Using Nitrox or Enriched Air while scuba diving has many benefits, provided you have the appropriate training.
I can bet that at least once during one of your scuba trips you have observed some scuba divers using scuba tanks marked with green and yellow stickers.
Those divers were actually diving with an Enriched Air mix, also known as EAN, EANx, Oxygen-Enriched Air, or Enriched Air Nitrox.
Diving with Nitrox has many benefits including increased no decompression limits, less fatigue, shorter surface intervals, and longer bottom times on repetitive dives. However, there can be also some dangers linked to oxygen toxicity.
This is why it is essential to have adequate Nitrox training before doing any dive with an oxygen mix exceeding 21% (percentages of oxygen in the air we breathe).
WIth most diving agencies, before obtaining your NItrox certification, you will need to be at least certified as open water diver.
If you are interested in how to become a certified open water diver with PADI, check out my ultimate guide. You might also be interested in other cool PADI specialties that every diver should take.
Diving Nitrox with oxygen mixes exceeding 40% and reaching up to 100% requires specialised technical diving training. In fact, pure oxygen can lead to oxygen toxicity at very shallow depths.
Let’s look in more details at what Nitrox actually is and how you can benefit from diving with it.
What is Enriched Air Nitrox?
You might recall that Air consists of approximately 79% of Nitrogen and 21% of Oxygen. Enriched Air, or simply Nitrox refers to a gas mix where the oxygen component is higher than 21%.
Sometimes you will read Enriched Air Nitrox abbreviated as EAN, EANx, or EANx followed by a specific number. The number refers to the proportion of oxygen contained in the gas mix.
For example, EANx32 refers to a gas blend made of 32% of Oxygen and 68% of Nitrogen. EANx40 on the other hand refers to a gas blend made of 40% of oxygen and 60% of Nitrogen.
In recreational diving, the most commonly used blends are EANx32 and EANx36. Enriched air certifications will generally allow you to dive with a gas blend that does not exceed 40% of oxygen (EANx40).
Nitrox has been used in diving since the mid-1990s with the main objective of extending no-decompression bottom times.
Let’s take a look in more details at all the benefits of Nitrox diving.
Benefits of Diving with Nitrox
In short, the benefits of diving with Enriched Air are:
- Extends your no-decompression bottom time
- Lowers your Nitrogen load in repetitive dives
Two other benefits reported by divers, without medical evidence are:
- Shortens surface interval
- Reduces fatigue, particularly in repetitive dives
Enriched Air Diving Extends Your No-Decompression Bottom Time
By increasing the proportion of Oxygen in the gas blend, you will increase the amount of Oxygen while at the same time reducing the amount of Nitrogen you breathe during a dive.
This means that whenever you are diving nitrox, your body will be absorbing more oxygen and less nitrogen as compared to Air.
The increased amount of oxygen you absorb will reduce the amount of bubbles formation after a dive. This will allow you to have longer no-decompression limits.
The extended length of the no-decompression limits will depend on the proportion of Oxygen in the gas mix. For a given depth, the higher the percentage of Oxygen in your gas mix, the longer the no decompression limit.
Enriched Air Diving Lowers your Nitrogen Load in Repetitive Dives
Although using Enriched Air extends your no-deco limits or no-decompression bottom time in a single dive, you will actually experience the full benefits of Nitrox diving in repetitive dives.
This is particularly the case during diving trips or liveabords where 3 or 4 dives per day are not uncommon.
In fact, given the higher percentage of Oxygen in the gas you breathe, you will have less residual nitrogen at the end of each dive. This means that you will be able to extend your repetitive dive times without reaching your non-deco time in the third or fourth daily dive.
Note that although nitrox diving lowers your nitrogen load in repetitive dives, it does not reduce the risk of decompression sickness. Recreational divers often say that they use nitrox to avoid decompression sickness, but there is no medical evidence in support of such statements.
Nitrox Diving Shortens Surface Interval
As you might expect, given that Nitrox will reduce the amount of Nitrogen you will be breathing during a dive, you will in most cases end a nitrox dive with a lower amount of Nitrogen absorbed in your blood.
This means that you can theoretically reduce your off-gassing time or surface interval. Note however, that if you are diving Nitrox, you will most likely have longer dives.
This means that you will never be 100% sure about the Nitrogen levels in your blood after a nitrox dive. And you will definitely not be able to tell if they are lower as compared to a dive with normal Air.
This is why most scuba diving training agencies recommend having a surface interval of at least one hour, irrespectively of the gas you are using.
