CHAPTER 4 ARSON 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 2
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. 3
COMBUSTION Combustion reactions — oxidation reactions that involve oxygen and produce flames Heat of combustion — excess heat energy Exothermic reactions — chemical reactions that release heat 4
THE FIRE TETRAHEDRON Four ingredients are required to start a fire and keep it burning Oxygen Fuel Heat Chain reaction 5
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 6
FLASH POINT & IGNITION TEMPERATURE 7
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? 8
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 9
FUNCTION OF A FIRE INVESTIGATOR 10
DETERMINING CAUSE 11
FORENSIC SCIENCE II: ARSON AND FIRE INVESTIGATION, CHAPTER 4 © 2012 CENGAGE LEARNING. ALL RIGHTS RESERVED 12
INVERTED CONE PATTERN FORENSIC SCIENCE II: ARSON AND FIRE INVESTIGATION, CHAPTER 4 © 2012 CENGAGE LEARNING. ALL RIGHTS RESERVED 13
DETERMINING CAUSE 14
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 15
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 16
CRIME SCENE What tests would you conduct? What can you conclude from this picture? 17
FINDING THE IGNITER Matches — often burns in the fire Cigarette lighters — often removed by arsonist Molotov cocktail — may leave glass fragments Molotov cocktail Faulty electrical wiring — causes an arc which causes a predictable pattern Knowing the igniter helps form the criminal profile 18
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 19
LAB ANALYSIS 2. Passive headspace extraction procedure Suspend a charcoal-coated strip inside the can Replace lid Heat container 4-16 hours at o C Charcoal absorbs the vapor 20
LAB ANALYSIS Passive headspace extraction procedure 21
LAB ANALYSIS Separates hydrocarbon components Most sensitive and reliable instrument for detecting and characterizing flammable residues 22
PSYCHOLOGY OF AN ARSONIST Sense of power An emotional high No typical arsonist; possible characteristics: 23 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: 24