Education

Equivalent Air Depth Explained

EAD lets you use air decompression tables with nitrox mixes. Learn the formula, see a worked example, and understand when to use it.

Equivalent Air Depth is the tool that makes nitrox practical. It lets you translate a nitrox dive into an equivalent air dive so you can use standard air decompression tables and get credit for the reduced nitrogen loading.

What it is

When you breathe nitrox (enriched air), you are getting more oxygen and less nitrogen than you would on air. Less nitrogen means less decompression obligation. EAD tells you the depth at which air would give you the same nitrogen partial pressure as your nitrox mix at your actual depth.

If you are diving EAN32 at 30 meters, your nitrogen exposure is equivalent to diving on air at a shallower depth. That shallower depth is your EAD.

The formula

EAD = ((fN2 × P) / 0.79 - 1) × 10
VariableMeaning
EADEquivalent Air Depth in meters of seawater
fN2Fraction of nitrogen in the mix (e.g., 0.68 for EAN32)
PAbsolute pressure at depth in bar: (depth / 10) + 1
0.79Fraction of nitrogen in air
10Meters of seawater per atmosphere

Worked example

What is the EAD for a dive to 30 meters on EAN32?

Step by step

fN2 = 1 - 0.32 = 0.68
P = (30 / 10) + 1 = 4.0 bar
EAD = ((0.68 × 4.0) / 0.79 - 1) × 10
EAD = (2.72 / 0.79 - 1) × 10
EAD = (3.443 - 1) × 10
EAD = 24.43 msw

Diving to 30 meters on EAN32 gives you the same nitrogen loading as diving to 24.4 meters on air. That is a significant advantage — you get the no-decompression limits of a 24-meter air dive while actually at 30 meters.

Why it matters

EAD is what makes nitrox genuinely useful rather than just a theoretical curiosity:

  • Longer no-deco times: Your decompression obligation corresponds to the EAD, not your actual depth. At 30 meters, EAN32 typically gives you about 50% more no-deco time compared to air
  • Table compatibility: You can use any air-based dive table by entering your EAD instead of your actual depth
  • Safety margin: Some divers use nitrox at air depths — they accept the same no-deco limits as air but with a built-in safety margin from lower nitrogen loading

Safety considerations

  • EAD does not change your MOD: Even though your nitrogen depth is shallower, oxygen toxicity limits still apply at your actual depth. Always check your MOD first
  • EAD assumes a binary gas: The standard formula treats the mix as oxygen and nitrogen only. For trimix (with helium), use END instead
  • Computer vs. tables: Modern dive computers calculate nitrogen loading in real time. EAD is most useful when planning with tables or as a quick mental check

Sources