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INTERPRETATION AND ASSOCIATION OF FIRE SCENE EVIDENCE

المؤلف:  Max M. Houck، Jay A. Siegel

المصدر:  Fundamentals of Forensic Science

الجزء والصفحة:  476-478

2026-08-22

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INTERPRETATION AND ASSOCIATION OF FIRE SCENE EVIDENCE

In a fire scene investigation, there are two major goals: determining the type of fire (e.g., accidental, natural, incendiary) and if the fire was deliberately started, who did it. In most cases, it is not particularly difficult to determine the type of fire. It is much more difficult to determine who committed the crime. Of course, the presence of evidence such as fingerprints, DNA, or trace evidence can be quite useful in determining the identity of the perpetrator. In the absence of such evidence, there is not much else that can provide identification. When the forensic scientist extracts some of the accelerant residue from the matrix using the methods presented above, the resulting chromatogram seldom   looks exactly like the standards made from pure samples of various ignitable liquids. Remember that the accelerant has been in a fire and heat may have evaporated some of the more volatile substances away. There may be contamination by the matrix or other materials present. If the scientist is to report that a class or type of accelerant is present, then there must be a clear majority of characteristic peaks present with few if any unexplainable peaks. For example, examine the chromatogram of gasoline liquid in Figure 1(a). If a real fire residue sample had some of the early peaks missing, that would be explainable by evaporation caused by heat. But if all of the peaks were present at the beginning and end of the chromatogram but some were missing in the middle, then that would be a circumstance that might necessitate a finding of inconclusive or even negative in the report. A negative finding may also be reached even if there are some indications that an accelerant was used. This can occur when there is not enough material to give a good quality chromatogram or when there is too much contamination to identify the necessary peaks. The term weathering is used to describe the degradation of an accelerant due to heat or other environmental factors. It is also important to note that a negative finding in a report does not preclude the presence of an accelerant at a fire. As was pointed out previously, there are several reasons why an accelerant might not be found even it were actually used. It could have been burnt to such an extent that there is not enough left to detect or perhaps the evidence that contained the accelerant residues may have been overlooked. Fire scene investigators always try and take this into account when reaching conclusions about fire causation.

FIGURE 1 Chromatograms of neat (pure liquid) gasoline and kerosene. Note how different the pat terns in the peaks of these chromatograms are. Gasoline is much more volatile as can be seen by the large number of peaks at the beginning of the run.