{{Short description|Lowest temperature at which a substance spontaneously combusts}}
[[File:Flashover001.jpg|thumb|A flashover occurs when most combustible material reach their autoignition temperature in an enclosed space]] 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.<ref name="LAURENDEAU"/> 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.{{Dubious|Relation with pressure|date=February 2026}}<ref>{{cite journal | url=https://www.purkh.com/articles/autoignition-temperature-understanding-the-science-behind-spontaneous-combustion-101934.html#:~:text=Pressure%20can%20influence%20the%20auto,aerospace%20or%20deep%2Dsea%20exploration | title=Auto-Ignition Temperature: Understanding the Science behind Spontaneous Combustion | journal=To Chemistry Journal | date=29 March 2023 | volume=10 | issue=1 | pages=1 | last1=Lin | first1=Guanyou }}</ref>
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 {{convert|500|ml|adj=on}} flask placed in a temperature-controlled oven in accordance with the procedure described in ASTM E659.<ref>E659 – 78 (Reapproved 2000), "Standard Test Method for Autoignition Temperature of Liquid Chemicals", ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959.</ref>
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.<ref>S. Grynko, "Material Properties Explained" (2012), {{ISBN|1-4700-7991-7}}, p. 46.</ref>
==Autoignition time equation== The time <math>t_\text{ig}</math> it takes for a material to reach its autoignition temperature <math>T_\text{ig}</math> when exposed to a heat flux <math>q''</math> is given by the following equation:<ref>Principles of Fire Behavior. {{ISBN|0-8273-7732-0}}. 1998.</ref>
:<math>t_\text{ig} = \frac{\pi}{4} k \rho c \left [ \frac{T_\text{ig} - T_0}{q''} \right]^2, </math>
where ''k'' = thermal conductivity, ''ρ'' = density, and ''c'' = specific heat capacity of the material of interest, <math>T_0</math> is the initial temperature of the material (or the temperature of the bulk material).
==Autoignition 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.<ref>Zabetakis, M. G. (1965), Flammability characteristics of combustible gases and vapours, U.S. Department of Mines, Bulletin 627.</ref>
{| class="wikitable sortable" |- ! Substance !! data-sort-type="number" | Autoignition{{ref label|standCond|D|D}}!!scope="col" class="unsortable" |Note |- | Barium || {{convert|550|C|F|sortable=on|abbr=on}} ||550±90<ref name="LAURENDEAU">{{cite journal |last1=Laurendeau |first1=N. M. |last2=Glassman |first2=I. |title=Ignition Temperatures of Metals in Oxygen Atmospheres |journal=Combustion Science and Technology |date=1971-04-01|volume=3 |issue=2 |pages=77–82 |doi=10.1080/00102207108952274 |language=en}}</ref>{{ref label|Pressure|C|C}} |- | Bismuth || {{convert|735|C|F|sortable=on|abbr=on}} || 735±20<ref name="LAURENDEAU"/>{{ref label|Pressure|C|C}} |- | Butane || {{convert|405|C|F|sortable=on|abbr=on}} || <ref>{{cite web |url=http://www.wolframalpha.com/input/?i=butane|title=Butane - Safety Properties |publisher=Wolfram|Alpha}}</ref> |- | Calcium || {{convert|790|C|F|sortable=on|abbr=on}} || 790±10<ref name="LAURENDEAU"/>{{ref label|Pressure|C|C}} |- | Carbon disulfide || {{convert|90|C|F|sortable=on|abbr=on}} || <ref name=ETB/> |- | Diesel or Jet A-1 || {{convert|210|C|F|sortable=on|abbr=on}} || <ref name=TCForensics/> |- | Diethyl ether || {{convert|160|C|F|sortable=on|abbr=on}} || <ref>{{cite web |url=http://www.wolframalpha.com/input/?i=diethyl+ether|title=Diethyl Ether - Safety Properties |publisher=Wolfram|Alpha}}</ref> |- | Ethanol || {{convert|365|C|F|sortable=on|abbr=on}} || <ref name=ETB>{{citation |url=http://www.engineeringtoolbox.com/fuels-ignition-temperatures-d_171.html |title=Fuels and Chemicals - Autoignition Temperatures |publisher=engineeringtoolbox.com}}</ref> |- | Gasoline (Petrol) || {{convert|247|-|280|C|F|sortable=on|abbr=on}} || <ref name=ETB/> |- | Hydrogen || {{convert|535|C|F|sortable=on|abbr=on}} || |- | Iron || {{convert|1315|C|F|sortable=on|abbr=on}} || 1315±20<ref name="LAURENDEAU"/>{{ref label|Pressure|C|C}} |- | Lead || {{convert|850|C|F|sortable=on|abbr=on}} || 850±5<ref name="LAURENDEAU"/>{{ref label|Pressure|C|C}} |- | Leather / parchment ||{{convert|200|-|212|C|F|sortable=on|abbr=on}} || <ref name=TCForensics>{{cite web|last1=Cafe|first1=Tony|title=PHYSICAL CONSTANTS FOR INVESTIGATORS|url=http://www.tcforensic.com.au/docs/article10.html|website=tcforensic.com.au|publisher=TC Forensic P/L.|access-date=11 February 2015}} {{dead link|date=May 2026}}</ref><ref name=LeatherInt>{{cite web|title=Flammability and flame retardancy of leather|url=http://www.leathermag.com/features/featureflammability-and-flame-retardancy-of-leather/|website=leathermag.com|publisher=Leather International / Global Trade Media|access-date=11 February 2015}}</ref> |- | Magnesium || {{convert|635|C|F|sortable=on|abbr=on}} || 635±5<ref name="LAURENDEAU"/>{{ref label|Magnesium|B|B}}{{ref label|Pressure|C|C}} |- | Magnesium || {{convert|473|C|F|sortable=on|abbr=on}} || <ref name=ETB/>{{ref label|Magnesium|B|B}} |- | Methane || {{convert|537|C|F|sortable=on|abbr=on}} || |- | Molybdenum || {{convert|780|C|F|sortable=on|abbr=on}} || 780±5<ref name="LAURENDEAU"/>{{ref label|Pressure|C|C}} |- | Paper ||{{convert|218|-|246|C|F|sortable=on|abbr=on}} || <ref name=TCForensics/><ref>{{cite journal |url=http://www.tcforensic.com.au/docs/article10.html |title=Physical Constants for Investigators|author=Tony Cafe |journal=Journal of Australian Fire Investigators}} (Reproduced from "Firepoint" magazine) {{dead link|date=May 2026}}</ref> |- | Phosphorus (white)|| {{convert|34|C|F|sortable=on|abbr=on}} || <ref name=ETB/>{{ref label|Phosphorus|A|A}}{{ref label|Magnesium|B|B}} |- | Silane || {{convert|21|C|F|sortable=on|abbr=on}} || <ref name=ETB/> <small>or below</small> |- | Strontium || {{convert|1075|C|F|sortable=on|abbr=on}} || 1075±120<ref name="LAURENDEAU"/>{{ref label|Pressure|C|C}} |- | Tin || {{convert|940|C|F|sortable=on|abbr=on}} || 940±25<ref name="LAURENDEAU"/>{{ref label|Pressure|C|C}} |- | Triethylborane || {{convert|-20|C|F|sortable=on|abbr=on}} || <ref name=ETB/> |} {| |- |{{note label|Phosphorus|A|A}} On contact with an organic substance, melts otherwise. |- |{{note label|Magnesium|B|B}} There are two distinct results in the published literature. Both are separately listed in this table. |- |{{note label|Pressure|C|C}} At 1 atm. The ignition temperature depends on the air pressure. |- |{{note label|standCond|D|D}}Under standard conditions for pressure. |}
==See also== * Fire point * Flash point * Gas burner (for flame temperatures, combustion heat energy values and ignition temperatures) * Spontaneous combustion
==References== {{Reflist}} {{Refbegin}} {{Refend}}
== External links == * [http://www.fire.nist.gov/bfrlpubs/fire03/art015.html Analysis of Effective Thermal Properties of Thermally Thick Materials].
{{Firelighting}} {{Authority control}}
{{DEFAULTSORT:Autoignition Temperature}} Category:Chemical properties Category:Fire Category:Threshold temperatures