Along your scuba diving journey, you may have noticed that some tanks or cylinders have bright green and yellow markings. These tanks represent enriched air, which means the divers are diving with nitrox, a special blend of gas to enrich your diving experience. However, like everything else in diving, nitrox can be highly effective if used properly, or very dangerous if used incorrectly. Let’s take a look at what nitrox diving is, the pros and cons of diving with it, and why some divers prefer diving with this enriched air!
What is Nitrox or Enriched air?
To start out, we’re already trying to confuse you by having two names for the same thing.
Scuba divers are notoriously lazy, which is why we use highly effective fins to swim with, we aim to breathe easily and lazily to conserve our air, and we also like to shorten every name that we can; submersible pressure gauge S.P.G, buoyancy control device B.C.D and so on, and the same is true with Enriched Air Nitrox.
Read More: SCUBA Acronyms – Useful Terms to Know
The word Nitrox is an abbreviation of Nitrogen and Oxygen. This is a term given to any mixture of gas where the oxygen content is higher than 21%.
When this happens we have enriched the mix with more oxygen, so the full name is Enriched Air Nitrox (EANx). Since divers are already lazy, and Enriched Air Nitrox is a bit of a mouthful (I’m already annoyed at typing it out so much), we just shorten this term to Nitrox.
To make it easy to identify Nitrox tanks, they will be marked differently from normal air tanks. The most common markings are green and yellow stickers or fabric bands, with the word Nitrox or Enriched Air written on them. Different parts of the world may have other colour systems or markings so check locally.
Why Dive with Nitrox?
In scuba diving it is always the amount of nitrogen in our bodies that dictates how deep and how long we can stay down diving underwater.
The deeper and longer we are down the more nitrogen is absorbed into our bodies. Sometimes, depending on the diver and the dive, you will have enough air in your tank to continue diving, but have reached your maximum nitrogen consumption for the dive. This can be frustrating as now you need to end the dive due to your no-decompression limits (NDL).
Diving with Nitrox, however, reduces the amount of Nitrogen entering the body due to the higher oxygen percentage. This means that your NDLs are extended, and in the same situation as before, you would now be able to continue your dive and have an increased bottom time.
Pros and Cons of Nitrox Diving
So far, Nitrox sounds pretty awesome, reducing nitrogen loading to allow more dives in a day or longer, deeper dives (depending on air supply), but it also has some downsides, so let’s look at the pros and cons of using nitrox.
| PROS OF NITROX | CONS OF NITROX |
|---|---|
| Longer NDLs | Nitrox costs more per tank |
| No need to push decompression limits | Additional preparation before each dive |
| Reduced nitrogen load on multiple dives in a day | No benefit if diving with non-nitrox divers* |
| Potential increased energy due to more oxgyen | Extra training is necessary |
- *As we know from our training, we should always follow the most conservation no-decompression limits, which means if your buddy is not diving with nitrox, then you would need to still follow their limits.
Enriched Air Nitrox Diving Tables
Just as diving with normal air, Nitrox has its own set of diving tables to calculate your no-stop times.
Due to the reduced consumption of Nitrogen while diving on Nitrox we need to use different tables when planning our dives. Nitrox tables are easy to recognise as they will typically be bright yellow and green in color, compared to the standard recreational dive planner (RDP) tables.
These tables will usually come with NDLs or no-stop times based on 32% and 36% oxygen. These figures are the common nitrox blends.
| Oxygen Percentage | Depth | No-Decompression Limit |
|---|---|---|
| 21% | 18 m / 60 ft | 56 Minutes |
| 32% | 18 m / 60 ft | 95 Minutes |
| 36% | 18 m / 60 ft | 125 minutes |
As you can see from above, using 36% EANx gives you more than double the NDL for an 18 m / 60 ft dive. Planning the dives is exactly the same, making sure you don’t have too much nitrogen in your body throughout any singular or repetitive dive series.
