Forensic Fire Investigation
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Mon Jan 8 08:17:34 UTC 2018
Forensic Fire Investigation
This refers to the application of scientific methods & techniques to determine the origin and cause of fire once firefighters have extinguished the fire.
The practice is similar to the examination of crime scenes in that the scene must be preserved and evidence collected and analyzed, but with numerous additional difficulties and dangers. The investigation will include closely surveying the damaged scene to establish the origin of the fire and eventually establishing the cause.
However in order to effectively examine and evaluate a fire scene, it is imperative that the investigator has a detailed knowledge of the chemistry and behavior of fire and its effects.
Understanding The Nature & Chemistry of Fire
Fire occurs due to the exothermic reaction of combustion (burning), producing heat and light. In order for a fire to occur, three vital components must be present: a fuel source, an oxidant (O 2 ) and a sufficient amount of energy in the form of heat. Together these make up the fire triangle. A fourth factor can also be described – a self-sustaining chemical chain reaction – to produce the fire tetrahedron. The absence of any of these conditions will result in a fire not starting or extinguishing through smothering (oxygen removal), cooling (heat removal) or starving (fuel removal).
Solid and liquid materials do not actually combust, but the process of heating causes them to produce vapors which can burn. This is the process of pyrolysis. Through this pyrolysis products will be formed, flammable and volatile substances of low molecular weight caused through the decomposition of materials by fire.
Heat produced by a fire can spread in one of three ways; convection, conduction and radiation. Convection is the transfer of heat through air circulation, and only occurs in liquids and gases. An example of convection is the heat from a fire rising and heating the ceiling of a room. Conduction is the transfer of heat through a medium by direct contact, such as a fire heating a metal beam which transfers the heat elsewhere. Radiation is the emission of heat as infrared radiation without a medium, such as a fire heating and igniting a nearby sofa.
The primary purposes of a fire investigation is to establish the origin (seat) of the fire, determine the likely cause, and thus conclude whether the incident was accidental, natural or deliberate. It is vital to establish the cause to ensure similar events do not occur (in the case of natural or accidental) or to allow a legal investigation to be conducted (in the case of deliberate fires).
The initial concern with regards to a fire incident scene is safety. Such a scene has an increased risk factor with possible hazards including heated materials, structural collapse, damaged electricity and gas mains, debris, asbestos, dangerous combustion products and other toxic substances. A dynamic risk assessment should be conducted, the scene must be declared safe and all individuals entering the scene should wear appropriate protective clothing such as hardhats, fire-resistant overalls, steel-capped boots, thick gloves and, in some cases, a face mask. Supplies of gas and electricity should be switched off before the investigation begins.
Article by Peace Okorogu SCSP HSE Lead
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