1. FORENSIC ASPECTS OF ARSON AND EXPLOSION INVESTIGATIONS
Chapter 24

2. DETECT AND IDENTIFY CHEMICAL MATERIALS RECONSTRUCT AND IDENTIFY DETONATORS OR IGNITORS

3. The Chemistry of Fire
Oxidation – The combination of oxygen with other substances to produce new substances.

4. Definitions
Combustion: the rapid combination of oxygen with another substance accompanied by the production of noticeable heat and light.
Heat of Combustion: the heat evolved when a substance is burned in oxygen.

5. Flash Point: The minimum temperature at which a liquid fuel will produce enough vapor to burn.
Pyrolysis: The decomposition of organic matter by heat.
Flammable Range: The entire range of possible gas or vapor fuel concentrations in air that are capable of burning.
Glowing Combustion: Burning at the fuel-air interface.

6. Requirements for initiating and sustaining burning:
1. Fuel must be present.
2. Oxygen must be available in
sufficient quantity to
combine with the fuel.
3. Heat must be applied to initiate
the combustion, and sufficient
heat must be generated to
sustain the reaction.

7. Methods of Heat Production
CHEMICAL
RAPID OXIDATION
MECHANICAL
FRICTION
ELECTRICAL
ARCING, SHORTING
COMPRESSED GAS
NUCLEAR

8. Searching the Fire Scene
Origin and Cause Determination
Fire moves upward
Origin located closest to lowest point of most intense burning
Drafts & winds
Secondary fires
Stairways, holes, elevator shafts
Flammable liquids flow down

9. Searching the Fire Scene
Accidental vs. Incendiary
Patterns – How does fire burn?
Ignitable Liquids
“Sniffers” – Portable vapor detectors

10. Collection and Preservation of Arson Evidence
What to sample?
Porous materials (rugs, upholstery, flooring, rags)
2-3 Quarts of ash and soot
Airtight Packaging
Clean paint cans
Wide mouth glass jars
Avoid plastic polyethylene bags
Substrate controls

11. Other types of evidence
Matches
“Molotov cocktails”
Cigarettes
Candle remains
Newspapers
Suspect’s clothing
Soil, vegetation

13. Laboratory Analysis – Recovery of Ignitable Liquids
Detect hydrocarbons
(petroleum distillates)
Simple Headspace
(gas chromatograph)
Steam Distillation
Vapor Concentration by Charcoal Strips
(dynamic headspace)

14. Laboratory Analysis – Identification of Ignitable Liquids
Gas Chromatography
pattern recognition
Gas Chromatography/Mass Spectrometry
identify substance

15. Can we identify the brand of gasoline?

16. No! Comparison of two samples 1. Chromatographic or mass
spectral data comparison
2. Thin layer chromatography
for the dyes

18. EXPLOSIVES

19. EXPLOSION
A chemical or mechanical action resulting in the rapid expansion of gases

20. EXPLOSION

21. LOW EXPLOSIVES Black Powder Potassium or Sodium Nitrate
Charcoal
Sulfur
Smokeless Powders
Nitrocellulose (Single Based) + Nitroglycerine (Double Based)
Potassium Chlorate + Sugar
Natural Gas

22. HIGH EXPLOSIVES Primary Explosives – Ultrasensitive to heat, shock
or friction - Primers
Lead Azide
Lead Styphnate
Diazodinitrophenol

23. Secondary Explosives –
Relatively insensitive to
heat, shock, or friction
Dynamite
TNT (Trinitrotoluene)
PETN
Tetryl
RDX – most popular and powerful of the military explosives

24. BE CAREFUL!!!!!!!!! Collection & Analysis of Explosives
Undetonated residues
Debris from crater
Porous and non-porous material
EGIS screens for explosive residues
BE CAREFUL!!!!!!!!!

25. Collection & Analysis of Explosives
Collect in separate sealed metal or plastic containers
Examine debris with stereomicroscope
Confirm residues with
GC/MS
HPLC
IR (organic)
X-ray Diffraction (non-organic)
Proposed TAGGANT program

26. FORENSIC ASPECTS OF ARSON AND EXPLOSION INVESTIGATIONS
Chapter 24