What is the lowest temperature at which the vapors of a flammable liquid ignite and cause self-sustained combustion?

The correct answer is the autoignition temperature, which is the lowest temperature at which the vapors of a flammable liquid ignite spontaneously in the atmosphere without the need for an external ignition source, such as a spark or flame. At this temperature, the heat produced by the combustion process is sufficient to sustain the reaction without additional energy input.

The fire point is often confused with the autoignition temperature; however, the fire point refers to the lowest temperature at which a liquid gives off vapors that can ignite but requires an external ignition source to support combustion. The flash point is even lower and indicates the temperature at which the vapors can ignite in the presence of a spark or flame. Vaporization temperature does not directly relate to ignition, as it simply indicates the temperature at which a liquid turns into vapor.

Understanding these terms is crucial for safety and operational practices in dealing with flammable liquids, as it helps in identifying the risks involved and implementing appropriate precautions in hazardous environments.