Communication from the Commission concerning the non-binding guide of good practice for implementing Directive 1999/92/EC of the European Parliament and of the Council on minimum requirements for improving the safety and health protection of workers potentially at risk from explosive atmospheres
Date: 2003-08-25
Institutions: European Commission
Subjects: explosive, national implementing measure, occupational health, occupational safety, workplace

COMMISSION OF THE EUROPEAN COMMUNITIES

Brussels, 25.8.2003
COM(2003) 515 final

COMMUNICATION FROM THE COMMISSION

concerning the non-binding guide of good practice for implementing Directive
1999/92/EC of the European Parliament and of the Council on minimum requirements
for improving the safety and health protection of workers potentially at risk from
explosive atmospheres

.

COMMUNICATION FROM THE COMMISSION

concerning the non-binding guide of good practice for implementing Directive
1999/92/EC of the European Parliament and of the Council on minimum requirements
for improving the safety and health protection of workers potentially at risk from
explosive atmospheres

Article  11  of  Directive  1999/92/EC1  provides  that  the  Commission  shall  draw  up  practical
guidelines in a guide of good practice of a non-binding nature to assist the Member States, in
pursuance  of  the  Directive,  in  drawing  up  their  national  policies  for  the  protection  of  the
health and safety of workers, in particular as regards the topics referred to in Articles 3, 4, 5,
6,  7  and  8,  Annex  I  and  Annex  II,  Part  A.  To  discharge  this  duty,  the  Commission  has
produced  a  guide  covering  explosion  prevention  and  protection,  assessment  of  explosion
risks,  the  employer's  duties  to  safeguard  the  safety  and  health  of  workers,  the  duty  of  the
employer responsible for the workplace to coordinate all measures where workers of several
undertakings  are  present  at  the  same  workplace,  zoning  of  places  where  explosive
atmospheres  may  occur  and  the  way  in  which  the  employer  must  produce  the  explosion
protection document.

In producing this guide, the Commission was assisted by the Advisory Committee on Safety,
Hygiene  and  Health  Protection  at  Work,  which  delivered  a  favourable  opinion  on
15 May 2003.

The  Advisory  Committee  considers  that  the  guide  deals  adequately  with  the  fundamental
questions, namely the identification of hazards,  risk evaluation and the  specific  measures to
be taken to safeguard the safety and health of workers exposed to explosive atmospheres. It
also  takes  the  view  that  the  guide  takes  due  account  of  the  aspects  enabling  the  “explosion
protection  document”  to  be  drawn  up,  in  particular  by  SMEs.  Finally,  it  believes  that  the
guide will assist employers responsible  for  workplaces at risk of the  formation of explosive
atmospheres  in  taking  the  measures  needed  to  implement  the  necessary  coordination  where
workers of several undertakings are present at the same workplace.

The  Commission  asks  the  Member  States,  in  accordance  with  Article  11  of  Directive
1999/92/EC,  to  take  the  greatest  possible  account  of  the  guide  in  drawing  up  their  national
policies  for  the  protection  of  the  health  and  safety  of  workers  and  to  ensure  that  it  is
distributed as widely as possible in interested circles.

1

OJ L 23, 28.1.2003.

2

                                                
COVER PAGE

Non-binding Guide of Good Practice
for implementing of the European Parliament
and Council Directive 1999/92/EC
on minimum requirements for improving the
safety and health protection of workers
potentially at risk from explosive atmospheres

European Commission
DG Employment and Social Affairs
Health, Safety and Hygiene at Work

Final version April 2003

Preface

To create more and better jobs has always been an objective of the European  Union. This objective
was formally adopted by the Council at the Lisbon European Council in March 2000 and it is one of
the key elements to enhance the quality of work.

To confront the new challenges to social policy, resulting from the radical transformation of Europe's
economy and society, the European Social Policy Agenda, endorsed by the Nice European Council, is
based on the need to ensure a positive and dynamic interaction of economic, social and employment
policies. The Social Policy Agenda must strengthen the role of social policy and enable it at the same
time to be more effective in assuring the protection of individuals, the reduction of inequalities, and
social cohesion. The Stockholm European Council addressed quality at work – the desire, not just to
defend minimum standards, but to raise them and ensure a more equitable sharing of progress – as a
key element in re-gaining full employment. In this context, safety and health at work constitutes one of
the social policy issues on which the European Union has concentrated its efforts.

Fortunately, explosions and flash fires accidents are not the most common causes of accidents at work.
However, their consequences are spectacular and dramatic in terms of human lives lost and economic
costs.

The  need  to  reduce  the  incidence  of  explosions  and  flash  fires  at  work  is  prompted  by  both
humanitarian and economic considerations and has led to the adoption by the European Parliament and
the  Council  of  the  ATEX  Directive  1999/92/EC.  The  humanitarian  considerations  are  obvious:
explosions and fires can cause hideous injuries and deaths. The economic considerations are contained
in every study into the true costs of accidents, which all show that improved risk (health and safety)
management  can  substantially  increase  company  profits.  This  latter  being  particularly  true  where
potential explosions are concerned.

Adoption of legislative measures is a part of the commitment to include health and safety of workers
at work in the global approach to well-being at work. The European Commission combines a variety
of instruments to consolidate a real culture of risk prevention.

This  Guide  of  Good  Practice  is  one  of  those  instruments,  and  it  was  mandated  by  the  European
Parliament and the Council in Article 11 of the ATEX Directive: that the Commission shall draw up a
practical  guideline  of  non-binding  nature.  It  may  be  used  as  the  base  for  national  guides  aimed  at
helping small and medium enterprises to improve both their safety and their profitability.

Finally, I would like to use this opportunity to encourage all health and safety actors, and in particular
national authorities and employers, to apply with responsibility and firmness this Directive in order to
avoid, or at least to reduce to the minimum, the risks arising from explosive atmospheres and to create
a good working environment.

Odile Quintin
General Director

Contents

1. HOW TO USE THIS GUIDE
1.1
1.2
1.3
1.4

Relationship with Directive 1999/92/EC
Scope of the Guide
Pertinent regulations and further information
Official and non-official advice centres

2. ASSESSMENT OF EXPLOSION RISKS
2.1
2.2

Methods
Assessment criteria

2.2.1
2.2.2
2.2.3
2.2.4
2.2.5
2.2.6

Are flammable substances present?
Can sufficient dispersal in air give rise to an explosive atmosphere?
Where can explosive atmospheres occur?
Is the formation of a hazardous explosive atmosphere possible?
Is the formation of hazardous explosive atmospheres reliably prevented?
Is the ignition of hazardous explosive atmospheres reliably prevented?

3. TECHNICAL MEASURES FOR EXPLOSION PROTECTION
3.1

Prevention of hazardous explosive atmospheres
Use of substitutes for flammable substances
Limiting of concentrations
Inerting
Preventing or limiting the formation of explosive atmospheres in the vicinity of plant
Removal of dust deposits
Gas alarms

3.1.1
3.1.2
3.1.3
3.1.4
3.1.4.1
3.1.5 

3.2

Avoidance of ignition sources

3.2.1
3.2.2
3.2.3

Zoning of hazardous places
Extent of protective measures
Types of ignition source

3.3

Mitigation of the effects of explosions (mitigation measures)

3.3.1
3.3.2
3.3.3
3.3.4

Explosion resistant equipment
Explosion relief
Explosion suppression
Prevention of explosion propagation (explosion decoupling)

3.4
3.5

Application of process control engineering
Requirements for work equipment

3.5.1
3.5.2

Selection of work equipment
Assembly of work equipment

4. ORGANISATIONAL MEASURES FOR EXPLOSION PROTECTION
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8

Operating instructions
Worker competence
Training of workers
Worker supervision
Permit-to-work system
Maintenance
Inspection and surveillance
Marking of hazardous places

5. COORDINATION DUTIES
5.1
5.2

Coordination arrangements
Protective measures to ensure safe cooperation

1
4
5
6
6

7
8
8
10
10
12
13
14
14

15
15
15
15
15
16
17
18
19
19
23
23
27
27
27
28
28
30
32
32
33

34
35
35
35
36
36
37
37
38

39
39
40

6 EXPLOSION PROTECTION DOCUMENT
Requirements under Directive 1999/92/EC
6.1
Implementation
6.2
Specimen layout for an explosion protection document
6.3
Description of the workplace and working areas
Description of the process steps and/or activities
Description of the substances used / safety parameters
Results of the risk analysis
Explosion protection measures taken
Implementation of the explosion protection measures
Coordination of the explosion protection measures
Annex to the explosion protection document

6.3.1
6.3.2
6.3.3
6.3.4
6.3.5
6.3.6
6.3.7
6.3.8

ANNEXES
A.1
A.2

Glossary
Legislation, standards and sources of further information on explosion protection

A.2.1
A.2.2

A.2.3
A.2.4
A.2.5

European directives and guidelines
EU Member States' national regulations transposing Directive 1999/92/EC  (items in italics to be
completed by the Commission)
 Selected European standards
Further national regulations and literature (to be completed by national authorities)
National advice centres (to be completed by national authorities)

A.3

Specimen forms and checklists

A.3.1
A.3.2
A.3.3

A.3.4
A.3.5
A.3.6

Checklist: Explosion protection inside apparatus
Checklist: Explosion protection around apparatus
Specimen: Permit-to-work form for work involving ignition sources in places with hazardous
atmospheres
Checklist: Coordination for on-site explosion protection
Checklist: Tasks of the coordinator for on-site explosion protection
Checklist: Completeness of the explosion protection document

A.4

Text of the Directive in the appropriate language to be inserted by the Commission

42
42
42
43
43
43
43
43
43
44
44
44

45
45
49
49

50
51
52
52
53
54
57

59
60
61
62
65

Introduction

Explosion  protection  is  of  particular  importance  to  safety;  since  explosions  endanger  the  lives  and
health of workers as a result of the uncontrolled effects of flame and pressure, the presence of noxious
reaction products, and consumption of the oxygen in the ambient air, which workers breathe.

For this reason, the establishment of a coherent strategy for the prevention of explosions requires that
organisational  measures  be  taken  at  the  workplace.  Framework  Directive  89/391/EEC1  requires  the
employer  to  implement  the  measures  necessary  for  the  safety  and  health  protection  of  workers,
including  prevention  of  occupational  risks,  and  provision  of  information  and  training,  as  well  as
provision of the necessary organisation and means.

It must be emphasised that compliance with the minimum requirements set out in the Directive does
not guarantee compliance with the appropriate national laws. The Directive was adopted under Article
137 of the Treaty establishing the European Community, and this Article expressly does not prevent
Member States from maintaining or introducing more stringent protective measures compatible with
the Treaty.

1.

How to use this Guide of Good Practice

Explosion  hazards  may  arise  in  all  undertakings  which  work  with  flammable  substances.  These
include many input materials, intermediate products, final products and wastes from the routine work
process, as shown in Figure 1.

This  Guide  of  Good  Practice  should  be  used  in  conjunction  with  Directive  1999/92/EC2,  the
Framework Directive 89/391/EEC and Directive 94/9/EC3.

Directive  1999/92/EC  lays  down  the  minimum  requirements  for  improving  the  safety  and  health
protection  of  workers  potentially  at  risk  from  explosive  atmospheres.  Article  11  of  this  Directive
requires the Commission to draw up practical guidelines in a guide of good practice of a non-binding
nature.

1 

2 

3 

Council  Directive  89/391/EEC  of  12  June  1989,  on  the  introduction  of  measures  to  encourage
improvements in the safety and health of workers at work, O.J. No L 183 of 29/06/1989, page 1.
Directive  1999/92/EC  of  the  European  Parliament  and  the  Council  of  16  December  1999,  on  the
minimum requirements for improving the safety and health protection of workers potentially at risk from
explosive atmospheres, O.J. No L 23 of 28/01/2000, page 57.
Directive 94/9/EC of the European Parliament and the Council of 23 March 1994, on the approximation
of  the  laws  of  the  Member  States  concerning  equipment  and  protective  systems  intended  for  use  in
potentially explosive atmospheres, O.J. L100 of 19/04/1994, page 1.

1

                                                     
Figure 1: Examples of situations in which explosive atmospheres arise4

The Guide is primarily intended to assist Member States in drawing up their national policies for the
protection of the health and safety of workers.

Its aim is thus to enable the employer, particularly Small and Medium Enterprises (SME's), to perform
the following explosion protection functions:

to identify hazards and assess the risks;

to  lay  down  specific  measures  to  safeguard  the  safety  and  health  of  workers  at  risk  from
explosive atmospheres;

to ensure a safe working environment and appropriate surveillance during the presence of
workers in accordance with the risk assessment;

to  take  the  necessary  steps  and  make  the  necessary  arrangements  for  coordination  when
several firms are operating at the same workplace;

to produce an explosion protection document.

Virtually all branches are affected, since hazards from explosive atmospheres arise in a wide range of
processes and operations. Examples are given in Table 1.1.

4 

From the ISSA leaflet "Gas Explosions", International Section for the Prevention of Occupational Risks
in the Chemical Industry, International Social Security Association (ISSA), Heidelberg, Germany

2

                                                     
Table 1.1: Examples of explosion hazards in various branches

Branch
Chemical
industry

Explosion hazard
Flammable gases, liquids and solids are converted and processed
in  many  different  processes  in  the  chemical  industry.  These
processes may give rise to explosive mixtures.

Landfill  tips  and
Civil Engineering

Power generating
companies

Flammable  landfill  gases  may  arise  in  landfill  tips.  Elaborate
technical  arrangements  are  needed  to  avoid  uncontrolled  gas
emission  and  possible  ignition.  Flammable  gases  from  various
sources may collect in poorly ventilated tunnels, cellars, etc.
Lump coal, which is not explosive in mixture  with  air,  may  be
converted in the conveying, grinding  and  drying  processes into
coal dusts capable of forming explosive dust/air mixtures.

Waste disposal
companies

When waste waters are treated in clarification  plants, the  gases
generated may form explosive gas/air mixtures.

Gas suppliers

Explosive  gas/air  mixtures  may  be  formed  when  natural  gas  is
released, e.g. by leakage.

Wood-working
industry

Wood-working  gives  rise  to  wood  dusts.  These  can  form
explosive dust/air mixtures, e.g. in filters or silos.

Paint-spraying
operations

The  overspray  generated  in  paint  spray  bays  and  the  solvent
vapours  released  may  give  rise  to  explosive  atmospheres  when
mixed with air.

Agriculture

Biogas production plants are operated on some farms. Explosive
biogas/air  mixtures  may  arise  if  the  gas  is  released,  e.g.  by
leakage.

Metal-working
operations

When  shaped  parts  are  manufactured  from  metals,  explosive
metal  dusts  may  be  produced  during  surface 
treatment
(grinding). This particularly applies to light metals. These metal
dusts may give rise to an explosion hazard in dust collectors.

Food and
feedstuffs
industry

Explosive dusts may arise during transport and storage of grain,
sugar,  etc.  If  they  are  exhausted  and  collected  by  filtering,
explosive atmospheres may arise in the filter.

Pharmaceutical
industry

Alcohols  are  often  used  as  solvents  in  the  production  of
pharmaceuticals. Agents and auxiliary materials that give rise to
dust explosions, such as lactose, may also be used.

Refineries

Recycling
operations

The  hydrocarbons  handled  in  refineries  are  all  flammable  and,
depending  on  their  flash  point,  may  give  rise  to  explosive
atmospheres  even  at  ambient  temperature.  The  area  around  oil
processing  plant  is  generally  regarded  as  a  place  where
explosive atmospheres may occur.
Processing  of  waste  for  recycling  can  give  rise  to  explosion
hazards, e.g.  from  cans  or  other  containers  of  flammable  gases
and/or  liquids  that  have  not  been  completely  emptied  or  from
paper or plastic dusts.

3

An  explosion  occurs  if  a  fuel  is  present  in  mixture  with  air  (i.e.  sufficient  oxygen)  within  the
explosion limits, together with a source of ignition (see Figure 1.2). It is to be noted that the directive
has a special definition of "explosion" that includes those fires where combustion spreads to the entire
unburnt mixture.

Oxygen

Ignition
source

Explosion

Fuel

Figure 1.2: Explosion triangle

In the event of an explosion, workers are at risk from uncontrolled flame and pressure effects in the
form  of  heat  radiation,  flames,  pressure  waves  and  flying  debris,  and  from  harmful  products  of
reaction and the depletion of the breathable oxygen in the ambient air.

Examples:1. An  explosion  occurred  during  cleaning  in  a  coal-fired  boiler.  The  two  workmen
suffered fatal burns. The cause was found to be a lamp with a defective supply lead.
The short-circuit ignited coal dust that had been raised into suspension.

2. Solvent-impregnated  dusts  were  being  blended  in  a  mixer.  The  workman  did  not
inert the mixer sufficiently before the start of the process. While the dust was being
loaded into the mixer, an explosive mixture of solvent vapour and air was formed,
and was ignited by electrostatic sparking generated  during  the filling  process. This
workman also suffered severe burns.

3. A  fire  occurred  in  a  mill  building.  Ceiling  penetrations  allowed  secondary  fires  to
develop, giving rise to a dust explosion. Four workmen were injured and the whole
building destroyed. The material damage amounted to € 600 000.

This Guide is a non-binding aid to protecting workers' lives and health against the danger of explosion.

1.1

Relationship with Directive 1999/92/EC

In accordance with Article 11 of Directive 1999/92/EC of the European Parliament and of the Council
on minimum requirements for improving the safety and health protection of workers potentially at risk
from explosive atmospheres, this Guide addresses Articles 3, 4, 5, 6, 7 and 8 and Annexes I and II A
of  the  Directive  (see  Annex  4).  Table  1.2  is  a  concordance  of  the  sections  of  this  Guide  with  the
Articles of the Directive.

