Arson%20and%20Explosives

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Arson and Explosives

• Using Forensic Chemistry to Identify Substances

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Arson Incendiary Fires

• Accelerant something used to promote and spread
  a fire
• Solid accelerants include paper, trash, highway
  flares, black powder, paraffin and an oxidizer,
  or sugar and chlorate.
• Liquid accelerants include petroleum products,
  alcohols, paint thinners, industrial solvents,
  and ether. Either sloshed about or used in
  firebomb (Molotov cocktail).
• Gaseous accelerants include propane and natural
  gas (disconnected gas line)

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Incendiary Device

• Combine a means of ignition with a time delay.
• Candle is allowed to burn down to come into
  contact with accelerant.
• Fuses, flares, matches with lit cigarette,
  chemical mixes, electronic devices.

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Collection of Potential Evidence

• Use clean, vapor-tight containers.
• Screw-cap glass jars, metal cans, unused paint
  cans with tight-fitting lids
• Care must be taken to avoid loss of evidence due
  to evaporation, and to avoid cross-contamination
  of exhibits

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Search for Evidence

• Some materials will survive the fire
• Start at point of origin (determined by arson
  investigator)
• Wires, batteries, bottles, wax, soap (used to
  gel flammable liquid), ash residues, unburned
  residual liquids

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Testing Evidence

• Gas Chromatography
• Heat airtight container to drive volatile
  residues from collected evidence
• Remove vapor with syringe and inject into GC
• Unburned liquids can be removed from evidence by
  steam distillation, vacuum distillation, solvent
  extraction, solvent rinsing, or air flushing.
• Compare resulting chromatogram with those of
  known substances

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Explosives

• 1920s - dynamite bombs used by political
  anarchists aimed at rich and powerful, also used
  by unions
• 1930s the mob used stink bombs in theaters and
  restaurants to persuade them to sell
• November 1, 1955 midair explosion of United
  Airlines flight 629 first bomb aimed at
  general public

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Bomb Investigations

• Investigation of flight 629 was very similar to
  how such investigations are carried out today
• Large grid was established (pieces were scattered
  over a 5-mile radius)
• Wreckage was pieced together, and it was
  determined what type of bomb was used (from
  residues) and where it exploded

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Types of Explosives

• Low explosives cause relatively small damage
• Explode at a few thousand feet per second
• Emit low frequency sound (puff or boom)
• Examples are gasoline and gunpowder
• High explosives cause large damage
• 25,000 feet per second
• High-frequency blast
• Examples are dynamite and nitroglycerin

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• Military Explosives TNT (trinitrotoluene), RDX,
  PETN (Pentaerythritol Tetranitrate C5H8N4O12)
• Commercial Explosives black powder, ANFO
  (ammonium nitrate-fuel oil), dynamite,
  nitrostarch
• Improvised Explosives usually low explosives
  (require confinement) homemade black powder,
  fuel mixed with an oxidizer.

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Crime Scene Searches

• Focus on blast seat
• Diligent search for remnants must be performed
• Explosive residues, metal fragments, fuse or
  blasting cap, wire and/or insulation, electrical
  tape, batteries, clocks or timers
• FBI has extensive databases (batteries,
  detonators, accessories, timers, radio-control
  devices

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Laboratory Tests

• Microscope locate unconsumed explosive
• Acetone is used to extract soluble explosives
  from debris TLC or HPLC
• Evidence is screened with an explosives
  detector a special GC that identifies known
  explosives.