• Essentially a combustion reaction with a fuel, oxygen and sufficient temperature. This is the fire triangle.

• Deliberately set. Also sometimes called an incendiary fire
• May involve the use of an accelerant
• Accelerant is a substance that causes a fire to start that would not ordinarily start or to burn faster than in the absence of the accelerant. These are usually fuels such as gasoline

• Done by fire scene investigator
• Search for point(s) of origin

1. Accidental
2. Natural
3. Deliberate

• Eliminate all natural and accidental causes: leaves only arson
• Multiple points of origin
• Fire trail
• Presence of accelerant in debris
• Presence of accelerant in observation of fire: thick black smoke

• Presence of an accelerant does not necessarily mean that fire is arson
• Absence of an accelerant does not rule out arson

• Lab does not determine if fire is arson or not
• Examines debris to determine if an accelerant may be present
• Isolates and identifies accelerants

• Heated headspace
• Purge and trap
• Thermal desorption
• Solvent extraction
• Steam distillation

• Closed container
• Samples headspace over residue
• Henry’s law - heating drives equilibrium to vapor
• Favors volatile components

• Closed container
• Uses charcoal strip or charcoal tube or tenax tube
• Uses vacuum or positive pressure with inert gas to force accelerant vapor through adsorbent
• Desorbed with CS₂
• Favors volatiles

• Closed container
• Tenax tubes
• Heated and left overnight
• Desorption by CS₂

• Add CS₂ to residue in open container
• Filter and evaporate CS₂
• Traps all residues

• Use steam to distil off petroleum products
• Weakness is limited amount of material that can be treated
• Favours volatiles but gets most of other fractions

• Uses GC-FID or GC/MS for comparisons
• MS has advantage of removing backgrounds more efficiently by using selective ion monitoring and ion extraction
• Analyst should have own library of knowns for comparison

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