4

Table 1.2: Match  between  Articles  of  the  Directive  and  sections  of  this  Guide  (Annex  4  contains  the  original

text of the Articles of the Directive)

Articles of
Directive
1999/92/EC

Art. 2

Art. 3

Art. 4

Art. 5

Art. 6

Art. 7
Annex I
Annex II

Art. 8

Title

Sections of the Guide

Definition

Annex 1: Glossary

Prevention of and protection against
explosions

3.1 Prevention of hazardous explosive

atmospheres

3.3 Mitigation of effects
3.4 Application of process control

engineering

3.5 Requirements for work equipment

Assessment of explosion risks

2. Assessment of explosion risks

General obligations

Duty of coordination

Places where explosive atmospheres
may occur

4. Organisational measures

5. Coordination duties

3.2 Avoidance of ignition sources

Explosion protection document

6. Explosion protection document

For ease of use, the order of sections in this Guide diverges from that of the Articles of 1999/92/EC at
two points:

1.  assessment  of  explosion  risks  in  section  2  (Article  4  of  the  Directive)  is  discussed  before

explosion protection measures (Articles 3, 5–7 of the Directive);

2.  means of preventing the ignition of hazardous explosive atmospheres are discussed in section
3.2 (Article 7, Annex I and II of the Directive)  as  part of the technical explosion  protection
measures under section 3 (Article 3 of the Directive).

1.2

Scope of the Guide

This Guide is intended for all undertakings in which working with flammable substances may give rise
to  hazardous  explosive  atmospheres  and  hence  explosion  hazards.  It  applies  to  work  under
atmospheric conditions. "Working" includes manufacture, treatment, processing, destruction, storage,
readying, transhipment and in-house transportation in pipelines or by other means.

Note:

In  accordance  with  the  legal  definition  of  "explosive  atmosphere"  in  Directive
1999/92/EC, this Guide applies only under atmospheric conditions. The Directive and
Guide  thus  do  not  apply  under  non-atmospheric  conditions,  but  the  employer  is
certainly not absolved of his explosion protection duties under such conditions, to which
the requirements of the other worker health and safety legislation continue to apply.

The discussion of the aspects of explosion protection addressed in the various sections is particularly
geared  to  small  firms.  This  Guide  thus  concentrates  on  conveying  basic  knowledge  and  principles,
which  are illustrated  with  brief  examples.  Specimen  forms  and  checklists  for  firms  can  be  found  in
Annex 3. Pertinent regulations and further sources of information are listed in Annex 2.

5

In accordance with Article 1 of Directive 1999/92/EC, this Guide does not apply to:

areas used directly for and during the medical treatment of patients;

the use of appliances burning gaseous fuels in accordance with Directive 90/396/EEC;

work with explosive substances or unstable chemical substances;

mineral-extracting industries covered by Directives 92/91/EEC or 92/104/EEC;

the  use  of means  of  transport  by  land,  water  and  air  to  which  the  pertinent  provisions  of
international  agreements  (e.g.  ADNR,  ADR,  ICAO,  IMO,  RID),  and  the  Community
Directives giving effect to those agreements, apply. Means of transport intended for use in a
potentially explosive atmosphere are not excluded.

Directive 94/9/EC applies to the placing on the market, putting into service and design of equipment
and protective systems intended for use in potentially explosive atmospheres.

1.3 Pertinent regulations and further information

Use  of  this  Guide  does  not  in  itself  ensure  compliance  with  statutory  explosion  protection
requirements in the various EU Member States. The authoritative instruments are the rules of law by
which the Member States have transposed Directive 1999/92/EC. These may go beyond the minimum
requirements of the Directive, on which this Guide is based.

In  carrying  out  the  duties  under  Article  8  of  Directive  1999/92/EC,  e.g.  designing  new  equipment
according to Directive 94/9/EC, consultation of the ATEX 94/9/EC websites is considered useful:

- http://europa.eu.int/comm/enterprise/atex/index.htm

- http://europa.eu.int/comm/enterprise/atex/whatsnew.htm

As  a  further  aid  to  implementing  the  regulations  by  technical  and  organisational  means,  there  are
European standards (EN), which may be obtained from the national standardisation institutions against
payment. A list is provided in Annex 2.2.

Further  information  can  be  obtained  from  the  national  regulations  and  standards  and  the  pertinent
literature.  Annex  2.3  contains  references  to  individual  publications  by  the  competent  Member  State
authorities  which  are  regarded  as  helpful  and  incorporated  into  the  Guide.  However,  inclusion  of  a
publication in the Annex need not mean that all of its content is entirely consistent with this Guide.

1.4 Official and non-official advice centres

Where  this  Guide  does  not  answer  questions  arising  on  how  to  fulfil  the  explosion  protection
requirements,  the  national  sources  should  be  contacted  directly.  They  include  labour  inspectorates,
accident insurance agencies or associations and chambers of commerce, industry and craft trades.

6

2. Assessment of explosion risks

Whenever possible, the employer should prevent the occurrence of explosive atmospheres. In order to
comply  with  this  highest  priority  as  defined  by  Article  3  of  Directive  1999/92/EC,  the  first  step  in
assessing explosion risks is to determine whether a hazardous explosive atmosphere  can arise under
the circumstances obtaining. It must then be established whether it can ignite.

This  assessment  process  must  always  relate  to  the  individual  case  and  cannot  be  generalised.  The
specific considerations according to Article 4 of Directive 1999/92/EC are the likelihood and duration
of  the  occurrence  of  a  hazardous  explosive  atmosphere,  the  likelihood  that  ignition  sources  will  be
present  and  become  active  and  effective,  the  installations,  substances  used,  processes,  and  their
possible interactions, and the scale of the anticipated effects.

Note: 

Assessment of explosion risks initially focuses on:

•

•

the likelihood that an explosive atmosphere will occur

and subsequently on

the likelihood that sources of ignition will be present and become effective.

Consideration of the effects is of secondary importance in the assessment process, since
explosions  can  always  be  expected  to  do  a  great  deal  of  harm,  ranging  from  major
material  damage  to  injury  and  death.  Quantitative  approaches  to  risk  in  explosion
protection are secondary to the avoidance of hazardous explosive atmospheres.

The  assessment  procedure  must  be  carried  out  for  every  work  or  production  process  and  for  every
operational status and change of status of a plant. Assessment of new or existing plant should be based
on the following operational statuses:

normal operating conditions, including maintenance;

commissioning and decommissioning;

malfunctions, foreseeable fault conditions;

misuse which may reasonably be foreseen.

Explosion risks must be assessed overall. Important factors are

the work equipment used;

the building fabric and configuration;

the substances used;

work and process conditions; and

their possible interactions with each other and the working environment.

Places  which  are  or  can  be  connected  via  openings  to  places  in  which  explosive  atmospheres  may
occur (hereafter "hazardous places") must also be taken into account in assessing explosion risks.

If  an  explosive  atmosphere  contains  various  flammable  gases,  vapours,  mists  or  dusts,  this  must  be
taken  duly  into  account  in  assessing  the  explosion  risks.  The  presence  of  e.g.  hybrid  mixtures  can
considerably increase the effect of the explosion.

Warning: As a general rule, hybrid mixtures of mists or dusts with gases and/or vapours may form
an explosive atmosphere when the concentrations of the individual fuels are still below
their lower explosion limit.

                 Additionally the risk that the detection equipment may be adversely affected by one of

the phases (e.g. the "poisoning" of catalysts by mists) must be evaluated.

7

2.1

Methods

Suitable methods for assessing the explosion risks associated with work processes or plant are those
which lend themselves to a systematic approach to checking plant and process safety. In this context,
"systematic" means that the work is done in a structured manner, on an objective and logical basis. An
analysis is made of the existing sources of hazardous explosive atmospheres and the effective sources
of ignition which could occur at the same time.

In practice, it is usually sufficient to determine and assess the explosion risk by working systematically
through a set of focused questions. A simple procedure is described in section 2.2 below using typical
criteria.

Note:

Other  methods  of  risk  assessment  described  in  the  literature,  for  identifying  hazards
(e.g.  use  of  checklists,  failure  mode  and  effects  analysis,  operating  error  analysis,
HAZOP  analysis)  or  assessing  hazards  (e.g.  event  tree  or  fault  tree  analysis),  are
worthwhile  for  explosion  protection  purposes  only  in  exceptional  cases,  e.g.  to
determine ignition sources in complex plants.

2.2 Assessment criteria

Assessment  of  the  explosion  hazard thus  does  not  depend  solely  on  whether  sources  of  ignition  are
present or may arise.

The following four conditions must be satisfied simultaneously for explosions with hazardous effects
to occur:

a high degree of dispersion of the flammable substances;

concentration of the flammable substances in air within their combined explosion limits;

hazardous quantities of an explosive atmosphere;

an effective source of ignition.

To check whether these conditions are met, explosion risks can in practice be assessed by means of
seven  questions.  Figure  2.1  shows  the  assessment  flowchart,  with  the  questions  underlined.  The
criteria for answering them are explained in the sections indicated. The first four questions are used to
determine in principle whether there is an explosion risk and whether explosion protection measures
are necessary at all. Only if this is the case should the other three questions be considered to determine
whether  the  proposed  protective  measures  limit  the  explosion  risk  to  an  acceptable  level.  This  step
must be performed in conjunction with the choice of protective measures in accordance with section 3
of  this  Guide and repeated  if  necessary  until  an  overall  solution  appropriate  to  the  circumstances  is
found.

For assessment purposes, it must be borne in mind that explosion protection parameters are generally
valid  only  under  atmospheric  conditions.  Under  non-atmospheric  conditions,  the  safety  parameters
may be significantly different.

Examples:1. The  minimum  ignition  energy  can  be  greatly  reduced  at  elevated  oxygen

concentrations or temperatures.

2. Elevated initial pressures give rise to higher maximum explosion pressures and rates

of pressure rise.

3. The  range  between  the  explosion  limits  is  widened  at  elevated  temperatures  and
pressures.  This  means  that  the  lower  explosion  limit  may  be  lower  and  the  upper
explosion limit higher.

8

Are flammable substances
present [2.2.1]?

No

Can sufficient dispersal in air give rise
to an explosive mixture [2.2.2]?

No

Where can explosive atmospheres
occur [2.2.3]?

Is the formation of an explosive
atmosphere possible [2.2.4]?

No

Yes

Yes

Cont.

Yes

No explosion
protection measures
necessary
No explosion
protection measures
necessary

No explosion
protection measures
necessary

Explosions
Explosion
schutzmaß-
protection
nahmen
measures
necessary

Prevent the formation of hazardous explosive
atmospheres as far as possible

Is the formation of hazardous
explosive atmospheres
reliably prevented [2.2.5]?

No

Yes

Apply adequate
explosion
protection measures
necessary

Further
Weitere Ex-
explosion
plosionsschutz-
protection
maßnahmen
measures
necessary

To what zones can the places with
hazardous explosive atmospheres be
assigned [3.2.1]?

Cont.

Avoid effective ignition sources in
places with hazardous explosive
atmospheres as per zoning

Is the ignition of hazardous
explosive atmospheres highly
improbable [2.2.6]?

No

Yes

Apply adequate and
proportionate
mitigation measures

Further
Weitere Ex-
explosion
plosionsschutz-
protection
measures
necessary

Mitigate the detrimental effects of an explosion so as to
ensure the health and safety of workers.

Figure 2.1: Assessment flowchart for recognition and prevention of explosion hazards

Figure  2.1  contains  questions  about  "reliable"  prevention  of  the  formation  of  hazardous  explosive
atmospheres. The answer "Yes" can be given only if the technical and organisational measures already
taken are such that there is no need to take into account the occurrence of an explosion, having regard
to all operating conditions and reasonably foreseeable cases of malfunction.

9

2.2.1 Are flammable substances present?

An  explosion  will  occur  only  if  flammable  substances  are  present  in  the  working  or  production
process. This means that at least one flammable substance is used as a raw or auxiliary material, arises
as  a  waste,  intermediate  or  final  product  or  can  be  formed  in  the  event  of  a  common  operational
malfunction.

Example: Flammable substances may also occur accidentally, e.g. when weak acids or alkalis are
stored  in  metal  containers.  In  such  cases  hydrogen  may  be  formed  by  an  electro-
chemical reaction and accumulate in the gaseous phase.

All  substances  capable  of  an  exothermic  oxidation  reaction  are  to  be  regarded  as  flammable.  In
particular, these include all substances which are already classified and labelled as flammable (R10),
highly flammable (F and R11/R15/R17) or extremely flammable (F+ and R12) under the Dangerous
Substances  Directive  67/548/EEC.  However,  they  also  include  all  other  substances  and  preparations
that  are  not  (yet)  classified  but  satisfy  the  appropriate  ignitability  criteria  or  are  generally  to  be
regarded as ignitable.

Examples:1. Flammable  gases  and  gas  mixtures,  e.g.  liquefied  gas  (butane,  butene,  propane,
propylene),  natural  gas,  combustion  gases  (e.g.  carbon  monoxide  or  methane)  or
gaseous flammable chemicals (e.g. acetylene, ethylene oxide or vinyl chloride).

2. Flammable  liquids,  e.g.  solvents,  fuels,  petroleum,  heating,  lubricating  or  waste

oils, paints, water-insoluble and water-soluble chemicals.

3. Dusts  of 

coal,  wood, 
(e.g. sugar, flour or cereals), plastics, metals or chemicals.

flammable 

solids, 

e.g. 

food 

and 

feedstuffs

Note:

A  number  of  substances  are  not  readily  flammable  under  normal  conditions  but  are
explosive  when  mixed  with air  if  the  particle  size  is  particularly  small  or  the  ignition
energy sufficiently high (e.g. metal dusts, aerosols).

Explosion hazards need be further considered only if flammable substances are present.

2.2.2 Can sufficient dispersal in air give rise to an explosive atmosphere?

Whether an explosive atmosphere can form in the presence of flammable substances depends on the
ability to ignite of the mixture formed with air. If the necessary degree of dispersion is attained and if
the  concentration  of  the  flammable  substances  in  air  lies  within  their  explosion  limits,  an  explosive
atmosphere is present. By their very nature, gases and vapours have a sufficient degree of dispersion.

To answer the above question, one must take into account the following properties of the substances
and their possible processing states.

1.  Flammable gases and gas mixtures:
Lower and upper explosion limit

Maximum (sometimes also minimum) concentrations of the flammable substances arising or
obtaining during work with them

2.  Flammable liquids:

Lower and upper explosion limit of vapours

Lower explosion limit of mists

Flash point

Note:

Explosive mixtures are not to be assumed to be present inside containers if the
temperature within the container is at all times kept far enough below the flash
point (by about 50 C to 150 C – see example in section 3.1.2).

10

Working or ambient temperatures

Note:

If  e.g.  the  maximum  working  temperature  is  not  far  enough  below  the  flash
point of the liquid, explosive vapour/air mixtures may be present.

Manner  of  working  with  a  liquid  (e.g.  spraying,  squirting  and  dispersal  of  a  jet  of  liquid,
evaporation and condensation)

Note:

If  liquids  are  dispersed  into  droplets,  e.g.  by  spraying,  explosive  atmospheres
may be formed even at temperatures below the flash point.

Use of a liquid at high pressure (e.g. in hydraulic systems)

Note:

Where there are leaks in the enclosures of high-pressure flammable liquids, the
liquid may, depending on size of leak, overpressure and material stability, squirt
out and form explosive mists, which may then become explosive vapours.

Maximum (sometimes also minimum) concentrations of the flammable substances arising or
obtaining during work with them (only inside apparatus/installations)

3.  Dusts of flammable solids:

Presence or formation of dust/air mixtures or dust deposits

Examples:1. grinding or screening;

2. conveying, filling or discharging;

3. drying.

Maximum  concentrations  of  the  flammable  substances  arising  or  obtaining  during  work
with compared to the lower explosive limit.

Figure 2.2: Examples for the formation of dust/air mixtures in filling and transport operations4

4 

From the ISSA leaflet "Gas Explosions", International Section for the Prevention of Occupational Risks
in the Chemical Industry, International Social Security Association (ISSA), Heidelberg, Germany

11

                                                     
Lower and upper explosion limit

Note:

In practice, explosion limits are not as useful for dusts as for gases and vapours.
The  dust  concentration  can  be  greatly  changed  when  deposits  are  raised  into
suspension  or  suspended  dust  settles.  Explosive  atmospheres  may  thus  arise
when dust is raised into suspension.

Particle size distribution (the < 500 µm fines fraction is of interest), moisture, smouldering
point.

2.2.3 Where can explosive atmospheres occur?

If explosive atmospheres can be formed, one must determine where they occur at the workplace or in
the  plant  in  order to  delimit  the  potential  risk.  To  this  end,  the  properties  of  the  substances  and  the
plant, process engineering and environmental factors applying must in turn be taken into account:

1.  Gases and vapours:

Density  ratio  to  air  –  the  heavier  gases  and  vapours  are,  the  faster  they  sink,  mixing
progressively with the available air and accumulating in trenches, conduits and shafts.

- Gases are generally denser than air e.g. propane. Such accumulations tend to sink and

spread out, and can also "creep" over long distances and then be ignited.

-

Some  gases  have  approximately  the  same  density  as  air,  e.g.  acetylene,  hydrogen
cyanide, ethylene, carbon monoxide. There is little natural tendency for these gases to
dissipate, or to sink.

- A  few  gases  are  much  lighter  than  air,  e.g.  hydrogen,  methane.  These  gases  have  a

natural tendency to dissipate into the atmosphere unless they are enclosed..

Even slight air movements (natural draught, people moving about, thermal convection) may
considerably speed up mixture with air.

Figure 2.3: Spread of liquefied gases (example) 4

4 

From the ISSA leaflet "Gas Explosions", International Section for the Prevention of Occupational Risks
in the Chemical Industry, International Social Security Association (ISSA), Heidelberg, Germany

12

                                                     
2.  Liquids and mists:

Evaporation  number,  characterising  the  amount  of  explosive  atmosphere  that  forms  at  a
particular temperature

Size  of  evaporation  area  and  working  temperature,  e.g.  when  liquids  are  sprayed  or
squirted

Overpressure  by  means  of  which  the  sprayed  liquids  are  discharged  and  form  explosive
mists.

