Snippet from Wikipedia: Autoignition temperature

The autoignition temperature or self-ignition temperature, often called spontaneous ignition temperature or minimum ignition temperature (or shortly ignition temperature) and formerly also known as kindling point, of a substance is the lowest temperature at which it spontaneously ignites in a normal atmosphere without an external source of ignition, such as a flame or spark. This temperature is required to supply the activation energy needed for combustion. The temperature at which a chemical ignites decreases as the pressure is decreased.

• Substances which spontaneously ignite in a normal atmosphere at naturally ambient temperatures are termed pyrophoric.

Autoignition temperatures of liquid chemicals are typically measured using a 500-millilitre (18 imp fl oz; 17 US fl oz) flask placed in a temperature-controlled oven in accordance with the procedure described in ASTM E659.

When measured for plastics, autoignition temperature can also be measured under elevated pressure and at 100% oxygen concentration. The resulting value is used as a predictor of viability for high-oxygen service. The main testing standard for this is ASTM G72.

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The auto-ignition temperature is also known as the minimum ignition temperature.

The lowest temperature at which a substance spontaneously ignites in a normal atmosphere without an external ignition source such as a flame or spark.

It decreases with increasing pressure.

Substances that spontaneously ignite in a normal atmosphere at natural ambient temperatures are called pyrophoric.

Taken from UCH Wiki. https://wiki.ulascemh.com/doku.php?id=en:eng:common:ait