Heartsaver First Aid Part I Progress Indicator: Question 3 of 22 3.  At sea level, the pressure of all gases is 760 mm Hg, or 760 Torr.  If the concentration of oxygen in the atmosphere at sea level is 21%, the partial pressure of oxygen at sea level is approximately: Choices: 150 mm Hg 160 mm Hg 180 mm Hg 210 mm Hg