Opposed Flame Spread in Narrow Channel Apparatus to Assist in Suppression Studies

In this paper, we study the performance of a testing apparatus that could be used for evaluating the effectiveness of gaseous suppressants and solid fuel retardants under opposed flame spread conditions. A narrow channel, 3 mm in height, 110 mm in width and 375 mm in length, constitutes the most important component of this apparatus. To establish the flow and flame spread parameters in this apparatus, thermally thick plates of a well characterized solid fuel, i.e., PMMA, were placed at the bottom of the channel whereas the top was a glass plate. A mixture of oxygen-enhanced air was introduced into the channel, and the fuel was ignited downstream to allow the flame to propagate in the direction opposite to the gas stream. The tests were recorded with a digital video camera and the rate of flame spread and the flame length were determined by analyzing the recorded images. The mass loss during an experiment was quantified by weighing a sample before and after each experiment. Extensive experimentation demonstrated that, the flame spread over the fuel in the channel is dominated by the velocity and oxygen content of the introduced gas stream, and a steady flame can be readily and reproducibly established. Simple theory and analysis provides correlations between the flame spread speed, the flame length and the mass of the material pyrolyzed during the flame spread by separating the thermal and flow from the chemical parameters. Thus, it is possible to investigate and assess the effectiveness of gaseous suppressants and solid fire retardants on reducing the flame spread and eventually leading to extinction.