Research on the flow and dropping behaviour of droplets generated by burning of flexible polyurethane foam

The combustion of flexible polyurethane foam (FPUF) poses a significant fire safety risk due to the flow and dropping behavior of its liquid products, which can accelerate fire growth and spread between nonadjacent objects. In this work, the formation, flow, and dropping phenomena of FPUF liquid products were investigated in the laboratory. The findings show that the polyols pyrolyzed by FPUF initially form bead-like droplets on the foam surface, which undergo a morphological transformation from spherical to hemispherical and striped shapes on the side of the foam. The downward flow velocity of the largest droplet is measured to be 5.3 +/- 0.4 mm s(-1). Furthermore, it is found that droplets with diameters less than 0.70 mm float up, while droplets above the critical dropping diameter have a high risk of igniting flammable materials below. The critical dropping diameter increases linearly with the drop height. These results contribute to a better understanding of the behavior of FPUF during combustion and have important implications for fire safety engineering.