Effects of altitude and inclination on flame spread over poly(methyl methacrylate) slabs

Flame spread experiments over poly(methyl methacrylate) slabs with different inclinations were conducted in Hefei (with an altitude of 29.8 m) and Lhasa (with an altitude of 3658.0 m). It is shown that the flame spreads significantly slower in Lhasa than in Hefei. For steep slabs with inclination angles of 75 degrees and 90 degrees, the preheat length in Lhasa is longer than in Hefei, whereas for mild inclinations (30 degrees and 45 degrees), it is slightly shorter in Lhasa than in Hefei. The peak total heat flux received by the fuel surface is lower in Lhasa than in Hefei. The measured flame temperatures did not present significant difference. This is actually caused by the combined effects of combustion inhibition due to the low oxygen concentration and less soot formation caused by lower ambient pressure and oxygen concentration in the plateau region, which result in less heat loss by radiation. Based on the analysis, it is concluded that the slower spread behavior in Lhasa is mainly a result of the lower heat feedback level to the solid surface.