The air we breathe contains 21% oxygen and 79% nitrogen. However, compressed oxygen gas is 99.5% pure oxygen.
Manufacturers extract oxygen from the atmosphere and simply compress the oxygen gas molecules, then fill the aluminum tanks.
So the oxygen tanks are under enough pressure.
Oxygen labeled as having been produced by the air-liquefaction process may be exempted from the requirements of the tests for carbon monoxide and carbon dioxide. Acute severe asthma, Anxiety, Artificially ventilated patients, Carbon monoxide poisoning, COPD,Cyanosis, Major trauma, Resuscitation, Severe hemorrhage, Shock.