Analysis of information sources in references of the Wikipedia article "Altitude sickness" in English language version.
Visitors unaccustomed to high elevations may experience symptoms of Acute Mountain Sickness (AMS)[...s]uggestions for alleviating symptoms include drinking plenty of water[.]
The relative amount of oxygen in the air (21 percent) does not vary appreciably at altitudes up to 21,350 meters (70,000 feet).
The relative amount of oxygen in the air (21 percent) does not vary appreciably at altitudes up to 21,350 meters (70,000 feet).