Forensic Arson and Forensic Arson and Explosive InvestigationsExplosive Investigations

Forensic Arson and Explosive Forensic Arson and Explosive InvestigationsInvestigations

Two Main Areas of Interest:

• isolation and analysis of flammable residues

• collection and analysis of explosive material

Any flammable liquid or substance used to start and/or maintain a fire is known as an accelerant

Not all flammable or explosive material will burn in a fire – accelerants always get trapped in pores in material and will not burn

The Chemistry of FireThe Chemistry of Fire

Fire is the product of combustion - the rapid combination of oxygen with another substance accompanied by the production of light and heat

Two Important Points:

• Most combustion reactions will not happen by themselves (they are not spontaneous)….they need help getting started

•The energy released comes from the breaking and reforming of the bonds that hold the compounds together

Accelerants and ExplosivesAccelerants and Explosives

Accelerants and explosives are almost always organic in nature (wood, gasoline, kerosene, paper, etc)

If an organic molecule burns completely, the products are always carbon dioxide and water. Smoke, ash, carbon monoxide result from incomplete combustion.

Explosive materials are often compounds that are chemically unstable – they want to react and form more stable molecules

Investigating Arson or BombingsInvestigating Arson or Bombings

Steps to Follow:

1. Begin collecting evidence as soon as possible.

2. Collect totally burned, partially burned, and unburned samples from the scene for comparison

3. Back in the forensic lab, isolate and concentrate the accelerant material

- there are four common methods used to isolate and concentrate this material

4. Analyze the material to determine its composition

Investigating Arson or BombingsInvestigating Arson or Bombings

Steps to Follow:

1. Begin collecting evidence as soon as possible.

2. Collect totally burned, partially burned, and unburned samples from the scene for comparison

3. Back in the forensic lab, isolate and concentrate the accelerant material

- there are four common methods used to isolate and concentrate this material

4. Analyze the material to determine its composition

Methods for Isolating and Concentrating Methods for Isolating and Concentrating AccelerantsAccelerants

a. Steam Distillation

b. Solvent Extraction

c. Head Space Analysis

d. Vapor Concentration on Charcoal

e. Solid Phase Extraction

Methods for Isolating and Concentrating Methods for Isolating and Concentrating AccelerantsAccelerants

a. Steam Distillation

b. Solvent Extraction

c. Head Space Analysis

d. Vapor Concentration on Charcoal

e. Solid Phase Extraction

Analyzing the ResultsAnalyzing the Results

Arson labs often use a method called gas chromatography/mass spectrometry (GC/MS) to determine the composition of the accelerants or

explosives found

GCGCMSMS

Analyzing the ResultsAnalyzing the Results

Important Parts of a Gas Chromatograph:

• injection port and vaporization chamber

• column – usually inside coated with non-polar material

• a “carrier gas” to push accelerant molecules through the column

• a detector (usually this is the mass spectrometer)

Analyzing the ResultsAnalyzing the Results

Important Parts of a Mass Spectrometer:

• ionizing chamber

• analyzer tube

• detector

Analyzing the ResultsAnalyzing the Results

Analyzing the ResultsAnalyzing the Results

Analyzing the ResultsAnalyzing the Results

Ion Mobility Spectrometer

• vaporize with heat

• ionize the sample with electrons

• detect by how fast they move in an electric field