Editing Mount Everest (section)

===Death zone===
{{See also|Effects of high altitude on humans}}
[[File:Everest Peace Project - Everest summit.jpg|thumb|The summit of Mount Everest from the North side]]
[[File:Everest-fromKalarPatar.jpg|thumb|From [[Kala Patthar]], Nepal]]
At the higher regions of Mount Everest, climbers seeking the summit typically spend substantial time within the [[death zone]] (altitudes higher than    {{convert|8000|m|ft|abbr=on|disp=or}}), and face significant challenges to survival. Temperatures can dip to very low levels, resulting in [[frostbite]] of any body part exposed to the air. Since temperatures are so low, snow is well-frozen in certain areas and death or injury by slipping and falling can occur. High winds at these altitudes on Everest are also a potential threat to climbers.

Another significant [[Breathing#Effects of ambient air pressure|threat to climbers is low atmospheric pressure]]. The atmospheric pressure at the top of Everest is about a third of sea level pressure or {{convert|0.333|atm|mbar}}, resulting in the availability of only about a third as much oxygen to breathe.<ref>{{cite web|url=http://www.altitude.org/calculators/air_pressure.php |archive-url=https://archive.today/20120729214053/http://www.altitude.org/calculators/air_pressure.php |url-status=dead |archive-date=29 July 2012 |title=Online high altitude oxygen calculator |publisher=altitude.org |access-date=15 August 2007}}</ref>

Debilitating effects of the death zone are so great that it takes most climbers up to 12 hours to walk the distance of {{convert|1.72|km|mi}} from South Col to the summit.<ref>{{cite web|url=http://www.alanarnette.com/everest/everestsouthroutes.php|title=Mount Everest South Col Route Maps|publisher=alanarnette.com|access-date=15 August 2013|archive-date=19 December 2018|archive-url=https://web.archive.org/web/20181219105351/http://www.alanarnette.com/everest/everestsouthroutes.php|url-status=live}}</ref> Achieving even this level of performance requires prolonged altitude acclimatisation, which takes 40–60 days for a typical expedition. A sea-level dweller exposed to the atmospheric conditions at the altitude above {{convert|8500|m|abbr=on}} without acclimatisation would likely lose consciousness within two to three minutes.<ref>{{cite journal|url=http://www.semae.es/wp-content/uploads/2009/11/climbers-on-mt-everest-.pdf|title=Arterial Blood Gases and Oxygen Content in Climbers on Mount Everest|journal=The New England Journal of Medicine|year=2009|first=Michael P.W.|last=Grocott|doi=10.1056/NEJMoa0801581|volume=360|issue=2|pages=140–9|pmid=19129527|display-authors=etal|access-date=29 October 2011|archive-url=https://web.archive.org/web/20160304102433/http://www.semae.es/wp-content/uploads/2009/11/climbers-on-mt-everest-.pdf|archive-date=4 March 2016|url-status=dead}}</ref>

In May 2007, the Caudwell Xtreme Everest undertook a medical study of oxygen levels in human blood at extreme altitude. Over 200 volunteers climbed to Everest Base Camp where various medical tests were performed to examine blood oxygen levels. A small team also performed tests on the way to the summit.<ref>{{cite web|url=http://www.xtreme-everest.co.uk/news_detail.php?article=196|archive-url=https://web.archive.org/web/20080606065437/http://www.xtreme-everest.co.uk/news_detail.php?article=196|archive-date=6 June 2008|title=Everest 2007|publisher=Caudwell Xtreme Everest 2007}}</ref> Even at base camp, the low [[partial pressure]] of oxygen had direct effect on blood oxygen saturation levels. At sea level, [[Oxygen saturation (medicine)#Definition|blood oxygen saturation]] is generally 98 to 99 per cent. At base camp, blood saturation fell to between 85 and 87 per cent. Blood samples taken at the summit indicated very low oxygen levels in the blood. A side effect of low blood oxygen is a greatly increased breathing rate, often 80–90 breaths per minute as opposed to a more typical 20–30. Exhaustion can occur merely by attempting to breathe.<ref>{{cite web |url=http://www.altitude.org/oxygen_levels.php |title=Altitude physiology |publisher=altitude.org |access-date=6 July 2010 |archive-url=https://web.archive.org/web/20180616140234/http://www.altitude.org/oxygen_levels.php |archive-date=16 June 2018 |url-status=dead}}</ref>

Lack of oxygen, exhaustion, extreme cold, and climbing hazards all contribute to the death toll. An injured person who cannot walk is in serious trouble, since rescue by helicopter is generally impractical and carrying the person off the mountain is very risky. People who die during the climb are typically left behind. As of 2015, over 200 bodies remain on the mountain.<ref name="Nuwer"/>

{{Blockquote|Debilitating symptoms consistent with high altitude cerebral oedema commonly present during descent from the summit of Mount Everest. Profound fatigue and late times in reaching the summit are early features associated with subsequent death.|Mortality on Mount Everest, 1921–2006: descriptive study<ref>{{cite journal |doi=10.1136/bmj.a2654 |pmid=19074222 |pmc=2602730 |title=Mortality on Mount Everest, 1921-2006: Descriptive study |journal=BMJ |volume=337 |pages=a2654 |year=2008 |last1=Firth |first1=P.G |last2=Zheng |first2=H |last3=Windsor |first3=J. S |last4=Sutherland |first4=A.I |last5=Imray |first5=C.H |last6=Moore |first6=G W K |last7=Semple |first7=J.L |last8=Roach |first8=R.C |last9=Salisbury |first9=R.A|issue=dec11 1 }}</ref> }}

