Autoignition temperature
Lowest temperature at which a substance spontaneously combusts
The autoignition temperature (often called self-ignition temperature, spontaneous ignition temperature, minimum ignition temperature, or shortly ignition temperature, formerly also known as kindling point) of a substance is the lowest temperature at which it spontaneously ignites in a normal atmosphere without an external source of ignition, such as a flame or spark. This temperature is required to supply the activation energy needed for combustion. The temperature at which a chemical ignites decreases as the pressure is decreased.
Substances which spontaneously ignite in a normal atmosphere at naturally ambient temperatures are termed pyrophoric.
Autoignition temperatures of liquid chemicals are typically measured using a 500-millilitre (18 imp fl oz; 17 US fl oz) flask placed in a temperature-controlled oven in accordance with the procedure described in ASTM E659.
When measured for plastics, autoignition temperature can also be measured under elevated pressure and at 100% oxygen concentration. The resulting value is used as a predictor of viability for high-oxygen service. The main testing standard for this is ASTM G72.
01Autoignition time equation
The time 
![t_{\text{ig}}={\frac {\pi }{4}}k\rho c\left[{\frac {T_{\text{ig}}-T_{0}}{q''}}\right]^{2},](https://wikimedia.org/api/rest_v1/media/math/render/svg/9bfd512fd290fe84ebf0e46b62c79627ce9f8417)
where k = thermal conductivity, ρ = density, and c = specific heat capacity of the material of interest, 
02Autoignition temperature of selected substances
Temperatures vary widely in the literature and should only be used as estimates. Factors that may cause variation include partial pressure of oxygen, altitude, humidity, and amount of time required for ignition. Generally the autoignition temperature for hydrocarbon/air mixtures decreases with increasing molecular mass and increasing chain length. The autoignition temperature is also higher for branched-chain hydrocarbons than for straight-chain hydrocarbons.
| Substance | Autoignition[D] | Note |
|---|---|---|
| Barium | 550 °C (1,022 °F) | 550±90[C] |
| Bismuth | 735 °C (1,355 °F) | 735±20[C] |
| Butane | 405 °C (761 °F) | |
| Calcium | 790 °C (1,450 °F) | 790±10[C] |
| Carbon disulfide | 90 °C (194 °F) | |
| Diesel or Jet A-1 | 210 °C (410 °F) | |
| Diethyl ether | 160 °C (320 °F) | |
| Ethanol | 365 °C (689 °F) | |
| Gasoline (Petrol) | 247-280 °C (477-536 °F) | |
| Hydrogen | 535 °C (995 °F) | |
| Iron | 1,315 °C (2,399 °F) | 1315±20[C] |
| Lead | 850 °C (1,560 °F) | 850±5[C] |
| Leather / parchment | 200-212 °C (392-414 °F) | |
| Magnesium | 635 °C (1,175 °F) | 635±5[B][C] |
| Magnesium | 473 °C (883 °F) | [B] |
| Methane | 537 °C (999 °F) | |
| Molybdenum | 780 °C (1,440 °F) | 780±5[C] |
| Paper | 218-246 °C (424-475 °F) | |
| Phosphorus (white) | 34 °C (93 °F) | [A][B] |
| Silane | 21 °C (70 °F) | or below |
| Strontium | 1,075 °C (1,967 °F) | 1075±120[C] |
| Tin | 940 °C (1,720 °F) | 940±25[C] |
| Triethylborane | −20 °C (−4 °F) |
| A On contact with an organic substance, melts otherwise. |
| B There are two distinct results in the published literature. Both are separately listed in this table. |
| C At 1 atm. The ignition temperature depends on the air pressure. |
| D Under standard conditions for pressure. |
Sources and credits
This article is adapted from the Wikipedia article “Autoignition temperature”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.
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