Diving Nitrox reduces fatigue
Although may scuba divers report less post-dive exhaustion and fatigue when diving Nitrox, there is no scientific evidence in support of such claim.
If you are further interested in the scientific evidence or the lack thereof, I suggest reading the following article from the Divers Alert Network.
From personal experience, I do feel less tired when diving with Nitrox in case of repetitive short and shallow dives. But if I am using Nitrox to extend my diving time range, I do feel equally tired as when I am diving with normal Air.
In conclusion, the main scientifically proven benefit of diving with Nitrox is the possibility to extend your no-decompression bottom time. Let’s now take a look at the possible risks and dangers of diving with Nitrox, particularly if you do not have adequate training and credentials (more on training and credentials in the FAQ section of this post).
Dangers of Diving with Nitrox
Before entering into the details of the risks associated with Enriched Air or Nitrox diving, I would like to note that diving with Nitrox is not more dangerous than diving with Air, provided this is done well inside the limits of your training.
Although statistical data suggests that there is no evidence supporting the claim that Nitrox diving reduces the risk of decompression sickness, you should take into consideration that whereas Nitrox diving reduces your Nitrogen intake, it will increase your oxygen exposure.
Under certain conditions, a higher oxygen exposure is possibly more dangerous than exposure to nitrogen.
In fact, an excessive exposure to oxygen at increased pressures can affect a diver’s central nervous system.
Such phenomenon is called oxygen toxicity and can manifest in the form of convulsions, ringing ears, visual disturbances, seizures, nausea, twitching, dizziness and irritability.
Although none of those symptoms of oxygen toxicity are dangerous at surface, convulsions and seizures can be extremely dangerous underwater as in most cases they lead to drowning.
In recreational diving, oxygen toxicity is rare, particularly if you do not exceed the depth limits for a given percentage of oxygen in your Nitrox mix.
The more oxygen in your Nitrox mix, the shallower your depth limit.
In Nitrox diving, the depth limit is set in such a way that the partial pressure of oxygen is 1.4 ata or lower.
How to Calculate your PPO2
In the early days of recreational diving, nitrox divers had to compute their own depth limits manually, without the help of dive tables nor dive computers.
Today, thanks to modern oxygen analysers, dive tables and dive computers, it is pretty easy to compute the Nitrox depth limits. Some times it is as easy as inputting the oxygen percentage of your Nitrox mix in your dive computer, which will automatically tell you the no deco depth limits.
However it is always good to understand what are the technicalities behind your dive computer computations. This is why in virtually every Nitrox or Enriched Air diving course, you will learn how to compute the Partial Pressure of Oxygen, abbreviated as PPO2.
The partial pressure of oxygen tells you the oxygen equivalent you would be breathing at surface, based on the percentage of oxygen that is contained in your breathing gas.
It is computed by multiplying the oxygen percentage of the EANx by the absolute pressure expressed in atmospheres or bar.
For example, a diver breathing normal air (21% of oxygen) at 65 feet (20 meters) is breathing a partial pressure (PP) of oxygen (PPO2) of 0.21 x 3ata = 0.63. If you are wondering where the 3ata came from, that is the absolute pressure at a depth of 65 feet (20 meters).
A diver breathing EANx32 (32% of oxygen in the gas mix) at 65 feet (20 meters) is breathing a partial pressure (PP) of oxygen (PPO2) of 0.96. this would be equivalent to breathing 96% of oxygen at surface.
For example, the pressure component of the oxygen limit is calculated using partial pressures. You can find it by multiplying the oxygen percentage of the EANx by the absolute pressure (in atmospheres or bar). For example, a diver breathing air (21 percent O2) at 132 feet (5 ata) is breathing a partial pressure of oxygen (PPO2) of 1.05. This would be equivalent to breathing 105 percent oxygen at the surface. In other words, you can’t breathe that PPO2 at the surface even using pure oxygen.
Diving with Nitrox and Depth Limits
Finding the Nitrox depth limits is relatively easy. You just need to take into account that in recreational diving, the partial pressure of oxygen should not exceed 1.4. Going beyond such limit can be extremely dangerous if you are not trained for technical diving.
Given the PPO2 limit of 1.4, the maximum depth formula for a given percentage of oxygen is given by:
Max Depth = (1.4 ÷ mix%) – 1) X 33
So, for example if you are diving nitrox with a percentage of oxygen of 32%, your maximum depth limit will be:
Max depth = (1.4 ÷ 0.32) – 1) X 33 = 111 feet or 33 meters.
