Arson and Explosion Investigations Arson Facts 75,000 structure fires were deliberately set or suspected of having been deliberately set, an increase of 4.2 percent from a year ago, and 14.8 percent of all structure fires. Incendiary or suspicious structure fires also resulted in $1.340 billion in property damage. This is a 15.7 percent representation of all structure property loss. Incendiary or suspicious structure fires killed 505 civilians (non- firefighters), an increase of 36.5 percent from 1999. There were 46,500 incendiary or suspicious vehicle fires, a 3.3 percent increase from a year ago. Source: Fire Loss in the United States During 2000, NFPA, 09/01 Arson And Explosion Arson and Explosion Investigations present the investigator with difficult circumstances to investigate committed at the convenience of the perpetrator who has time to thoroughly plan the criminal act and has had time to leave the scene Proof of the offense is more difficult to obtain due to extensive destruction of the scene and evidence Criminalist is one of many who investigate along with chemists, arson investigators, etc. criminalist trained to identify and detect chemical material collect and reconstruct and identify igniters or detonating mechanisms Cause of Fire Chemist tries to identify trace amount of gasoline or kerosene in debris chemist cannot identify if paper or cigarette were to start fire no way to scientifically test these Fire can have accidental causes that will not leave chemical trace evidence faulty wiring overheated electric motors cigarette smoking All require extensive on site investigation CHEMISTRY OF FIRE Fire is a transformation process where oxygen is united with other substance to produce noticeable quantities of heat and light (flame) Part of a chemical reaction Oxidation is the combination of oxygen with other substances to produce new substances CHEMISTRY OF FIRE Chemical equation for the burning methane gas, a major component of natural gas: CH (4) + 2 O (2) CO (2) + 2 H(2) O Methane + oxygen yields carbon dioxide + water Rust is another example of oxidation Chemical equations do not give us a complete insight into oxidation process NRG Other factors must be taken into consideration Especially to consider fire We know that when methane unites with oxygen, it burns, but the mere mixing of methane and oxygen will not produce a fire nor will gasoline burn when exposed to air We need a match, or a spark We need energy energy is defined as the capacity for doing work. NRG energy can take many forms heat energy electrical energy mechanical energy nuclear energy chemical energy When Methane is burned the stored chemical energy in methane is converted to energy in the form of light and heat. This heat can boil water to provide high-pressure steam to turn a turbine. (example of converting chemical energy to mechanical energy) The turbine is used to generate electricity transformation from mechanical to electrical energy. Electrical energy is then used to turn a motor energy can enable work to be done- heat is energy Combustion Combustion is the rapid combination of oxygen with another substance accompanied by the production of noticeable heat and light These reactions are said to be exothermic A chemical transformation in which heat energy is liberated These reactions usually posses what is referred to as a energy barrier Ignition Temperature Ignition temperature, is the minimum temperature at which a fuel will spontaneously ignite Once combustion starts the heat energy given off is usually enough to keep the reaction going The fire will continue to burn until either the supply of oxygen or the fuel is exhausted Combustion 3 requirements for combustion 1) fuel must be present 2) oxygen must be available in quantity to combine with fuel 3) heat must be applied to initiate the combustion, and sufficient heat must be generated to sustain the reaction Searching The Fire Scene Its important to search the scene for arson as soon as the fire has been extinguished Most arsons are started with petroleum-based accelerants such as gasoline or kerosene. If petroleum residues remain after extinguishments, they may evaporate within days or hours Search must focus on finding the fire’s origin- look for accelerant or ignition device at site of origin May be evidence of unconnected fires or use of ―streamers‖ to spread fire -- -pour trail of gasoline to cause fire to move from room to room Searching The Fire Scene Look for signs of breaking and entering and theft- interview eyewitnesses FIRE’S ORIGIN- fire moves in upward direction- therefore, origin will be located to lowest point that shows the most intense characteristics of burning Many deviations will look different---Drafts and winds or secondary fires from collapsed floors or ceilings, stairs, holes in floor, roof, etc Flammable liquids always flow to the lowest point- more severe burning on floor than on ceiling indicates presence of Containers holding accelerant- or time delay device of accelerant. Searching The Fire Scene Point of origin must be protected- do not touch or move before notes, photographs, etc. In most arson cases- will find accelerants- gas, kerosene, diesel. Not all combustible liquids can be consumed during a fire- when poured on a surface, fuel will seep into porous surface- cracks in the floor, upholstery, plaster, wallboards, carpet- often protected and detectable. Searching The Fire Scene When fire is extinguished with water- rate of evaporation is slowed- water cools and covers materials- preserving for lab. Search of arson scene –arson investigators may use portable vapor detector- sniffer- used to detect accelerant as air is passed over heated filament- if combustible vapor is present, it oxidizes and immediately increases temp of filament- rise in filament temp registers on detector’s meter Also use of dogs trained to recognize odor of hydrocarbon accelerants. Collection and preservation of Arson Evidence At scene, 2-3 quarts of ash and soot debris must be colleted at the point of origin Collection should include all porous materials- wood flooring, rugs, upholstery Immediately packaged in airtight containers so no loss can occur through evaporation- most use clean paint cans- airtight and unbreakable- or glass jars. Cans and jars should be packed ½- 2/3 full-leaving air space in the container above debris Collection and preservation of Arson Evidence Plastic bags are not suitable for packing- they react with hydrocarbons and permit volatile hydrocarbon vapors to be depleted Important to collect materials at origin, but must also collect uncontaminated control specimens from other areas of fire scene- known as SUBSTRATE CONTROLS. Samples that are the same same; carpet, wood types, etc.—unburned is best. Collection and preservation of Arson Evidence Plastic floor tiles, carpet, linoleum and adhesive s can produce volatile hydrocarbons when burned. these could be mistaken for accelerant. Often overlooked by arson investigators is clothing of the suspect perpetrator clothing will hold residual quantities of accelerant in clothing Analysis of Flammable Residues Gas chromatography is most sensitive and reliable instrument for detecting and characterizing flammable residues Arson uses petroleum distillates such as gasoline- liquids are actually composed of complex mixture of hydrocarbons. Gas chromatograph separates the hydrocarbon components and produces chromatographic pattern characteristic of a particular petroleum product Analysis of Flammable Residues Best way to recover accelerant residues is heat airtight container When container is heated- volatile residues will be driven off and trapped in the container’s enclosed air space. Vapor or ―headspace‖ is removed with a syringe and injected into gas chromatograph Analysis of Flammable Residues Separated into components- each peak is recorded with chromatogram identity of volatile residue is determined by pattern of chromatogram compared to patterns produced by known petroleum products Alternative to headspace technique is ―vapor concentration‖ that uses charcoal-coated strip to collect vapors.
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