for National Geographic News
The National Geographic 50th Anniversary Everest Expedition commemorates the first ascent of the world's highest mountain, by Edmund Hillary and Tenzing Norgay in May 1953. It also honors the first Americans to stand on the top of the world, including Barry Bishop, in 1963.
The sons of Everest pioneers Hillary, Norgay, and BishopPeter Hillary, Jamling Norgay, and Brent Bishopare helping make a documentary that will air on the National Geographic Channel in the United States and internationally in 2003.
The National Geographic 50th Anniversary Everest Expedition is made possible in part by the generous support of American International Group, Inc.
The margin of safety is razor-thin on a mountain like Mount Everest. Some hazards, such as thundering avalanches, freak storms, and hidden crevasses are beyond a climber's control.
But many deaths and near-death experiences are the result of human errors brought about or compounded by the effects of high altitude. Climbers are vulnerable to altitude sickness once they climb above 8,000 feet (2,400 meters). The region above 25,000 feet (7,600 meters) is called the death zone.
Climbers who venture into this zone cannot escape the potentially deadly effects of oxygen deprivation; they can only attempt to minimize and control what breathing the thin air at high altitudes does to their bodies.
Everest's "Thin Air"
Air, whether at the summit of Mount Everest or at sea level, contains about 21 percent oxygen. But at high altitudes, the density of air changesit becomes thin. Thin air is not nearly as rich in oxygen as the dense, more heavily compressed air found at sea level.
At the top of Mount Everest, more than 29,000 feet (8,840 meters) above sea level, the atmospheric pressure is about one-third that of sea level. Climber and filmmaker David Breashears has described climbing at such altitudes, even with bottled oxygen, as equivalent to "running on a treadmill and breathing through a straw."
For reasons not entirely understood, each person reacts differently to high altitude. On mountains as high as Everest, however, no one is immune.
The first effect a climber will notice upon reaching higher altitudes is an increased breathing rate. Any exertion, even eating a meal or crawling into a sleeping bag, leaves climbers short of breath.
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