FORENSIC ASPECTS OF ARSON AND EXPLOSION INVESTIGATIONS Chapter 24
DETECT AND IDENTIFY CHEMICAL MATERIALS RECONSTRUCT AND IDENTIFY DETONATORS OR IGNITORS
The Chemistry of Fire Oxidation – The combination of oxygen with other substances to produce new substances.
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.
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.
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.
Methods of Heat Production CHEMICAL RAPID OXIDATION MECHANICAL FRICTION ELECTRICAL ARCING, SHORTING COMPRESSED GAS NUCLEAR
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
Searching the Fire Scene Accidental vs. Incendiary Patterns – How does fire burn? Ignitable Liquids “Sniffers” – Portable vapor detectors
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
Other types of evidence Matches “Molotov cocktails” Cigarettes Candle remains Newspapers Suspect’s clothing Soil, vegetation
Laboratory Analysis – Recovery of Ignitable Liquids Detect hydrocarbons (petroleum distillates) Simple Headspace (gas chromatograph) Steam Distillation Vapor Concentration by Charcoal Strips (dynamic headspace)
Laboratory Analysis – Identification of Ignitable Liquids Gas Chromatography pattern recognition Gas Chromatography/Mass Spectrometry identify substance
Can we identify the brand of gasoline?
No! Comparison of two samples 1. Chromatographic or mass spectral data comparison 2. Thin layer chromatography for the dyes
EXPLOSIVES
EXPLOSION A chemical or mechanical action resulting in the rapid expansion of gases
EXPLOSION
LOW EXPLOSIVES Black Powder Potassium or Sodium Nitrate Charcoal Sulfur Smokeless Powders Nitrocellulose (Single Based) + Nitroglycerine (Double Based) Potassium Chlorate + Sugar Natural Gas
HIGH EXPLOSIVES Primary Explosives – Ultrasensitive to heat, shock or friction - Primers Lead Azide Lead Styphnate Diazodinitrophenol
Secondary Explosives – Relatively insensitive to heat, shock, or friction Dynamite TNT (Trinitrotoluene) PETN Tetryl RDX – most popular and powerful of the military explosives
BE CAREFUL!!!!!!!!! Collection & Analysis of Explosives Undetonated residues Debris from crater Porous and non-porous material EGIS screens for explosive residues BE CAREFUL!!!!!!!!!
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
FORENSIC ASPECTS OF ARSON AND EXPLOSION INVESTIGATIONS Chapter 24