Which gas mixture is most commonly used in Enriched Air Nitrox?

The most commonly used gas mixture in Enriched Air Nitrox is indeed a combination of oxygen and nitrogen. This mixture increases the percentage of oxygen available to divers compared to standard air, which typically consists of about 21% oxygen and 79% nitrogen.

By enriching the air with a higher percentage of oxygen, divers can extend their no-decompression limits and reduce the risk of nitrogen narcosis during deeper dives. The specific mixes can vary, but common nitrox blends include EAN32 (32% oxygen, 68% nitrogen) and EAN36 (36% oxygen, 64% nitrogen).

Other options, such as helium and oxygen or nitrogen and hydrogen, are not typically used in the context of enriched air nitrox diving for recreational purposes. Helium is used in technical diving due to its unique properties at greater depths, but it is not a primary component of nitrox. Similarly, air and carbon dioxide, and nitrogen and hydrogen, do not represent standard gas mixtures used in diving practices. Thus, oxygen and nitrogen is the definitive choice for Enriched Air Nitrox.