Mountaineers carry oxygen cylinders when climbing high mountains as the air pressure is low. At the average sea level, the atmospheric pressure level is 101.325 kPa. This is sufficient for oxygen to selectively permeate into the blood. However, at higher altitudes, the air pressure considerably decreases. At the top of Mount Everest, the air pressure is just 30 kPa, which is insufficient for oxygen to selectively permeate into the blood. Hence, mountaineers end up carrying pressurized oxygen cylinders on high mountains.
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