Oil, gas and mining applications require explosion-proof certified products such as slip rings. These certification requirements are defined by the certification body and are divided into explosion groups, zones, product groups and temperature classes.
Potentially explosive atmospheres are divided into 6 zones; gases and vapours are placed in Zone 2, 1 and 0, in increasing order, whilst dust are placed in Zones 22, 21 and 20, in increasing order.
Product groups are defined as Group I and Group II. Group I is usually used for underground applications such as mining, for the prevention of gas and dust explosions, usually from firedamp. Group II normally covers all other hazardous applications. Within these groups, there are 6 categories; 1G, 2G, 3G, 1D, 2D and 3D. G is for gas explosion protection, whereas D is for dust. Therefore, 1G, 2G and 3G are equivalent to Zones 0, 1 and 2, and 1D, 2D and 3D are equivalent to Zones 20, 21 and 22.
Explosion groups apply to gases and vapours, and is a means to measure the gases' ability to ignite. It is divided into three groups, in increasing order (IIA-IIB-IIC) according to the type of protection being used.
Temperature classes are divided into 6 classes and only apply to Group II applications. The classes are listed as T1 - T6 in increasing order of temperature; 450, 300, 200, 135, 100, 85°C. This figure is the maximum permissible surface temperature of the equipment in relation to +40°C ambient temperature on any surface area, and should not be exceeded at any time.