It is called the "death zone" because acclimatization is essentially impossible. Here, the air has so little oxygen and the stress is so high that the body begins to consume its own flesh to survive, and the brain starts to crash.

In the "Death Zone", the air holds only 30 per cent as much oxygen as at sea level, heightening the chances of:

• acute mountain sickness
• headaches
• loss of vision
• frostbite
• hypothermia
• pulmonary or cerebral oedema
• erratic breathing rhythms
• heart attacks
• and hallucinations