Flammable gases and liquids are the cause of many fires and explosions, and must be handled with particular care in ATEX zones. Indeed, certain substances can self-ignite under certain conditions. Here’s everything you need to know about self-ignition temperature.
What is the auto-ignition temperature (TAI)?
The auto-ignition temperature (AIT) is the lowest temperature at which a gaseous mixture (air-vapor) ignites spontaneously in the absence of an ignition source, such as a flame or spark.
In reality, ignition results from the production of vapors, which are themselves caused by a sufficiently high temperature in the atmosphere.
This is referred to as the self-ignition or ignition point, or the spontaneous ignition point.
The auto-ignition pointshould not be confused with the flash point, i.e. the temperature at which self-combustion, once initiated, can continue. It is, in a way, the octave above the flash point.
The latter refers to the temperature at which a liquid produces sufficient vapors to ignite in the presence of an ignition source.
It is therefore essential to check temperature classes in ATEX zones zones.
What happens when the auto-ignition point is reached?
When the self-ignition temperature is reached, so is the activation energy required for combustion. Temperatures vary according to a number of factors, such as :
- partial pressure of oxygen ;
- altitude ;
- humidity level ;
- the time required for ignition.
The temperature at which a gas mixture can ignite decreases as the pressure or oxygen concentration increases.
Above the auto-ignition point, a vapor-air mixture ignites on its own. In fact, the mere contact of hot air is sufficient.
How can we explain this phenomenon? The higher the temperature of an atmosphere, the more gases become agitated at the molecular level, and the greater the likelihood of a chemical reaction between two molecules.
From this point onwards, all it takes is a little steam to ignite the whole mixture.
This is how many fires and explosions are caused in ATEX zones.
What is the auto-ignition temperature of gases and liquids?
Most flammable gases and liquids have an auto-ignition temperature of between 300°C and 550°C.
However, some have very low auto-ignition points, e.g. 160° for diethyl ether.
Here is a brief list of gases and liquids whose TAI you need to know:
Auto-ignition temperatures of gases
- Diethyl ether: 160°C
- Butane: 287°C
- Acetylene: 305°C
- Propane: 450°C
- Methane: 455°C
- Ethane: variable 520/630°C
- Ethylene: variable 490°/540°C
- Dihydrogen: 571°C
Self-ignition temperatures of liquids
- Gasoline: 280°C
- Benzine: variable 230/450°C
- Ethyl alcohol: 425°C
- Acetone: variable 540°/630°C
- Benzol: 590°C
- Oil: variable 250°/450°.
- Diesel: 330°C
- Heavy lubricating oil: 440°C
Would you like to know more about the risks associated with self-ignition of gases and liquids in ATEX zones?
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