Editing Death zone

{{Short description|Altitudes above about 8,000 m (26,000 ft)}}
{{Other uses|Zone of Death (disambiguation){{!}}Zone of Death}}
[[File:Hillary Step near Everest top (retouched).jpg|thumb|The summit of [[Mount Everest]] lies in the death zone.]]
In [[mountaineering]], the '''death zone''' refers to altitudes above which the pressure of [[oxygen]] is [[Effects of high altitude on humans|insufficient to sustain human life]] for an extended time span. This point is generally considered to be {{cvt|8000|m|ft|-2}}, where atmospheric pressure is less than {{convert|356|mbar|inHg psi}}.<ref name="PBS">{{cite web
|url= https://www.pbs.org/wgbh/nova/transcripts/2506everest.html|title= Everest: The Death Zone| work=Nova|publisher= PBS|date= 1998-02-24}}</ref> The concept was conceived in 1953 by [[Edouard Wyss-Dunant]], a Swiss doctor, who called it the '''lethal zone'''.<ref>{{cite journal |journal= The Mountain World |year=1953 |pages=110–117|title= Acclimatisation |last=Wyss-Dunant|first=Edouard |url=https://archive.org/details/mountainworld195029881mbp |format=PDF |access-date=March 10, 2013 }}</ref> All [[eight-thousander|14 peaks above 8000 m]] (the "eight-thousanders") in the death zone are located in the [[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 [[climbing route]]), or physical weakening leading to accidents (e.g., falls). An extended stay above {{cvt|8000|m|ft|-2}} without [[Bottled oxygen (climbing)|supplementary oxygen]] will result in deterioration of bodily functions and death.<ref name="PBS"/><ref name=Huey>{{Cite journal|url=http://jeb.biologists.org/content/204/18/3115.abstract|title=Limits to human performance: elevated risks on high mountains|first1=Raymond B.|last1=Huey|first2=Xavier|last2=Eguskitza|date=2 July 2001|journal=Journal of Experimental Biology|volume=204|pages=3115–9|pmid=11581324|issue=18|doi=10.1242/jeb.204.18.3115|bibcode=2001JExpB.204.3115H |url-access=subscription}}</ref><ref name=Grocott>{{cite journal|journal=N Engl J Med|year=2009|volume=360|pages=140–9|title=Arterial Blood Gases and Oxygen Content in Climbers on Mount Everest|first1=Michael P.W.|last1=Grocott|first2=Daniel S.|last2=Martin |first3=Denny Z.H.|last3=Levett |first4=Roger|last4=McMorrow |first5=Jeremy|last5=Windsor |first6=Hugh E. |last6=Montgomery|doi=10.1056/NEJMoa0801581|pmid=19129527|issue=2}}</ref>

== Physiological background ==
The [[human body]] has optimal endurance below {{cvt|150|m|ft}} elevation.<ref>{{cite journal|title=Effects of Altitude on Performance of Elite Track-and-Field Athletes|first1=MJ|last1=Hamlin|first2=WG|last2=Hopkins|first3=SC|last3=Hollings|journal=International Journal of Sports Physiology and Performance|year=2015|volume=10|issue=7 |pages=881–887|doi=10.1123/ijspp.2014-0261|pmid=25710483 }}</ref> The [[Atmospheric chemistry|concentration of oxygen]] (O<sub>2</sub>) in air is 20.9% so the [[partial pressure]] of O<sub>2</sub> (PO<sub>2</sub>) at sea level is about {{cvt|21.2|kPa|inHg psi}}. In healthy
individuals, this saturates [[hemoglobin]], the oxygen-binding red pigment in [[red blood cells]].<ref>{{cite web |url=http://www.flightstat.nonin.com/documents/Hypoxia,%20Oxygen%20and%20Pulse%20Oximetry.pdf |title=Hypoxia, Oxygen, and Pulse Oximetry|work=FlightState Pulse Oximeter |access-date=2006-12-29}}</ref>

