Hazardous Areas Are Defined by Three Main Criteria

7/23/2019 Hazardous Areas Are Defined by Three Main Criteria

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Hazardous areasare defined by three main criteria:

The type of hazard

The likelihood of the hazard being present in flammable concentrations

The (auto) ignition temperature of the hazardous material

The type of hazard (Groups)

The hazard will be in the form of a gas, vapour, dust or fibre.

Gases and Vapours

Gases and vapours are categorized in terms of their ignition energy or themaimum eperimental safe gap (in respect of flameproof protection). Thiscategorization leads to the Gas Groups:

Mining Surface Industry

Group I Group II

MethaneIIA IIB IIC

Propane thy!ene Hydrogen

(The gases noted in the table are typical gases for each group.)

Group !!" is the most severe group. #azards in this group can be ignited veryeasily indeed.

$%uipment marked as suitable for Group !!" is also suitable for !!& and !!'.

$%uipment marked as suitable for !!& is also suitable for !!' but T for !!".

!f e%uipment is marked, for eample, $ e !! T* then it is suitable for allsubgroups !!', !!& and !!".

"usts and #i$res (Group III)


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Group III is subdivided into three sub groups:

IIIA "ombustible flyings

IIIB on+conductive dust

IIIC $lectrically conductive dusts

usts and fibres are also defined in terms of their ignition properties includingdust cloud ignition properties.

% BAC& T' T'P %

The !ie!ihood of the hazard $eing present in

f!aa$!e concentrations (*ones)The likelihood of the hazard being present in flammable concentrations willvary from place to place. ' location very close to an open source of hazard willhave a high likelihood of a flammable atmosphere. n the other hand, outsidea flanged pipe containing a flammable li%uid, the likelihood of a flammableatmosphere being present is much lower since it will only occur if the flangeleaks. -ather than work with an infinite range of possibilities, three zones aredefined.

Gases and Vapours

There are three zones for gases and vapours:

*one + #!aa$!e atosphere high!y !ie!y to $e present % ay$e present for !ong periods or e,en continuous!y

*one -#!aa$!e atosphere possi$!e $ut un!ie!y to $e

present for !ong periods

*one .#!aa$!e atosphere un!ie!y to $e present e/cept forshort periods of tie % typica!!y as a resu!t of a process

fau!t condition0
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one zero is the most severe zone (the highest probability of flammableatmosphere presence). $%uipment for this zone needs to be very wellprotected against providing a source of ignition.

"usts

There are three zones for dusts:

*one .+"ust c!oud !ie!y to $e present continuous!y or for !ong

periods

*one .-"ust c!oud !ie!y to $e present occasiona!!y in nora!

operation

*one .."ust c!oud un!ie!y to occur in nora! operation1 $ut if it

does1 2i!! on!y e/ist for a short period

(The presence of dust layers does not automatically lead to the dust zone.

The likelihood of the dust layer being disturbed to create a cloud needs to beconsidered. ust layers also need careful consideration in terms of ignitiontemperature. &ecause the dust layer can make the e%uipment under it hotterthen normal, a factor of safety is applied to the layer ignition temperature.)

% BAC& T' T'P %

The (auto) ignition teperature of the hazardousateria! (Teperature C!asses)

's well as considering the protection against electrical arcs and sparks ignitinga flammable atmosphere, consideration needs to be given to the surfacetemperature of e%uipment. (/ost electrical apparatus dissipates some heat0)1lammable materials are categorized according to their ignition temperature.
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'gain, rather than work with an infinite range, si temperature classes aredefined as follows:

T%C!ass Hazards 2hich 2i!! not ignite at teperatures $e!o23

T- 45+6C

T. 7++6C

T7 .++6C

T4 -756C

T5 -++6C

T8 956C

The bigger the T+number the lower is the temperature.

The Temperature classification will be marked on items of e%uipment. !f thehazardous area in which you are installing e%uipment has gases or vapourswith a low autoignition temperaturethen you will need e%uipment with a biggerT-Numberso as to ensure that any hot surfaces on the e%uipment will notignite the hazard.

1or eample, if a hazard has an autoignition temperature of 2345", then itwould be safe to use e%uipment which is marked T6 or T7 or T*. !t would notbe safe to use e%uipment marked T8 or T9 or T2 as this e%uipment couldehibit surface temperatures which are hot enough to ignite the hazardousatmosphere.

ont forget that, unless the certification documents state otherwise (in whichcase there will be an addition to the T-Classification code on the equipmentlabel such as T4 (60C Ambthe e%uipment is only certified in ambienttemperatures up to *45". !f eposed to higher temperatures there are twopossible dangers. 1irst the stated T+"lass temperature may be eceeded andsecondly safety components within the e%uipment could fail to an unsafecondition. !f you epect e%uipment to be sub;ected to temperatures above*45" (such as in direct sunshine or in a roof space) you should installe%uipment which is certified for a higher ambient temperature.

