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Spontaneous IgnitionSpontaneous ignition is caused by chemical reactions, biochemical actions, and chemical characteristics of the combustibles. Materials subject to spontaneous ignition cover a wide range of organic materials, chemicals and agricultural products. In this classification there are agricultural products such as hay, silage and grain; organic materials such as oil, fats, metals, charcoal and coal; and combinations of chemicals such as sodium, potassium, ammonia, chlorine, oxygen and hydrogen. Another classification includes the oxides (elements combined with oxygen). Unique characteristic of spontaneous fire ignition is the varying length of time they take to develop. The formation of pyrophoric carbon from wood (which is a form of spontaneous ignition) can take as long as fifteen years to heat and ignite the wood. Fires of spontaneous origin starting in silos or coal storages can take a month to develop, while rags soaked with volatile fluids can cause ignition within hours and highly volatile fluids can start a fire within minutes. An arsonist who understands the principle of spontaneous ignition can use this to start a fire at a desired time. The variations in the rate of chemical reactions can delay ignition from a few minutes to as many hours as needed to establish an alibi. The unique characteristics of spontaneous ignition are variations in the time and chemical processes required to achieve ignition. This phenomenon is termed "spontaneous heating". The end product of a spontaneous heating and ignition process is spontaneous combustion. Once the combustible has been heated above the ignition point, flaming or glowing combustion occurs and a full-fledged fire is in progress. The spontaneity which created the fire may continue until the material has been consumed and no evidence of the cause of the fire remains. All the elements which contributed to the spontaneous heating, ignition and combustion will have been destroyed. In order to know the cause of the fire the investigator should know those substances which can cause spontaneous combustion. The most common compound of this category of substances is calcium oxide (unslaked lime), which has been found to cause fires when exposed to combustibles. Similar reactions are experienced from barium oxide, sodium peroxide, phosphorous, chlorine and sodium These chemicals are used by arsonists to create the impression of a spontaneous fire. These chemicals serve as timing mechanism, providing time to arsonist to leave the scene of fire.
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