Guide for Risk Assessmentin Small and Medium Enterprises

7 Hazards arising fromExplosionsIdentification and Evaluation of Hazards; Specification of Measures

Section for ElectricitySection for Iron and MetalSection for Machine and System Safety

Hazards arising fromExplosions7

Guide forRisk Assessment inSmall and Medium Enterprises

Identification and Evaluationof Hazards;Specification of Measures

Section for ElectricitySection for Iron and MetalSection for Machine and System Safety

2

Imprint

Authors: Stephanos Achillides,Department of Labour Inspection, Cyprus

Dipl.-Ing. Daniela Gecelovská,Národný inšpektorát práce Košice, Slovakia

Jürgen Gehre, ISSA,Section Metal, Germany

In cooperation withDr. Martin Gschwind, Ake Harmanny, Ing. Klaus Kopia,Explosion Protection Group of the ISSA Section Machinery andSystem Safety

Production: Verlag Technik& Information e.K.,Wohlfahrtstrasse 153, 44799 Bochum, GermanyTel. +49(0)234-94349-0, Fax +49(0)234-94349-21

Printed in Germany March 2010

ISBN 978-3-941441-50-7

3

This brochure is intended to assist smalland medium enterprises (SMEs) to identi-fy gas and dust explosion hazards atthe workplace, evaluate the associatedrisks and recommend possible preventiveand protective measures.

This brochure does not cover other typesof explosions such as runaway reactions,detonations of high explosives, or burst-ing pressure vessels.

The brochure is structured as follows:

1. Basic Information – Principles

2. Checklists for Risk Assessment(Hazard Identification)

3. Risk Assessment

4. Risk Reduction – Taking Measures

5. Explosion Protection Document

Other topics treated in this series ofbrochures organised along the samelines and already published or being pre-pared are:

� Hazards arising frommachinery and other workequipment

� Hazards arising from electricity

� Slipping and falling froma height

� Hazards arising fromwhole-body/hand-arm vibrations

� Chemical hazards

� Physical strain(e.g. heavy and one-side work)

� Noise

� Mental workload

Introductory Note

4

1. Basic Information – Principles

Explosion is an abrupt oxidation or de-composition reaction producing an in-crease in temperature, pressure or inboth simultaneously [EN 1127-1].

A gas or dust explosion therefore can bedescribed as the consequence of a fastcombustion of gas/dust mixed with air.

1.1 What is an explosion?

1.2 How it is generated?

Some of the effects of an explosion areloud noise and pressure waves, whichcan collapse walls and shatter windows.

Also, searing heat, clouds of smoke andballs of flame are other deadly effectsproduced by the sudden violent expan-sion of gases.

To create an explosion there has to befuel (i.e. gas, such as hydrogen or dust,such as flour), an oxidizer (the oxygenin air) and an ignition source (i.e. a hotsurface or an electrical spark). Oncethe mechanism of mixing the fuel with

the air is established and the concen-tration of the fuel is within the explosionlimits, the resulting mixture can be ignit-ed if the ignition source has sufficientstrength.

1.3 Elements of an explosion

Explosive atmosphere can be createdwhen a flammable gas escapes, or aflammable liquid or vapour leaks, or aflammable dust disperses in the workingenvironment.

When the flammable material is mixedwith air, an explosive atmosphere can beformed. If the concentration of materialin the mixture is within the explosionlimits (Lower and Upper), then thepresence of an active ignition sourcecould ignite the mixture and create anexplosion.

Lower explosion limit (LEL) – is theminimum concentration of flamm-able gas, flammable liquid vapour ordust with air, where an explosion canoccur.

Upper explosion limit (UEL) – is themaximum concentration of flamm-able gas, flammable liquid vapour ordust with air where an explosion canoccur.

When the concentration is lower thanthe lower explosion limit, the explo-

5

The following Table shows some exam-ples of explosion limits:

Flammable Lower Uppersubstance explosion limit explosion limit

Natural gas 5% 13%

Propane 1,5% 9,5%

Acetylene 2,5% 81%

Sugar 30g/m3 –

Flour 30g/m3 –

sion cannot occur. When the concen-tration is higher than the upper explosionlimit, the mixture is «too rich» andthus there is insufficient oxygen for anexplosion.

