What is the standard percentage of oxygen in normal air?

Prepare for the IANTD Enriched Air (Nitrox) Test. Enhance your understanding with multiple choice questions and explanations. Boost your confidence and readiness!

Normal air is composed of approximately 21% oxygen by volume. This percentage is significant for various reasons, particularly in diving and the use of enriched air (Nitrox) mixtures. The oxygen content in the air is important because it directly affects our breathing and physiological responses. The presence of oxygen at this percentage is essential for human metabolism, as it facilitates aerobic respiration.

In diving, when using Nitrox, varying the percentage of oxygen can enhance safety and performance, but understanding the baseline of what normal air contains—21% oxygen—is critical for divers to make informed decisions about gas mixtures. A significant deviation from the normal level could lead to issues like oxygen toxicity or hypoxia, which reinforces the importance of understanding standard air composition.

The other options do not reflect the true composition of normal air. For instance, 15% is too low for a breathable atmosphere, while 35% and 78% (which actually refers to nitrogen) do not represent the correct fraction of oxygen at sea level. Therefore, the standard of 21% is key in many applications in both diving and general oxygen usage.

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