Study of Diesel Residues from Fire Debris in a Bus Arson Experiment

In suspicious bus arson cases, what is important to evaluate the fire behavior and conduct fire investigations is to simulate bus arson and perform chemical analysis on ignitable liquids in fire debris. In this study, a bus fire test has been carried out to investigate the effect of diesel on the development of a bus fire and to ensure the suitability of analytical methods. The commercial bus was equipped with several rows of foam seats, and the diesel was applied under one of the seats. The fire growth and the heat release process were determined during the experiment. Meanwhile, the analytical studies on fire debris were carried out immediately after fire extinction. Solvent extraction and headspace extraction, followed by gas chromatography-mass spectrometry, were used to analyze potential diesel substances in fire debris samples, respectively. Three samples obtained from residual liquid, seat, and soot with varied matrix interferences were analyzed and the detectability of diesel was demonstrated as well. The results show that the time to flashover is only 65 s and the peak HRR reaches about 949 kW. The relative content of alkylbenzenze becomes more than that of alkane after fire. It is possible to provide evidence of ignitable liquids in all samples. For the solvent GC-MS tests, the matrix interferences have a strong effect on the test results. The solvent GC-MS is more suitable for the detection of ignitable liquids in samples with relative weak interferences (e.g., soot). While, the headspace GC-MS is prior to analyze the samples with heavy interferences which can give the evidence of the volatile substances of diesel more specifically.