Autoignition, by its very nature, is dependent on the chemical and physical properties of the material and the method and apparatus employed for its determination. The autoignition temperature by a given method does not necessarily represent the minimum temperature at which a given material will self-ignite in air. The volume of the vessel used is particularly important since lower autoignition temperatures will be achieved in larger vessels. (See Appendix X2.) Vessel material can also be an important factor.

The temperatures determined by this test method are those at which air oxidation leads to ignition. These temperatures can be expected to vary with the test pressure and oxygen concentration.

This test method is not designed for evaluating materials which are capable of exothermic decomposition. For such materials, ignition is dependent upon the thermal and kinetic properties of the decomposition, the mass of the sample, and the heat transfer characteristics of the system.

This test method can be employed for solid chemicals which melt and vaporize or which readily sublime at the test temperature. No condensed phase, liquid or solid, should be present when ignition occurs.

This test method is not designed to measure the autoignition temperature of materials which are solids or liquids at the test temperature (for example, wood, paper, cotton, plastics, and high-boiling point chemicals). Such materials will thermally degrade in the flask and the accumulated degradation products may ignite.

This test method was developed primarily for liquid chemicals but has been employed to test readily vaporized solids. Responsibility for extension of this method to solids of unknown thermal stability, boiling point, or degradation characteristics rests with the operator.