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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