Abdul-Karim, N; (2015) The Spatial Distribution of Post-blast Condensed Phase Explosive Residues. Doctoral thesis , UCL (University College London).

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Abstract

During bomb scene investigation the collection of trace explosive residue is a principal forensic task which allows the cause of the explosion to be determined. However the optimum locations around a detonation from where these undetonated trace residues should be sampled has not been determined scientifically. Crime scene investigation guides describe several methods for collecting and analysing explosive residues, but literature regarding the most efficacious areas to sample from is relatively scarce. In this thesis, analysis of the spatial distribution patterns of post-blast explosive residues from detonation and simulation experiments with 0.5 kg, 1 kg and 2 kg aluminised ammonium nitrate and RDX composition charges are the primary original contributions to the literature. Residue samples were collected by swabbing sample sites positioned around the explosive charges and condensed phase particles were collected onto smaller sample sites in order to ascertain the physical morphology of the residues. Both organic and inorganic residues ultimately decreased in concentration nonlinearly with increasing distance from the charge centre. However, the distribution trends between different explosive analytes varied, suggesting the dispersal mechanisms or factors which affected the distribution for each were different. The post-blast particles had varying morphologies at different distances from the detonation and also exhibited different features based on the explosive type. Computational simulations of residue distributions compared well to the experimental results; substantiating the capability of numerical methods to be used as a forensic investigation aid. The key findings from this thesis have provided empirical evidence which validates the current forensic practice of concentrating trace evidence collection near the central region of a detonation area during bomb scene investigation. The findings also imply that surfaces which are downwind of the detonation should be focused on for residue sampling and that microscopic examination of items in the vicinity of a detonation may allow identification of the explosive used based on particle morphology, prior to any chemical analyses. Furthermore, having demonstrated the reliability and capability of simulation techniques to model explosive residue distribution, these can now be developed and validated through further tests which also assess the detonations of further explosives under different conditions.

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