What does FO2 stand for in Nitrox diving?

FO2 stands for the Fraction of Oxygen in a given gas mixture, particularly in the context of Nitrox diving. In Nitrox diving, divers typically use breathing gases that are a mixture of nitrogen and oxygen, with the purpose of reducing the percentage of nitrogen and increasing the percentage of oxygen compared to normal air.

The fraction is an essential concept in understanding how the gas behaves and how it impacts the diver's physiology, especially regarding the risks of oxygen toxicity and nitrogen narcosis. When divers refer to FO2, they are specifically discussing the proportion of oxygen within the blend they are breathing, which is critical for safe and effective planning of dives at various depths. This knowledge allows divers to calculate their exposure limits to both oxygen and nitrogen during a dive, ensuring greater safety when using enriched air nitrox mixtures.