An accelerant is a substance that is used to cause the rapid spread of a fire. An example of a commonly used accelerant is petroleum distillate, the liquid that is collected from the vaporization of petroleum-containing liquids. This fire-starting fluid is sold in hardware stores and is utilized to rapidly ignite coals in a barbeque.
The accelerant used in a barbeque is deliberately applied. So it is with the accelerants that are of forensic concern. A fire in a building, vehicle, or other location can be deliberately set. This is known as arson . In an investigation of a fire whose origin is suspicious, a forensic investigator will be interested to find out how the fire started. As part of this investigation, the investigator will look for evidence of the presence or use of an accelerant.
During a fire, the fuel available for burning combines with the oxygen in the air in a reaction that is called combustion. Often, a fire will start in one location and subsequently spread. However, if an accelerant has been spread in an area, the pattern of the fire's origin can be different. The origin can be spread out more than is the case naturally. As well, the fire may start more explosively than would occur naturally. These differences can yield patterns that are distinctive to the trained eyes of the forensic investigator.
Once the origin of a fire has been determined, the area can be probed for the presence of residual amounts of the accelerant. This can be done using specially trained dogs that literally sniff out the chemical. In addition, samples of the scene can be collected and taken to a laboratory for analysis with specialized instruments.
For liquid samples, an instrument called a gas chromatograph is typically used. The liquid is heated to convert it to a mixture of gases. The identity of each of the gas components can be determined and this pattern will tell the investigators whether or not the liquid was an accelerant.
Similar analyses can be done on articles of clothing and even the skin of a suspect. Detection of traces of the accelerant on a person or their clothing can be powerful evidence linking them to the arson site.
see also Accident reconstruction; Arson; Canine substance detection; Childers hostel blaze; Fire investigation.