Opposed flow burning of PMMA cylinders in normoxic atmospheres

The influence of environmental conditions on the flammability of combustible solids is of importance to spacecraft fire safety because of the differences with the conditions encountered on Earth. In a manned spacecraft there is reduced gravity and low velocity flows. Additionally, the environment is maintained at a Normoxic condition, 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 (P_O2 =21kPa). Future spacecraft will have atmospheres with reduced pressures and oxygen concentrations at Normoxic conditions (Space Exploration Atmospheres - SEA), designed to reduce preparation time for spacewalks. This work studies the effect of ambient pressure and oxygen concentration, on opposed flame spread and mass burning in cylindrical samples of polymethyl methacrylate (PMMA). Experiments in normal gravity are conducted using ambient pressures ranging between 100 and 60 kPa and oxygen concentrations between 21% and 35% by volume, while maintaining Normoxic conditions. Results show that moving to Normoxic environments with reduced pressure and increased oxygen concentration increases the flammability of the PMMA cylinders. The data presented here provide information about the flammability of spacecraft materials in future SEA, yielding insight for future designs when considering fire safety in spacecrafts.