Forensic workflow for residue recovery from oversized post-blast exhibits in anfo detonations

Post- blast investigations involving ammonium nitrate fuel oil (ANFO) often generate oversized debris with irregular surfaces, complex matrices, and uneven residue distribution, limiting the effectiveness of conventional forensic recovery methods. This study proposes a workflow-centred forensic approach specifically designed for residue recovery from oversized post-blast exhibits following ANFO detonations. The workflow emphasises structured surface coverage through spatial subsampling, sequential solvent swabbing, and syringe filtration to mitigate heterogeneity and matrix-derived interference prior to instrumental analysis. Organic and inorganic residues recovered through this process were examined using thin-layer chromatography (TLC), gas chromatography–mass spectrometry (GC–MS), classical chemical tests, and Fourier-transform infrared (FTIR) spectroscopy. The analytical results served primarily to evaluate workflow performance rather than to introduce new chemical signatures. Diesel-range hydrocarbons and nitrate-based oxidisers, including ammonium and potassium nitrate, were consistently identified, while chlorates, perchlorates, and metallic additives were absent. Spatially informed sampling improved representative residue collection across large surfaces, and syringe filtration enhanced extract cleanliness and analytical stability. The study demonstrates that adapting forensic procedures to the scale and heterogeneity of post-blast exhibits is critical for reliable residue recovery. The proposed workflow offers a reproducible and casework-oriented framework for forensic laboratories handling oversized debris in ANFO-related explosive investigations.