1. Arson

2. Arson Vocabulary accelerant arson char depth combustion reaction
exothermic reaction
fire
flash point
heat of combustion
hydrocarbon
oxidation reaction
pyrolysis
substrate control

3. What is Fire?
A study of arson needs to begin with an understanding of fire.
Fire is a rapid oxidation of a material in the chemical process of combustion. This process also produces heat and light.
Fire is an exothermic reaction.
The vapor of the fire is also
undergoing combustion.

4. What is Arson?
Arson is the intentional setting of a fire to a structure or wild land area.
Arson is a complex crime and difficult to prove.
The crime scene generally has extensive destruction.
The crime scene technician has a limited role. A trained arson investigator will conduct a thorough investigation and make the final determination.

5. The Fire Tetrahedron
Also called the fire “triangle” if the chain reaction is removed.
Four ingredients are needed to start a fire and to keep it burning:
Oxygen – readily available in the air
Fuel – material that is burning, if an accelerant is present it will burn first
Heat – once the ignition temperature is reached the fuel will burn
Chain Reaction – the fire will continue to burn until all the oxygen or the fuel is used or removed
Flashover Demonstration (5.27) ch?v=BtMmymOxdjc

6. The Fire Tetrahedron
If the fire is a case of arson, the arsonist will have manipulated one or more of the components of the fire triangle. This manipulation must be proven in order to state the fire is an arson.
They may increase the fuel load by adding accelerant or flammable items.
More oxygen may be introduced by opening windows or punching holes in walls or the ceiling.

7. Flash Point & Ignition Temperature
Most accelerants are hydrocarbons in a gas state
Hydrocarbons are compounds that are made of only hydrogen and carbon atoms
gasoline, kerosene, lighter fluid
In a gas state, molecular bonding is weaker
Vaporization — liquid changes to gas
Flash Point — lowest temperature at which vaporization occurs

8. Pyrolysis
Pyrolysis - decomposition of organic matter by heat in the absence of oxygen
The vapors given off from the resins in wood are flammable and will burn.

9. Arson is Difficult to Prove
The crime is usually carefully planned.
The arsonist leaves the scene before anyone notices a fire.
The fire destroys evidence.
Extinguishing the fire also destroys evidence.
Six Signs of Arson (3.51) BlTSU

10. Function of a Fire Investigator
Investigation must begin quickly, before evidence is lost
Find the fire’s point of origin
Examine possible causes
Accidental
Arson
Classify the fire

11. Function of a Fire Investigator

12. Is it an Accident? Accidental causes of fire include:
Cigarette smoking
Overheated electrical motors
Improperly cleaned and regulated heating systems
Faulty wiring
To answer this question, the investigator must study the fire in terms of the fire tetrahedron.

13. Clues of an Arson Multiple points of origin Strange odors
Accelerant soaked rags will keep the fire low or localized, not traveling up as usual
Extensive regions of low burn
Faster and hotter fire than would be expected.
Empty containers of accelerants, time delay devices, and other items left by the perpetrator

14. Ways the Fire Begins
Arsonists can start fires with a cigarette, matches, firearms and ammunition, electrical spark and a Molotov cocktail.
The most common method is with gasoline or kerosene or some other flammable liquid.

15. Determining Cause

16. Other Fire Patterns Protected Area Clean Burn Run Down Burn
Ignitable Liquid Pour Pattern

17. Classic V-Shape

18. Inverted Cone

19. Protected Area

20. Clean Burn

21. Run Down Burn

22. Ignitable Liquid Pour Pattern

23. Arson Investigation
A criminologist needs to detect and identify relevant chemical materials collected at the scene, reconstruct the crime and identify detonating mechanisms.

24. Collecting Evidence Begin immediately; no warrant required
Collect 3-4 liters of ash from point of origin and other suspected areas
Use portable vapor detectors, or sniffers
Use trained dogs to sniff
Place each sample in its own container
Collect a substrate control — a debris sample that has not been contaminated by the accelerant
Comparisons to the substrate control may help prove an accelerant was used
Some products may look like accelerants when burned
Use airtight containers such as a new clean paint can and lid
Leave head space at the top of the can

25. The Search for Relevant Chemical Materials
Search for traces of flammable liquid residues may be aided by the use of a highly sensitive portable vapor detector or a “sniffer.”

26. Arson Dogs as “Sniffers”
Another approach is to use trained dogs that have been conditioned to recognize the odor of hydrocarbon accelerants.

27. Arson
Even dogs need protective gear.

28. Recreating the Crime: Fire Patterns
Major objectives of a fire examination is the recognition, identification, and analysis of fire patterns.
The circumstances of every fire are different from every other fire because of differences in structures, fuel load, ignition factors, airflow, ventilation, and other variables.
Patterns can represent the history of the fire.

29. Escalator Fire
Think about the fire pattern that develops.

30. Dynamic of Patterns
Recognition of fire patterns depends on the investigators understanding of the development of fire, heat, and flame spread.
Heat moves by convection, conduction, and radiation.
These produce the fire patterns and the nature of flame, heat, and smoke movement within a structure.

31. Arson Investigation
The investigator must also find the point of origin or where the fire began. The fire pattern should indicate the origin.

32. Fire Behavior
The picture shows the point of origin to be the computer.
Normally a fire moves in an upward direction and so the point of origin will most likely be located closest to the lowest point that shows the most intense burning.

33. Fire Behavior Investigators follow the
V-shaped burn pattern down to locate the point of origin.

34. Fire Behavior
The depth of wood charring, or alligatoring, is also a good indicator of point of origin.

35. Difficulties in the Investigation
Evidence is destroyed and transformed
Water, water, water
Destruction and alteration of structures
Perpetrator is usually long gone

36. Arson Sketch
At a crime scene, nothing should be touched or moved before notes, sketches and photographs are made. The fire pattern should be included on the sketch.

37. Lab Analysis
Heat the debris container to collect vapors in the head space
Direct headspace extraction procedure
Remove vapors with a syringe
Analyze vapors with gas chromatography
Passive headspace extraction procedure
Suspend a charcoal-coated strip inside the can
Replace lid
Heat container 4-16 hours at 50-80oC
Charcoal absorbs the vapor

38. Temperature and Speed of the Fire
The melting of materials such as metals and plastic can be used to determine the temperature of the fire.
Cracking lines in windows are helpful in determining the speed of the fire. Longer cracks develop with slower fires.

39. Why?
Arsonist cause fires at different locations for different reasons.

40. Psychology of an Arsonist
Less than 25 years old
Father not in the home
Domineering mother
Academically challenged
Emotionally and/or psychologically disabled
Unmarried
Living with parents
Inadequacy, insecurity
Fascination with fire
Alcoholism
Parental neglect or abuse

41. Motivation for Arson Includes:
Vandalism – both mischievous and malicious
Excitement – a thrill seeker, wants attention
Revenge – retaliation for a personal or societal “injustice”
Crime Concealment – to cover up a primary crime, such as a murder
Profit – Insurance money
Extremist – beliefs on social issues, such as abortion clinics or churches
Vanity/Heroism – trying to make themselves look good

42. Finding the Arsonist An arson profiler will use information from:
the arson scene
any potential witnesses
the types of accelerants used

43. Famous Fires
Great Chicago Fire Speculated point of origin is a barn fire
Davidian Branch Compound Fire, allegedly caused by pyrotechnic tear gas.

44. Famous Fires
Space Shuttle Challenger exploded because of a fuel leak on the rocket booster.
Swiss Air Flight crashed due to a fire caused by faulty wiring.