Fire and the Analysis of Fire Residues

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