4.1 Autoignition 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. Vessel material can also be an important factor.

4.2 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.

4.3 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.

4.4 This test method is not designed for evaluating for solid chemicals which melt and vaporize or which readily sublime at the test temperature.

4.5 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.

4.6 This test method is not designed to measure the autoignition temperature of chemicals that are gaseous at atmospheric temperature and pressure.