What is autoignition temperature?

The autoignition temperature is defined as the lowest temperature at which a substance will ignite and sustain combustion without the need for any external ignition source, such as a spark or flame. This concept is critical in understanding fire safety, especially in the context of handling flammable materials, as it indicates the temperature at which a material can spontaneously ignite when exposed to heat.

When a substance reaches its autoignition temperature, it means that the energy from heat alone is sufficient to initiate a chemical reaction, leading to combustion. This property is essential for evaluating risks in environments where flammable gases or liquids are stored or handled.

The other options, while related to fire and combustion concepts, do not accurately define autoignition temperature. They cover different aspects of combustion or thermal reactions, but they do not capture the specific characteristic of sustained combustion occurring in the absence of an external ignition source that defines autoignition temperature.