Fire behaviors of flame-retardant cables part I: Decomposition, swelling and spontaneous ignition

Electrical cable is a potential ignition source and fire hazard in residential houses, nuclear power plants, aircraft, and spacecraft. In this work, a bench-scale flame-retardant cable, consisted of the outer PVC sheath, middle XLPE insulation, and inner copper core, was heated uniformly inside a novel cylindrical heating chamber. The applied heat flux was transient, which increased with time close to a parabolic function. Once heated, the outer PVC sheath swelled and shrank under multiple stages. Before ignition, the swelling behavior was found to follow the same trend as the mass-loss rate. Analysis showed that the observed spontaneous ignition was likely a result of pyrolysis gas from inner XLPE insulation piloted by the smoldering hot spot (600 similar to 700 degrees C) on the outer charring PVC sheath. For the first time, the spontaneous ignition time was found to linearly increase with the integral heat flux, and it was different from other ignition experiments under the transient heat flux in the literature. Moreover, the measured critical mass flux of ignition increased with the heating power, and the critical surface temperature of PVC was above 500 degrees C. The results of this work provide important information about the swelling and ignition behaviors of the flame-retardant cable under a real fire, and may guide the design of future fire-safety cable.