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Fire

Published on Nov 18, 2015

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PRESENTATION OUTLINE

1.

FIRE INVESTIGATION

BY CLAIRE BRAZEEL
2.

CHEMISTRY OF FIRE

  • Fire is a type of oxidation
  • For a fire to start, ignition temperature must be reached
  • Heat from a substance burning is known as heat of combustion
  • Liberation of energy and the rate of the oxidation reaction are needed to explain fire
  • A fuel can only produce flames with oxygen only when it is in a gaseous state
  • Liquids burn when it's hot enough to be vaporized (flash point)
  • Solids must be hot enough to turn into a gas (pyrolysis)
  • Glowing combustion: burning at the fuel-air interface
  • Spontaneous combustion: natural heat-producing process in poorly ventilated containers/areas
  • Combustion needs: fuel, oxygen, and heat
3.

SEARCHING THE FIRE SCENE

  • Investigators need to start looking for signs of arson as soon as the fire is extinguished
  • Most arsons begin with a petroleum-based accelerant
  • This investigation even takes precedence over needing to get a search warrant
  • The main focus is finding the fire's origin
  • Signs of arson include: unconnected fires, use of "streamers", and severe burning on the floor rather than ceiling
  • Combustible liquids are rarely entirely consumed in a fire; needed evidence is often found
4.

COLLECTION/PRESERVATION OF EVIDENCE

  • Traces of flammable liquids can be located with a vapor detector
  • Similar but uncontaminated control specimens are important
  • A search for igniters is also done
5.

ANALYSIS OF FLAMMABLE RESIDUES

  • Gas chromatography is the most reliable tool for detecting/characterizing flammable residues
  • The gas chromatography separates hydrocarbon components and makes a pattern
  • These patterns are compared to those of known flammable liquids; a forensic analyst may now be able to identify the accelerant used
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PHOTO CITATIONS

Claire Brazeel