3.  Dusts:

Occurrence of dust raised into suspension, e.g. in filters, during transport in containers, at
transfer points or inside dryers

Formation of dust deposits, especially on horizontal or slightly inclined surfaces, and raising
of dust into suspension

Grain size.

Other local and operating conditions must also be taken into account:

Manner of working with substances: under gas-, liquid- or dust-tight enclosure or in open
apparatus, e.g. charging and discharging

Possible leakage at valves, pipe connections, etc.

Ventilation conditions and other spatial factors

Places which are not ventilated, e.g. unventilated below ground level areas such as trenches,
conduits  and  shafts,  are  particularly  prone  to  the  presence  of  flammable  substances  or
mixtures.

2.2.4

Is the formation of a hazardous explosive atmosphere possible?

If  an  explosive  atmosphere  may  occur  locally  in  such  quantities  as  to  require  special  protective
measures to maintain the safety and health of the workers concerned, it is described as a  hazardous
explosive atmosphere and the places in question are classified as hazardous places.

Figure 2.4: Evaporation of even small quantities of flammable liquids (such as liquefied propane) may
give  rise  to  large  quantities  of  flammable  vapours.  Note:  1  litre  of  liquid  propane  when
transformed  into  gas  and  diluted  in  air  to  the  lower  explosive  limit  would  give  a  13,000
litre explosive atmosphere. 4

4 

From the ISSA leaflet "Gas Explosions", International Section for the Prevention of Occupational Risks
in the Chemical Industry, International Social Security Association (ISSA), Heidelberg, Germany

13

                                                     
Once the existence of a potential explosive atmosphere has been established, whether it is a hazardous
explosive atmosphere depends on its volume and the harmful consequences of any ignition. In general,
however, it can initially be assumed that an explosion will cause substantial harm and that a hazardous
explosive atmosphere is present.

Exceptions  to  this  rule  may  apply  to  work  with  very  small  quantities,  e.g.  in  laboratories.  In  such
cases,  it  has  to  be  decided  on  the  basis  of  local  and  operational  conditions  whether  the  anticipated
amounts of explosive atmosphere are hazardous.

Examples:1. A continuous volume of over 10 litres of explosive atmosphere in a confined space
must  always  be  regarded  as  a  hazardous  explosive  atmosphere,  irrespective  of  the
size of the room.

2. A  rough  estimate  can  be  made  by  the  rule  of  thumb  that  in  such  rooms  explosive
atmospheres must be regarded as potentially hazardous if they occupy more than one
ten thousandth of the room volume, e.g. only 8 litres in a room of 80 m3. However,
this does not mean that the whole room is to be regarded as a hazardous place, but
only the part in which the hazardous explosive atmosphere can arise.

3. For most combustible dusts, a deposit less than 1 mm deep evenly distributed over
the whole floor area is sufficient, if raised into suspension, to fill completely a room
of normal height with an explosive dust/air mixture.

4. Where explosive atmospheres are contained in vessels incapable of withstanding the
potential  explosion  pressure,  much  smaller  volumes  than  indicated  above  must  be
regarded as hazardous because of the danger which may arise, e.g. from flying debris
on rupture. No lower limit for this hazard can be indicated.

A further factor to be taken into account in assessing whether a hazardous explosive atmosphere can
arise in a particular situation is the effect resulting from the destruction of nearby items of plant.

Note:

An  explosion  may  also  cause  damage  in  the  surrounding  area,  which  in  turn  causes
flammable or other dangerous substances to be released and perhaps ignited.

2.2.5

Is the formation of hazardous explosive atmospheres reliably prevented?

If it is possible for a hazardous explosive atmosphere to be formed, explosion protection measures are
necessary. An attempt should first be made to avoid the occurrence of explosive atmospheres. Section
3.1  describes  possible  technical  measures  to  this  end,  to  be  considered  in  conjunction  with
organisational measures as described in section 4.

The  effectiveness  of  the  explosion  protection  measures  taken  must  be  assessed.  To  this  end,  all
operational statuses and all malfunctions (including rare ones) must be taken into account. Only if the
occurrence  of  hazardous  explosive  atmospheres  is  reliably  prevented  is  it  possible  to  dispense  with
further measures.

2.2.6

Is the ignition of hazardous explosive atmospheres reliably prevented?

If it cannot be entirely ruled out that hazardous explosive atmospheres may form, measures to avoid
effective  ignition  sources  are  necessary.  Thus  the  more  likely  it  is  that  hazardous  explosive
atmospheres will arise, the more certain must be the avoidance of such sources. Section 3.2 describes
possible  technical  measures,  to  be  considered  in  conjunction  with  organisational  measures  as
described in section 4.

If it is not highly improbable that hazardous explosive atmospheres and effective sources of ignition
will occur simultaneously, explosion mitigation measures must also be taken as described in section
3.3  in  conjunction  with  organisational  measures  as  described  in  section  4.  Otherwise  proportionate
mitigation measures must be taken.

14

3. Technical measures for explosion protection

"Explosion protection measures" means all measures that

prevent the formation of hazardous explosive atmospheres,

avoid the ignition of hazardous explosive atmospheres or

mitigate the effects of explosions so as to ensure the health and safety of workers.

3.1

Prevention of hazardous explosive atmospheres

According  to  Article  3  "Prevention  of  and  protection  against  explosions"  of  Directive  1999/92/EC,
preventing the formation of hazardous explosive atmospheres must always be given priority.

3.1.1 Use of substitutes for flammable substances

The formation of hazardous explosive atmospheres can be prevented by avoiding or reducing the use
of flammable substances. An example is the replacement of flammable solvents and cleaning agents
with aqueous solutions. As regards dusts, it is sometimes possible to increase the particle size of the
substances used, so that explosive mixtures cannot be formed. Care must then be taken to ensure that
further  processing  does  not  reduce  particle  size,  e.g.  through  abrasion.  A  further  possibility  is  to
moisten the dust or use paste products, so that they can no longer be raised into suspension.

3.1.2 Limiting of concentrations

Gases  and  dusts  are  explosive  only  within  certain  limits  of  concentration  in  air.  Under  certain
operating  and  ambient  conditions,  it  is  possible  to  remain  outside  these  explosion  limits.  If  these
conditions are reliably assured, there is no explosion hazard.

In closed containers and plant, it is usually fairly easy to keep the concentration of gases and vapours
of flammable liquids outside the explosion limits.

Example:  The  concentration  in  the  headspace  above  flammable  liquids  can  be  guaranteed  to
remain below the lower explosion limit if the temperature at the surface of the liquid is
at  all  times  kept  far  enough  below  the  flash  point  (a  temperature  difference  of  50  C
usually affords adequate safety for pure solvents and 150 C for solvent mixtures). The
upper explosion limit is usually exceeded for flammable liquids with a low flash point
(e.g. in a car petrol tank).

Where dusts are concerned, it is harder to avoid explosive mixtures by limiting the concentration. If the
airborne  dust  concentration  is  below  the  lower  explosion  limit,  dust  deposits  form  by  settlement  if
there is insufficient air movement. These can be raised into suspension, creating explosive mixtures.

Note: 

Dust particles are separated in filters, where they form accumulations which may have
considerable fire and explosion potential.

3.1.3

Inerting

A hazardous explosive atmosphere can also be avoided by diluting the fuel or the atmospheric oxygen
inside plant with chemically non-reactive (inert) materials. This is known as "inerting".

To  design  this  measure,  it  is  necessary  to  know  the  highest  oxygen  concentration  at  which  no
explosion  yet  occurs:  the  limiting  oxygen  concentration.  This  is  determined  experimentally.  The
maximum  permissible  oxygen  concentration  is  obtained  by  deducting  a  safe  concentration  margin

15

from  the  limiting  oxygen concentration.  If  the fuel is  diluted  with  an  inert  substance,  the  maximum
permissible fuel concentration must be determined in the same way. If the oxygen concentration could
vary quickly, or could be very different in different parts of the plant, a large safety margin would be
required.  Operating  mistakes  and  equipment  faults  should  be  considered.  A  further  aspect  to  be
considered  is  the  time  required  for  any  protective  measures  or  emergency  functions  triggered  to
become effective.

Example:  The main inert gases used are nitrogen, carbon dioxide, noble gases, combustion gases
and water vapour. Inert dusts include calcium sulphate, ammonium phosphate, sodium
hydrogen carbonate, stonedust, etc. In choosing the inert substance, it is important that it
should not react with the fuel (aluminium, for example, can react with carbon dioxide).

Note: 

Dust deposits may give rise to glowing or smouldering fires even at low oxygen or fuel
concentrations,  well  below  those  which  are  adequate  to  ensure  reliable  avoidance  of
explosions.  A  mixture  of  95  %  wt  limestone  and  5  %  wt  coal,  for  example,  can  still
exhibit a strong exothermal reaction.

Inertisation with gases can generally be practised only in enclosed plant, where it is possible to ensure
a fairly low rate of  gas  replacement.  If  inert  gas is  emitted through  openings  in  the  plant  which  are
present in normal operation or result from defects, workers may be at risk from oxygen displacement
(suffocation). Workers may be poisoned if combustion gases used for inerting are emitted from plant.
Openings  present  in  normal  operation  may,  for  example,  be  manual  charging  ports.  If  these  are
opened,  it  has  to  be  borne  in  mind  that  inert  gas  may  be  emitted  from  the  plant  and  atmospheric
oxygen may enter it.

3.1.4 Preventing or limiting the formation of explosive atmospheres in the vicinity of plant

Formation of hazardous explosive  atmospheres around  plant  should be  prevented  as far  as possible.
This can be achieved by means of enclosed plant. The items of plant must therefore be leakproof. The
plant  design  must  be  such  that  no  significant  leakage  occurs  under  the  foreseeable  operating
conditions. One of the ways of ensuring this is by regular servicing.

If  the  release  of  flammable  substances  cannot  be  prevented,  forming  of  hazardous  explosive
atmospheres can often be prevented by ventilation. The following points must be taken into account in
judging how effective ventilation is:

Gases, vapours and mists: to design a ventilation system, one must estimate the maximum
amount of gases, vapours and mist that might be  released (source  strength)  and  know the
source location and dispersion conditions.

Dusts:  ventilation  generally  affords  adequate  protection  only  if  the  dust  is  exhausted  at
source and hazardous dust deposits are reliably prevented.

In  the  best  case,  adequate  ventilation  can  preclude  hazardous  places.  However,  because  of
the  limitations  mentioned,  all  that  is  achieved  may  be  a  reduction  in  the  likelihood  of
hazardous explosive atmospheres or a reduction in the extent of the hazardous places (zones).

It is recommended that spot checks be made of the concentrations arising at different places and times
under unfavourable operating conditions.

16

Figure 3.1: Example  of  the  correct  arrangement  of  ventilation  openings  for  heavier-than
air gases and vapours 4

3.1.4.1 Removal of dust deposits

Hazardous dust deposits can be avoided by regular cleaning of work and technical rooms. A proven
approach is the use of cleaning schedules prescribing the nature, extent and frequency of cleaning and
the  responsibilities  of  those  concerned.  These  instructions  can  be  tailored  to  the  specific  case.
Particular attention should be paid to (e.g. elevated) surfaces which are difficult to inspect  or reach,
where considerable amounts of dust may be deposited over time. Where appreciable quantities of dust
are released as a result of operational malfunctions (e.g. damage to or bursting of containers, leakage)
additional steps should be taken to remove the dust deposits with as little delay as possible.

Wet  cleaning  and  exhausting  of  dust  deposits  (using  central  extraction  systems  or  mobile  industrial
vacuum  cleaners  containing  no  ignition  sources)  has  proved  to  have  safety  advantages.  Cleaning
processes  in  which  dust  is  raised  into  suspension  should  be  avoided  (see  Figure 3.2).  It  should  be
borne  in  mind  that  wet  cleaning  can  create  extra  problems  of  disposal.  Where  light-metal  dusts  are
collected in  wet  scrubbers,  it  must  be  borne in  mind  that hydrogen  may  be  formed.  The  practice  of
blowing away deposited dust should be avoided.

4 

From the ISSA leaflet "Gas Explosions", International Section for the Prevention of Occupational Risks
in the Chemical Industry, International Social Security Association (ISSA), Heidelberg, Germany

17

                                                     
Figure 3.2: Removal of dust deposits4

The  cleaning  arrangements  can  be  laid  down  as  part  of  operational  instructions  for  working  with
flammable substances.

Note: 

Only vacuum cleaners containing no ignition sources may be used for flammable dusts.

3.1.5  Gas alarms

Concentrations  in  the  vicinity  of  plant  can  be  monitored  e.g.  by  means  of  gas  alarms.  Major
prerequisites for their use are as follows:

The substances likely to be  present,  the  location  of  the  sources,  maximum  source  strength
and dispersion conditions must be adequately known.

The  instrument  performance  must  be  appropriate  to  the  conditions  of  use,  especially  as
regards response time, alarm level and cross-sensitivity.

No dangerous conditions may arise on failure of individual functions of gas alarm systems
(reliability).

The  number  and  location  of  measuring  points  must  be  so  chosen  that  the  anticipated
mixtures can be detected quickly and reliably.

It  must  be  known  what  area  is  at  risk  until  the  protective  measures  triggered  by  the
instrument become effective. In this immediate area – which depends on the above points –
sources of ignition must be avoided.

The  protective  measures  triggered  must  prevent  the  occurrence  of  hazardous  explosive
atmospheres outside the immediate  area with  a  sufficient  degree  of  certainty  and  spurious
triggering may not give rise to other hazards.

Gas  alarms  for  use  in  hazardous  places  must  be  approved  and  suitably  marked  as  safe  electrical
equipment pursuant to the European Directive 94/9/EC.

Note: 

Gas  alarms  for  use  as  safety,  controlling  and  regulating  devices  in  avoiding  ignition
sources (e.g. to switch off a non-explosionproof item of equipment on the occurrence of
a hazardous explosive atmosphere) must undergo individual or type checks/calibration
to  ensure  their  suitability  for  their  intended  use.  The  requirements  of  the  European
Directive 94/9/EC must be satisfied (see also 3.4 Process control engineering).

4 

From the ISSA leaflet "Gas Explosions", International Section for the Prevention of Occupational Risks
in the Chemical Industry, International Social Security Association (ISSA), Heidelberg, Germany

18

                                                     
3.2

Avoidance of ignition sources

If it is not possible to prevent the formation of a hazardous explosive atmosphere, its ignition must be
avoided.  This  can  be  achieved  by  protective  measures  which  avoid  or  reduce  the  probability  of
ignition  sources.  To  lay  down  effective  precautions,  one  must  know  the  various  types  of  ignition
source and the ways in which they operate. The probability that a hazardous explosive atmosphere and
a  source  of  ignition  will  be  present  at  the  same  time  and  place  is  estimated  and  the  extent  of  the
measures required is determined accordingly. This is done on the basis of the zone system described
below, from which the necessary precautions are derived.

Figure 3.3: Examples of the most common potential ignition sources4

3.2.1 Zoning of hazardous places

A  hazardous  place  is  a  place  in  which  an  explosive  atmosphere  may  occur  in  such  quantities  as  to
require special precautions to protect workers against explosion hazards. Such a quantity is termed a
hazardous  explosive  atmosphere.  As  a  basis  for  determining  the  extent  of  protective  measures,  any
remaining  hazardous  places  must  be  classified  in  terms  of  zones  according  to  the  likelihood  of
occurrence of such atmospheres.

Zone 0: A  place  in  which  an  explosive  atmosphere  consisting  of  a  mixture  with  air  of  flammable
substances in the form of gas, vapour or mist is present continuously or for long periods or
frequently.

Example:  Zone 0 conditions generally arise only inside containers or plant (evaporators, reaction

vessels, etc.), but can also occur near vents and other openings.

Zone 1: A  place  in  which  an  explosive  atmosphere  consisting  of  a  mixture  with  air  of  flammable
substances  in  the  form  of  gas,  vapour  or  mist  is  likely  to  occur  in  normal  operation
occasionally.

Example:  This may include:

•

•

•

the immediate vicinity of zone 0;

the immediate vicinity of feed openings;

the immediate area around fragile vessels or pipes made of glass, ceramics, and 
the  like,  unless  the  contents  are  too  small  to  form  a  hazardous  explosive

atmosphere;

•

the immediate area around inadequately sealed glands, e.g. at pumps and valves;

4 

From the ISSA leaflet "Gas Explosions", International Section for the Prevention of Occupational Risks
in the Chemical Industry, International Social Security Association (ISSA), Heidelberg, Germany

19

                                                     
•

the inside of plant such as evaporators or reaction vessels.

Zone 2: A  place  in  which  an  explosive  atmosphere  consisting  of  a  mixture  with  air  of  flammable
substances in the form of gas, vapour or mist is not likely to occur in normal operation but,
if it does occur, will persist for a short period only.

Example:  Zone 2 may include, e.g.

• places surrounding zones 0 or 1.

Note: 

Places  where  flammable  substances  are  transported  only  in  pipes  which  are  durably
technically leakproof are not hazardous places.

Zone 20: A place in which an explosive atmosphere in the form of a cloud of combustible dust in air

is present continuously, or for long periods or frequently.

Example:  In general, these conditions arise only inside containers, pipes, vessels, etc., i.e. usually
only  inside  plant  (mills,  dryers,  mixers,  pipelines,  silos,  etc.),  when  explosive  dust
mixtures in hazardous quantities can form continuously, over long periods or frequently.

Zone 21: A place in which an explosive atmosphere in the form of a cloud of combustible dust in air

is likely to occur in normal operation occasionally.

Example:  This  zone  can,  for  example,  include  places  in  the  immediate  vicinity  of  e.g.  powder
filling  and  emptying  points  and  places  where  dust  deposits  occur  and  in  normal
operation give rise occasionally to an explosive concentration of combustible dust when
mixed with air.

Zone 22: A place in which an explosive atmosphere in the form of a cloud of combustible dust in air
is not likely to occur in normal operation but, if it does occur, will persist for a short period
only.

