Interpretation of fire debris analysis

Once ignitable liquid residues (ILRs) have been extracted from a fire debris sample and analyzed through gas chromatography–mass spectrometry, the most complex step of fire debris analysis, the interpretation of the results, must be conducted. Because ignitable liquids (ILs) are extremely diverse and composed of many compounds over a wide boiling point range, they are arranged in eight classes (gasoline, petroleum distillates, naphthenic paraffinic, isoparaffinic, aromatic, n-alkanes, oxygenated solvents, and miscellaneous) and three subclasses (light, medium, and heavy). For each class, characteristic patterns exhibited by the liquids are available, aiding in the interpretation of the chromatograms.

While the interpretation is quite straightforward for neat ILs, it becomes relatively complicated with ILR from fire debris samples. In this case, not only is the original composition of the IL weathered, diminished, and degraded, but also other products, called interfering products, are coextracted. These products include precursory products (compounds already present in the substrate prior to the fire), pyrolysis products, combustion products, and fire suppression products. Therefore, in order to properly interpret the chromatographic pattern, the fire debris analyst must take into account the nature of the substrate and the environment in which it was recovered.