Editing Mount Everest (section)

===Supplemental oxygen===
[[File:Iván Ernesto Gómez Carrasco en la cima del Monte Everest.jpg|thumb|upright|Climber at the summit wearing an oxygen mask]]
[[File:Everest Oxygen Graph.jpg|thumb|Available oxygen at Everest]]

Most expeditions use [[oxygen mask]]s and [[bottled oxygen|tanks]] above   {{convert|8000|m|ft|0|abbr=on}}.<ref>{{cite web|url=http://classic.mountainzone.com/everest/98/climb5-21oxygen.html|archive-url=https://archive.today/20000822075357/http://classic.mountainzone.com/everest/98/climb5-21oxygen.html|archive-date=22 August 2000|title=Chamber of Horrors: The Oxygen Mask|publisher=MountainZone.com|date=21 May 1998|access-date=1 April 2007}}</ref> Everest can be climbed without supplementary oxygen, but only by the most accomplished mountaineers and at increased risk. Humans' ability to think clearly is hindered with low oxygen, and the combination of extreme weather, low temperatures, and steep slopes often requires quick, accurate decisions. While about 95 per cent of climbers who reach the summit use [[bottled oxygen]] in order to reach the top, about five per cent of climbers have summited Everest without supplemental oxygen. The death rate is double for those who attempt to reach the summit without supplemental oxygen.<ref>{{cite news |title =Field Test on Everest: To Os or not to Os| work=National Geographic| date =18 May 2012| url =http://ngm.nationalgeographic.com/everest/blog/2012-05-18/to-os-or-not-to-os| access-date = 11 May 2015|archive-url=https://web.archive.org/web/20171228111038/http://ngm.nationalgeographic.com:80/everest/blog/2012-05-18/to-os-or-not-to-os|archive-date=28 December 2017}}</ref> Travelling above {{convert|8000|m|ft|abbr=on}} altitude is a factor in [[cerebral hypoxia]].<ref name=thom/> One study found that Mount Everest may be the highest an acclimatised human could go, but also found that climbers may suffer permanent neurological damage despite returning to lower altitudes.<ref name=thom/>

The use of bottled oxygen to ascend Mount Everest has been controversial. It was first used on the [[1922 British Mount Everest Expedition]] by [[George Finch (chemist)|George Finch]] and [[Geoffrey Bruce (mountaineer)|Geoffrey Bruce]] who climbed up to {{convert|7800|m|ft|abbr=on}} at a spectacular speed of {{convert|1000|ft/h|m/h|order=flip|adj=pre| vertical }}. Pinned down by a fierce storm, they escaped death by breathing oxygen from a jury-rigged set-up during the night. The next day they climbed to {{convert|8100|m|ft|abbr=on}} at {{convert|900|ft/h|m/h|order=flip|abbr=on}} – nearly three times as fast as non-oxygen users. Yet the use of oxygen was considered so unsportsmanlike that none of the rest of the Alpine world recognised this high ascent rate.{{Citation needed|date=June 2011}}

[[George Mallory]] described the use of such oxygen as unsportsmanlike, but he later concluded that it would be impossible for him to summit without it and consequently used it on his final attempt in 1924.<ref>{{cite book|author1=Tom Holzel|author2=Audrey Salkeld|title=The Mystery of Mallory & Irvine|year=1986}}</ref> When [[Tenzing Norgay|Tenzing]] and Hillary made the first successful summit in 1953, they also used [[Bottled oxygen (climbing)|open-circuit bottled oxygen sets]], with the expedition's physiologist [[Griffith Pugh]] referring to the oxygen debate as a "futile controversy", noting that oxygen "greatly increases subjective appreciation of the surroundings, which after all is one of the chief reasons for climbing."<ref>{{cite book|title=The Ascent of Everest|first=John|last=Hunt|publisher=Hodder & Stoughton|year=1953|chapter=Appendix VII}}</ref> For the next twenty-five years, bottled oxygen was considered standard for any successful summit.

