The ignition temperature (also flash point , autoignition temperature , ignition temperature or flash point is) the temperature to which one a material or a contact surface must be heated, so that a combustible substance ( solid , liquid whose vapors or gas ) in the presence of oxygen exclusively due to its temperature - i.e. without an ignition source like an ignition spark - self-ignited . It is different for each fabric and in many cases depends on the pressure. Self-ignition is caused by an exothermic oxidation reaction when the rate of heat production exceeds the heat dissipation through conduction , radiation and convection . The ignition temperature does not correlate with the boiling point or flash point temperature of a flammable substance. Rather, it is a measure of the substance's sensitivity to oxidation.
The auto-ignition temperature is not a material parameter in the true sense, as it depends in particular on the volume of the substance under consideration. Larger volumes ignite at lower temperatures. The time to self-ignition can be months. The theory of the heat explosion deals with the calculation of the auto-ignition temperature. It proposes a concept that allows the physical properties and self-ignition temperature of self-igniting materials to be clearly determined by means of warm storage tests. The kinetic parameters relevant for the numerical simulation are obtained in adiabatic hot storage tests. The auto-ignition temperature is important for fire protection , for example in drying processes, storage and transport. In coal seam fires and some other fires, ignition can also occur in situ , i.e. in the natural formation of coal seams .
At significantly lower flash point a can of gas - air mixture of the same substance only by means of the ignition source are inflamed. At its flash point temperature, a liquid reaches a vapor pressure and thus a saturation vapor concentration that is so high that the corresponding gas-air mixture can be ignited.
The ignitability of a gas mixture also depends on the oxygen content of the surrounding atmosphere. Normal conditions refer to 21% oxygen in air. Since large systems (tanks, containers) cannot be inertized with nitrogen up to a residual oxygen content of 0% , the minimum required limit oxygen content for ignition is determined in special measurements (e.g. 2 to 4%).
Solvents with particularly low ignition temperatures (approx. 120–180 ° C) are:
- Carbon disulfide - a hot glass rod is enough to ignite.
- Diethyl ether
- Ethylene glycol dimethyl ether
- Propylene glycol dimethyl ether
- Diethylene glycol dimethyl ether and dipropylene glycol dimethyl ether - can self-ignite during distillation on hot apparatus parts, with dipropylene glycol dimethyl ether the ignition temperature is 10 ° C below the boiling point (see flash point )
Oils and fats
If laundry is improperly cleaned and heated, vegetable oils or animal fats can catch fire at temperatures above 70 ° Celsius. In particular when using tumble dryers or ironers, there is an increased risk of these processes, which can quickly lead to a fire in the entire device.
- Coal dust
- Flour dust
- see also: Dust explosion - conditions of ignition of dusts
- White phosphorus - quickly ignites automatically in air (principle of the phosphor bombs in World War II ).
- Oil-smeared rags - can self-ignite when lying in waste bins for a long time.
- Pyrophoric iron - consists of ultra-fine iron filings, melted in ampoules under inert gas. When pouring out , a shower of sparks forms in the air , similar to metal chips when grinding .
- Electrostatically charged powders (e.g. some synthetic resin powders and polymer granulates, methyl-substituted cellulose derivatives) - are formed when pouring out of transport packaging. Potential ignition sources on the one hand and explosive dust on the other hand are present at the same time.
|Ignition temperature of some solids:
|Ignition temperature and flash point of some liquid fuels:
|Ignition temperature of some gases at normal pressure:
- Roy Bergdoll, Sebastian Breitenbach: Die Roten Hefte, Issue 1 - Burning and Extinguishing . 18th edition. Kohlhammer, Stuttgart 2019, ISBN 978-3-17-026968-2 .
- Ignition limit
- Combustion triangle
- Deflagration temperature
- Minimum ignition charge
- Drip ignition point
- Self-ignition of laundry - fats and oils are to blame , Vorarlberg Fire Prevention Office, accessed on August 8, 2018
- Self-ignition of laundry , Hetzel laundry machines, accessed on August 8, 2018
- point and ignition temperature: gasoline at www.chemieunterricht.de
- Petroleum data sheet (PDF) from Merck , accessed on March 10, 2014.
- Data sheet of a turpentine oil ( Memento from January 25, 2005 in the Internet Archive )