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Spontaneous combustion: Under normal conditions, when ordinary combustible materials come into contact with air, a slow cyanidation process occurs; however, this process is very slow, producing little heat, and the heat is continuously dissipated into the surrounding environment, so no light is emitted as in the case of combustion. If the temperature rises or other conditions change, the cyanidation process speeds up, generating more heat. If this heat cannot be dissipated entirely, it accumulates and causes the temperature to rise gradually. The lowest temperature at which such a substance catches fire on its own when heated is known as its autoignition point; it is also referred to as the spontaneous combustion temperature. At natural temperatures, combustible materials can burn in contact with air without the need for an open flame. The autoignition point is not a fixed value; it mainly depends on the heat generated during oxidation and the way in which heat is conducted away. It can be seen that the same combustible material has different auto-ignition points due to varying oxidation conditions and the influence of different factors. Spontaneous combustion can be divided into two cases. Spontaneous combustion that occurs as a result of an external heat source is called heat-induced spontaneous combustion. Certain combustible materials generate heat due to biological, physical, or chemical processes taking place within them, even in the absence of any external heat source; when the conditions are right, this heat is sufficient to cause the material to burn on its own, and this is known as self-spontaneous combustion. The essence of spontaneous combustion and combustion triggered by heat is the same; only the source of heat differs ； The former is the thermal effect of the substance itself, while the latter is the result of external heating. Spontaneous combustion of materials occurs under certain conditions; it can happen at room temperature, and it can also occur at low temperatures. The phenomenon of spontaneous combustion itself indicates that this substance poses a greater latent fire hazard than other substances. Under normal circumstances, common substances that can cause spontaneous combustion include plant products, oils and fats, coal, iron sulfide, and other chemicals. Substances such as phosphorus and phosphine have a low natural ignition point.