A Practitioner's Handbook for Potentially Explosive Atmospheres

A Practitioner's Handbook for Potentially Explosive Atmospheres

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This publication offers guidance for safe installation, inspection and maintenance work in potentially explosive atmospheres, in such areas as petroleum and petrochemical plants, processing industries, power plants, fuel filling stations and more, when the failure to adopt safe working practices could result in the ignition of flammable gases or combustible dusts.

This 7th Edition has been further updated to align with the latest versions of the relevant standards, in particular the 5th Editions of IEC 60079-17 and 60079-17.

The Chapters on equipment, installation and inspection in particular have been revised extensively. This includes EEMUA’s recommendations on barrier gland selection.

The publication is closely associated with the CompEx® training and competency assessment scheme which provides trainees with essential knowledge and practical skills for safe working in potentially explosive atmospheres.

Published in March, 2016. 320 pages.

Table of Content


1. Directives, standards and legislation

1.1 European directives

1.1.1 Background

1.1.2 Trade directives

1.1.3 Health and safety directives

1.1.4 Directives relevant to explosive atmospheres

1.1.5 CE mark

1.2 Standards

1.2.1 National Standards and Codes

1.2.2 European and international standards

1.2.3 Other bodies involved in relevant standards and codes

1.2.4 Standards numbering

1.2.5 Using standards in electrical working in hazardous areas

1.3 Product certification

1.3.1 Product certification by an IECEx certification body within the IECEx system

1.3.2 ATEX Certification by a Notified Body

1.3.3 Impact of ATEX Equipment Directive on certification procedures

1.3.4 Assessment

1.4 Health and safety requirements in law

1.4.1 Basic requirements concerning the workplace

1.4.2 The Health and Safety at Work Act 1974 (HASAW Act)

1.4.3 The Electricity at Work Regulations

1.4.4 Provision and Use of Work Equipment Regulations

1.4.5 The Management of Health and Safety at Work Regulations

1.4.6 Personal Protective Equipment at Work Regulations

1.4.7 Factories Act 1961 Section 31

1.4.8 Control of Substances Harmful to Health Regulations

1.4.9 Dangerous Substances & Explosive Atmospheres Regulations

2. Gases and vapors and are classification

2.1 Characteristics of gases and vapors

2.1.1 General

2.1.2 Gas subdivisions

2.1.3 Types of flammable material

2.1.4 Flammable limits

2.1.5 Ignition energy

2.1.6 Relative density of vapor

2.1.7 Ignition requirements

2.2 Temperature classification: T Class

2.3 Area classification ‒ Gases

2.3.1 Zones

2.3.2 The extent of a zone

2.3.3 Factors affecting the release rate of gas or vapor

2.3.4 Grades of release

2.3.5 Artificial ventilation

2.3.6 Area classification documentation

3. Equipment ‒ Explosive gas atmospheres

3.1 Equipment types ‒ General

3.1.1 Overview

3.1.2 Zones of use

3.1.3 Equipment protection levels

3.1.4 Explosion protection concepts

3.1.5 Ex components

3.1.6 Temperature classification of equipment

3.1.7 Clearance and creepage definitions

3.1.8 Static electricity

3.1.9 Mechanical impact

3.1.10 Selection of radiating equipment

3.1.11 Selection of ultrasonic equipment

3.2 Type of Protection ‘d’ ‒ Flameproof enclosure

3.2.1 Definition

3.2.2 Standards and selection

3.2.3 Construction and use

3.3 Type of Protection ‘p’ ‒ Pressurised equipment

3.3.1 Definition

3.3.2 Standards and selection

3.3.3 General details

3.3.4 Pressurising criteria

3.3.5 Safety requirements

3.4 Type of Protection ‘e’ ‒ Increased safety

3.4.1 Definition

3.4.2 Standards and selection

3.4.3 Characteristics

3.5 Type of Protection ‘n’ ‒ Reduced risk

3.5.1 Definition

3.5.2 Standards and selection

3.5.3 Construction and use

3.6 Type of Protection ‘i’ ‒ Intrinsic safety

3.6.1 Definitions

3.6.2 Standards and selection

3.6.3 Equipment for connection in the hazardous area

3.6.4 Safety barriers

3.6.5 Earthing of intrinsically safe apparatus

3.6.6 Surge suppression

3.6.7 Voltages

3.6.8 Circuit capacitance (C0) and inductance (L0)

3.6.9 External terminations, clearances, marking and color

3.7 Type of Protection ‘m’ ‒ Encapsulation

3.7.1 Definition

3.7.2 Standards and selection

