Melt-flowing of expanded polystyrene in large-scale discrete flame spread

Large-scale experiments were performed to investigate the influence of the melting flow of thermoplastic materials on discrete downward flame spread in façade fires. Expanded polystyrene, one of the flammable insulation materials broadly used in buildings, was selected as the study object. The fuel coverage (f = hfuel/(hfuel + hb)) was adjusted via barrier heights (hb = 30, 50, 70, and 90 cm) to explore its impact on flame propagation and heat release rate. The discrete flame spread process with burning flows was clarified into five stages, and the critical fuel coverage for preventing flame spread was found to be 0.40–0.46. The heat release rate of the entire burning process was measured, revealing that fuel coverage significantly impacted the HRR curve shape and peak value by influencing the formation time of pool fires above and below the barrier. Additionally, the properties of burning flows were characterised by area and HRR. A proportional relationship was established between the pool fire height and spill fire area. This research provides a novel observation of melting flows developed from burning thermoplastic material and uncovers the influence of melting flows on flame propagation in façade fires.