Integrated analytical workflow for the identification of vegetable oil residues in fire debris

Industrial fires involving oil-contaminated waste materials represent a growing forensic challenge, particularly when conventional ignition sources are absent. This study reports a real-case investigation of multiple fire incidents at a waste receiving and recycling company in Jebel Ali, Dubai, where the ignition origin was linked to stored oil-soaked fabrics. A multidisciplinary analytical approach combining Fourier Transform Infrared Spectroscopy (FT-IR), Gas Chromatography-Mass Spectrometry (GC–MS), and Micro X-ray Fluorescence (μ-XRF) was employed to characterize the residues and determine the source of ignition. FT-IR analysis of the oil extracted from the fabrics revealed strong absorption bands corresponding to long-chain fatty acids, particularly oleic acid, suggesting an organic origin inconsistent with the company's claim of recycled motor oil. GC–MS profiling following hexane and ethyl acetate extraction, as well as derivatization with BSTFA, identified diagnostic vegetable-oil-derived compounds including linoleic, oleic, and palmitic acids, along with phytosterols such as β-sitosterol, γ-sitosterol, and campesterol. Comparison with eight reference vegetable oils confirmed a close compositional match to linseed oil, a drying oil with high oxidative reactivity and a well-documented tendency for self-heating. Complementary μ-XRF analysis detected several transition metals such as Fe, Zn, Cr, and Ti, which are known to catalyze lipid oxidation and promote exothermic reactions leading to spontaneous ignition. Collectively, the chemical and elemental results provided consistent evidence that the fire originated through self-heating of linseed-oil-contaminated fabrics. This case highlights the need to expand forensic fire debris protocols to include biological and plant-based oil residues and demonstrates an effective analytical workflow for distinguishing between petroleum and vegetable oil derived contaminants in complex industrial fire scenes. These results support updating fire investigation protocols to screen oily textile debris for drying-oil markers and catalytic metals to strengthen origin determination. • First documented forensic case in the UAE confirming spontaneous ignition of linseed oil-soaked fabrics, expanding regional understanding of industrial fire origins. • Introduced a novel multidisciplinary analytical workflow combining FT-IR, GC–MS (with derivatization), and μ-XRF for comprehensive fire debris analysis. • Identified vegetable-oil-specific markers such as linoleic, oleic, and palmitic acids and phytosterols (β-sitosterol, γ-sitosterol, campesterol) to differentiate plant-based oils from petroleum products. • Applied μ-XRF to detect catalytic transition metals (Fe, Zn, Cr, Ti) in residues, an innovative step linking elemental profiles to spontaneous ignition risk. • Established a forensic screening framework for non-petroleum-based accelerants, calling for updates to global fire debris protocols to include biological and plant-based oils.