3.8 Type of Protection ‘o’ ‒ Oil immersion

3.8.1 Definition

3.8.2 Standards and selection

3.9 Type of Protection ‘q’ ‒ Powder filling

3.9.1 Definition

3.9.2 Standards and selection

3.10 Type of Protection ‘s’ ‒ Special protection

3.10.1 Definition

3.10.2 Standards and selection

3.11 Type of protection ‘op’ ‒ Optical radiation

3.12 Cable glands and their selection

3.12.1 Objective

3.12.2 Gland standards

3.12.3 Ex cable gland specifications

3.12.4 Mechanical gland construction

3.12.5 Gland markings

3.12.6 Selection of cable gland and cable entry device

3.13 Wiring systems

3.13.1 Cables

3.13.2 Cables in areas requiring EPL ‘Ga’ or Category 1 equipment t © 2016 JT Limited

3.13.3 Wiring in areas requiring EPL ‘Gb’ and ‘Gc’ or Category 2 and 3 equipment

3.14 Marking on explosion protected equipment

3.14.1 ATEX

3.14.2 IEC equipment protection levels (EPLs) for gas atmospheres

3.14.3 Certification authority marks

3.14.4 Markings required by IEC 60079-0

3.14.5 Additional marking for types of protection

3.15 Ingress protection

3.15.1 The IP code

3.15.2 Deluge proof

4. Installation

4.1 Introduction

4.1.1 Contractor’s responsibility

4.2 Prior to commencement of work

4.2.1 General requirements ‒ Off site preparation

4.2.2 Safety rules and permits

4.3 On site preparation

4.3.1 Location of zones

4.3.2 Access equipment

4.3.3 Authorised safe storage place

4.3.4 Identifi cation of all the equipment

4.3.5 Location of place of work

4.3.6 Cable routes

4.3.7 Cable accessories

4.3.8 Composite cable systems

4.3.9 Safe mains isolation

4.4 Installation of equipment on site

4.4.1 General requirements for all types of protection

4.4.2 Earthing

4.4.4 Special requirements: Ex ‘d’ ‒ Flameproof

4.4.5 Special requirements: Ex ‘e’ ‒ Increased safety

4.4.6 Special requirements: Ex ‘i’ ‒ Intrinsic safety .

4.4.7 Glanding

4.5 Earthing

4.5.1 Introduction

4.5.2 Earthing terminology

4.5.3 Earthing and bonding systems

4.5.4 Earthing continuity

4.5.5 Lightning protection

4.5.6 Static electricity

4.6 Completion of the installation

4.6.1 Advising appropriate bodies

4.6.2 Compliance with job specifi cation

4.6.3 Signing off

4.6.4 Typical electrical permit to work

5. Inspection

5.1 Introduction

5.2 Services to be provided by the inspection body

5.2.1 Examination of electrical equipment to appropriate standards

5.2.2 Advise the plant owner or operator as to condition

5.2.3 Check any remedial work

5.2.4 Advice regarding future periodic inspection dates

5.2.5 Clarity of information

5.3 Requirements prior to commencement of work

5.3.1 General requirements

5.3.2 Safety rules and permits

5.3.3 On site preparation

5.3.4 Documentation

5.4 Types and grades of inspection

5.4.1 Types of inspection

5.4.2 Grades of inspection

5.5 Specific inspection requirements

5.5.1 General

5.5.2 Specific inspection criteria appropriate to equipment‒ Types ‘d’, ‘e’, ‘n’ (except ‘nL’) and ‘t/tD’

5.5.3 Criteria appropriate to equipment Type ‘i’ ‒ Intrinsic safety (including ‘nL’)

5.5.4 Specific inspection criteria appropriate to equipment‒ Type ‘p’ and ‘pD’ pressurisation

5.6 Requirements on completion of inspection

5.6.1 Inspection and maintenance records

5.6.2 Utilisation of reports

5.6.3 On completion of work and leaving site

6. Maintenance

6.1 Introduction

6.1.1 General

6.1.2 Joint inspection and maintenance yright © 2016 JT Limited

6.2 Services to be provided by the maintenance body

6.2.1 General

6.2.2 Specific duties

6.3 Requirements prior to commencement of work

6.4 Common maintenance requirements

6.4.1 Alterations

6.4.2 Damaged parts

6.4.3 Taking out for repair elsewhere

6.4.4 Damaged cables

6.4.5 Spare parts

6.5 Specific maintenance requirements

6.5.1 Type of Protection ‘d’, flameproof enclosure

6.5.2 Type of protection ‘e’, increased safety

6.5.3 Type of protection ‘n’, reduced risk

6.5.4 Type of protection ‘p’, pressurised

6.5.5 Type of protection ‘i’, intrinsic safety

6.5.6 Type of protection ‘o’, oil immersion

6.5.7 Type of protection ‘m’, encapsulation

6.5.8 Type of protection ‘q’, powder filling

6.6 Requirements on completion of maintenance

6.6.1 Content of reports

6.6.2 Utilisation of reports

6.7 On completion of work and leaving site

7. Combustible dusts

7.1 General

7.2 Directives, regulations and standards relevant to dusts

7.2.1 Directives

7.2.2 Regulations

