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In mountaineering, the death zone refers to altitudes above which the pressure of oxygen is insufficient to sustain human life for an extended time span. This point is generally agreed as 8,000 m (26,000 ft), where atmospheric pressure is less than 356 millibars (10.5 inHg; 5.16 psi). [ 1 ]
In the death zone, the human body cannot acclimatize. An extended stay in the death zone without supplementary oxygen will result in deterioration of bodily functions, loss of consciousness, and, ultimately, death. [3] [4] [5] The summit of K2, the second highest mountain on Earth, is in the death zone.
The mountain was first climbed on October 19, 1954, via the north-west ridge by Herbert Tichy, Joseph Jöchler and Sherpa Pasang Dawa Lama of an Austrian expedition. [10] Cho Oyu was the fifth eight-thousander to be climbed, after Annapurna in June 1950, Mount Everest in May 1953, Nanga Parbat in July 1953 and K2 in July 1954.
Humans are generally adapted to lowland environments where oxygen is abundant. [12] At altitudes above 2,500 meters (8,200 ft), such humans experience altitude sickness, which is a type of hypoxia, a clinical syndrome of severe lack of oxygen. Some humans develop the illness beginning at above 1,500 meters (5,000 ft). [13]
The first couple and team to summit all 14 eight-thousanders were the Italians Nives Meroi (who was the second woman to accomplish this feat without supplementary oxygen), and her husband Romano Benet on 11 May 2017. [15] [16] The couple climbed alpine style, without the use of supplementary oxygen or other support. [16] [17]
In the region from sea level to around 3,000 m (10,000 ft), known as the physiological-efficient zone, oxygen levels are usually high enough for humans to function without supplemental oxygen and altitude decompression sickness is rare. The physiological-deficient zone extends from 3,600 m (12,000 ft) to about 15,000 m (50,000 ft).
Over 81 million people live permanently at high altitudes (>2,500 m or 8,200 ft) [52] in North, Central and South America, East Africa, and Asia, and have flourished for millennia in the exceptionally high mountains, without any apparent complications. [53] For average human populations, a brief stay at these places can risk mountain sickness. [54]
In May 2019, Sirbaz became the first Pakistani to successfully summit the 8,516-metre (27,940-foot) high Mount Lhotse – the world’s 4th highest mountain - without using supplementary oxygen. [8] In July 2019, Sirbaz climbed the summit of the 8,047-metre (26,401 ft) Broad Peak mountain in Pakistan, without using supplementary oxygen. [9]