{{blockquote|...although an acclimatised lowlander can survive for a time on the summit of Everest without supplemental oxygen, one is so close to the limit that even a modicum of excess exertion may impair brain function.|Thomas F. Hornbein in ''The high-altitude brain''<ref name=thom>{{cite journal|url=http://jeb.biologists.org/content/204/18/3129.full|title=The high-altitude brain|issue=18|pages=3129–3132|journal=Journal of Experimental Biology|volume=204|access-date=20 September 2015|date=15 September 2001|last1=Hornbein|first1=Thomas F.|doi=10.1242/jeb.204.18.3129|pmid=11581326|doi-access=free|bibcode=2001JExpB.204.3129H }}</ref>}}

[[Reinhold Messner]] was the first climber to break the bottled oxygen tradition and in 1978, with [[Peter Habeler]], made the first successful climb without it. In 1980, Messner summited the mountain solo, without supplemental oxygen or any porters or climbing partners, on the more difficult northwest route. Once the climbing community was satisfied that the mountain could be climbed without supplemental oxygen, many purists then took the next logical step of insisting that is how it ''should'' be climbed.<ref name=Krakauer-1997>{{cite book|last1=Krakauer|first1=Jon|title=Into Thin Air: A Personal Account of the Mt. Everest Disaster|date=1997|publisher=Villard|location=New York|isbn=978-0-679-45752-7}}</ref>{{RP|154}}

The aftermath of the [[1996 Mount Everest disaster|1996 disaster]] further intensified the debate. [[Jon Krakauer]]'s ''[[Into Thin Air]]'' (1997) expressed the author's personal criticisms of the use of bottled oxygen. Krakauer wrote that the use of bottled oxygen allowed otherwise unqualified climbers to attempt to summit, leading to dangerous situations and more deaths. The disaster was partially caused by the sheer number of climbers (34 on that day) attempting to ascend, causing bottlenecks at the Hillary Step and delaying many climbers, most of whom summited after the usual 14:00 turnaround time. He proposed banning bottled oxygen except for emergency cases, arguing that this would both decrease the growing pollution on Everest—many bottles have accumulated on its slopes—and keep marginally qualified climbers off the mountain.

The 1996 disaster also introduced the issue of the guide's role in using bottled oxygen.<ref name="salon">{{cite web |url=http://www.salon.com/wlust/feature/1998/08/07featurea.html|title=Everest controversy continues| website=Salon|date=7 August 1998|access-date=17 June 2016|author=DeWalt, Weston|archive-url=https://web.archive.org/web/20110514043017/http://www.salon.com/wlust/feature/1998/08/07featurea.html | archive-date=14 May 2011}}</ref>

Guide [[Anatoli Boukreev]]'s decision not to use bottled oxygen was sharply criticised by Jon Krakauer. Boukreev's supporters (who include G. Weston DeWalt, who co-wrote ''[[The Climb (book)|The Climb]]'') state that using bottled oxygen gives a false sense of security.<ref>{{cite web|url=http://www.boukreev.org/The%20Oxygen%20Illusion.htm|title=The Oxygen Illusion|publisher=The Anatoli Boukreev Memorial Fund|access-date=24 June 2010|archive-date=30 July 2019|archive-url=https://web.archive.org/web/20190730093801/http://www.boukreev.org/The%20Oxygen%20Illusion.htm|url-status=live}}</ref> Krakauer and his supporters point out that, without bottled oxygen, Boukreev could not directly help his clients descend.<ref name="salongarner">{{cite news|url=http://www.salon.com/wlust/feature/1998/08/cov_03feature3.html|archive-url=https://web.archive.org/web/20000303032319/http://www.salon.com/wlust/feature/1998/08/cov_03feature3.html|archive-date=3 March 2000|title=Coming Down|page=3|first=Dwight|last=Garner|work=Salon|date=August 1998}}</ref>

The low oxygen can cause a mental fog-like impairment of cognitive abilities described as "delayed and lethargic thought process, clinically defined as bradypsychia" even after returning to lower altitudes.<ref name=altitude>{{cite web|url=http://www.boulderweekly.com/article-8924-this-is-your-brain-this-is-your-brain-at-altitude.html|title=This is your brain. This is your brain at altitude|website=Boulder Weekly|access-date=20 September 2015|date=14 June 2012}}</ref> In severe cases, climbers can experience hallucinations. Some studies have found that high-altitude climbers, including Everest climbers, experience altered brain structure.<ref name=altitude/>