Temperature and pressure also influ-ence flammability limits. Higher temper-ature results in lower LEL and higherUEL, while greater pressure increasesboth values.

It is important to know that less than1 mm of dust can already create anexplosive atmosphere.

Although an explosion happens at theblink of an eye, there are several phaseswhich happen at that instant: the originalshock wave blast of the explosion; theflying fragments of the explodingcontainer; and, depending on the pres-sure of the blast, parts of walls, roof,floors, doors, windows and ceilingscould collapse. Also, the generated heatmay cause secondary fires, burnsand secondary structural collapse/dam-age. Moreover, shock waves may sever-ly damage gas, water, electric andsewer pipes. The effects of an explosionare severe and the consequencesin human lives and destruction of pro-perty dramatic.

Very dangerous are also the noxiousreaction products, which are developedduring an explosion and the consump-tion of oxygen in the ambient air whichcan cause suffocation of workers.

Figure 1: Outcome of an explosion

Information about the explosion limits forgas or vapour is usually given in theMaterial Safety Data Sheets suppliedby the producer or importer of theflammable substance/product or othersources of information.

In practice, the UEL for dusts are hardlyknown since they are not useful fordusts because of the difficulty to con-trol explosive mixtures by limiting theconcentration. The UEL of most duststypically ranges from 2000 – 6000g/m3.Information on the LEL of many dustscan be found e.g. on the GESTIS web-site. Please bear in mind that dustdeposits can create a dust cloud.For example, due to a sudden move-ment of air from an open door or a minorexplosion, or dust deposits falling froma cable tray.

6

1.5 Relevant European legislation

The Council Directive 1999/92/EC, usuallyreferred to as ATEX-137, (hereinafter “UserATEX Directive”), is the legal basis for thenecessary measures at the workplace toimprove the safety and health protection ofworkers potentially at risk from explosiveatmospheres.

The User ATEX Directive defines theminimum requirements for the protection ofsafety and health of workers at risk fromexplosive atmospheres.

With a view to preventing and providingprotection against explosions, the employ-er shall take technical and/or organisation-al measures appropriate to the nature ofthe operation, in order of priority and in ac-

cordance with the following basic princi-ples:● the prevention of the formation of explo-

sive atmospheres, or where the natureof the activity does not allow that,

● the avoidance of the ignition of explo-sive atmospheres, and

● the mitigation of the detrimental effectsof an explosion so as to ensure thehealth and safety of workers and otherpersons at risk.

The Council Directive 94/9/EC, usually re-ferred to as ATEX-95, is also relevant sinceit specifies the essential requirements forequipment and protective systems intend-ed for use in explosive atmospheres.

1.4 What could trigger an explosion?

There are a number of different ignitionsources which can be found in SMEs withthe potential to ignite the flammable mate-rial/air mixture. Typical ignition sources are:hot surfaces, flames and hot gases, me-chanically generated sparks (while grindingor cutting), electrical sparks, static electric-ity, etc. Other ignition sources are: light-ning, electromagnetic fields, chemicalreactions, etc.

Details on the various types of ignitionsources can be found in the Europeanstandard EN 1127-1.

1.6 Hazardous area classification?

In the sense of the User ATEX Directive,If an explosive atmosphere may occurat a place in such quantities as to

require special protective measures tosafeguard the safety and health of theworkers concerned, then that place is

Figure 2: Ignition sources

7

described as a hazardous place andthe corresponding atmosphere in thatplace as a hazardous explosive atmo-sphere.

At such workplaces, aspecial warning signmust be placed. TheEX sign warns workersand other persons ofan explosion risk atcertain areas of the workplace due tothe presence of flammable materials.The flammable material could be in theform of liquid vapour, gas or flammabledust.

Explosive atmospheres could be createdin several branches of economic activitysuch as in the chemical industry, inrefineries, in power generating com-panies, gas equipment, etc. In SMEsexplosive atmospheres could be createdin the wood-working industry, in vehiclepaint booths, in agriculture farms, inthe food processing industry, at fuelstations, etc.

It is important to know that once theexistence of an explosive atmospherehas been established, whether it is ahazardous explosive atmosphere de-pends on its volume and the harmfulconsequences of any ignition. In gener-al, however, it can be assumed thatan explosion will cause substantial harmand that a hazardous explosive atmo-sphere is present.