One limiting factor with some agencies’ dive tables is you can only get them in two or three oxygen percentages such as seen in the table above. This is where using a dive computer has massive advantages.
Nitrox diving is considered a gas mix with any blend higher than 21% oxygen. Dive computers (depending on the model) allows you to set the oxygen percentages from a range of 22% through to 50% with some technical computers allowing you to set it up as high as 100% oxygen. This allows much more flexibility when planning dives and having the best mix for the dive you wish to perform.
Read More: Best Diving Computers for Beginners
Dangers of Diving with Nitrox (Why do you need a Nitrox Certification?)
Just as with any diving, using Nitrox comes with its own set of dangers with the main one being Oxygen Toxicity.
Oxygen Toxicity happens when a diver exceeds the maximum partial pressure of oxygen in a gas mix. The deeper we dive, the higher the partial pressure of oxygen becomes. On-land we are able to breathe 100% oxygen safely with no problems, however, at depth this is another story. Because nitrox has a higher oxygen content, we reach the partial pressure oxygen limit at shallower depths. This is the main reason why you need nitrox training and a certification to go diving with nitrox.
Oxygen Toxicity symptoms include;
- Coughing
- Chest pain
- Trouble breathing
- Muscle twitching in face and hands
- Dizziness
- Blurred vision
- Nausea.
- Death
Without the nitrox certification it’s highly unlikely that divers would know how to plan what mix to use and what depth to stay above to prevent oxygen toxicity from happening. This is why it is so important to take an Enriched Air Nitrox course before diving and breathing from a nitrox tank.
Scuba Diving Nitrox Certification
The main part of the nitrox diving course is teaching people how to avoid oxygen toxicity, through good planning and understanding of limits imposed by the gas mixture in your tank.
So, what’s involved with a Nitrox certification?
Theory
- During this part of the course you will learn all the science behind partial pressures and maximum operating depths, how to use Nitrox safely and what to do in emergencies. You will also have knowledge reviews and an exam to complete during this section.
Tank Marking
- While diving on Nitrox certain information is written on the tanks. You need to write the name of the person using the tank, date the tank was analyzed, oxygen percentage and max operating depth. This is done so important details can be found quickly if any problems occur.
Analyzing Tank
- This is completed pre-dive to make sure the gas in the tank is what you asked for. The process is completed by calibrating an oxygen analyser using a normal air tank of 21% oxygen, then the analyzer is used on the Nitrox tank to record the exact oxygen percentage in the tank.
Dive Computer
- If using a dive computer during your Nitrox course your instructor will show you how to set your computer for the Oxygen percentage you will be diving with. They may do a simulation with you, so you can set your own computer on future Nitrox dives.
This is based around the PADI Enriched Air Diver course. Other agencies will have similar courses and structures but may differ slightly. Contact your local dive centre for more information.
Calculating your PPO²
PPO² stands for Partial Pressure of Oxygen. You will sometimes see this written PO².
When diving on Nitrox we are mostly concerned with the pressure being exerted on the oxygen part of the mix, hence, the partial pressure. We calculate the concentration of oxygen that is absorbed at various depths when using Nitrox to remain safe.
To calculate the partial pressure of O², you multiply the percentage of oxygen by the amount of pressure you are under at depth.
Remember, on the surface we are under 1 Bar/1 ATA of pressure and for every 10 meters of depth we enter a new Bar/ATA of pressure.
So for example if we were using a Nitrox tank with 25% Oxygen and diving to 20 meters (65 ft). We would do the following calculation: 0.25% O² x 3 bar/ATA = 0.75 PO²
In recreational diving, the maximum partial pressure should be 1.6. Though we plan all dives with a contingency limit of 1.4. This gives us a small buffer in case we accidentally exceed our maximum operating depth before Oxygen Toxicity kicks in.
