Autoignition temperature

The autoignition temperature or self-ignition temperature, often called spontaneous ignition temperature or minimum ignition temperature (or shortly ignition temperature) and 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.<ref>Template:Cite journal</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 Template:Convert 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), Template:ISBN, 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. Template:ISBN. 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>

Substance	AutoignitionTemplate:Ref label	Note
Barium	Template:Convert	550±90<ref name="LAURENDEAU">Template:Cite journal</ref>Template:Ref label
Bismuth	Template:Convert	735±20<ref name="LAURENDEAU"/>Template:Ref label
Butane	Template:Convert	citation	CitationClass=web }}</ref>
Calcium	Template:Convert	790±10<ref name="LAURENDEAU"/>Template:Ref label
Carbon disulfide	Template:Convert	<ref name=ETB/>
Diesel or Jet A-1	Template:Convert	<ref name=TCForensics/>
Diethyl ether	Template:Convert	citation	CitationClass=web }}</ref>
Ethanol	Template:Convert	<ref name=ETB>Template:Citation</ref>
Gasoline (Petrol)	Template:Convert	<ref name=ETB/>
Hydrogen	Template:Convert
Iron	Template:Convert	1315±20<ref name="LAURENDEAU"/>Template:Ref label
Lead	Template:Convert	850±5<ref name="LAURENDEAU"/>Template:Ref label
Leather / parchment	Template:Convert	citation	CitationClass=web }}</ref><ref name=LeatherInt>{{#invoke:citation/CS1|citation	CitationClass=web }}</ref>
Magnesium	Template:Convert	635±5<ref name="LAURENDEAU"/>Template:Ref labelTemplate:Ref label
Magnesium	Template:Convert	<ref name=ETB/>Template:Ref label
Methane	Template:Convert
Molybdenum	Template:Convert	780±5<ref name="LAURENDEAU"/>Template:Ref label
Paper	Template:Convert	<ref name=TCForensics/><ref>Template:Cite journal (Reproduced from "Firepoint" magazine)</ref>
Phosphorus (white)	Template:Convert	<ref name=ETB/>Template:Ref labelTemplate:Ref label
Silane	Template:Convert	<ref name=ETB/> or below
Strontium	Template:Convert	1075±120<ref name="LAURENDEAU"/>Template:Ref label
Tin	Template:Convert	940±25<ref name="LAURENDEAU"/>Template:Ref label
Triethylborane	Template:Convert	<ref name=ETB/>

Template:Note label On contact with an organic substance, melts otherwise.

Template:Note label There are two distinct results in the published literature. Both are separately listed in this table.

Template:Note label At 1 atm. The ignition temperature depends on the air pressure.

Template:Note labelUnder standard conditions for pressure.

See also

• Fire point
• Flash point
• Gas burner (for flame temperatures, combustion heat energy values and ignition temperatures)
• Spontaneous combustion

External links

• Analysis of Effective Thermal Properties of Thermally Thick Materials.