mountaineering Mountaineering or alpinism, is a set of outdoor activities that involves ascending tall mountains. Mountaineering-related activities include traditional outdoor climbing, skiing, and traversing via ferratas. Indoor climbing, sport climbing, a ...

, the death zone refers to altitudes above a certain point where the pressure of

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

is insufficient to sustain human life for an extended time span. This point is generally tagged as , less than 356 millibars of atmospheric pressure). The concept was conceived in 1953 by

Edouard Wyss-Dunant Edouard Wyss-Dunant (17 April 1897 – 30 April 1983) was a Swiss physician and alpinist. He had a distinguished career in medicine, both in his own country and abroad. He published a number of treatises in his professional capacity and was the ...

, a Swiss doctor, who called it the lethal zone. All 14 peaks above 8000 m in the death zone are located in the

Himalaya The Himalayas, or Himalaya (; ; ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the planet's highest peaks, including the very highest, Mount Everest. Over 100 ...

and

Karakoram The Karakoram is a mountain range in Kashmir region spanning the borders of Pakistan, China, and India, with the northwest extremity of the range extending to Afghanistan and Tajikistan. Most of the Karakoram mountain range falls under the ...

of Asia. Many deaths in high-altitude mountaineering have been caused by the effects of the death zone, either directly by loss of vital functions or indirectly by wrong decisions made under stress, or physical weakening leading to accidents. An extended stay above without

supplementary oxygen Oxygen therapy, also known as supplemental oxygen, is the use of oxygen as medical treatment. Acute indications for therapy include hypoxemia (low blood oxygen levels), carbon monoxide toxicity and cluster headache. It may also be prophylactica ...

will result in deterioration of bodily functions and death.

Physiological background

The

human body The human body is the structure of a Human, human being. It is composed of many different types of Cell (biology), cells that together create Tissue (biology), tissues and subsequently organ systems. They ensure homeostasis and the life, viabi ...

has optimal endurance below elevation. The concentration of oxygen (O₂) in air is 20.9% so the

partial pressure In a mixture of gases, each constituent gas has a partial pressure which is the notional pressure of that constituent gas as if it alone occupied the entire volume of the original mixture at the same temperature. The total pressure of an ideal gas ...

of O₂ (PO₂) at sea level is about 21.2 kPa. In healthy individuals, this saturates

hemoglobin Hemoglobin (haemoglobin BrE) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein present in red blood cells (erythrocyte ...

, the oxygen-binding red pigment in

red blood cells Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek language, Greek ''erythros'' for "red" and ''k ...

. Atmospheric pressure decreases with altitude while the O₂ fraction remains constant to about , so PO₂ decreases with altitude as well. It is about half of its sea level value at , the altitude of the

Mount Everest base camp There are two base camps on Mount Everest, on opposite sides of the mountains: South Base Camp is in Nepal at an altitude of (), while North Base Camp is in Tibet, China at (). The base camps are rudimentary campsites at the base of Mount Ev ...

, and less than a third at , the summit of Mount Everest. When PO₂ drops, the body responds with

altitude acclimatization The effects of high altitude on humans are mostly the consequences of reduced partial pressure of oxygen in the atmosphere. The oxygen saturation of hemoglobin determines the content of oxygen in blood. After the human body reaches around above ...

. 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 The human digestive system consists of the gastrointestinal tract plus the accessory organs of digestion (the tongue, salivary glands, pancreas, liver, and gallbladder). Digestion involves the breakdown of food into smaller and smaller compone ...

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 Altitude sickness, the mildest form being acute mountain sickness (AMS), is the harmful effect of high altitude, caused by rapid exposure to low amounts of oxygen at high elevation. People can respond to high altitude in different ways. Sympt ...

, including

high-altitude pulmonary edema High-altitude pulmonary edema (HAPE) is a life-threatening form of non-cardiogenic pulmonary edema that occurs in otherwise healthy people at altitudes typically above . However, cases have also been reported between in more vulnerable subjects. ...

(

HAPE High-altitude pulmonary edema (HAPE) is a life-threatening form of non-cardiogenic pulmonary edema that occurs in otherwise healthy people at altitudes typically above . However, cases have also been reported between in more vulnerable subjects. ...

) or

cerebral edema Cerebral edema is excess accumulation of fluid (edema) in the intracellular or extracellular spaces of the brain. This typically causes impaired nerve function, increased pressure within the skull, and can eventually lead to direct compressio ...

(

HACE High-altitude cerebral edema (HACE) is a medical condition in which the brain swells with fluid because of the physiological effects of traveling to a high altitude. It generally appears in patients who have acute mountain sickness and involves di ...

