Lindsey Grady Fire
Published on Nov 21, 2015
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PRESENTATION OUTLINE
FIRE INVESTIGATION
LINDSEY GRADY
CHEMISTRY OF FIRE
- Fire is a type of oxidation - the combination of oxygen with other substances to produce new substances
- Ignition temperature: the minimum temperature needed to spontaneously ignite fuel
- Heat of combustion: the heat evolved when a substance burns
CHEMISTRY OF FIRE
- Besides the liberation of energy, the rate or speed at which the oxidation reaction takes place is a factor
- Only in a gaseous state, a fuel will achieve a reaction rate with oxygen sufficient to produce a flame
CHEMISTRY OF FIRE
- Flash point: a liquid burns when the temperature is high to vaporize it
- Pyrolysis: a solid must be hot enough to decompose into gaseous products
CHEMISTRY OF FIRE
- Glowing combustion: smoldering is burning at the fuel-air interface
- Spontaneous combustion: the result of a natural heat-producing process in poorly ventilated containers or areas
CHEMISTRY OF FIRE
- To initiate and sustain combustion:
- Fuel present
- Available oxygen
- Applied heat
HEAT TRANSER
- Conduction: movement of heat through a solid object
- Radiation: transfer of heat energy by electromagnetic radiation
- Convection: transfer of heat energy by the movement of molecules within liquid or gas
THE FIRE SCENE
- Arson investigator needs to begin the examination for arson
- Most arsons consist of petroleum-based accelerants
- Immediate investigation trumps search warrant
THE FIRE SCENE
- The focus of the search is to find the fire's origin
- Signs of arson: separate and unconnected fires, "streamers", severe floor burning
- Fire has a tendency to move in an upward direction
- Combustible liquids are rarely entirely consumed by the fire
COLLECTION
- Ash and soot and porous materials should be collected and stored in airtight containers with an airspace to remove samples
COLLECTION AND PRESERVATION
- Vapor detector: locates traces of flammable liquid
- Uncontaminated control specimens must be collected
- Igniters must be searched for and collected
ANALYSIS
- The gas chromatography is the most reliable for detecting and characterizing flammable residues
- Arsons are usually ignited by petroleum
ANALYSIS
- The gas chromatograph separates the hydrocarbon components and produces a chromatograph pattern of a particular petroleum product
- By comparing select gas chromatograph peaks, the accelerant of the fire can be identified
