Каталог Weidmuller: Enclosures and Cable Glands

Allocation of explosion groups, zones and equipment categories
Technical appendix
Classification of explosive groups in gas Ex protection
Flammable gases, vapours or mists are divided according to
their ignition resistance capacity into the explosive groups IIA, IIB
and IIC. This classification is based on the respective maximum
experimental safe gap (MESG) and the minimum ignition current
of the gases. The lower this value, the higher the danger
presented by the gases. The danger of the gas increases from
IIA to IIC so that all equipment certified for use in IIC areas may
also be used in IIA and IIB areas.
Explosion group
Maximum experimental
safe gap (MESG)
IIA > 0.9 mm > 0.8
Minimum
ignition current
IIB 0.5 mm to 0.9 mm 0.45 to 0.8
IIC < 0.9 mm < 0.45
Classification of zones and equipment categories
Combustible
ingredients
Explosive
atmospheres
Zone
division
Equipment group
Identification
Device category
Gas, mist,
vapours/fumes (G)
permanent, long-term Zone 0 II 1G
occasionally Zone 1 II 2G
unlikely,
short-term
Zone 2 II 3G
Dusts (D) permanent, long-term Zone 20 II 1D
W
occasionally Zone 21 II 2D
unlikely,
short-term
Zone 22 II 3D
W.6