doi:10.3850/978-981-08-7724-8_13-05

ABSTRACT

A systematic study of flame spreading on electric cables at low pressure is made experimentally. The main focus of the present study is to investigate the effect of the wire character on the spread behaviour. The cables employed were specially-designed for the present purpose, with a thin-polyethylene (PE) coated over a metal (core) wire. Various combinations of coating thickness, wire diameter, and metal material (NiCr, Fe, Cu) are considered in this study. Pressure is varied in order to modify the preheat process of the unburned cable. Upon the spreading event, a teardrop-shaped flame is formed over liquefied polyethylene (called molten PE), suspended beneath the core wire. The size of the molten PE varies substantially, depending on the imposed pressure condition and wire material. The flame spread rate becomes slower when the diameter of the core wire increases, whereas it becomes faster when a higher conductive material (like Cu) is used. These facts reveal that the metal wire may act in two ways upon the fire behaviour: one assisting the flame spread and promoting the preheating of unburned PE, the other inhibiting the flame spread, to increase the induction time and attain the decomposition temperature of PE. Additionally, the inherent time-dependent behaviour of molten PE during the spread event is confirmed, although the averaged spread rate did not vary much. A quasi-steady flame model is, therefore, necessary to develop an analytical model to predict the flame behaviour theoretically.

Keywords: Flame spread, Electric cable, Low pressure.

© 2011 CPD Unit, University of Leeds