Flame spread over solid surface coated with a layer of noncombustible porous material

Small-scale experiments are performed to determine the influence of noncombustible coating material on the behavior of flame propagation over solid fuels. Thick polymethylmethacrylate (PMMA) sheets are used as combustible materials, and sand layer is used as the solid coating material in the experiments. The results of the experiments show that the size of the sand and the thickness of the sand layer have significant effects on the flame spread rate. The influence is through the amount of heat flux absorbed by the unburned fuel surface and the mass diffusion of the vaporized fuel to react with the oxygen in the ambient air. As the sand layer thickness increases, the flame spread rate decreases. An inverse trend is observed with the increase of the sand size. In this paper, a simplified heat transfer model is proposed for the flame spread rate over the combustible material with a layer of noncombustible porous material. The experimental results have been found to be in agreement with the results from the model. Results from this study can be used in two areas. One is in understanding how flame spread is retarded by application of porous material as an extinguishing agent. Another aspect is that more and more household items nowadays have a noncombustible coating on the surface as a means of decoration, more fundamental information on how the flame spreads is useful in future building fire safety designs.