EAD — Equivalent Air Depth

Equivalent Air Depth (EAD) is the depth at which air would provide the same amount of nitrogen as your specific gas mixture.

How EAD works in practice

Nitrogen absorption depends on partial pressure. When you breathe Nitrox, you consume less nitrogen because oxygen takes up more space in your tank.

You use a formula to find this depth. If I dive EAN32 at 30 m in Komodo, my body absorbs nitrogen as if I were at 25.7 m on air. This math is vital because it changes how your computer tracks deco limits.

The calculation is simple. You divide the ambient pressure by the fraction of nitrogen in your mix to find the new depth.

Why EAD matters for safety

Lowering your nitrogen load allows for longer bottom times. I remember a wreck dive in Cebu where we used EAN36 to stay down longer.

Safety margins depend on this number. Because you are breathing more oxygen, you can stay at 28 m for 15 minutes longer than on air. This extra time is useful when currents push you away from the boat.

Nitrogen is the enemy of long dives. EAD helps you manage that risk.

Mistakes to avoid in the field

Entering the wrong percentage into your computer is a fatal error. I saw a student at Koh Tao in 2019 set his computer to EAN32 while actually breathing EAN36.

This mistake ruins your safety margins. He thought he had more nitrogen than he actually did, so he stayed down too long. His computer showed he was safe, but his body was already nearing a limit.

Always check your gas. Verify your mix manually before you descend below 18 m.

Connection to other concepts

EAD is closely linked to Oxygen Toxicity. While EAD manages nitrogen, the increased oxygen levels can cause central nervous system issues if you go too deep.

You must track both limits. If you dive EAN32 at 40 m, your partial pressure of oxygen (PO2) reaches 1.6 ata. This is the absolute limit for most recreational diving protocols.

Nitrogen and oxygen work together. You cannot calculate one without respecting the other.

Check your cylinder labels twice before every descent.