On the basis of the above mentionedprinciples, a risk assessment of an ex-plosion risk at the workplace of the SME,should be carried out. The hazardousplaces must be identified and classifiedinto zones according to the frequencythat an explosive atmosphere will occurand its duration.

Ex sign

For example:

Zone 0A place in which an explosive atmo-sphere consisting of a mixture with airof flammable substances in the formof gas, vapour or mist is present con-tinuously or for long periods or frequent-ly.

Zone 1A place in which an explosive atmo-sphere consisting of a mixture with airof flammable substances in the form ofgas, vapour or mist is likely to occurin normal operation occasionally.

Zone 2A place in which an explosive atmo-sphere consisting of a mixture with airof flammable substances in the form ofgas, vapour or mist is not likely tooccur in normal operation but, if itdoes occur, will persist for a short periodonly.

Zone 20A place in which an explosive atmo-sphere in the form of a cloud of flamm-able dust in air is present continuously,or for long periods or frequently.

Zone 21A place in which an explosive atmo-sphere in the form of a cloud of flamm-able dust in air is likely to occur in nor-mal operation occasionally.

Zone 22A place in which an explosive atmo-sphere in the form of a cloud of flamm-able dust in air is not likely to occur innormal operation but, if it does occur,will persist for a short period only.

A widely used standard to determinearea extent and classification for flamm-

8

able vapour is EN 60079-10. This stan-dard makes a clear link between theamount of flammable vapour that maybe released, the ventilation at that loca-tion, and the zone number.

Various other sources have tried toplace time limits on to these zones, butnone have been officially adopted.

Examples of some common values usedare:

● Zone 0: Explosive atmosphere formore than 10 % of the operation timeof the plant, or 1000 h/yr.

● Zone 1: Explosive atmosphere formore than 0,1 % of the operation timeor 10 h/yr, but less than 10 % ofthe operation time, or 1000 h/yr.

Hazard means anything that can causeharm (e.g. chemicals, electricity, work-ing from ladders, an open pit, a circularsaw, etc).

Risk is the chance, high or low, thatsomeone could be harmed by these andother hazards together with an indicationof how serious the harm could be.

To assess the risk it is necessary toconsider the likelihood of an explosive

2. Checklists for Risk Assessment(Hazard Identification)

atmosphere and the potential con-sequences, following its subsequentignition, from an explosion.

Risk Assessment can be carried outusing the following checklist to identifyexplosion hazards at the workplaceand following an assessment of therisk, come up with the proper preventiveand protective measures.

● Zone 2: Explosive atmosphere forless than 0,1 % of the operation time,or 10 h/yr, but still sufficiently likelyas to require controls over ignitionsources.

The number given in terms of h/yr couldbe used in cases where the plant isoperational throughout the year.Where people wish to quantify the zonedefinitions, these values are the mostappropriate, but for the majority of situa-tions a purely qualitative approach isadequate.Zoning can also be used to determinethe extent of protective measures withrespect to the category of the protectivesystems to be used in the hazardousplace.

9

ExplosionHazards

Measures

Remarks

General

�Ar

efla

mm

able

subs

tanc

es(g

ases

,vap

ours

,dus

t)pr

esen

t?

�Is

gene

ratio

nof

expl

osiv

em

ixtu

res

poss

ible

due

tosu

ffici

entd

ispe

rsio

nin

air(

Estim

ate

sour

ces

and

quan

tity

ofex

plos

ive

atm

osph

ere)

?

�Is

gene

ratio

nof

haza

rdou

sex

plos

ive

atm

osph

ere

poss

ible

?

�Is

the

gene

ratio

nof

haza

rdou

sex

plos

ive

atm

osph

ere

prev

ente

dth

orou

ghly

byth

em

eas-

ures

abov

e?

�Is

igni

tion

ofha

zard

ous

expl

osiv

eat

mos

pher

epr

even

ted

safe

lyby

the

mea

sure

sab

ove?

