fire and arson
TRANSCRIPT
Dr. Sangeetha BalakrishnanPG Department of ChemistryWomen’s Christian College
Chennai – 600 006
Fire
25 January, 2017
Forensic Science PCH/NM/01
Some Definitions • Fire
Fire is the evolution of energy in the form of light, heat and smoke.Fuel + oxygen carbon dioxide + water + energy
• Activation EnergyThe energy required for this reaction to occur is called activation energy.This energy is required to break molecular oxygen into atomic oxygen.
• Activation Energy
The Chemistry of FireThe Fire Tetrahedron What can we do if we need to
stop a fire?
Classification of Fire
Fire
Natural Fire Accidental Fire Arson
Arson: The crime of setting fires willfully and intentionally.
Also called: incendiary fires.
Investigation of a fire scene to determine if it is arson
1. Eliminate all possible natural or accidental causes of fire.
2. Have compelling evidence for arson.a) Presence of a fire-setting device like a Molotov
Cocktail.b) Presence of Fire Trail.c) Presence of Point of Origin.
a) Molotov Cocktail
Bottle containing accelerant + wick ignite throw!
b) Fire trail
Pour the accelerant Set fire Efficient way to carry the fire from one place to another.
c) The Point of Origin• It is the location where the fire started.• This is where the most extensive burning
takes place, and is the hottest!• If an accelerant was used to start a fire, its
residue will be seen at the point of origin.
Characteristic Features of Point of Origin
• V-Patterns of burning.• Blistering of concrete.• The beginning of a fire trail.• The obvious presence of accelerants.
V-Pattern of burning
Blistering of concrete
Detection and Collection of Accelerants
1. By hydrocarbon sensors.2. By arson dogs.
3. By substances that absorb accelerants.
Give examples of
such substances.
Analysis of Fire Scene Residue1. Separate the accelerant residue from the
material it was trapped in. 2. Concentrate these residues.3. Analyse.
• Concentration Method: Passive Headspace• Analysis: Gas-Chromatography/Mass
Spectrometry
Passive Headspace
