currentCircuitLimitLoad

= 10600

= 60 SAK 2.5 terminals

March 2010 © 13

Terminal Assemblies

Component Approved Terminal Group 1. Mounting rail; 2. Terminals - certified components; 3. End plate; 4. End bracket; 5. Distance sleeve; 6. Partition; 7. Copper cross-connection; 8. Zinc plated screw; 9. Copper cross-connection; 10. Copper cross-connection.

Insulated comb alternative for linking terminals

March 2010 © 14

Terminal Assemblies

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

March 2010 © 15

Installation of cable glands & accessories The illustrations below show the minimum requirements for the installation of cable glands and accessories, i.e. earth tags, IP washers, serrated washers and locknuts, depending on whether the enclosure is metal, or plastic with or without an internal continuity plate and the entries are threaded, or unthreaded. Note: Minimum requirements infer maintaining IP54 which a threaded entry 6mm in

length will achieve.

Metal enclosure without removable gland plate and has unthreaded entry

Metal enclosure with threaded entry 6mm long

Plastic enclosure with clearance entry and no internal continuity plate Metal enclosure

with removable gland plate and clearance entries

Enclosure wall or gland plate

Enclosure wall or gland plate

March 2010 © 16

Installation, Inspection and Maintenance It is essential that Increased Safety enclosures are installed and maintained in accordance with the relevant Standards and Codes of Practice in order to comply with the Certification. The following list specifies the main points.

1. Enclosure content should not be modified without consulting the manufacturer.

2. Only components specifically approved should be fitted in the enclosure.

3. All terminal screws, used and unused, should be tightened down.

4. Conductor insulation should extend to within 1 mm from the metal throat of the

terminal.

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

6. Only one conductor should be fitted to each terminal side (unless more than one is permitted in the equipment certificate).

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

terminal way when an insulated comb is used.

8. Only the conductors from each cable entry shall be loomed together.

9. The insulation of cables shall be suitable for use at least 80°C for a T5 temperature class.

10. The individual earth continuity plates within plastic enclosures must be bonded

together and locknuts used to secure glands to the continuity plates. For clearance holes, serrated metal washers must be used between locknuts and the glandplate.

11. When Intrinsic and Increased Safety circuits occupy the same enclosure the two

types of circuit must have at least 50 mm clearance between them.

12. There must be adequate clearance between adjacent enclosures to allow proper installation of cables and glands.

13. All unused cable entries should be closed using suitable plugs.

14. The schedule of the appropriate certificate should be consulted before cable entry

holes are drilled.

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

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

March 2010 © 17

Increased Safety EEx e / Ex e Motors These motors are similar in appearance to standard industrial motors and inspection of the certification/rating plate is usually necessary to identify them. These motors are not designed to withstand an internal explosion and hence have special design features to prevent arcs, sparks and excessive surface temperatures occurring both internally and externally. The principal design features are:

1. Special attention to airgap concentricity and clearance of all rotating parts.

2. Impact testing of motor frame.

3. Temperature rise 10 °C lower than normal.

4. T2 or T3 surface temperature limitation.

5. Compliance with tE characteristic.

6. Special terminal block with specific creepage/clearance distances and locking devices on terminals.

7. Minimum ingress protection to IP54. Under stall (locked rotor) conditions, the rotor surface temperature will normally increase faster than that of the stator windings, and hence, the T-rating applies to both internal and external surface temperatures. Under fault conditions, the motor must trip within the tE time specified on the motor data plate. tE time Defined as: ‘the time taken to reach the limiting temperature from the temperature reached in normal service (i.e. hot) when carrying the starting current IA at maximum ambient temperature. In the graph shown on page 17, ‘OA’ represents the maximum ambient temperature and ‘OB’ the temperature reached at maximum rated current. If the rotor locks as a result of a fault, the temperature will rise rapidly towards ‘C’ as shown in part 2 of the graph, which is less than the T rating of the motor. The time taken to reach ‘C’ from ‘B’ is known as the tE time, and during fault conditions the thermal overload device in the motor starter must trip the motor within this time. Increased safety motors are intended for continuous duty only, i.e. they are unsuitable for applications which require frequent stopping and starting and/or long run-up times.

March 2010 © 18

Determination of tE Time

Limiting Temperature

Temperature limited either by selected T-Rating or Limit for Class of Winding Insulating Material

A = Maximum ambient temperature. B = Maximum temperature at rated current. C = Limiting temperature. θ = Temperature. (1) = Temperature rise at rated current. (2) = Temperature rise during locked rotor test. tE = Time from maximum temperature (B) at rated current to limiting

temperature (C).

Max limiting temperature

Tem

pera

ture

C

0

θ

Hours Secs

Rotor locked

A

B

C

Time

0

March 2010 © 19

Tripping Characteristic of Thermal Overload device The thermal overload device will be selected for suitability according to its tripping characteristic. The tE time and IA/IN current ratio are influential in the selection of the device and are marked on the motor nameplate. IN = rated current of motor. IA = locked rotor current of motor. Example 1: IA/IN = 5 and tE time = 10 secs The above characteristic would trip the motor after 8 secs, which is

within the tE time and therefore acceptable. Example2: IA/IN = 4.5 and tE time = 8 secs For these values the tripping time is 10 secs, which is outwith the tE

time assigned to the motor, therefore an overload device with this characteristic would not be suitable for the values specified.

40

20

10

1

2

5

3 4 5 6 7 8 9 10

t

tim

eE

I / I current ratioA N

March 2010 © 20





*

*

*

*

*

*

*

*

*

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

*


maintained * * *


*

*

*

*

*

*

*

*

*

7 Fault loop impedance (TN system) or earthing resistance (IT systems is satisfactory)

* * *


limits * * *

10 Automatic electrical protective devices are set correctly (auto reset not possible)

* * *



14 Variable voltage/frequency installation in accordance with documentation

* * * * * *




March 2010 © 21

Note 1: Apparatus using a combination of both ‘d’ and ‘e’ types of protection will require reference to both columns during inspection.

Note 2: The use of electrical test equipment, in accordance with items B7 and B8, should

only be undertaken after appropriate steps are taken to ensure the surrounding area is free of a flammable gas or vapour.

Unit 5:

Type ‘n’ Apparatus Ex N / EEx n / Ex n

March 2010 © 2

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 in enclosures etc.

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

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

March 2010 © 3

Type ‘n’ Protection Since the presence of a flammable gas or vapour is less likely in Zone 2, the constructional requirements for electrical equipment used in these hazardous locations are not as strict as those for equipment used in Zone 1. A method of protection which falls into this category is type ‘n’ apparatus, which is basically similar to increased safety type “e” apparatus except that there is a relaxation in the constructional requirements. Type ‘n’ protection, a UK innovation, became an accepted method of explosion protection by CENELEC around the year 1999 through the publication of the standard EN50021. Prior to the issue of this standard by CENELEC, this type of protection was symbolised by the (upper case) letter ‘N’ when constructed to UK standards and, as far as Europe is concerned, was only acceptable for use in the UK. Now that EN50 021 has been approved, this type of apparatus will be symbolised by the (lower case) letter ‘n’ and will also display the European Community mark thus enabling wider use of this type of protection in the EC. Standards

BS EN60079-15: 2005 Electrical apparatus for explosive gas atmospheres. Type of protection “n”

BS EN50 021: 1999 Type of protection “n” BS 6941: 1988 Electrical apparatus for explosive atmospheres with

type of protection N BS 4683: Part 3: 1972 Type of protection ‘N’ IEC 60079-15: 2010 Construction, test and marking of type of protection

“n” electrical apparatus BS EN60079-14: 2008 Electrical apparatus for explosive gas atmospheres:

Part 14. Electrical installations in hazardous areas (other than mines)

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


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

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

‘A type of protection applied to electrical apparatus such that, in normal operation and in certain specified abnormal conditions, it is not capable of igniting a surrounding explosive atmosphere’.

March 2010 © 4

EPL: Gc Zone of use: 2 Ambient conditions Type ‘n’ apparatus is normally designed for use in ambient temperatures in the range -20 °C to + 40 °C unless otherwise marked. Principle In Zone 2 hazardous locations, the presence of a flammable gas or vapour is not likely to be present, or if it is present it’s duration will be for a short time only. This fact allows the use of less expensive methods of protection, i.e. non-incendive or type ‘n’ protection. As previously stated, type ‘n’ protection is similar in concept to increased safety type ‘e’ protection. The design features for this type of protection ensure that, in normal operation, sources of ignition in the form of excessive surface temperatures, arcs or sparks are prevented from occurring either internally or externally. Since the design requirements are not as strict as those for increased safety type ‘e’ protection, it is possible for the manufacturer to install within type ‘n’ apparatus, components which produce hot surfaces, arcs or sparks, providing these components have incorporated in them additional methods of protection. These additional methods are described later in this unit. The principal design features for type ‘n’ apparatus are as follows.

1) Enclosures, guards, protective covers, motor fan guards and cable glands, are required to be impact tested to 7J where the risk of impact is high, or 4J where the risk of impact is low;

2) Minimum ingress protection IP54 where an enclosure has exposed live parts internally, or IP44 where insulated live parts are used internally;

3) Use of certified terminals; 4) Terminals manufactured form high quality insulation material; 5) Specified creepage and clearance distances incorporated into the design of the

terminals; 6) Terminal locking devices to ensure conductors remain secure in service.

7) Cable glands to comply with the requirements of IEC 60079-0.

Gland entries must maintain enclosure integrity

Material must be suitable for the environment and must withstand impact

March 2010 © 5

Cable gland selection The requirements for cable glands entering Ex e equipment, as specified in BS EN60079-14: 2003 states that they maintain the type of protection and ingress protection of the equipment, and meet the impact test requirements. The inference here would appear to suggest that provided uncertified cable glands were manufactured to BS6121 their use would be acceptable with Ex e equipment. This of course does not apply to uncertified plastic cable glands.

The introduction of the latest standards, however, has effectively removed this option by virtue of the requirement for revised ‘seal aging’ tests involving repeated heating and cooling cycles, which is now a requirement for all cable glands as detailed in IEC 60079-0 The latest issue of IEC 60079-14: 2007 now requires all cable glands to be certified or approved by the manufacturer. Additional protection measures As previously mentioned, components which produce arcs/sparks or hot surfaces may be installed in type ‘n’ apparatus provided additional protection measures are included. These are explained below. Energy limited apparatus and circuits The technique of energy limitation applies the principles of intrinsic safety by the use of components, which are part of the apparatus circuits, or out-with the apparatus, to prevent ignition of a flammable gas. Energy limitation will involve the use of Associated energy-limited apparatus and Energy limited apparatus where both are separate entities, but when both are contained in the same item of equipment, the equipment is known as Self protected energy-limited apparatus. Associated energy-limited apparatus

Apparatus of this type will use zener diodes and series resistors to limit the voltage and current available to sparking contacts and energy storing components within the energy-limited apparatus, or at the output terminals of the associated energy-limited apparatus. Where the supply to the apparatus is mains voltage via a transformer, an upward tolerance of 10% must be assumed unless alternative measures allow dispensation of this requirement.

Energy limited circuits:

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

Limited output energy

March 2010 © 6

Sealed device A device containing normally sparking components or hot surfaces constructed in such a way that opening is prevented in normal operation and in which the sealing effectively prevents access by a flammable gas or vapour. The free internal volume must be less than 100 cm3. Enclosed break device This technique is used in, for example, the lamp holders of type ‘n’ apparatus. The example below shows a typical lamp holder in which there are two sets of contacts. One set of contacts is enclosed in what is effectively a flameproof enclosure in which the free internal volume must not exceed 20 cm3. This enclosure is designed to withstand an internal explosion and the voltage and current limitations are 690 V and 16 A respectively.

Note: Lamps for Ex n, luminaries, which have mono-pin, bi-pin or screw connections where the caps are made from non-conductive material with a conductive coating, are not permitted unless tested with the equipment.

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

March 2010 © 7

Encapsulated device The device in this instance will be totally sealed by an encapsulating material, typically ‘epoxy resin’, to prevent access of a flammable gas or vapour to an ignition source within. The encapsulant is required to have a continuous operating temperature (COT) 200k greater than the marked maximum temperature and be free of intentional voids. The encapsulant should have a minimum thickness of 3mm, or not less than 1mm if the free surface area is less than 200mm2. Restricted breathing A technique mainly used in type ‘n’ lighting fittings whereby entry to the interior of the apparatus by a flammable gas or vapour is restricted by virtue of good sealing at all joints and cable entries. For apparatus fitted with a device for routine testing of it’s restrictive breathing properties the manufacturer will have tested to ensure that an internal pressure of 300Pa (30mm water gauge) below atmospheric will not change to 150Pa (15mm water gauge) in less than 80 seconds. If the apparatus does not have a device for routine testing then the internal pressure must not change from 3kPa (300mm water gauge) below atmospheric to 1.5kPa (150mm water gauge) in less than 3 minutes. This type of protection is suitable for use in Zone 2 only. Type ‘n’ apparatus variations

Type ‘n’ apparatus variations Marking

Restricted breathing enclosures R

Energy limited apparatus L Includes devices protected by: sealing, encapsulation, hermetic-sealing, enclosed-break and non-incendive methods

C

Non-sparking apparatus A

Note: It is intended that Ex nL equipment will be replaced by

Ex ic equipment as described in page 7 of Unit 7 since they are of similar design.

Marking The above table shows the marking on Type ‘n’ apparatus to indicate the method applied to either eliminate or control spark energy and/or hot surfaces. The following is an example of marking applied to type-n apparatus containing sparking contacts protected by another method.

EEx nC IIB T5

March 2010 © 8





*

*

*

*

*

*

*

*

*


*

11 Flange gap dimensions are within maximal permitted values * * 12 Lamp rating, type and position are correct * * * 13 Electrical connections are tight * * 14 Condition of enclosure gaskets is satisfactory * * 15 Enclosed-break and hermetically sealed devices are undamaged * 16 Restricted breathing enclosure is satisfactory * 17 Motor fans have sufficient clearance to enclosure and/or covers * * * 18 Breathing and drainage devices are satisfactory * * * * * * B INSTALLATION 1 Type of cable is appropriate * * * 2 There is no obvious damage to cables * * * * * * * * * 3 Sealing of trunking, ducts, pipes and/or conduits is satisfactory * * * * * * * * * 4 Stopping boxes and cable boxes are correctly filled * 5 Integrity of conduit system and interface with mixed system is

maintained * * *


*

*

*

*

*

*

*

*

*


* * *


limits * * *


* * *







March 2010 © 9

Note 1: Apparatus using a combination of both ‘d’ and ‘e’ types of protection will require reference to both columns during inspection.

Note 2: The use of electrical test equipment, in accordance with items B7 and B8, should


Unit 6:

Pressurisation EEx p / Ex p

March 2010 © 2

Objectives: On completion of this unit, ‘Pressurised EEx p / Ex p apparatus, you should know:

a. The principle of operation and the importance of purging.

b. The control measures required to ensure the safe operation of apparatus and systems.

c. The variations of pressurisation methods.

d. The action required on loss of overpressure.

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

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

March 2010 © 3

Pressurised Equipment Introduction Pressurisation is a simple technique for providing explosion protection. If the interior of an enclosure is at a pressure above that externally, any flammable gases around the enclosure will be prevented from entering the enclosure. Components which are a source of ignition, i.e. they produce arcs/sparks or hot surfaces, are permitted within the enclosure and, clearly, safety is dependent on the maintenance of the safe gas. The safe gas, which is taken from a known non-hazardous area via the inlet duct, is the medium which ‘segregates’ the flammable gas from the source of ignition, and its continued presence will be confirmed by an approved/certified ‘fail-safe’ control/monitoring system. A slight over-pressure is usually adequate to maintain safe operation.

The latest standard for this type of protection, BS EN60079-2, has introduced three types of pressurisation, namely px, py and pz, around which the requirements of the standard are based. Some of these requirements are considered in this Unit.

