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.
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|
|Ethane||i-Amyl acetate||Diesel fuel||Ethyl ether|
|Ethyl ethanoate||n-Butane||Aircraft fuel|
|Ammonia||n-Butyl alcohol||Heating oils|
|II B||Coal gas||Ethylene|
|II C||Hydrogen||Acetylene||Carbon disulphide|
The explosive nature of dust is generally classified into three groups.
|IIIA||Combustible Flyings||Material, 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.
|IIIB||Non-conductive dust||Dust with electrical resistivity greater than lOK ohm.m|
|IIIC||Conductive dust||Metal particles such as Aluminium or Titanium that are deposited on equip- ment as dust layers and form as dust clouds in the local atmosphere