Senior Airman Christopher Helton , an aerospace physiology technicians stationed at Langley AFB, checks to see if one of the Federal Aviation Administration students is showing signs of hypoxia during an altitude chamber exercise 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)