itsesytytystä

Itsesytytys, or self-ignition (autoignition), describes the ignition of a material in air without an external flame or spark. It occurs when heat released by exothermic oxidation inside the material raises its temperature to a point where the oxidation becomes self-sustaining and combustion begins. The key concept is the autoignition temperature, the lowest temperature at which a material will ignite under given conditions.

Mechanisms and factors

Self-ignition relies on a balance between heat generation from chemical reactions and heat loss to the surroundings. If heat production exceeds dissipation—for example due to high reaction rates, restricted heat transfer, high pressure, or confinement—the material temperature climbs until ignition occurs. Materials differ widely in their autoignition behavior; solvents, oils, fuels, coal, metal powders, and organic solids can display autoignition under suitable conditions. In engineering, autoignition is exploited in diesel engines, where fuel-air mixtures ignite from compression heating rather than a spark.

Applications and safety

Autoignition temperatures are important in risk assessment and storage of flammable substances. Knowledge of SIT helps prevent fires during processing, storage, and transport. Safety measures include controlling ambient temperature, improving heat removal, reducing concentration of reactive vapors, and avoiding conditions that promote runaway oxidation. In some contexts, spontaneous combustion—ignition arising from slow, unmanaged heat buildup in piles or confined spaces—is discussed alongside self-ignition, though the terms are used in different scopes.

See also

Autoignition temperature; spontaneous combustion; combustion safety.