Atmospheric pressure decreases with altitude while the O<sub>2</sub> fraction remains constant to about {{cvt|85|km}}, so PO<sub>2</sub> decreases with altitude as well. It is about half of its sea level value at {{cvt|5500|m|ft|-2}}, the altitude of the [[Everest base camps|Mount Everest base camp]], and less than a third at {{cvt|8849|m|ft}}, the summit of Mount Everest.<ref>{{cite web|url=http://www.physicalgeography.net/fundamentals/7d.html|title=Introduction to the Atmosphere|work=PhysicalGeography.net|access-date=2006-12-29}}</ref> When PO<sub>2</sub> drops, the body responds with [[altitude acclimatization]].<ref name=Acclimatization>{{cite journal |author=Muza, SR |author2=Fulco, CS |author3=Cymerman, A |title=Altitude Acclimatization Guide. |journal=US Army Research Inst. Of Environmental Medicine Thermal and Mountain Medicine Division Technical Report |issue=[[USARIEM|USARIEM-TN-04-05]] |year=2004 |url=https://www.usariem.army.mil/assets/docs/partnering/altitudeacclimatizationguide.pdf |archive-url=https://web.archive.org/web/20161020162036/http://www.usariem.army.mil/assets/docs/partnering/altitudeacclimatizationguide.pdf |url-status=dead |archive-date=October 20, 2016 |access-date=2009-03-05 }}</ref> 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);<ref>{{ cite journal | last =Westerterp | first =Klaas | title =Energy and Water Balance at High Altitude | journal =News in Physiological Sciences | volume =16 | issue =3 | pages =134–137 | pmid =11443234 | url =http://physiologyonline.physiology.org/cgi/content/full/16/3/134 | date = June 1, 2001 | doi =10.1152/physiologyonline.2001.16.3.134 | s2cid =26524828 | url-access =subscription }}</ref> and one [[respiratory system|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]]).<ref name=MedicalProblems>{{cite web |author=Cymerman, A |author2=Rock, PB |title=Medical Problems in High Mountain Environments. A Handbook for Medical Officers |publisher=US Army Research Inst. of Environmental Medicine Thermal and Mountain Medicine Division Technical Report |id=USARIEM-TN94-2 |url=https://apps.dtic.mil/sti/citations/ADA278095 |access-date=2009-03-05}}</ref><ref>{{cite web|url=http://www.princeton.edu/~oa/safety/altitude.html|title=Outdoor Action Guide to High Altitude: Acclimatization and Illnesses|work=Outdoor Action First Aid & Safety Training|access-date=2006-12-29}}</ref>

Humans have survived for 2 years at {{cvt|5950|m|ft|-2}} [{{convert|475|mbar|inHg psi}} of atmospheric pressure], which appears to be near the limit of the permanently tolerable highest altitude.<ref>{{cite journal|last=West|first=JB|pmid=12631426|title=Highest permanent human habitation|journal=High Altitude Medical Biology|volume=3|number=4|pages=401–407|year=2002|doi=10.1089/15270290260512882}}</ref> At extreme altitudes, above {{cvt|7500|m|ft|-2}} [{{convert|383|mbar|inHg psi}} of atmospheric pressure], sleeping becomes very difficult, digesting food is near-impossible, and the risk of HAPE or HACE increases greatly.<ref name=MedicalProblems/><ref name="pmid3215854">{{cite journal |last1=Rose|first1=MS|last2=Houston|first2=CS|last3=Fulco|first3=CS|last4=Coates|first4=G|last5=Sutton|first5=JR|last6=Cymerman|first6=A |title=Operation Everest. II: Nutrition and body composition |journal=J. Appl. Physiol. |volume=65 |issue=6 |pages=2545–51 |year=1988 |pmid=3215854 |doi= 10.1152/jappl.1988.65.6.2545|url=http://jap.physiology.org/cgi/pmidlookup?view=long&pmid=3215854 |access-date=2009-03-05|url-access=subscription}}</ref><ref name="pmid1483750">{{cite journal |author=Kayser B |title=Nutrition and high altitude exposure |journal=Int J Sports Med |volume=13 |pages=S129–32 |year=1992 |issue=Suppl 1 |pmid=1483750 |doi=10.1055/s-2007-1024616|s2cid=5787317 }}</ref>

