Fs Ch 15

Chapter 15

Forensic Aspects of Fire Investigation

Forensic ScienceRichard Saferstein

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

All Rights Reserved.2

Introduction Complex and difficult:-planned-not present-destruction is extensive

Criminalist’s function:-detecting/identifying-relevant chemical materials




Arson Facts

Second leading cause of death by fire (US)

#1 cause of property damage (fires)

>500 killed in 1996

> property damage $2 billion.




Arson Facts

1996:-63%= under 20 years old-35%= under 15 years old >90 percent of all arson deaths occur

in homes Growing link between arson and drugs -20% - 25% cases are drug-related.




The Chemistry of Fire Oxidation-oxygen + other substances=new

substances

Ignition temperature:-minimum temperature-spontaneously ignite fuel

Combustion:-heat evolved when a substance burns

Rate/speed of oxidation reaction




The Chemistry of Fire Liquids:-flash point Solids:-pyrolysis Glowing/combustion/smoldering:-burning at fuel-air interface Spontaneous combustion:-rare-heat-producing process-poorly ventilated containers/areas




Chemistry of fire




Heat Transfer

Conduction:-movement of heat through solid objects Radiation:-transfer of heat energy by electromagnetic

radiation Convection:-transfer of heat energy by the movement of

molecules within a liquid/gas.




ARSON FIRES

Covert:-hide arson

Overt:-send message




ARSONISTS

Profit: (torch)

Pleasure: (spark)

Anger: (murderer)




The Fire Scene Majority of arson fires:-petroleum-based accelerants

Walk through of scene:-locate point of origin-locate anything suspicious -no warrant needed at this point-ignitors such as matches, an electrical

sparking device, or parts of a “Molotov cocktail” must also be conducted.




ARSON-separate/unconnected fires-“streamers” -severe burning on floor

Fires burn up/out-point of origin-lowest point-showing intense characteristics

Combustible liquids rarely entirely consumed




Up and out




Burn patterns




Collection of Fire Evidence Point of origin:-ash/soot-porous materials -airtight containers Traces of flammable residues located:-vapor detector/sniffer-dog Sampling:-similar/uncontaminated control specimens-”substrate control”




Awwww. Isn’t he cute?




Analysis of Flammable Residues

Heat:-airtight container-volatile residue -driven off -trapped in airspace-vapor (headspace) removed with syringe-injected into GC-separated into its components-recorded on the chromatogram




Gas Chromatography Most sensitive/reliable instrument:-detecting/characterizing residues-petroleum distillates-gasoline/kerosene GC:-separates hydrocarbon components-chromatographic pattern -particular product Comparison of GC peaks from scene debris to

known flammable liquids-identify accelerant used




Analysis of Flammable Residues

Vapor concentration technique:

- charcoal strip in the container heated-absorbs vapors-washed with solvent-recover vapors-solvent injected into GC




GC/MS of Flammable Residues Complex patterns:

-simplified-passing separated components -GC column -through mass spectrometer-component fragmented into collection of

ions-analyst identified peaks associated with

ions of a particular accelerant




Burn pattern




Dirty work




Under a house




Can you locate point of origin?




Obvious point of origin




Indicates accelerants. Fire burns up even when a wall collapses the floor underneath it doe not burn down like here.




Pour pattern




Pour pattern on wood floor. The accelerant is burned away leaving the floor undamaged.




Pour pattern




Not a smart BBQ technique







Some scenes are large




Burn pattern




Oh yeah Sherlock. You certainly hid that pour pattern well

Fs Ch 15

Technology

arson facts

arson fires covert

origin lowest point

obvious point of origin

movement of heat

floor fires

arson deaths

arson overt