Experimental Dimension and Boundary Analysis of Upward Flame Spread Over U-Shaped Facade in Energy-Saving Building Fires

Insulation layer is usually used in building facade for energy-saving design, and it also endangers the human safety in buildings due to its combustibility. U-shaped facade is a commonly used structure form in high-rise buildings for energy-saving design since it could improve both the light and ventilation conditions indoors. Through a series of experiments, this paper investigated the flame spread over insulation in u-shaped building facade fires under effect of structural dimensions (back wall length W, side wall length L, height H) and boundary conditions based on the flame spread rate, temperature and heat flow. It was found that the flame spread rate V_f, the temperature rise ΔT and the heat flow q over u-shaped facade were all positively correlated with the side wall length L and structural height H, while they were negatively correlated with the back wall length W. On the other hand, the lateral air entrainment restriction and flame interaction were both significantly increased the temperature and heat flow, strengthened the thermal feedback, accelerated the flame spread. However, the bottom air entrainment restriction slowed down the flame spread. Further, a modified structure factor was introduced to comprehensively analyze the influence of L, W and H on flame spread behavior over u-shaped structures, and the theoretical equations of V_f^*, ΔT^*_max and q′^*_max were established. This study provides theoretical basis and technical guidance for the fire prevention design of building facade covered with insulation.