This is called Maximum Operating Depth and is often abbreviated as MOD. As you will see in the next few paragraphs, one of the ways to recognize Nitrox divers is by looking at the MOD decals on their scuba tanks.
Before moving on with Nitrox diving and Scuba Equipment Safety, I would like to note once more that your dive computer will most likely compute the maximum operating depth for you.
It is therefore extremely important that you get aquainted with your dive computer settings and learn how to set it up for nitrox before your first nitrox dive. You can also ask for help to your dive shop or scuba instructor while taking your nitrox course.
Diving with Nitrox and Scuba Equipment Safety
As we saw at the beginning of this post, scuba diving with enriched air nitrox requires specialised training. Such training is not only useful to understand the benefits and risks associated with nitrox diving but also to understand which kind of equipment is needed, how to identify it and how to use it.
Scuba tanks that are filled in with nitrox mixes instead of normal air are usually marked with yellow and green decals, indicating that the breathing gas has a percentage of oxygen greater than 21%.
In addition, each single scuba tank usually has an additional sticker with the name of the diver that will be using it, and the exact percentage of oxygen contained in the breathing gas.
In most dive centers, particularly if they adhere to the PADI standards, you will actually be asked to confirm such percentage by using an oxygen analyzer before using it to compute your maximum operating depth.
In Europe, it is quite common to use decals indicating the maximum operating depth (MOD decals) on tanks that are filled with EANx mixes. Those decals are not green and yellow. They are simply big black numbers on a white background.
When it comes to first and second stages, most scuba regulators can be used without problems for EANx mixes up to 40% (within recreational diving limits).
In some countries, however, local regulation might require Nitrox divers to use some specific equipment that is specifically produced for diving with enriched air.
You can easily distinguish these kind of products as they are marked in green, and usually have green O-rings.
The green marking indicates that such products are “air clean”, meaning that they have never been exposed to air.
These products are particularly visible in Europe, where local nitrox regulation is extremely strict as compared to the rest of the world.
Given the differences in local regulations, I strongly suggest you to check with your dive shop which are the local requirements.
How to get certified to Dive with Nitrox
Getting certified to dive with Nitrox is extremely easy. Almost every scuba diving agency has its own course.
For example, with PADI, you can easily start the Enriched Air (Nitrox) Diver specialty online and obtain your certification after a couple of practical sessions in your dive shop.
This is actually one of the few PADI specialties that do not require in-water sessions, making it a perfect specialty to take in the coldest months of the year.
Irrespectively of the agency you will choose, I suggest you to check the requirements online and decide whether it is better to take it in winter, summer, or during your next diving holiday.
One consideration that you might want to pay attention to concerns prices. Having nitrox in exotic and remote locations is usually quite cumbersome and complex. This is why for example, taking a nitrox certification in the maldives is more expensive than taking it in the US or Europe.
I therefore suggest you to carefully check the prices before taking your nitrox certification and decide accordingly. Many divers prefer to take a nitrox course close to home and have their first EANx dive at a later stage.
Conclusion
Summing up, Nitrox Diving is definitely a certification that every diver should take. DIving with EAN has many advantages, particularly if you are a frequent diver or if you make several repetitive dives.
The more you improve your diving skills, the more you will realize that normal air fillings will impose a serious limitation in terms of dive time. Such limitation can easily and safely be avoided by diving with EANx.
That said, diving with nitrox does have some risks, and no diver should ever give it a try without having a nitrox certification.
Diving with Nitrox FAQs
What is the primary benefit of using enriched air nitrox?
The primary benefit of using enriched air nitrox is that it gives you longer no stop times as compared to air (at recreational diving depths). This is due to the fact that enriched air nitrox breathing gases contain a higher proportion of oxygen as compared to normal air.
What are the potential hazards of improper enriched air filling procedures?
Potential hazards include fire or explosion, questionable oxygen percentage in your gas mix and enhanced risk of narcosis. This is why it is essential to have your Nitrox tank filled at reputable filling stations.
What is the primary hazard when exceeding oxygen limits in your nitrox mixture?
The primary hazard is oxygen toxicity. In case of acute oxygen toxicity, you might experience convulsions which may lead to drowning.
What should I do if I accidentally exceed the oxygen limits of my computer?
You should not dive again for the next 24 hours and follow the instructions of your dive computer’s manufacturer.
Does diving nitrox reduce post dive fatigue?
Although many scuba divers (both recreational and technical divers) report to be less tired after diving with EANx, ther is no scientific evidence supporting this claim. If you are interested in how to prevent overexertion while diving, check out the PADI OWD Knowledge Review questions frmo chapter 2.