Gas Groups

The explosive gases, vapours, and mists present in the atmosphere are grouped into temperature classes and gas groups according to various properties such as ignition temperature, the energy required to ignite the mixture, the energy produced by an explosion, flame transmission capability etc.


Gas GroupDescription
Group I Electrical equipment for use underground in mines susceptible to the hazard of firedamp (methane)
Group II Electrical equipment for use in all other hazardous areas. This group is then subdivided into 3 further groups (IIA, IIB and IIC) according to the maximum experimental safety gap for non-transmission of an internal ignition plus the minimum ignition current of the mixture.
Gas Group  Temperature Class   
II AAcetoneEthanolBenzeneAcetaidehyde
Ethanei-Amyl acetateDiesel fuelEthyl ether
Ethyl ethanoaten-ButaneAircraft fuel
Ammonian-Butyl alcoholHeating oils
Benzol (pure)n-Hexane
Ethanoic acid
Carbon oxide
II BCoal gasEthylene
II CHydrogenAcetyleneCarbon disulphide
Dust Groups

The explosive nature of dust is generally classified into three groups.

Dust GroupDescriptionExample
IIIACombustible FlyingsMaterial, fibres and flyings produced by machinery found in industries such as textile, cotton and wood cutting which settles around equipment and is vulner- able to ignition from heat or sparks.
IIIBNon-conductive dustDust with electrical resistivity greater than lOK ohm.m
IIICConductive dustMetal particles such as Aluminium or Titanium that are deposited on equip- ment as dust layers and form as dust clouds in the local atmosphere