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Chapter 4 Arson and Fire Investigation

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1 Chapter 4 Arson and Fire Investigation
© 2012 Cengage Learning. All Rights Reserved

2 Introduction—Objectives
Define combustion reactions. Discuss the four factors that are required to ignite and maintain a fi re. Explain the conditions in which fuels will burn. Examine reasons why arson is difficult to detect. Identify the four categories of fire. Forensic Science II: Arson and Fire Investigation, Chapter 4 © 2012 Cengage Learning. All Rights Reserved

3 Introduction—Objectives
Evaluate the significance of burn patterns discovered at an arson investigation. Discuss the proper methods for detecting, collecting, preserving, and analyzing arson evidence. Describe the psychological profile of an arsonist. Examine the various motives for arson. Forensic Science II: Arson and Fire Investigation, Chapter 4 © 2012 Cengage Learning. All Rights Reserved

4 Introduction—Vocabulary
accelerant - in fire investigation, any material used to start or sustain a fire; the most common are combustible liquids arson - the intentional and illegal burning of property combustion reaction – oxidation reaction that involves oxygen and that releases heat and light exothermic reaction – chemical reaction that releases heat heat of combustion - excess heat that is given off in a combustion reaction Forensic Science II: Arson and Fire Investigation, Chapter 4 © 2012 Cengage Learning. All Rights Reserved

5 Introduction—Vocabulary
hydrocarbon - any compound consisting only of hydrogen and carbon oxidation reaction - the complete or partial loss of electrons or gain of oxygen pyrolysis - decomposition of organic matter by heat in the absence of oxygen substrate control - a similar, but uncontaminated, sample; used for making comparisons Forensic Science II: Arson and Fire Investigation, Chapter 4 © 2012 Cengage Learning. All Rights Reserved

6 Happy Land Fire Julio Gonzalez and Lydia Feliciano dated off and on for six years. When Lydia ended the relationship, Julio set fire to the Happy Land Club in the Bronx. 87 people were trapped and died. Julio purchased the accelerant at a local station. Julio’s home and shoes smelled of gasoline. 6 Forensic Science II: Arson and Fire Investigation, Chapter 4 © 2012 Cengage Learning. All Rights Reserved

7 Chemistry of Fire (Obj 4.1, 4.2, 4.3)
Fire — a rapid oxidation reaction that involves a combustible material Oxidation — the complete or partial loss of electrons or the gain of oxygen 2NA + Cl2  2NaCl Forensic Science II: Arson and Fire Investigation, Chapter 4 © 2012 Cengage Learning. All Rights Reserved

8 Combustion Combustion reactions — oxidation reactions that involve oxygen and produce flames Heat of combustion — excess heat energy Exothermic reactions — chemical reactions that release heat Forensic Science II: Arson and Fire Investigation, Chapter 4 © 2012 Cengage Learning. All Rights Reserved

9 The Fire Tetrahedron Four ingredients are required to start a fire and keep it burning Oxygen Fuel Heat Chain reaction Forensic Science II: Arson and Fire Investigation, Chapter 4 © 2012 Cengage Learning. All Rights Reserved

10 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 Forensic Science II: Arson and Fire Investigation, Chapter 4 © 2012 Cengage Learning. All Rights Reserved

11 Flash Point & Ignition Temperature
Forensic Science II: Arson and Fire Investigation, Chapter 4 © 2012 Cengage Learning. All Rights Reserved

12 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. Forensic Science II: Arson and Fire Investigation, Chapter 4 © 2012 Cengage Learning. All Rights Reserved

13 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. Forensic Science II: Arson and Fire Investigation, Chapter 4 © 2012 Cengage Learning. All Rights Reserved

14 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 Forensic Science II: Arson and Fire Investigation, Chapter 4 © 2012 Cengage Learning. All Rights Reserved

15 Function of a Fire Investigator
Forensic Science II: Arson and Fire Investigation, Chapter 4 © 2012 Cengage Learning. All Rights Reserved

16 Determining Cause Forensic Science II: Arson and Fire Investigation, Chapter 4 © 2012 Cengage Learning. All Rights Reserved

17 Determining Cause Forensic Science II: Arson and Fire Investigation, Chapter 4 © 2012 Cengage Learning. All Rights Reserved

18 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 Forensic Science II: Arson and Fire Investigation, Chapter 4 © 2012 Cengage Learning. All Rights Reserved

19 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 Forensic Science II: Arson and Fire Investigation, Chapter 4 © 2012 Cengage Learning. All Rights Reserved

20 Packaging the Debris Use airtight containers such as a new clean paint can and lid Leave head space at the top of the can Forensic Science II: Arson and Fire Investigation, Chapter 4 © 2012 Cengage Learning. All Rights Reserved

21 Finding the Igniter Matches — often burns in the fire
Cigarette lighters — often removed by arsonist Molotov cocktail — may leave glass fragments Faulty electrical wiring — an arc causes a predictable pattern Knowing the igniter helps form the criminal profile Forensic Science II: Arson and Fire Investigation, Chapter 4 © 2012 Cengage Learning. All Rights Reserved

22 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 Forensic Science II: Arson and Fire Investigation, Chapter 4 © 2012 Cengage Learning. All Rights Reserved

23 Lab Analysis Passive headspace extraction procedure
Forensic Science II: Arson and Fire Investigation, Chapter 4 © 2012 Cengage Learning. All Rights Reserved

24 Psychology of an Arsonist
Sense of power An emotional high No typical arsonist; possible characteristics: Less than 25 y.o. 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 Forensic Science II: Arson and Fire Investigation, Chapter 4 © 2012 Cengage Learning. All Rights Reserved

25 Motives for Arson Financial gain — insurance fraud Revenge, spite
Excitement Vanity, hero syndrome Crime concealment — destroy evidence Vandalism Forensic Science II: Arson and Fire Investigation, Chapter 4 © 2012 Cengage Learning. All Rights Reserved

26 Chapter Summary Fire is an oxidation reaction that involves a combustible material. Not all oxidation reactions produce fire. The fire tetrahedron represents the four requirements for sustained fire—oxygen, fuel, heat, and a chain reaction. Most fuels are hydrocarbons and typically have very high ignition temperatures. The ignition temperature is when a fuel will light and continue to burn even if the heat source is removed. Forensic Science II: Arson and Fire Investigation, Chapter 4 © 2012 Cengage Learning. All Rights Reserved

27 Chapter Summary The initial focus is to find the fire’s point of origin The burn pattern helps determine whether the fire was natural, accidental, or deliberate. Ash and debris are collected from the point of origin and any other suspected area. Each sample of debris is placed in a separate airtight container. Forensic Science II: Arson and Fire Investigation, Chapter 4 © 2012 Cengage Learning. All Rights Reserved

28 Chapter Summary For comparison purposes, investigators also collect a substrate control. Two methods of collecting accelerant vapors for analysis are: direct headspace extraction procedure and vapor concentration. Gas chromatography is used to analyze the accelerant residue — comparing the lab chromatogram with one of known hydrocarbons. Forensic Science II: Arson and Fire Investigation, Chapter 4 © 2012 Cengage Learning. All Rights Reserved

29 Chapter Summary Arsonists tend to exhibit a set of characteristics that helps investigators focus their search. Most of the motives fit into six broad categories — financial gain, revenge, excitement, vanity, crime concealment, and vandalism. Forensic Science II: Arson and Fire Investigation, Chapter 4 © 2012 Cengage Learning. All Rights Reserved

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