Forensic Workflow for Residue Recovery from Oversized Post-Blast Exhibits in ANFO Detonations

Background: Post-blast forensic investigations frequently involve oversized debris such as concrete and metallic fragments, where heterogeneous residue distribution and complex surface matrices complicate explosive residue recovery. Conventional extraction techniques optimized for small and homogeneous samples often prove inadequate for such exhibits, resulting in reduced sensitivity and interpretative uncertainty. This study addresses these challenges by developing and validating an integrated residue recovery workflow specifically tailored for oversized post-blast exhibits associated with ammonium nitrate fuel oil (ANFO) detonations. Results: Oversized exhibits were examined using a combined approach incorporating sequential solvent swabbing, spatial subsampling, and syringe filtration. Organic residues were analyzed by thin-layer chromatography (TLC) and gas chromatography–mass spectrometry (GC–MS), while inorganic residues were characterized using classical chemical spot tests and Fourier-transform infrared (FTIR) spectroscopy. GC–MS analysis confirmed the presence of high-boiling petroleum hydrocarbons consistent with diesel fuel fractions, and inorganic analyses identified nitrate-based oxidizers, including ammonium and potassium nitrate. Chlorates, perchlorates, and metallic additives were not detected. Spatial subsampling improved trace residue recovery from heterogeneous surfaces, while syringe filtration significantly reduced background interference and enhanced analytical clarity. Conclusion: The integrated workflow demonstrated reliable and reproducible recovery of both organic and inorganic ANFO residues from oversized post-blast debris. The combined application of spatial subsampling, sequential swabbing, and syringe filtration enhanced analytical sensitivity and forensic interpretability in complex detonation scenarios. This validated approach provides a practical and adaptable framework for forensic laboratories handling large, heterogeneous post-blast exhibits and strengthens the chemical basis for reconstructing ANFO-related explosive events.