Why Everest's 'death zone' claims so many lives

UNDER THE MICROSCOPE:THE SUMMIT OF Mount Everest is the highest point above sea level on earth and, consequently, climbing this peak will always be alluring to mountaineers. Climbing Everest is a dangerous activity and, on average over many years, there was one death for every 10 successful attempts. And as dangerous as it is to climb Everest, coming back down is even more hazardous, as reported in a study in The British Medical Journal (BMJ), Vol 337, December 2008, by PG Firth and colleagues.

Mount Everest is 8,848 metres high (ie, 8,848 metres above sea level). It rises a few more millimetres every year due to geological forces. Several other mountains on earth are taller than Everest when measured from base to summit, but none are higher above sea level. For example, Mauna Kea in Hawaii rises more than 10,200 metres measured from its base on the ocean floor, in which respect it is the world’s highest mountain, but it only reaches 4,205 metres above sea level.

Everest is located in the Himalayas on the border between Nepal and Tibet. It is named after Col Sir George Everest (1790-1866), a surveyor general of India. The Tibetan name for the mountain is Chomolungma, which means “saint mother”. The Chinese claim that the mountain should always be called by its Tibetan name as it was marked as such on a Chinese map more than 280 years ago.

The mountain has two main climbing routes, the south-east ridge from Nepal and the north-east ridge from Tibet. The south-east route is technically easier and is the most frequently used. It was the route used by the first conquerors of Everest, Edmund Hillary and Tenzing Norgay, in 1953. Base camp on the south-east ridge is at an altitude of 5,380 metres. Climbers spend a couple of weeks there acclimatising to altitude. On the ascent they rest at camps two, three and four at successively higher altitudes before pushing for the summit. The youngest person to climb Everest was a 15-year-old Sherpa girl and the oldest was a 76-year-old man.

The BMJ study examined the pattern of mortality among climbers on Everest in the period 1921-2006. In total the mountaineers included 8,030 climbers and 6,108 Sherpas. There were 212 climbing deaths (a death rate of 1.3 per cent), 192 of which occurred above the base camp. Among climbers who died higher than 8,000 metres above sea level, 56 per cent succumbed on their descent from the summit and 17 per cent died after turning back. Only 15 per cent died on the way up or before leaving the final camp.

The reason more people die descending Everest than ascending is because they are exhausted after the effort of ascending. Most of the deaths were among climbers, not Sherpas. Sherpas are native to this area and are better adapted physiologically to high altitudes, having broader arteries and capillaries to carry oxygen-bearing blood more efficiently. Altitudes higher than 8,000 metres on Everest are known as the “death zone” because the oxygen levels there will not support life for long. Consequently, most expeditions use oxygen masks and tanks at this height. The mountain can be climbed without supplementary oxygen, but this increases the risk to climbers. The first oxygen-less ascent was in May 1978.

Humans don’t think clearly when oxygen is low and conditions on Everest often call for quick and accurate decisions. A side-effect of low oxygen levels is that a climber must breathe much faster. Breathing rate can increase from 20-30 breaths per minute to 80-90 breaths. You can get exhausted just trying to breathe. Conditions are so dangerous in the “death zone” that most corpses are left lie where they fall. A large proportion of climbers die from altitude-related illness. High-altitude cerebral oedema and high-altitude pulmonary oedema are both forms of altitude sickness which cause a potentially fatal build-up of fluid in the brain or lungs.

Small black jumping spiders are found at elevations as high as 6,700 metres on Everest. They live in crevices and feed on frozen insects that are blown there by the wind.

In May 2006 a climbing ethics controversy broke out when double-amputee climber Mark Ingles revealed that his and other climbing parties had passed a distressed climber, David Sharp, sheltering under a rock 450 metres beneath the summit without attempting a rescue. It was claimed that rescue efforts would have been futile and would have caused more deaths.

I can understand the temptation offered by Mount Everest to professional mountaineers, but I am puzzled as to why amateurs attempt this extreme challenge. I know that they are led by experienced guides, but nevertheless I am mystified. They must have a very high threshold for excitement.

William Reville is associate professor of biochemistry and public awareness of science officer at UCC. See understandingscience.ucc.ie