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Fire and the Analysis of Fire Residues

Fire and the Analysis of Fire Residues. The Problem with Arson. One of the fastest growing crimes in US Arson for its own sake – pyromania Arson to cover up other crimes such as murder or embezzlement Not hard to determine if a fire is arson Difficult to determine who caused the fire.

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Fire and the Analysis of Fire Residues

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  1. Fire and the Analysis of Fire Residues

  2. The Problem with Arson • One of the fastest growing crimes in US • Arson for its own sake – pyromania • Arson to cover up other crimes such as murder or embezzlement • Not hard to determine if a fire is arson • Difficult to determine who caused the fire

  3. What Is Fire? • Essentially a combustion reaction with a fuel, oxygen and sufficient temperature. This is the fire triangle. • 2C8H18 + 25O2 = 18H2 O + 16CO2 • An explosion and a fire involve the same process. • The only difference is the speed of the reaction. • Combustion may cause an explosion if confined

  4. The Fire Triangle oxygen heat fuel

  5. Types of Fires • Burning or flaming fire • Sufficient oxygen and fuel • Flames and smoke visible • Smoldering fire • Oxygen deprived • Can burst into explosive flame if oxygen is suddenly supplied

  6. Arson • 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

  7. Conditions for a Fire • A fire must have: • Oxygen • Fuel • Sufficient heat to get the fire started • Deprive the fire of one of these and it will cease or won’t start

  8. Conditions for a fire • Generally only gases (vapors) will burn. Solids and liquids will not burn • Sufficient heat is required to vaporize some of the fuel and break oxygen molecules apart into oxygen atoms • Fire will produce enough heat to continue vaporization and keep fire going

  9. Investigating the Fire Scene • Done by fire scene investigator • Search for point(s) of origin • Possible causes: • Accidental (leave the stove on, accidental malfunction in appliance) • Natural (lightening) • Deliberate (Use an accelerant, deliberately sabotage an appliance)

  10. The Point of Origin • Crucial piece of evidence in determining type of fire • Often most intense location of burning • Usually at a low point in the building-may be buried under tons of rubble • Smoke or damage often shows “V” pattern

  11. Determination of Arson • 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

  12. The Role of an Accelerant • The accelerant supplies the heat needed to get substances into the vapor phase so they can burn. • Presence of an accelerant does not necessarily mean that fire is arson. Why? • Absence of an accelerant does not rule out arson. Why?

  13. Finding Accelerants • Find point of origin • Look for absorbent materials • Use fire dog – capable of sniffing out miniscule quantities of accelerants • Look for fire trails

  14. Role of the Crime Laboratory • Lab does not determine if fire is arson or not • Examines debris to determine if an accelerant may be present • Isolates and identifies accelerants • This may support the fire scene investigator in determination of arson

  15. Methods of Isolating and Concentrating Accelerant Residues • Heated headspace • Purge and trap

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

  17. Headspace Analysis syringe headspace ~~~~~~~~~~~~ fire debris

  18. Purge and Trap • Closed container • Uses charcoal strip or charcoal tube to trap accelerants • Uses vacuum or positive pressure with inert gas to force accelerant vapor through charcoal trap

  19. Purge and Trap vacuum headspace ~~~~~~~~~~~~~~ Fire debris

  20. Analysis of Residues • Uses GC or GC/MS for comparisons • MS has advantage of identifying particular compounds which are present in certain accelerants • Analyst should have own library of knowns for comparison

  21. GC of Gasoline

  22. 50% Evaporated Gasoline

  23. Gasoline Residue

  24. Furniture Polish

  25. Cases • Dentist who liquidated his assets • Smoldering fire • Body in the trunk of the car

  26. Dentist Who Liquidated His Assets • Dentist had failing practice in deteriorating neighborhood • Had offer to relocate practice with partner but needed $$$$$$$$$$ to get started • Used gasoline to make fire trail to each room in office • Building destroyed but witness saw him leave building before fire started • Convicted of arson

  27. Smoldering Fire • Man catches wife fooling around and decides to set trap for her. • He seals up all windows and doors to house and sets a fire in living room • Fire flames first and then, having used up oxygen, settles into glowing, smoldering fire.

  28. Smoldering Fire • He expects wife to come home from work and enter house. This will cause influx of oxygen into house and rekindle the fire explosively, killing her instantly • She has an auto accident on the way home and is delayed. Meanwhile a neighbor smells smoke and calls fire department • They arrive at scene and recognize that whole house is sealed up and enter very carefully. • Husband is charged with arson and attempted murder

  29. Body in the Trunk • This was believed to be a “gangland” killing over drugs • Police were called to scene of fire in a car • They popped the trunk and found a charred body • ME said that body was burned and then put in trunk

  30. Body in the Trunk • Inside of car was searched for accelerant and fingerprints (superglue fumed entire inside of car). • Gasoline was found in car on seats. Since gas tank didn’t explode, gasoline came from elsewhere • Fingerprints found but no suspect. AFIS search came up empty. Case still open

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