How nitrox and equivalent air depth extend bottom time
The gas physics behind enriched air, why EAD lengthens no-stop limits, and where the oxygen ceiling caps the benefit.
Nitrox swaps nitrogen for oxygen
Air is roughly 21 percent oxygen and 79 percent nitrogen. Enriched air nitrox raises the oxygen fraction, so EAN32 is 32 percent oxygen and 68 percent nitrogen while EAN36 is 36 and 64. Nitrogen is the inert gas your tissues absorb under pressure and must release slowly on the way up, so lowering its fraction directly lowers how fast you load nitrogen. That single change is the whole reason recreational divers reach for nitrox.
Why the EAD number stretches your limits
No-decompression limits on an air table are really nitrogen limits in disguise. Because a nitrox mix loads nitrogen more slowly, breathing it at 30 m loads you as if you were shallower on air, and the calculator names that shallower figure as the equivalent air depth. Looking up the EAD instead of the real depth in an air table gives you a longer allowed bottom time. For EAN32 at 30 m the EAD is about 24.43 m, so you plan against the shorter loading of 24 m rather than 30.
The oxygen ceiling that limits nitrox
The benefit is not free, because more oxygen means oxygen toxicity becomes the limiting risk as you go deeper. Divers cap the oxygen partial pressure of the breathing gas, commonly at 1.4 atmospheres for the working part of a dive, which sets a maximum operating depth for each mix. A richer mix like EAN36 gives a shallower EAD and even longer no-stop times, but it also has a shallower depth ceiling. EAD and maximum operating depth are two different calculations, and a safe plan respects both.
Using EAD in a real dive plan
In practice a diver analyses the cylinder with an oxygen sensor, confirms the actual oxygen percentage, then computes both the maximum operating depth and the equivalent air depth for the planned depth. The EAD feeds the no-decompression table or a computer set to that mix, while the maximum operating depth sets the hard bottom limit. Because rounding and table choices vary, always plan conservatively, add margin, and let your dive computer, which tracks your real profile continuously, have the final say.