The autoignition temperature is the lowest temperature at which a substance will spontaneously ignite without an external ignition source, such as a flame or spark. This temperature varies for different materials and is an important factor in fire safety and chemical engineering. Knowing the autoignition temperature helps in assessing the risks associated with handling and storing flammable substances. When a material reaches its autoignition temperature, the heat generated by chemical reactions within the material exceeds the heat lost to the environment, leading to combustion. This phenomenon is crucial for understanding the behavior of various substances, including gases like propane and liquids like gasoline, in different conditions.