Apparatus Group

There are two apparatus groups for gas/vapour environments:

Group I covers the use of equipment in underground mining environments where methane is present.

Group II covers all other environments

Group II is further divided into subgroup IIA, IIB or IIC:
  • IIA - propane (least incendiary)
  • IIB - ethylene (more incendiary)
  • IIC - hydrogen and acetylene (most incendiary)
Apparatus Groups are sometimes referred to, erroneously, as ‘Gas Groups’.


Equipment is approved for use in hazardous areas by accredited testing laboratories known as Notified Bodies or by the manufacturers. To qualify for ATEX approval, manufacturers must show that their products incorporate measures to prevent the ignition of unavoidable explosive atmospheres.

Area classification

The process by which sources of leak of flammable gas, liquid, mist or combustible dust are identified, the frequency and duration of those leaks determined and the extent to which those leaks will travel before they become non-flammable. The area (strictly a volume) is then marked on a drawing showing the Zones and their extents.


Australian standard, equivalent to Zone 2 in ATEX terminology.