The IEC Ex scheme, issued by the International Electrotechnical Commission (IEC), is the world's first international certification scheme. Certificates issued under this scheme will be accepted by all member countries including the UK, France, Germany, Australia, Canada and USA. Being a member of the IEC Ex certification scheme, Australian Standards are matched to those of the IEC.
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
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 can 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/)
