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What is Nitrox Diving?

Wanda Albano
Wanda Albano

Nitrox diving is a method of scuba diving steadily gaining popularity among divers who would like to dive for longer periods of time. It also reduces the chances of having common complications that divers may suffer, like decompression illness, also known as the bends.

The word "nitrox" is a portmanteau of the words nitrogen and oxygen, and can actually be used to mean a mix of the two gasses in any ratio. The air on Earth's surface, which is comprised of about 78% nitrogen and 21% oxygen (with 1% trace gasses), is a form of nitrox. Nitrox used for diving, however, has more oxygen than the type on Earth's surface.

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Man with a backpack

The basic difference between regular scuba diving and nitrox diving is in the type of air used in the diver's tank. Regular scuba has a very specific ratio of nitrogen to oxygen; it tries to mimic the air found on the surface of the Earth as closely as possible. Nitrox diving, on the other hand, tweaks this mixture to maximize bottom time (i.e., the diver's time spent underwater) and minimize surface intervals (i.e., the time the diver must stay on the surface before diving back in).

While nitrox can come in a variety of ratios, they are usually classified into two types: hypoxic which contains a lower percentage of oxygen than regular air (i.e., less than 21%), and hyperoxic nitrox which contains more than 21% oxygen. Recreational and sport divers may only use hyperoxic nitrox mixes. These types of nitrox may also be called SafeAir, or enriched air nitrox (EAN or EANx). There are two general types of diving nitrox: Nitrox I, also called Nitrox 32, which is comprised of 32% oxygen and 68% nitrogen; and Nitrox II, also called Nitrox 36, which is comprised of 36% oxygen and 64% nitrogen.

The underlying principle behind nitrox diving is relatively simple. The longer and deeper a diver is underwater, the more nitrogen enters his system. Too much nitrogen in his system can lead to a slew of debilitating illnesses, some of which may ultimately result in death. To combat this, a diver must ascend slowly, make decompression stops, and adhere to the recommended surface interval before the next dive. For the recreational or sport nitrox diver, however, the plan is a little different. Since his "enriched" air has more oxygen and less nitrogen, his body will absorb less nitrogen than the diver that uses a regular scuba tank. As a result, the nitrox diver may spend more time underwater, less time on decompression stops and surface intervals, and in some cases, may not need to make them at all. Some divers also report a benefit of being less tired after nitrox diving than after a regular dive.

While nitrox certainly has its benefits, there are some additional precautions nitrox divers should observe. Since nitrox has more oxygen in it, and oxygen is actually toxic at certain depths, nitrox divers have an increased risk of oxygen toxicity, or oxygen poisoning. As a result, nitrox divers should be sure to observe the depth limitations associated with particular nitrox mixes.

The increased amount of oxygen in nitrox doesn't only affect associated depth limitations. Since nitrox contains a larger proportion of oxygen, it is actually flammable. Nitrox tanks and valves must therefore be properly handled and cleaned so as not to cause any unintended explosions.

While nitrox diving has certainly been gaining a lot of followers, there is still quite a lot of confusion surrounding it, usually taking one of two forms. While some may believe that nitrox diving will allow them to dive deeper, this is not the case. In reality, the higher the percentage of oxygen in the nitrox mix, the more shallow the maximum operating depth becomes. Another common misconception among some untrained divers is that nitrox diving doesn't come with the normal scuba risks of suffering illnesses like the bends. While it is true that the risk of nitrogen narcosis may go down it is not eliminated.

In such a highly technical sport such as nitrox diving, it is vital that one understands and adheres to the principles involved. After all, it could help save your life.

Discussion Comments


I use multiple tanks as most divers do, plus mounted regulators, with rigs tied on the anchor line, at different depths and mix (N2 - N1 - Air) respectively depending on dive plan, therefore when diving if I change my dive plan (on the fly), I get the best possible BT, usually under NDL, regardless of depth, time and tank size. By off gassing with Nitrox 1 and 2 during shallower ends of each dive, making repetitive diving more enjoyable and practical with very short surface intervals and much more bottom time on every dive.


A nice summary. The only point I have issue with is the safety improvement bit in your first line. The safety side of it is so small as to be not worth mentioning.

The risk if getting DCI is very very small when diving on air and very very small when diving on EANx-- the difference between 1/10 of FA and 2/10 of FA. And then you add OxTox in as a risk, making EANx as safe or slightly more dangerous than air.

But it's down to the diver. The gas isn't responsible for incidents. Galpinii, as for the order you use them in it doesn't matter, just make sure you update your computer. Air sucking dogs shouldn't waste time with Exif; you run out of air before you hit your NDL, so there's no point in extending your NDL.

You could get a bigger cylinder, in which case EANx might start to be of use.


There also seems to be a misconception that if you use Nitrox, you will therefore consume less air, and that it is this decreased consumption that will give you a longer bottom time. That is not true at all, but it is remarkable how many Nitrox sites blithely state - "gives you longer bottom time etc".

I have dived plenty times with Nitrox divers while I'm on normal air, and they have consumed their volume and are down at 50bar while I am still at 100bar. So I think the wording needs to be examined here. Just because you are diving Nitrox does not mean you will use less volume, or that the needle on your air gauge will move more slowly!


no anon, you will not use less with nitrox. you're still sucking down the same volume.


galpini, if you don't know the answer to that you shouldn't be diving it.


Thanks for the great info, it really helped. Cheers.



suppose I have planned two dive the same days, and I have two tanks. One filled up with N32 and another with N36. Which one should I use first ?


I am a air sucker,will I use less with nitrox? Can I stay down longer?

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