U.S. Air Force Senior Airman Francia Holt, an aerospace and operational physiology technician assigned to 633rd Aerospace Medicine Squadron, adjusts the straps on a Reduced Oxygen Breathing Device at Langley Air Force Base, Va., April 19, 2016. Aerospace physiologists ensure aircrew members understand the potential threats oxygen deprivation and depressurization have on the body. (U.S. Air Force photo by Airman 1st Class Kaylee Dubois)

U.S. Air Force Maj. David McGraw, a combat rescue officer assigned to Air Combat Command, prepares for oxygen deprivation training at Langley Air Force Base, Va., April 19, 2016. Oxygen deprivation, commonly known as hypoxia, is one of the biggest threats to aircrew members. (U.S. Air Force photo by Airman 1st Class Kaylee Dubois)

U.S. Air Force Senior Airman Francia Holt, an aerospace and operational physiology technician assigned to 633rd Aerospace Medicine Squadron, prepares to lead Chief Master Sgt. Todd Popovic, a pararescueman, and Maj. David McGraw, a combat rescue officer, both assigned to Air Combat Command, in an oxygen deprivation simulation at Langley Air Force Base, Va., April 19, 2016. Aircrew members are taught to watch out for vision loss, confusion, slurred speech and unconsciousness, which are all caused by a lack of oxygen. (U.S. Air Force photo by Airman 1st Class Kaylee Dubois)

U.S. Air Force Maj. David McGraw, a combat rescue officer assigned to Air Combat Command, prepares for oxygen deprivation training at Langley Air Force Base, Va., April 19, 2016. After their initial training with the Reduced Oxygen Breathing Device, aircrew members must re-qualify with aerospace physiology every five years. (U.S. Air Force photo by Airman 1st Class Kaylee Dubois)

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)