Standards

BS EN60079-2: 2007 Pressurised enclosures ‘p’

BS EN50 016: 2002 Pressurised Apparatus ‘p’

BS 5501-3: 1977 Pressurised Apparatus ‘p’

IEC 60079-2: 2007 Pressurised enclosures ‘p’

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

BS EN60079-17: 2007

Electrical apparatus for explosive gas atmospheres: Part 17. Inspection and maintenance of electrical installations in hazardous areas (other than mines)

March 2010 © 4

Definition Pressurisation is defined as:

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

EPL’s: Type px - Gb ( See explanation for types below ) Type py - Gb Type pz - Gc

Zones of use: 1 & 2

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

Types of pressurisation The latest construction standard, BS EN60079-2, identifies three types of pressurisation (px, py and pz), their selection being dependent on the zone of use, the likelihood of an internal release of gas, and the presence/absence of an internal source of ignition. Type px establishes non-hazardous conditions within an enclosure when the enclosure is located in Zone 1, or Group 1 for mining applications. Type py establishes a Zone 2 classification within the enclosure when the enclosure is located in Zone 1. Type pz establishes a non-hazardous classification within the enclosure when the enclosure is located in Zone 2. The table on page 16 illustrates how the protection type is determined based on the Zone of use, and whether or not there are flammable materials and sources of ignition in the enclosure.

March 2010 © 5

Principle The basic principle of operation involves raising and maintaining the internal pressure of the enclosure to a level slightly above the atmospheric pressure out with the enclosure. This ensures that any flammable gases or vapours out with the enclosure cannot enter the enclosure. The minimum over-pressure specified in the latest standard BS EN60079-2 is 0.5 mBar or 50 Pa for types px and py, and 0.25 mBar or 25 Pa for type pz. Previous standards specified 0.5 mBar or 50 Pa. The safe gas used to provide the over-pressure will normally be air but an inert gas such as nitrogen may also be used in certain instances.

Note: Manufacturers must indicate the operational maximum and minimum overpressure for enclosures and the maximum rate of leakage which occurs at maximum overpressure.

Purging When a pressurised system has not been in use for some time it is important that electrical apparatus inside the enclosure is not energised prior to what is known as the ‘purge’ cycle. Purging, which must occur automatically, involves passing a quantity of the safe gas through the enclosure for a specified time in order to remove any flammable gases which may have entered the enclosure. The standards specify that the minimum quantity of the safe gas required to achieve adequate purging is equivalent to 5 times the internal volume of the enclosure and associated ducting. The purge duration will be controlled by a timer in association with a flow-rate sensor in the control circuit. Manufacturers may, however, recommend a greater number of air changes. Very large systems, which are installed on site, will require on-site tests to establish the purge duration necessary for safe operation. If loss of pressure occurs during operation, the control system must automatically purge the enclosure again.

March 2010 © 6

Enclosures The European and IEC standards require a minimum level of ingress protection for pressurised enclosures to IP 4X but, not all enclosures are suitable for pressurisation. An enclosure may have ingress protection to IP54 but, it’s lid seal, for example, is designed to prevent entry of contaminants and not to maintain an over-pressure within the enclosure. Enclosures must, therefore, be appropriately designed, i.e. be strong enough to withstand impact tests and the internal over-pressure with regard to the strength of the walls, and have effective and correctly orientated door seals. The enclosure and its associated ducts must be capable of withstanding, in normal operation, an over-pressure equivalent to 1.5 times the maximum working over-pressure declared by the manufacturer. Alternatively, the enclosure must be capable of withstanding the maximum over-pressure obtained when all outlet ducts are closed. In either instance the minimum overpressure will be 2 mBar (200 Pa).

Protective gas The protective gas, which is normally air except for certain applications, may be an inert gas such as nitrogen or another suitable gas. When air is the protective gas, it may be provided by either a motor driven fan, a compressor, or from storage cylinders. The protective gas must be non-toxic and free from contaminants such as moisture, oil, dust, fibres and chemicals, and other contaminants which could jeopardise the safe operation of the system. Normally, the temperature of the safe gas entering the inlet duct should not exceed 40°C. Where temperatures above or below this value are required, the pressurised enclosure will be marked with this temperature. When air is used as the safe gas its oxygen content must not be greater than that normally present in the atmosphere, i.e. 20.9%. A duplicate supply of the protective gas is also desirable when, on loss of pressure, it would be more dangerous to de-energise the electrical apparatus within the enclosure. When an inert gas such as nitrogen is used as the protective gas and personnel can gain access to enclosures, it is essential that doors/covers are fitted with warning labels since there is a danger of asphyxiation. Doors should also be fitted with suitable locks.

Enclosure covers/doors Where the interior of a type px pressurised enclosure can be accessed via doors/covers without the use of tools or keys, an interlock is required to automatically de-energise the electrical supply when the door/cover is opened, and restore the electrical supply only when the doors/covers are closed. Doors/covers requiring the use of a tool or key for opening must display the warning: “Do not open when energised”. When a pressurised enclosure contains components which have hot surfaces, or are capable of storing energy, e.g. capacitors, doors/covers should be fitted with a warning notice which states the time delay after isolation of the electrical supply to the components before opening the doors/covers.

March 2010 © 7

Control circuit/safety devices The level of overpressure will be monitored by an overpressure sensor or switch and located at a point in the enclosure which has been found by test or experience to be the most difficult to maintain the overpressure, e.g. the internal circulation fan in a pressurised machine. The exact point must be specified either on the enclosure or on the certificate. The rate of flow through the enclosure will be monitored by a flow-rate sensor or switch. A pressure gauge is also desirable and should be located where it can be easily read. The table below, from the latest standard BS EN60079-2, specifies the safety devices required according to the protection type.

1. Over-pressure monitoring device. 2. Protective gas flow-rate monitoring device. 3. Pressure gauge. 4. Pressure relief valve: setting 75% of maximum declared

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

March 2010 © 8

Safety device requirements for protection types

Design criteria Type px Type py Type pz

Safety device to detect loss of minimum overpressure

Pressure sensor

(see 7.9)

Pressure sensor

(see 7.9) Indicator or pressure sensor

Safety device(s) to verify purge period

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

Time and flow marked

(see 7.7c)

Time and flow marked

(see 7.7c)

Safety device for a door or cover that requires a tool to open

Warning

(see 6.2b)

Warning

(see 6.2b) No requirement

Safety device for a door or cover that does not require a tool to open

Interlock, (see 7.12)

(no internal hot parts)

Warning

See 6.2b

(no internal hot parts)

Warning

(see 6.2b)

Safety device for hot internal parts when there is a containment system (see clause 15)

Alarm and stop flow of flammable substance

Not applicable for protection type since internal hot parts not permitted

Alarm

(normal release not permitted)

Ducts The entry of the inlet duct must be positioned in a non-hazardous location (except where cylinders provide the protective gas) and this location must be periodically reviewed in case plant modifications have altered its classification. The exhaust duct, ideally, should have its outlet situated in a non-hazardous location in which there are no sources of ignition, but may be located in a hazardous location if a spark/particle arrestor is fitted. The table below offers guidance in this respect. Ducts should be located in non-hazardous areas as far as possible. Where inlet or outlet ducts pass through hazardous areas, they are required to be free of leakage if there is a possibility that the pressure of the protective gas is below the minimum requirement specified in the standards or that specified by the manufacturer. It is essential that both the inlet and outlet ducts are arranged in such a way that they cannot be obstructed causing restriction of the flow of the protective gas. The ducts should also have adequate mechanical strength, be located where accidental damage is unlikely and have adequate protection against corrosion.

March 2010 © 9

Spark particle barriers:

Type of apparatus within enclosure Zone in which exhaust duct is located A B

Zone 2 Required Not required

Zone 1 Required * Required *

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

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

* A device to prevent rapid entry of a flammable gas into the enclosure upon loss of pressure should be fitted if the surface temperature of apparatus within the enclosure is likely to be a source of ignition.

Duct arrangements The density of the safe gas relative to the flammable gas has an influence on the position of the inlet and outlet ducts on the enclosure. This will speed up the rate of displacement of the flammable gas and so ensure efficient purging of the system. If the safe gas is heavier than the flammable gas the inlet duct will be positioned at the bottom of the enclosure and the exhaust duct at the top. If the safe gas is lighter than the flammable gas the positions of the ducts will be reversed.

1. When the safe gas is more dense than the flammable gas:

2. When the safe gas is less dense

than the flammable gas:

March 2010 © 10

Variations of Pressurisation Several variations of pressurised systems are available. These are:

a. Static pressurisation.

b. Pressurisation with continuous flow;

c. Pressurisation with leakage compensation;

d. Pressurisation with continuous dilution;

a. Static pressurisation

This form of pressurisation has limited applications and, therefore, is not widely used. The technique involves pressurising and sealing the enclosure in a non-hazardous area prior to transportation into a hazardous area. Clearly the seals of the enclosure must be very good to minimise leakage once the source of the safe gas is disconnected.

b. Pressurisation with continuous flow

In this variant the internal over-pressure is maintained as a result of continual flow of the safe gas through the enclosure. The safe gas in this instance has a dual purpose. In addition to maintaining the over-pressure, it may also be used to cool hot parts within the enclosure such as thyristors, or the windings of a pressurised rotating machine. The rate of flow of the safe gas is set at a level which will prevent the temperature of the hot parts exceeding their temperature limit, thereby ensuring that the pressurised enclosure operates within it’s T-rating.

March 2010 © 11

c, Pressurisation with leakage compensation

This method of pressurisation is used when enclosures are poorly sealed at their joints. The system is purged in the usual manner with the damper at the exhaust duct open but, on completion, the damper is closed and the flow of protective gas reduced to a level sufficient to compensate for leakages occurring at the seals/joints of the enclosure.

d. Continuous dilution

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

Purging may be disregarded in Zone 2 if the concentration of the flammable gas released within the enclosure is considerably below the lower-explosive limit, e.g. 25% LEL. Gas detectors may be installed to verify that the atmosphere within the enclosure remains non-hazardous.

March 2010 © 12

d. Continuous dilution (continued)

Types and Magnitude of Internal Release The recommended action when loss of pressure occurs in pressurised apparatus using continuous dilution is addressed in BS EN60079-2 by consideration of the types of release given in the tables below.

1. Normal release

None No release of flammable gas or vapour.

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

2. Abnormal release

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

Unlimited A release of flammable gas or vapour which is not limited to a value which can be diluted to well below the lower explosive limit (LEL).

March 2010 © 13

Combination of Release

Combination 1 No normal release, limited abnormal release

Combination 2 No normal release, unlimited abnormal release

Combination 3 Limited normal release, limited abnormal release

Combination 4 Limited normal release, unlimited abnormal release

The above combinations of release are applied in the table on page 14 which specifies the action necessary on loss of pressure within an enclosure using the technique of continuous dilution. Action on Loss of Pressure 1. No internal source of release The over-pressure within the enclosure is monitored by a pressure switch/sensor, and a flow-rate switch/sensor, located at the exhaust duct, is used to monitor the rate of flow of the safe gas through the enclosure. Loss of over-pressure or rate of flow will activate either an alarm or shutdown of the internal electrical components, the action taken being dependent on:

a. The Zone in which the system is located;

b. The type of apparatus/components within the enclosure. For a system which does not have an internal source of release and contains electrical equipment, BS EN60079-14 specifies the action to be taken on loss of pressure as follows.

Area classification Enclosure contains

ignition-capable apparatus

Enclosure contains apparatus which does not produce a source of ignition in normal

operation

Zone 1 Alarm and switch off b Alarm a

Zone 2 Alarm a No action

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

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

March 2010 © 14

Action on Loss of Pressure (continued)

3. With an internal source of release

Internal release Combination

Normal Abnormal

Area classification

Ignition-capable apparatus

Apparatus with no sources of ignition

Zone 1 Alarm and switch off Alarm

1 None Limited Zone 2 or non-

hazardous Alarm

No protective measures required

Zone 1 Alarm and switch off Alarm

2 None Unlimited Zone 2 or non-

hazardous Alarm

No protective measures required

3 Limited Limited Zone 1

or Zone 2

Alarm and switch off Alarm

4 Limited Unlimited Zone 1

or Zone2

Alarm and switch off Alarm

Externally Mounted Electrical Apparatus Electrical apparatus mounted on the exterior of a pressurised enclosure must be explosion protected in accordance with the Zone in which the enclosure is situated. Typical examples are pressure/flow rate sensors or switches which may use Ex i apparatus, junction boxes may use Ex d, Ex e or Ex n methods of protection. This requirement also applies to the motor and its starter, of the fan which provides the flow of air, unless they are situated in a non-hazardous area. It is preferable that the motor and its starter are located in a non-hazardous area. Apparatus Energised During Absence of Overpressure An anti-condensation heater may be used in a rotating electrical machine to prevent the internal surfaces and atmosphere becoming cold, thereby preventing the formation of moisture in the windings. Because the heater will be energised when the machine is without over-pressure, it is essential that it is explosion protected. Emergency lighting will normally be installed in pressurised control rooms, cabins etc. and energised when there is loss of over-pressure, hence, these fittings must also be explosion protected, typically Ex e. Solenoids for fire dampers will be Ex d protected. Alarms, over-pressure and flow-rate sensors may use IS protection. Ex d enclosures will be used for control panels.

March 2010 © 15

March 2010 © 16

Determination of protection type

Enc

losu

re d

oes

not c

onta

in

igni

tion-

capa

ble

appa

ratu

s

Type

py

No

pres

suris

atio

n re

quire

d

Type

py

Type

py

b

Type

py

No

pres

suris

atio

n re

quire

d d

Enc

losu

re c

onta

ins

igni

tion-

capa

ble

appa

ratu

s

Type

px

a

Type

pz

Type

px

a

Type

px

(and

igni

tion-

capa

ble

appa

ratu

s is

not

loca

ted

in th

e di

lutio

n ar

ea)

Type

px

a (in

ert)

c

Type

pz

(iner

t) c

Exte

rnal

Zon

e cl

assi

ficat

ion

1 2 1 2 1 2

Flam

mab

le s

ubst

ance

in th

e co

ntai

nmen

t sys

tem

No

cont

ainm

ent s

yste

m

No

cont

ainm

ent s

yste

m

Gas

/ va

pour

Gas

/ va

pour

Liqu

id

Liqu

id

NO

TE:

If th

e fla

mm

able

sub

stan

ce is

a li

quid

, nor

mal

rele

ase

is n

ever

per

mitt

ed

a)

Pro

tect

ion

type

px

also

app

lies

to G

roup

I b)

If

no n

orm

al re

leas

e, s

ee a

nnex

E

c)

The

prot

ectiv

e ga

s sh

all b

e in

ert

if “(

iner

t)” is

sho

wn

afte

r th

e pr

essu

risat

ion

type

; see

cla

use

13.

d)

Prot

ectio

n by

pr

essu

risat

ion

is

not

requ

ired

sinc

e it

is

cons

ider

ed u

nlik

ely

that

a fa

ult c

ausi

ng a

rel

ease

of l

iqui

d w

ill si

mul

tane

ousl

y oc

cur

with

a fa

ult i

n th

e eq

uipm

ent t

hat w

ould

pr

ovid

e an

igni

tion

sour

ce

March 2010 © 17

Design requirements relevant to protection type

Type

pz

with

ala

rm

IP3X

min

imum

IEC

600

79-0

, hal

f the

val

ue in

ta

ble

4

Tim

e an

d flo

w m

arke

d

Spa

rk

and

parti

cle

barri

er

requ

ired,

se

e 5.

8 un

less

in

cand

esce

nt

parti

cles

no

t no

rmal

ly p

rodu

ced

No

requ

irem

ent

( Not

e 2

)

Spa

rk

and

parti

cle

barri

er

requ

ired,

see

5.8

Spa

rk

and

parti

cle

barri

er

requ

ired,

se

e 5.

8 un

less

in

cand

esce

nt

parti

cles

no

t no

rmal

ly p

rodu

ced

War

ning

, see

5.3

and

6.2

b) i

i)

No

requ

irem

ent

( Not

e 3

)

War

ning

, see

5.3

and

6.2

b) i

i)

Type

pz

with

indi

cato

r

IP4X

min

imum

IEC

600

79-0

, tab

le 4

Tim

e an

d flo

w m

arke

d

Spa

rk

and

parti

cle

barri

er

requ

ired,

se

e 5.

8 un

less

in

cand

esce

nt

parti

cles

no

t no

rmal

ly p

rodu

ced

No

requ

irem

ent

( Not

e 2

)

Spa

rk

and

parti

cle

barri

er

requ

ired,

se

e 5.

8

Spa

rk

and

parti

cle

barri

er

requ

ired,

se

e 5.

