GuideforRiskAssessment inSmallandMediumEnterprises 7 ... · the lower explosion limit, the explo-5...
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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
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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-
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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.
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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
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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[email protected]
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: [email protected]
ISSA Section forElectricity
c/o BerufsgenossenschaftEnergie Textil ElektroMedienerzeugnisseGustav-Heinemann-Ufer 13050968 Köln · GermanyFon: +49 (0) 221 - 3778 - 6007Fax: +49 (0) 221 - 3778 - 196007E-Mail: [email protected]
ISSA Section forMachine and System Safety
Dynamostrasse 7-1168165 Mannheim · GermanyFon: +49 (0) 621-4456-2213Fax: +49 (0) 621-4456-2190E-Mail: [email protected]