Death zone

Source: Wikipedia, the free encyclopedia.
For other uses, see Zone of Death.
The summit of Mount Everest lies in the death zone.

In

Himalaya and Karakoram
regions of Asia.

Many deaths in high-altitude mountaineering have been caused by the effects of the death zone, either directly by the loss of vital functions or indirectly by poor decisions made under stress (e.g., not turning back in deteriorating conditions, or misreading the

supplementary oxygen will result in deterioration of bodily functions and death.[3][4][5]

Physiological background

The human body has optimal endurance below 150 m (490 ft) elevation.[6] The concentration of oxygen (O2) in air is 20.9% so the partial pressure of O2 (PO2) at sea level is about 21.2 kPa (6.3 inHg; 3.07 psi). In healthy individuals, this saturates

red blood cells.[7]

Atmospheric pressure decreases with altitude while the O2 fraction remains constant to about 85 km (53 mi), so PO2 decreases with altitude as well. It is about half of its sea level value at 5,500 m (18,000 ft), the altitude of the

HACE).[11][12]

Humans have survived for 2 years at 5,950 m (19,520 ft) [475 millibars (14.0 inHg; 6.89 psi) of atmospheric pressure], which appears to be near the limit of the permanently tolerable highest altitude.[13] At extreme altitudes, above 7,500 m (24,600 ft) [383 millibars (11.3 inHg; 5.55 psi) of atmospheric pressure], sleeping becomes very difficult, digesting food is near-impossible, and the risk of HAPE or HACE increases greatly.[11][14][15]

Bottled oxygen can help mountaineers survive in the death zone

In the death zone 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

hypoxia in patients with chronic mountain sickness and normal fetuses in-utero, both of which present pO2 levels similar to those at the summit of Mount Everest.[16]

Mountaineers use supplemental oxygen in the death zone to reduce deleterious effects. An open-circuit oxygen apparatus was first tested on the

Ed Hillary and Tenzing Norgay used open-circuit oxygen apparatus; after ten minutes taking photographs on the summit without his oxygen set on, Hillary said he "was becoming rather clumsy-fingered and slow-moving".[17]

Physiologist Griffith Pugh was on the 1952 and 1953 expeditions to study the effects of cold and altitude; he recommended acclimatising above 4,600 m (15,000 ft) for at least 36 days and the use of closed-circuit equipment. He further studied the ability to acclimatise over several months on the 1960–61 Silver Hut expedition
to the Himalayas.

In 1978, Reinhold Messner and Peter Habeler made the first ascent of Mount Everest without supplemental oxygen.

Notable disasters

Several expeditions have encountered disaster in the death zone that led to multiple fatalities, including:

See also

References

  1. ^ a b "Everest: The Death Zone". Nova. PBS. 1998-02-24.
  2. ^ Wyss-Dunant, Edouard (1953). "Acclimatisation" (PDF). The Mountain World: 110–117. Retrieved March 10, 2013.
  3. ISBN 978-1-884980-81-7.[permanent dead link
    ]
  4. ^
    PMID 11581324
    .
  5. ^
    PMID 19129527
    .
  6. PMID 25710483
    .
  7. ^ "Hypoxia, Oxygen, and Pulse Oximetry" (PDF). FlightState Pulse Oximeter. Retrieved 2006-12-29.
  8. ^ "Introduction to the Atmosphere". PhysicalGeography.net. Retrieved 2006-12-29.
  9. USARIEM-TN-04-05
    ). Retrieved 2009-03-05.
  10. S2CID 26524828
    .
  11. ^ a b Cymerman, A; Rock, PB. "Medical Problems in High Mountain Environments. A Handbook for Medical Officers". US Army Research Inst. of Environmental Medicine Thermal and Mountain Medicine Division Technical Report. USARIEM-TN94-2. Retrieved 2009-03-05.
  12. ^ "Outdoor Action Guide to High Altitude: Acclimatization and Illnesses". Outdoor Action First Aid & Safety Training. Retrieved 2006-12-29.
  13. PMID 12631426
    .
  14. PMID 3215854
    . Retrieved 2009-03-05.
  15. S2CID 5787317
    .
  16. ^ Zubieta-Castillo, G.; Zubieta-Calleja, G.R.; Zubieta-Calleja, L.; Zubieta-Castillo, Nancy (2008). "Facts that Prove that Adaptation to life at Extreme Altitude (8842m) is possible" (PDF). Adaptation Biology and Medicine. 5 (Suppl 5): 348–355.
  17. ^ Hunt, John (1953). The Ascent of Everest. London: Hodder & Stoughton. p. 206.
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