8 un

less

in

cand

esce

nt

parti

cles

no

t no

rmal

ly p

rodu

ced

War

ning

, see

5.3

and

6.2

b) i

i)

No

requ

irem

ent

( Not

e 3

)

War

ning

, see

5.3

and

6.2

b) i

i)

Type

py

IP4X

min

imum

IEC

60

079-

0,

tabl

e 4

Tim

e an

d flo

w

mar

ked

No

requ

irem

ent

( Not

e 1

)

No

requ

irem

ent

( Not

e 2

)

Spa

rk

and

parti

cle

barri

er

requ

ired,

se

e 5.

8

No

requ

irem

ent

( Not

e 1

)

War

ning

, se

e 5.

3 (n

ote

1)

War

ning

, se

e 5.

3 (n

ote

1)

Not

app

licab

le

Type

px

IP4X

min

imum

IEC

600

79-0

, tab

le 4

Req

uire

s a

timin

g de

vice

an

d m

onito

ring

of

pres

sure

& fl

ow

Spar

k an

d pa

rticl

e ba

rrie

r re

quire

d, s

ee 5

.8 u

nles

s in

cand

esce

nt

parti

cles

no

t nor

mal

ly p

rodu

ced

No

requ

irem

ent

( Not

e 2

)

Spar

k an

d pa

rticl

e ba

rrie

r re

quire

d, s

ee 5

.8

Spar

k an

d pa

rticl

e ba

rrie

r re

quire

d, s

ee 5

.8 u

nles

s in

cand

esce

nt

parti

cles

no

t nor

mal

ly p

rodu

ced

War

ning

, see

5.3

and

6.2

b)

ii)

Inte

rlock

, see

7.1

2 ( N

o in

tern

al h

ot p

arts

)

Com

ply

with

6.2

b) i

i)

Des

ign

crite

ria

Deg

ree

of

encl

osur

e pr

otec

tion

acco

rdin

g to

IE

C

6052

9 or

IE

C

6003

4-5

Res

ista

nce

of e

nclo

sure

to im

pact

Verif

ying

pur

ge p

erio

d

Pre

vent

ing

inca

ndes

cent

pa

rticl

es

from

exi

ting

a no

rmal

ly c

lose

d re

lief

vent

into

a Z

one

1 ar

ea

Pre

vent

ing

inca

ndes

cent

pa

rticl

es

from

exi

ting

a no

rmal

ly c

lose

d re

lief

vent

into

a Z

one

2 ar

ea

Pre

vent

ing

inca

ndes

cent

pa

rticl

es

from

exi

ting

a ve

nt o

pen

to a

Zon

e 1

area

in n

orm

al o

pera

tion

Pre

vent

ing

inca

ndes

cent

pa

rticl

es

from

exi

ting

a ve

nt o

pen

to a

Zon

e 2

area

in n

orm

al o

pera

tion

Doo

r /

cove

r re

quiri

ng

a to

ol

to

rem

ove

Doo

r /

cove

r no

t re

quiri

ng a

too

l to

re

mov

e

Inte

rnal

hot

par

ts th

at re

quire

a c

ool-

dow

n pe

riod

befo

re

open

ing

encl

osur

e

See

Not

es o

n fo

llow

ing

page

March 2010 © 18

Design requirements relevant to protection type ( continued )

The following notes are relevant to the table on the previous page.

Note 1: Sub clause 6.2b) ii) is not applicable for type py since neither hot internal parts nor

normally created incandescent particles are permitted. Note 2: There is no requirement for spark and particle barriers since in abnormal operation,

where the relief vent opens, it is unlikely that the external atmosphere is within explosive limits.

Note 3: There is no requirement for marking or tool accessibility on a pz enclosure since in

normal operation the enclosure is pressurised with all covers and doors in place. If a cover or door is removed, it is unlikely that the atmosphere is within the explosive limits.

Temperature classification Type px or type py pressurisation The temperature classification allocated to pressurised apparatus is required to be in accordance with IEC 60079-0 and determined from the higher of either:

a) the hottest point of the enclosure external surface; or b) the internal component with the hottest surface.

With regard to (b), however, the surface temperature of an internal component may exceed the temperature class of the pressurised enclosure if the component complies with 5.3 of IEC 60079-0, or the pressurised enclosure is marked with the time required for the component to cool to the marked temperature class. This may be achieved by the following methods.

c) The joints of the enclosure and its ducts are designed to prevent the ingress of a flammable gas coming into contact with the hot surfaces before they have cooled to below the T rating.

d) By the introduction of a secondary ventilation system. e) By encapsulating the hot surfaces or enclosing them in gas-tight containers.

Type pz pressurisation For this type of pressurisation, the hottest external surface will be used to determine the temperature class of the enclosure but, internal explosion protected apparatus remaining energised in the absence of over-pressure will also have to be taken into consideration for determining the temperature classification.

March 2010 © 19

Marking The construction standard BS EN60079-2 specifies that pressurised enclosures must be marked as detailed in IEC 60079-0. The apparatus marking must be visible and contain the following information:

a) the manufacturers name; b) the manufacturers type number; c) the manufacturers serial number; d) the symbol Ex p, followed by the pressurisation category, i.e. px, py, or pz; e) the gas group symbol II; f) the temperature class, or the maximum surface temperature, or both, e.g. T3,

or 200 °C, or 200 °C (T3); g) the name or acronym of the testing station; h) the test station certificate number; i) the internal free volume excluding the ducts; j) the protective gas (when a gas other than air is used); k) the minimum quantity of the safe gas necessary to purge the enclosure based

on the minimum purge flow rate and the minimum purge duration, and the minimum additional purge duration per unit volume of additional ducting**;

l) the minimum and maximum permissible over-pressure; m) the minimum flow of protective gas; n) the minimum and maximum supply pressure to the pressurised system; o) the maximum leakage rate from the pressurised enclosure; p) the temperature or temperature range of the safe gas at the inlet duct; q) the point(s) where the pressurisation must be monitored

**Note: In order to ensure adequate purging of the system the user must

increase the volume of the safe gas to compensate for the additional volume of the ducts.

March 2010 © 20

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

Check that: Grade of inspection Visual

APPARATUS 1 Circuit and/or apparatus documentation is appropriate to area

classification * * *

2 Apparatus installed is that specified in the documentation – Fixed apparatus only

* *

3 Circuit and/or apparatus category and group correct * * 4 Apparatus temperature class is correct * * 5 Installation is clearly labelled * * 6 There are no unauthorised modifications * 7 There are no visible unauthorised modifications * * 8 Safety barrier units, relays and other energy limiting devices are of

the approved type, installed in accordance with the certification requirements and securely earthed where required

* * *

9 Electrical connections are tight * 10 Printed circuit boards are clean and undamaged * B INSTALLATION 1 Cables are installed in accordance with the documentation * 2 Cables screens are earthed in accordance with the documentation * 3 There is no obvious damage to cables * * * 4 Sealing of trunking, ducts, pipes and/or conduits is satisfactory * * * 5 Point-to-point connections are all correct * 6 Earth continuity is satisfactory (e.g. connections are tight and

conductors are of sufficient cross-section *

7 Earth connections maintain the integrity of the type of protection * * * 8 The intrinsically safe circuit is isolated from earth or earthed at one

point only ( refer to documentation ) *

9 Separation is maintained between intrinsically safe and non-intrinsically safe circuits in common distribution boxes or relay cubicles

*

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

*

11 Special conditions of use (if applicable) are complied with * 12 Cables not in use are correctly terminated * C ENVIRONMENT 1 Apparatus is adequately protected against corrosion, weather,

vibration and other adverse factors * * *

2 No undue accumulation of dust and dirt * * *

Unit 7:

Intrinsic Safety EEx i / Ex i

March 2010 © 2

Objectives: On completion of this unit, ‘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. e. The inspection requirements according to BS EN 60079-17.

March 2010 © 3

Intrinsic Safety EEx / Ex i Intrinsic Safety is a widely used method of explosion protection. It is used for very low power applications only, and typical examples are control and instrumentation circuits.

Standards

BS EN60079-11: 2007 Equipment protection by intrinsic safety ‘i’

BS EN50020: 2002 intrinsic safety ‘i’ BS 5501: Part 7. 1977 (EN50 020) Intrinsic safety ‘i’

BS EN60079-25: 2004 Electrical apparatus for explosive gas atmospheres: – Part 25 Intrinsically safe systems

BS 5501: Part 9 1982 (EN50 039) Intrinsically safe electrical systems ‘i’

BS 1259: 1958 Intrinsically safe electrical apparatus and circuits for use in explosive atmospheres

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

IEC 60079-25: 2010 Electrical apparatus for explosive gas atmospheres: – Part 25 Intrinsically safe systems

IEC 60079-27: 2008 Explosive atmospheres: – Part 28: Protection of equipment and transmission systems using optical radiation



BS 5345: Part 4 1977 (Withdrawn)

Code of Practice for the selection, installation and maintenance of electrical apparatus with a type of protection ‘i’.

March 2010 © 4

Definition BS EN60079-11 defines an intrinsically safe circuit as: ‘A type of protection based on the restriction of electrical energy within apparatus and of interconnecting wiring exposed to the potentially explosive atmosphere to a level below that which can cause ignition by either sparking or heating effects.’ EPL’s: ia - Ga

Ib - Gb Ic - Gc

Zones of use: 0, 1 & 2 (Ex ia) ( based on traditional approach ) 1 & 2 (Ex ib)

2 (Ex ic) Basic Principles of IS Intrinsically Safe circuits achieve safety by maintaining very low energy levels such that hot surfaces will not be produced, and electrical sparks, if they occur, will have insufficient energy to ignite the most easily ignitable concentration of a flammable mixture. This is achieved by limiting the voltage and current supplied to the apparatus in the hazardous area. To maintain safety, it is of paramount importance that these levels of voltage and current are not exceeded under normal, or even fault conditions. The circuit parameters, i.e. voltage, current, resistance, inductance and capacitance are factors which have to be considered in the design of an IS circuit. Consultation with the characteristic ignition curves given in the construction standard (shown in this unit on pages 9, 12 and 13), and the application of appropriate safety factors, will ensure that safe values are established for these parameters during the design stage.

An IS system, which usually comprises a safe to hazardous area interface, cables, junction boxes and field (hazardous) area apparatus, must also be designed in such a way as to guard against the possibility of particular faults occurring. In contrast to other methods of explosion protection, intrinsic safety is a system concept which applies to the whole system and not to any one item only. Apparatus in the safe area, namely the interface, connected to apparatus in the hazardous area is known as ‘associated apparatus’, and each item making up the system, other than ‘simple apparatus’, will have a Certificate of Conformity. Associated apparatus, such as the interface is typically marked with square

[Ex ib] IIC Ex ib IIC

March 2010 © 5

brackets [Ex ia]IIC, may be used in the hazardous area if installation is within another method of explosion protection, e.g. flameproof. Also, power supply modules supplying the system may be installed in flameproof or pressurised Ex p enclosures if installed in the hazardous area. An overall system certificate may cover the installation. Only the equipment specified in the system documentation may be installed in the system. The voltage supply to electrical apparatus, which is connected to the non-IS terminals of associated apparatus, must not be greater than the voltage Um marked on the associated apparatus label or specified in the system documentation. The Code of Practice BS5345 recommended this value should not exceed 250Vrms. The electrical supply prospective short-circuit current must not be in excess of 1500A. Advantages of IS are:

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

wiring may be used c. Safe – low voltage not harmful to personnel d. Can be used in Zone 0

Interface types Interface types include the zener shunt diode barrier, described below, and the galvanic isolator described on page 18. The purpose of the interface is to prevent high energy levels entering the hazardous area and not to protect the hazardous area equipment to which it is connected. The Zener Barrier The faults which can jeopardise the security of IS systems are either overvoltage or overcurrent, and protection against these conditions is afforded by the use of an interface, typically a Zener barrier, the construction of which will be considered in terms of its individual components. The interface, which is connected between the safe area and hazardous area apparatus, is normally located in the safe area and situated as close as possible to the boundary with the hazardous area, but may be located in the hazardous area if installed in a flameproof enclosure.

A simple zener barrier has three principal components, (1) a resistor, (2) a zener diode, and (3) a fuse, all of which must have infallible properties.

March 2010 © 6

Infallibility, with regard to the current limiting resistor, means that in the event of it failing, failure will be to a higher resistance value or open-circuit. Clearly, failure to a lower resistance value or short-circuit would allow more current to flow in the IS circuit, which is contrary to the concept of this type of protection. Infallibility will be satisfied by the use of a quality wire-wound or metal film resistor which should not operate at more than 2/3 of its rated current, voltage and power for a specified temperature range. The next component for consideration is the zener diode, the purpose of which is to limit the voltage available to the apparatus in the hazardous area. The zener diode, as a single item, is not considered to be an infallible component, must also be operated at only 2/3 of its rated current, voltage and power. For infallibility to be satisfied, the zener diode is required to fail to a short-circuit. Failure to a higher resistance or open-circuit could allow voltage levels beyond safe limits to “invade” the hazardous area. Note: Tests by manufacturers have shown that diodes virtually always fail to a short-circuit

state, but there can be no guarantee of this. Diodes can only be considered infallible when two or more are connected in parallel as discussed later.

The third component, a fuse, is located at the input (safe) end of the zener barrier, its purpose being to protect the zener diodes, and not to protect against, for example, a short-circuit in the field apparatus. Infallibility of the fuse is assured by the use of a sand-filled ceramic type capable of operating properly even when exposed to a prospective fault-current of up to 4000 A. A fuse of this type avoids the problem which can occur with other types of fuses when they rupture, namely vaporisation which can allow the fuse to continue to conduct. As required by the standards, the fuse is encapsulated along with the other components of the barrier to deter replacement. The repair of Zener barriers is not permissible, even by the manufacturer. Note: Categories (levels of protection), ‘ia’, ‘ib’ and ‘ic’, are described on the following page

but with regard to the infallibility of components, this applies to ‘ia’ and ‘ib’, but is not applicable to ‘ic’. Furthermore, for level of protection ‘ic’ the 2/3 safety factor applies only to the power rating; it does not apply to the voltage and current provided the rated values are not exceeded.

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

March 2010 © 7

If a voltage greater than the normal maximum voltage of the IS system invades the circuit at the input terminals of the zener barrier, this will trigger the zener diode, and the resulting fault current will be shunted to earth. The excessive voltage is, therefore, prevented from reaching the apparatus in the hazardous area as illustrated in the diagram on the following page.

Levels of protection for IS Previously referred to as categories of intrinsic safety, these are now called levels of protection of which there are three, namely ‘ia’, ‘ib’ and ‘ic’, the level of safety provided by each being dependant on the number component faults which are considered. For the first level of protection, ‘ic’, no faults are considered in order to maintain safety. The second level of protection, ‘b’ will maintain safety in the event of one fault occurring. The third level of protection, ‘ia’, is required to maintain safety should two simultaneous faults occur. Clearly, for the zener barrier (interface) to maintain safety with one or two faults, additional zener diodes are necessary since they are the components most likely to fail. Since the use of infallible components, or the occurrence of faults are not a consideration for the level of protection ‘ic’, equipment marked in this way is suitable for use only in zone 2. Also, it is intended that the level of protection ‘ic’ will replace the energy limited method used in type ‘n’ equipment, i.e. ‘nL’

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

March 2010 © 8

fault. A third zener diode connected in parallel with the other two will satisfy the conditions for category ‘ia’ intrinsic safety in which safety is assured with two faults.

Category ‘ib’ intrinsic safety may be used in Zones 1 & 2, but not Zone 0, and category ‘ia’ intrinsic safety is permitted in Zones 0, 1 and 2. Note 1: A simple test to verify if the fuse of a zener barrier has blown is to disconnect both

the input and output and measure the resistance between the input and output terminals.

Note 2: Equipment in the hazardous area connected to Associated equipment in the non-

hazardous area must be compatible, e.g. the same group and level of protection. If, for example, a zener barrier was marked [Ex ib] IIC and the equipment in the hazardous area marked Ex ia IIC, the level of protection would be reduced to ib.

