Itämislämpötila

Itämislämpötila, or autoignition temperature, is the lowest temperature at which a material in air will ignite spontaneously without an external flame or spark, given specified test conditions. For many substances it is measured at standard atmospheric pressure and with dry air, though other conditions may be reported.

Autoignition temperature is distinct from the flash point, which is the temperature at which a liquid’s vapors can ignite when exposed to an ignition source. It also differs from the general concept of ignition temperature, which can refer to burns due to an external heat source.

Measurement of autoignition temperature is performed using standardized test methods published by organizations such as ASTM and ISO. Values depend on factors including pressure, oxygen concentration, sample form (gas, liquid, solid), particle size and moisture, presence of catalysts or impurities, and surface area. In solids, decomposition before ignition can occur, complicating measurement.

Typical ranges are broad: many organic liquids and solids have autoignition temperatures from around 200°C up to well above 600°C. Finely divided powders and small particles may ignite at lower temperatures due to higher surface area and faster oxidation, while moisture or impurities can modify the value.

Knowing the autoignition temperature is important for industrial safety, storage and handling of fuels and chemicals, design of combustion equipment, and risk assessment. It informs procedures such as heating, drying, grinding, and inerting to prevent accidental self-ignition.

See also: Flash point, Ignition temperature, Combustion, Hazard safety data sheets.