). Humans have survived for 2 years at 75 millibars of atmospheric pressure which appears to be near the limit of the permanently tolerable highest altitude. At extreme altitudes, above

83 millibars of atmospheric pressure 83 may refer to: * 83 (number) * 83 (film), ''83'' (film), a 2021 Indian cricket film * one of the years 83 BC, AD 83, 1983, 2083 * "83", a song by John Mayer on his 2001 album ''Room for Squares'' See also

* * List of highways numbered {{N ...

sleeping becomes very difficult, digesting food is near-impossible, and the risk of HAPE or HACE increases greatly. Sauerstoffflasche

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

will result in deterioration of body functions, loss of consciousness and, ultimately, death. Scientists at the High Altitude Pathology Institute in Bolivia dispute the existence of a death zone, based on observation of extreme tolerance to

hypoxia Hypoxia means a lower than normal level of oxygen, and may refer to: Reduced or insufficient oxygen * Hypoxia (environmental), abnormally low oxygen content of the specific environment * Hypoxia (medical), abnormally low level of oxygen in the tis ...

in patients with

chronic mountain sickness Chronic mountain sickness (CMS) is a disease in which the proportion of blood volume that is occupied by red blood cells increases (polycythaemia) and there is an abnormally low level of oxygen in the blood (hypoxemia). CMS typically develops after ...

and normal fetuses in-utero, both of which present pO₂ levels similar to those at the summit of Mount Everest. Mountaineers use supplemental oxygen in the death zone to reduce deleterious effects. An open-circuit oxygen apparatus was first tested on the

1922 Events January * January 7 – Dáil Éireann (Irish Republic), Dáil Éireann, the parliament of the Irish Republic, ratifies the Anglo-Irish Treaty by 64–57 votes. * January 10 – Arthur Griffith is elected President of Dáil Éirean ...

and

1924 Events January * January 12 – Gopinath Saha shoots Ernest Day, whom he has mistaken for Sir Charles Tegart, the police commissioner of Calcutta, and is arrested soon after. * January 20– 30 – Kuomintang in China hol ...

British Mount Everest expeditions; the bottled oxygen taken in

1921 Events January * January 2 ** The Association football club Cruzeiro Esporte Clube, from Belo Horizonte, is founded as the multi-sports club Palestra Italia by Italian expatriates in First Brazilian Republic, Brazil. ** The Spanish lin ...

was not used (see George Finch and

Noel Odell Noel Ewart Odell FRSE FGS (25 December 1890 – 21 February 1987) was an English geologist and mountaineer. In 1924 he was an oxygen officer on the Everest expedition in which George Mallory and Andrew Irvine famously perished during their summit ...

). In

1953 Events January * January 6 – The Asian Socialist Conference opens in Rangoon, Burma. * January 12 – Estonian émigrés found a Estonian government-in-exile, government-in-exile in Oslo. * January 14 ** Marshal Josip Broz Tito i ...

the first assault party of

Tom Bourdillon Thomas Duncan Bourdillon ( ; 16 March 1924 – 29 July 1956) was an English mountaineer and member of the 1953 British Mount Everest Expedition which made the first ascent of Mount Everest. He died in the Valais, Switzerland, on 29 July 1956 age ...

and Charles Evans used closed-circuit oxygen apparatus. The second (successful) party of

Ed Hillary Sir Edmund Percival Hillary (20 July 1919 – 11 January 2008) was a New Zealand mountaineer, explorer, and philanthropist. On 29 May 1953, Hillary and Sherpa mountaineer Tenzing Norgay became the first climbers confirmed to have reached t ...

and

Tenzing Norgay Tenzing Norgay (; ''tendzin norgyé''; perhaps 29 May 1914 – 9 May 1986), born Namgyal Wangdi, and also referred to as Sherpa Tenzing, was a Nepali-Indian Sherpa mountaineer. He was one of the first two people known to reach the sum ...

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 Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical a ...

Griffith Pugh Lewis Griffith Cresswell Evans Pugh (29 October 1909 – 22 December 1994), generally known as Griffith Pugh, was a British physiologist and mountaineer. He was the expedition physiologist on the 1953 British expedition that made the first asce ...

was on the

1952 Events January–February * January 26 – Black Saturday in Egypt: Rioters burn Cairo's central business district, targeting British and upper-class Egyptian businesses. * February 6 ** Princess Elizabeth, Duchess of Edinburgh, becomes m ...

and 1953 expeditions to study the effects of cold and altitude; he recommended acclimatising above 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 Year 196 ( CXCVI) was a leap year starting on Thursday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Dexter and Messalla (or, less frequently, year 949 ''Ab urbe condita ...

to the Himalayas. In

1978 Events January * January 1 – Air India Flight 855, a Boeing 747 passenger jet, crashes off the coast of Bombay, killing 213. * January 5 – Bülent Ecevit, of Republican People's Party, CHP, forms the new government of Turkey (42nd go ...

Reinhold Messner Reinhold Andreas Messner (; born 17 September 1944) is an Italian mountaineer, explorer, and author from South Tyrol. He made the first solo ascent of Mount Everest and, along with Peter Habeler, the first ascent of Everest without supplemental ...

and

Peter Habeler Peter Habeler (born 22 July 1942) is an Austrian mountaineer. He was born in Mayrhofen, Austria. He developed an interest in mountain climbing at age six.http://www.everesthistory.com/climbers/habeler Among his accomplishments as a mountaineer a ...

made the first ascent of Mount Everest without supplemental oxygen.

References

{{Consequences of external causes Mountaineering Eight-thousanders Human physiology de:Höhenbergsteigen#Todeszone