Minimum Ignition Current Curves Since it is necessary to limit the voltage and current in an IS circuit to ensure operational safety, the design of the circuit will be based on the minimum ignition current curves given in the construction standard and reproduced on page 9. Pages 12 and 13 also illustrate the curves for determining the maximum circuit inductance and capacitance respectively. Resistive Circuits For a purely resistive circuit, if the voltage is known, the maximum circuit current can be determined from the graph, which enables selection of the correct interface. Thus, for a purely resistive circuit for operation in a IIC hazard, it is intended that a 28 V, 300 Ω zener barrier will be used. A safety factor of 10% must be applied to the voltage of this device since a rise in its temperature may raise the triggering voltage of the zener diodes. Applying the safety factors of 10% (1.1 x 28 V = 30.8 V) produces a value of 30.8 V, which is then located on the horizontal (voltage) axis of the graph. Moving vertically from this point towards the IIC curve, and then moving horizontally from the point of contact with the curve towards the vertical (current) axis, gives a safe current of 140 mA. A safety factor of 1.5 must be applied to this value, i.e. 2/3 of 140mA is equal to 93.33 mA. By applying ohm’s law, 28V/93.33 mA = 300 Ω, the same resistance as the zener barrier, it has been verified that the 28V, 300 Ω interface is suitable for maintaining the integrity of the IS circuit in a IIC hazard.

March 2010 © 9

Minimum Ignition Current Curves: Resistive Circuits

March 2010 © 10

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

THIS ENCLOSURE CONTAINS IS CIRCUITS

March 2010 © 11

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

a. Obtaining the worst case parameters from the cable manufacturer, or b. Measurement of the parameters using a sample of the cable, or c. Adoption of the following values –

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

Where field apparatus has both appreciable inductance and capacitance, it is important that the combined inductance and capacitance of the field apparatus and cables does not exceed the values specified by the manufacturer of the interface. Evaluation of Cable Parameters Inductance The maximum inductance of the interconnecting cables can be established from the inductive circuit curves after first of all evaluating the maximum source current. Assuming an interface with a maximum output of 28 V and 300 Ω resistance, the maximum source current is: 28 V/ 300 Ω = 93.33 mA Applying a safety factor of 1.5: 1.5 x 93.33 mA = 140 mA From the graph on page 13, the maximum safe inductance for the interconnecting cables, assuming connection to simple apparatus in the hazardous area, is found to be approximately 4.0 mH. This value is found by projecting vertically form 140 mA on the current axis, and then horizontally towards the inductance axis form the point of contact on the IIC curve. Capacitance For capacitance circuits, the procedure is exactly the same. A safety factor of 1.5 is applied to the zener barrier voltage of 28 V. i.e. 1.5 x 28 V = 42 V Using the IIC curve in the graph on page 13, the maximum safe capacitance for the interconnecting cables, assuming that connection is to ‘simple apparatus’ in the hazardous area, is found to be 0.08 μF approximately. Comparison of the above values with the data provided by the cable manufacturer will establish of the interconnecting cable run is satisfactory.

March 2010 © 12

Inductive Circuit Curves for Group II

March 2010 © 13

Capacitive Circuit Curves for Group II

March 2010 © 14

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

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

Note: The IS circuit in the hazardous area must be able to withstand a 500V insulation

resistance test to earth.

March 2010 © 15

Earthing and Bonding

March 2010 © 16

Earthing and Bonding

March 2010 © 17

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

a. A dedicated high-integrity earth is necessary to divert fault currents away from the hazardous area.

b. A direct connection exists between the hazardous and safe area circuits and earth, which tends to apply constraints on the rest of the system.

c. Hazardous area apparatus must withstand a 500 V insulation resistance test to earth. Devices which overcome these difficulties are isolation interfaces typically relays, opto isolators and transformers. Since there is no direct connection between the hazardous and non-hazardous areas when these interfaces are used an IS earth is not required and earthing of, for example, cable screens may be carried out at the plant/enclosure earth. Relay/Transformer Isolation In the example below, isolation between the hazardous and safe areas is achieved by means of an high integrity component approved transformer and component approved relay. The design of these devices ensures that high voltage invasion of the IS circuit will be prevented from reaching the hazardous area apparatus.

Opto-coupler/Transformer Isolation This method comprises a component certified opto-isolator and a component approved transformer. Light (or infrared) emitted from the LED when it is forward biased falls onto the phototransistor which is shielded from external light.

March 2010 © 18

Installation of IS Apparatus The apparatus which make up an IS installation, i.e. field apparatus, associated apparatus/interfaces, are required to be certified items which have been manufactured in accordance with relevant standards (see page 3). Such apparatus, including interconnecting cables, must be installed in accordance with the manufacturer’s instructions, system documentation and with regard to the recommendations in BS EN60079-14. Existing installations, however, may have been installed in accordance with the Code of Practice BS5345. Installation Requirements for Cables The conductors of IS cables are required to be insulated with elastomeric or thermoplastic insulation which has a minimum thickness of 0.3mm. The cables must be capable of withstanding 500Va.c. or 750Vd.c. test voltages between conductors and earth, conductors and screens and screens and earth. Alternatively, mineral insulated cable may be used. The conductors of cables in the hazardous area, and this includes the individual strands of finely stranded cables, must have a diameter not less than 0.1mm. Separation of the individual strands of cables must be prevented by, for example, the use of core-end ferrules. Though not a mandatory requirement, the colour of IS cables (and terminals) is light blue. Minimum Conductor Sizes Although the Code of Practice BS5345 has been withdrawn it is still relevant to existing plant and installations installed in accordance with its recommendations. The following table, taken from BS5345, specifies the maximum current and minimum cross-sectional area for copper conductors for temperature classifications within the range T1-T4 so that the cables may operate within the temperature class established for the IS system when carrying maximum current during fault conditions.

Maximum Current (A)

1.0

1.65

3.3

5.0

6.6

8.3

Minimum csa (mm2)

0.017

0.03

0.09

0.19

0.28

0.44

Mechanical Protection The interconnecting cables of an IS circuit are required to have an overall sheath in order to maintain the integrity of the system, i.e. to prevent contact with cables of other circuits, or earth, as a result of damage, and to ensure the circuit parameters in terms of inductance and capacitance are not exceeded. Armouring or screening of cables for mechanical protection is not required except for IS circuits with multi-core cables in Zone 0.

March 2010 © 19

Segregation of IS and Non-IS Circuits Segregation of IS and non-IS circuits in both hazardous and non-hazardous areas is important to avoid the possibility of higher voltages from non-IS circuits invading IS circuits. This may be achieved by any one of the following methods.

a. Adequate separation between IS circuit cables and non-IS circuit cables, or b. Positioning of the IS circuit cables such as to guard against the risk of mechanical

damage, or c. The use of armoured, metal sheathed, or screened cables for either the IS or non-IS

cables. In addition to the above requirements, cables must not carry the conductors of both IS circuits and non-IS circuits. Where IS cables and the cables of other circuits share the same duct, bundle or tray, both types of circuit must be segregated by means of an insulated or earthed metal partition. Separation is not necessary of either the IS cables or the cables of the other circuit are armoured, screened or metal sheathed. The armouring of cables should be securely bonded to the plant earth. Unused Cable Cores Where multi-core cables have one or more unused cores, either of the following termination methods may be used to maintain the integrity of the installation.

a. Connected to separate terminals at both ends so that the cores are insulated from one another and earth, or

b. Connected to the same earth point, if applicable, as used by the IS circuits in the cable, typically a zener barrier earth-bar. The unused cores at the other end of the cable, however, must be insulated from each other and earth by means of suitable terminals.

Cable Screens Where the interconnecting cables of IS circuits have overall screens, or groups of conductors with individual screens, the screens are required to be earthed at one point only, as specified in the loop diagram for the installation, which is usually the zener barrier earth bar. If, however, the IS circuit is isolated from earth, connection of the screen to the equipotential bonding system should be made at one point only. The Code of Practice BS5345 specified that, prior to connection of the screens to the barrier earth bar, an insulation resistance (IR) test should be carried out between each pair of screens. The test readings should be not less than 1MΩ/km when measured at 500V at 20°C for 1 minute. Overall screens are required to be insulated from the external metalwork, i.e. cable tray etc.

March 2010 © 20

Induced Voltage IS circuits must be installed using methods that avoid external electric or magnetic fields affecting them. Generally, induced voltage in IS interconnecting cables is not likely but may occur if the IS cables are placed parallel to and in close proximity to single-core cables carrying heavy current, or overhead power lines. Adequate segregation between the different circuits will overcome this difficulty as will the use of screens and/or twisted cores. Marking of Cables The sheath or core insulation of IS circuit cables may be coloured light blue in order that they may be easily identified as part of an IS circuit. Hence, to avoid confusion, light blue cables must not be used for other types of circuits. Marking of IS cables is not deemed necessary if either the IS or non-IS cables are armoured, screened, or metal sheathed. Where IS circuits and non-IS circuits share the same enclosure, e.g. measuring and control cabinets, switchgear, distribution apparatus, etc., appropriate measures must be implemented to distinguish between the two types of circuit, and avoid confusion where a blue neutral conductor may be present. These measures are:

a. Combining the IS cores in a common light blue harness, b. Labelling, c. Clear arrangement and spatial separation.

Multi-core Cables More than one IS circuit may be run in a multi-core cable, but it is NOT permissible for IS and non-IS circuits to be run in the same multi-core cable. The conductor insulation must have adequate radial thickness but not less than 0.2mm and be capable of withstanding an rms a.c. test voltage equal to twice the nominal voltage of the IS circuit but not less than 500V. For each IS circuit in a multi-core cable the cores are required to be adjacent to one another for the entire length of a cable. If, however, a cable has, for example, individually screened pairs, then ideally each circuit should be connected to cores from the same screen and not to cores within other screens. An exception to this applies where an IS circuit requires a triple screened cable, i.e. three cores within a screen, but a cable with screened pairs only is available. This screened pair cable may be used where two adjacent screened pairs are utilised, with the spare unused core dealt with as specified in ‘Unused cores’ on the previous page. Connection to earth of this core, if required, should be at the same point as other earthed cores in the circuit as detailed in the hook-up diagram.

March 2010 © 21

Test Requirements (multi-core cables) Multi-core cables must be capable of withstanding the following dielectric tests.

a. 500Vr.m.s (or 750Vd.c.) applied across the cores connected together and the cable screens and/or armouring connected together.

b. For multi-core cables not having screens for individual circuits, 1000Vr.m.s (or 1500Vd.c.) applied across half the cores which are connected together and the remaining cores which are also connected together.

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

Fault Conditions (multi-core cables) The type of multi-core cable used in IS installations will have an influence on faults, if any, which may be taken into consideration. Type A cable: If the IS circuits are individually screened with a minimum surface area

coverage of 60%, no faults between circuits are taken into consideration.

Type B cable: If the cable is fixed and protected against mechanical damage and none of its circuits has a maximum voltage greater than 60V, no faults between circuits are taken into consideration.

Type C cable: For this cable type, but without the requirements specified for Type A and Type B cables, two short-circuits between conductors and up to four simultaneous open-circuits of conductors have to be considered. No faults need be considered if all the circuits in the cable are identical and have a safety factor of four times that required for categories ‘ia’ or ‘ib’.

Where multi-core cables do not comply with the requirements specified in page 20, the number of short-circuits between conductors and simultaneous open-circuits of conductors has no limit. As previously stated, BS5345 has been withdrawn but is still relevant to existing plant and installations, and includes the following recommendations for multi-core cables. Where a multi-core cable, which is located in Zone 0, has more than one IS circuit, it is essential that no combination of faults between the IS circuits within the cable will cause an unsafe condition. An exemption to this requirement applies if:

a. The risk of mechanical damage to the cable is minimal or, where the risk of damage is high, additional protection is provided, and

b. The cables are firmly secured along their length, and c. Each IS circuit uses adjacent cores in the cable throughout it’s length, and d. None of the IS circuits can operate during normal or fault conditions at more than

60V peak, or e. The cores of each IS circuit are within a screen which is insulated and earthed as

previously discussed.

March 2010 © 22

Clearance Distances The clearance distance between the bare parts of cable conductors, connected to terminals, and earth or other conducting parts should not be less than 3mm. The clearance between the bare parts of cable conductors of separate IS circuits connected to terminals should not be less than 6mm. Where IS and non-IS circuits occupy the same enclosure there must be adequate separation between the two circuit types. This may be achieved by either:

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

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

terminals. The partition must reach to within 1.5mm of the enclosure walls, or maintain at least 50mm creepage between the terminals in all directions around the partition.

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

Peak Voltage

(V)

Minimum clearance in air between terminals of separate circuits

(mm)

Minimum clearance in air between terminals and earth

(mm)

0-90 6 4

90-375 6 6 Test Instruments IS electrical test instruments are available for testing installations in the presence of flammable gases. Such instruments will have output parameters not in excess of 1.2V, 0.1A, 25mW and not capable of storing more than 20μJ of energy. It must be remembered, however, there exists the possibility that the parameters, inductance and capacitance, of the circuits under test may be large enough to modify the spark energy produced at the test probes of the instruments and cause ignition of the surrounding flammable gases. Testing in the presence of flammable gases, therefore, requires careful consideration of the circuits to be tested.

March 2010 © 23

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

Grade Inspection

Check That: Detailed Close Visual A Apparatus

1 Circuit and/or apparatus documentation is appropriate to area classification * * *

2 Apparatus installed is that specified in the documentation – Fixed apparatus only * *

3 Circuit and/or apparatus category and group correct * * 4 Apparatus temperature class is correct * * 5 Installation is clearly labelled * * 6 There are no unauthorised modifications * 7 There are no visible unauthorised modifications * * 8 Safety barrier units, replays and other energy limiting devices are of


* * *

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

B Installation

1 Cables are installed in accordance with the documentation * 2 Cables screens are earthed in accordance with the documentation * 3 There is no obvious damage to cables * * * 4 Sealing of trunking, ducts, pipes and/or conduits is satisfactory * * * 5 Point-to-point connections are all correct * 6 Earth continuity is satisfactory (e.g. connections are tight and

conductors are of sufficient cross-section) *

7 Earth connections maintain the integrity of the type of protection * * * 8 The intrinsically safe circuit is isolated from earth or earthed at one

point only (refer to documentation) *


*

10 As applicable, short-circuit protection of the power supply is in accordance with the documentation *

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

C Environment

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


March 2010

24

IS Inspection Record No: A Safe Area Apparatus Apparatus Location

Cable Connection Drawing No.

Junction Box No.

Instrument Loop Drawing No.

Tag No.

Correctly labelled

No damage

Barrier or Replay or Safe Area Apparatus

Securely mounted on earth bar

Correctly labelled

Connected to correct unit and terminals

Cable Cores

Crimped OK and tight in terminal blocks

No damage Terminal Blocks Creepage and clearance OK

Date

Inspectors Initials

Comments

March 2010 ©

25

IS Inspection Record B IS Cables Location

Junction Box No.

Junction Box Connection Drawing No.


Cable No.

Segregated from Non-IS Cables

No damage IS Cables in Hazardous Areas

Properly supported

Date

Inspector’s Initials

Correctly labelled

No damage IS Cables in Safe Area

Segregated from Non-IS Cables

Cable Screen

Unused Cores

Date


March 2010 26

IS Inspection Record No: C Junction 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


Terminal blocks No damage

Creepage and clearance OK

Date


Comments:

March 2010 © 27

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 terminals

Cable Cores


No damage Terminal Blocks Creepage and clearance OK

Date


Comments:

March 2010 © 28

Inspection of IS earth system

IS Inspection Record No:

1

Check that the IS bars are correctly mounted on insulating blocks.

2

Check that the IS earth bars are firmly supported.

3

Check that the IS earth bars are protected against accidental connection to any non-IS earth (e.g. supporting rack or cubicle).

4

Check that the IS cable bars are labelled ‘IS EARTH’.

5

Check that the IS earth bars are connected together in accordance with the approved drawing.

6

Check that the cables connecting IS earth bars have the correct conductor size (refer to drawing) and an insulating sheath which is undamaged.

7

Check that the cable connections to the IS earth bars are clean and tight.

8

Check that the main IS earth bar is connected back to the sub-station or switchroom earth bar in accordance with the approved drawing.

9

Check that the cables (there should be two) connecting the main IS earth bar to the sub-station or switchroom earth bar have the correct conductor size (refer to drawing) and an insulating sheath which is undamaged along its full length and not in contact with unarmoured cables. These cables should be inspected along their entire route.

10

Check that the cable connections to the main IS earth bar and the substation or switchroom earth bar are clean and tight.

Date: Inspector’s Initials Comments:

Unit 8:

Other Methods of Protection EEx o / Ex o, EEx q / Ex q,

EEx m / Ex m & Ex s

March 2010 © 2

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.

