Haz­ardous area - the un­told story

DEMM Engineering & Manufacturing - - HEALTH & SAFETY -

A house­hold light switch may emit a small, harm­less vis­i­ble spark when switch­ing. In an or­di­nary at­mos­phere this arc is of no con­cern, but if a flammable vapour is present, the arc might start an ex­plo­sion. Elec­tri­cal equip­ment in­tended for use in a chem­i­cal fac­tory, Oil re­fin­ery, Flour or Grain mill is de­signed ei­ther to con­tain any ex­plo­sion within the de­vice, or is de­signed not to pro­duce sparks with suf­fi­cient en­ergy to trig­ger an ex­plo­sion.

Did you know that flour (grain), white/gran­u­lated sugar and co­coa are highly ex­plo­sive and come un­der the head­ing of “com­bustible dusts”? Some of the worst in­dus­trial ex­plo­sions have been due to com­bustible dusts. Other ex­am­ples in­clude coal and cit­ric acid.

DEF­I­NI­TION: HAZ­ARDOUS AREA

This def­i­ni­tion for a haz­ardous area comes from AS/NZS 3000 Clause 1.4.11.

“Area in which an ex­plo­sive at­mos­phere is present, or may be ex­pected to be present, in quan­ti­ties such as to re­quire spe­cial pre­cau­tions for the con­struc­tion, in­stal­la­tion and use of equip­ment [AS/NZS 60079.0].”

In elec­tri­cal en­gi­neer­ing, Haz­ardous Ar­eas are de­fined as places where fire or ex­plo­sion haz­ards may ex­ist due to flammable gases, flammable liq­uid– pro­duced vapours, com­bustible liq­uid– pro­duced vapours, com­bustible dusts, or ig­nitable fi­bres/fly­ings present in the air in quan­ti­ties suf­fi­cient to pro­duce ex­plo­sive or ig­nitable mix­tures. Elec­tri­cal equip­ment that must be in­stalled in such clas­si­fied lo­ca­tions should be spe­cially de­signed and tested to en­sure it does not ini­ti­ate an ex­plo­sion, due to arc­ing con­tacts or high sur­face tem­per­a­ture of equip­ment.

Haz­ardous Area clas­si­fi­ca­tion di­vides ar­eas in to Zones based on the likely fre­quency and du­ra­tion of a re­lease, re­lease rate, con­cen­tra­tion, ve­loc­ity and ven­ti­la­tion of the area. Haz­ardous area clas­si­fi­ca­tion zones in­clude:

• Flammable Gas and Vapour at­mos­pheres (Group II) Zone 0,1, 2.

• Com­bustible dust at­mos­pheres (Group III) Zones 20, 21, 22.

BUT THIS I S NOT THE WHOLE PIC­TURE.

Tech­ni­cal stan­dards were de­vel­oped to iden­tify the fea­tures of elec­tri­cal ap­pa­ra­tus that would pre­vent elec­tri­cal ini­ti­a­tion of ex­plo­sions due to en­ergy or ther­mal ef­fects. Sev­eral phys­i­cal meth­ods of pro­tec­tion are used. For ex­am­ple, the ap­pa­ra­tus may be de­signed to pre­vent en­try of flammable gas (Exd Flame Proof) or dust (Exe In­creased Safety) into the in­te­rior. The ap­pa­ra­tus may be strong enough to con­tain and cool any com­bus­tion gases pro­duced in­ter­nally. Or, elec­tri­cal de­vices may be de­signed so that they can­not pro­duce a spark strong enough (i.e. – In­trin­sic Bar­ri­ers) or tem­per­a­tures high enough ( Tem­per­a­ture clas­si­fi­ca­tion ( T) Rat­ing) to ig­nite a spec­i­fied haz­ardous gas.

It is rarely pos­si­ble by sim­ple ex­am­i­na­tion of a plant or plant de­sign, with­out ex­ten­sive ex­pe­ri­ence, to de­cide which parts of the plant are haz­ardous ar­eas. More de­tailed in­for­ma­tion is nec­es­sary and this in­volves the anal­y­sis of the ba­sic prop­er­ties of the ma­te­ri­als present and the pos­si­bil­ity of a re­lease oc­cur­ring. Haz­ardous area clas­si­fi­ca­tion is a spe­cial­ist area

Athenry Elec­tri­cal has qual­i­fied staff to clas­sify and de­sign any po­ten­tial ex­plo­sive area along with in­stal­la­tion and main­te­nance of all nec­es­sary ap­pa­ra­tus in­stalled within these ar­eas.

DE­TAILS, PH 09 273 7325, WWW.ATHENRYELECTRICAL.CO.NZ

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