2019-06-202019-06-202019-07-07ICES_2019_101https://hdl.handle.net/2346/84505Sandra Olson, National Aeronautics and Space Administration (NASA), USAPaul Ferkul, Universities Space Research Association (USRA), United States Minor Outlying IslandsCarlos Fernandez-Pello, University of California, Berkeley, USAFletcher Miller, San Diego State University, USAIndrek Wichman, Michigan State University, USASubrata Bhattacharjee, San Diego State University, USAJames T'Ien, Case Western Reserve University, USAICES509: Fire Safety in Spacecraft and Enclosed HabitatsThe 49th International Conference on Environmental Systems was held in Boston, Massachusetts, USA on 07 July 2019 through 11 July 2019.Normal gravity flammability limits are often reported as downward spread limits (Limiting Oxygen Index), or upward spread limits (NASA Test 1, UL 94V). In microgravity, the comparable limits are opposed flow and concurrent flow. During BASS-II experiments in the Microgravity Science Glovebox on the ISS, PMMA (polymethylmethacrylate) rods, sheets, and slabs, and cotton-fiberglass fabric sheets were burned in microgravity with a variety of oxygen concentrations and at different flow speeds in both opposed and concurrent flow directions. Flame extinctions occurred under conditions indicating that materials can burn at a lower oxygen concentration in microgravity compared to normal gravity. Flames at very low velocity shrink to small spherical sections at the ends of rods, or to small nearly circular disks (a.k.a. flamelets) above flat samples. These spherical/circular flames sometimes oscillate prior to extinction. At high velocity, flames quickly grow but the stabilization zone thins and then fails as the flow time becomes too short for the reactions to occur in that hot flame stabilization zone. The flame blows off, often after a few oscillations. At the other extreme, the flames always quenched when the fan was turned off. This shows that the first line of fire defense on the ISS, to turn off all ventilation systems when a fire is detected, is an excellent mitigation strategy for the ISS. Previous quiescent testing at elevated oxygen concentrations, however, suggests that ventilation may not be necessary for a flame to survive under conditions that may be present in high oxygen low pressure atmospheres in spacecraft or in partial gravity environments, so this mitigation strategy may not be applicable in future exploration missions. The role of heat losses, sample dimension, and near-limit phenomena are discussed. A normal gravity test method is suggested that can account for partial gravity flammability, where more research is needed.application/pdfengflammabilitymicrogravityblowoffquenchingextinctionPresentations