�ot

her_

____

____

____

____

____

____

Measureslimitingorpreventinggenerationofhazardous

explosiveatmosphere

�R

epla

cefla

mm

able

subs

tanc

esby

non

flam

mab

leor

less

flam

mab

lesu

bsta

nces

�Li

mit

the

quan

tity

ofm

ater

ials

stor

edat

wor

kpla

ces

toth

atre

quire

dfo

rpro

gres

sof

wor

k

�St

ore

was

te,r

esid

ues

occu

rring

atth

een

dof

wor

k/sh

iftin

term

edia

tely

atsa

fepl

aces

�Pr

even

tion

orlim

itatio

nof

expl

osiv

eat

mos

pher

ein

the

inte

rnal

volu

me

ofsy

stem

san

dpa

rtof

syst

ems

by–

limita

tion

ofco

ncen

tratio

n;–

Iner

tisat

ion

�Pr

even

tion

orlim

itatio

nof

expl

osiv

eat

mos

pher

ew

ithin

the

vici

nity

ofsy

stem

san

dpa

rtsof

syst

ems

by–

tight

syst

em

Extra

ctio

nsy

stem

s;–

forg

ases

:ven

tilat

ion

(nat

ural

orfo

rced

)–

ford

ust:

mea

sure

sto

elim

inat

ede

posi

ts

�M

onito

ring

ofga

sco

ncen

tratio

n

�M

easu

res

prev

entin

gor

limiti

ngig

nitio

nof

haza

rdou

sex

plos

ive

atm

osph

ere

�As

sess

men

tofp

roba

bilit

yan

ddu

ratio

nof

occu

rrenc

eof

haza

rdou

sex

plos

ive

atm

osph

ere

(cla

ssifi

catio

nin

tozo

nes)

�Ac

cord

ing

toth

ecl

assi

ficat

ion

ofzo

nes,

elec

trica

land

non

elec

trica

ldev

ices

and

com

pone

nts

shal

lbe

sele

cted

inco

nfor

mity

with

the

corre

spon

ding

equi

pmen

tcat

egor

ies

�D

esig

nm

easu

res

fore

xplo

sion

prot

ectio

nlim

iting

the

effe

cts

ofan

expl

osio

nto

aha

rmle

ssex

tent

.–

expl

osio

nre

sist

antd

esig

n–

expl

osio

nve

ntin

g–

expl

osio

nsu

ppre

ssio

n–

expl

osio

nis

olat

ion

inco

mbi

natio

nw

ithth

epr

evio

usm

easu

res

�ot

her_

____

____

____

____

____

____

10

ExplosionHazards

Measures

Remarks

Ignitionsources

�Ar

eig

nitio

nso

urce

spr

esen

t?

Igni

tion

haza

rds

by:

�Fl

ames

orho

tgas

es(e

.g.s

mok

ing,

fire,

nake

dfla

mes

,wel

ding

and

cutti

ng

�m

echa

nica

llyge

nera

ted

spar

ks(e

.g.d

urin

ggr

indi

ng,r

ubbi

ngan

dha

mm

erin

g)

�el

ectri

cals

yste

ms

(e.g

.sw

itche

s,re

lays

)

�ho

tsur

face

s(e

.g.d

ryer

,boi

ler,

hotd

ucts

,due

toru

bbin

gan

dm

achi

ning

)

�st

atic

elec

trici

ty,(

e.g.

resu

lting

from

rubb

ing,

pneu

mat

icco

nvey

ing,

flow

ing

ofliq

uids

)

�ot

her_

____

____

____

____

____

____

PreventiveMaintenance

Hot

wor

k(e

.g.g

rindi

ng,f

lam

ecu

tting

,wel

ding

)in

area

sw

ithpo

tent

iale

xplo

sion

haza

rds

(gen

eral

)

�ot

her_

____

____

____

____

____

____

Preventeffectiveignitionhazardswithinhazardouszones

–D

ono

tallo

wan

yig

nitio

nso

urce

sw

ithin

the

wor

king

area

ofea

sily

flam

mab

lesu

bsta

nces

–Pr

even

tign

ition

sour

ces

and

proh

ibit

fire,

nake

dfla

mes

and

smok

ing

�M

echa

nica

llyge

nera

ted

spar

ksca

nbe

limite

dby

,for

inst

ance

,w

ater

cool

ing

atth

egr

indi

ngsp

otor

byse

lect

ing

the

mos

tfav

oura

ble

com

bina

tions

ofm

ater

ials

�Se

lect

suita

ble

elec

trica

lequ

ipm

ent(

e.g.

