Visual and oxide analysis for identification of electrical fire scene

•By visual and microstructure/metallographic analysis to determine the cause of fire.•The mechanism relies on the morphology, micro-structure and chemical composition.•It is possible to correlate fire cause with morphologies and nonmetallic elemental.•The truth will hopefully ease the way for future cases. Three aluminum wires with different melted mark, which were found inside a burned distribution board from the electrical fire debris in rural areas of Northeast China were characterized to determine the cause of fire. By visual and microstructure/metallographic analysis, one melted bead shows typical morphology (microstructure/characteristics) as a result of overheating or electric short circuit (ESC) arc beads which was identified as the most possible ignition source. The macro-/micro-structure of the metallic wire, the chemical composition of the beads surface and the state of the polymer insulating sheath combining the tension state of the electric wire provided solid evidence on the exposure temperature and time of each aluminum wire. Consequently, the fire source was identified. Therefore, the characterization on the macro-/micro-structure and chemical composition of metallic surface with scientific technique is greatly helpful in determining heating process of metallic parts and subsequently the cause of fire.