What’s the Difference Between Air and Nitrox?
Air and Nitrox are both breathing gases used for scuba diving, but they have different proportions of oxygen and nitrogen. So what exactly is Nitrox, why do divers use it, and what are the advantages and limitations compared with ordinary compressed air?
Nitrox can be particularly useful for recreational divers making repetitive dives, especially on liveaboard cruises where several dives are made each day. In this guide, we look at the difference between air and Nitrox, the benefits and limitations of enriched air, maximum operating depths, no-decompression limits and the training required to use Nitrox.
In this article, we answer your most common questions about Nitrox:
What’s the Difference Between Air and Nitrox?
The air we breathe every day is a gas made up of approximately 21% oxygen, 78% nitrogen and 1% other gases.
Nitrox, also called Enriched Air, is a breathing gas made from the same basic gases but in different proportions. We enrich the air with extra oxygen, so the oxygen proportion is higher and the nitrogen proportion is lower.
The name Nitrox comes from the combination of Nitrogen and Oxygen.
We refer to Nitrox according to its oxygen percentage. For example, a Nitrox 32 mix contains 32% oxygen and is one of the most commonly used recreational Nitrox mixes.
What Are the Advantages of Using Nitrox?
If you remember your Open Water theory class, the amount of nitrogen entering your tissues is one of the factors that limits the time you can spend at a certain depth.
Using Nitrox means breathing a gas with less nitrogen than ordinary air. At a given depth and dive time, this can reduce nitrogen uptake and provide a longer no-decompression limit than air.
This gives Nitrox divers several practical advantages:
- The ability to stay longer at a certain depth before reaching the same nitrogen blood level.
- For example, if you dive at 30 meters, you could spend about 20 minutes on air before a decompression stop becomes compulsory, 30 minutes with a nitrox 32 and 40 minutes with a nitrox 36!
- Having less nitrogen in your body also means your surface intervals could be shorter (which is a big advantage in some situation when you want to squeeze in 2 dives in a limited time).
One of the reasons Nitrox is so popular with liveaboard divers is the repetitive nature of diving. When you are making several dives every day for a number of consecutive days, Nitrox can be a useful way of managing nitrogen exposure while staying within the appropriate no-decompression and oxygen limits.
What about diving with a friend who is using air? There is still a potential benefit to using Nitrox. If you follow the same dive profile as an air diver, you may have a lower nitrogen exposure than you would have had on air. However, Nitrox should not be considered automatically safer than air, and it does not eliminate the risk of decompression illness. Safe diving still depends on proper training, planning, depth control and following appropriate procedures.
You may also hear divers say that Nitrox makes them feel less tired after diving. Some divers report this experience, but it should not be presented as a guaranteed physiological effect. The main established benefit of Nitrox is its effect on nitrogen exposure and no-decompression limits, not a guaranteed reduction in fatigue.
What Are the Disadvantages of Using Nitrox?
The main disadvantage of Nitrox is the depth limitation.
The more oxygen there is in your Nitrox mix, the more quickly the oxygen partial pressure increases as you descend. Oxygen can become toxic when its partial pressure becomes too high, so divers must respect the maximum operating depth of the particular Nitrox mix they are using.
At excessive oxygen partial pressures, a diver can be exposed to central nervous system oxygen toxicity, which can potentially result in a convulsion underwater. This is why understanding oxygen exposure and maximum operating depth is such an important part of Nitrox training.
These limits are straightforward to manage when the gas is analysed correctly and the dive is planned using the appropriate oxygen exposure limits. Nitrox is not inherently safer or more dangerous than air; it is a different breathing gas with different limits that need to be understood and respected.
Can I Dive Deeper with Nitrox?
It is sometimes believed that Nitrox is used for very deep dives, but the reality is quite different. Recreational Nitrox is generally used to allow longer no-decompression times at suitable recreational depths, rather than to allow divers to go deeper.
The reason is simple: Nitrox contains more oxygen than normal air. As depth increases, the partial pressure of oxygen also increases. Because there is already more oxygen in the Nitrox mix, the maximum operating depth can be shallower than it would be for air.
For example, a Nitrox 32 mix has a maximum operating depth of approximately 34 metres when using a maximum oxygen partial pressure of 1.4 ATA. A Nitrox 36 mix reaches the same 1.4 ATA oxygen partial pressure at approximately 29 metres.
These figures are examples based on a commonly used planning limit. The actual depth limit depends on the oxygen percentage of the mix and the oxygen exposure limits being used.
But don’t get scared! After your Nitrox course, you will know how to determine the maximum operating depth for your particular mix and plan your dive accordingly.
Can I Dive Longer with Nitrox?
Nitrox can make your NDL (no-decompression limit) longer, but if you breathe through your gas quickly, you will still need to ascend before you are “out of air”.
So, Nitrox can make your dive longer only if your gas supply allows you to take advantage of the longer no-decompression limit. Your actual dive duration can still be limited by your cylinder size, breathing rate, depth, current and other factors.
While Nitrox has many advantages, reducing your breathing rate isn’t one of them. You should not expect a noticeable reduction in your gas consumption simply because you switch from air to Nitrox.
In other words, Nitrox changes the composition of your breathing gas, not the amount of gas you consume. The advantage is primarily related to nitrogen exposure and no-decompression limits.
Where Can We Dive with Nitrox?
Nitrox is used all over the world, and it becomes particularly useful when doing multiple dives a day, such as on liveaboard diving cruises.
On a liveaboard, divers may make several dives every day for a week or more. Nitrox can therefore be particularly convenient for repetitive diving because it can provide longer no-decompression limits at appropriate depths.
At The Smiling Seahorse, Nitrox is available on our liveaboard cruises for divers who have the appropriate training. Whether you are exploring the reefs of Thailand or travelling to Myanmar, enriched air can be a useful option for repetitive recreational diving.
Do I Need Another Certification to Dive Nitrox?
Yes! Because Nitrox has oxygen-related limits that are different from those of ordinary air, you need appropriate training before using enriched air. The Nitrox course teaches you how to plan and conduct dives safely using a specific Nitrox mix.
The Nitrox course is one of the most commonly taught specialities in the diving industry. It is also relatively quick and can be completed without even getting wet.
During the course, you learn about oxygen exposure, maximum operating depth, analysing your cylinder, planning dives and setting your dive computer for the correct Nitrox mix.
On the MV Smiling Seahorse, we teach PADI Enriched Air Nitrox for 8,000 THB. It can be completed onboard in a few hours, or you can complete the theory online beforehand through PADI eLearning.
Don’t hesitate to get in touch if you have any questions about Nitrox or whether it is suitable for your upcoming liveaboard cruise.
We hope you enjoyed this article and found the information you were looking for. Nitrox can be a very useful tool for recreational divers, particularly when making repetitive dives, but it should always be used with the correct training and within the depth and oxygen limits of the chosen mix.
