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Temperature Codes & Auto-Ignition Temperature (AIT)

AIT (Auto-Ignition Temperature) is the temperature at which a gas, vapour or dust will ignite spontaneously without any other sources of ignition. Years ago, the IEC recognized that there was no relation between the gas, vapour and dust groupings, and the AITs of the various compounds. As such, temperature codes were established for equipment used in hazardous locations, and adopted by CEC and NEC.

IEC and North American Temperature Codes

IEC Temperature Codes
(European Standard)
Temperature, °C North American
Temperature Codes

T1 450 T1
T2
-
-
-
-
300
280
260
230
215
T2
T2A
T2B
T2C
T2D
T3
-
-
-
200
180
165
160
T3
T3A
T3B
T3C
T4
-
135
120
T4
T4A
T5 100 T5
T6 85 T6

Notes:
(1) As an alternative to the above temperature codes, the actual maximum temperature that a device can attain, under normal or overload conditions, may be shown.
(2) In North America, if no temperature or temperature code is shown, the maximum external temperature is assumed to be 280°C for Groups A and B, 160°C for Group C and 215°C for Group D.

IMPORTANT NOTE
When considering a particular gas, vapour or dust, we must not only consider the Class and Group of the compound, but also the AIT. For example, Ethyl Ether is rated as Class I, Group C, but the AIT is 160°C (320°F), which is lower than the Ruffneck™ FX5 Explosion-Proof Electric Air Unit Heater's T3B rating. Another example would see Hydrogen's AIT at 550°C (1022°F), but it is rated as a Class I, Group B gas. The FX5 is rated for Group C, D, E, F & G only.

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