U.S. Air Force Senior Airman Clariece Kyles (center), 633rd Aerospace Medical Squadron Physiological Flight aerospace and physiology technician, instructs an altitude chamber class during 30 minutes of denitrogenation at ground level at the Physiological Training Center at Langley Air Force Base, Va., Feb. 14, 2012. Aviators train in the chamber to experience and recognize the signs and symptoms of hypoxia, or oxygen deprivation, while executing aircraft specific emergency procedures to correct the problem. (U.S. Air Force photo by Senior Airman John D. Strong II/Released)