What Is Nitrox?
Nitrox — also called Enriched Air Nitrox or EANx — is any breathing gas mixture containing more oxygen than the standard 21% found in regular atmospheric air. In plain terms: less nitrogen, more oxygen.
The two most common recreational mixes are EAN32 (32% O₂, also marketed as "Nitrox 32") and EAN36 (36% O₂). Both are widely available at dive centres around the world and form the foundation of the PADI Enriched Air specialty course.
The core principle is straightforward: because nitrox contains less nitrogen than air, divers absorb less nitrogen during a dive at any given depth. Less nitrogen absorption means it takes longer to reach the no-decompression limit — and that translates directly into longer bottom times.
How Does Nitrox Differ from Air?
The table below shows the gas composition of standard air versus the two most popular nitrox blends.
| Mix | O₂ % | N₂ % | Key Effect |
|---|---|---|---|
| Air | 21% | 79% | Baseline reference |
| EAN32 | 32% | 68% | Longer NDLs, shallower MOD |
| EAN36 | 36% | 64% | Longest NDLs, shallowest MOD |
The key trade-off is inescapable: less nitrogen gives you longer no-decompression limits, but more oxygen lowers your maximum operating depth. Both variables move together — you cannot have one benefit without the other constraint. Understanding this balance is what nitrox training is all about.
The Main Benefit: Extended No-Decompression Limits
No-decompression limits (NDLs) define the maximum time you can spend at a given depth before your body has absorbed enough nitrogen to require mandatory decompression stops on ascent. With air, NDLs are fixed. With nitrox, they stretch — sometimes dramatically.
| Depth | Air NDL | EAN32 NDL | EAN36 NDL |
|---|---|---|---|
| 12 m / 40 ft | 147 min | unlimited* | unlimited* |
| 18 m / 60 ft | 56 min | 95 min | ~120 min |
| 25 m / 82 ft | 30 min | 47 min | 64 min |
| 30 m / 98 ft | 20 min | 30 min | — (below MOD) |
*within gas supply limits. NDL figures are approximate and vary by dive table / algorithm used.
At 18 m on air, you have roughly 56 minutes before hitting your NDL. On EAN32 at that same depth, that extends to approximately 95 minutes — nearly double. For reef dives, wreck explorations, and multi-level dives in the 15–25 m range, this is a substantial and very tangible benefit.
Extended NDLs also give you a larger safety margin if you drift slightly deeper than planned, and they reduce residual nitrogen between dives — which can improve surface intervals and repetitive dive planning.
Maximum Operating Depth (MOD): The Trade-Off
More oxygen in your mix sounds like a good thing — but at depth, high oxygen partial pressures become toxic. Too much oxygen causes Central Nervous System (CNS) oxygen toxicity, which can trigger convulsions with little to no warning. Underwater, a convulsion is almost certainly fatal.
The safe ceiling for partial pressure of oxygen (PO₂) in recreational diving is 1.4 ATA for the planned maximum depth, with 1.6 ATA used as an absolute contingency limit only. This places a hard ceiling — the Maximum Operating Depth (MOD) — on how deep you can take a given nitrox mix.
MOD = Maximum Operating Depth in metres
PO₂ limit = max oxygen partial pressure (1.4 ATA recreational)
FO₂ = fraction of oxygen as a decimal (e.g. 0.32 for EAN32)
For context: air has an effective MOD of 57 m at PO₂ 1.4. EAN32 limits you to 33 m. EAN36 to just 28 m. Nitrox dives shallower, but stays longer. Always calculate and mark your MOD before the dive, and never exceed it.
Always know your MOD before entering the water.
Calculate it, write it on your slate, and set your dive computer to the correct oxygen fraction before the dive — not after. CNS oxygen toxicity strikes without warning and does not give you time to ascend.
Common Myths About Nitrox
Nitrox attracts more misconceptions than almost any topic in recreational diving. Here are the four most common myths — and the facts behind them.
"Nitrox lets you dive deeper."
False. The opposite is true. Nitrox has a shallower MOD than air because its higher oxygen fraction reaches toxic partial pressures at lower depths. Nitrox is for diving longer at the same depth, not deeper. If deep diving is the goal, trimix and technical gas blending are the tools — not nitrox.
"Nitrox gives you more energy after a dive."
There is no scientific evidence for this claim. Any perceived improvement in post-dive energy is most likely due to the placebo effect, improved hydration habits that accompany nitrox training, or simply diving within more conservative limits. Oxygen in a breathing mix does not have a stimulant effect at recreational pressures.
"Nitrox is only for advanced or technical divers."
False. The PADI Enriched Air Diver course is one of the most popular specialty certifications in the world, and it is open to all certified divers. The course typically takes a single day and involves no additional open-water dives — just knowledge development and gas analysis. Any open-water certified diver can qualify.
"Nitrox is dangerous."
Nitrox used correctly — within its MOD and with a properly configured dive computer — is very safe. The hazard only materialises when divers exceed the MOD or configure their equipment incorrectly. With proper training and planning, nitrox is no more dangerous than air for recreational depths.
How to Use Nitrox Safely
Following a consistent pre-dive routine eliminates most of the risk associated with enriched air diving.
- Analyse your cylinder before every dive. Never assume the mix matches the label. Use a calibrated oxygen analyser and record the result.
- Check tank markings. Nitrox cylinders should display a yellow/green EANx sticker and the actual oxygen percentage. If the labelling is absent or unclear, do not dive on that gas.
- Set your dive computer to the correct mix. Before entering the water, update your computer's oxygen fraction to match your analysed result. A computer set to air while breathing EAN32 will give you incorrect NDL and PO₂ readings.
- Calculate and know your MOD. Write it on your wrist slate. Treat it as a hard ceiling, not a guideline.
- Plan your dive using nitrox tables or EAD. Use tables or algorithms appropriate for your actual mix, not air tables, unless you are using the Equivalent Air Depth method (see below).
Equivalent Air Depth (EAD)
Equivalent Air Depth (EAD) is a useful concept that lets you use standard air dive tables with a nitrox mix. It works by finding the shallower air depth that produces the same nitrogen loading as your actual depth on nitrox.
EAD = Equivalent Air Depth in metres
FN₂ = fraction of nitrogen as a decimal (e.g. 0.68 for EAN32)
depth = actual dive depth in metres
0.79 = nitrogen fraction in air
This means that a dive to 25 m on EAN32 creates the same nitrogen loading as a dive to roughly 20 m on air. You can therefore look up the NDL for 20 m on an air table and use it as your planning limit at 25 m on EAN32 — giving you significantly more bottom time than the air table for 25 m would suggest.
Most modern dive computers handle EAD calculations automatically when you set the correct oxygen fraction. The EAD formula is most useful when planning dives without a computer or when cross-checking your tables before the dive.
Calculate Your MOD, PO₂, and EAD
Use our free Nitrox / MOD Calculator to instantly calculate your Maximum Operating Depth, oxygen partial pressure, best mix for a target depth, and Equivalent Air Depth.
Open Nitrox & MOD Calculator →