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Searching the Fire Scene. The Fire Scene. The arson investigator needs to begin examining a fire scene for signs of arson as soon as the fire has been extinguished. Experience shows that most arsons are started with petroleum-based accelerants.
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The Fire Scene • The arson investigator needs to begin examining a fire scene for signs of arson as soon as the fire has been extinguished. • Experience shows that most arsons are started with petroleum-based accelerants. • The necessity to begin an immediate investigation even takes precedence over the requirement to obtain a search warrant.
Investigation of Fire Scenes Fires are investigated to determine the cause of the fire and its origin 1. Burn Patterns: • Since heat travels upward, pyrolysis occurs in materials above the area of combustion, producing a burn pattern that looks like an “inverted cone” or “V” pattern • The inverted cone is a strong indicator that the point of origin of the fire lies at the point of the cone or base of the V • Locating the point or points of origin is critical to the initial investigation of possible causes of the fire
Investigation of Fire Scenes 2. Search for Causes: • An important objective of the scene investigation is to determine the cause of the fire • Determining the cause of a fire is basically a reconstruction • Accidental causes include electrical short circuit, cooking accidents, and careless smoking
The Fire Scene • Some telltale signs of arson include evidence of separate and unconnected fires, the use of “streamers” to spread the fire from one area to another, and evidence of severe burning found on the floor as opposed to the ceiling of a structure, due to a flammable liquid. • Normally, a fire has a tendency to move in an upward direction, and thus the probable origin will most likely be the lowest point showing the most intense characteristics of burning.
The Fire Scene • Fortunately, combustible liquids are rarely entirely consumed during a fire.
Collection • At the suspect point of origin of a fire, ash and soot, along with porous materials which may contain excess accelerant, should be collected and stored in airtight containers, leaving an airspace to remove samples.
Collection • Traces of flammable liquid residues may be located with a vapor detector (sniffer). • It is important that a sampling of similar but uncontaminated control specimens be collected. • A search for ignitors such as matches, an electrical sparking device, or parts of a “Molotov cocktail” must also be conducted.
