Influences of Sub-Atmospheric Pressure on Upward Flame Spread over Flexible Polyurethane Foam Board with Multiple Inclinations

Fire propagation and burning characteristics of upward flame spread over flexible polyurethane (FPU) foam board were investigated under coupling effects of pressure and orientation. As a further comparative research of our previous work, three pressures (70, 85 and 100 kPa) and four fuel surface inclination angles (0°, 30°, 60°, 90°) were applied, respectively, as before, to study the variation of typical parameters including flame spread rate (FSR), burning rate, heat transfer components, flame length, etc. First, a phenomenological interpretation was taken to show the special spreading process with melting flow combustion and flash burning observed. Second, an overall theoretical analysis was proposed to reveal the individual or coupling effects of pressure and inclined burning surface on spreading behavior. A semi-quantitative correlation was developed and formulated to show the tendency of FSR as a function of pressure, inclination and other burning parameters, which was validated by data in paper. Meanwhile, comparison of detailed differences between upward and downward spread was conducted to give a full insight on FPU fire development. At last, comprehensive discussions of coupling effects on variation of spreading characteristics and heat transfer mechanisms were performed based on fire dynamics.