ATEX

95).

�M

onito

rand

limit

the

tem

pera

ture

ofho

tsur

face

s

�Sa

fedi

ssip

atio

nof

char

ges

byus

eof

cond

uctiv

em

ater

ials

and

byea

rthin

gm

easu

res

�ot

her_

____

____

____

____

____

____

�El

imin

ate

mov

able

flam

mab

lesu

bsta

nces

and

rem

ove

dust

depo

sits

,ifn

eces

sary

�ke

epw

ork

area

clea

nby

regu

larc

lean

ing

bym

eans

ofpr

oper

clea

ning

equi

pmen

tand

mat

eria

l

�m

aint

ain

elec

trica

land

mec

hani

cale

quip

men

treg

ular

lyfo

llow

ing

the

man

ufac

ture

r’sin

stru

ctio

ns

�ot

her_

____

____

____

____

____

____

11

3. Risk Assessment

The selection of the preventive andprotective measures which should beimplemented may be established from

the Probability Factor and the SeverityFactor using the risk assessment matrixshown below:

Severity Factor

Minor Significant Major Catastrophic(Light (Medium (Serious (Multipleinjuries) injuries) injuries or death)

deaths)

High 4 5 6 7(Likely tooccur at leastevery yearduring theplant lifetime

Medium 3 4 5 6(Likely tooccur morethan onceduring theplant lifetime)

Low 2 3 4 5(Unlikely touccur duringthe plantlifetime)

Very low 1 2 3 4(Remotelypossible tooccur, if ever)

In the above scenario, the plant lifetimeis estimated at 20 years. Based on thevalues established from the table above,

the necessary action and the time framein which it must be taken is indicatedfrom the table below:

Measured value Action taken and time frame

1 – 2(acceptable risk)

3 – 4(Reduction ofrisk necessary)

5 – 7(Reduction ofrisk urgentlynecessary)

No additional control measures are required. Possible improve-ment measure should consider the cost/benefit relationship. Stead-fast monitoring to ensure that control measures are implemented.

Within a fixed time frame measure must be implemented to reducerisk to an acceptable level.

Commencement of work is forbidden until risk mitigation. The re-quired improvement measures are important and should be imple-mented immediately for work tasks which are already in progress.If risk cannot be reduced to an acceptable level, the prohibition ofwork activities must remain in effect.

Propability

Factor

12

4. Risk Reduction – Taking Measures

If the risk assessment has indicated thatthere is a risk of explosion at the work-place, then measures must be devisedand implemented to:

● eliminate the risk,

or

● reduce the risk to an acceptablelevel.

The necessary measures could be pre-ventive or protective or a combinationof those. Furthermore, the aforemen-

tioned measures could be technical andorganisational.

Important:

If such preventive and protective meas-ures cannot be organized due to lack ofcompetent personnel in the SME, theemployer shall enlist competent externalservices or persons.

4.1 Introduction

The purpose of the preventive measuresis to eliminate, if possible, the risk ofexplosion by preventing the creation ofan explosive atmosphere, or by prevent-ing ignition sources.

Such preventive measures include:

4.2.1 Prevent or reduce flammablematerial

Following the prevention principles ofthe safety and health legislation, thistype of measure is high in the hierarchyof prevention. In many cases however,the flammable material cannot be re-placed by a non flammable, eitherbecause the material itself is theoutcome of specific process of the SME,or it is essential to the process itselfas an ingredient.

In such a case, the quantity of the flam-mable material kept at the workplaceshould be reduced to the absolute mini-mum needed. Flammable materialsshould be stored in suitable fireproofstorage containers, properly labelled andaway from potential ignition sources. Itis important not to store them togetherwith incompatible materials that mayreact with each other and initiate anexplosion.

4.2.2 Keeping the concentration ofthe flammable materialin the material/air mixtureoutside the explosion limits

The formation of explosive atmospheresoutside of installations should be pre-vented as far as possible. This may be

4.2 Preventive measures

13

achieved by closed installations. Theseparts of the installation shall be of suffi-ciently tight construction to prevent leak-age. The installations shall be so de-signed that no leakage can occur underthe foreseeable operating conditions.This shall also be ensured by regularmaintenance and testing.

