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Signs of Hypoxia Tied to Altitude, Decompression

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TIMES MEDICAL WRITER

Posing a grave danger to pilots and passengers in a plane that is not pressurized, the air at 30,000 feet contains about 70% less oxygen than it does at sea level, Gary Barnes, a meterologist at the University of Hawaii, said Tuesday.

People aboard an unpressurized aircraft at high altitude will soon be starved for oxygen--a condition known as hypoxia--unless they get compressed oxygen through a mask.

At the same time, pilots are trained to take aircraft to lower altitudes to restore pressure.

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Among the early signs of hypoxia are tingling or numbness in limbs, bluish extremities, nausea, euphoria and headaches. Pilots are trained to recognize these signs. Mental stupor, unconsciousness and death may quickly ensue.

The speed with which symptoms develop depends on the altitude and the suddenness of the decompression.

With a gradual loss of cabin pressure at 18,000 feet, the period before mental confusion sets in is 20 to 30 minutes, said Major Joseph Balas, an aerospace physiologist at Peterson Air Force Base in Colorado Springs. At 35,000 feet, it takes just 30 seconds to one minute.

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But if the decompression is sudden, that crucial period--what aviators call the time of useful consciousness--may be cut in half, Balas said. In such a case, a pilot at 35,000 feet would have only a matter of seconds to strap on an oxygen mask and deal with the emergency before becoming too confused to act and then blacking out.

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