The lower this value, the higher the danger
presented the gases.9 0.5 0.45 0.9 0. This classification based the respective maximum
experimental safe gap (MESG) and the minimum ignition current
of the gases.
Explosion group Maximum experimen-
tal safe gap (MESG)
Minimum
ignition current
IIA 0.45
Combustible
ingredients
Explosive
atmospheres
Zone
division
Identification
Equipment group Device category
Gas, mist,
vapours/fumes (G)
permanent, long-term Zone 1G
occasionally Zone 2G
unlikely,
short-term
Zone 3G
Dusts (D) permanent, long-term Zone 1D
occasionally Zone 2D
unlikely,
short-term
Zone 3D
Classification zones and equipment categories
.Technicalappendix
W
W.9 0. The danger the gas increases from
IIA IIC that all equipment certified for use IIC areas may
also used IIA and IIB areas.8
IIC 0.6
Allocation explosion groups, zones and equipment categories
Classification explosive groups gas protection
Flammable gases, vapours mists are divided according to
their ignition resistance capacity into the explosive groups IIA, IIB
and IIC.8
IIB 0
