Upward Flame Spread over a 0.1 mm Thick PMMA Sheet in Normoxic Atmospheres

In a manned spacecraft and habitats, the environment is maintained at normoxic conditions, which is the combination of ambient pressure and oxygen concentration that results in a partial pressure of oxygen equal to that of normal atmosphere at sea level. Future spacecraft will have atmospheres with reduced pressures and increased oxygen concentrations at normoxic conditions (Space Exploration Atmospheres - SEA), designed to reduce preparation time for extravehicular activities. This paper presents experimental results on the upward spread of flames over a flat PMMA sheet 0.1 mm thick under normoxic conditions. The experiment methodology resembles that of NASA test NASA-STD-6001B, with varied environmental conditions. Experiments are conducted in a pressure chamber with ambient pressures ranging between 100 and 60 kPa and oxygen concentrations between 21% and 35% by volume. Results show that moving to normoxic environments with reduced pressure and increased oxygen concentration increases the flammability of the thin PMMA and the flame spread rate. Normoxic conditions also showed an increase in distance between the outer flame and the PMMA surface at lower pressures. O2, CO, and CO2 were measured at the exhaust of the pressure chamber, and were used to calculate the heat release rate at different pressures and in normoxic conditions. The results show that as the environment transitions to normoxic conditions with higher O2 concentrations, the heat released by the flame also increases. The data presented here provides information about the flammability of spacecraft materials in future SEA, yielding insight for future designs when considering fire safety in spacecrafts.