A Study on Fire Spread Behavior on Plywood Walls of Various Thickness

In predicting the ignition and/or flame spread of lining materials, “thermally thick walls” is often assumed. However, if the lining material is thin, the time to ignition and flame spread rate depend on the backing materials. In addition, the rise of back surface temperature can lead to combustion on the back side surface. Therefore, in this study, small-scale and intermediate-scale room tests were conducted with plywood of various thickness (5.5, 9, 12 and 30 mm). In the small-scale tests, cone calorimeter and reduced-size LIFT tests were conducted to measure basic combustion properties. In the intermediate-scale room tests, model room fire tests were carried out. In case of a room lined with 5.5 mm-thick plywood, lining material burned out quickly and did not reach flashover. In case of lined with plywood thicker than 9 mm, lining materials burned intensively and reached flashover, triggered by gas phase burning at the bottom of smoke layer. The time to flashover was shortest in case of 12 mm-thick plywood due to the pyrolysis of back side surface. The intermediate-scale test results were compared with the calculations using the combustion properties obtained by the small-scale tests. The calculation results reproduced the threshold of flashover occurrence. The calculated times to flashover were shorter than experiments. It was suggested that the dependence of heat release rate upon lining thickness should be considered to improve the accuracy.