What nitrox really does (rec on-ramp)

Posted 11 June 2026 · Field Note #4

Nitrox 101: more bottom time, not more depth

Nitrox, often labelled EAN for enriched air nitrox, is simply air with the recipe adjusted: more oxygen, less nitrogen. Ordinary air is about 21% oxygen and 79% nitrogen. A common nitrox blend like EAN32 is 32% oxygen and 68% nitrogen. That's the entire idea, just a richer dose of oxygen in place of some of the nitrogen.

Why would less nitrogen help? Because nitrogen is the inert gas your body absorbs at depth, and absorbing it is what eventually forces you to surface or do stops. With less nitrogen in every breath, your tissues load that gas more slowly, which means your no-decompression limit, the time you can stay before mandatory stops, gets longer at recreational depths. More minutes on the reef, same depth. That is the genuine, well-documented benefit.

Now the part people get backwards. Nitrox is not a deep gas. The extra oxygen that buys you bottom time also raises your oxygen partial pressure faster as you descend, so your maximum operating depth becomes shallower, not deeper. EAN36, for instance, hits the standard 1.4 bar working ppO₂ limit at about 29 m, so that is its MOD. Take a rich nitrox blend deeper and you trade a nitrogen problem for an oxygen-toxicity problem, which is far worse.

A second myth worth retiring: nitrox won't make you feel less tired after diving unless you were genuinely flirting with your decompression limits on air to begin with. The "I felt great" effect is mostly down to better hydration, rest, and a relaxed dive, not the gas itself.

The practical discipline is the same on every fill, recreational or technical. Analyse the gas yourself with a calibrated analyser, write the actual oxygen percentage and the resulting MOD on the cylinder, confirm your computer is set to the same mix, and then dive within that depth. Treat an unanalysed cylinder as an unknown gas.

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⚠ Educational only — not a substitute for training or a dive computer. Verify every number independently and dive within your certification.