(self-ignition, and spontaneous combustion) — occurs when an exothermic chemical or biological process within a material increases the temperature of the material without the application of an external heat source. If self-heating increases the temperature of the vapors to above their ignition point with sufficient oxygen present, self-ignition will occur. Whether or not self-heating reaches the ignition point is determined by the rate of heat generation, the effects of ventilation, and the insulating effect of surrounding materials. These factors must come into delicate balance for ignition to occur. Heating must be faster than the rate of heat dissipation. Sufficient air must be present for oxidation, but not so much air that the heat is dissipated and the temperature does not rise to the ignition point. Common examples of materials that can self-ignite are linseed oil rags, coal dust, hay, wood chips, manure, and latex. Self-ignition is often indicated by more damage to the center of a stack or pile of the material than to the outside.

For more information on this term, see the interFIRE VR Resource File article: Spontaneous Ignition, Part II: Investigation