arson and explosives
DESCRIPTION
Arson and Explosives. Using Forensic Chemistry to Identify Substances. 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. - PowerPoint PPT PresentationTRANSCRIPT
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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.