Effects of Sample Width and Sidewalls on Downward Flame Spread over XPS Slabs

Abstract

To study the effects of sample width and sidewalls on downward flame spread over extruded polystyrene (XPS) slabs, a series of laboratory-scale experiments were conducted. Flame shape, flame spread rate, mass loss rate and temperature were recorded. For XPS without sidewalls, the average maximum flame height (H) and average flame area per unit of width (A/w) rise linearly with an increase in sample width (w) and mass loss rate per unit of width. When sidewalls are absent, flame spread rate first drops and then rises with an increase in width. This trend is determined by gas-phase heat transfer. When sidewalls are present, flame spread rate increases with a rise in width, and solid-phase heat conduction determines the trend. Sidewall effects are comprised of four aspects: oxygen concentration near the sidewalls and gypsum board is low, which leads to reduced flame heat flux; upward and front air flow is intensified; the flame is stretched, and the surface flame is weakened; and molten XPS mass decreases. For narrow samples, H and A/w with sidewalls are higher than those without sidewalls, while the reverse was observed in wider samples. The mass loss rate, preheating length and average flame spread rate with sidewalls are smaller than those obtained without sidewalls. Flame spread acceleration with sidewalls occurs at a broader width than that without sidewalls. The experimental results agree well with the theoretical analysis.

Fire Spread Characteristics of Metal-Polyethylene Sandwich Panels

“…Equation m l = m a /L indicates a positive correlation between the average mass loss rate per unit length and the characteristic length. The same conclusion in the XPS sandwich panel in high-rise building fire spreading was also produced [31]. It was deduced that m l rose with an increase in the sample length.…”

Effect of the Backboard on the Pyrolysis Front Morphology of Downward Flame Spread: A Simulation Study

“…Because the air enrolling in the X direction is mainly concentrated in the front [7,16], and the influence of the back plane on the air enrolling is mainly reflected near the back plane. Therefore, this paper only analyzes the change of air velocity in Y and Z directions near the backboard.…”

“…Carmignani et al [6] studied the two-dimensional downward fire propagation of PMMA plate (side limited, no backboard), and the results showed that the pyrolysis front was linear. An et al [7], Luo et al [8], Yan et al [9] experimentally studied the effect of U-shaped structure (side limited with backboard) on the downward spreading of expanded polystyrene (XPS) and PMMA plates, respectively. The results showed that, under the U-shaped structure, the temperature of XPS and PMMA plates decreased significantly.…”