If leakage of flammable substances can-not be eliminated, the formation of explo-sive atmosphere must be preventedby suitable measures so that the con-centration of the flammable material inthe material/air mixture is kept out-side the explosion limits. Such possiblemeasures include ventilation and clean-ing.

Specifically for gases or vapours:● Natural ventilation

(air exchange without forcedtechnical means)

● Mechanical ventilation(room ventilation with directed forcedtechnical means)

For dusts, extraction measures are con-sidered effective to prevent dust leakagefrom equipment. Preferably, the flamm-able dust should be extracted directly atthe point of generation. Also, properhousekeeping is very important. Flamm-able dust deposits can be avoided byregular cleaning measures using suit-able cleaning equipment. Stirring theflammable dust should be avoided asit could generate a dust cloud. Wettingthe flammable dust before removingprevents dispersion.

It should be noted that despite the effec-tiveness of the ventilation systemsand cleaning operations, there couldalways be a residual risk that need tobe reassessed and mitigated by furthermeasures.

4.2.3 Control the size ofthe flammable materialgranules/fines

This measure can be used for dust/airmixtures. If the particles of the flamm-able material are sufficiently large, e.g.greater than 0,5mm, the probability ofexplosive mixtures is reduced.

Warning:Even with coarse materials fines can al-ways be present, or arise due to friction.

4.2.4 Elimination/control ofpossible ignition sources frombecoming active

Potential ignition sources, such as weld-ing, grinding, smoking, hot surfaces,electrical and electrostatic sparks,mechanical sparks, exothermic chemicalreactions, etc, are amongst those com-monly found in SMEs.

Operational ignition sources and sour-ces resulting from equipment/process

Figure 3: Improper and proper methodsfor removing flammable dust

14

malfunction or misuse could be prevent-ed from becoming active by:

● electrostatic grounding,

● avoiding materials and objects of lowelectrical conductivity,

● reducing the size of non-conductivesurfaces,

● avoiding the use for dustconveying and filling operations ofconducting pipes and containerswith an electrically insulating innercoating,

● selection of low speed mechanicalequipment,

● selection of electrical and mechanicalequipment as per the requirements ofthe ATEX 95 Directive. It should be

noted that the equipmentmust be suitable for thenature of the hazardousworkplace environment,e.g. gas certified equipmentmust only be used in areaswith gas explosive atmos-pheres.

4.2.5 Detection of and explosiveatmosphere

Suitable detection systems may be usedto provide an early warning when anexplosive atmosphere is formed. Thesesystems typically trigger the alarm whenthe concentration of the flammablematerial/air mixture is around 10 % ofthe LEL. Such systems may shut downnon explosion proof equipment, startthe exhaust fan, etc.

The effectiveness of measures may beamplified if these are combined withwork organisation measures.Organisational measures must interactharmoniously with the other measuresto create a work environment in whichworkers can carry out their work withoutrisk to their safety and health, or to per-sons who might be affected by the workactivities.Common ignition sources, such assmoking, welding, or grinding, couldbe controlled by suitable organisation-al measures, such as prohibition ofsmoking, handing out written operatinginstructions to the workers, issuingcodes of behaviour, issuing Work Per-mits, providing adequate training andsupervision. Possible organisationalmeasures include:

4.3 Organisational measures

Figure 4: Organisational measures

15

4.3.1 Issue of written operatinginstructions

Operating instructions should containwritten rules of conduct issued by theemployer to the workers. Also, a list ofall mobile work equipment permittedfor use in the hazardous place con-cerned. They should also indicate whatpersonal protective equipment mustbe worn by persons entering such aplace.

4.3.2 Provide trainingEmployers must provide workers withtraining on the explosion hazards pre-sent at the workplace and on the re-levant prevention and protection meas-ures taken. This training must takeplace before work commencement andwhen job description changes, whennew work equipment is introduced orchanged and when new technology isintroduced.

The training should explain, for exam-ple, how the explosion hazard arisesand in what parts of the workplace itis likely to appear, the measurestaken and the correct use and mainte-nance of the work equipment. Also,workers must be instructed on howto work safely in or near hazardousareas. The employer should also briefthird persons, such as visitors to theSME as well as subcontractors, onthe risk of explosion.

