Glossary / Physical properties
Autoignition temperature
Autoignition temperature is the lowest temperature at which a substance will ignite spontaneously in air without any spark, flame or other ignition source. It describes how hot a surface or process can get before a flammable vapor catches fire on its own.
Explanation
Many people confuse autoignition temperature with Flash point. The flash point needs an ignition source and is usually far lower. The autoignition temperature needs only heat. A liquid can have a modest flash point and a much higher autoignition temperature, and both facts matter.
The value is found by laboratory tests and depends on the test conditions, such as vessel size, the vapor concentration and how long the mixture is held hot. Because of this, published figures are best treated as approximate and as a warning level, not a guaranteed safe margin. In real equipment, catalysts, rust, oily rags or porous insulation can lower the temperature at which ignition happens.
The concept is important wherever hot surfaces meet vapors: heaters, steam lines, hot plates, ovens, exhausts, bearings and electrical equipment. Equipment used in classified hazardous locations is rated by the maximum surface temperature it can reach, which must stay below the autoignition temperature of the gases present.
Some materials, such as Pyrophoric chemicals, ignite in air at or near ordinary temperatures. They are classified separately, with their own handling rules.
What to do and watch for
- Keep hot surfaces and process temperatures well below the autoignition temperature of any vapor that could reach them.
- Do not assume a liquid is safe near heat just because no flame is present.
- Check that equipment in areas with flammable vapors is rated for the area.
Where it appears on an SDS
- Section 9: Physical and chemical properties. May list the autoignition temperature alongside flash point and explosive limits, or state that no data is available.
- Section 7: Handling and storage. Handling advice often tells you to keep the product away from heat, hot surfaces and ignition sources.
SDS content and wording vary by supplier. This page is general reference and does not replace the current SDS for your product.