fire and arson

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