Effect of reduced ambient pressures and opposed airflows on the flame spread and dripping of LDPE insulated copper wires

Abstract

The effect of ambient pressure on flame spread and insulation dripping of copper-cored, LDPE-insulated wires exposed to opposed airflows was investigated to increase understanding of electrical wire fire hazards in spacecraft environments. Utilized wire samples consisted of 0.64 mm-diameter copper cores surrounded by 4 mm-outer diameter LDPE insulation sheaths. The wire characteristics were selected for comparison with future experiments planned in the International Space Station (ISS) with similar wires. Environmental pressure was varied from sub-atmospheric (40 kPa) to atmospheric (100 kPa). Wires oriented horizontally were exposed to opposed airflows with speeds of 10 or 20 cm/s. Results showed that flame spread rates increase with pressure and decrease with increasing opposed flow speeds. Melted and burning insulation left behind by flame spread dripped with a frequency that increased with pressure; the total mass dripped decreased with pressure. It was also found that lower flows produced more frequent dripping with less total mass dripped, and higher flows produced the opposite. Coincidingly, as the mass of dripped insulation increased, the flame spread rate decreased. Comparison of present results with those from studies with different wire samples show that the effect of environmental parameters on flame spread and insulation dripping depends strongly on core conductivity and core/insulation diameters. Consequently, care should be taken in extending results obtained from specific wire tests to other wires without justification.