What is the standard percentage of oxygen in regular air?

What is the standard percentage of oxygen in regular air?

• A. Approximately 18%.
• B. Approximately 21%.
• C. Approximately 25%.
• D. Approximately 30%.

Answer: (B)

The correct answer is approximately 21% because this is the internationally recognized standard percentage of oxygen found in the Earth's atmosphere at sea level. This composition is consistent in most environments where people normally breathe. Understanding this value is fundamental in diving, especially when discussing enriched air nitrox, because it helps divers comprehend how increasing the proportion of oxygen in the breathing gas affects their physiology, particularly in relation to oxygen toxicity and no-decompression limits. The other options suggest lower or higher percentages of oxygen, which do not reflect the true composition of the atmosphere and could lead to misconceptions about the effects of varying oxygen levels during diving operations.

The correct answer is approximately 21% because this is the internationally recognized standard percentage of oxygen found in the Earth's atmosphere at sea level. This composition is consistent in most environments where people normally breathe. Understanding this value is fundamental in diving, especially when discussing enriched air nitrox, because it helps divers comprehend how increasing the proportion of oxygen in the breathing gas affects their physiology, particularly in relation to oxygen toxicity and no-decompression limits. The other options suggest lower or higher percentages of oxygen, which do not reflect the true composition of the atmosphere and could lead to misconceptions about the effects of varying oxygen levels during diving operations.