Fire Investigator
Chapter 15: Origin Determination
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· The fire’s area of origin refers to the room, building, or general area where the point of origin is located. The point of origin is the exact physical location where a heat source and a fuel come into contact with each other and a fire begins.
· The methodology recommended for examination of a fire scene includes an initial scene assessment, development of a preliminary fire spread hypothesis, an in-depth scene examination, reconstruction of the fire scene, and development of a final fire spread hypothesis.
· Care should be taken to limit damage to any potential ignition sources, initial fuels, or other important evidence identified during excavation of the scene.
· Persons familiar with the involved structure (e.g., owners, occupants, workers, neighbors) can provide information regarding the type and placement of contents, general conditions or alterations to the structure, fire protection systems, and so forth.
· The origin hypothesis should explain not only where the fire started but how it spread throughout the structure, and the hypothesis must be supported by the evidence (data) gathered through the fire investigation process.
· The fire patterns present after suppression represent what is left of all patterns recorded during the life of the fire.
· Consistency of the method of measuring char depth is critical to generating reliable data.
· Arc mapping is a technique in which the investigator uses the identification of locations of electrical arcing to aid in determining the area of origin and is based on the predictable behavior of energized electrical circuits exposed to a spreading fire.
· Once the origin hypotheses have been tested, only one hypothesis should survive the testing.
· The inability to identify the point or area of origin does not, in and of itself, preclude a valid determination of cause.