Death zone

Physiological background

The human body has optimal endurance below 150 m elevation. 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. In healthy individuals, this saturates hemoglobin, the oxygen-binding red pigment in red blood cells.

Atmospheric pressure decreases with altitude while the O2 fraction remains constant to about 85 km, so PO2 decreases with altitude as well. It is about half of its sea level value at 5500 m, the altitude of the Mount Everest base camp, and less than a third at 8849 m, the summit of Mount Everest. When PO2 drops, the body responds with altitude acclimatization. Additional red blood cells are manufactured; the heart beats faster; non-essential body functions are suppressed, food digestion efficiency declines (as the body suppresses the digestive system in favor of increasing its cardiopulmonary reserves); and one breathes more deeply and more frequently. But acclimatization requires days or even weeks. Failure to acclimatize may result in altitude sickness, including high-altitude pulmonary edema (HAPE) or cerebral edema (HACE).

Humans have survived for 2 years at 5950 m [475 mbar of atmospheric pressure], which appears to be near the limit of the permanently tolerable highest altitude. At extreme altitudes, above 7500 m [383 mbar of atmospheric pressure], sleeping becomes very difficult, digesting food is near-impossible, and the risk of HAPE or HACE increases greatly.

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 supplementary oxygen will result in deterioration of body functions, loss of consciousness, and ultimately, death.

Supplemental oxygen

Main article: High-altitude breathing apparatus#High-altitude mountaineering

Mountaineers use supplemental oxygen in the death zone to reduce deleterious effects. An open-circuit oxygen apparatus was first tested on the 1922 and 1924 British Mount Everest expeditions; the bottled oxygen taken in 1921 was not used (see George Finch and Noel Odell). In 1953 the first assault party of Tom Bourdillon and Charles Evans used closed-circuit oxygen apparatus. The second (successful) party of Edmund 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".

Physiologist Griffith Pugh was on the 1952 and 1953 expeditions to study the effects of cold and altitude; he recommended acclimatising above 15000 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:

• 1996 Mount Everest disaster
• 2008 K2 disaster

References

de:Höhenbergsteigen#Todeszone

References

1. Wyss-Dunant, Edouard. (1953). "Acclimatisation". The Mountain World.
2. (2 July 2001). "Limits to human performance: elevated risks on high mountains". Journal of Experimental Biology.
3. (2009). "Arterial Blood Gases and Oxygen Content in Climbers on Mount Everest". N Engl J Med.
4. (2015). "Effects of Altitude on Performance of Elite Track-and-Field Athletes". International Journal of Sports Physiology and Performance.
5. "Hypoxia, Oxygen, and Pulse Oximetry". FlightState Pulse Oximeter.
6. "Introduction to the Atmosphere". PhysicalGeography.net.
7. Muza, SR. (2004). "Altitude Acclimatization Guide.". US Army Research Inst. Of Environmental Medicine Thermal and Mountain Medicine Division Technical Report.
8. Westerterp, Klaas. (June 1, 2001). "Energy and Water Balance at High Altitude". News in Physiological Sciences.
9. Cymerman, A. "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.
10. "Outdoor Action Guide to High Altitude: Acclimatization and Illnesses". Outdoor Action First Aid & Safety Training.
11. West, JB. (2002). "Highest permanent human habitation". High Altitude Medical Biology.
12. (December 2025). "Operation Everest. II: Nutrition and body composition". J. Appl. Physiol..
13. Kayser B. (1992). "Nutrition and high altitude exposure". Int J Sports Med.
14. (2008). "Facts that Prove that Adaptation to life at Extreme Altitude (8842m) is possible". Adaptation Biology and Medicine.
15. Hunt, John. (1953). "The Ascent of Everest". Hodder & Stoughton.
16. "First without Oxygen". PBS.