4.3.3 Adopt a Work Permit SystemWorks, which may cause an explosion,in or near a hazardous place must becarried out through a Work Permit Sys-tem. A Work Permit Form signed by theresponsible person should be issued

which should include at least the follow-ing:

● The work location.

● A description andduration of the work to beundertaken.

● The number and namesof workers involved.

● The work equipment tobe used.

● Identification of the hazards.

● List of the precautionarymeasures followed by an acknow-ledgement by the responsibleperson that they have beenimplemented.

● The personal protective equipmentneeded.

● An acknowledgement thatthe workers involved have receivedadequate training.

For example, before maintenance workcommences in a hazardous area aWork Permit must be issued. Experi-ence shows that a high accident riskis associated with maintenance andservicing work. Before, during andafter completion of the work, it mustbe ensured that all necessary protec-tive measures are taken.

4.3.4 InspectionBefore a workplace that contains areaswhere an explosive atmosphere mayoccur, is used for the first time, itsoverall explosion safety must be as-sessed by a competent person. Inspec-tion should also be carried out whenalterations, with an impact on thesafety levels, take place in an area

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and also after the use of the area inquestion.

4.3.5 SupervisionAppropriate workers´ supervision mustbe ensured during the presence ofworkers in workplaces where an explo-sive atmosphere may occur.

4.3.6 MarkingThe points of entry to hazardous place,must be properly marked using theproper warning signs.

See section 2.6.

4.4.1 Explosion protectionmeasures

Where the possibility of explosion can-not be eliminated to an acceptable level,additional measures must be taken.These measures do not prevent explo-sions, but help to minimize their effectsso as to avoid or reduce casualties ordamages to the installation or the enter-prise itself.

The repercussions of an explosion maybe limited by constructional protectionmeasures, as follows:● explosion resistant design,● explosion venting,● explosion suppression

and● explosion isolation in combination

with the aforementioned.

The protective systems to be used mustcomply with the ATEX 95 Directive.

4.4.2 Explosion resistant design

When this measure is applied all plantitems concerned, must be so designedthat they can withstand an internal ex-plosion without rupturing.

4.4 Protective measures

Figure 5: Explosion resistant vessel (left),explosion venting (top) and explo-sion suppression (bottom right)

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Explosion pressure resistant containersand vessels withstand the expected ex-plosion overpressure without becomingpermanently deformed. The design isbased on the expected explosion over-pressure.

Explosion pressure shock resistant con-tainers and vessels are so constructedthat, in the event of an internal explo-sion, they may with stand a shock at-taining the expected explosion overpres-sure, but may become permanentlydeformed.

After every explosion, the affected itemsof plant must be checked and screenedfor deformation before further operationis allowed.

4.4.3 Explosion venting

Explosion venting comprises of allmeasures used to vent the initiallyclosed vessel or equipment in a nonhazardous direction. The explosion vent-ing devices are intended to ensure thatthe plant/installation is not subjectedto explosion stresses exceeding itsdesign strength. Bursting discs or explo-

sion doors are, for example, such vent-ing devices.

Explosion venting however, may notbe used if vented substances are haz-ardous, e.g. toxic, corrosive, etc.

4.4.4 Explosion suppression

Explosion suppression systems aredevices which, as in the case of explo-sion venting, prevent the buildup ofan inadmissibly high pressure duringexplosions in vessels. They functionby sensing the pressure rise, or theflame propagation, during the onsetof an explosion and suppressing theexplosion by the release of extinguishingagents.

4.4.5 Explosion isolation

An explosion occurring in one part of aplant can propagate to upstream anddownstream parts, where it may causefurther explosions. Excessive explosionoverpressure is caused by displace-ment, turbulence during the propagationof an explosion. The explosion overpres-

Figure 6: Explosion venting Figure 7: Explosion isolation equipment

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sures developed can be much higherthan the maximum explosion pressureunder normal conditions and may de-stroy unprotected sections of an installa-tion, or even items of a plant which areof the explosion pressure resistant, orexplosion pressure shock resistanttype.

It is therefore important to isolate possi-ble explosions to single parts ofthe plant. This is achieved by explosionisolation.

