Temperature (T) Class Ratings

Temperature (T) Class Ratings

Hazardous Area Zone Classification

Ignition Temperatures 

The ignition temperature is the lowest temperature on the surface at which an explosive atmosphere will ignite.

Gases and dusts have been divided into temperature classes according to their ignition temperatures so that electrical equipment can be further sub-divided into six temperature classes T1 to T6.

Note. The maximum operating surface temperature of a piece of electrical equipment must always be below the ignition temperature of the explosive mixture. 

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Hazardous Area Electrical Equipment

Temperature Class Maximum Surface Temperature °C 

  • T1     450ºC
  • T2     300ºC
  • T3     200ºC
  • T4     135ºC
  • T5     100ºC
  • T6     85ºC
Typical Self Ignition Temperatures for Gases, Temp + °C
Gas Temperature
Butane 287ºC
Ethyl Acetate 425ºC
Acetylene 300ºC
Carbon Disulphide 90ºC
Hydrogen 500ºC
Acetone 465ºC
Ammonia 650ºC
Ethyl Nitrate 90ºC
Benzene 498ºC
Industrial Methane 535ºC
Carbon Monoxide 605ºC


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Typical Self Ignition Temperatures for Dust, Temp + °C  - Cloud - Layer
Dust Temperature (Cloud) Temperature (Layer)
Cellulose 490ºC 430ºC
Cocoa 500ºC 200ºC
Flour 490ºC 430ºC
Lead 460ºC 240ºC
Lignite 380ºC 225ºC
Polyacrylonitrate 540ºC 400ºC
Soya Meal 540ºC 340ºC
Zinc 570ºC 440ºC


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