Interview Question : Hazardous Area Zoning


#1

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


#2

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: