Nitrox Diving 101: What is Enriched Air Diving?

Nitrox Diving 101: What is Enriched Air Diving?
Never leave your Nitrox tank standing, you’ll risk knocking it over – Jed Brown

For most divers, Nitrox diving is the first taste of diving with exotic air and opens up a world of longer, safer dives

Nitrox is the common name used for breathing gasses with a higher percentage of oxygen than in normal atmospheric air.

Actually Nitrox is somewhat of a misnomer as it’s an abbreviation of Nitrogen and Oxygen, which are the main components of both atmospheric air and Nitrox. The proper term for the gas is Enriched Air Nitrox (EANx), pointing to the extra oxygen that the mix is enriched with.

The good of Diving Nitrox

The reason for diving with Nitrox is to use the added oxygen to push out some of the nitrogen in the atmospheric air. By lowering the amount of nitrogen in the mix, and through that, the amount of nitrogen our tissues absorb during the dive, the risk of decompression sickness is decreased. This allows for longer dive times spent at greater depths.

For repetitive dives, the nitrogen load carried from one dive to the next is lower than with atmospheric air, again decreasing the risk of decompression illness.

Many divers also report feeling more alert, and less tired after diving with Nitrox.

The Nitrox is ready, are you? – Andrea Izzotti

The bad of diving Nitrox

Torben Lonne –

However, there is a downside. Oxygen is actually toxic for the human body if breathed under pressure.

How much pressure depends on the oxygen content of the gas mix breathed.

100% of oxygen becomes toxic at only 20 feet or so. The less oxygen in a mix (the more “lean” it is) the deeper you can go before it becomes toxic.

As the first symptoms of oxygen toxicity are violent convulsions, followed by powerful inhalations and loss of consciousness, it can be fatal during a dive.

What is the Enriched Air Nitrox Partial Pressure

Oxygen toxicity happens when the oxygen reaches a critical level of what is known as partial pressure.

Partial pressure is the pressure of any given gas in a mix and the recommended partial pressure for oxygen is 1.4, with 1.6 used as a margin of safety.

As Nitrox comes in varying mixes, the partial pressure of 1.4 is reached at varying depths, depending on the mix.

Therefore, one of the things a Nitrox course teaches you is to measure the mix in your tank and calculate the maximum safe depth it can be used on.

The Different Nitrox mixes


The most common mixes used are EANx32 and EANx36, with 32 % and 36 % oxygen, respectively, compared to 21 % oxygen in atmospheric air.

Other mixes are also used but a mix richer than 40 % is quite rare in recreational diving. For a dive shop to supply Nitrox to divers, they need to clearly specify what mixes their tanks have.

Maximum Depths with Nitrox

Needless to say, once you’ve measured the mix in your tank, which is done with an O2 meter and you have calculated the maximum safe depth that mix can be used at, it is imperative that you stay above that depth.

Keeping a close watch on your depth gauge is critical, especially in situations where the maximum possible depth of the dive exceeds your mix’s maximum depth such as wall dives.

Most modern dive computers allow you to set a depth alarm, where it will give you an audible warning when a certain depth is reached. This is highly recommended if you dive with Nitrox.

Diving Nitrox with your Dive Computer

Some dive computers have a Nitrox setting built into them. These come in two versions, either where the dive computer has a selection of preset mixes that you can choose from. Or where you enter the mix yourself and the computer subsequently determines the maximum depth and dive-time based on that. The latter is typically found in more advanced computers.

If your computer has presets and your mix doesn’t match any of them exactly. The general advice is to always err on the side of caution and round up, not down, especially for deeper dives.


Say your computer has a preset for Nitrox mixes of 32 %, 34 %, and 36 %, yet the mix in your tank reads as 33 % when you measure it on the O2 meter. In that case, set your dive computer to the preset for 34 %, which will reduce your depth compared to the mix you actually have, allowing for a margin of safety.

If, however, your dive is a particularly long one, where you’ll be coming up on the maximum dive time of your mix, and with little or no risk of exceeding the depth limit (say you’re diving in an area where the bottom is quite a bit shallower than your maximum depth). It’s safer to set the preset to 32 %, which will reduce your maximum bottom time, again, giving you a margin of safety.

Always know what you’re doing

Nitrox diving is for many the first taste of non-atmospheric gasses, and with that, an early intro to technical diving.

For this reason, it should be taken seriously and no diver should attempt diving with Nitrox without having taken a Nitrox course with an accredited dive center.

With this certification, though, diving can become safer and more enjoyable.

Have you tried Nitrox?

Have you ever tried diving with Enriched Air Nitrox before? Tell us about your first “almost tech” diving experience.


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Hey Katja, I think 40m is exactly the MOD at ppo2 1.4 for a EAN28, isn’t it?

pp02 1.4 / fo2 0.28 = 5 bar (=40m).

I wouldn’t really mind to dive with Paul, his dive plan calcs make absolutely sense! 😉

Safe diving!

Katja Schlegel
Katja Schlegel

You BELIEVE it gives you a max ppo2 not higher than 1.4 at 40mt?
Wow! I would not want you as my buddy!

Paul Begley
Paul Begley

EANx is good in that you feel better after repetitive dives. Surface interval is also shorter. In Coron, Philippines last month the Irako WWII Japanese wreck was dived (40m on deck level 3 where the engine room was) using 28% EANx which I believe gives you a max depth of 40m not exceeding the Po2 partial pressure limit of 1.4. The Urkraine dives who hired out 2 boats used all the Nitrox so I had to use air. The surface interval on the 2nd dive was 1.75 hrs so not ideal. The 3rd ‘shallow’ dive was another penetration dive down to 32m again on air. On all dives we got to 1min NST Deco limit. I had a rash the following day which caused me a little concern – anti fungal cream sorted it as was thankfully due to being in a wetsuit at 32 deg C. Being banged up down to 165ft in a hyperbaric chamber would not have Impressed My Filipino girlfriend at all!! Lol Will insist on Nitrox next time for sure!!

jim olinger
jim olinger

I earned my nitrox card in Bonaire. It was a great place to start using it as you can easily do 4 tanks / day there and greatly reduce the nitrogen loading.
That puts to me to thinking of the instructor for the course. Here name was “F” and she was from Italy and stunningly attractive! She was on the boat for my first nitrox dive and after surfacing she said, “So tell me Jim, do you feel “jounger?” Do you feel “strongger”? There are rumors of this you know?”
I glanced over at my wife and realized I was in VERY dangerous waters!
“yes, it was a great dive!” I replied with a big grin on my face.
So I’m not sure if it was “F’s” statement or something more physiological, but I did in fact feel a bit better…almost refreshed with the enriched O2 content.


Started diving Nitrox 2 years ago. I am 62 years old and it allows me to do 4 dives a day and maintain my alertness and minimal fatique. It also allows for shorter wait times between dives hence 4 is quite doable. Nitrox is a good way to dive for us seniors. I am certified advanced and certified nitrox and it makes you think when gearing up as you have to check the O2 level in the tank as well as set your computer and make sure you know what depth is your max.

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