% BAC& T' T'P %
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Protecting !ectrica! Apparatusto ae it suita$!e foruse in hazardous areas

$lectrical apparatus for use in hazardous areas needs to be designed andconstructed in such a way that it will not provide a source of ignition. There areten recognized types of protection for hazardous area electrical apparatus.$ach type of protection achieves its safety from ignition in different ways andnot all are e%ually safe. !n addition to the e%uipment being suitable for the GasGroup and the Temperature "lass re%uired, the type of protection must besuitable for the zone in which it is to be installed. The different types ofprotection and the zones for which they are suitable are as follows:

#or inforation on e:uipent aring1c!ic here(opens new page)

Types of Protection for Gas ; Vapour Hazards

See a!so inforation on Types of Protection1C!ic here(opens new page)

:uipentCode

"escriptionSuita$!e for

zones000:uipentCategory 000

/ ia Intrinsic safety


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/ $ ncapsu!ation -0. .G

/ c ncapsu!ation . 7G

/ o 'i! iersion -1. .G

/ :Sand ; po2der (:uartz)

fi!!ing-1. .G

/ n Type % n protection . 7G

/ s Specia! protection=ora!!y - and

.

$%uipment complying with $uropean ("$$


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ic" Intrinsic Safety .. 7"

:uipent Protection >e,e!s % P>

1rom 944> onwards, the !$" Technical =tandards in the series !$" 644>?, andin particular !$" 644>? @art 2*, have recognised that there may be occasionswhere it is necessary to increase, above the normal levels, the protectionagainst ignition sources. This concept allows for consideration of risk (ieconse%uences of an eplosion) as opposed to ;ust the probability of aflammable atmosphere eisting + the conventional selection criteria betweenthe types of protection and the zone of use.

Three $%uipment @rotection


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/ p/ Purge;pressurized protection


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numbering will apply for other aspects such as installation.

Top !e,e! standard

$229>+2 $plosive atmospheres: $plosion prevention and protection.@art 2: &asic concepts and methodology

Standards for :uipent

IC 8++@% >CT?ICA> APPA?ATS #'? P>'SIV GASATM'SPH?S

@art 4 General re%uirements

@art 2 "onstruction and test of flameproof enclosures of electricalapparatus

@art 9 $lectrical apparatus + type of protection DpE

@art 8 =park test apparatus for intrinsically safe circuits

@art * /ethod of test for ignition temperature

@art 7 @owder filling D%E

@art 6 il+immersion DoE

@art > !ncreased safety De

@art 22 "onstruction and test of intrinsically safe and associated apparatus

@art 27 $lectrical apparatus for eplosive gas atmospheres, type of

protection DnE@art 23 $ncapsulation DmE

@art 97 !ntrinsically safe systems

@art 96 =pecial re%uirements for construction test and marking of zone 4electrical apparatus

@art 9> 1ieldbus intrinsically safe concept (1!=")

Standards for Insta!!ation etc0(gases and vapours)

IC 8++@% >CT?ICA> APPA?ATS #'? P>'SIV GASATM'SPH?S

@art 24 "lassification of hazardous areas


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@art 2* !nstallation (and selection) of e%uipment in hazardous areas

@art 2> !nspection and maintenance of e%uipment

ote that the 644>? series of standards will gradually address dust hazards aswell as gasAvapour hazards. The standard number will have an additional suffi2 or 9. Thus, for eample, 629*2+2* (see below) will be replaced by 644>?+2*+9 Finstallation for e%uipment in dust hazards, with 644>?+2*+2 dealing withinstallations in gasAvapour hazards.

Standards for "ust Hazard :uipent and Insta!!ation

IC 8-.4- >CT?ICA> APPA?ATS #'? S I= TH P?S=C'# C'MBSTIB> "ST

@art 4 General -e%uirements

@art 2 @rotection by enclosure DtE

@art 9+2 /ethods for determining the minimum ignition temperature of dusts

@art 9+9 /ethod for determining the resistivity of dust in layers@art 9+8 /ethod for determining minimum ignition energy of dust air

mitures

@art * Type of protection DpE

@art 24 "lassification of areas where combustible dusts are or may bepresent

@art 22 @rotection by intrinsic safety DiE

@art 2* =election and installation

@art 2> !nspection and maintenance

@art 23 @rotection by encapsulation DmE

Documents

Hazardous Areas Are Defined by Three Main Criteria