Arson Investigation - Arson and by fjhuangjun

VIEWS: 265 PAGES: 21

									Arson and Explosion
                          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
       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
                          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
   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 +
   Rust is another example of oxidation

   Chemical equations do not give us a complete insight
    into oxidation process
   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.
   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 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

   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
       The fire will continue to burn until either the
        supply of oxygen or the fuel is exhausted

   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

   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
   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
       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,

   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
       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
Analysis of Flammable Residues
   Gas chromatography is most sensitive and reliable
    instrument for detecting and characterizing flammable

   Arson uses petroleum distillates such as gasoline- liquids
    are actually composed of complex mixture of

   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.

To top