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Process of Investigation
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Process of Investigation
1. Identification of initial fuel: In a collision fire investigation, each fluid system must be examined for collision damage and resultant leakage. In a non-collision fire investigation, odors, service history or pavement stains where the vehicle is typically parked may provide supporting information about the leakage of specific fluids, and therefore their availability for fire (to see an Interview check list, click here). Witness descriptions of the fire and burn pattern may also help differentiate between fluids in selecting those possible for fire origination.
2. There are additional material properties not covered in the tables provided in this course material, such as the energy available in a given volume of the fluids (heat of combustion). In the absence of meaningful test data, the authors will present anecdotal reports of testing and experience. This information can be used to assist in differentiating between fuels in an investigation.
Gasoline: Most researchers found gasoline difficult to ignite on a hot surface such as an exhaust manifold, particularly one without shielding that may harbor vapors. However, once ignited, a gasoline fire burns with an intensity greater than many of the other fuels and tends to propagate quickly. [1]
In the Ignition section there is a case study of a gasoline pool fire that spread quickly and blocked occupant egress. To see it now, click here.
Engine oil, power steering and transmission fluids: These lubricants tend to ignite readily on hot surfaces and by spark ignition. The authors have also observed instances in which these fuels were able to sustain a small fire for some time prior to propagation. When present adjacent to a hot surface, these fluids have also been observed to re-start readily after being extinguished.
Coolant: In tests of shielded manifolds, coolant was observed to readily ignite on hot surfaces. However, the resultant ignition sometimes burned the available vapor cloud quickly without propagating to other materials. Coolant apparently was not likely to sustain a small, stable flame in the manner of lubricants, and is thus considered less likely to propagate a fire.
3. Trends: Autoignition temperatures vary by many factors. While no single autoignition temperature value can be cited for a fluid, there are trends that can be relied upon. a) The minimum autoignition temperature measured using the ASTM procedure can be considered the lowest value probable. [2, 3] b) Autoignition temperatures in vehicle environments are likely to be much higher than the ASTM values. [2] c) To estimate the autoignition temperature in a given circumstance, it is helpful to review the range of values measured in tests of various conditions. d) Air flow increases the autoignition temperature. [4] e) Geometry that increases residence time decreases autoignition temperature. [3]
4. Fires are relatively infrequent events requiring the alignment of specific conditions. If a defect is suspected to be the cause of fire for a vehicle in a fleet, one would expect to find many such defects in similar vehicles that have not had a fire. As part of the investigation, one should study similar vehicles for their history related to the suspected problem.
5. Assessment of a liquid as the initiating fuel for a fire must be made while simultaneously considering the ignition sources available. Ignition sources are covered separately in the course (see the Ignition section in the index on the left of the screen, or read ahead with the "next" button to reach the section later in the course).
References
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