March 2010 © 3

Other Methods of Protection Oil-immersion EEx / Ex o Oil-immersion is not a popular method of explosion protection but is typically used for heavy duty transformers and switchgear. Standards

BS EN50 015: 2005 Oil immersion ‘o’

BS 5501-2: 1977 Oil immersion ‘o’

IEC 60079-6: 2007 Oil-immersed apparatus

BS 5345: Part 9 *

Installation and maintenance requirements for electrical apparatus with type of protection ‘o’ oil-immersed apparatus

* Since BS EN60079-14 and BS EN60079-17 do not provide selection, installation,

inspection and maintenance requirements for oil-immersed apparatus, BS 5345: Part 9 remains the only reference for guidance in these areas for the present.

Definition The definition for this type of protection is: ‘A type of protection in which the electrical apparatus or parts of the electrical apparatus are immersed in protective liquid in such a way that an explosive atmosphere, which may be above the liquid or outside the enclosure, cannot be ignited.’

Breathing device

Oil-level indicator

Drain plug

Oil-filling point

March 2010 © 4

EPL: Gb Zones of Use: 1 & 2 Principle The oil level is used to completely cover the components within the apparatus which arc/spark or produce hot surfaces during normal operation, thereby effectively establishing a barrier between the components below the oil and any flammable gases which may be present above the oil or outside the enclosure. A particular advantage of this method of protection is that circulation of the oil, by convection, enables hot-spots to be dispersed.

One function of the oil is to quench arcs occurring at the contacts and, where mineral oil is used, a by-product of this process is the production of hydrogen and acetylene. This condition was considered to be undesirable for apparatus intended for use in hazardous locations, which may explain why, until recently, its use was limited to Zone 2 in the UK. The revised standards, however, have stricter specifications and this type of protection is now permitted in Zone 1. Construction The construction standard requires a breather to be fitted to the apparatus to allow release of the flammable gases produced during arc quenching, and thereby preventing the build-up of these gases in the space above the oil, whilst simultaneously preventing the ingress of dust or moisture, and hence, contamination of the oil. The enclosure ingress protection will be IP66.

It is also a requirement that the apparatus is fitted with a gauge which can display the highest and lowest levels of oil, and that the apparatus is installed in such a way that the gauge can be easily read while the apparatus is in service. In the event of breakage of the gauge, even at it’s lowest point, the minimum depth of oil remaining above the arc/heat producing components, after leakage of oil at this point, should be not less than 25 mm.

The standard specifies unused mineral oil which complies with IEC 60296 for the protective liquid, but other types may be used, e.g. unused silicone insulating liquids. Silicone liquids are required to have specific properties, which include:

a) a minimum fire point of 3000C in accordance with the test method given in HD 565 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 with

IEC 60588-2 (Note: reference to this standard is for the test method only and not to permit the use of materials banned by legislation.)

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

March 2010 © 5

Construction (continued) A label indicating the maximum and minimum levels of the protective liquid must be visible, which take into account level variations due to expansion/contraction of the protective liquid over the entire ambient temperature range. The free surface temperature of the protective liquid is required to be 25 K less than the specified minimum flashpoint for the protective liquid. Internal and external fasteners, fluid level indicators and parts for filling and draining the protective liquid including plugs must have measures applied to prevent them becoming loose. Such measures include:

a) locking washers; b) cementing of threads; c) wiring of bolt heads.

Sealed enclosures are required to be fitted with a pressure-relief device, and non-sealed enclosures with an expansion device which incorporates a mechanism for automatic tripping of the electrical supply on detection of gas evolution from the protective liquid as a result of a fault within the enclosure. The trip mechanism may only be manually reset.

March 2010 © 6

Powder Filling EEx q / Ex q The explosion protection concept powder filling is not widely used and typical applications are, for example, capacitors in Increased Safety Ex ‘edq’ lighting fittings, and telecommunications equipment in some European countries. Standards

BS EN60079-5: 2007 Powder filling ‘q’

BS EN50017: 1998 Powder filling ‘q’

BS 5501-4: 1977 Powder filling ‘q’

IEC 60079-5: 2007 Sand-filled apparatus

BS 5345: Part 9 *

Installation and maintenance requirements for electrical apparatus with type of protection ‘q’ sand filled apparatus

* Since BS EN60079-14 and BS EN60079-17 do not provide selection, installation,

inspection and maintenance requirements for powder-filled apparatus, BS 5345: Part 9 remains the only reference for guidance in these areas for the present.

Definition The definition for this type of protection is: ‘A type of protection in which the parts capable of igniting an explosive atmosphere are fixed in position and completely surrounded by a filling material to prevent the ignition of an external explosive atmosphere.’

EPL: Gb Zone of Use: 1 & 2

Source of ignition , e.g. (capacitor)

Powder filling

March 2010 © 7

Principle The filling, which may be quartz or glass particles, achieves safety by what is known as “suppression of flame propagation”. It is inevitable that a flammable gas or vapour may permeate the granules and reach the parts producing arcs/sparks or hot surfaces. The quantity of gas or vapour, however, will be too small to support an explosion within the inert powder. The depth of granules is influenced by the level and duration of the of the arc current produced by the components within the filling material, and tests specified in the construction standard enable a safe correlation between these two parameters to be established. This method of protection is suitable for use in all group II gases or vapours. Construction The minimum ingress protection for this type of protection is IP54, but apparatus constructed to provide IP55 must be fitted with a breathing device. Where use is in clean, dry environments only, the ingress protection must be at least IP43, which requires the apparatus to be marked with the suffix ‘X’. The size of granules for the filling material must be in accordance with the sieve limits specified in the standard ISO 565. The upper limit for the granules may be achieved using a sieve manufactured from metal wire cloth or a perforated metal plate with a nominal perforation size of 1 mm. For the lower limit, metal wire cloth with a nominal perforation size 0.5 mm may be used. The filling material is required to withstand an electric strength test where the leakage current must not be in excess of 10-6A. The minimum clearance distances between electrically conducting parts and insulated components or the inner surface of the enclosure wall are given below.

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

Minimum distance mm

U < 275 5

275 < U < 420 6

420 < U < 550 8

550 < U < 750 10

750 < U < 1000 14

1000 < U < 3000 36

3000 < U < 6000 60

6000 < U < 10000 100

Components having a free volume less than 3 cm3, for example relays, which are surrounded by the filling material, must have minimum clearance distances between the component and the inner wall of the enclosure in accordance with the table above. For free volumes in the range 3 cm3 - 30 cm3 the above distances apply but should not be less than 15 mm.

March 2010 © 8

Encapsulation EEx / Ex m The method of protection, encapsulation, is used mainly for smaller items of equipment such as solenoid coils and electronic components. Standards

BS EN60079-18: 2004 Encapsulation ‘m’

EN50 028: 1987 Encapsulation ‘m’

BS 5501-8: 1987 Encapsulation ‘m’

IEC 60079-18: 2009 Encapsulated apparatus

Definition The definition for this type of protection is: ‘A type of protection whereby parts that are capable of igniting an explosive atmosphere by either sparking or heating are enclosed in a compound in such a way that the explosive atmosphere cannot be ignited under operating or installation conditions.’

March 2010 © 9

Levels of protection: ma Encapsulated apparatus having a level of protection ‘ma’ must not be capable of

causing ignition during the following situations:

i) in normal operation and installation conditions; ii) any specified abnormal conditions; iii) in defined failure conditions.

mb Encapsulated apparatus having a level of protection ‘mb’ must not be capable of

causing ignition during the following situations:

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

mc No information at time of writing. EPL’s: ma - Ga

mb - Gb mc - Gc

Zone of Use: ma 0, 1 & 2

mb 1 & 2

mc 2

Principle With this type of protection, the encapsulant, typically a thermosetting, thermoplastic, epoxy resin or elastomeric material, establishes a complete barrier between any surrounding flammable gas or vapour and the source of ignition within the compound. Construction The construction standards state that the encapsulant must be free of voids and, therefore, this method of protection is unsuitable where components have exposed moving parts. Very small components which have enclosed moving parts, e.g. a reed relay, may be protected by encapsulation. Encapsulated apparatus may be manufactured with one of two protection levels, i.e. ‘ma’ or ‘mb’. Switching contacts, however, are not permitted in protection level ‘ma’. Encapsulation with the level of protection ‘ma’ must not have an operating voltage in excess of 1 kV and be incapable of causing ignition during:

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

March 2010 © 10

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

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

The encapsulant must be capable of remaining intact during electrical input variations in the range 90% - 110% of the specified rating, adverse load conditions and any internal electrical fault. The apparatus is required to remain safe with one internal fault for the level of protection ’mb’ and two faults for the level of protection ‘ma’. This applies to a short-circuit occurring in any component, failure of any component, or a fault in the printed circuit boards. Minimum clearance distances within the encapsulant will be dependent on the construction of the apparatus, i.e. within a metallic enclosure which is either closed or unclosed on all sides, or has 100% free surface area. As these requirements are extensive, the table below shows some of the applicable distances for apparatus with 100% free surface area.

Protection level ma mb

Free surface < 2 cm3 > 1 mm * > 3 mm

Free surface > 2 cm3 > 3 mm *

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

March 2010 © 11

Special Protection Ex s Apparatus which has not quite met the requirements of a particular construction standard will have been additionally certified under the BASEEFA Standard ‘Special Protection Ex s’ provided it had been established that, after close scrutiny of the design and testing of the apparatus, it was capable of operating safely in the hazard for which it was designed. Special Protection is not included in the BS EN500 or BS EN600 series of harmonised construction standards, or in the installation, inspection and maintenance series of standards, BS EN60079-14 and BS EN60079- 17 respectively. Standards

SFA 3009 Special protection

BS 5345: Part 8

Installation and maintenance requirements for electrical apparatus with type of protection ‘s’ special protection

Zones of Use: 0, 1 & 2 Principle The constructional requirements of this standard, in terms of test and acceptance criteria, were intended to be unspecific in order to allow a broad range of designs to be considered for certification. Because apparatus may be of unorthodox design, the experience of test-house staff plays an important part in contriving appropriate tests and acceptance criteria. Special protection is not an easy option for obtaining certification for apparatus not quite meeting the requirements of a given standard, nor is this type of protection inferior to other more popular methods of explosion protection. Indeed the tests on apparatus presented for certification under Special Protection are likely to be more onerous than the tests for other types of explosion protection. A hand torch is a typical example of apparatus certified under Special Protection. Thorough testing will have established that the construction is robust enough to withstand a specified impact without causing, for example, a short-circuit of the battery, and breakage of the bulb, its holder and the glass cover are unlikely. A further requirement is that opening of the torch, i.e. to replace the battery, is only possible with the aid of a special tool, which is required to be kept in a non-hazardous area. Another known example of apparatus certified under Special Protection Ex s is a 6.6 kV poly-phase cage induction pump motor in which the method of explosion protection is basically dependent on the interior of the motor being completely filled with water. Any free space within the motor is occupied by water, and hence, the entry of a flammable gas is prevented. Clearly, it is imperative that the interior of the motor remains completely full of water at all times, and this is ensured by a header tank to compensate for expansion due to thermo-cycling. The motor, which drives a pump, is intended for use in Zone 1.

Unit 9:

Combined (Hybrid) Methods of Protection

March 2010 © 2

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

a. The advantages of combining two or more methods of protection in apparatus. b. The installation requirements according to BS EN 60079-14. c. The inspection requirements according to BS EN 60079-17.

March 2010 © 3

Combined (Hybrid) Methods of Protection Electrical equipment may be manufactured with more than one method of explosion protection. Equipment of this type has combined methods of protection but may also be known as a hybrid. Such an approach combines the best features of each type of protection into one piece of equipment for both economic and practical purposes.

A traditional push-button station for use in an hazardous location comprises a flameproof EEx d or Ex d enclosure, in which a standard industrial switch is fitted. An alternative to this arrangement is an Increased Safety EEx e or Ex e enclosure with a small flameproof EEx d or Ex d component certified switch fitted inside. Because the switch produces sparks in normal operation, clearly it has to be flameproof to comply with the Increased Safety concept of protection. Such equipment will be marked EEx ed, Ex ed, EEx de or Ex de.

The advantages of the hybrid arrangement over the traditional flameproof method are:

a. Lower cost and weight, b. Glanding arrangements are simplified, c. Minimum ingress protection IP54 but may be as high as IP66

Ignition by sparking components contained within flameproof enclosure

EEx d

Ignition by sparking contacts contained within the ‘small volume’ EEx d or Ex d switch EEx e / Ex e

l

March 2010 © 4

Standards Hybrid apparatus may be constructed using any combination of the various methods of explosion protection and, therefore, the apparatus will be marked with the symbolic letters and construction standard numbers relative to the types of explosion protection used. Probably the most commonly used combination involves ‘d’ and ‘e’ types of apparatus, and so the table below shows these standards only. The full list of standards can be found in Unit 2. Hybrid apparatus must also be installed and maintained in accordance with relevant standards.

BS EN60079-1: 2007 Flameproof enclosures ‘d’

BS EN50 018: 2000 Flameproof enclosure ‘d’

BS 5501-5: 1977 Flameproof enclosure ‘d’

BS EN60079-7: 2007 Increased safety enclosure ‘e’

BS EN50 019: 2000 Increased safety enclosure ‘e’

BS 5501-6: 1977 Increased safety enclosure ‘e’



Motors – EEx de / Ex de

March 2010 © 5

Motors – EEx de / Ex de Manufacturers also produce electric motors in which there are combined methods of protection. The main body of the motor will be flameproof EEx d or Ex d and the terminal box increased safety EEx e or Ex e. An alternative terminal plate is fitted to a motor of this type to accommodate special terminals which are screwed into the terminal plate. These are hybrid terminals, i.e. they employ both flameproof and increased safety features in their construction.

EEx de / Ex de Motor Terminal Box To achieve the required level of ingress protection, gaskets are fitted between the terminal box and its cover, between the terminal plate and box, and between the gland plate and terminal box. On no account, however, should a gasket be fitted between the terminal plate and the frame of the motor as this joint is a flamepath. It must be emphasised that, on some motors, the increased safety terminal box looks very much like a flameproof box in terms of its construction. This likeness means that there is a possibility that personnel unaware of this concept may remove the gaskets and, therefore, it is important that certification labels are studied before any work is carried out. Removal of the gaskets in an attempt to return the box to its assumed status, i.e. flameproof, would be an unauthorised modification which would invalidate the certification. Cable gland selection As already mentioned in unit 4, the requirements for cable glands entering Ex e equipment, and in this instance the Ex e terminal box of a type de motor, as specified in BS EN60079-14: 2003, states that cable glands must maintain the type of protection and ingress

1. Terminal box cover and screws

2. Gasket 3. Certified cable glands 4. Gland plate 5. Increased Safety

terminals 6. Terminal plate 7. Terminal box and screws

March 2010 © 6

protection of the equipment, and meet the impact test requirements. The inference here would appear to suggest that provided uncertified cable glands were manufactured to BS6121 their use would be acceptable with Ex e equipment. This of course does not apply to uncertified plastic cable glands. The introduction of the latest standards, however, has effectively removed this option by virtue of the requirement for revised ‘seal aging’ tests involving repeated heating and cooling cycles, which is now a requirement for all cable glands as detailed in IEC 60079-0 The latest issue of IEC 60079-14: 2007 now requires all cable glands to be certified or approved by the manufacturer. EEx de – Sample Certification Label – ( pre ATEX ) Ex de – Sample Certification Label – ( ATEX )

II 2 G

Ex de IIB T4 Duty S1 No. E956732 Ins. cl F IP55

V Hz kW r/m cosφ 440 60 37 1760 0.8

LCIE 07ATEX599X

0081

IEC 60034-1

March 2010 © 7

Lighting Fittings – EEx edq / Ex edq The lighting fitting illustrated below employs three protection concepts, i.e. increased safety type ‘e’, flameproof type ‘d’ and powder filing type ’q’. This type of fitting is widely used in the petro-chemical industry.

The constructional features are:

1. Flameproof mono-pin lamp holder’s; 2. Increased safety choke designed not to overheat if the lamp fails; 3. Temperature rating based on internal and external surface temperatures; 4. Enclosure sealing providing high ingress protection;

5. Increased safety enclosure including glands designed to withstand specified impact.

In this lighting fitting, the circuits include capacitors which are protected by a method of protection, powder filling type ‘q’. Switches will be flameproof type ‘d’ construction and terminals will be increased safety type ‘e’. Lamps for Ex e, (and also Ex n), luminaries, which have mono-pin, bi-pin or screw connections where the caps are made from non-conductive material with a conductive coating, are not permitted unless tested with the equipment.

