What percentage of atmospheric air is made up of oxygen?

Atmospheric air is composed of approximately 21% oxygen by volume. This percentage is crucial for divers to understand due to its impact on both diving physiology and the management of diving emergencies. Oxygen is essential for human respiration, providing the necessary gas for cellular metabolism and energy production.

In diving, awareness of the oxygen content in the air is particularly important when considering the effects of different gas mixtures under pressure. While most air compressors and dive tanks contain a standard air mix that includes roughly 21% oxygen, specialized breathing gases may modify this composition.

The other percentages listed correspond to gases that are not present in significant amounts in the atmosphere. For example, there is only about 78% nitrogen, with trace amounts of other gases. Understanding the exact composition of atmospheric air helps divers make informed decisions during planning and emergency responses.