Most of the 200+ climbers who have died on Mount Everest have died in the death zone. Due to the inverse relationship of atmospheric pressure to altitude, at the top of Mount Everest the average person takes in about 30% of the oxygen in the air that they would take in at sea level; a normal human person used to breathing air at sea level could only be there for a few minutes before they became unconscious. Most climbers have to carry oxygen bottles to be able to reach the top. Visitors become weak and have inability to think clearly and make decisions, especially under stress. Since helicopters also perform poorly in thin air, many bodies of dead visitors are left on the mountain.