FIRE INVESTIVATION

CHEMISTRY OF FIRE

• Fire is a type of oxidation
• Must reach the ignition temperature to ignite fuel and start fire
• Oxidation only takes place when the oxygen is in a gaseous state
• Liquids burn at the flash point, when the temperature is high enough to vaporize it

CHEMISTRY OF FIRE (CONT.)

• Solids burn through pyrolysis, in which the heat decomposes it into gaseous products
• Glowing combustion (smoldering) is burning at the fuel air interface
• Spontaneous combustion occurs when a natural heat producing process is held in a poorly ventilated container/area
• Combustion needs: a fuel, a sufficient supply of oxygen, and applied heat

SEARCHING THE FIRE SCENE

• Examination of a fire scene begins as soon as the fire is extinguished
• Search focuses on finding the origin of the fire (which can help discover accelerants or ignition sources used)
• Because fire tends to move upwards, the origin is typically the lowest point showing the most intense characteristics of burning

COLLECTION OF ARSON EVIDENCE

• Ash, soot, and porous materials are collected from the origin
• These are all stored in airtight containers
• Control specimens are also collected
• A search for igniters and for flammable liquid residues is conducted as well

ANALYSIS OF FLAMMABLE RESIDUES

• Gas chromatography is the best method of identifying a flammable residue
• The machine separates the hydrocarbon components and creates a chromatographic pattern
• This pattern is compared to those from known petroleum products in order to identify the substance