A 2008 study noted that the "death zone" is indeed where most Everest deaths occur, but also noted that most deaths occur during descent from the summit.<ref>{{cite web|url=http://www.climbing.com/climber/climbing-everest-who-makes-it-to-the-top/|title=Climbing Everest: Who Makes It to the Top?|website=Climbing|date=23 November 2009|access-date=20 September 2015|archive-date=18 December 2015|archive-url=https://web.archive.org/web/20151218082432/http://www.climbing.com/climber/climbing-everest-who-makes-it-to-the-top/|url-status=live}}</ref> A 2014 article in ''[[The Atlantic]]'' about deaths on Everest noted that while falling is one of the greatest dangers the death zone presents for all 8000ers, avalanches are a more common cause of death at lower altitudes.<ref name=atlan>{{cite web|url=https://www.theatlantic.com/international/archive/2014/04/mortality-on-mount-everest/360927/|title=Charting Deaths on Mount Everest|author=Svati Kirsten Narula|website=The Atlantic|access-date=20 September 2015|date=21 April 2014|archive-date=14 May 2022|archive-url=https://web.archive.org/web/20220514081833/https://www.theatlantic.com/international/archive/2014/04/mortality-on-mount-everest/360927/|url-status=live}}</ref>

Despite this, Everest is safer for climbers than a number of peaks by some measurements, but it depends on the period.<ref name=safer>{{cite web|url=http://mentalfloss.com/article/30757/5-mountains-deadlier-everest |title=5 Mountains Deadlier Than Everest |website=Mental Floss |access-date=20 September 2015 |url-status=dead |archive-url=https://web.archive.org/web/20150923175946/http://mentalfloss.com/article/30757/5-mountains-deadlier-everest |archive-date=23 September 2015}}</ref> Some examples are [[Kangchenjunga]], [[K2]], [[Annapurna Massif|Annapurna]], [[Nanga Parbat]], and the [[Eiger]] (especially the ''<abbr title="north wall">nordwand</abbr>'').<ref name=safer/> Some factors that affect total mountain lethality include the level of popularity of the mountain, the skill of those climbing, and the difficulty of the climb.<ref name=killermountains>{{cite web|url=https://uk.news.yahoo.com/everest-anniversary--world-s-five-deadliest-mountain-ranges-siula-grande-k2-mont-blanc-annapunna-155951170.html#9eTWTzo|title=Everest anniversary: World's five deadliest mountains|date=28 May 2013|website=Yahoo News UK|access-date=20 September 2015|archive-date=14 May 2022|archive-url=https://web.archive.org/web/20220514072501/https://uk.news.yahoo.com/everest-anniversary--world-s-five-deadliest-mountain-ranges-siula-grande-k2-mont-blanc-annapunna-155951170.html#9eTWTzo|url-status=live}}</ref>

Another health hazard is [[retinal haemorrhage]]s, which can damage eyesight and cause blindness.<ref name=eyes>{{cite news|url=https://www.independent.co.uk/news/world/asia/everest-team-forced-to-leave-sick-british-climber-to-die-1988979.html|title=Everest team forced to leave sick British climber to die|work=The Independent|access-date=20 September 2015|archive-date=19 August 2022|archive-url=https://web.archive.org/web/20220819162222/https://www.independent.co.uk/news/world/asia/everest-team-forced-to-leave-sick-british-climber-to-die-1988979.html|url-status=live}}</ref> Up to a quarter of Everest climbers can experience retinal haemorrhages, and although they usually heal within weeks of returning to lower altitudes, in 2010 a climber went blind and died in the death zone.<ref name=eyes/>

{{Blockquote|At one o'clock in the afternoon, the British climber Peter Kinloch was on the roof of the world, in bright sunlight, taking photographs of the Himalayas below, "elated, cheery and bubbly". But Mount Everest is now his grave, because only minutes later, he suddenly went blind and had to be abandoned to die from the cold.|A. McSmith<ref name=eyes/>}}

The team made a huge effort for the next 12 hours to try to get him down the mountain, but to no avail, as they were unsuccessful in getting him through the difficult sections.<ref name="theweek1">{{cite web |author=Peter Gillman |url=http://www.theweek.co.uk/politics/14247/what-killed-peter-kinloch-%E2%80%98left-die%E2%80%99-everest |title=What killed Peter Kinloch, 'left to die' on Everest |work=The Week UK |date=2 June 2010 |access-date=17 June 2016 |archive-date=2 April 2017 |archive-url=https://web.archive.org/web/20170402234654/http://www.theweek.co.uk/politics/14247/what-killed-peter-kinloch-%E2%80%98left-die%E2%80%99-everest |url-status=dead}}</ref> Even for the able, Everest's Northeast Ridge is recognised as a challenge. It is hard to rescue someone who has become incapacitated and it can be beyond the ability of rescuers to save ''anyone'' in such a difficult spot.<ref name="theweek1"/> One way around this situation was pioneered by two Nepali men in 2011, who had intended to paraglide off the summit. They had no choice and were forced to go through with their plan anyway, because they had run out of bottled oxygen and supplies.<ref name="abcnews1">{{cite web |url=https://abcnews.go.com/Travel/paragliding-everests-peak-kayaking-indian-ocean/story?id=21097292 |title=Paragliding From Everest's Peak, Then Kayaking to Indian Ocean |publisher=ABC News |date=5 December 2013 |access-date=17 June 2016 |archive-date=5 October 2024 |archive-url=https://web.archive.org/web/20241005161214/https://abcnews.go.com/Travel/paragliding-everests-peak-kayaking-indian-ocean/story?id=21097292 |url-status=live }}</ref> They successfully launched off the summit and para-glided down to [[Namche Bazaar]] in just 42 minutes, without having to climb down the mountain.<ref name="abcnews1"/>