Evaporation of Ignitable Liquid Residues in Soil

Dan Muller, Ignitable liquids, Explosives and Poisons Lab, DIFS Israel Police, Jerusalem, Israel (dmarson@police.gov.il)
Yonit Kasherman, Ignitable Liquids, Explosives And Poisons Lab, Difs Israel Police
Gilad Shafir, Ignitable Liquids, Explosives And Poisons Lab, Difs Israel Police
Erez Stier, Serious Crimes Unit, Difs Israel Police, Jerusalem, Israel
Sarit Kimchi, Ignitable Liquids, Explosives And Poisons Lab, Difs Israel Police
Yaniv Avissar, Ignitable Liquids, Explosives And Poisons Lab, Difs Israel Police

The sample collected from a scene of a suspected arson subsequently analyzed by a laboratory provides important information to the fire investigators regarding the presence/or absence of ignitable liquid residues. Ignitable liquids are volatile compounds that need to be separated from  the sample  matrices, therefore, the most popular sample preparation techniques are headspace sampling followed by injection to GCMS. The GC-MS data is first examined as the total ion chromatogram (TIC) pattern and comparing it with a reference standard data. Then, the analyst uses a combination of pattern and extracted ion chromatography (EIC) in order to identify the used accelerants. Gasoline is the most common accelerant but other fuels, including lighter fluids, charcoal lighter, paint thinners or diesel fuels are not uncommon. These products contain hundreds of compounds in relatively broad boiling ranges. Therefore, the effect of environmental stressors (exposure, heat) can result in notable changes in the accelerant composition. Compounds with relatively low boiling point evaporate at a higher rate than less volatile compounds. As a result, the chromatographic pattern of the less volatile compounds will be amplified. This change, results in a shift of the chromatographic pattern towards higher boiling compounds. The GC data for fresh ignitable liquid can be significantly different from that of evaporated, therefore, the use of adequate evaporated reference material is essential for comparison and matching. In the study, the evaporation of gasoline as a function of adsorption time into three different kinds of soils was performed resulting in a significant difference between the types of soils. These findings aid the fire investigator to collect the best possible soil according to the elapsed time since the fire, and to evaluate the exact sampling location at the crime scene to achieve successful analysis in the laboratory.