U.S. Air Force Master Sgt. Christopher Hoopes, 1st Operations Group Aerospace and Operational Physiology flight chief operates the Reduced Oxygen Breathing Device at Joint Base Langley-Eustis, Virginia, June 13, 2019. Once an individual notices one of these symptoms, they are instructed to supply themselves with 100 percent oxygen. (U.S. Air Force photo by Senior Airman Tristan Biese)