FIRE

CHEMISTRY OF FIRE

• Fire is a type of oxidation
• Meaning it is the combination of oxygen with other substances
• This then produces new substances
• For a fire to start the minimum temperature needed to start the fuel,known as ignition temperature, must be reached. The heat evolved when a substance burns is known as heat of combustion.
• To create combustion and control it the following is required: 1. A fuel must be present; 2. Oxygen must be available in sufficient quantity to combine with the fuel; 3. Heat must be applied to initiate the combustion, and sufficient heat must be generated to sustain the reaction.

THE FIRE SCENE

SEARCHING THE FIRE SCENE

• Once fire is put out the investigator must immediately begin
• Most arson cases have a definitive accelerate or fire starter that needs to be found
• First we must find the origin or where the fire started
• One common sign of arson is the use of "streamers" or the use of the accelerate to spread the fire from one place to another
• Fires tend to rise so the lowest point with most fire damage done to is probable area of origin

COLLECTION

PRESERVATION OF ARSON EVIDENCE

• At the point of origin,ash,soot, along with porous materials that could contain excess accelerant, should be collected and stored in airtight containers
• Traces of flammable liquid residues may be located with a vapor detector (sniffer)
• It is important that a sampling of similar but uncontaminated control specimens be collected
• A search for ignitors such as matches, an electrical sparking device, must also be conducted

ANALYSIS

ANALYSIS OF FLAMMABLE RESIDUES

• In the laboratory, the gas chromatograph is the most sensitive and reliable instrument for detecting and characterizing flammable residues
• The vast majority of arsons are initiated by petroleum distillates such as gasoline and kerosene.
• The gas chromatograph separates the hydrocarbon components and produces a chromatographic pattern characteristic of a particular petroleum product.
• By comparing select gas chromatographic peaks recovered from fire-scene debris to known flammable liquids, a forensic analyst may be able to identify the accelerant used to initiate the fire.