Service members train for high altitudes
A U.S. Army Ranger makes adjustments to his MA-1 portable oxygen emergency back-up device as he is instructed on how to use it inside a hypobaric altitude chamber at Langley Air Force Base, Va., Nov. 14, 2014. The Rangers went through a series of tests that familiarized them with oxygen equipment used in high-altitude and emergency situations. (U.S. Air Force photo by Staff Sgt. Natasha Stannard/Released)