Pressure Response in Enclosures During and After Large-Scale Flame Spread: Testing and Modeling

Abstract

As part of the risk mitigation effort supporting the development of a zero-gravity largescale fire demonstration experiment, normal-gravity flame-spread tests were conducted on thin fuels in a sealed chamber capable of accommodating large-scale samples. The primary objective of these tests was to measure pressure rise in a large sealed chamber during and after flame spread and to characterize that data as a function of sample material, burning direction (upward/downward), heat release rate, total heat release, and heat loss mechanisms. Ignition at the bottom of a sample resulted in a rapid acceleratory upward turbulent flame spread. As the amount of fuel burned increases, the pressure rise in the chamber increases since the volume of hot gas generated is larger. The upward flame spread slows down as initial pressure is reduced, causing a drop in peak pressure and a shift to the right in time for peak pressure. Ignition at the top of a sample resulted in a slow, steady flame spread with a very small flat flame across the top of each burning cheesecloth sample. For downward flame spread, the pressure rises to a maximum steady-state pressure during the burn. This indicates that the heat dissipation to the surroundings has matched the heat generated by the flame for this long, slow burn. Heat sinks were used for overpressure mitigation above the burning samples so that the flame plume would pass through the heat sink and deposit the heat there instead of heating the atmosphere. For upward and downward flame spread, the heat sink was very effective in reducing the pressure by a factor of at least four. The heat sink was determined to be an effective mitigation strategy for the flight experiment.