Limiting Oxygen Concentration of Burning PMMA Cylinders under External Radiant Heating and Subatmospheric Pressures

Understanding flame spread over combustible solids under different environmental conditions is important for fire safety in spacecraft applications due to the criticality associated with such events. Environmental variables such as oxygen concentration, ambient pressure, external radiant heating, or gravity may change the flammability and fire dynamics of materials. The overall objective of this work is to study the effect of an external radiant flux on the opposed flame spread rate and the limiting oxygen concentration (LOC) for flames spreading over the surface of cylindrical samples of polymethyl methacrylate (PMMA) in Space Exploration Atmospheres (SEA). In the work presented here, experiments under normal gravity and subatmospheric pressure are conducted using a variable heat flux with peak values ranging from 0 kW/m2 to 1.9 kW/m2. A forced flow of air with a velocity of 10 cm/s is used to mimic the air flow velocity generated by the HVAC system inside a spacecraft. Flame spread rates and limiting conditions for flame spread were measured from video processing of the experiments at different environmental conditions and external radiant heat flux. Results show that the limiting oxygen concentrations depend on the amount of radiant heating received by the PMMA sample, decreasing as the radiant flux is increased. The data presented in this work provides a baseline for comparison with future microgravity experiments to be performed by NASA as part of the SoFIE/MIST project aboard the International Space Station. It is expected that the results will provide insight for what is to be expected in different conditions relevant for fire safety in future space facilities.

The work presented here was supported by NASA Grants NNX10AE01G and NNX13AL10A.