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Temperature Area Classification | A Complete Guide


For Hazardous locations, electrical equipment selection is made according to Temperature Area Classification. In this article, I will share with you the complete guide to Temperature Area Classification.

What is temperature classification?

  • Temperature classification defines how much maximum surface temperature should be allowed for a piece of specific equipment or apparatus.
  • The types of equipment or apparatus used in hazardous areas are designed on the basis of temperature class only.
  • The maximum surface temperature here means that under fault conditions or worst case what is the maximum temperature that the equipment or apparatus should. Because above that temperature more disastrous conditions can occur.
  • Temperature classification is also known as T-class or temperature class.

Why do we need temperature classification?

There are three ingredients responsible for Fire and Explosion. And it is known as the fire triangle or Explosion triangle. The heat source is one of the key ingredients for explosion or Fire.

Fire or Explosion Triangle

And as you know electrical equipment generates heat during its operation and in the worst-case scenario dusting short circuits is great extreme heat and sparks.

it will become an ignition source if the leakage of flammable gas happens in the plant. And there are many incidents recorded in history when flammable gas is leaked and gas is found in an ignition source and a Blast and fire was accord.

  • Every industry has some other hazards.
  • The hazards may be due to flammability, toxicity, or other reactive properties of the gases or apparatus used in that industry.
  • Now if we talk of flammable gases, what if a leak occurs in industry and all nearby types of equipment are having temperatures above the auto-ignition temperature of the flammable gas. Or think what if even 1 equipment’s temperature is above the autoignition temperature of the flammable gas.
  • Yes, my friend, you are right. A blast will occur and create a big disaster.
  • For this reason, using certified temperature class equipment or apparatus with proper temperature class is very important.
  • Using any improper temperature classified equipment or martial arts can be very dangerous.

What are different temperature classifications?

  • There is a total of 6 main temperature classifications from T1 to T6
  • Each of these classes has a defined maximum surface temperature.
  • Let’s see what the values of maximum temperature in each class are.

Temperature ClassMaximum Temperature
T1 Class450 °C
T2 Class300 °C
T3 Class200 °C
T4 Class135 °C
T5 Class100 °C
T6 Class85 °C
Maximum Temperature as per Temperature Class as per European Standard

  • Hence it is clear that a device that has a rating of T2 can be used in areas where T1 classified equipment or apparatus is needed.

Temperature classified as per AreaSuitable Equipment or Apparatus
T1 ClassT1, T2, T3, T4, T5, T6
T2 ClassT2, T3, T4, T5, T6
T3 ClassT3, T4, T5, T6
T4 ClassT4, T5, T6
T5 ClassT5, T6
T6 ClassT6
Temperature Area Classification

  • The classification we discussed is based on European standards.
  • Another classification available in the North American standard has the following classifications.

Temperature ClassMaximum Temperature
T1 Class450 °C
T2 Class300 °C
T2A Class280 °C
T2B Class260 °C
T2C Class230 °C
T2D Class215 °C
T3 Class200 °C
T3A Class180 °C
T3B Class165 °C
T3C Class160 °C
T4 Class135 °C
T4A Class120 °C
T5 Class100 °C
T6 Class85 °C
Maximum Temperature as per Temperature Class as per North American Standard


  • Does this seem confusing? Let us have a look at an example of apparatus with a given temperature classification.

1. Junction Box Example

  • Suppose there is an electrical junction box installed in the field and the plant is of acetaldehyde whose boiling point is 176 degrees centigrade.
  • Now here is what classification of electrical junction box will you use?
  • Yes, T4 classified junction box should be used here because the maximum surface temperature will go up to 135 degrees centigrade only.
  • Now how will the junction box’s temperature go up to 176 degrees centigrade?
  • Imagine there is a short circuit inside the junction box. Now due to its temperature inside junction box will increase and may reach 176 degrees centigrade or can go even more than that also.
  • In this case, if the junction box is made such that it will withstand this short circuit and will not allow the temperature to come out. This can be achieved using the explosion-proof concept.
  • Here you can also use T5 classified or T6 classified junction box also.

2. Electric Motor Example

Let’s assume you have to mount one electric motor in the hazardous area. Now you have to choose what temperature class you have to choose.

First, you have to look for what kind of flammable gases or substances are present in the hazardous location. when you have an idea about flammable gas.

Now you have to check the autoignition temperature available in the hazardous area. in the below table, you can see the auto-ignition temperatures of popular gasses and substances.

Let’s assume the available gas or substance is Gasoline (Petrol) and the auto-ignition temperature of Gasoline is 247 °C.

In this example, we follow the European Standard and I provided a whole table for temperature area class and Maximum Temperature as per Temperature area classification.

According to the table, the suitable temperature area class is T3 because when you choose the T2 class Maximum temperature of this class is higher than the autoignition temperature of gasoline.

For this application, you cannot choose the T1 and T2 classes but suitable equipment for the T3 application is T3, T4, T5, and T6. So, you have to choose an electric motor that has temperature class T3 or Above.

Auto-ignition Temperature

  • After reading this thing you might have developed a doubt that what is auto-ignition temperature?
  • Autoignition temperature is the temperature at which the gas or material will burn or ignite in a normal atmosphere without any ignition source.
  • Some materials and their auto-ignition temperatures are

SubstanceAutoignition Temperature
Triethyl borane−20 °C (−4 °F)
Phosphorus (white)34 °C (93 °F)
Carbon disulfide90 °C (194 °F)
Diethyl ether160 °C (320 °F)
Diesel or Jet A-1210 °C (410 °F)
Paper218–246 °C (424–475 °F)
Gasoline (Petrol)247–280 °C (477–536 °F)
Ethanol365 °C (689 °F)
Butane405 °C (761 °F)
Barium550 °C (1,022 °F)
Magnesium635 °C (1,175 °F)
Molybdenum780 °C (1,440 °F)
Calcium790 °C (1,450 °F)
Lead850 °C (1,560 °F)
Tin940 °C (1,720 °F)
Gas auto-ignition temperature

  • So, if your plant has usage or production of Diesel, then you need to use T3 classified JB.
  • I hope now it is clear which temperature classification is used.


I hope now you have a clear idea about temperature class and how to choose electrical equipment according to temperature area class.

If you have any questions then please comment below if you like this article then share it with your friend.

You can also watch this YouTube video for a visual understanding of this topic.

You will also like my previous article on instrument impulse tubing.

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KISHAN MENDAPARAhttps://worldofinstrumentation.com
Instrumentation and Control Engineer

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