Kinetic Molecular Theory

Approximately twenty percent of the atmosphere is oxygen. This gas is essential for life. In environments where oxygen is in low supply or not breathable by humans, it can be provided from a tank. Gases are compressible and a large amount of oxygen is easily stored in a relatively small container. When the oxygen is released, the volume of the gas expands as the pressure decreases. The gas is then available for breathing under normal pressure.

How does this work for scuba divers swimming underwater? The scuba diver uses a tank of compressed gas, and the gas is released through a regulator. The regulator reduces the pressure of the breathing gas providing the gas to the diver at normal pressure.