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Swanson, Charles R., Chamelin, Neil C., and Territo, Leonard. Fire Setting and Related Mechanisms. Criminal Investigations, Sixth Edition. pp. 666 - 671.

Abstract: Chapter 20 of Criminal Investigations discusses the methods of arson. An incendiary device requires an ignition device and a "plant" to feed the initial flame. Some arsonists also use trailers to spread the fire throughout the building and the more elaborate arsonist will use a timing device.

There are many different ignition devices used for arson. The traditional match is not usually used by arsonists because of its immediacy. Most firesetters want a delay so they will attach the match to a timed device. A commonly used timer is a cigarette. The cigarette will continue to burn if laying on its side and can easily ignite a match located towards the middle of the cigarette.

Candles are another ignition source used by arsonists for years. The book contains a table listing the time it takes different compositions and sizes of candles to burn. When used as incendiary devices, candles are often placed in containers of highly combustible materials and placed near an accelerant. Candles are often detectable because they leave deposits of wax behind.

Chemicals are another popular ignition device. A common method of chemical ignition requires acid to mix with a combination of chemicals. The acid is usually stored in a container that it will slowly eat its way through. Most fires started by chemicals will have signs pointing to their cause. Usually, debris will contain chemical residue and have a distinct odor.

Gas is a less common ignition device, but it is simple to use in a residential house. Gas rises to the ceiling and will escape in a well-ventilated room. If the room is sealed, gas cannot escape and will accumulate. When the gas reaches the pilot light on a stove, it will ignite and explode.

Electrical systems have also been used as ignition devices. Circuits may be deliberately overloaded causing them to heat. Sometimes an accelerant is placed in the switch box, which will explode when the overload occurs. Some arsonists will replace normal wiring with lighter wiring causing the wire to overheat without blowing any fuses. Investigators will usually discover physical evidence implicating wiring as the cause of a fire.

Mechanical devices can also be used as ignition sources, although they are not common. Clocks were once a popular device for arsonists. The hammer for the alarm would be rigged to hit a glass tube containing a flammable liquid. This tube would in turn break another small tube containing another liquid. These combined liquids would ignite the fire. This method was abandoned because many of the machines used would not burn, leaving evidence at the scene.

 
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