Melting and Dripping Flow Behaviors on the Downward Flame Spread of a Wide XPS Foam

The XPS foam is an economical and popular material for building insulation. The fire hazard of the polymer foams is a big threat due to their fast burning with melting, dripping and flowing. The objective of this work is to investigate the complicated downward flame spread characteristics of a wide polymer foam. An image division and calculation method is used to analyze the dynamic downward movement of the irregular flame leading curves based on the experiments. The results show that the lagged sub-flames might suddenly spread downward fast and catch up the neighboring flames. And the increasing of the flame spread velocity and flame height illustrate the acceleration of the downward burning, which is induced by the dripping and accumulating of liquid fuel. Additionally, the local peaks of the flame spread velocity arrive later than the flame height for both overall flame and detailed sub-flames. The flame height increases in the stage of liquid fuel accumulation but decreased in the dripping stage. The dripping of liquid fuel results in the increasing of the flame spread velocity and decreasing of the flame height. The results also show that the relationship between the non-dimensional local peak sub-flame flow velocities and the corresponding non-dimensional peak sub-flame heights can be well described with a power function, which indicates that the introduction of the small sub-flames is effective to model the complicated downward flame spread behaviors of XPS foams with stochastic dripping. Finally, most of the delay times of local peak sub-flame velocities here are in the range of [15 s, 25 s].