The crime of arson is the willful burning of someone elseÆs property, and the crime is more dangerous to human life than murder because statistically, murderers usually do not kill again but arsonists will continue to set fires until they are caught (US Army). Arson investigations are highly complex processes, and unless conducted immediately, valuable evidence may be lost forever. To determine whether a fire is accidental or a case of arson, it is necessary to understand the basics of the chemistry and behavior of fires.
Fire is a chemical reaction in which fuel, heat and oxygen
combine in a chain reaction (US Army). Fuels are decomposed into their gaseous elements by heat in a reaction known as pyrolysis. When wood is heated, for example, it pyrolyzes into hydrogen, oxygen, ethane, and methane gases, and into methyl alcohol. It is these highly flammable vapors that burn. Fuel in its natural form as a vapor, such as natural gas, does not need to be pyrolyzed to burn. Only gases burn, so solids and liquids must be heated until they vaporize before they can burn.
Heat ignites the fuel and begins the chemical reaction, but once this has happened, the fire produces its own heat and becomes self-generating as long as it has access to fuel and oxygen (US Army). The ignition point of a fuel is the lowest temperature at which it will ignite, and every substance has its own ignition point, which is a constant. Once a vapor is heated to its ignition point it will ignite, even without direct contact with the heat source. The size, temperature, and dryness of the material determines the degree of heat needed to reach its ignition point, e.g. a match stick and a pine board both have an ignition point of 502oF, but it takes a lot more heat to raise the temperature of a pine board to 502oF than it does to raise a matchstick to the same temperature, and it takes even more heat to raise a wet pine board to that temperature tha...