Downward flame spread over extruded polystyrene: Effects of sample thickness, pressure, and sidewalls

An experimental study on the characteristics of downward flame spread of extruded polystyrene (XPS) is presented. The parameters investigated include average mass loss rate per unit of thickness ( m ′), average flame height (H _f), average flame spread rate (v _f), and mass growth rate ( m 1) of molten XPS. The effects of sample thickness (d), sidewalls and atmospheric pressure (p), and the combined effects of these factors on the flame spread are studied. The larger sample thickness corresponds to larger m ′ and higher flame upon most occasions. As d rises, v _f and m 1 increase under all conditions; v _f and d follow the equation: v f = A (1 - exp(- Cd)). The dimensionless heat release rate: Q- ∞ exp (- 0.3 d). m ′, v _f, and m 1 obtained without sidewalls are higher than those with sidewalls. m ′, v _f, and H _f obtained on the plain (p = 100.8 kPa) are larger than those obtained on the plateau (p = 65.5 kPa). m 1 obtained on the plain is lower than that on the plateau. In most cases without sidewalls, m ∞ p n 0, where 1.9 <n ₀ <2, and H f = a + μ p n 0. H _f obtained in the cases without sidewalls is larger than that with sidewalls when the sample thickness is small, while the opposite is true for thicker samples. When sidewalls are absent, on the plain, with a rise in thickness, the increase of v _f is significant for thin samples while the variation is not considerable for thick samples; on the plateau, this increase is significant for all thicknesses tested. The experimental results agree well with the theoretical analysis.