Example:  This zone can include, e.g.:

•

places  in  the  vicinity  of  plant  containing  dust,  if  dust  can  escape  at  leaks  and  form
deposits in hazardous quantities.

N.B.

Layers,  deposits  and  heaps  of combustible  dust  must  be  considered,  like  any  other  source
which can form a hazardous explosive atmosphere.

"Normal  operation"  means  the  situation  when  installations  are  used  within  their  design
parameters.

Note: 

Deposited  combustible  dust  has  considerable  explosion  potential.  Dust  deposits  may
accumulate  on  all  deposition  surfaces  in  a  technical  room.  A  primary  explosion  may
raise  deposited  dust  into  suspension  and  initiate  a  chain  reaction,  causing  many
successive explosions with devastating effects.

3.2.1.1 Example of zoning for hazardous places resulting from flammable gases

Figure  3.4  shows  a  tank  for  flammable  liquids.  The  tank  is  in  the  open  air,  is  filled  and  emptied
regularly  and  is  connected  to  the  ambient  atmosphere  by  means  of  a  pressure  equalising  port.  The
flash point of the flammable liquid is close to the average annual temperature and the density of the
resulting  vapours  is  greater  than  that  of  air.  There  is  thus  a  chronic  risk  of  hazardous  explosive
atmospheres' occurring inside the tank. The inside of the tank is therefore classified as zone 0.

20

Zone 0

Zone 1

Zone 2

Surface of
the liquid

Figure 3.4: Example of zoning at a tank for flammable liquids

Vapours  may  occasionally  be  emitted  from  the  pressure  equalising  port  and  may  form  explosive
mixtures.  The  area  around  the  opening  is  therefore  classified  as  zone 1.  Under  infrequent  adverse
weather  conditions,  the  vapours  may  run  down  the  outside  of  the  tank  wall  and  form  a  hazardous
explosive atmosphere. An area around the tank is therefore classified as zone 2.

The  size  of  the  zones  outside  the  tank  depends  on  the  anticipated  amount  of  vapour  release.  This
depends  on  the  properties  of  the  liquid,  the  size  of  the  aperture  and  the  frequency  of  filling  and
emptying, as well as the average change in the liquid level. The size of the hazardous places largely
depends on the availability of natural ventilation.

3.2.1.2 Example of zoning for hazardous places resulting from flammable dusts

Zone 20
Zone 21

Zone 22

Figure 3.5:

Example of zoning for flammable dusts

21

Figure 3.5 shows a mill with a (manually charged) feed hopper, product discharge and filter. A dust
forming, flammable product is loaded by hand from a drum into the hopper.

During  the loading  process,  an  explosive  mixture  of  dust  and  air  may  occasionally  form  in  the  area
where the drum is emptied into the loading hopper. This area is classified as zone 21. There are dust
deposits in an area around the hopper. These may form a hazardous explosive atmosphere when raised
into suspension, which occurs infrequently and briefly. This area is classified as zone 22.

In normal operation, there is a cloud of dust in the mill. A dust cloud is also formed at regular intervals
by cleaning of the filter bags. The inside of the mill and the filter are therefore classified as zone 20.
The  ground  product  is  discharged  continuously.  A  dust  cloud  consisting  of  an  explosive  mixture  is
thus formed in normal operation in the discharge container, which is therefore classified as zone 20.
As a result of leakage, there are dust deposits around the discharge. This area is classified as zone 22.
The size of zones 21 and 22 depends on the dusting propensity of the product used.

22

3.2.2 Extent of protective measures

The  extent  of  protective  measures  depends  on  the  likelihood  that  hazardous  explosive  atmospheres
will arise (zoning) and should therefore be determined in accordance with Table 3.1 below.

Table 3.1: Extent of protective measures in the various zones

Zoning

0 or 20

1 or 21

2 or 22

Ignition sources*) to be reliably avoided:
(cid:1)  in normal operation (no malfunction)
(cid:1)  in foreseeable cases of malfunction and
(cid:1)  in the event of rare malfunctions
(cid:1)  in normal operation (no malfunction) and
(cid:1)  in foreseeable cases of malfunction
(cid:1)  in normal operation (no malfunction)

*)

In zones 20, 21 and 22, the possibility of deposited dust ignition must also be taken into account.

The table applies to all types of ignition source.

3.2.3 Types of ignition source

Standard EN 1127-1 distinguishes thirteen types of ignition source:

hot surfaces

flames and hot gases

mechanically generated sparks

electrical apparatus

stray electrical currents, catrhodic corrosion protection

static electricity

lightning

electromagnetic  fields in the frequency range from 9 kHz to 300 GHz
electromagnetic  radiation  in  the  frquency  range  from  300  GHz  to  3  x  106  GHz  or
wavelength range from 1000µm to 0.1 µm (optical spectrum)

ionising radiation

ultrasonics

adiabatic compression, shock waves, gas flows

chemical reactions.

The following sections discuss only ignition  sources that  are  of  particular  importance in  operational
practice. Further details on the various types of ignition source and their assessment can be found in
EN 1127-1.

3.2.3.1 Hot surfaces

Explosive  atmospheres  can  be  ignited  by  contact  with  hot  surfaces,  if  the  temperature  of  a  surface
reaches the atmosphere's ignition temperature.

Example:  Surfaces  which  become  hot  in  normal  operation  are  e.g.  heating  systems,  some
electrical  equipment  and  hot  pipes.  Hot  surfaces  resulting  from  malfunction  are  e.g.
moving parts which overheat because of inadequate lubrication.

23

If  hot  surfaces  can  come  in  contact  with  explosive  atmospheres,  a  safety  margin  should  be  ensured
between  the  maximum  surface  temperature  and  the  atmosphere's  ignition  temperature.  This  margin
depends on the zoning and is determined in accordance with EN 1127-1.

Note: 

Dust deposits have an insulating effect and therefore inhibit dissipation of heat into the
surrounding atmosphere. The thicker the layer, the less heat dissipates. This can lead to
heat  build-up  and  hence  to  a  further  rise  in  temperature.  This  process  can  result  in
ignition  of  the  dust  layer.  Equipment  which  according  to  Directive  94/9/EC  can  be
operated safely in an explosive gas/air atmosphere is thus not necessarily suitable for
operation in places where there is a dust/air explosion hazard.

3.2.3.2 Flames and hot gases

Both flames and incandescent solid particles can ignite explosive atmospheres. Even very small flames
are  among  the  most  effective  sources  of  ignition  and  must  therefore  generally  be  eliminated  from
hazardous places belonging to zones 0 and 20. In zones 1, 2, 21 and 22, flames should occur only if
they are safely enclosed (see EN 1127-1). Naked flames from welding or smoking must be prevented
by organisational measures.

3.2.3.3 Mechanically generated sparks

Friction, impact and abrasion processes, such as grinding, can give rise to sparking. Such sparks can
ignite flammable gases and vapours and certain mist/air or dust/air mixtures (especially metal dust/air
mixtures).  In  deposited  dust,  smouldering  can  be  caused  by  the  sparks,  and  this  can  be  an  ignition
source for explosive atmospheres.

Ingress  of  foreign  materials,  e.g.  stones  or  tramp  metals,  into  equipment  or  items  of  plant  must  be
considered as a cause of sparking.

Note: 

Friction, impact and abrasion processes involving rust and light metals (e.g. aluminium
and  magnesium)  and  their  alloys  may  initiate  an  aluminothermic  (thermite)  reaction
which can give rise to particularly incendive sparking.

Incendive  frictional  and  impact  sparking  can  be  limited  by  choosing  suitable  material  combinations
(e.g. in fans). The combination of light metal and steel (except stainless steel) must always be avoided
at  places  where  friction,  impact  or  abrasion  can  occur  in  equipment  which  in  normal  operation  has
moving parts.

3.2.3.4 Chemical reactions

Chemical  reactions  which  develop  heat  (exothermic  reactions)  can  cause  substances  to  heat  up  and
thus become a source of ignition. Such self-heating is possible if the rate of heat generation exceeds
the rate of heat loss to the surroundings. If heat dissipation is impeded or the ambient temperature is
high (e.g. in storage), the rate of reaction can so increase that the conditions for ignition are attained.
Among  the  decisive  parameters  are  the  volume/surface  ratio  of  the  reacting  system,  the  ambient
temperature  and  the  residence  time.  The  high  temperatures  developed  can  lead  to  the  initiation  of
smouldering  and/or  burning  and  also  to  the  ignition  of  explosive  atmospheres.  Any  flammable
substances arising from  the  reaction (e.g.  gases  or  vapours)  can in  turn form  explosive  atmospheres
with the surrounding air and thus greatly increase the hazardousness of such systems.

In  all  zones,  substances  prone  to  spontaneous  combustion  should  therefore  be  avoided  as  far  as
possible. When it is necessary to work with such substances, the necessary protective measures must
be tailored to each individual case.

24

Note: 

Suitable protective measures are, e.g.

1. inerting;

2. stabilisation;

3. improving heat dissipation, e.g. by dividing the substances into smaller portions or

providing separating spaces between stored quantities;

4. control of the plant temperature;

5. storage at lowered ambient temperatures;

6. keeping residence times shorter than the time required for dust fires to be initiated.

3.2.3.5 Electrical apparatus

Even at low voltages, electrical sparking and hot surfaces may occur as sources of ignition in electrical
apparatus (e.g. on making and breaking circuits and as a result of stray electric currents).

Electrical equipment may therefore be used in hazardous places only if it complies with Annex II to
Directive 1999/92/EC. In all zones, new equipment must be selected on the basis of the categories set
out in Directive 94/9/EC. In accordance with the explosion protection document the work equipment,
including warning devices, must be designed, operated and maintained with due regard for safety.

3.2.3.6 Static electricity

Separation  processes  involving  at  least  one  material  with  a  specific  electrical  resistance  of  over
109 Ωm or objects with a surface resistance of over 109 Ω may under certain conditions give rise to
incendive discharges of static electricity. Figure 3.1 shows various ways in which electrostatic charges
may  result  from  charge  separation.  The  following  forms  of  discharge  may  occur  under  normal
operating conditions:

Spark discharges:
Spark discharges may arise from charge accumulation on unearthed conductive parts.

Brush discharges:
Brush  discharges  may  arise  on  charged  parts  made  of  non-conductive  materials,  which
include most plastics.

Propagating brush discharges:
"Propagating brush  discharges"  may  occur in fast  separation  processes, e.g. films  moving
over  rollers,  during  pneumatic  transport  in  metal  pipes  or  containers  with  an  insulating
coating or on drive belts.

Cone discharges:
Cone discharges may occur, e.g. during pneumatic filling of silos.

All  the  above  forms  of  discharge  are  to  be  regarded  as  capable  of  igniting  most  gases  and  solvent
vapours.  Mist  or  dust/air  mixtures  can  also  be  ignited  by  these  forms  of  discharge,  though  brush
discharges are to be regarded as merely a possible source of ignition for explosible dusts.

25

Figure 3.6: Examples of charge separation which can lead to electrostatic charges4

For  the  necessary  assessment  and  possible  protective  measures,  see  CENELEC  Report  R044-001
"Guidance and recommendations for the avoidance of hazards due to static electricity".

Examples:Important protective measures to be taken, depending on the zone:

1. earthing conductive objects and installations;

2. wearing  suitable  footwear  at  all  times  on  suitable  floorings,  total  person-to-earth

resistance not to exceed 108 Ω;

3. avoiding materials and objects of low electrical conductivity;

4. reducing non-conductive surfaces;

5. avoiding the use for dust conveying and filling operations of metallically conducting

pipes and containers with an electrically insulating inner coating.

4 

From the ISSA leaflet "Gas Explosions", International Section for the Prevention of Occupational Risks
in the Chemical Industry, International Social Security Association (ISSA), Heidelberg, Germany

26

                                                     
3.3

Mitigation of the effects of explosions (mitigation measures)

In  many  cases,  it  is  not  possible  to  avoid  explosive  atmospheres  and  sources  of  ignition  with  a
sufficient degree of certainty. Measures must then be taken to limit the effects of an explosion to an
acceptable extent. Such measures are

explosion-resistant design;

explosion relief;

explosion suppression;

prevention of flame and explosion propagation.

These  measures  generally  relate  to  mitigation  of  the  hazardous  effects  of  explosions  starting  within
installations. Equipment and  protective  systems  which  comply  with  Directive  94/9/EC  are  generally
used in mitigation measures. Structural measures, e.g. blast walls, may also be adopted.

3.3.1 Explosion resistant equipment

Items of plant, such as containers, vessels and piping, are so  constructed that they  can  withstand  an
internal  explosion  without  rupturing.  The  initial  pressure  in  the  item  of  plant  must  be  taken  into
account if it differs from normal atmospheric pressure.

In general, a distinction is made between explosion-resistant designs:

for the maximum explosion overpressure;

for the reduced explosion overpressure associated with explosion relief or suppression.

Plant design can be either explosion pressure resistant or explosion pressure shock resistant.

Note:

If  the  inside  of  plant  is  divided  into  subvolumes  or  two  tanks  are  connected  by  a
pipeline, during an explosion in one of the subvolumes the pressure in the other may be
increased and the explosion may thus enter it at an elevated initial pressure. Pressure
peaks  thus  occur  which  may  be  higher  than  the  "maximum  explosion  pressure"
determined  for  atmospheric  conditions.  If  such  arrangements  cannot  be  avoided,
appropriate measures should be taken, e.g. explosion-resistant design sufficient for the
elevated explosion pressure or explosion decoupling.

3.3.1.1 Explosion pressure resistant design

Explosion  pressure  resistant  containers  and  vessels  withstand  the  expected  explosion  overpressure
without  becoming  permanently  deformed.  The  design  is  based  on  the  expected  explosion
overpressure.

Note:

For  most  gas/air  and  dust/air  mixtures,  the  maximum  explosion  overpressure  is  8–10
bar, but it may be higher for light-metal dusts.

3.3.1.2 Explosion pressure shock resistant design

Explosion pressure shock resistant containers and vessels are so constructed that, in the event  of  an
internal  explosion,  they  withstand  a  shock  attaining  the  expected  explosion  overpressure,  but  may
become permanently deformed.

After explosions, the affected items of plant must be checked for deformation.

3.3.2 Explosion relief

In the broadest sense, "explosion relief" covers everything that contributes to ensuring that, when an
explosion is initiated or propagates to some degree, the originally closed plant within which it is taking

27

place is vented in a safe direction, either briefly or for an extended period, if the actuation pressure of
an explosion relief device is attained.

The explosion relief device is intended to ensure that the plant/installation is not subjected to explosion
stresses exceeding its strength. A reduced explosion overpressure results.

Note:

The reduced explosion overpressure is higher than the actuation pressure of the relief
devices.

Bursting discs or explosion doors, for example, can be used as relief devices.

Note:

Only tested relief devices which comply with Directive 94/9/EC should be used. Self-
made relief devices are often not effective and have in the past led to serious accidents.
Unlocked container lids and covers, doors etc. that are placed over the vent openings are
usually not suitable. If in-house designs which have proved satisfactory in practice are
nonetheless  used,  their  suitability  for  explosion  protection  purposes  must  be
demonstrated by a risk assessment, and the result recorded in the explosion protection
document.  The  requirements  of  Directive  94/9/EC  must  also  be  satisfied,  where  this
applies.

The safety-related parameters of the mixture must be known in order to calculate the necessary relief
areas for plants.

Explosion relief is not permissible if the vented products can endanger persons or cause harm to the
environment (e.g. release of toxic substances).

Note:

When relief devices are actuated, a great deal of flame and pressure may develop in the
direction of discharge. Relief devices must therefore be so installed that the pressure is
vented  in  a  safe  direction.  Venting  into  workrooms  should  thus  always  be  avoided.
Experience shows that it can be difficult to comply with the necessary safety clearances
when retrofitting relief devices in existing plant.
Exception: If "Q-Pipe" systems are used, venting into a room is permissible, since the
flame  and  pressure  effects  are  reduced  to  such  a  degree  that  they  are  not  dangerous.
However,  the  possible  release  of  toxic  combustion  gases  must  then  be  taken  into
account.

Note:

If  "explosion  relief"  is  used  as  a  means  of  protection,  explosion  decoupling  from
upstream and downstream parts of the plant must be ensured.

3.3.3 Explosion suppression

Explosion  suppression  systems  prevent  attainment  of  the  maximum  explosion  pressure  by  rapidly
injecting  extinguishing  agents  into  containers  and  plant  in  the  event  of  an  explosion.  The  items  so
protected need thus be designed to withstand only a reduced explosion pressure.

Unlike  explosion  relief,  this  ensures  that  the  effects  of  an  explosion  are  contained  within  the  plant.
Depending on design, the explosion overpressure may be reduced to about 0.2 bar.

Note:

Note:

New explosion suppression systems should be tested and marked as protective systems
in accordance with Directive 94/9/EC.

Explosion  suppression  may  also  require  explosion  decoupling  from  upstream  and
downstream parts of the plant.

3.3.4 Prevention of explosion propagation (explosion decoupling)

An explosion occurring in one part of a plant can propagate to upstream and downstream parts, where
it  may  cause  further  explosions.  Acceleration  caused  by  plant  fittings  or  propagation  in  pipes  may
intensify  the  explosion  effects.  The  explosion  pressures  so  developed  can  be  much  higher  than  the
maximum explosion pressure under normal conditions and may destroy items of plant even if they are

28

of explosion pressure resistant or explosion pressure shock resistant design. It is therefore important
to limit possible explosions to single parts of the plant. This is achieved by explosion decoupling.

Explosion decoupling can be performed e.g. by means of:

rapid-action mechanical isolation;

flame extinction in narrow gaps or by injection of an extinguishing agent;

arresting of flame by high counterflow;

water seals;

rotary valves.

The following aspects are important in practice:

Note: 

Since the propagation velocities in explosions of mixtures with air of gases, vapours or
mists  can  sometimes  be  very  high  (detonations),  active  isolation  or  extinguishing
systems  are  often  too  slow,  and  preference  is  then  given  to  passive  systems  such  as
flame arresters (e.g. crimped ribbon or water seal arresters).