Here is a table showing Partial Pressures for the most common Nitrox / Enriched Air Blends.
| Depth (M) | Pressure in BAR/ATA | 21% O² | 32% O² | 34% O² | 36% O² |
|---|---|---|---|---|---|
| 0m | 1 | .21 | .32 | .34 | .36 |
| 10m | 2 | .42 | .64 | .68 | .72 |
| 20m | 3 | .63 | .96 | 1.02 | 1.08 |
| 30m | 4 | .84 | 1.28 | 1.36 | 1.44 |
| 40m | 5 | 1.05 | 1.60* | Exceeds limit | Exceeds limit |
| 50m | 6 | 1.26 | Exceeds limit | ||
| 60m | 7 | 1.47 |
As you can see from the table, without allowing the partial pressure to exceed 1.4 or normal air (21%) we can dive to a depth of around 56 meters.
However, when using a Nitrox mix of 36% we are limited to about 28 meters. These depths are known as the maximum operating depths (MOD).
This is where you need to be highly mindful of your depth when using nitrox. As an Advanced Open Water Diver you would be certified to go to 30 meters, but using EANx36 you can only go to to a depth of 28m safely.
Using a computer makes this much easier. Once you input your gas mixture and the maximum partial pressure you want to follow, the computer will calculate your MOD and some computers will even give you a warning if you exceed this depth limit. Though you should not just rely on the computer’s safety feature; good buoyancy and checking your depth regularly is always the best option to stay safe.
This is also why Nitrox tanks are clearly marked with bright yellow and green bands, so you don’t accidentally use an enriched mix and dive too deep exceeding the safe partial pressure.
How Deep Can You Scuba Dive with Nitrox?
Looking at the above table, the depth you can dive to is going to be greatly affected by the mixture in your tank.
The less oxygen you have in the tank means the deeper you can go, so technically the lowest amount of oxygen in an Nitrox tank would be 22% bringing your max depth to around 53 m / 173 ft.
The maximum depth of recreational diving is 40 m / 130 ft, so unless further technical training is acquired the deepest you can go on Nitrox is 40 meters.
Can You Dive Longer with Nitrox?
This is a very common misconception with Nitrox!
Sadly, Nitrox is not a wonder drug that gives us infinite air while diving. As we have read, diving with enriched air does reduce nitrogen loads which means we can go to a deeper depth for longer. However, we are still constrained by air consumption and at some point we all run our tanks down to the point when we have to end the dive safely.
This is the same when diving on Nitrox. Though sometimes, as we are able to stay deeper for longer, this means we use our gas quicker than on normal air dives. But why? I hear you say. This is because we are under more pressure for longer resulting in breathing our tank quicker.
This is the balancing act of diving on nitrox; not staying at a maximum depth for so long that we get short dives, but also being able to stay long enough to have the benefits of the reduced nitrogen load.
Pro Tip: UW Photographers love using enriched air for the longer no-deco times. This allows them additional time at a certain depth to capture the perfect shot. Read our tips on how to become an Underwater Photographer.
Does Nitrox Reduce Narcosis?
As we still have nitrogen content in our tanks while diving on Nitrox, the effects of narcosis are exactly the same as diving on normal air.
Read More: What is Gas Narcosis?
If you encounter gas narcosis on a Nitrox dive, follow the same steps you would when experiencing narcosis on normal air. Ascend to a shallower depth until the effects wear off. If you still feel uncomfortable then you should end the dive.
Scuba Diving with Enriched Air
Hopefully, you now have a much clearer understanding of Nitrox diving and what enriched air is. As you can see, like with any diving it has its risks but as long as it is used safely and responsibly nitrox can really enrich any dive (see what I did there!).
Nitrox is one of the most common specialties for divers to learn, especially for people planning diving holidays with multiple dives per day. With the reduction of nitrogen load and no need to push NDL limits, it really makes those trips more enjoyable. Some divers use the nitrox scuba diving course as a gateway into technical diving. Whatever the reason, nitrox is a great certification to have and let’s be honest, you just look cooler diving with Nitrox!
