Investigation And Characterization Of Interfering Pyrolysis Products Of Wood Debris In Fire Arson Analysis

Abstract

Laboratory identification of flammable products in fire debris is vital in crime scene investigations. Debris collected from a fire scene is intricate and contains background compounds from the substrate material and pyrolysis products that arise from combustion and pyrolysis of the material produced in the fire. Effective isolation of the target compounds from the pyrolysis products is one of the main problems encountered by forensic scientists in any fire arson analysis. This study focused on interference caused by pyrolysis products of wood debris. The main objective was to investigate and characterize selected pyrolysis products of wood debris in fire arson analysis. Mahogany, Medium Density Fiberboard, chipboard and block board were pyrolyzed using a muffle furnace at a controlled temperature of 350 °C and 450 °C for thirty minutes. The sample analysis was done in triplicates to establish reproducibility. The interfering pyrolysis products obtained ranged from straight chained aliphatic hydrocarbons to highly fused aromatic hydrocarbons. These hydrocarbons were found to elute at retention times similar to certain specific target compounds of gasoline and diesel. However pyrolysis products of chipboard showed very little interference with Ignitable Liquid residues (ILR) of diesel and gasoline. Chromatographic analysis based on retention time of the compounds eluted revealed possible conflicts between some of the pyrolysis compounds and the target ILR compounds of gasoline and diesel. Some of the compounds in diesel, for example 17-pentatriacontene, were found to be present in the pyrolysis compounds. The % abundance of these pyrolysis products in the samples were determined and compared with the % abundance of the target compounds in gasoline and diesel. The % abundance of the pyrolysis products were higher than the target compounds of gasoline and diesel hence possible shielding of the target compounds during analysis. The presence of pyrolysis products makes it difficult to elucidate and analyze the vi chromatograms effectively hence may lead to false positive interpretations. On the other hand, a false negative conclusion may be reached if the pyrolysis compounds are not known hence disregarding compounds originating from ILR. Therefore Creation of databases of pyrolysis products and ILR are important. Further studies are recommended on clean wood samples to set a database of their pyrolysis and interfering products. Keywords: Pyrolysis, fire, debris