7.2.3 Principal standards

7.3 Definitions, groups and subdivisions

7.3.1 Definitions

7.3.2 Dust group and subdivisions

7.4 Area classification ‒ Combustible dusts

7.4.1 General

7.4.2 Grades of release

7.4.3 Zones

7.4.4 Area classifi cation documentation

7.4.5 Dust ignition considerations

7.5 Equipment protection measures

7.5.1 General

7.5.2 Surface temperature safety factors

7.6 Zones of use: Explosion protected equipment

7.7 Installation in combustible dust locations

7.7.1 General

7.7.2 Equipment designed for use in combustible dust locations

7.7.3 Equipment designed for use in gas locations

7.8 Inspection of installations

7.9 Maintenance

8. Fuel filling stations

8.1 General

8.2 Directives, legislation and standards

8.3 Definitions, groups and subdivisions

8.4 Area classification

8.4.1 General

8.4.2 Fuel properties

8.4.3 Zone extents

8.5 Temperature classification

8.5.1 Equipment classification194

8.5.2 Gas temperature classification

8.6 Equipment selection

8.6.1 Type of protection ‘d’, flameproof enclosure

8.6.2 Type of protection ‘e’, increased safety

8.6.3 Type of protection ‘n’, reduced risk

8.6.4 Type of protection ‘i’, intrinsic safety

8.6.5 Other types of protection

8.7 Equipment marking

8.8 Site equipment

8.8.1 Tanker unloading area and earthing

8.8.2 Storage tanks

8.8.3 Vent pipes

8.8.4 Dispenser units

8.8.5 Illumination and luminaires

8.8.6 Loudspeaker equipment and closed circuit video

8.8.7 Battery charging equipment

8.9 Electrical circuits

8.9.1 Emergency switching

8.9.2 Switching and isolation of power supply

8.9.3 Restoration of power supply

8.9.4 Protection against shock

8.10 Cable glands and systems

8.10.1 Cable glands

8.10.2 Cables

8.10.3 Cable installation

8.11 Earthing

8.11.1 General

8.11.2 Static electricity

8.11.3 Protective conductor

8.11.4 Equipotential bonding conductors

8.11.5 Type of system earthing TN-C

8.11.6 Type of system earthing TN-S

8.11.7 Type of system earthing TN-C-S

8.11.8 Type of system earthing TT

8.11.9 Type of system earthing IT

8.11.10 Systems for petroleum installations

8.11.11 Earth loop impedance

8.12 Cathodic protection

8.12.1 Corrosion

8.12.2 Minimising corrosion

8.12.3 Precautions

8.13 Safety issues

8.13.1 Safety method statement

8.13.2 Permits to work

8.13.3 Safe isolation

8.13.4 Completion reports

8.14 Inspection and test

8.14.1 Introduction

8.14.2 Specific inspection points

8.14.3 New installations

8.14.4 Existing sites

8.14.5 Reports

8.15 De-commissioning

8.15.1 Electrical requirements

8.15.2 Non-electrical work

8.16 Maintenance

8.17 Good housekeeping

8.18 List of ‘Blue Book’ report forms and programmes

8.18.1 Report forms

8.18.2 Verification programmes

8.18.3 Testing programmes

8.19 Types of system earthing

8.19.1 TN-C type of system earth

8.19.2 TN-S type of system earth

8.19.3 TN-C-S type of system earth

8.19.4 TT type of system earth

8.19.5 IT type of system earth

9. Hazardous areas in the water and wastewater industries

9.1 Introduction

9.2 Dangers to be aware of at wastewater treatment facilities

9.3 Dangers to be aware of at water handling facilities

9.4 Most significant hazards

9.5 Water and waste treatment industries’ Codes of Practice

9.6 Competence certification

9.7 Installation and maintenance work in hazardous areas

9.7.1 Example of good practice for a relatively simple installation

9.7.2 Work in areas with higher explosive risk

9.8 Maintenance and inspection activities

9.9 Examples of typical hazardous area zoning diagrams to be found in thewater and waste treatment sector

10. Mechanical

10.1 Introduction

10.2 Directives, regulations and standards

10.2.1 Directives

10.2.2 Regulations

10.2.3 Standards

10.3 Design requirements

10.3.1 Hazardous area classification

10.3.2 Risk assessments

10.3.3 Types of

10.4 Eff ectiveignition sources

10.4.1 Hot surfaces

10.4.2 Mechanically generated sparks

10.4.3 Flames and hot gases

10.4.4 Electrical sparks

10.4.5 Other electrical sources

10.4.6 Lightning

10.4.7 Equipment specific ignition sources

10.4.8 Adiabatic compression

10.4.9 Chemical reactions

10.5 Mechanical maintenance

10.5.1 Specific machinery aspects

10.5.2 Key properties

11. Application design engineering and duties of the Responsible Person

11.1 Application design engineering

11.2 Responsible Person

12. Definitions

