HAZARDOUS AREA PROTECTION

Hazardous Area Protection

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:

  1. The Area classification
  2. The Apparatus or Gas group
  3. The 't' rating or the ignition temperature of the hazard
  4. 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
Ex ia Intrinsically Safe
Ex ma Encapsulation
Ex d  Flameproof
Ex ib Intrinsically Safe
Ex p Pressurised Enclosed
Ex pl Purged Enclosure
Ex px Purge/pressurised
Ex py Purge/ pressurised
Ex mb Encapsulation
Ex e  Increased Safety
Ex s  Special
Ex m  Encapsulation
Ex o  Oil Immesion
Ex q Powder/Sand Filled
Zone 2
Ex n  Non Sparking
Ex pz Purge/Pressurised
Ex ic Intrinsic Safety

2. Apparatus or Gas Group

Gases and vapours are divided into two main groups

Group I Coal Mining industry (Methane or Firedamp)
Group II Other Industries

Group II

Group IIA Propane, Butane
Group IIB Ethylene, Butadiene
Group IIC Acetylene, Hydrogen

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

T Rating Maximum Temperature
T1 450ºC
T2 300ºC
T3 200ºC
T4 135ºC
T5 100ºC
T6 85ºC

For more information about hazardous area protection classifications, please visit the International Electrotechnical Commission website (link: http://www.iecex.com/)


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