Ignition temperature


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Ignition temperature

Ignition temperature is one of the safety-relevant parameters of gases, liquids, and their vapors.

This indicates the lowest surface temperature at which a flammable substance or flammable mixture ignites on a hot surface in air without an external ignition source. It can be viewed as a measure of the spontaneous ignition of a substance or mixture (see Regulation (EC) No 440/2008).

As with the flash point, the ignition temperature of a substance or mixture is not a physicochemical constant of the substance. Influencing factors can include the volume of the atmosphere, for example, or the condition of the hot surface and the amount of the substance.

In an ignition test, a defined quantity of a test object is placed in an open, temperature-controlled Erlenmeyer flask that is encased in an electric heating oven. The test object is observed to determine whether an ignition of the sample quantity at the respective selected temperature occurs at the surface of the Erlenmeyer flask within a certain time. The lowest temperature at which ignition is no longer observed is determined first, and then the sample quantity is varied (1 to 10 drops). The dosing can be performed manually or by means of an automatic dosing device.

Schematic diagram of the test apparatus

The method for determining ignition temperature is in accordance with, among others, the standards DIN 51794 and DIN EN 14522, whose procedures for determination are largely identical. However, since determination of the result interpreted as “ignition temperature” varies slightly for the two aforementioned standards, the ignition temperature is always stated in conjunction with the DIN standard used in each case.


Table 1: Differences in determining the ignition temperature according to the applicable DIN standards.

DIN 51794 DIN EN 14522
Number of
3 test series

Deviation of results

≤ 10 K for temperatures up to 300 °C

≤ 20 K for temperatures from 300 °C per repeated test series

3 test series

Deviation of results >2% per two additional test series

Description of
Ignition temperature
Lowest temperature of the 3 test series, rounded to an integer multiple of 5 °C Lowest temperature of the 3 test series, reduced by 1.5%, rounded to an integer value

The ignition temperature is determined for both operational use and for registration of chemicals (REACH) in the IUCLID6 dossier.

Particularly for operational use, the ignition temperature provides valuable information for determining the temperature classes required in operation and thus for determining which equipment can be used. These are commonly already divided into different temperature classes by the manufacturer (see table 2).

Table 2: Overview of the different temperature classes and their respective ignition temperatures.

Temperature class Ignition temperature TZ [°C]
T1 > 450
T2 300 < TZ ≤ 450
T3 200 < TZ ≤ 300
T4 135 < TZ ≤ 200
T5 100 < TZ ≤ 135
T6 85 < TZ ≤ 100

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1] Regulation (EC) No 440/2008, A.15.
[2] DIN 51794 (2003): Testing of mineral oil hydrocarbons – Determination of ignition temperature.
[3] DIN EN 14522 (2005): Determination of the auto ignition temperature of gases and vapors.
[4] TRBS 2152: Hazardous explosive atmospheres.