autoignition temperature

{{Short description|Lowest temperature at which a substance spontaneously combusts}}

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.{{cite journal | url=https://www.purkh.com/articles/autoignition-temperature-understanding-the-science-behind-spontaneous-combustion-101934.html#:~:text=Pressure%20can%20influence%20the%20auto,aerospace%20or%20deep%2Dsea%20exploration | title=Auto-Ignition Temperature: Understanding the Science behind Spontaneous Combustion | journal=To Chemistry Journal | date=29 March 2023 | volume=10 | issue=1 | pages=1 | last1=Lin | first1=Guanyou }}

• 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 {{convert|500|ml|adj=on}} flask placed in a temperature-controlled oven in accordance with the procedure described in ASTM E659.E659 – 78 (Reapproved 2000), "Standard Test Method for Autoignition Temperature of Liquid Chemicals", ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959.

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.S. Grynko, "Material Properties Explained" (2012), {{ISBN|1-4700-7991-7}}, p. 46.