12.1 Defined terms

12.2 Units of measurement

12.3 Abbreviations

13. The Compex® competency scheme

13.1 CompEx®: an overview

13.1.1 Prior knowledge required for CompEx®

13.1.2 CompEx® added knowledge

13.1.3 The units

13.1.4 The assessment  

13.1.5 The competency validation assessment outcome

13.1.6 Refresher courses

13.1.7 Signifi cance of the CompEx® certifi cate

13.2 Licensed CompEx® assessment centres



Table 1 Principal standards for gases

Table 2 Principal standards for combustible dusts

Table 3 Gas subdivisions based on MESG

Table 4 Gas subdivisions based on MIC

Table 5 Explosive range of typical gases

Table 6 Ignition energy ‒ typical gases

Table 7 Properties of a selection of flammable gases

Table 8 Temperature classification

Table 9 ATEX Relationship between Zones, Equipment Groups, Equipment Protection Levels (EPLs) and ATEX Categories

Table 10 Types of protection which may be used based on EPL/category requirements

Table 11 Types of protection, zones of use, categories and EPLs for gas zones

Table 12 Tests for resistance to impact

Table 13 Simplified table of maximum allowable gaps in flameproof equipment from IEC 60079-1:2007

Table 14 Pressurisation ‒ determination of type of protection (with no flammable release within the enclosure)

Table 15 Action to be taken when pressurisation with the protective gas fails

for electrical equipment without an internal source of fl ammable gas

Table 16 Spark and particle barriers

Table 17

Table 18 Details of the IP code

Table 19 Minimum distance of obstruction from the flameproof flange joints related to the gas group of the hazardous area

Table 20 Protective conductor size

Table 21 Power system bare earthing conductor size (mm2)

Table 22 Types of protection ‘d’, ‘e’, ‘n’ (except ‘nL’) and ‘t/tD’

Table 23 Type of protection ‘i’ (including ‘nL’)

Table 24 Type of protection ‘p’ and ‘pD’

Table 25: Inspection data

Table 26 IEC standards for combustible dusts

Table 27 Combustible dusts ‒ Ignition energies

Table 28 Combustible dusts ‒ Ignition temperatures

Table 29 Combustible dusts ‒ IP rating requirements

Table 30 Combustible dusts ‒ Types of protection, zones of use, categories and EPLs

Table 31 Combustible dusts ‒ Zones of use, categories and EPLs

Table 32 Properties of typical fuels

Table 33 Temperature classification

Table 34 Core resistanceted

Table 35 ATEX categories and IEC equipment protection levels where only zones have been assigned

Table 36 Protection concepts: Non-electrical


Figure 1 The Fire Triangle

Figure 2 Preferred markings for Zone 0

Figure 3 Preferred markings for Zone 1

Figure 4 Preferred markings for Zone 2

Figure 5 Zones surrounding a fi xed roof fl ammable liquid storage tank

Figure 6 Representative area classifi cation drawing

Figure 7 Typical arrangement of fl ange and spigot joints

Figure 8 Basic Zener diode circuit

Figure 9 Practical Zener diode barrier

Figure 10 Diagram of a galvanic isolation barrier

Figure 11 Construction of mechanical gland

Figure 12 The CE conformity mark

Figure 13 Certifying authority marks

Figure 14 Entry blanking plugs

Figure 15 Typical compression gland

Figure 16 Gland selection diagram from IEC 60079-14

Figure 17 Component parts of an MICC Gland

Figure 18 Section through an Ex ‘e’ MICC termination

Figure 19 Connections for measurement of earth loop impedance

Figure 20 TN-C type of system earth

Figure 21 TN-C type of system earth

Figure 22 TN-C-S type of system earth

Figure 23 TT type of system earth

Figure 24 IT type of system earth

Figure 25 Explosion at a sewage pumping station in northern England, caused by a release of petrol into the sewer

Figure 26 Abbeystead pumping station 1984 (1)

Figure 27 Abbeystead pumping station 1984 (2)

Figure 28 Badly corroded Ex-rated equipment must always be replaced

Figure 29 Zoning diagram for typical on-site electrolytic chlorination plant,

with hypochlorite tank, when installed outside a building

Figure 30 Zoning diagram and documentation for a typical wastewater treatment works

Figure 31 Zoning diagram and documentation for a typical wastewater pumping station

Figure 32 Zoning diagram for a sludge digester

Figure 33 Zoning diagram for a sludge gas holder

Figure 34 The role of CompEx® in the global competency route to safety for hazardous areas


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