NATS 1575 Chapter Notes - Chapter 13: Fire Investigation, Arson, Air Interface

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16 Aug 2016
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Chapter 12 // Forensic Aspects of Fire Investigation
Introduction
-arson investigations often present complex and difficult circumstances to investigate due to
the fact that perpetrator has thoroughly planned the act, is not present during the act, and the
destruction is so extensive.
-the criminalists function is rather limited to detecting and identifying relevant chemical
materials collected at the scene and reconstructing and identifying igniter mechanisms.
The Chemistry of Fire
-chemically, fire is a type of oxidation, which is the combination of oxygen with other
substances to produce new substances
-to start fire, the minimum temperature needed to spontaneously ignite fuel, known as ignition
temperature, must be reached.
Heat of Combustion - heat evolved when a substance burns.
-besides the liberation of energy, needed to explain fire is the rate or speed at which the
oxidation reaction takes place
-a fuel will achieve a reaction rate with oxygen sufficient to produce a flame only when it is in
the gaseous state
-the liquid burns when the temperature is high enough to vaporize it (flash point), while a solid
must be hot enough to decompose into gaseous products (pyrolysis)
Glowing Combustion - burning at the fuel air interface, such as cigarette
Spontaneous Combustion - is the result of a natural heat - producing process in poorly ventilated
containers or areas.
-to initiate and sustain combustion the following is required:
1. a fuel must be present
2. oxygen must be available in sufficient quantity to combine with the fuel
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