The construction of explosion protected electrical equipment intended for use in potentially flammable atmospheres (Explosive Atmospheres) is defined clearly in two separate categories to suit the nature of the Explosive Atmospheres application. The two categories recognised under both the CENELEC (European) Normatives and the IEC Standards are stated as being equipment groups or apparatus groups, and are defined as follows :-

Apparatus Group I - Electrical equipment for mining applications
Apparatus Group II - Electrical equipment for surface industry Explosive Atmospheres, other than mining applications

Equipment that is approved in accordance with European Normatives, under either Apparatus Group I or Apparatus Group II is permitted to carry the approval mark of the European Union as shown.