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 ZONING For 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