March 2010 © 8

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

EEx e enclosure

March 2010 © 9

EEx pde / Ex pde Enclosures using the protection concept, pressurisation type ‘p’, may have internal apparatus which have to remain energised in the absence of overpressure. Such apparatus must be protected in accordance with the Zone in which the enclosure is located. A typical example is an anti-condensation heater within a pressurised machine which will be energised when the machine is idle. Apparatus out with the machine, e.g. junction boxes, pressure sensors etc., will also have to be protected in accordance with the Zone. Note: Since anti-condensation heaters are normally ‘live’ when a machine is idle, a notice warning of this danger should be displayed.

EEx pi / Ex pi The part(s) of an IS system which are marked to indicate that they should be installed in a non-hazardous area may be used in a hazardous area if installed in, for example, a pressurised enclosure as illustrated below.

Unit 10:

Wiring Systems

March 2010 © 2

Objectives: On completion of this unit, ‘Wiring systems’, you should know:

a. Appropriate cable types for use with explosion protected apparatus.

b. The selection procedure for cable glands by consideration of ‘Zone’, ‘Gas Group’, ‘volume’, ‘method of entry’, ‘cable construction’ and’ ‘internal components’ of flameproof enclosures.

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

d. Recognised practices for terminating single and multiple pair cables with or without

screens.

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

f. Earthing requirements in hazardous areas.

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

h. The knowledge and skills requirements for technicians (operatives) undertaking the

selection and erection of explosion protected equipment in hazardous areas.

March 2010 © 3

Wiring Systems Electrical equipment in hazardous areas may be wired using cable having metallic or non-metallic sheath, or conduit. The use of cable is generally predominant mainly for it’s ease of installation compared to conduit. With regard to conduit, one of it’s disadvantages, particularly on offshore installations, is it’s susceptibility to corrosion as a result of exposure to a salt-laden atmosphere. Deterioration due to corrosion can occur relatively quickly and, as a consequence, can reduce the strength of the conduit. This is undesirable particularly where conduit is the method of entry to a flameproof enclosure because of the possible inability of the conduit to contain an internal explosion in the run of conduit between the enclosure and the sealing device. Furthermore, corroded conduit may not meet the impact resistance requirements essential for use with Increased Safety apparatus.

Standards

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

IEC 60079-14: 2007 Explosive atmospheres - Part 14: Electrical installations design, selection and erection

BS EN50262: 1999 Metric cable glands for electrical installations

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

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

March 2010 © 4

Cables Cables for use in hazardous areas are not certified but are required to be constructed from materials as specified in BS EN60079-14 and constructed to relevant standards so that, providing the cable has been correctly installed, failure is unlikely. A typical standard for the manufacture of cables for marine, offshore mobile and fixed platforms is BS 6883. The selection of cables is important with regard to their performance in a fire and important considerations include fire survival, fire resistance, fire retardancy, fire propagation, toxicity and smoke emission. Thus, in circuits essential for safety the cables installed are required to operate in a fire for a specified time. Cables may also be manufactured from materials, typically polymer compounds that produce lower smoke and fume emissions during a fire. Cables with this capability will be identified as halogen free, low smoke & fume (LSF), low smoke zero halogen (LSZH), or zero halogen low smoke (ZHLS). Fixed apparatus in zones 1 and 2 Cables for fixed apparatus in hazardous areas are required to be manufactured from thermoplastic, thermosetting, elastomeric or mineral insulating materials. The cables should be suitable for the ambient conditions where used, be circular, compact, have extruded bedding and any fillers should be non-hygroscopic. Cables commonly used in the industry are of the EPR/CSP type (see diagrams on page 5). Mineral insulated metal sheathed (MIMS) cable is also suitable for use in hazardous areas, but it’s aluminium variation requires careful consideration before use.

Aluminium conductors, except those for IS or energy-limited installations, must only be connected to suitable terminals and have a cross-sectional area (c.s.a.) not less than 16 mm2. Examples of the various cable insulation types are given in the table below.

chlorosulphonated polyethylene CSP

cross-linked polyethylene XLPE

ethylene propylene rubber EPR

ethylene vinyl acetate EVA

natural rubber NR

polychloroprene PCP

Elastomeric

silicone rubber SR

polyethylene PE

polypropoline PP

Thermoplastic

polyvinyl chloride PVC

Portable and transportable apparatus in zones 1 and 2 Portable and transportable electrical apparatus may be wired using cables having a heavy polychloroprene or alternative equivalent synthetic elastomeric sheath, or a heavy tough

March 2010 © 5

rubber sheath, or manufactured from materials providing equally robust construction. The minimum cross-sectional area for such cables is 1.0mm2. Where the voltage to earth and current of portable electrical apparatus does not exceed 250V and 6A respectively, cables having an ordinary polychloroprene or alternative equivalent synthetic elastomeric sheath, or a heavy tough rubber sheath, or manufactured from materials providing equally robust construction may be used. The sheath of flexible cables may be manufactured from ordinary tough rubber, ordinary polychloroprene, heavy tough rubber, heavy polychloroprene, or plastics providing the equivalent strength to heavy tough rubber. Elastomeric Cables Elastomeric cables comprising EPR insulated conductors, CSP inner and outer sheath, which are heat and oil resistant and flame retardant (HOFR). Operating temperature range 30 °C - 90 °C.

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

March 2010 © 6

Cables (continued) Cables may also be selected with consideration to their fire resistant and/or flame retardant properties, and two standards are relevant in this respect. IEC 60331 (Fire resistant): A cable manufactured in compliance with this standard will

continue to operate in a fire without disruption of essential circuits and emergency circuits.

IEC 60332 (Flame retardant): A cable manufactured in compliance with this standard is

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

March 2010 © 7

Requirements for Cables and Glands Cable glands must be selected with due regard to the methods of explosion protection employed and also environmental conditions. The requirements for cable glands include:

(a) to firmly secure the cable entering the apparatus; (b) to maintain the ingress protection of the apparatus; (c) to maintain earth continuity between the apparatus and any armouring in the

cable; (d) to ensure containment of an internal explosion in flameproof apparatus; (e) to maintain the integrity of ‘restricted breathing’ apparatus.

Glands for Mineral Insulated Cables Cable glands for use with MICC (Mineral Insulated Copper Cable) or MIMS (Mineral Insulated Metal Sheath) cable for use in hazardous areas will be marked Ex d. This gland, however, may be used as a means of entry to Increased Safety apparatus providing an alternative Ex e seal is used. This seal is specially constructed to comply with the requirements for Increased Safety apparatus as illustrated by the diagrams below. Seal Assemblies It will be observed from the Ex e seal assembly illustrated in the lower diagram that the ‘headed PTFE sleeving’ passes through the holes in the stub cap. This arrangement ensures that creepage/clearance distances are maintained within the seal. The compound used within the Ex e seal assembly was previously required to be doublebond non-metallic black epoxy putty 1536, with the Component Certificate for this seal containing a ‘schedule for conditions of use’. Current specifications, however, allow use of the same compound for both Ex d and Ex e applications. Difficulty may be experienced in achieving the desired level of ingress protection with MICC/MIMS cable glands due to the very small shoulder on the gland body, and may be overcome by the use of hard plastic washers manufactured for this purpose.

Ex d type seal

Ex e type seal

March 2010 © 8

Selection of Cable Glands The correct selection of cables and glands, particularly for flameproof apparatus, is very important since there are a number of factors which can jeopardise the integrity of this type apparatus. As previously discussed the cable construction, ingress protection, earth continuity and secureness of the cable entering the apparatus must be maintained. An additional consideration is electrolytic action caused by contact between dissimilar metals, which results in increased corrosion and premature degradation of glands and cable entries. Cable glands with a suffix ‘X’ in the certificate number may only be used in fixed installations and not on portable or transportable equipment. The ‘special installation conditions’ specified in the certificate for the cable gland may require that a clamp is fitted within 300mm from the end of the gland to avoid twisting or pulling of the cable and hence unnecessary stress on the terminals inside the equipment. For portable and transportable equipment cable glands without the suffix ‘X’ should be used. Flameproof equipment Since an explosion is permitted within flameproof equipment it follows that the cable glands used must be capable of maintaining the integrity of the equipment. Such glands will be capable of resisting the force of an internal explosion by virtue of their strong construction, flamepaths where applicable and also compression, diaphragm, or compound filled seals. The type of cable gland used will be selected from consideration of the six points listed below which take into consideration the strength of an internal explosion.

1. Does the cable have filled interstices? 2. Is the enclosure direct or indirect entry? 3. Does the enclosure contain a source of ignition? 4. What is the gas group of the apparatus? 5. In what zone is the apparatus is installed? 6. What is the internal volume of the enclosure?

These considerations are addressed in the flowchart on page 10. Note: The standard specifying the constructional requirements for cable glands, BS6121,

now replaced by BS EN50262, uses certain references numbers to identify their function. For example, a cable gland for use with unarmoured cable is allocated the reference ‘A2’. The reference ‘E1’ is used to identify a cable gland for use with armoured cable. Wire armour will be identified by a ‘W’ and ‘F’ indicates flameproof. So the reference for a flameproof gland for use with wire-armoured cable will be E1FW.

March 2010 © 9

Direct Entry Method (Flameproof Ex d)

a) Flameproof Ex d / EEx d Indirect Entry Methods

b. Flameproof EEx d / Ex d

c. Flameproof I Increased Safety EEx de / Ex de

March 2010 © 10

Maintaining Ingress Protection at Cable Gland Entries The cable gland selected, as the means of entry to an enclosure, must suit the cable used and, for type ‘e’ or type ‘n’ enclosures, where the ingress protection will be at least IP54 or greater, the cable gland must maintain the ingress protection of the enclosure. Where such enclosures have unthreaded entries IP sealing washers will be necessary. Where enclosures have threaded entries the requirement for an IP sealing washer will depend on the wall thickness in order to maintain a minimum of IP54. If the wall thickness is less than 6mm, an IP sealing washer (or thread sealant) is necessary to maintain IP54, but if the wall thickness is 6mm or greater an IP washer (or thread sealant) is deemed not necessary to maintain IP54 unless a greater ingress protection level is required. For flameproof enclosures, a sealing washer may be fitted between the cable gland and the wall of the enclosure to improve the ingress protection providing the thread engagement is maintained, i.e. five full threads or 8mm, whichever gives the greater engagement. Cable Gland Selection for Flameproof Apparatus Cable glands for use with flameproof enclosures may be selected by following the procedure recommended in BS EN60079-14 as detailed below. The method of entry must be in compliance with one of the following: (a) A cable entry device, which meets the requirements of IEC 60079-1, certified as part

of the flameproof enclosure when tested with a section of the cable intended to be used.

(b) A flameproof cable entry device in which a sealing ring is an integral part of the

construction and used with cables manufactured from thermoplastic, thermoseting or elastomeric materials. The cable must be compact and circular, have extruded bedding and have non-hygroscopic fillers in the case of a filled cable. Selection of the cable entry device to be in accordance with the flow chart illustrated on page 11.

(c) Mineral insulated cable and a suitable flameproof cable entry device. (d) Flameproof stopping box or sealing chamber, which are either specified in the

apparatus certification document or have component approval, having cable entry devices suitable for the cables intended for use. The compound or seals in these devices are required to provide sealing around the individual cable cores. The stopping box or sealing chamber must be fitted to the apparatus at the cable entry.

(e) Flameproof entry devices, typically barrier glands, with compound filled seals or

similar arrangements which seal around the individual cores of the cable; (f) Alternative methods designed to maintain the integrity of the flameproof apparatus.

March 2010 © 11

Cable gland selection for flameproof apparatus (continued) The flowchart below, taken from BS EN60079-14, may be used to determine the most suitable type of cable gland for entry to flameproof apparatus. Application of 10.4.2 requires the use of either a flameproof compound filled sealing device in which the compound provides ‘stopping’ around the individual cores of the cable, or a flameproof gland where ‘stopping’ around the individual cores of the cable is achieved by either compound or elastomeric seals.

Start

Does this enclosure contain an internal source of ignition?

Does the hazardous gas require IIC apparatus?

Is the area of installation Zone 1?

Use a suitable cable entry device with a sealing ring

Is the volume of the enclosure greater than 2 dm3?

Apply 10.4.2

(d) or (e)

Ye

Yes

Yes

Yes

No

No

No

March 2010 © 12

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

March 2010 © 15

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

March 2010 © 20

Conduit The use of conduit in hazardous areas requires particular care, especially when used with flameproof enclosures. In addition to maintaining the ingress protection (IP) rating of an enclosure - this applies to all types of protection - the integrity of the enclosure must be maintained, i.e. the conduit in the run between the enclosure wall and the conduit sealing device must also be able to withstand the force of an explosion within the enclosure so that the flames/hot gases are prevented from reaching the external atmosphere. Where two flameproof enclosures are connected by means of conduit, seals must be fitted to avoid pressure piling occurring during an internal explosion. Sealing devices are also used to prevent the migration of gases from one hazardous location to another. Although not entirely gas-tight, they will limit, to an acceptable level, the quantity of gas which will pass at normal atmospheric pressure. Where positive or negative pressures are likely, appropriate measures must be implemented. Appropriate installation practices must, therefore, be observed and this requires observation of the manufacturer’s installation specification and the recommendations given in BS EN60079-14. Selection of conduit Conduit used with explosion protected apparatus will be that recommended by the manufacturer and selected from either:

(a) screwed, heavy gauge steel, solid drawn or seam welded conduit; or (b) flexible conduit of metal or composite material construction, for example metal

conduit with a plastic or elastomer jacket, of heavy or very heavy mechanical strength classification manufactured in accordance with ISO 10807.

Note: The current issue of BS EN60079-14: 2003, in contrast to the 1997 issue,

specifies that conduits as detailed above manufactured to IEC 60614-2-1 and IEC 60614-2-5 are unsuitable for protecting cables connected to flameproof apparatus. Reference to national or other standards should be sought in this instance.

Conduit entering flameproof enclosures is required to be engaged by 5 full threads. Sealing of conduit Stopper boxes must be fitted where conduit leaves or enters an hazardous area. Where conduit is used with flameproof enclosures containing a source of ignition, stopping boxes are required to be fitted as close to the enclosure wall as possible, or not more than 50mm from the enclosure wall to limit pressure piling. Alternatively, the manufacturer may fit a stopping box in the enclosure as part of the certified design of the enclosure

March 2010 © 21

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

Maximum surface area mm2

Location EPL requirement IIA location IIB location IIC location

Ga 5000 2500 400

Gb 10000 10000 2000

Gc 10000 10000 2000

The dimensions in the above table may be increased by a multiple of 4 if the non-metallic material is surrounded by a conductive earthed frame.

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The knowledge and skills of technicians (operatives) Selection and erection Technicians, or operatives as they are called in the standard, are required to have sufficient knowledge to achieve the correct selection and erection of explosion protected equipment in hazardous areas. This knowledge, which includes the basic requirements for safe work in hazardous areas, also includes:

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

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

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

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

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

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

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

Competency Furthermore technicians (operatives) are required to provide evidence of their competency in the areas specified immediately above. In addition, documentary evidence of competency in respect of the following:

(a) the use and availability of documentation;

(b) the compilation of job reports to the user/operator;

(c) the practical skills required for the preparation and installation of the various types of explosion protection;

(d) use and compilation of installation records. Assessment The 2008 issue of BS EN60079-14 specifies that those persons, i.e. Responsible Persons, Operatives (Technicians) and Designers, involved in work in, or associated with, hazardous locations are required to provide evidence of competence in accordance with national regulations, standards, or user requirements. The person is required to provide evidence that he/she:

(a) has the necessary skills required for the scope of work;

(b) can act competently across the specified range of activities;

(c) has the relevant knowledge and understanding underpinning competency.

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Electrical Isolation Safe work on electrical equipment can only be achieved by ensuring the equipment is properly isolated by means of isolators, fuses or links. The means of isolation applies to the circuit and neutral conductors of each circuit or group of circuits. In order to enable speedy identification, clear labelling should be positioned in close proximity to the means of isolation. Fault finding The tracing of electrical faults in explosion protected equipment, which involves the use of test instruments, may be possible when gas-free conditions are verified through continual monitoring or the issue of a gas-free certificate. IS Cable Requirements

The requirements for IS cables will be specified in the system documentation. Cables need not be mechanically protected since the energy in an IS circuit is below that which is necessary to ignite a flammable mixture, even if a spark is produced at a break in the cables.

Non-hazardous Hazardous

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IS Cable Requirements

1. Insulation between screen and SWA or braid.

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

3. Individual insulated conductors.

4. SWA or braid (optional) - normally earthed at each end, and at any intervening

junction boxes through the cable glands.

1 2 3 4


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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


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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.


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Earthing and bonding The principal reasons for earthing and bonding in electrical installations are:

1) to eliminate the possibility of electric shock to personnel; 2) to enable protection devices to operate correctly so that the duration of fault

currents are kept to a minimum;

3) to equalise the voltage potential of normally non-current carrying metalwork;

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

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Types of systems

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

(b) TT A system in which one point of the source of energy is directly

earthed but which is electrically independent of the electrodes used to earth the exposed conductive parts of the electrical installation.

(c) TN-C A system in which a single conductor serves as both neutral

and protective conductor throughout the system. (d) TN-C-S A system in which a single conductor serves as both neutral

and protective conductor in part of the system. (e) IT A system in which there is no direct connection between live

parts and earth but exposed conductive parts of the electrical installation are earthed.

Classification of systems A system comprises an electrical supply to which an electrical installation is connected. The first letter indicates the supply earthing arrangements where:

1) T represents a system having one or more points of the supply directly connected to earth;

2) I represents a system in which the supply is not earthed, but may be earthed

through a fault-limiting impedance. The second letter indicates the installation earthing arrangements where:

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

4) N represents the exposed conductive parts of the installation which are

connected directly to the earthed point of the supply. The third letter indicates the earthed supply conductor where:

5) S represents separate neutral and protective conductors; 6) C represents neutral and protective conductors combined in a single

conductor.

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System earthing configurations (a) TN-S

Generally, this method will be used when the electrical supply is provided via underground cables having metal sheaths and armour. The consumer’s earth terminal will be connected to the supply authorities protective conductor, that is the metal sheath and armour of the underground cable, thereby establishing a continuous path back to the supply transformer star-point which is earthed.

(b) TT

Generally, this method will be used when the electrical supply is provided via overhead cables but with no earth terminal provided by the supply authority. The consumer may have to provide an earth electrode for connection of the circuit protective conductors. With this system, it is recommended that consumers use residual current devices because of the difficulty in obtaining an effective earth connection.

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(c) TN-C

In this system the same conductor, perhaps the outer conductor of a concentric cable, is used for both the neutral and circuit protective conductor (PEN conductor) throughout the system. It is typically used where the electrical supply is provided by a privately owned transformer or converter, i.e. where there is no electrical connection between the consumer and the supply authority, or where the supply is provided by a private generator.

(d) TN-C-S

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

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(e) IT

In this arrangement the system may have no connection to earth, or be connected to earth via a relatively high impedance, the ohmic value of which will depend on the level at which fault currents will be limited. Protection in this method is afforded by a relay which monitors any earth-leakage current as a result of an earth-fault. This will activate an audio or visual alarm, or disconnect the electrical supply.

Regulations and standards The requirements for earthing practice within the UK may be found in the following documents.

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

BS 5345 ( withdrawn )

Code of practice for: Selection, installation and maintenance of electrical apparatus for use in potentially explosive atmospheres (other than mining applications or explosive processing and manufacture)

BS 7671: 2008 IEE Wiring Regulations

IEE Recommendations for the Electrical and Electronic Equipment of Mobile and Fixed Offshore Installations

Electricity Supply Regulations 1988

Electricity at Work Regulations 1989

BS 7430: 1998 Code of Practice for Earthing

BS 6651: 1999 Protection of Structures against Lightning

PD CLC/TR 50404: 2003 Electrostatics – Code pf practice for the avoidance of hazards due to static electricity

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

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Earthing systems in hazardous areas BS EN60079-14 specifies the conditions of use for the following earthing systems in hazardous areas. The conditions apply to electrical installations, except IS circuits, in zones 1 and 2 up to 1000Vac(rms) / 1500Vdc. In the absence of harmonised requirements for installations operating above these voltages, national requirements should be observed.

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

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Maximum Disconnection Times for TN Systems Table 41A

U0 (volts) t (seconds)

120 0.8

220 to 277 0.4

400 0.2

greater than 400 0.1

Where U0 = Nominal voltage

Earthing conductor cross-sectional area Calculation of csa The cross-sectional area of earthing conductors may be calculated using the following formula from the 16th Edition of the I.E.E. Wiring Regulations, BS7671.

k

t2IS =

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

I = fault-current for a negligible impedance fault that will flow through the associated protective device (the current-limiting effect of circuit impedance’s and limiting capacity (I2t) of protective device will be taken into account. A further consideration is the increase in resistance of the conductors as a result of the temperature rise during clearance of the fault.

(A)

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

(secs)

k = factor which takes into account resistivity, temperature coefficient and heat capacity of conductor material, and the appropriate initial and final temperatures.

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

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CSA of CPC in relation to phase conductor Alternatively, the minimum cross-sectional area of the protective conductor, in relation to the cross-sectional area of the associated phase conductor, may be determined by consideration of table 54G shown below. Table 54G Minimum CSA of protective conductor in relation to the CSA of associated phase conductor.

Minimum CSA of corresponding protective conductor (Sp)

CSA of phase conductor If the protective conductor is

of the same material as the phase conductor

If the protective conductor is not the same material as the phase conductor

mm2

S ≤ 16

16 ≤ S ≤ 35

S > 35

mm2

S

16

S 2

mm2

k1S k2

k116 k2

k1S k22

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

as follows where:

k1 is the value of k for the phase conductor, selected from table 43A in Chapter 43 according to the materials of both conductor and insulation.

k2 is the value of k for the protective conductor, selected from Tables 54B,

54C, 54D, 54E or 54F as applicable.

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Main equipotential bonding conductors The IEE Wiring Regulations, BS 7671, specify that the main equipotential bonding conductor in an installation, other than a PME system, is required to have a cross-sectional area not less than half the cross-sectional area specified for the installation earthing conductor and not less than 6 mm2. If a copper bonding conductor is used, the cross-sectional need not be greater than 25 mm2 or, where other metals are used, the cross-sectional area which provides equivalent conductance will apply. With regard to a PME system, Table 54H below details the requirements for the main equipotential bonding conductor in relation to the neutral conductor of the supply. Table 54H

Copper equivalent cross-sectional area of the supply neutral conductor

Minimum copper equivalent cross-sectional area of the main equipotential bonding conductor

35 mm2 or less 10 mm2

over 35 mm2 up to 50 mm2 16 mm2



over 150 mm2 50 mm2

Practical example with and without earth bonding The diagram on page 29 shows a simple installation comprising a motor, distribution transformer, fuses and connecting cable. The fuses are necessary to provide protection against short-circuits which may occur between phases or between phase and earth. Electrical faults such as these must be disconnected as quickly as possible to prevent further damage to equipment and, more importantly, to prevent injury to personnel. The speed at which a fuse ruptures is dependent not only on the type of fuse, but also the circuit parameters, e.g. the resistance of the fault path - the earth-loop impedance - and the fault current magnitude. The lower the earth-loop impedance, the higher the fault-current will be and the faster the fuse will rupture. The 16th edition of the I.E.E. Regulations specifies the requirements for earth-loop impedance. Normally the star-point of the distribution transformer secondary winding is connected to an earth mat buried in the soil, but this alone will not provide a low enough earth-loop impedance, and so an earthing bond is required between the motor frame and the star-point of the transformer secondary winding. Let us now investigate the situation with and without the bonding conductor between the/

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main earth conductor and the motor frame when a fault occurs between one phase and earth within the motor. It will also be assumed that the motor is bolted securely to the bedplate but, due to dirt, rust or paint, the resistance between the feet of the motor and the bedplate is l Ω.

Case 1: No earth connection between main earth conductor and motor frame.

Consider the circuit on page 35 which comprises a motor, transformer and interconnecting cable. For simplicity resistive values only are used.

Rg = the resistance of one phase of the generator; Rm = the resistance of one phase of the motor R = the resistance between the motor feet and bedplate; Vph = the phase voltage.

Voltage across motor frame and bedplate, V = VphxRRmRg

R++

V = 240x10.010.05

1++

V = 208 V Thus, anyone standing next to the motor and touching it’s frame would receive a severe shock particularly if the deck was wet. Case 2: Earth connection between main earth conductor and motor frame.

The above situation is avoided with appropriate earthing and bonding. If the bonding conductor is connected between the motor frame and the main earth, the resistance of 1 Ω between the motor feet and bedplate is shunted and the effective resistance at this point is significantly reduced. Similarly, a bonding conductor connected between the motor feet and bedplate would achieve a similar result.

It is, therefore, essential that earth conductors have sufficient cross-sectional area (csa) to carry prospective fault-currents, which can be very high but usually of short duration, until they are interrupted by the electrical protection. It has been demonstrated that a contact resistance of 1 Ω can result in the presence of dangerous voltage levels. In order to avoid this difficulty, the earth-loop impedance should be significantly lower than 0.1 Ω.

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Practical example with and without earth bonding (continued)

No earth bond connected between motor frame and main earth conductor

Earth bond connected between motor frame and main earth conductor

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

1) slowing the flow rate of fluids through pipes; 2) adding compounds to liquids; 3) the use of pipes manufactured from materials with high carbon content.

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Static electricity (continued) BS 5958 recommendations for earthing resistances BS 5958 is termed at the time of writing – current, superseded – which infers that it applies only to existing installations, for example, installations installed in accordance with the Code of Practice BS 5345. For new installations guidance for the control of static electricity may be found in PD CLC/TR 50404. A summary of the recommendations in this document is given in page 38.

Type of installation Area classification

Recommended maximum resistance

to earth (Ω)

Comments

Main metal plant structure,

Zones 0, 1 & 2 10 Ω Earthing normally inherent in the structure.

Large fixed metal plant items. Reaction vessels + powder silos etc.

Zones 0, 1 & 2 10 Ω Earthing normally inherent in the structure. Occasionally items may be mounted on non-conducting supports and special earthing connections may then be required.

Metal pipelines. Zones 0, 1 & 2 10 Ω Earthing normally inherent in the structure. Special earthing connections may be required across joints if there is doubt that the 10 Ω criterion will be satisfied.

Transportable metal items: drums tanks etc.

Zones 0, 1 & 2 10 Ω Special earthing connections are normally required.

Metal plant with some non-conducting elements: Rotating shafts, stirrers etc.

Zones 0, 1 & 2 10 Ω In special cases a limit of 100/ 1Ω may be acceptable, but in general if 1MΩ criterion cannot be satisfied a special earthing connection should be used to obtain a resistance of less than 10 Ω to earth.

Higher resistivity non-conducting items with or without isolated metal components: e.g. bolts in a plastic pipeline

Zones 0, 1 & 2 10 Ω The general electrostatic ignition risk and the fire hazard normally preclude the use of such non-conducting materials unless it can be shown that significant charge accumulation will not occur. In the absence of charge accumulation, earthing is not required in Zone 2 areas

Items fabricated from conductive or antistatic materials

Zones 0, 1 & 2 1MΩ - 10MΩ

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Static electricity (continued) PD CLC/TR 50404: summary of maximum earthing resistances for the control of static electricity. Sub clause Type of installation Maximum

resistance to earth ( Ω )

Comments

11.3.1.1 Main plant structure

106 Earthing normally inherent in the structure

11.3.1.1 Large fixed metal plant (reaction vessels, powder silos, etc.)

106

Earthing normally inherent in the structure. Special earthing could be required for items mounted on non-conducting supports

11.3.1.1 Metal pipelines 106

Earthing normally inherent in the structure. Special earthing connection required across joints if resistance could exceed the 106Ω criterion

11.3.1.2 Movable metal items (drums, road and rail tankers, etc.)

106

Earthing connections are normally required during filling and emptying

11.3.2 Metal plant with some non-conductive elements (valves, etc.)

106*

In special cases a limit of 100// Ω could be acceptable, but in general if a 106 Ω criterion cannot be satisfied, a special earthing connection should be used

11.3.3 Non-conductive items with or without isolated metal components (e.g. bolts in a plastic pipeline)

No generally applicable value*

The general electrostatic ignition risk and the fire hazard normally preclude the use of such materials unless it can be shown that significant charge accumulation will not occur. In the absence of charge accumulation earthing is not required in zone 2 and in zone 22.

11.3.4 Items fabricated from non-conductive or dissipative materials

106 to 108

* Very small conductive items need not be earthed, see 4.4.2. Note 1: The above recommendations should be read in conjunction with the paragraphs

indicated in the first column above. Note 2: In zone 2 and in zone 22 earthing is required only when charge accumulation is

continuous. Note 3: In order to provide protection against lightning or to meet the electricity power

supply earthing requirements a lower value of resistance to earth is normally required.

Unit 11:

Inspection & Maintenance to BS EN 60079-17

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Objectives: On completion of this unit ‘Inspection & Maintenance’, you should know:

a. The importance of appropriate and regular inspection and maintenance. b. The requirements of types of inspection ‘initial’, ‘periodic’ and ‘sample’. c. How to apply inspection schedules, Tables 1, 2 & 3 form BS EN60079-17 for ‘visual’,

‘close’ and ‘detailed’ grades of inspection.

d. The knowledge and skills requirements for technicians (operatives) undertaking inspection and maintenance of explosion protected equipment in hazardous areas.

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Inspection and Maintenance Introduction This unit is concerned with the inspection and maintenance of electrical apparatus used in hazardous locations in accordance with relevant standards. This is very important because, in addition to the risk of mechanical damage to apparatus, there is also the risk that degradation of the apparatus, due to environmental conditions and other factors, could affect the integrity of the apparatus and allow ignition of any flammable gas or vapour in an hazardous area. Inspection of equipment should be carried out on a regular basis to enable detection of potential faults early enough to prevent major breakdowns occurring, minimise downtime and loss of production, and also possible injury to personnel. A maintenance programme based on the results of inspection surveys can then be implemented, which will allow continued reliability and safe operation of the equipment. Apparatus will only remain approved/certified if it is maintained in accordance with the recommendations provided by manufacturers and relevant standards. Standards

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

IEC 60079-17: 2007 Explosive atmospheres – Part 17: Electrical installations inspection and maintenance

BS 5345 (Withdrawn) Code of practice for the selection, installation and maintenance of electrical apparatus for use in potentially explosive atmospheres.

Qualifications of Personnel It is essential that personnel involved in the selection, installation, inspection and maintenance of explosion protected apparatus in hazardous areas have a clear understanding of the various types of explosion protection, installation practices, rules and regulations, and the general principles of area classification. Manufacturers have gone to great lengths to design and build apparatus in accordance with relevant standards and have it tested and certified by a third party test house to ensure the apparatus is safe for use in hazardous areas. All this effort will have been in vain if the technician in the field does not have the necessary knowledge to install and/or maintain apparatus in accordance with the manufacturer’s requirements, relevant standards and Codes of Practice. Personnel operating in this field must, therefore, have appropriate training, and thereafter, regular refresher training. Records detailing the experience and training of personnel must be maintained. Apparatus may be explosion protected at the time of leaving the manufacturer’s premises but, the way the apparatus is subsequently handled, selected, installed and maintained, will have an influence on whether the apparatus will be safe for use in an hazardous area and/or remain certified. Personnel need to be aware of, for example, the

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consequences of a broken foot on a flameproof motor. Increased Safety apparatus may have ‘special conditions of use’ and failure to observe these will reduce margins of safety and invalidate the certification. Furthermore, the incorrect selection of cable glands with regard to, for example, flameproof apparatus will affect the integrity of such apparatus. Knowledge and skills of technicians (operatives) Inspection and maintenance Technicians, or operatives as they are called in the standard, are required to have sufficient knowledge to enable proper inspection and maintenance of explosion protected equipment in hazardous areas. This knowledge includes:

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

(b) an understanding of the general principles of types of protection and marking;

(c) an understanding of those aspects of equipment design which affect the protection concept;

(d) an understanding of certification and relevant parts of IEC60079-17;

(e) an understanding of the additional importance of Permit to Work systems and safe isolation in relation to Explosion Protection;

(f) familiarity with the particular techniques to be employed in the inspection and maintenance of equipment referred to in IEC60079-17;

(g) a comprehensive understanding of the selection and erection requirements of IEC60079-14:

(h) a general understanding of the repair and reclamation requirements of IEC60079-19.

