Senior Airman Chris Helton, an aerospace physiology technician stationed at Langley AFB, checks the oxygen regulator control panel in the altitude chamber prior to use by Federal Aviation Administration students, on 19 Apr 2006 at the Aerospace Physiology facility on Langley. While in the altitude chamber students are exposed to atmospheric conditions at 25,000 ft. Without the aid of an oxygen mask they experience symptoms of hypoxia, a oxygen deficiency of the tissue and blood cells that causes impairment of function at high altitudes. (USAF Photo By SSgt Samuel Rogers)