Study on the rule of blister formation and identification technology of multi-cores copper wires in fire

The common presence of the wire blisters in fire indicates that the wire was exposed to fire. Yet current overload happening before fire also causes some wire blisters. Most trace evidences on the wire from fire are required to examine melted blisters marks of the wire. Thus, it is critical to clearly identify and determine the differences between blisters merely exposure to fire and current overload for fire investigators. Two fire scenarios, fire heating and overcurrent, and 2.5 mm2 multi-cores copper wires were selected by this paper to make blisters. Then, the identification technology of blisters was studied. The experimental results suggested that the external appearance and metallographic structure taken on by blisters were not the precise evidences to identify whether blisters are merely exposed to fire or overcurrent. Therefore, the metallographical method of polarized light was used to analyse Cu2O content in blisters. Besides, such content was used to accurately identify two kinds of blisters. The content of Cu2O of the overcurrent blisters was larger than that of the fire heating blisters notably.