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FORENSIC ASPECTS OF ARSON AND EXPLOSION INVESTIGATIONS

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.

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FORENSIC ASPECTS OF ARSON AND EXPLOSION INVESTIGATIONS

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  1. FORENSIC ASPECTS OF ARSON AND EXPLOSION INVESTIGATIONS Chapter 24

  2. DETECT AND IDENTIFY CHEMICAL MATERIALSRECONSTRUCT 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

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

  13. Laboratory Analysis – Identification ofIgnitable Liquids • Gas Chromatography • pattern recognition • Gas Chromatography/Mass Spectrometry • identify substance

  14. Can we identify the brand of gasoline?

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

  16. EXPLOSIVES

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

  18. EXPLOSION

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

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

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

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

  23. 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

  24. FORENSIC ASPECTS OF ARSON AND EXPLOSION INVESTIGATIONS Chapter 24

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