Fire Debris Analysis
Contributed by Michael A. Trimpe; Dana Greely; and Emily Weber
Fire investigators search a fire scene to determine the cause and origin of a fire. If the cause of the fire appears suspicious the investigators may collect debris from the origin of the fire for analysis in the forensic laboratory. The debris is typically porous material in which an ignitable liquid could penetrate and remain even after an intense fire. Ignitable liquids are mixtures of volatile chemicals usually distilled from petroleum. Due to their volatility, ignitable liquids can easily evaporate. Therefore, samples must be collected in airtight containers for submission to the laboratory.
The forensic analyst carefully extracts the vapors from the container and concentrates them in a way that can be analyzed by gas chromatography and mass spectrometry. The gas chromatograph separates the chemicals into a pattern that can be compared to known ignitable liquid standards. The mass spectrometer allows for identification of the individual chemicals within the mixture. These techniques and instrumentation are very sensitive and can detect vapors of ignitable liquids that may not even be detected by the human olfactory senses. The technique also allows for an experienced analyst to differentiate between ignitable liquids and the matrix materials often present in fire debris samples.
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2. Kirk’s Fire Investigation, DeHaan, John, Brady Publishing, Prentice-Hall, 5th Edition, 2002, ISBN: 0-13-060458-5
3. ASTM E 1412-12, “Standard Practice for Separation of Ignitable Liquid Residues from Fire Debris Samples by Passive Headspace Concentration With Activated Charcoal,” ASTM International.
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