Arson

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

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.

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.

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) https://www.youtube.com/wat ch?v=BtMmymOxdjc

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.

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

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.

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) https://www.youtube.com/watch?v=jYaLO- BlTSU

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

Function of a Fire Investigator

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.

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

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.

Determining Cause

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

Classic V-Shape

Inverted Cone

Protected Area

Clean Burn

Run Down Burn

Ignitable Liquid Pour Pattern

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

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

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.”

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

Arson Even dogs need protective gear.

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.

Escalator Fire Think about the fire pattern that develops.

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.

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

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.

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

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

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

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.

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

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.

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

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

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

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

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

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.