Interview Question : Hazardous Area Zoning

Two types of standards are there

For Europe CENELEC – in process of being transferred to IEC/EN (European Committee for Electrical Standardization) IEC (International Electrotechnical Commission)

North America NEC 500 NEC 505 (National Electric Code)

Hazardous Area Zoning For Gases Vapor & Mists (CENELEC & IEC)

Zone 0 - Explosive gas atmosphere is present continuously or for long periods (typically > 1000 hours/year)

Zone 1 - Explosive gas atmosphere is likely to occur under normal operating condition

Zone 2 - Explosive gas atmosphere is not likely to occur in normal operation and if it occurs, will only exist for a short period (typically < 10 hours/year)

Hazardous Area Zoning For Dusts (CENELEC & IEC)

Zone 20 - Explosive gas atmosphere in the form of a cloud of combustible dust in air is present continuously or for long periods or frequently

Zone 21 - Explosive gas atmosphere in the form of a cloud of combustible dust in air is likely to occur in normal operation occasionally

Zone 22 - Explosive gas atmosphere in the form of a cloud of combustible dust in air is not likely to occur in normal operation but if it occurs, will only exist for a short period

HAZARDOUS AREA ZONINGFor Gases, Vapors & Mists (NEC 500) Division 1
An area in which an explosive atmosphere exist continuously or some time under normal operating conditions Division 2
An area in which explosive atmosphere is not likely to exist under normal operating conditions

EXPLOSION MEDIUM CLASSIFICATION (NEC 500) There are 3 general classes which define the flammable materials present in the atmosphere :

Class I Mixture of Gas/Vapor
with atmosphere

Class II Mixture of Dust with atmosphere

Class III Mixture of Fibers with atmosphere LOCATION TERMINOLOGY(NEC 500)

CLASS 1, DIVISION 1

Location where ignitable concentrations of flammable gases, vapours or liquids Can exist under normal operating conditions May exist continuously, intermittently, or periodically because of repair or maintenance operations or because of leakage May exist because of equipment breakdown that simultaneously causes the equipment to become a source of ignition

CLASS 1, DIVISION 2

Location where ignitable concentrations of flammable gases, vapours or liquids Where volatile flammable liquids or flammable gases May exist continuously, intermittently, or periodically because of repair or maintenance operations or because of leakage May exist because of equipment breakdown that simultaneously causes the equipment to become a source of ignition Usually for the non-incendive, non-sparking, pressurized, hermetically sealed or sealed device type

We use IECEx gear here in the pulp mill where I usually work, in New Zealand. There is equipment around that is tested to other standards but they are keeping all new equipment to IECEx standard.

I have only just got into hazardous area work and am enjoying it a lot. Another little side avenue to electrical industry.:slight_smile: