The air pressure at Camp IV is one-third of that at sea level. Tying a shoelace or getting rid of body wastes become monumental tasks requiring intense concentration. The thin air slows every movement and every thought. At Camp IV, it's critical. A regulator controls the flow of oxygen, which comes at about two to three litres per minute.
Climbers sleep with their oxygen masks on.
It helps keep their outer extremities warm and their minds clearer. On the descent, climbers may use an additional two bottles of oxygen for sleeping on the South Col. The team plans to climb down as far as Camp II after summitting, but they are prepared to stop and sleep at Camp IV if necessary. Everyone retreated to their nylon domes the moment they reached the Col and did their best to nap, but the machine-gun rattle of the flapping tents and the anxiety over what was to come made sleep out of the question for most of us. On the way up, teams stop at Camp IV only long enough to rest for the final summit climb.