Competency Furthermore technicians (operatives) are required to provide evidence of their competency in the areas specified immediately above and, in addition, documentary evidence of competency in respect of the following:

(a) the use and availability of documentation;

(b) the practical skills required for the inspection and maintenance of the various types of explosion protection.

Assessment The competency of technicians (operatives) shall be verified and approved at intervals not exceeding 5 years from sufficient evidence that the person:

(a) has the necessary skills required for the scope of work;

(b) can act competently across the specified range of activities; and

(c) has the relevant knowledge and understanding underpinning the competency.

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Principal causes of apparatus deterioration BS EN60079-17 lists factors which have a significant effect on the deterioration of equipment in hazardous locations. These factors are listed below.

1) Susceptibility to corrosion; 2) Exposure to chemicals or solvents; 3) Likelihood of accumulation of dust or dirt; 4) Likelihood of water ingress; 5) Exposure to excessive ambient temperatures; 6) Ultraviolet radiation; 7) Risk of mechanical damage;

8) Exposure to undue vibration; 9) Training and experience of personnel;

10) Likelihood of unauthorised modifications or adjustments; 11) Likelihood of inappropriate maintenance, for example not in accordance with

manufacturer’s recommendations. Apparatus withdrawn from service Where it is required to withdraw apparatus during maintenance, any exposed conductors from the apparatus must be made safe by:

(a) termination in a suitable enclosure, or (b) isolated from all sources of power supply and insulated, or (c) isolated from all sources of power supply and earthed.

Where the intention is to permanently remove apparatus, the associated wiring must be isolated from all sources of power supply and terminated in a suitable enclosure, or completely removed. IEC Standards The International Electrotechnical Commission (IEC) Standards relative to explosion protected apparatus have been available since the late nineteen-sixties when they were published under the IEC 79-xx series, which subsequently evolved into the IEC 60079-xx series. These Standards, however, had not kept pace with the advances in made by the European Standards. Attempts to remedy this situation were implemented by the various committees within IEC to effect a complete revision of their Standards. There has also been greater co-operation between IEC and CENELEC to achieve technical alignment of their respective Standards.

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With regard to the EU, explosion protected apparatus is normally constructed in accordance with national and harmonised standards. IEC standards, however, have tended not to be used for this purpose but, because of the trend towards global harmonisation of standards, in which the IEC has an important role, this situation has changed. To fuel this change there have been instances where manufacturers have been requested by larger users of explosion protected apparatus to have such apparatus constructed and certified to the IEC Standards. The certification of such apparatus has created difficulties for the manufacturers and, in one instance, has led to the manufacturer issuing a ‘self declaration’ for apparatus they have manufactured to a particular IEC Standard. An IEC Standard which has become more widely accepted is IEC 60079-17, which is now a British Standard, BS EN60079-l7. This Standard comprises a series of Tables for the inspection of the various methods of explosion protection. Table 1 is an inspection schedule which lists the areas to be inspected for the types of apparatus Ex d, Ex e and Ex n. Table 2 and Table 3 are schedules for the inspection of IS apparatus and Pressurised Ex p apparatus respectively. These Tables are illustrated at the end of this section. For each type of explosion protection, three grades of inspection are specified which are ‘visual’, ‘close’ and ‘detailed’ and defined as follows: Visual: An inspection which identifies, without the use of access equipment or tools,

those defects, e.g. missing bolts, which will be apparent to the eye. Close: An inspection which encompasses those aspects covered by a Visual

Inspection and, in addition, identifies those defects, e.g. loose bolts, which will be apparent only by the use of access equipment, e.g. step ladders (where necessary), and tools. Close inspections do not normally require the enclosure to be opened, or the equipment to be de-energised.

Detailed: An inspection which encompasses those aspects covered by a Close

Inspection and, in addition, identifies those defects, e.g. loose termination’s, which will only be apparent by opening the enclosure, and/or using, where necessary, tools and test equipment.

Inspection schedules are, therefore, a means by which electrical installations may be systematically assessed for the correct installation of apparatus and also the effects of environmental conditions such as water, ambient temperature, vibration etc. Documentation Prior to the implementation of an inspection / maintenance programme it is essential that all necessary documentation is available. These will include hazardous area drawings of the plant, apparatus group and temperature class, list and location of apparatus spares, technical information, manufacturer’s instructions, and a complete inventory of all hazardous area equipment installed in the plant including their location in the plant and up-to-date records of all previous inspections and maintenance tasks carried out. It is also vitally important that the certification documents for each item of explosion protected apparatus are available so that, for example, clarification of any ‘Special Installation Conditions’ may be verified at a later date. The maintenance of comprehensive records is thus an essential requirement for the safe operation of electrical equipment in hazardous areas. Experience has shown that

March 2010 ©

7

modifications to existing hazardous area equipment and also the installation of additional hazardous area equipment, has occurred in hazardous areas installations without these actions being recorded in the relevant documentation. Inspections types Three types of inspection are specified in BS EN60079-17. These are:

a) initial inspection; b) periodic inspection; c) sample inspection.

An installation, including its systems and apparatus, should be subjected to an ‘initial inspection’ before being brought into service to establish that the types of protection selected, and their method of installation are suitable. The grade of inspection shall be ‘detailed’ in accordance with Tables 1, 2 and 3 of BS EN60079-17. No faults are permissible on handover. Thereafter, ‘periodic inspections’ should be implemented to verify that the installation is being maintained in an appropriate condition for continued use in the hazardous area. The grade of inspection for ‘periodic inspections’ may be ‘visual’ or ‘close’ and should be carried out at regular intervals, the interval being influenced by the environmental conditions, but should not be greater than 3 years unless expert advice is sought. Depending on the outcome of a ‘visual/close inspection’, it may be necessary to carry out a further ‘detailed inspection’. Experience gained in similar situations with regard to apparatus, plants and environments may be used to establish the inspection programme. Factors having an influence on the frequency and grade of ‘periodic inspections’ are:

a) type of apparatus; b) manufacturers recommendations; c) environmental conditions; d) Zone of use; e) results of previous inspections

It is recommended that, however, the interval between ‘periodic inspections’ does not exceed three years. Interim ‘sample inspections’ may be implemented to either support or modify the frequency of ‘periodic inspections’ and may be of a grade ‘Visual’, ‘Close’ or Detailed. The flowchart on page 8 illustrates how a typical maintenance programme may be established and how the various grades of inspection, i.e. ‘visual’, ‘close’ or ‘detailed’, may be applied during the various types of inspection, i.e. ‘initial’, ‘periodic’ or ‘sample’. Consideration is also given to frequency of periodic inspections. Note: I.C. appearing in the flowchart on page 8 infers that electrical equipment contains

components which are ignition capable in normal operation. Typical components are switches, contactors, relays etc. where ignition capable arcs or sparks are produced at their contacts, and, for example, resistors which may produce excessive surface temperatures.

March 2010 ©

9





*

*

*

*

*

*

*

*

*


*


maintained * * *


*

*

*

*

*

*

*

*

*


* * *


limits * * *


* * *




* * * * * *

Note: table continued on following page

March 2010 ©

10

Check that: Ex’d’ Ex’e’ Ex’n’ Grade of Inspection D C V D C V D C V C ENVIRONMENT 1 Apparatus is adequately protected against corrosion, weather,


2 No undue accumulation of dust and dirt * * * * * * * * * 3 Electrical insulation is clean and dry * * Note 1: Apparatus using a combination of both ‘d’ and ‘e’ types of protection will require

reference to both columns during inspection. Note 2: The use of electrical test equipment, in accordance with items B7 and B8, should


Moveable equipment The movement of electrical equipment, i.e, portable, hand-held and transportable, can result in damage due to incorrect handling and hence there may be a need for a shorter interval between periodic inspections. The recommendation is that a close inspection is carried out every 12 months. Where equipment is frequently opened, typically battery compartments, the recommendation is a detailed inspection every 6 months. Furthermore, it is the responsibility of the user to visually inspect equipment prior to use to ensure freedom from apparent damage.

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Grade Inspection


1 Circuit and/or apparatus documentation is appropriate to area



* *



* * *


B Installation



7 Earth connections maintain the integrity of the type of protection * * * 8 The intrinsically safe circuit is isolated from earth to earthed at one



*


*

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

C Environment

1 Apparatus is adequately protected against corrosion, weather,



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

Grade Inspection


1 Apparatus is appropriate to area classification * * * 2 Apparatus group is correct * * 3 Apparatus temperature class is correct * * 4 Apparatus circuit identification is correct * 5 Apparatus circuit identification is available * * * 6 Enclosures, glass parts and glass-to-metal sealing gaskets and/or

compounds are satisfactory * * *

7 There are no unauthorised modifications * 8 There are no visible unauthorised modifications * * 9 Lamp rating, type and position are correct *

B Installation

1 Type of cable is appropriate * 2 There is no obvious damage to cables * * * 3 Earthing connections, including any supplementary earthing

bonding connections are satisfactory (e.g. connections are tight and conductors are of sufficient cross section - Physical check - Visual check

*

*

*

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

*

5 Automatic electrical protective devices operate within permitted limits

*

6 Automatic electrical protective devices are set correctly * 7 Protective gas inlet temperature is below maximum specified * 8 Ducts, pipes and enclosures are in good condition * * * 9 Protective gas is substantially free form contaminants * * * 10 Protective gas pressure and/or flow is adequate * * * 11 Pressure and/or flow indicators, alarms and interlocks function

correctly *

12 Pre-energising purge period is adequate * 13 Conditions of spark and particular barriers of ducts for exhausting

the gas in hazardous area satisfactory *

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

C Environment

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

* * *


Unit 12:

Sources of Ignition

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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

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

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

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

Unit 13:

Induction to Competence

Validation Testing

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Objectives: On completion of this unit, ‘Induction to Competence Validation Testing’, you should know:

a. The procedures and competence requirements for EX01: the preparation and installation of Ex d, Ex e and Ex n apparatus.

b. The procedures and competence requirements for EX02: the inspection and of Ex d,

Ex e and Ex n apparatus. c. The procedures and competence requirements fro EX03: the preparation and

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

maintenance of an Ex i system and associated apparatus.

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Induction to Competence Validation Testing Competence Validation Tests EX01, EX02, EX03 and EX04

Off-site preparation: Implement, with reference to Assessment Workpacks, all off-site procedures to include selection of materials, apparatus, equipment and tools. Safe working practices to be adhered to at all times and include the mandatory use of Personal Protective Equipment in the designated areas.

Permit-to-work and safe electrical isolation:

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

On-site preparation: Implement, with reference to Assessment

Workpacks, all on-site procedures to achieve the competence standard required for Installation, Inspection and Maintenance relative to Units EX01, EX02, EX03 and EX04.

EX01 Preparation and Installation of EEx d, e & n Apparatus Section A Preparation and Safe Isolation of the electrical Circuit:

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

Section B Installation comprising Ex d, Ex e and Ex n apparatus:

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

b) Install appropriate cables and glands in a manner which will maintain the integrity of the pre-fixed apparatus.

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

d) Fit apparatus covers and live-test installation.

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EX02 Inspection of EEx d, e & n Apparatus Sections A, B & C Inspection of apparatus and environment:

With reference to Table 1 of BS EN60079-17:

a) Identify and record five Visual faults.

b) Identify and record five Close faults.

c) Identify and record five Detailed faults.

d) Compile a report of the faults found and specify the remedial action necessary to return the installation to specification.

Section D Safe Isolation of the electrical circuit. (Prior to Section C):

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

EX03 Preparation and Installation of EEx i Apparatus Section A Installation comprising Ex i apparatus:

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

b) Install appropriate cables, glands and safety interfaces in a manner which will maintain apparatus integrity.

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

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EX04 Inspection of EEx i Apparatus Sections A, B & C Inspection of apparatus and environment:

With reference to Table 2 of BS EN60079-17:

a) Identify and record five Visual faults.

b) Identify and record five Close faults.

c) Identify and record five Detailed faults.

d) Compile a report of the faults found and specify the remedial action necessary to return the installation to specification.

Section D Safe Isolation of the electrical circuit. (Prior to Section C):

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

March 2010 ©

6





*

*

*

*

*

*

*

*

*


*


maintained * * *


*

*

*

*

*

*

*

*

*


* * *


limits * * *


* * *




* * * * * *

Note: table continued overleaf

March 2010 ©

7

Check that: Ex’d’ Ex’e’ Ex’n’ Grade of Inspection D C V D C V D C V C ENVIRONMENT 1 Apparatus is adequately protected against corrosion, weather,


2 No undue accumulation of dust and dirt * * * * * * * * * 3 Electrical insulation is clean and dry * * Note 1: Apparatus using a combination of both ‘d’ and ‘e’ types of protection will require

reference to both columns during inspection. Note 2: The use of electrical test equipment, in accordance with items B7 and B8, should


`

March 2010 ©

8


Grade Inspection


1 Circuit and/or apparatus documentation is appropriate to area



* *



* * *


B Installation



7 Earth connections maintain the integrity of the type of protection * * * 8 The intrinsically safe circuit is isolated from earth to earthed at one



*


*

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

C Environment

1 Apparatus is adequately protected against corrosion, weather,



Unit 14:

Permit to Work System

and Safe Isolation

March 2010 © 2

Objectives: On completion of this unit, ‘Permit to Work and Safe Isolation’, you should know:

a. the procedure to complete a ‘permit to work’ to enable safe completion of tests EX01, EX02, EX03 and EX04;

b. the procedures to identify, from drawings, the location of protection and control

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

apparatus for tests EX01, EX02, EX03 and EX04.

March 2010 © 3

Permit-to-work and safe isolation Candidates attending the 5-day CompEx course are required to carry out four practical assessments in the simulated hazardous areas. During these assessments, candidates must demonstrate their ability to work safely by ensuring that all precautions are taken to prevent ignition of a flammable gas which, for the purpose of the assessments, it is assumed may be present at any time. Work permit In order to ensure that safety is maintained, candidates must operate within the control of a work permit - a sample is shown overleaf - which must be requested from the Assessor/Authorised Person. In association with the work permit, a gas-free certificate must be endorsed by the Assessor/Authorised Person at all instances when, for example, a particular action is likely to produce a source of ignition. Such situations occur when electrical test instruments and/or portable electric tools are used. Procedures for CVT’s EX01, EX02, EX03 & EX04 Isolation

Candidates are required to: a) Request a ‘work permit’. b) Complete parts 1, 2 and 3 of the ‘Work Permit’ and obtain ‘Authorisation to

Isolate’ the electrical circuit for the respective workbay.

Note: PPE in the designated areas is mandatory c) Identify the ‘point of isolation’ plant reference No. and apparatus ID for

‘zero voltage testing’. d) Isolate the electrical circuit and secure using two locks (candidate +

assessor’s locks) and warning label. e) Request ‘gas-free certificate’. f) Select appropriate test instrument, carry out ‘zero voltage test’ and confirm

result on part 3 of ‘work permit’.

(Note: instrument must be proved before and after use) g) Obtain approval to proceed with work (part 4 of work permit). Note: Step ‘d’ does not apply to EX03 since isolation is achieved by switching

off and removal of keys in the fire and gas panel.

March 2010 © 4

Final instrument testing

h) Request endorsement of ‘gas-free certificate’ prior to final instrument testing (part 5 of work permit).

i) Prepare installation for live testing and clear worksite (part 6 of work permit).

De-isolation

j) Obtain authorisation to de-isolate (part 6 of work permit). k) Confirm de-isolation is complete (part 6 of work permit). l) Obtain cancellation of work permit (part 7 of work permit).

March 2010 © 5

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)

March 2010 © 6

GAS TEST CERTIFICATE

This certificate confirms that the work bay nominated below in the Ex Training Facility has been tested and deemed to be free of flammable gases for only the specific task(s) authorised below.

Work Details (tick box)

EX01

EX02

EX03

EX04

Location

Workbay No.

Authorised by_________________(signed) Date____________

Action to be authorised

Authorised person

(signed)

Zero voltage test (isolation)

Use of portable heat gun

Final ‘instrument’ circuit testing

CompEx-Atex course Manual 1210.pdf

Documents

Transcript of CompEx-Atex course Manual 1210.pdf