Chapter 17: Forensic Aspects of Fire & Explosion Investigation

Forensic Aspects of Fire & Explosion Investigation provides a comprehensive overview of the forensic protocols and scientific principles governing fire and explosion investigations, beginning with the fundamental chemistry of oxidation and combustion. It explains the thermodynamics of fire, defining critical concepts such as exothermic reactions, energy barriers, and ignition temperatures, while distinguishing between the flash point required for liquid fuels and the pyrolysis process necessary for solid fuels to burn. The text explores the physics of heat transfer through conduction, convection, and radiation, which are essential mechanisms for reconstructing fire spread and locating the point of origin, often identified by specific burn patterns like V-shapes or intense charring at the lowest levels. Significant attention is given to the challenges of arson investigation, particularly the identification of accelerants and the phenomenon of flashover, which can create misleading burn patterns that mimic intentional ignition. The chapter outlines rigorous evidence collection procedures, emphasizing the use of airtight containers like paint cans and the necessity of substrate controls to preserve volatile residues. Laboratory analysis techniques are detailed, specifically the use of headspace analysis and vapor concentration with charcoal strips, followed by gas chromatography and mass spectrometry (GC/MS) to identify hydrocarbon signatures. The discussion then shifts to explosives, categorizing them based on their speed of decomposition into low explosives, such as black and smokeless powders that deflagrate, and high explosives that detonate with supersonic shock waves. High explosives are further divided into ultrasensitive primary explosives used in detonators and stable secondary explosives like dynamite, TNT, RDX, and PETN. The summary also covers the threat of homemade explosives like TATP and ammonium nitrate-based mixtures (ANFO), concluding with bomb scene investigation tactics, including the use of Ion Mobility Spectrometry (IMS) for field screening and confirmatory laboratory tests involving acetone extraction and infrared spectrophotometry.