A Comparative Study of Bench-Scale Flammability Properties of Electric Cables with Different Covering Materials

Cone calorimeter tests were conducted on eight different elec tric cable samples at four different external heat flux levels between 20 and 50 kW/m². Four of the cable samples were sheathed with PVC-based materi als and four with polyolefin-based materials. Some of the cone calorimeter test results were compared with those of the horizontally ventilated laboratory-scale gallery fire test and the oxygen index test which had been previously conducted on these samples. From the ignitability data in the cone calorimeter test, these cable samples were considered to be thermally thick materials. The ignition times of the cables sheathed with a PVC-based mate rial were shorter than those of the cables sheathed with a halogen-free poly olefin. In addition, the heat and smoke release properties of the cable samples also depended mostly on the type of the main base polymer of the sheath ma terial. The correlations between the flame propagation property in the duct fire test and the peak heat release rate in the cone calorimeter test were un clear. On the other hand, there appeared to be relatively good correlations be tween the minimum O₂ and maximum CO₂ concentrations in the exhaust gas in the duct fire test and the peak heat release rate in the cone calorimeter test. Moreover, a considerably good nonlinear correlation between the limiting oxygen index and the peak heat release rate in the cone calorimeter test on the cable samples, particularly at the relatively low external heat flux level of 20 kW/m², was shown.