Horizontal Flame Spread Characteristics of Rigid Polyurethane and Molded Polystyrene Foams Under Externally Applied Radiation at Two Different Altitudes

Abstract

To investigate the characteristics of horizontal flame spread over two kinds of typical insulation materials (rigid polyurethane and molded polystyrene foams) under externally applied radiant flux, a series of laboratory-scale experiments are conducted on the Tibetan plateau (at an altitude of 3,658 m) and in the Hefei plain (at an altitude of 30 m) in China for comparisons. The external radiation intensity ranges from 1.0 kW/m2 to 4.5 kW/m2. The temperature distribution in the solid and gaseous phase and the flame spread rate under different external radiations are examined. The different flame spread behaviors of rigid polyurethane and molded polystyrene foams are scrutinized. The rates of flame spread over the two different materials in the plain are larger than those on the plateau at the same external radiant flux. At both altitudes, the flame spread rate increases with the increasing external radiation intensity. And the square root of the reciprocal of flame spread rate vf−1/2 has a negative linear relation with the external radiation intensity, which is consistent with the predictions of prior theory. The calculation of theoretical value of parameter C is 0.039, which is nearly the same as the slope of fitting line. The mechanism of heat transfer during the flame spread process is analyzed in detail, and the simplified expressions of flame spread rate of the two insulation materials under external applied radiation are achieved.