3.3.4.1 Flame arresters for gases, vapours and mists

Flame arresters can be used to prevent flame transmission in the presence of explosive atmospheres,
e.g. through piping, breathers and filling and emptying lines that are not full of liquid at all times. If
the formation  of a  hazardous explosive  atmosphere cannot  be  avoided,  e.g.  in  a  non-explosionproof
container for flammable liquids, arrangements to arrest flame transmission must be made at permanent
openings communicating with places where sources of ignition can be expected to occur and allowing
an explosion to be transmitted to the container.

Note:

This  applies  e.g.  to  ventilation  devices  and  reservoir  level  gauges  and  to  filling  and
emptying lines, if they are not full of liquid at all times.

Conversely, equivalent measures must be taken to prevent the emission of flame from a vessel into a
hazardous place.
The operation of flame arresters essentially depends on one or more of the following mechanisms:

flame  extinction  in  narrow  gaps  and  channels  (e.g.  crimped  ribbon  and  sintered  metal
arresters);

halting  a  flame  front  by  discharge  of  the  unburned  mixtures  at  an  appropriate  velocity
(high-velocity valves);

halting a flame front by means of a liquid seal.

Note:

Flame  arresting  devices  are  classified  as  explosion  proof,  endurance  burning  proof  or
detonation proof. Devices which are not endurance burning proof withstand burning for
only a limited time (the fire resistance time) and then lose their flame arresting capacity.

3.3.4.2 Decoupling devices for dusts

Flame  arresters  for  gases,  vapours  and  mists  cannot  be  used  for  dusts  because  of  the  danger  of
blockage. The following are of proven practical value in preventing the propagation of dust explosions
through connecting pipework, conveying equipment, etc. and the emission of flame from plant:

29

Extinguishing barriers:
The explosion is detected by sensors. The extinguishing agent is injected from dispersers into the
pipework  and  the  flame  quenched.  This  does  not  affect  the  explosion  pressure  developed
upstream of the barrier. Pipework and vessels downstream of the barrier, too, must be designed to
withstand the expected pressure. The extinguishing agent must be appropriate for the type of dust
in question.

Rapid-action valves or flaps:
An explosion travelling through a pipe is detected by sensors. An actuating mechanism closes the
valve or flap within milliseconds.

Quick-acting shut-off valves (explosion isolation valves):
When  a  given  flow  velocity  is  exceeded,  a  valve  in  the  pipe  closes.  The  velocity  required  for
actuation  is  generated  either  by  the  blast  wave  or  a  sensor-controlled  pilot  flow  (e.g.  a  jet  of
nitrogen  directed  on  to  the  valve  cone).  The  quick-acting  shut-off  valves  so  far  known  may  be
fitted only in horizontal pipe ranges and are suitable only for pipes with a fairly low dust burden
(e.g. the exit side of filter units).

Rotary valves:
Rotary valves may be used as "flame traps" only if their non-transmission of an internal ignition
and their pressure resistance have been proven under the service conditions obtaining. In the event
of  an  explosion,  a  sensor  must  stop  the  rotor  automatically,  so  that  no  burning  product  is
discharged.

Explosion diverters:
An explosion diverter consists of pipe segments joined by a special fitting. The seal to atmosphere
is  in  the  form  of  a  venting  device  (cover  plate  or  bursting  disc;  actuation  overpressure  usually
p  (cid:2)  0.1  bar).  The  aim  is  to  prevent  explosion  propagation  by  diverting  the  flow  through  180
degrees  while  providing  explosion  relief  on  opening  of  the  venting  device  at  the  point  of  flow
reversal.

Projection of fragments of the venting device must be prevented, e.g. by means of a wire guard.
Venting must always take place in a safe direction, never into working areas or travelling ways.
This  means  of  protection  may  not  be  used  if  persons  can  be  endangered  or  the  environment
harmed by the discharge.

Explosion  diverters  do  not  always  reliably  prevent  the  propagation  of  explosions.  However,
development of the flame front is so disrupted that a slowly moving explosion is the worst that is
to be expected in the downstream pipe run. Where mixtures at explosive concentrations are not to
be  expected  in  the  piping,  e.g.  in  many  dedusting  units,  it  can  be  assumed  that  the  decoupling
effect is adequate.

Product barrier choke:
In combination with explosion relief, chokes consisting of an adequate depth of the product being
handled  (e.g.  at  a  silo  discharge)  are  suitable  for  decoupling  parts  of  a  plant.  The  amount  of
material must be monitored by level indicators and must be sufficient to ensure that the explosion
pressure cannot cause the flame to penetrate through the product.

Double valves:
Product discharges from explosion proof vessels can be protected with a double valve system to
prevent flame  transmission. The  valves  must  be  at  least  as  strong  as  the  vessels.  They  must  be
controlled to ensure alternating closure such that there is always one valve closed.

Note:

All explosion decoupling systems falling under Directive 94/9/EC should be tested and
marked as protective systems in accordance with the Directive's requirements.

3.4

Application of process control engineering

The explosion protection measures so far described can be kept operational, monitored or triggered by
safety, controlling and regulating devices (hereafter referred to as process control engineering – PCE).
Generally, PCE devices can be used to prevent the occurrence of hazardous explosive atmospheres or
ignition sources or to mitigate the harmful effects of an explosion.

30

Potential ignition sources, such as a hot surface, can be monitored by PCE devices and controlled to
ensure that a safe value is not exceeded. Potential ignition sources can also  be  switched  off  when  a
hazardous explosive atmosphere arises. For example, non-explosionproof electrical equipment can be
made  dead  when  a  gas  alarm  is  triggered,  if  this  allows  the  potential  ignition  sources  within  the
equipment to be de-energised. The occurrence of hazardous explosive atmospheres can be prevented,
e.g. by starting a fan before the maximum permissible gas concentration is reached. The use of such
PCE  devices  can  reduce  the  size  of  hazardous  places  (zones),  make  it  less  likely  that  a  hazardous
explosive atmosphere will arise or prevent it from arising altogether. PCE devices in conjunction with
devices  for  mitigating  the  harmful  effects  of  an  explosion  are  protective  systems  (e.g.  explosion
suppression systems) and are described under mitigation measures in section 3.3. The design and scale
of such PCE devices and the measures triggered by them depend on the probability of occurrence of a
hazardous explosive atmosphere and of effective ignition sources. The reliability of the PCE devices
in conjunction with the technical and organisational measures taken must ensure that the danger of an
explosion is limited to an acceptable level, under all operating conditions. In certain cases, it can be
useful  to  combine  PCE  devices  for  preventing  ignition  sources  with  PCE  devices  for  preventing
hazardous explosive atmospheres.

The degree of reliability required of PCE devices depends on the assessment of  the  explosion  risks.
Reliability of the safety function of PCE devices and their components is achieved by fault avoidance
and  fault  control  (having  regard  to  all  operating  conditions  and  the  planned  servicing  and/or
maintenance arrangements).

Example: If assessment of the  explosion risks  and  the  explosion protection  strategy  leads to the
conclusion  that  there  will  be  a  high  risk  without  PCE  devices,  e.g.  that  hazardous
explosive atmospheres are present continuously, for long periods or frequently (zone 0,
zone 20) and that an operational malfunction is liable to give rise to an effective ignition
source, the PCE devices must be so designed that a single PCE fault cannot make the
safety  arrangements  ineffective.  This  can  be  achieved  e.g.  by  redundant  use  of  such
devices.  A  comparable  result  can  be  achieved  if  a  single  PCE  device  for  avoiding
hazardous explosive atmospheres is combined with an independent single PCE device
for avoiding effective ignition sources.

Table 3.2  shows  approaches  to  using  these devices,  instead  of  or  in addition  to  process  engineering
measures, in order to avoid effective ignition sources under normal operating conditions and for likely
and infrequent malfunctions.

Example: A transmission with several bearings is to be operated in zone 1. In normal operation,
the temperature of the bearings is reliably below the ignition temperature of the gas/air
mixture.  In  the  event  of  a  fault  (e.g.  resulting  from  a  loss  of  lubricant),  the  bearing
temperature may reach the ignition temperature if no protective measures are taken. An
adequate  standard  of  safety  can  be  achieved  by  monitoring  the  temperature  of  the
bearings, the unit being shut down if the maximum permissible surface temperature is
reached.

The requirements for PCE devices as shown in Table 3.2 can likewise be applied to the prevention of
hazardous  explosive  atmospheres  if  the  likelihood  of  potential  ignition  sources  is  given  and  it  is
necessary to ensure that the area in question meets the criteria for a particular zone.

Example: Solvent-covered workpieces are dried in a drying cabinet. In the event of a malfunction,
the surface temperature of the heating unit can reach the ignition temperature. A PCE
device linked to a fan has to be used to ensure that the solvent concentration does not
exceed the limit value (LEL minus safety margin specific to the plant). This fan-linked
device must remain effective in the event of a malfunction (e.g. a power cut).

31

Note:

1. The  PCE  measures  described  can  be  adopted  only  if  the  physical,  chemical  and
process  parameters  relevant  to  explosion  protection  can  in  fact  be  regulated  or
controlled,  in  an  acceptably  economical  way  and  within  a  sufficiently  short  time.
Materials properties, for example, generally cannot be influenced by such devices.

2. New  PCE  devices  used  for  the  avoidance  of  ignition  sources,  or  of  an  explosive
atmosphere  arising  (without  reliably  preventing  it)  in  a  hazardous  zone  must
conform to European Directive 94/9/EC. Such PCE devices must always be tested to
the same category as the equipment to be protected.

Table 3.2: Use of PCE devices to reduce the probability of effective ignition

Hazardous
place
None

Zone 2 or
zone 22

Zone 1 or
zone 21

Zone 0 or
zone 20

Occurrence of
ignition sources

Operationally necessary
Operationally necessary

Unlikely in normal operation

Operationally necessary

Unlikely in normal operation

Unlikely in normal operation or in the event of
malfunction
Unlikely in normal operation

Unlikely in normal operation or in the event of
malfunction
Unlikely in normal operation, in the event of
malfunction or in the event of rare malfunctions

* or an equivalent device tested in accordance with Directive 94/9/EC

3.5

Requirements for work equipment

Requirements for
PCE devices

None
Suitable single device for avoiding
ignition sources
None

Two suitable devices for avoiding
ignition sources*
Suitable single device for avoiding
ignition sources
None

Two suitable devices for avoiding
ignition sources
Suitable single device for avoiding
ignition sources*
None

The employer must ensure that work equipment and all installation materials  are  suitable for  use in
hazardous  places.  In  doing  so,  he  must  take  account  of  the  possible  ambient  conditions  at  the
workplace  in  question.  The  work  equipment  must  be  so  assembled,  installed  and  operated  that  it
cannot cause an explosion.

3.5.1

Selection of work equipment

Equipment  and  protective  systems  in  the  places  where  hazardous  explosive  atmospheres  may  be
present  must  be  chosen  in  accordance  with  the  categories  in  Directive  94/9/EC,  unless  otherwise
provided in the explosion protection document on the basis of the risk assessment. Further criteria such
as  temperature  class,  type  of  protection  and  explosion  group  must  be  considered  to  ensure  safe
operation of equipment in hazardous places. These criteria depend on the combustion and explosion
properties of the substances used.

Work equipment for use in places where explosive atmospheres may occur which is already in use or
is  made  available  in  the  undertaking  or  establishment  for  the  first  time  before  30  June  2003  shall
comply  from  that  date  with  the  minimum  requirements  laid  down  in  Annex  II,  Part  A,  if  no  other
Community Directive is applicable or is so only partially.

Work equipment for use in places where explosive atmospheres may occur which is made available in
the undertaking or establishment for the first time after 30 June 2003 shall comply with the minimum
requirements laid down in Annex II, Parts A and B.

32

Although work equipment not falling under the definition of "equipment" given in Directive 94/9/EC
cannot be compliant with this directive, it must nevertheless be compliant with Directive 1999/92/EC.

If the assessment of explosion risks (material properties, processes) indicates that the potential risk to
workers and other persons is abnormally high, the equipment and work equipment chosen may have to
have a higher degree of protection. If the manner in which mobile work equipment is used may lead to
its  operation  in  areas  with  different  hazard  potentials  (different  zoning),  it  must  be  selected  on  the
basis of the worst case. If an item of work equipment is used in both zone 1 and zone 2, it must satisfy
the requirements for operation in zone 1.

Exceptions  are  permissible  if  suitable  organisational  measures  ensure  safe  operation  for  the  whole
period in which the mobile equipment is used in a hazardous place. These measures should be detailed
in the Permit to Work, and/or the explosion protection document.  Such work equipment may be used
only by suitably trained personnel (89/655/EEC).

Table 3.3: Equipment for use in the various zones

Zones

Categories 
further measures

usable  without

If designed for

0

1

2

20
21
22

II 1 G

II 1 G or 2 G

II 1 G or 2 G or 3 G

II 1 D
II 1 D or 2 D
II 1 D or 2 D or 3 D

(cid:1)  gas/air mixture
(cid:1)  vapour/air mixture
(cid:1)  mist
(cid:1)  gas/air mixture
(cid:1)  vapour/air mixture
(cid:1)  mist
(cid:1)  gas/air mixture
(cid:1)  vapour/air mixture
(cid:1)  mist
(cid:1)  dust/air mixture
(cid:1)  dust/air mixture
(cid:1)  dust/air mixture

Note:

If equipment is to be used in hybrid mixtures, it must be suitable for such use and tested
if appropriate. An item of equipment marked II 2 G/D is thus not  necessarily  suitable
and permissible for use in hybrid mixtures.

3.5.2 Assembly of work equipment

Work equipment and connecting devices (e.g. pipework, electrical connections) must be so assembled
that they cannot cause or trigger an explosion. They may be put into service only if the assessment of
explosion  risks  establishes  that  their  operation  does  not  cause  ignition  of  an  explosive  atmosphere.
This also applies to work equipment and associated connecting devices which are not equipment and
protective systems within the meaning of Directive 94/9/EC.

In accordance with the European Directive 89/655/EEC (safety and health requirements for the use of
work equipment by workers at work) the employer must ensure that the equipment used is suitable for
the actual operating and service conditions. When selecting installation materials, work clothing and
personal protective equipment, he must likewise ensure that they are suitable.

33

4. Organisational measures for explosion protection

If  there  is  a  potential  risk  of  explosion  at  a  workplace,  this  also  implies  that  the  work  organisation
must  meet  certain  requirements.  Organisational  measures  must  be  taken  where  technical  measures
alone  cannot  ensure  and  maintain  explosion  protection  at  the  workplace.  In  practice,  the  work
environment can also be made safe by combining technical and organisational measures.

Example: If  inert  gas  is  emitted  through  openings  in  the  plant  which  are  present  in  normal
operation  or  result  from  defects,  workers  may  be  at  risk  from  oxygen  displacement
(suffocation). When an item of apparatus has been inerted, for example, it may not be
entered until inerting has been discontinued and sufficient atmospheric oxygen supplied,
or if proper precautions and breathing apparatus are used.

Organisational  measures  so  arrange  the  working  procedures  that  workers  cannot  be  harmed  by  an
explosion.  Arrangements  must  also  be  laid  down  for  inspection,  servicing  and  repair  to  ensure  that
technical  measures  remain  operational.  Organisational  measures  must  also  take  account  of  possible
interaction  between  explosion  protection  measures  and  working  procedures.  These  combined
explosion  protection  measures  must  ensure  that  workers  can  perform  the  work  assigned  to  them
without danger to their safety and health or to the safety and health of others.

Figure 4.1: Examples of organisational explosion protection measures4

4 

From the ISSA leaflet "Gas Explosions", International Section for the Prevention of Occupational Risks
in the Chemical Industry, International Social Security Association (ISSA), Heidelberg, Germany

34

 
                                                     
The following organisational measures must be carried out:

produce  written  operating  instructions,  where  required  by  the  explosion  protection
document;

instruct workers in explosion protection;

ensure workers have adequate competence;

apply  a  permit-to-work  system  for  dangerous  work,  where  required  by  the  explosion
protection document;

carry out maintenance;

carry out inspection and surveillance;

mark hazardous places, where necessary.

The  organisational  measures  taken  must  be  recorded  in  the  explosion  protection  document  (see
section 6). A few examples are shown in Figure 4.1.

4.1

Operating instructions

Operating instructions are activity-related binding instructions and rules of conduct issued in writing
by the employer to the employees. They describe the workplace-related dangers to human beings and
the environment and indicate the protective measures taken or to be observed.

Operating  instructions  are  produced  by  the  employer  or  a  competent  person  whom  he  appoints  to
perform the task and must be observed by workers. They relate to a particular workplace or part of the
establishment. Among the matters to be covered by operating instructions for workplaces where there
are  explosive  atmosphere  risks  are  what  explosion  hazards  exist  and  where,  what  mobile  work
equipment may be used and whether special personal protective equipment must be worn.

Example: The  operating  instructions  may  include a  list  of  all  mobile  work  equipment  permitted
for  use  in  the  hazardous  place  in  question.  They  should  indicate  what  personal
protective equipment must be worn by persons entering this place.

They must be so worded that all workers can understand and apply them. If the establishment employs
workers  who  do  not  have  an  adequate  command  of  the  language  of  the  country,  the  operating
instructions must be written in a language that they understand.

It  may  be  appropriate  for  activity-related  sets  of  operating  instructions  which  describe  different
hazards or are produced on the basis of different statutory provisions to be combined into a single set
of operating instructions, so providing an overall view of the hazards.

It is advisable for the operating instructions in an establishment to have a uniform presentation in order
to take advantage of the familiarity effect.

4.2

Worker competence

For  every  workplace,  there  should  be  available  a  sufficient  number  of  workers  with  the  requisite
experience and training to perform the explosion protection tasks assigned to them.

