Death zone

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The death zone, in mountaineering, refers to altitudes above a certain point where the amount of oxygen cannot sustain human life. The point is generally tagged as between 7,000 to 8,000 m (23,000 to 26,200 ft).^[1] Many deaths in high-altitude mountaineering have been caused by the effects of the death zone, either directly (loss of vital functions) or indirectly (wrong decisions made under stress, physical weakening leading to accidents).

[edit] Physiological background

The death zone, in mountaineering terms, usually refers to altitudes above 7,000 metres (23,000 ft). The human body functions at its best at sea level, where the atmospheric pressure is measured at 1 atm (1013.25 hPa). The hemoglobin (the oxygen-binding red pigment in red blood cells) is saturated with oxygen (nearly 100 %) at that air pressure.^[2]

At higher altitudes, the air pressure drops and so does the amount of available oxygen. An important point of note is that, while the absolute available oxygen is decreased, the percentage of oxygen remains the same as at sea level. At 5,000 m (16,400 ft) (height of Mount Everest base camp), the amount of oxygen is only half that at sea level. At 8,848 m (29,030 ft) (summit of Mount Everest), only one-third as much is available.^[3] When the partial pressure of oxygen drops, the human body tries to compensate by a process known as altitude acclimatization.^[4] Additional red blood cells are manufactured, the heart beats faster, non-essential body functions are temporarily shut down, food digestion efficiency declines (as the body shuts the digestive system down)^[5] and one breathes more deeply and more frequently. However, acclimatization cannot take place immediately – in fact, it takes place over a period of days or even weeks. Failure to acclimatize may result in altitude sickness, including high altitude pulmonary edema (HAPE) or cerebral edema (HACE).^[6][7]

At extreme altitudes (above 7,500 m (24,600 ft)), sleeping becomes very difficult, digesting food is near-impossible, and the risk of HAPE or HACE increases greatly.^[6][8][9]

Finally, in the "death zone" at 7,000 to 8,000 m (23,000 to 26,200 ft) and higher, no human body can acclimatize. The body uses up its store of oxygen faster than it can be replenished. An extended stay in the zone without supplementary oxygen will result in deterioration of body functions, loss of consciousness and, ultimately, death.^[4][1]

[edit] See also

• 2008 K2 Disaster

[edit] References