In fire protection, an accelerant is any substance or mixture that accelerates or speeds the development and escalation of fire. Accelerants are often used to commit arson, and some accelerants may cause an explosion. Some fire investigators use the term "accelerant" to mean any substance that initiates and promotes a fire without implying intent or malice.
A fire is a self-sustaining, exothermic oxidation reaction that emits heat and light. When a fire is accelerated, it can produce more heat, consume the reactants more quickly, burn at a higher temperature, and increase the spread of the fire. An accelerated fire is said to have a higher "heat release rate," meaning it burns more quickly.
Indicators of an incendiary fire or arson can lead fire investigators to look for the presence of accelerants in fire debris. Accelerants can leave behind evidence of their presence and use. Accelerants present in areas they should not be can indicate an incendiary fire or arson. Investigators often use special dogs known as accelerant detection canines trained to smell ignitable liquids. The dog can pinpoint areas for the investigator to collect samples. Fire debris submitted to forensic laboratories employ sensitive analytical instruments with GC-MS capabilities for forensic chemical analysis.
Many accelerants are hydrocarbon-based fuels, sometimes referred to as petroleum distillates: gasoline, diesel fuel, kerosene, turpentine, butane, and various other flammable solvents. These accelerants are also known as ignitable liquids. Ignitable liquids can leave behind tell-tale marks in the fire debris. These irregular burn patterns can indicate the presence of an ignitable liquid in a fire.