4.3

Training of workers

Employers  must  provide  workers  with  training  which  informs  them  of  the  explosion  hazards  at  the
workplace  and  the  protective  measures  taken.  This  training  must  explain  how  the  explosion  hazard
arises and in what parts of the workplace it is present. The measures taken should be listed and their
operation  explained.  The  correct  way  of  working  with  the  equipment  available  must  be  explained.
Workers must be instructed in safe work in or near hazardous places. This also involves explaining
the meaning of any marking of hazardous places and specifying what mobile work equipment may be
used  there  (see  3.5.1).  Workers  must  also  be  instructed  in  what  personal  protective  equipment  they
must wear at work. The available operating instructions should be covered during the training.

35

Note:

Well-trained workers greatly increase safety at work. Any deviation from the desired
process can be detected, and hence corrected, more quickly.

Workers must receive training (89/391/EEC):

on recruitment (before starting work);

in the event of a transfer or a change of job;

when work equipment is introduced for the first time or changed;

when new technology is introduced.

Training of workers must be repeated at suitable intervals, for example once per year. On completion
of training, it can be useful to check on what has been learned.

The  duty  to provide training  also  applies to  the  employees  of  outside  contractors.  Training  must  be
given  by  a  competent person.  Records  should be  kept in  writing  of the  date  and  content  of  training
activities and the participants.

4.4

 Worker supervision

In working environments where explosive atmospheres may arise in such quantities as to endanger the
safety and health of workers, appropriate supervision during the presence of workers must be ensured,
in accordance with the risk assessment, by the use of appropriate technical means.

4.5

Permit-to-work system

If  work  liable  to  cause  an  explosion  is  to  be  carried  out  in  or  near  a  hazardous  place,  it  must  be
authorised  by  the  person  with  responsibility  for  this  function  within  the  establishment.  This  also
applies to activities which may interact with other work to cause hazards. A system of permits to work
has proved useful in such cases. This may be implemented by means of a permit-to-work form which
all concerned must receive and sign.

Example: The permit-to-work form should indicate at least the following details:

1. where exactly the work is to be carried out;

2. clear identification of the work to be undertaken;

3. hazard identification;

4. precautions  necessary,  person  undertaking  the  precautions  should  sign  on  to  show

that they have been taken;

5. personal protective equipment needed;

6. when the work will begin and when it is expected to end;

7. acceptance, confirming understanding;

8. extension/shift Hanover procedure;

9. handback, plant ready for testing and recommissioning;

10. cancellation, plant tested and recommissioned;

11. report on any anomaly discovered during the work.

Once the work has been finished, a check must be made to establish whether the plant is still safe or
has been made safe again. All concerned must be informed when the work is finished.

36

4.6

Maintenance

Maintenance  comprises  repair,  servicing  and  inspection.  Before  maintenance  work  begins,  all
concerned  must  be  informed  and  the  work  must  be  authorised,  e.g.  by  means  of  a  permit-to-work
system (see above). It may be carried out only by competent persons.

Experience  shows  that  a  high  accident  risk  attaches  to  servicing  work.  Before,  during  and  after
completion of the work, care must therefore be taken to ensure that all necessary protective measures
are taken.

Note: 

During  servicing,  items  of  equipment  or  plant  which  could  cause  an  explosion  if
inadvertently  switched  on  during  the  work  must  if  possible  be  mechanically  and/or
electrically  isolated.  For  example,  if  open  flame  operations  are  carried  out  in  a
container,  all  pipes  from  which  a  hazardous  explosive  atmosphere  may  be  emitted  or
which  are  connected  to  other  containers  where  such  an  atmosphere  could  be  present
must  be  separated  from  the  container  and  blinded  off  or  closed  by  some  comparable
means.

When maintenance involving a risk of ignition is carried out in a hazardous place, it should be reliably
ensured  that  it  will  be  free  of  hazardous  explosive  atmospheres  for  the  duration  of  the  work  and  if
necessary for some time thereafter (e.g. to allow cooling).

Except  in  exceptional  circumstances,  when  other  appropriate  and  adequate  precautions  have  been
taken,  the  items  of  plant  on  which  work  is  to  be  carried  out  must  as  necessary  be  emptied,
depressurised, cleaned, purged and must be free of flammable substances. While work is in progress,
such substances must not reach the place where it is being carried out.

Where work may give rise to flying sparks (e.g. welding, flame cutting, grinding), suitable screening
should be provided (see Figure 4.2) and a fire sentry posted if necessary.

Figure 4.2: Example of screening for work giving rise to flying sparks4

Once  maintenance  has  been  completed,  steps  must  be  taken  to  ensure  that  the  explosion  protection
measures required for normal service are again operative before the equipment is restarted. A permit-
to-work  system  (see  above)  is  particularly  useful  during  servicing  and  maintenance  work.  It  can  be
useful to use a checklist for the restoration of explosion protection measures.

4.7

Inspection and checking

Before a workplace containing places where hazardous explosive atmospheres may occur is used for
the first time, and after any damage or alterations with safety implications, its overall explosion safety
must be verified.

4 

From the ISSA leaflet "Gas Explosions", International Section for the Prevention of Occupational Risks
in the Chemical Industry, International Social Security Association (ISSA), Heidelberg, Germany

37

                                                     
The  effectiveness  of  the  explosion  protection  measures  taken  in  a  plant  must  be  checked  at  regular
intervals. The frequency of such checks depends on the type of measure. All checks may be carried
out by competent persons only.

Competent  persons  are  persons  with  comprehensive  expertise  in  explosion  protection  as  a  result  of
their professional training, experience and current professional activity.

Example:

The performance of gas alarm systems must be verified by a competent person after
installation and at suitable intervals, observing any pertinent national regulations and
manufacturer's instructions. Where hybrid mixtures could arise the detectors must be
suitable for both phases and be calibrated against the possible mixtures.

Example:  Ventilation  systems  intended  to  prevent  hazardous  explosive  atmospheres  and  the
associated monitoring systems  must be  checked  by  a  competent  person  against the
intended duty before they  are  first  brought into  service  and  should be  examined  at
regular intervals. Ventilation systems with adjustable items (e.g. regulators, baffles,
variable-speed  fans)  should  be  examined  every  time  the  settings  are  changed.  It  is
desirable for such items to be locked against interference. Where ventilation systems
are adjusted automatically, the examination should cover the entire range of settings.

4.8

Marking of hazardous places

Directive  1999/92/EC  stipulates  that  the  points  of  entry  to  places  where  hazardous  explosive
atmospheres may occur in such quantities as to endanger the health and safety of workers must where
necessary be marked by the employer with the following warning sign:

Figure 4.3: Warning sign for places where explosive atmospheres may occur

Distinctive features:

triangular shape,

black letters on a yellow background with black edging (the yellow part to take up at least
50 % of the area of the sign).

Such marking is required e.g. for rooms or areas in which a hazardous explosive atmosphere may arise
(such as rooms or fenced enclosures where flammable liquids are stored). On the other hand, there is
no point in marking an item of plant which is fully protected by mitigation measures. If the hazardous
place is not the whole space concerned, but only part of it, that part may be marked by yellow/black
diagonal stripes e.g. on the floor.

Other details may be added to the warning sign, indicating e.g. the nature and frequency of occurrence
of  the  hazardous  explosive  atmosphere  (substance  and  zone).  It  may  be  desirable  to  place  other
warning signs in accordance with 92/58/EEC, for example forbidding smoking, etc.

Workers' attention must be drawn to the sign and its meaning in the course of their training.

38

5. Coordination duties

Where  independent  persons  or  teams  are  working  simultaneously  and  in  proximity  to  one  another,
they may inadvertently place each other at risk, particularly since those concerned focus primarily on
their  own  tasks,  while  nothing  or  not  enough  is  often  known  about  the  commencement,  nature  or
extent of the work being done by others nearby.

Examples:Typical  results  of  poor  coordination  between  the  employer's  and  contractor's  staff,

giving rise to particular explosion risks, are as follows:

1. The  contractor  is  not  aware  of  the  environmental  hazard  at  the  firm  where  it  is

engaged and the implications for its own work.

2 The  in-house  departments  often  do  not  know  that  outside  staff  are  working  in  the
establishment and/or what potential hazard is being imported as a result of the work
carried out.

3. The house management is not told how it and its staff have to conduct themselves in

relation to the contractor.

Even  safe  working  practices  within  a  team  do  not  exclude  the  possibility  that  others  in  the  vicinity
may  be  endangered.  The  only  guarantee  against  hazardous  interaction  is  timely  coordination  of  all
involved.

When  work  is  contracted  out,  the  principal  and  contractor  are  therefore  required  to  coordinate  their
activities  in  order  to  avoid  placing  each  other  at  risk.  This  duty  also  relates  to  the  requirement  of
Article 7 (4) of the Framework Directive 89/391/EEC, where several employers' workers are working
at the same workplace. For worksites, the pertinent national regulations must also be complied with.

5.1

Coordination arrangements

Where  workers  from  several  undertakings  are  present  at  the  same  workplace,  each  employer  is
responsible for all matters coming under his control.

Without prejudice to the individual responsibility of each employer under Directive 89/391/EEC, the
task of coordination falls to the employer responsible for the workplace in accordance with national
law and/or practice shall coordinate the implementation of all the measures concerning workers' health
and safety. He has a duty to ensure that operations proceed safely in order to safeguard workers' lives
and  health.  To  this  end,  he  must  acquaint  himself  with  the  explosion  hazards,  discuss  protective
measures with the persons concerned, issue instructions and check that they are obeyed. He shall state
in the explosion protection document the aim of the coordination and the measures and procedures for
implementing it.

The employer responsible for the workplace in accordance with national law and/or practice, is also
responsible  for  coordinating  the  implementation  of  all  the  measures  concerning  workers'  health  and
safety with all other employers sharing the worksite.

Because of the size of the firm or for other reasons, the employer is not always able to discharge this
duty  alone.  He  should  therefore  appoint  suitable  persons  as  managers.  These  then  take  over  the
employer's duties on their own responsibility, coordination duties being taken over by the coordinator.

Note:

Specifically  as  regards  work  in  or  in  connection  with  hazardous  places  or  work  with
flammable  substances  that  may  give  rise  to  hazardous  explosive  atmospheres,
hazardous interaction must be assumed even if it is not immediately apparent. In case of
doubt, it is therefore suggested that the employer could appoint a coordinator.

39

In view of his special planning, safety and organisational responsibilities, the employer or coordinator
should satisfy the following requirements relevant to explosion protection:

explosion protection expertise;

knowledge of the national regulations transposing Directives 89/391/EEC and 1999/92/EC;

knowledge of the firm's organisational structure;

leadership  qualities  to  ensure  that  the  necessary  instructions  are  put  into  effect.

In  principle,  the  task  of  the  employer  or  his  coordinator  is  to  orchestrate  the  work  of  the  various
groups  irrespective  of  the  firms  they  belong  to,  in  order  to  detect  situations  in  which  they  may
endanger  each  other  and  to  be  able  to  take  any  necessary  action.  He  must  therefore  be  informed  in
good time of the work to be undertaken.

Note:

The house staff, the contractor(s) and all others working on the site should provide the
employer or his coordinator in good time with the following information:

•  work to be undertaken;

• planned start of work;

•

anticipated end of work;

• place of work;

• workers assigned;

• planned  method  of  work  plus  measures  and  procedures  for  implementing  the
explosion protection document;

• name of the person(s) in charge.

More  specifically,  the  duties  of  the  employer  or  his  coordinator  comprise  site  inspections  and
coordination  meetings,  as  well  as  planning,  supervision  and  if  necessary  replanning  of  work  in
response to difficulties arising. See checklist A.3.5.

5.2

Protective measures to ensure safe cooperation

In establishments where hazardous explosive atmospheres arise, different groups may work together at
various  levels  and  in  all  departments.  In  laying  down  and  executing  measures  to  avoid  hazardous
interaction, it is therefore  necessary  to  consider  all  cases  in  which  the  task  to  be performed  and the
way it is carried out may lead to persons' working together or in each other's vicinity, or interacting
over a distance (e.g. when working on the same pipework or electrical circuit in different locations).

In practice, the coordination measures relevant to explosion protection are usually part of the general
coordination functions:

1.  at the planning stage;

2.  at the execution stage;

3.  on completion of the work.

At  these  various  stages,  the  employer  or  his  coordinator  must  also  ensure  that  the  necessary
organisational  measures  are  taken  to  avoid  interaction  between  hazardous  explosive  atmospheres,
ignition sources and operational malfunctions.

40

Examples:1. Prevent  the  formation  of  hazardous  explosive  atmospheres  around  technical  plant
where  ignition  sources  are  to  be  expected  [see  3.1],  e.g.  by  using  substitutes  for
solvent-containing cleaning agents, paints, etc. or providing adequate ventilation.

2. Avoid  using  and  creating  ignition  sources  in  places  where  hazardous  explosive
atmospheres may arise, e.g. in welding, cutting, soldering and separation work [see
section 4.4/4.5 and specimen permit A.3.3].

3. Prevent  malfunctions  arising  e.g.  from  interruption  of  gas  supply,  inducing  of
pressure fluctuations or shutdown of power or protective systems as a result of work
in adjacent units.

A checklist can be used as an aid to determining whether the agreed protective measures are carried
out during the work and whether the persons concerned have received adequate instruction and duly
apply these measures [see Annex 3.4].

Note:

Irrespective of individuals' duties, all concerned should:

•

•

•

•

seek contact;

consult;

show consideration;

respect what has been agreed.

41

6

Explosion protection document

6.1

Requirements under Directive 1999/92/EC

As  one  of  his  duties  under  Article  4  of  Directive  1999/92/EC,  the  employer  must  ensure  that  an
explosion protection document is drawn up and kept up to date.

This document must at least demonstrate:

that the explosion risks have been determined and assessed;

that adequate measures will be taken to attain the aims of the Directive;

those places which have been classified into zones;

those  places  where  the  minimum  requirements  set  out  in  Annex  II  to  the  Directive  will
apply;

that the workplace and work equipment, including warning devices, are designed, operated
and maintained with due regard for safety;

that, in accordance with Council Directive 89/655/EEC, arrangements have been made for
the safe use of work equipment.

The  explosion  protection  document  must  be  drawn  up  prior  to  the  commencement  of  work  and  be
revised  when  the  workplace,  work  equipment  or  organisation  of  the  work  undergoes  significant
changes, extensions or conversions.

The  employer  may  combine  existing  risk  assessments,  documents  or  other  equivalent  reports  and
incorporate them into the explosion protection document.

6.2

Implementation

The  explosion  protection  document  is  intended  to  provide  an  overview  of  the  results  of  the  risk
assessment  and  the  consequent  technical  and  organisational  protective  measures  for  a  plant  and  its
working environment.

A specimen layout for an explosion protection document is shown below. It contains points which can
be  useful  in  addressing  the  above  requirements  and  can  be  used  as  an  aid  in  producing  such
documents.

However, this does not imply that all these points must be included. The document must be tailored to
conditions in the firm concerned. It should as far as possible be well-structured and easy to read and
the  degree  of  detail  should  be  such  as  to  allow  a  general  grasp  of  its  content.  The  amount  of
documentation should therefore not be excessive. When necessary, the document should be produced
in a form that allows additions, e.g. as a loose-leaf collection. This  is  particularly  recommended  for
larger plants or where the plant engineering is frequently changed.

Article 8 of Directive 1999/92/EC expressly allows existing explosion risk assessments, documents or
reports  to  be  combined  (e.g.  the  safety  report  under  Directive  96/82/EC5).  An  explosion  protection
document may thus contain references to other documents without explicitly including them in full.

When establishments have several plants containing  hazardous  places,  it  can  be useful to  divide the
explosion protection document into a general and a plant-specific part. The general part explains the
structure of the documentation and measures applying to all plants, such as training. The plant-specific
part describes the hazards and protective measures in the individual plants.

5 

Council  Directive  96/82/EC  of  9  December  1996  on  the  control  of  major-accident  hazards  involving
dangerous substances, O.J. L 10 of 14/01/1997, page 13

42

                                                     
If operating conditions in a  plant  change  frequently,  e.g.  as  a  result  of  batch processing  of  different
products,  the  most  dangerous  conditions  should  be  taken  as  the  basis  for  assessment  and
documentation.

6.3

Specimen layout for an explosion protection document

6.3.1 Description of the workplace and working areas

The  workplace  is  divided  into  working  areas.  The  explosion  protection  document  describes  the
working areas at risk from explosive atmospheres.

The  description  may  contain,  e.g.  the  name  of  the  establishment,  type  of  plant,  building/room
designation and persons in charge, number of workers employed.

Documentation  of  the  buildings  and topography  may  be  in  graphic  form,  e.g.  site  and  layout  plans,
including plans of escape and rescue routes.

6.3.2 Description of the process steps and/or activities

The process should be described in a brief text, perhaps accompanied by a flowchart. This description
should  contain  all  information  that  is  important  for  explosion  protection.  It  should  cover  the
operational  steps  including  startup  and  shutdown,  an  overview  of  design  and  operational  data  (e.g.
temperature, pressure, volume, throughput, rotational speed, work equipment), the nature and extent of
cleaning if relevant, and possibly details of space ventilation.

6.3.3 Description of the substances used / safety parameters

This  should  in  particular  indicate  what  substances  form  the  explosive  atmosphere  and  under  what
process conditions it arises. At this point, it is useful to list the safety parameters relevant to explosion
protection.

6.3.4 Results of the risk analysis

This  section  should  indicate  where  hazardous  explosive  atmospheres  may  arise,  possibly
distinguishing  between  the  inside  of  items  of  plant  and  their  surroundings.    Startup  and  shutdown,
cleaning and malfunctions must be taken into account as well as normal operation. The procedure for
process or product changes must also be addressed where appropriate. The hazardous places (zones)
can be described by means of a text and also represented graphically as a zone plan (see 3.2.1).

The explosion hazards should also be described at this point  (see section  2).  It  is  useful  to state the
procedure followed in identifying the explosion risks.

