ASTM D2155 Autoignition Temperature of Liquid Chemicals
When heated, some materials can form vapors that react with atmospheric oxygen to spontaneously combust or autoignite – no ignition source is needed. The lowest temperature at which this happens is the autoignition temperature (AIT). This test measures AITs up to 600ºC. There is a delay time between the sample reaching the AIT and combustion occurring. This is also determined in this test. A flask is heated to the test temperature. A small quantity of sample is injected into the flask and observed to see if ignition occurs. If it does not, the flask is cleaned and the process is repeated at a higher temperature.
When autoignition is observed, the temperature, delay time and barometric pressure are reported.
ASTM E659 is a more modern method for determining autoignition temperatures. It uses a diffiernt apparatus but gives similar results.