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Ignition and spread of electrical wire fires


Ignition of electrical wires by external heating is investigated in order to gain a better understanding of the initiation of electrical-wire fires. An ignition-to- spread model is developed to systematically explain ignition and the following transition to spread. The model predicts that for a higher-conductance wire it is more difficult to achieve ignition and the weak flame may extinguish during the transition phase because of a large conductive heat loss along the wire core. Wires with two metal-core materials, nichrome and copper having three different diameters, with polyethylene coatings of three different thicknesses are employed and a coil heater was adopted as the ignition source in the experimental study. Experiments show that additional heating times after flash are required in order to fully pass the transition and achieve a spreading flame, agreeing with model predictions. In addition, the effects of different heating lengths, ambient pressures and oxygen concentrations on wire ignition are discussed. Steady flame spread horizontally along thin electrical wires in normal and oxygen-enriched oxygen/nitrogen atmospheres is also investigated both theoretically and experimentally to gain a better understanding of the development of in electrical fires occurring in normal and modified environments. A simplified flame-spread model is developed in an effort to identify the most important effects of the wire thermal conductivity and diameter, the thickness of the insulation, and the oxygen concentration. The experimental results agree qualitatively with the model predictions in a number of respects, while no qualitative disagreements were found. This study may be useful for upgrading the design and standards of future fire-safe wires

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