2. The ignition point refers to the process that substances that can react exothermically reach a rapid combustion state. Small ignition sources (such as moderate electric spark discharge) that expose combustible materials to hot surfaces, heating wires and radiant energy may cause fires. There is usually an inverse relationship between the ignition energy or temperature listed here and the exposure time required for ignition. Strong ignition energy can be ignited quickly, and weak ignition sources need longer exposure time. Strong ignition sources can also directly cause detonation. Gases, liquids and solid combustible substances coexist with air, and when they reach a certain temperature, they will spontaneously ignite when they contact with fire sources. After the fire source is removed, the lowest temperature that can continue to burn becomes the ignition point or ignition point of the substance.