What is the equivalent air depth (EAD) at 30 meters with a Nitrox mix of 32% oxygen?

The equivalent air depth (EAD) provides a way to compare the effects of diving with enriched air (Nitrox) against the effects of diving with air. When using a Nitrox mixture, the amount of oxygen in the mixture allows divers to extend their no-decompression limits and reduce nitrogen absorption, which impacts their EAD calculation.

In this case, a Nitrox mix of 32% oxygen means that the remaining 68% is nitrogen. The EAD is calculated based on the partial pressure of nitrogen at the given depth. At 30 meters, the absolute pressure (total pressure experienced by a diver) is 30 meters plus 3 atmospheres from the surface pressure, which gives us 4 atmospheres absolute (ATA).

To find the partial pressure of nitrogen at this depth, multiply the total pressure by the fraction of nitrogen in the air:

• Nitrogen partial pressure at 30 meters = 4 ATA x 0.68 = 2.72 ATA of nitrogen.

To find the EAD in meters of air, you need to equate this nitrogen partial pressure to that of air:

• The partial pressure of nitrogen in normal air (which is 21% oxygen and 79% nitrogen) at the surface is