Hazardous area apparatus is classified according to the maximum surface temperature produced under the maximum operating capacity at an ambient temperature of 45°C, or as otherwise specified. The standard classifications are:

T1     450°C
T2     300°C
T3     200°C
T4     135°C
T5     100°C
T6     85°C

This is the lowest temperature at which a gas, vapour or dust will be ignited.  If a potentially hazardous explosive gas, vapour or dust is present, the equipment used within the installation must be given an appropriate 'T' classification in order to maintain the integrity.  For example, if that potentially hazardous explosive gas is hydrogen, then all equipment used must meet the 'T1' rating.  This means that all equipment used must not have a surface temperature of greater than 450°C.  Any equipment used that can generate a hotter surface temperature of greater than 450°C must not be used as this will then increase the likelihood of an explosion by igniting the hydrogen in the atmosphere.

A large percentage of offshore applications require a 'T3' rating.   The majority of our products are rated 'T4, T5 or T6' so are therefore suitable for 'T3' applications.  However, if an application requires a 'T5' rated-product, a 'T4' rated product would not be suitable.

The IP classification system designates by means of a number, the degree of protection provided by an enclosure against impact or dust and water ingress.  Please note that the IP classification should not be construed as indicating corrosion resistance.

Degrees of Protection to IEC 529

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.