Material and configuration testing for the Space Shuttle is mainly at 30 percent oxygen concentration at 70 kPa (10.2 psia). This is the worst case atmosphere during a mission and occurs 10 hours prior to extravehicular activity. The pressure is reduced from the nominal 101 kPa (14.7 paia) and the oxygen concentration is increased to 30 percent for medical reasons to prevent the bends during the extravehicular activity. NASA has tested many materials at 23.8, 25.9 and 30 percent oxygen levels for the Shuttle program. Data is given to show how flammability of material is affected by percentage of oxygen for those materials that would be considered for spacecraft applications.