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 [[Bottled oxygen (climbing)|supplementary oxygen]] will result in deterioration of body functions, loss of consciousness, and ultimately, death.<ref name="PBS"/><ref name=Huey/><ref name=Grocott/> Scientists at the High Altitude Pathology Institute in Bolivia dispute the existence of a death zone, based on observation of extreme tolerance to [[Hypoxia (medical)|hypoxia]] in patients with [[chronic mountain sickness]] and normal fetuses in-utero, both of which present pO<sub>2</sub> levels similar to those at the summit of Mount Everest.<ref name=nodeath>{{cite journal|last1=Zubieta-Castillo|first1=G.|last2=Zubieta-Calleja|first2=G.R.|last3=Zubieta-Calleja|first3=L.|last4=Zubieta-Castillo|first4=Nancy|title=Facts that Prove that Adaptation to life at Extreme Altitude (8842m) is possible|journal=Adaptation Biology and Medicine|year=2008|volume=5|issue=Suppl 5|pages=348–355 |url=http://zuniv.net/pub/Everest2.pdf}}</ref>

==Supplemental oxygen==
[[File:Sauerstoffflasche.jpg|thumb|right|upright|Bottled oxygen can help mountaineers survive in the death zone]]
Mountaineers use supplemental oxygen in the death zone to reduce deleterious effects. An open-circuit oxygen apparatus was first tested on the [[1922 British Mount Everest expedition|1922]] and [[1924 British Mount Everest expedition|1924]] British Mount Everest expeditions; the bottled oxygen taken in [[1921 British Mount Everest reconnaissance expedition|1921]] was not used (see [[George Finch (chemist)|George Finch]] and [[Noel Odell]]).  In [[1953 British Mount Everest expedition|1953]] the first assault party of [[Tom Bourdillon]] and [[Charles Evans (mountaineer)|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".<ref>{{cite book |last=Hunt |first= John |title= The Ascent of Everest |url=https://archive.org/details/ascentofeverest0000hunt |url-access=registration |year= 1953 |publisher= Hodder & Stoughton |location= London |page= [https://archive.org/details/ascentofeverest0000hunt/page/206 206] }} </ref> 

[[Physiologist]] [[Griffith Pugh]] was on the [[1952 British Cho Oyu expedition|1952]] and 1953 expeditions to study the effects of cold and altitude; he recommended acclimatising above {{cvt|15000|ft|order=flip}} for at least 36 days and the use of closed-circuit equipment.{{cn|date=May 2025}} He further studied the ability to acclimatise over several months on the [[1960–61 Silver Hut expedition]] to the Himalayas. 

In [[Timeline of Mount Everest expeditions#1978|1978]], [[Reinhold Messner]] and [[Peter Habeler]] made the first ascent of Mount Everest without supplemental oxygen.<ref>{{cite web|url=https://www.pbs.org/wgbh/nova/everest/history/firstwoo2.html|title=First without Oxygen|work=Nova|publisher=PBS|access-date=2025-05-17|archive-date=2025-05-17|archive-url=https://web.archive.org/web/20250517205812/https://www.pbs.org/wgbh/nova/everest/history/firstwoo2.html     |url-status=live}}</ref>

==Notable disasters==
Several expeditions have encountered disaster in the death zone that led to multiple fatalities, including:
*[[1996 Mount Everest disaster]]
*[[2008 K2 disaster]]

==See also==
*[[Effects of high altitude on humans]]
*[[Hypoxemia]]
*[[Hypoxia (medical)]]

== References ==
{{Reflist}}

{{Respiratory physiology}}
{{Consequences of external causes}}

[[Category:Mountaineering]]
[[Category:Eight-thousanders]]
[[Category:Human physiology]]

[[de:Höhenbergsteigen#Todeszone]]