CHAPTER 4ARSON AND FIRE INVESTIGATION
INTRODUCTION—OBJECTIVES
1. Define combustion reactions
2. Discuss the four factors that are required to ignite and maintain a fire
3. Explain the conditions in which fuels will burn
4. Examine reasons why arson is difficult to detect
5. Identify the four categories of fire
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INTRODUCTION—OBJECTIVES
6. Evaluate the significance of burn patterns discovered at an arson investigation.
7. Discuss the proper methods for detecting, collecting, preserving, and analyzing arson evidence.
8. Describe the psychological profile of an arsonist.
9. Examine the various motives for arson.
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COMBUSTION
Combustion reactions — oxidation reactions that involve oxygen and produce flames
Heat of combustion — excess heat energy
Exothermic reactions — chemical
reactions that release heat
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THE FIRE TETRAHEDRON
Four ingredients are required to start a fire and keep it burning
Oxygen
Fuel
Heat
Chain reaction5
FLASH POINT & IGNITION TEMPERATURE
Most accelerants are hydrocarbons in a gas state
In a gas state, molecular bonding is weaker
Vaporization — liquid changes to gas
Flash point — lowest temperature at which vaporization occurs
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FLASH POINT & IGNITION TEMPERATURE
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ARSON IS DIFFICULT TO PROVE
$15 billion of property damage a year in United States
Can be accidents, but if not…
What makes it hard to prove?
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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
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FUNCTION OF A FIRE INVESTIGATOR
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DETERMINING CAUSE
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FORENSIC SCIENCE II: ARSON AND FIRE INVESTIGATION, CHAPTER 4
© 2012 CENGAGE LEARNING. ALL RIGHTS RESERVED12
INVERTED CONE PATTERN
FORENSIC SCIENCE II: ARSON AND FIRE INVESTIGATION, CHAPTER 4
© 2012 CENGAGE LEARNING. ALL RIGHTS RESERVED13
DETERMINING CAUSE
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COLLECTING THE 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
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COLLECTING THE CONTROL
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
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CRIME SCENE
What tests would you conduct?
What can you conclude from this picture?
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FINDING THE IGNITER Matches — often burns in the fire
Cigarette lighters — often removed by arsonist
Molotov cocktail — may leave glass fragments
Faulty electrical wiring — causes an arc which causes a predictable pattern
Knowing the igniter helps form the criminal profile
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LAB ANALYSIS
Heat the debris container to collect vapors in the head space
1. Direct headspace extraction procedure Remove vapors with a syringe Analyze vapors with gas chromatography
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LAB ANALYSIS
2. 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
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LAB ANALYSIS
Passive headspace extraction procedure
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LAB ANALYSIS
Separates hydrocarbon components
Most sensitive and reliable instrument for detecting and characterizing flammable residues
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PSYCHOLOGY OF AN ARSONIST
Sense of power
An emotional high
No typical arsonist; possible characteristics:
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• 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
MOTIVES FOR ARSON
Six categories:
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