FIRE INVESTIGATION

CHEMISTRY OF FIRE

• The heat evolved when a substance burns is known as heat of combustion.
• You need to reach a temperature called the ignition temperature to start a fire.

CHEMISTRY OF FIRE

• Glowing combustion is burning at the air interface like a cigarette.
• Spontaneous combustion occurs naturally in poorly ventilated areas.

CHEMISTRY OF FIRE

• To start and maintain a fire the following are required:
• 1. You need a source of fuel.
• 2. There needs to be oxygen to combine with the fuel.
• 3. You need enough heat to start the fire and enough heat to sustain the fire.

THE FIRE SCENE

• As soon as the fire is extinguished, investigators must check the crime scene for signs of arson.
• Immediate investigations takes priority over getting a search warrant.
• Fire investigators must focus on find the origin of the fire, which may be the most important in search of accelerants.

THE FIRE SCENE

• Some signs of arson include evidence of separate and unconnected fires and evidence of severe burning found on the floor due to a flammable liquid.
• Normally, a fire has a tendency to move in an upward direction, and thus the probable origin will most likely be the lowest point.

COLLECTION

• Ash, soot, and other porous materials that may still have accelerant still on them are to be put in airtight containers.
• Traces of flammable liquid residues may be located with a vapor detector (sniffer).
• A search for ignitors such as matches, an electrical sparking device, or parts of a “Molotov cocktail” must also be conducted.

ANALYSIS

• In the lab, the gas chromatograph is the best and most reliable tool for detecting and characterizing flammable residues.
• Most arsons start fires using gasoline or kerosene.
• By comparing select gas chromatographic peaks recovered from fire-scene to known flammable liquids, they can determine what liquid they used to ignite the fire.