U.S. Air Force Tech. Sgt. Jennifer Ellis, aerospace and operational physiology flight chief assigned to the 633rd Aerospace Medicine Squadron, demonstrates the use of a Reduced Oxygen Breathing Device equipment at Langley Air Force Base, Va., April 19, 2016. The ROBD is worn like a normal oxygen mask; however, physiologists can change the gas in the mask to mirror the effects of hypoxia. (U.S. Air Force photo by Airman 1st Class Kaylee Dubois)