Downward flame spread over PMMA sheets in quiescent air: Experimental and theoretical studies

To explore the flame spread mechanisms over noncharring material, downward flame spread over polymethyl methacrylate (PMMA) sheets from 1.5 to 10 mm thick is studied experimentally in the quiescent air in an open space. The experimental results show that the flame spread rate decreases with increasing thickness of sheet and it tends to a constant value for thick samples. Also the angle of the pyrolysis region is roughly constant for different sheet thicknesses. In this study, a heat transfer model is proposed to examine the rate of heat transfer for noncharring materials. Based on this model and the experimental results, a correlation between the flame spread rate and thickness is derived, in which the flame spread rate is inversely proportional to the sheet thickness. The proposed model estimated the convection heat flux and the gradient of temperature in the solid and gas phases. The experimental data are in good agreement with the results of the theoretical model. (C) 2006 Elsevier Ltd. All rights reserved.