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While conditions for any area classified as a death zone apply to Mount Everest (altitudes higher than 8,000 m/26,246 ft), it is significantly more difficult for a climber to survive at the death zone on Mount Everest. Temperatures can dip to very low levels, resulting in frostbite of any body part exposed to the air. Because temperatures are so low, snow is well-frozen in certain areas and death by slipping and falling can also occur. High winds at these altitudes on Everest are also a potential threat to climbers. The atmospheric pressure at the top of Everest is about a third of sea level pressure, meaning there is about a third as much oxygen available to breathe as at sea level.
In May 2007, the Caudwell Xtreme Everest undertook a medical study of oxygen levels in human blood at extreme altitude. Over 200 volunteers climbed to Everest Base Camp where various medical tests were performed to examine blood oxygen levels. A small team also performed tests on the way to the summit.
Even at base camp the low level of available oxygen had direct effect on blood oxygen saturation levels. At sea level these are usually 98% to 99%, but at base camp this fell to between 85% and 87%. Blood samples taken at the summit indicated very low levels of oxygen present. A side effect of this is a vastly increased breathing rate, from 20-30 breaths per minute to 80-90 breaths, leading to exhaustion just trying to breathe.
Lack of oxygen, exhaustion, extreme cold, and the dangers of the climb all contribute to the death toll.
People who die during the climb are typically left behind. About 150 bodies have never been recovered. It is not uncommon that corpses are visible from the standard climbing routes.
One sometimes deadly phenomenon, however, does not plague climbers — lightning. Lightning does not strike Mount Everest. NASA's lightning detection system does record significant lightning in the Tibet plateau, but none along the high Tibetan mountains, from about 2000 m (7,000 feet) and above.