6.3.5 Explosion protection measures taken

This section is based on the risk assessment and describes the resulting explosion protection measures.
The  principle  underlying  the  protective  measures  should  be  stated,  e.g.  "Avoidance  of  effective
ignition sources". It is useful to distinguish between technical and organisational measures.

43

Technical measures
(cid:1)  Prevention

As the explosion protection strategy for the plant is based, fully or in part, on preventive measures
– avoidance of explosive atmospheres or of ignition sources – the way in which these measures are
implemented must be described in detail. (See 3.1 and 3.2)

(cid:1)  Mitigation

As  the  plant  will  be  protected  by  mitigation  measures,  their  nature,  manner  of  operation  and
location must be described. (See 3.3)

(cid:1)  PCE measures

If PCE  measures are part of the  explosion  protection  strategy,  their  nature,  manner  of  operation
and location must be described. (See 3.4)

Organisational measures

The  organisational  measures  must  also  be  described  in  the  explosion  protection  document.  (See
section 4)

The explosion protection document must demonstrate:

what operating instructions have been produced for a workplace or activity;

what steps are taken to ensure competence of the persons employed;

the content and frequency of training (and the participants);

any rules for the use of mobile work equipment in hazardous places;

what steps are taken to ensure that workers wear only suitable protective clothing;

whether a permit-to-work system is in place and, if so, how it is organised;

how maintenance, inspection and checking are organised;

how the hazardous places are marked.

If forms relating to these points are available, specimens can be attached to the explosion protection
document. A list of mobile work equipment authorised for use in hazardous places should be attached.
The  level  of  detail  should  depend  on  the  type  and  size  of  the  operation,  and  the  degree  of  risk
involved.

6.3.6

Implementation of the explosion protection measures

The  explosion  protection  document  should  indicate  who  is  responsible  for  carrying  out  particular
measures or who has been or will be appointed (e.g. to produce and update the explosion protection
document itself). It should also state when the measures have to be taken and how their effectiveness
is to be checked.

6.3.7 Coordination of the explosion protection measures

Where  workers  from  several  undertakings  are  present  at  the  same  workplace,  each  employer  is
responsible for all matters coming under his control. The employer responsible for the workplace must
coordinate  the  implementation  of  all  the  explosion  protection  measures  and  state  in  his  explosion
protection document the aim of that coordination and the measures and procedures for implementing
it.

6.3.8 Annex to the explosion protection document

The  annex  may  contain  e.g.  EC  type-examination  certificates,  EC  certificates  of  conformity,  safety
datasheets,  operating  instructions  for  plant  or  equipment.  Servicing  plans  relevant  to  explosion
protection may also be included.

44

ANNEXES

A.1

Glossary

As an aid to a clear understanding of this Guide, some major explosion protection terms are defined
below.  Sources  are  quoted  for  legal  definitions  taken  from  the  European  directives  and  harmonised
standards. Definitions for other terms were taken from the technical literature.

Atmospheric conditions:
Atmospheric conditions are generally understood to mean an ambient temperature between -20 °C and
60 °C and a pressure range of 0.8–1.1 bar. [ATEX Guidelines, Directive 94/9/EC]

Category:
Classification of equipment according to the required level of protection. [Directive 94/9/EC]

Components:
"Components" means any item essential to the safe functioning of equipment and protective systems
but with no autonomous function. [Directive 94/9/EC]

Degree of dispersion:
Measure  of  the  (finest)  distribution  of  a  solid  or  liquid  (disperse  phase)  in  another  gas  or  liquid
(dispersion  medium)  without  any  molecular  association,  as  an  aerosol,  emulsion,  colloid  or
suspension.

Effective source of ignition:
Sources  of  ignition  are  often  underestimated  or  overlooked.  Their  effectiveness,  i.e.  the  ability  to
ignite  an  explosive  atmosphere,  depends  e.g.  on  the  energy  of  the  source  and  the  properties  of  the
atmosphere.  Under  non-atmospheric  conditions,  there  are  changes  in  the  parameters  of  explosive
mixtures that determine whether ignition occurs: for example, the minimum ignition energy of high-
oxygen mixtures is reduced by several factors of ten.

Employer:
Any  natural  or  legal  person  who  has  an  employment  relationship  with  the  worker  and  has
responsibility for the undertaking and/or establishment.  [Directive 89/391/EEC]

Equipment:
"Equipment"  means  machines,  apparatus,  fixed  or  mobile  devices,  control  components  and
instrumentation thereof and detection or prevention systems which, separately or jointly, are intended
for  the  generation,  transfer,  storage,  measurement,  control  and  conversion  of  energy  and/or  the
processing  of  material  and  which  are  capable  of  causing  an  explosion  through  their  own  potential
sources of ignition. [Directive 94/9/EC]

Equipment category:
Equipment and protective systems may be designed for a particular explosive atmosphere. In this case,
they must be marked accordingly. [Directive 94/9/EC]

Note:

Equipment may also be designed for use in various explosive atmospheres, e.g. in both
dust/air and gas/air mixtures.

Equipment group:
Equipment group I applies to equipment intended for use in underground parts of mines, and to those
parts of surface installations of such mines, liable to be endangered by firedamp and/or combustible
dust. Equipment group II applies to equipment intended for use in other places liable to be endangered
by explosive atmospheres. [Directive 94/9/EC]

Note:

Group I equipment is not relevant for the purposes of this Guide. (See 1.2 Scope)

45

Explosion group:
On  the  basis  of  their  maximum  permitted  gap  (the  ability  of  an  explosion  flame  to  be  propagated
through a defined gap is determined in a standard apparatus) and minimum igniting current (current
leading to ignition in a standard apparatus), gases and vapours are divided into three groups (II A, II B,
II C – II C being the group with the smallest maximum permitted gap).

Explosion limits:
If the concentration of a sufficiently dispersed flammable substance in air exceeds a minimum value
(the  lower  explosion  limit),  an  explosion  is  possible.  No  explosion  occurs  if  the  gas  or  vapour
concentration exceeds a maximum value (the upper explosion limit).
Explosion  limits  change  under  conditions  other  than  atmospheric.  The  range  of  concentrations
between  the  explosion  limits  widens,  e.g.  generally  as  the  pressure  and  temperature  of  the  mixture
increase. An explosive atmosphere can form above a flammable liquid only if the temperature of the
liquid exceeds a minimum value.

Explosion pressure (maximum):
Maximum pressure occurring in a closed vessel during the explosion of an explosive atmosphere,
determined under specified test conditions. [EN 1127-1]

Explosion pressure resistant:
Property  of  vessels  and  equipment  designed  to  withstand  the  expected  explosion  pressure  without
becoming permanently deformed. [EN 1127-1]

Explosion pressure shock resistant:
Property  of  vessels  and  equipment  designed  to  withstand  the  expected  explosion  pressure  without
rupturing but allowing permanent deformation. [EN 1127-1]

Explosion relief area:
Geometric vent area of an explosion relief device.

Explosion relief device:
Device which closes a vent opening during normal operation and opens it in case of explosion.

Explosion relief:
Protective measure of limiting the explosion overpressure which will prevent a vessel, workplace or
building  from  exceeding  its  design  strength  (explosion  resistance)  by  exhausting  unburned  mixture
and products of combustion by opening a given area.

Explosion:
Abrupt oxidation or decomposition reaction producing an increase in temperature, pressure or in both
simultaneously. [EN 1127-1]

Explosive atmosphere:
"Explosive  atmosphere"  means  a  mixture  with  air,  under  atmospheric  conditions,  of  flammable
substances  in  the  form  of  gases,  vapours,  mists  or  dusts  in  which,  after  ignition  has  occurred,
combustion spreads to the entire unburned mixture. [Directive 1999/92/EC]

It  is  to  be  noted  that  an  explosive  atmosphere,  as  defined  by  the  directive,  may  not  be  capable  of
burning fast enough to produce an explosion, as defined by EN 1127-1.

Explosive mixture:
Mixture of a fuel finely divided in the gaseous phase and a gaseous oxidant in which an explosion can
propagate  after  ignition  has  occurred.  If  the  oxidant  is  air  under  atmospheric  conditions,  the  term
explosive atmosphere is used.

Flash point:
Minimum  temperature  at  which,  under  specified  test  conditions,  a  liquid  gives  off  sufficient
combustible  gas  or  vapour  to  ignite  momentarily  on  application  of  an  effective  ignition  source.
[EN 1127-1]

Hazardous explosive atmosphere:
Explosive atmosphere present in hazardous quantities.

46

Hazardous place (place where explosive atmospheres may occur):
A  place  in  which  an  explosive  atmosphere  may  occur  in  such  quantities  as  to  require  special
precautions  to  protect  the  health  and  safety  of  the  workers  concerned  is  deemed  to  be  hazardous.
[Directive 1999/92/EC]

Hazardous quantities:
Explosive  atmosphere  in  such  quantities  as  to  endanger  the  health  and  safety  of  workers  or  others.
[Directive 1999/92/EC]
As little as 10 litres of an explosive atmosphere as a continuous volume must generally be regarded as
hazardous in confined spaces irrespective of the size of the space.

Hybrid mixtures:
Mixture of flammable substances with air in different physical states, e.g. mixtures of methane, coal
dust and air. [EN 1127-1)

Ignition source:
An ignition source releases to an explosive mixture a quantity of energy capable of causing ignition to
spread in this mixture.

Ignition temperature:
The lowest temperature of a heated wall, as determined under specified test conditions, at which the
ignition of a combustible substance in the form of a gas, vapour or dust mixture with air will occur.
[EN 1127-1]

Intended use:
The use of equipment, protective systems, and devices referred to in Article 1 (2) in accordance with
the equipment group and category and with all the information supplied by the manufacturer which is
required for the safe functioning of equipment, protective systems and devices. [Directive 94/9/EC]

Limiting oxygen concentration:
Maximum  oxygen  concentration  in  a  mixture  of  a  flammable  substance  and  air  and  an  inert  gas  in
which an explosion will not occur, determined under specified test conditions. [EN 1127-1]

Lower explosion limit:
The  lower  limit  of  the  range  of  the  concentration  of  a  flammable  substance  in  air  within  which  an
explosion can occur. [EN 1127-1]

Materials which may form an explosive atmosphere:
Flammable and/or combustible substances are considered as materials which may form an explosive
atmosphere  unless  an  investigation  of  their  properties  has  shown  that  in  mixtures  with  air  they  are
incapable of independently propagating an explosion. [Directive 1999/92/EC]

Non-hazardous place:
A  place  in  which  an  explosive  atmosphere  is  not  expected  to  occur  in  such  quantities  as  to  require
special precautions is deemed to be non-hazardous. [Directive 1999/92/EC]

Particle size
Nominal diameter of a dust particle.

Protective system:
"Protective systems" means devices other than components of the equipment defined above which are
intended to halt incipient explosions immediately and/or to limit the effective range of an  explosion
and which are separately placed on the market for use as autonomous systems. [Directive 94/9/EC]

Note: 

The term "protective systems" also covers integrated protective systems placed on  the
market in conjunction with an item of equipment.

Q-Pipe:
Q-Pipes  can  be  placed  downstream  of  explosion  relief  devices.  A  special  wire  mesh  arrests  the
explosion flame, so that it does not spread beyond the Q-Pipe.

Smouldering point:
The  smouldering  point  is  the  temperature  above  which  the  decomposition  gases  evolved  must  be
expected to give rise to an explosive mixture.

47

Surface temperature, maximum permissible:
Maximum permissible temperature of a surface (e.g. of an item of equipment), obtained by deducting
a fixed temperature value from the ignition and/or glow temperature.

Technically leakproof:
A subunit is "technically leakproof" if a leak is not discernible during testing, monitoring or checking
for  leakproofness  by  a  method  appropriate  to  the  application,  e.g.  using  foaming  agents  or  leak
searching/indicating  equipment,  but  the  possibility  of  infrequent  small  releases  of  flammable
substances cannot be excluded.

Temperature class:
Equipment is classified by temperature class according to its maximum surface temperature. Similarly,
gases are classified according to their ignition temperatures.

Type of protection:
The special measures applied to equipment to prevent ignition of a surrounding explosive atmosphere.
[After EN 50014]

Upper explosion limit:
The  upper  limit  of  the  range  of  the  concentration  of  a  flammable  substance  in  air  within  which  an
explosion can occur. [After EN 1127-1]

Work equipment:
Any machine, apparatus, tool or installation used at work. [Directive 89/655/EEC]

Worker:
Any  person  employed  by  an  employer,  including  trainees  and  apprentices  but  excluding  domestic
servants. [Directive 89/391/EEC]

Zones:
See "Zoning".

Zoning:
Hazardous  places  are classified in  terms  of  zones  on  the  basis  of  the  frequency  and  duration  of  the
occurrence of an explosive atmosphere. [Directive 1999/92/EC]

48

A.2

Legislation, standards and sources of further information on explosion protection

Annex A.2 lists the EU directives and guidelines and the harmonised European standards in the same
language as the national version of the Guide. National regulations transposing Directive 1999/92/EC
–  insofar  as  they  are  known  at  the  time  of  producing  this  Guide  –  are  given  in  the  language  of
publication.

The annex contains further sections for completion by the competent national authorities with details
of further national regulations, literature and national advice centres.

A.2.1 European directives and guidelines1

89/391/EEC

89/655/EEC

90/396/EEC

92/58/EEC

92/91/EEC

92/104/EEC

94/9/EC

96/82/EC

1999/92/EC

Council  Directive  89/391/EEC  of  12  June  1989  on  the  introduction  of
measures  to  encourage  improvements  in  the  safety  and  health  of  workers  at
work (OJ L 183, 29.6.1989, p. 1)

Council  Directive  89/655/EEC  of  30  November  1989  concerning  the
minimum  safety  and  health  requirements  for  the  use  of  work  equipment  by
workers at work (second individual Directive within the meaning of Article 16
(1) of Directive 89/391/EEC) (OJ L 393, 30.12.1989 p. 13)

Council Directive  90/396/EEC  of 29 June  1990  on  the  approximation of the
laws  of  the  Member  States  relating  to  appliances  burning  gaseous  fuels
(OJ L 196, 26.7.1990, p. 15)

Council Directive 92/58/EEC of 24 June 1992 on the minimum requirements
for  the  provision  of  safety  and/or  health  signs  at  work  (ninth  individual
Directive within the meaning of Article 16 (1) of Directive 89/391/EEC) (OJ
L 245, 26.8.1992 p. 23)

Council Directive 92/91/EEC of 3 November 1992 concerning the minimum
requirements for improving the safety and health protection of workers in the
mineral-extracting  industries  through  drilling  (eleventh  individual  Directive
within  the  meaning  of  Article  16  (1)  of  Directive  89/391/EEC)  (OJ  L  348,
28.11.1992, p. 9)

Council  Directive  92/104/EEC  of  3  December  1992  on  the  minimum
requirements  for  improving  the  safety  and  health  protection  of  workers  in
surface  and  underground  mineral-extracting  industries  (twelfth  individual
Directive within the meaning of Article 16 (1) of Directive 89/391/EEC) (OJ
L 404, 31.12.1992, p. 10)

Directive  94/9/EC  of the  European  Parliament  and  the  Council  of  23  March
1994  on  the  approximation  of  the  laws  of  the  Member  States  concerning
equipment  and  protective  systems  intended  for  use  in  potentially  explosive
atmospheres (OJ L 100, 19.4.1994, p. 1)

Council  Directive  96/82/EC  of  9  December  1996  on  the  control  of  major-
accident hazards involving dangerous substances (OJ L 010, 14.1.1997 p. 13)

Directive  1999/92/EC  of  the  European  Parliament  and  of  the  Council  of
16 December  1999  on  minimum  requirements  for  improving  the  safety  and
health  protection  of  workers  potentially  at  risk  from  explosive  atmospheres
(15th  individual  Directive  within  the  meaning  of  Article  16 (1)  of  Directive
89/391/EEC) (OJ L 23, 28.1.2000, p. 57)

2001/45/EC

Directive  2001/45/EC  of  the  European  Parliament  and  of  the  Council  of  27
June 2001 amending Council Directive 89/655/EEC concerning the minimum

1  The  full  text  of  the  Directives  can  be  consulted  free  of  charge  on  the  EUR-LEX  European  law  website  at
http://europa.eu.int/eur-lex/en/search/search_lif.html.

49

                                                     
safety and health requirements  for  the  use  of  work  equipment  by  workers at
work  (second  individual  Directive  within  the  meaning  of  Article  16(1)  of
Directive 89/391/EEC) (OJ L 195, 19.7.2001 p. 46)

ATEX Guidelines Guidelines on the application of Council Directive 94/9/EC of 23 March 1994
on the approximation of the laws of the Member States concerning equipment
and protective systems intended for use in potentially explosive atmospheres,
May  2000  (published  by  the  European  Commission,  2001).  ISBN  92-894-
0784-0

67/548/EEC

Council Directive 67/548/EEC of 27 June 1967 on the approximation of laws,
regulations  and  administrative  provisions  relating  to  the  classification,
packaging and labelling of dangerous substances (OJ L 196, 16.8.1967, p. 1),
last amended on 6 August 2001 (OJ L 225, 21.8.2001, p. 1)

A.2.2 EU Member States' national regulations transposing Directive 1999/92/EC

(items in italics to be completed by the Commission)

Belgium

Designation

Full title (Short title), Date of issue, Source

Denmark

Designation

Full title (Short title), Date of issue, Source

Germany

BetrSichV

Verordnung  zur  Rechtsvereinfachung  im  Bereich  der  Sicherheit  und  des
Gesundheitsschutzes  bei  der  Bereitstellung  von  Arbeitsmitteln  und  deren
Benutzung 
Betrieb
überwachungsbedürftiger  Anlagen  und  der  Organisation  des  betrieblichen
Arbeitsschutzes - Betriebssicherheitsverordnung (BetrSichV)(BGBl. 2002 Teil
I S. 3777)

der  Arbeit, 

Sicherheit 

beim 

der 

bei 

United Kingdom

Designation

Full title (Short title), Date of issue, Source

Greece

Designation

Full title (Short title), Date of issue, Source

Sweden

Designation

Full title (Short title), Date of issue, Source

Spain

Designation

Full title (Short title), Date of issue, Source

France

Designation

Full title (Short title), Date of issue, Source

Ireland

Designation

Full title (Short title), Date of issue, Source

Italy

Designation

Full title (Short title), Date of issue, Source

Luxembourg

Designation

Full title (Short title), Date of issue, Source

Netherlands

Designation

Full title (Short title), Date of issue, Source

50

Austria

Designation

Full title (Short title), Date of issue, Source

Portugal

Designation

Full title (Short title), Date of issue, Source

Finland

Designation

Full title (Short title), Date of issue, Source

A.2.3  Selected European standards

A current list can be found on the website of the European Committee for Standardization (CEN) at:
http://www.cenorm. be/standardization/tech_bodies/cen_bp/workpro/tc305.htm.

