AIT refers to which characteristic?

• A. The energy required to ignite a gas cloud
• B. The minimum oxygen concentration required to propagate a flame
• C. The lowest temperature at which a material will spontaneously ignite and continue burning in a normal atmosphere
• D. The highest concentration to sustain combustion

Answer: (C)

Autoignition temperature is the temperature at which a material will ignite on its own in air, without an external flame or spark. If you heat the material to or beyond this point, the heat from the slow oxidation builds up fast enough to ignite the vapor or surface, producing a self-sustained flame in normal air. This concept helps explain why some substances can catch fire simply from being heated, rather than needing a flame or spark. The other options describe different fire properties: ignition energy is the energy needed to start a flame in a gas mixture, the minimum oxygen concentration to sustain a flame is a flammability-oxygen threshold, and the notion of the highest concentration to sustain combustion isn’t a standard term for autoignition. Therefore, the lowest temperature at which a material will spontaneously ignite and continue burning in normal air best matches autoignition temperature.