Explosion isolation can be performedby means of:

● rapid-action mechanical isolation;

Figure 8: Explosion isolation withrapid reaction valve

5. Explosion Protection Document

The User ATEX Directive provides forthe employer to prepare an ExplosionProtection Document. This documentshould be prepared for every processor installation initially, and be kept upto date when alterations take place.

Essentially, the Explosion ProtectionDocuments contains much of the infor-mation explained in sections 2.7, 3, 4and 5 of the Brochure.

For example:● The risk assessment

and the safety measures takento mitigate the risk,

● the zoning of the variouswork areas,

● the training and maintenanceprocedures, and

● how coordination of the safetymeasures is achieved.

● flame extinction in narrow gaps orby injection of an extinguishing agent;

● arresting of flame by high counterflow;● water seals;● rotary valves.

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National Aspects (respective legal transpositions)

CyprusThe Cyprus national legislation transpos-ing the provisions of the Council Directive1999/92/EC is the Safety and Health atWork (Minimum Requirements for theProtection of Persons at Work from Risksfrom Explosive Atmospheres) Regu-lations of 2002 (P.I. 291/2002) issued on21.6.2002.

GermanyThe German national legislation trans-posing the provisions of the CouncilDirective 1999/92/EC is the Betriebs-sicherheitsverordnung (BetrSichV, Ordi-nance on Industrial Safety and Health)„Ordinance concerning the protection ofsafety and health in the provision of workequipment and its use at work, concern-ing safety when operating installationssubject to monitoring and concerningthe organisation of industrial safety andhealth at work (Verordnung über Sicher-heit und Gesundheitsschutz bei der Be-reitstellung von Arbeitsmitteln und derenBenutzung bei der Arbeit, über Sicherheitbeim Betrieb überwachungsbedürftigerAnlagen und über die Organisationdes betrieblichen Arbeitsschutzes)“ ofSeptember 27, 2002, latest amendmentDezember 18, 2008.

Thematic focuses of the BetrSichV:

● Hazard evaluation(see § 3 BetrSichV)

● Explosion protection document(see § 6 BetrSichV)

● Testing of work equipment(siehe § 10 BetrSichV)

● Special regulations forplants requiring special supervision(see clause 3 of the BetrSichV)

● Zone classification of explosive areas(see Annex 3 of the BetrSichV)

● Minimum requirements for theimprovement of safety and health ofworkers possibly endangered byhazardous explosive atmosphere(see Annex 4, clause A of theBetrSichV)

● Criteria for the choice of devicesand protective systems(see Annex 4, clause B of theBetrSichV)

SlovakiaThe Slovak national legislation transpos-ing the provisions of the Council Directive1999/92/EC is the Slovak GovernmentDecree No. 393/2006 Coll. on minimumrequirements for improving the safety andhealth protection of workers potentiallyat risk from explosive atmosphere.

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National contact persons

V prípade záujmu o ďalšie informácie sa môžete obrátiť na miestne prílušné inšpek-toráty práce, regionálne úrady verejného zdravotníctva, ktoré nájdete na webspránkach:www.nip.sk a www.uvzsr.sk,

prípadne:

Národný inšpektorát práceOdbor riadenia inšpekcie práceMasarykova 10040 01 KošiceIng. Daniela Gecelovská+42155-7979918daniela.gecelovska@ip.gov.sk

The following ISSA International Sections on Prevention elaborated the brochure.They are also available for further information:

www.issa.intClick on “Prevention Sections” under “Quick Links”

ISBN 978-3-941441-50-7

ISSA Section forIron and Metal

c/o AllgemeineUnfallversicherungsanstaltOffice for InternationalRelationsAdalbert-Stifter-Strasse 651200 Vienna · AustriaFon: +43 (0) 1-33 111-558Fax: +43 (0) 1-33 111-469E-Mail: issa-metal@auva.at

ISSA Section forElectricity

c/o BerufsgenossenschaftEnergie Textil ElektroMedienerzeugnisseGustav-Heinemann-Ufer 13050968 Köln · GermanyFon: +49 (0) 221 - 3778 - 6007Fax: +49 (0) 221 - 3778 - 196007E-Mail: electricity@bgetem.de

ISSA Section forMachine and System Safety

Dynamostrasse 7-1168165 Mannheim · GermanyFon: +49 (0) 621-4456-2213Fax: +49 (0) 621-4456-2190E-Mail: info@ivss.org