What Are ATEX Gas Groups IIA, IIB and IIC?
IIA, IIB and IIC are fundamental gas subgroups used when selecting equipment for hazardous gas atmospheres. As the subgroup becomes more demanding, equipment must meet stricter explosion-protection requirements.
Why does the gas group matter?
Explosive gases do not have identical ignition and flame-propagation characteristics. Hazardous-area equipment is therefore classified by gas group, and the group stated in the project must be compatible with the group shown on the product marking.
The IIA, IIB and IIC sequence
Within Group II gas atmospheres, IIA, IIB and IIC are used. Typical reference gases are propane for IIA, ethylene for IIB and hydrogen for IIC. IIC is the most demanding of these three subgroups.
Is a higher group always the better choice?
Equipment with a broader protection scope may cover less demanding gas groups, but choosing the highest group by default is not always appropriate. Cost, availability, protection type, temperature class and actual site conditions should be considered together.
Dust atmospheres use a different grouping system
Combustible dust atmospheres use Group III with IIIA, IIIB and IIIC subgroups. These should not be confused with gas groups. Dust applications also require checks of maximum surface temperature and the relevant dust-protection concept.
Read the gas group together with the other markings
Gas group alone is not enough. It must be read together with Zone/EPL, protection type, temperature class and ambient-temperature range.