FIRE INVESTIGATIONS

THE CHEMISTRY OF FIRE

• Fire is a type of oxidation, which is the combination oxygen and other substances to make new substances
• Minimum temperature to start fire is called ignition temperature
• The heat when burning something is known as heat of combustion
• Energy and rate or speed of oxidation are two factors to explain fires
• Liquid burns at flashpoint, which is a temperature high enough to vaporize it
• Solid burns at pyrolysis, which is a temperature hot enough to decompose into gaseous state
• Glowing combustion is burning at air-fuel interface, like a cigarette
• Spontaneous combustion is the result of natural heat in poorly ventilated container
• To start and maintain combustion there must be a fuel, there must be oxygen present at all times, and heat must be applied

SEARCHING THE FIRE SCENE

• The necessity to begin a fire investigation takes precedent over a search warrant
• When the investigators first get there they try to find where the fire started
• They then try to find signs of arson, which are started by use of accelerants
• Signs of arson are separate and unconnected fires, spreading fire, and severe burning
• Most combustible liquids are not entirely consumed during a fire
• A fire usually moves in an upward position so most of the severe burns will be on the floor

COLLECTION/PRESERVATION OF ARSON EVIDENCE

• Ash, soot, and porous materials that may contain excess accelerants are to be put in airtight containers
• It is important to collect similar uncontaminated control specimens
• Traces of flammable liquid can be found with a vapor detector
• A search for ignitors must also be conducted

ANALYSIS OF FLAMMABLE RESIDUES

• Gas chromatograph is the most reliable for detecting and characterizing flammable residues
• The gas chromatograph separates hydrocarbon components and make a chromatographic pattern characteristic of a particular petroleum product
• By comparing the chromatographic peaks, forensic analysts can figure out the accelerant used

WORKS CITED

• Fire. Photography. Encyclopædia Britannica ImageQuest. Web. 25 Mar 2015.
• Fire fighters in a burnt house. Photography. Encyclopædia Britannica ImageQuest. Web. 26 Mar 2015.
• Gas chromatography. Photography. Encyclopædia Britannica ImageQuest. Web. 26 Mar 2015.