explosives

1. Forensic Arson andForensic Arson and
Explosive InvestigationsExplosive Investigations

2. Forensic Arson and ExplosiveForensic 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

3. 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

4. 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

5. 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

6. 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

7. Methods for Isolating and ConcentratingMethods for Isolating and Concentrating
AccelerantsAccelerants
a. Steam Distillation
b. Solvent Extraction
c. Head Space Analysis
d. Vapor Concentration on Charcoal
e. Solid Phase Extraction

8. Methods for Isolating and ConcentratingMethods for Isolating and Concentrating
AccelerantsAccelerants
a. Steam Distillation
b. Solvent Extraction
c. Head Space Analysis
d. Vapor Concentration on Charcoal
e. Solid Phase Extraction

9. 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

10. 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)

11. Analyzing the ResultsAnalyzing the Results
Important Parts of a Mass Spectrometer:
• ionizing chamber
• analyzer tube
• detector

12. Analyzing the ResultsAnalyzing the Results

13. Analyzing the ResultsAnalyzing the Results

14. 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