What is the death zone of Mount Everest?

The death zone is the name for the highest altitudes on Mount Everest, where low atmospheric pressure, along with freezing temperatures, mean conditions are harsher than most humans are capable of surviving.

Many climbers on Mount Everest use supplemental oxygen above 8,000 metres, but above approximately 8,750 metres (29,030 ft) the human body begins to deteriorate, no matter how much supplemental oxygen is used, resulting in a very high risk of death.

Most expeditions planning on reaching the summit begin using bottled oxygen around the South Col, at 7,950 metres (26,100 ft). Above 8,230 metres (27,000 ft), the partial pressure of oxygen in the air is so low that even when breathing pure oxygen from a tank, the oxygen tension in arterial blood is lower than can normally be tolerated at sea level.

Mountaineers who spend an extended amount of time in this thin air risk high-altitude cerebral oedema (HACE), which affects brain function causing confusion, loss of coordination and judgement, hallucination, and ultimately loss of consciousness. Additionally, the body produces more red blood cells to increase the oxygen-carrying capacity of the blood. This can lead to a dangerously increased risk of potentially life-threatening blood clots.

Ascents into this region are technically challenging and strenuous. The extreme effects of altitude also include a reduction in physical and mental performance, including slowed reaction times, confusion and impaired judgment. Moreover, the weather and storms may come with no warning and can easily dislodge ice and snow, leading to deadly avalanches.

All these factors combine to make the death zone the single most dangerous part of any ascent of Mount Everest.