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Forensics Arson. VOC. To know. Flash point- the minimum temperature at which a liquid fuel will produce enough vapor to burn Glowing combustion- or smoldering; fuel burning without the presence of a flame ex: red hot charcoal or burning cigarette
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VOC. To know • Flash point- the minimum temperature at which a liquid fuel will produce enough vapor to burn • Glowing combustion- or smoldering; fuel burning without the presence of a flame ex: red hot charcoal or burning cigarette • Ignition Temperature- the minimum temperature at which a fuel will spontaneously ignite
Occurrence and Prominence • Arson is usually treated as a low profile crime/occurrence and as a result the budget for it’s detection may be small. • Arson can become high profile if it involves civil rights/religious issues or becomes serial in nature.
Arson Three requirements needed for combustion to be initiated and sustained: • Fuel must be present • Sufficient oxygen must be available to combine with fuel • Heat must be applied to initiate the combustion and sufficient heat must be generated to sustain the reaction
Features of a combustion fire • Combustion is a chemical reaction where compounds are oxidized (combined with oxygen) • Fuel such as gasoline, kerosene, or wood. The vapor is actually under going combustion. • Oxygen found in the atmosphere or the oxidizing agent (a compound containing oxygen) is usually the limiting reactant • Source of Ignition could be a match, spark, sunlight, gunshot, or electrical spark
Arson Accidental causes of fire include: • Cigarette smoking • Overheated electrical motors • Improperly cleaned and regulated heating systems • Faulty wiring
Arson A criminologist needs to detect and identify relevant chemical materials collected at the scene and reconstruct and identify detonating mechanisms.
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 It is difficult to obtain evidence from a fire because of extensive destruction.
Searching a Fire Scene • Fire officials are charged with not only extinguishing a fire, but with finding their cause. • For this reason, fire officials need no warrant to enter a building due to a blaze nor to stay for a reasonable amt. of time after it has been extinguished. • They may also seize evidence without an warrant.
Arson Search for traces of flammable liquid residues may be aided by the use of a highly sensitive portable vapor detector or a “sniffer.”
Arson Another approach is to use trained dogs that have been conditioned to recognize the odor of hydrocarbon accelerants.
Arson Even dogs need protective gear.
Difficulties • So much evidence is destroyed • Evidence is transformed • Water, water, water • Destruction and alteration of structures • Perpetrator is usually long gone
There are several clues from fire to show evidence of arson: • Multiple points of origin • Strange odors • Accelerant soaked rags will keep the fire low or localized, not traveling up as usual • Streamers occur as the path of accelerant burns more deeply • Extensive regions of low burn ( normally extensive burning will be higher rather than lower • Faster and hotter fire than would be expected. • Doors, windows left open to insure oxygen supply • Empty containers of accelerants, time delay devices, and other items left by the perpetrator
Arson At a crime scene, nothing should be touched or moved before notes, sketches and photographs are made.
Arson 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.
Collection and Preservation of Evidence Two to three quarts of ash and soot debris should be collected from the point of origin, and sealed in an airtight container, such as paint can.
Collection and Preservation of Evidence Con’t • Plastic polyethylene bags are not suitable packaging because they react with hydrocarbons and will permit volatile hydrocarbon vapors to be depleted. • Along with collecting materials suspected of containing volatile chemicals, a substrate control , an uncontaminated specimen from another area of the fire scene, must be collected to reduce the possibility of argument that the carpet, etc. was exposed to flammable liquid such as cleaning supplies as normal maintenance
Lab tests may also be needed on unburned material to analyze the breakdown of products arising from the fire’s intense heat due to the fact that common materials have been known to produce volatile hydrocarbons when they are burned.
Catching the perpetrator • Matches have been matched back to a match book belonging to the perp. • If an individual is arrested within a few hours of the fire, residual quantities of the accelerant may still be present in the clothing. • Each item of clothing should be placed in a separate air tight container such as a clean paint can
Arson 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. The picture shows the point of origin to be the computer.
Arson Investigators follow the V-shaped burn pattern down to locate the point of origin.
Arson The depth of wood charring, or alligatoring (The formation of cracks on the surface of paint layers), is also a good indicator of point of origin.
Temperature and Speed • 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. • A fire line and pattern can point to the source of the fire.
Analysis of flammable residues • Easiest way to recover accelerant residues from debris is to heat the airtight container in which the sample was sent to the lab in. • When the container is heated, any volatile residues present will be driven off and trapped in the containers airspace. • The vapor is then removed with a syringe and injected into a chromatograph, where it is separated into its components and recorded on a chromatogram to be compared to patterns of known petroleum products. • A disadvantage- size of syringe limits the volume of vapor collected
A second method of analysis • Vapor concentration- • a charcoal–coated strip is placed within the container holding the debris • The container is then heated to 60°C for about one hour • The charcoal will absorb the accelerant vapor, collecting a significant quantity • The analyst will then remove the strip and recover the accelerant by washing it with a small volume of carbon sulfide. • The solvent will then be injected into a gas chromatograph for analysis
Arson Arsonist cause fires at different locations for different reasons.
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 *Males fit the profile of an arsonist
Arson 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.