EN 50 281-3

Classification of areas where combustible dusts are or may be present.

EN 1127-1

EN 13463-1

EN 12874

Explosive  atmospheres  -  explosion prevention and  protection  -  Part  1:  Basic
concepts and methodology; version EN 1127-1:1997

Non-electrical equipment for potentially explosive atmospheres - Part 1: Basic
method and requirements; version EN 13463-1:2001

Flame arresters - Performance requirements, test methods and limits for use;
version EN 12874: 2001

EN 60079-10

Electrical apparatus for explosive gas atmospheres - Part 10: Classification of
hazardous areas; version EN 60079-10:1996

prEN 1839

Determination of explosion limits of gases, vapours and their mixtures

prEN 13237-1

prEN 13463-2

prEN 13463-5

Potentially  explosive  atmospheres  -  explosion  prevention  and  protection  -
Part 1: Terms and definitions for  equipment  and  protective  systems  intended
for use in potentially explosive atmospheres; version prEN 13237-1:1998

Non-electrical  equipment 
in  potentially  explosive
atmospheres  -  Part  2:  Protection  by  flow  restricting  enclosure  "fr";
version prEN 13463-2:2000

for  use 

intended 

Non-electrical  equipment 
atmospheres 
prEN 13463-5:2000

in  potentially  explosive
-  Part  5:  Protection  by  constructional  safety;  version

for  use 

intended 

prEN 13463-8

Non-electrical  equipment  for  potentially  explosive  atmospheres  -  Part  8:
Protection by liquid immersion "k"; version prEN 13463-8:2001

prEN 13673-1

prEN 13673-2

prEN 13821

prEN 13980

prEN 14034-1

Determination  of  the  maximum  explosion  pressure  and  maximum  rate  of
pressure  rise  of  gases  and  vapours  -  Part  1:  Determination  of  the  maximum
explosion pressure; version prEN 13673-1:1999

Determination  of  maximum  explosion  pressure  and  maximum  explosion
pressure  rise  of  gases  and  vapours  -  Part  2:  Determination  of  the  maximum
explosion pressure rise

Determination  of  minimum 
version prEN 13821:2000

ignition  energy  of  dust/air  mixtures;

Potentially  explosive  atmospheres  -  Application  of  quality  systems;  version
prEN 13980:2000

Determination  of  explosion  characteristics  of  dust  clouds  -  Part  1:
Determination  of  the  maximum  explosion  pressure;  version  prEN 14034-
1:2002

51

prEN 14034-4

Determination  of  explosion  characteristics  of  dust  clouds  -  Part  4:
concentration  of  dust  clouds;
Determination  of 
version prEN 14034-4:2001

limiting  oxygen 

prEN 14373

Explosion suppression systems

prEN 14460

Explosion resistant equipment

prEN 14491

Dust explosion venting protective systems

prEN 14522

Determination of the minimum ignition temperature of gases and vapours

A.2.4 Further national regulations and literature (to be completed by national authorities)

National regulations

Designation

Full title (Short title), Date of issue, Source

...

Literature

Title, Author, Date of publication, Source

...

A.2.5 National advice centres (to be completed by national authorities)

Name of the organisation
Contact person, if any
Street/postbox
Postcode, locality
...

Tel.: ...
Fax: ...
E-Mail: ...

...

52

A.3

Specimen forms and checklists

The specimen forms and checklists are an aid to practical application of the Guide, but make no claim
to exhaustiveness.

A.3.1 Checklist: Explosion protection inside apparatus

A.3.2 Checklist: Explosion protection around apparatus

A.3.3

Specimen:  Permit-to-work  form  for  work  involving  ignition  sources  in  places  with
hazardous atmospheres

A.3.4 Checklist: Coordination for on-site explosion protection

A.3.5 Checklist: Tasks of the coordinator for on-site explosion protection

A.3.6 Checklist: Completeness of the explosion protection document

53

A.3.1 Checklist: Explosion protection inside apparatus

Checklist: Explosion protection
assessment I
- Focus: Inside apparatus -

Processed by

Date

Purpose

To evaluate explosion protection inside plant and apparatus, in order to assess the existing explosion
protection  strategy  on  the  basis  of  targeted  questions  and  to  take  any  further  action  necessary.
Points of doubt can be resolved by referring to the Guide sections indicated, consulting local health and
safety organisations or studying the current literature.

Yes

No

Measures taken/
comments

Apparatus/plant

Item

Is the presence of flammable substances avoided
as far as possible [see 2.2.1]?

Is the formation of explosive mixtures from the
flammable substances present prevented as far as
possible [see 2.2.2/2.2.3]?

Is the occurrence of hazardous quantities of
explosive atmospheres precluded as far as
possible [see 2.2.4]?

Can the formation of explosive mixtures inside
the apparatus be prevented or limited [see 3.1]?
(cid:1) Can process conditions ensure compliance

with safe concentrations [see 3.1.2]?
(cid:1) Is the concentration reliably and lastingly

kept below the lower explosion limit or above
the upper explosion limit [see 3.1.2]?

(cid:1) Is the explosion range avoided during startup

and shutdown of the plant [see 3.1.2]?
(cid:1) Can mixtures emerging from the apparatus
during operation above the upper explosion
limit form explosive atmospheres outside it
and is this prevented [see 3.1.4]?

54

Continued

Item

Checklist: Explosion protection assessment I
- Focus: Inside apparatus -

Yes

No

Measures taken/
comments

Page 2/3

(cid:1) When vacuum plant is operated above the

upper explosion limit, is air ingress and hence
the formation of explosive mixtures
prevented?

(cid:1) Is the explosion hazard or violence reduced

by lowered pressure (operation under
vacuum)?

(cid:1) Is the formation of explosive mixtures reliably

prevented in all operating conditions by
injection of inert substances (e.g. nitrogen,
carbon dioxide, noble gases, water vapour or
inert powders) [see 3.1.3]?
-  When inerting is carried out with water

vapour, is the effect of condensation taken
into account?

-  Has allowance been made for the possibility
that an inerted mixture may again become
explosive on addition of sufficient oxygen or
air (e.g. on discharge to the open air)?
(cid:1) Has a safety margin been specified between
the experimentally determined limiting
oxygen concentration and the maximum
permissible oxygen concentration, taking
account of spatial and temporal variations
resulting from operational factors and
malfunctions and of the delay between
triggering of protective measures and their
becoming effective?

(cid:1) Are undesirable dust deposits or

accumulations avoided [see 3.1.4.1]?

Is the prevention or limitation of explosive
mixtures inside apparatus monitored?

Can hazardous explosive atmospheres occur
inside the plant or apparatus despite the above
measures [see 2.2.5]?

55

Continued

Item

Checklist: Explosion protection assessment I
- Focus: Inside apparatus -

Yes

No

Measures taken/
comments

Page 3/3

Are all necessary measures taken to prevent the
ignition of a hazardous explosive atmosphere [see
3.2/ 3.2.2]?

(cid:1) Are zones known and classified [see 3.2.1]?
(cid:1) Are effective ignition sources of the 13 known
types to be expected according to the zoning
[see 3.2.3]?

Can a hazardous explosive atmosphere be ignited
inside the plant or apparatus despite all the above
measures [see 2.2.6]?

Are the effects of an explosion limited to an
acceptable extent by suitable mitigation measures
designed in accordance with the state of the art,
without endangering the surrounding area (e.g. by
venting) [see 3.3]?

(cid:1) Explosion-resistant design [see 3.3.1]?
(cid:1) Explosion relief [see 3.3.2]?
(cid:1) Explosion suppression [see 3.3.3]?
(cid:1) Prevention of flame and explosion

propagation to upstream and downstream
items of plant [see 3.3.4]?
-  Flame arresters for gases, vapours and

mists?

-  Decoupling devices for dusts?
-  Explosion decoupling for hybrid mixtures?

56

A.3.2 Checklist: Explosion protection around apparatus

Checklist: Explosion protection
assessment II
- Focus: Around apparatus -

Processed by

Date

Purpose

To evaluate explosion protection around plant and apparatus, in order to assess the existing explosion
protection  strategy  on  the  basis  of  targeted  questions  and  to  take  any  further  action  necessary.
Points of doubt can be resolved by referring to the Guide sections indicated, consulting local health and
safety organisations or studying the current literature.

Yes

No

Measures taken/
comments

Apparatus/plant

Item

Is the formation of explosive atmospheres around
apparatus prevented [see 3.1.4]?

(cid:1) Are explosive atmospheres prevented by
operational measures, design or spatial
configuration?

(cid:1) Is the apparatus/plant leakproof?
(cid:1) Is ventilation or extraction used?

Are arrangements in place to monitor the
concentration around apparatus [see 3.1.5]?

(cid:1) By means of gas instruments which trigger an

alarm?

(cid:1) By means of gas instruments which trigger

protective measures?

(cid:1) By means of gas instruments which trigger

emergency functions?

Can a hazardous explosive atmosphere occur
around the plant or apparatus despite the above
measures [see 2.2.5]?

57

Continued

Item

Checklist: Explosion protection assessment II
- Focus: Around apparatus -

Yes

No

Measures taken/
comments

Page 2/2

Are all necessary measures taken to prevent the
ignition of a hazardous explosive atmosphere [see
3.2/ 3.2.2]?

(cid:1) Are zones known and classified

[see 3.2.1]?

(cid:1) Are effective ignition sources of the 13 known
types to be expected according to the zoning
[see 3.2.3]?

What civil engineering measures are taken to limit
the effects of an explosion to an acceptable extent,
e.g.

(cid:1) Bricking of high-pressure autoclaves?

Are organisational measures taken to ensure the
effectiveness of the technical measures [see
section 4]?

(cid:1) Are operating instructions in place?
(cid:1) Are competent personnel used?
(cid:1) Are workers given training?
(cid:1) Is a permit-to-work system in place?
(cid:1) Are hazardous places marked?

Are protective measures in place for maintenance
work [see 4.5]?

58

A.3.3 Specimen:  Permit-to-work  form  for  work  involving  ignition  sources  in  places  with

hazardous atmospheres

Permit-to-work form
for work involving ignition sources in places with hazardous atmospheres

1 Working place

2

Task
(e.g. weld pipe)

.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................

.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................

3 Nature of work

4

Precautions  taken  before
starting work

5

Fire sentry

6 Alarm

7

8

Firefighting
equipment/extinguishing
agent
Authorisation

  Cutting
  Soldering
  ...........................................

  Welding
  Abrasive cutting
  Thawing
Remove  all  movable  combustible  objects  and  substances,  including  dust
deposits, within a radius of  ...... m and – where necessary – also in adjacent
rooms
Cover  the  immovable  combustible  objects,  e.g.  wooden  beams  and  floors
plastic parts, with protective materials
Seal openings, joints and cracks in the building and other apertures such as
gratings with non-flammable substances
Remove cladding and insulation
Eliminate 
possibly by inerting
Close openings in pipework, containers and accessories, etc.
Post a fire sentry with filled water buckets, fire extinguishers or connected
fire hose (spray only for dusts)
  While work is in progress
  After work is completed

Name: ....................................................
hrs
Name:

containers 

explosion 

pipework,

Duration:

hazard 

and 

in 

Location of the nearest
   Fire alarm   ....................................................................................................
   Telephone
.....................................................................................................
Fire service telephone number:

  Fire extinguisher with  
  Filled water buckets
  Connected fire hose

  water     

  CO2      

  powder

The  safety  measures  listed  must  be  taken.  The  statutory  provisions  for  accident
prevention and the insurers' safety regulations must be observed.

Date

Signature of the manager or the person
appointed by him

Signature of the person carrying out the work

59

A.3.4 Checklist: Coordination for on-site explosion protection

Checklist: Coordination measures
- Focus: On-site explosion protection -

Processed by

Date

Purpose

This checklist may serve as an aid to checking whether the protective measures are being carried out as
agreed to allow principal and contractor to work together safely, whether the persons concerned have
received adequate instruction and whether they are complying with the agreed protective measures.

Yes

No

Task

Item

Is a check made on compliance with statutory and company regulations
implementing Directive 1999/92/EC?

(cid:1)  Has a person (the coordinator) been appointed to coordinate work

carried out jointly [see 5.1]?

(cid:1)  Does the appointed person meet the necessary requirements [see 5.1]?
(cid:1)  Is the coordinator known on site?
(cid:1)  Are subcontractors notified to the employer?

Is the work procedure checked for hazardous interaction [see 5.2]?

(cid:1)  Is it impossible for hazardous explosive atmospheres to form in places

where there may be ignition sources?

(cid:1)  Is the use or creation of ignition sources prevented in places with

hazardous explosive atmospheres?

(cid:1)  Are malfunctions avoided in nearby operations involving hazardous

places?

Is the work procedure laid down [see checklist in Annex A.3.5]?

Are the agreed protective measures adapted to take account of the progress
of work or of any shortcomings detected?
(cid:1)  Is training provided throughout?
(cid:1)  Is there consultation throughout?
(cid:1)  Are instructions issued throughout?
(cid:1)  Are checks made throughout?

60

A.3.5 Checklist: Tasks of the coordinator for on-site explosion protection

Checklist: Coordination tasks
- Focus: On-site explosion protection -

Processed by

Date

Purpose

To specify the tasks of the person responsible for coordination (preferably a coordinator appointed by
the employer) in order to ensure that the work of the groups/contractors concerned is so orchestrated
that any possible hazardous interaction is detected and prevented in good time and action can be taken
quickly in the event of incidents.

Yes

No

Task

Item

Is a site inspection carried out?

Is a work schedule drawn up?

(cid:1)  Have the place and time of the individual tasks been indicated?
(cid:1)  Have the persons concerned been named, including the persons in

charge?

(cid:1)  Has the timeline been specified?
(cid:1)  Have the special requirements for carrying out the work been specified?
(cid:1)  Have specific explosion protection measures been laid down?
(cid:1)  Have the danger zones, and in particular the places where an explosive

atmosphere may occur, been determined and marked?
(cid:1)  Have measures been put in place in case of incident?

Are consultations arranged between the persons concerned?

Are checks made on compliance with the work schedule?

Are the operations replanned in the event of an incident?

61

A.3.6 Checklist: Completeness of the explosion protection document

Checklist: Explosion protection document
- Check on completeness -

Date

Processed by

Purpose

To  check  the  completeness  of  an  explosion  protection  document,  indicating  information  sources.
Points of doubt can be resolved by referring to the Guide sections indicated, consulting local health and
safety organisations or studying the current literature.

Explosion protection document (title, location)

Information source

Explosion
protection
document

Other
documents

Still
 to be
produced

Item

Description of the workplace and working areas
available [see 6.3.1]?

(cid:1)  Textual description
(cid:1)  Site plan
(cid:1)  Layout plan
(cid:1)  Plan of escape and rescue routes

Description of process steps / activities [see
6.3.2]?

(cid:1)  Textual description
(cid:1)  Process flowchart (where necessary)
(cid:1)  P&I flowchart (where necessary)
(cid:1)  tex (where necessary)

Description of the substances used
[see 6.3.3]?

(cid:1)  Textual description
(cid:1)  Safety datasheets
(cid:1)  Safety parameters

62

Continued

Item

Checklist: Explosion protection document
- Check on completeness -

Page 2/3

Information source

Explosion
protection
document

Other
documents

Still
 to be
produced

Results of the risk analysis described [see 6.3.4]?
(cid:1)  Statement of hazard identification procedure
(cid:1)  Hazardous places inside items of plant

(textual)

(cid:1)  Hazardous places around plant (textual)
(cid:1)  Zoning (textual)
(cid:1)  Zone plan (graphic)
(cid:1)  Hazards in normal operation
(cid:1)  Hazards during startup and shutdown
(cid:1)  Hazards in the event of malfunction
(cid:1)  Hazards during cleaning
(cid:1)  Hazards in the event of process/product

changes

Technical explosion protection measures
described [see 6.3.5]?

(cid:1)  Prevention
(cid:1)  Mitigation
(cid:1)  PCE measures
(cid:1)  Requirements for and selection of work

equipment

63

Continued

Item

Checklist: Explosion protection document
- Check on completeness -

Page 3/3

Information source

Explosion
protection
document

Other
documents

Still
 to be
produced

Organisational explosion protection measures
described [see 6.3.6]?

(cid:1)  Written operating instructions
(cid:1)  Instructions for use of work equipment
(cid:1)  Description of personal protective equipment
(cid:1)  Evidence of competence
(cid:1)  Documentation of training
(cid:1)  Description of the permit-to-work system
(cid:1)  Description of maintenance, inspection and

surveillance intervals

(cid:1)  Documentation of the marking of hazardous

places

(cid:1)  Checks on effectiveness

Documentation of persons responsible and
competent persons [see 6.3.7]?

Documentation of coordination measures and
arrangements [see 6.3.8]?

Content of the annex [see 6.3.9]:

(cid:1) 
(cid:1) 
(cid:1) 

.......................................................

.......................................................

.......................................................

                             . . . . .

64

A.4

Text of the Directive in the appropriate language to be inserted by the Commission

Directive 1999/92/EC of the European Parliament and of the Council of 16 December 1999  on
minimum requirements for improving the safety and health protection of workers potentially at
risk from explosive atmospheres

65