Burning of large-scale vertical surfaces

Measured burning rates per unit area in a large-scale vertical polymethyl methacrylate (PMMA) wall fire experiment are found to increase nearly linearly with height along the 3.56-m high slab. The radiative heat feedback from the flames to the fuel surface is derived from radiance measurements using a gray flame analysis. Radiative heat transfer accounts for 75 to 87 percent of the total heat feedback to the burning surface. Results for thin and gray flame models are compared, with fuel scale and flame absorption coefficient as parameters. The asymptotic burning rate, where the flame emissivity is unity, may be as high as 123 g/m 2 s, on the basis of an effective flame radiation temperatre of 1367 K for PMMA. Computed PMMA flame transmittance versus radiance characteristics in the radiance range 0 to 1.5 W/cm 2 sr are shown to be similar to that of turbulent ethane and propane flames.