Fire Safety Science Digital Archive

Smolder spread experiments for a thin horizontal cellulosic powder bed of high bulk density were conducted with an air stream over the bed. In the experiments, achievement of a two-dimensional structure of the smolder zone was attempted, and spread rate, cross-sectional views, and temperature profiles of the smolder zone were examined. It was observed that for forward smolder spread as the air stream velocity increases, the dependence of the spread rate on the air stream velocity increases at first, but above a critical air stream velocity the spread rate becomes almost independent of the air stream velocity and ultimately complete extinction of the smolder zone occurs. This variation is closely related with the variation of the structure of the smolder zone as seen in cross sectional views. From the comparison of experimental data, it is inferred that the heat balance around the intersection between the exposed, inclined surface of the char oxidation zone and the top surface of the virgin part of the bed is very important to the smolder spread behavior in a thin and high density fuel layer. The aerodynamic effects in the boundary layer over the smolder zone surface control the spread behavior through heat transfer processes.