The IEC Ex scheme, issued by the International Electrotechnical Commission (IEC) is the first international certification scheme in the world and certificates issued under this scheme will be accepted by all member countries which include UK, France, Germany, Australia, Canada and USA. Australian Standards are following IEC Standards with Australia being a member country of the IEC Ex certification scheme.
According to the IEC Ex scheme, In order to select electrical apparatus for use in hazardous areas it is necessary to have the following information:
The Area classification
The Apparatus or Gas group
The 't' rating or the ignition temperature of the hazard
The required IP rating of the apparatus
1. The Area Classification
The areas are classified into ZONES, and these zones are based on the frequency of the appearance of an explosive atmosphere and the duration for which it can last
Zone 0: An area in which an explosive gas air mixture is continuously present or present for long periods Zone 1: Combustible or conductive dusts are present. Area in which an explosive gas air mixture is likely to occur for short periods in normal operation Zone 2: An area in which an explosive gas-air mixture is not likely to occur, and if it occurs it will only exist for a very short time due to an abnormal condition
The type of protection for gas/vapour.
Zone 0, 1 and 2
2. Apparatus or Gas Group
Gases and vapours are divided into two main groups
Coal Mining industry (Methane or Firedamp)
3. Temperature Class or 'T' Rating
The source of ignition in a hazardous area cna be an arc or a spark or even a hot surface.
Since electrical equipment generates heat in normal operation we need to ensure that a hot surface on electrical apparatus cannot ignite a surrounding explosive gas atmosphere or a dust cloud or layer.
The maximum surface temperature of the equipment should not exceed the ignition temperature of the gas or vaour based on an ambient of 40ºC
For more information about hazardous area protection classifications, please visit the International Electrotechnical Commission website (link: http://www.iecex.com/)