Often I’m asked by beginning divers if nitrox is used for doing deep dives, or if using nitrox is considered technical diving, or if nitrox will prevent the bends. The quick and easy answers to those questions are: nitrox is not for going any deeper than recreational diving limits, it’s not considered technical diving, and it is not going to prevent the bends.
In this series of articles, I will try to demystify nitrox for the beginner diver, and will delve a little deeper into more advanced concepts.
Diving with nitrox can have many advantages for the recreational diver, but we must consider some technical issues associated with breathing compressed air, and with the higher content of oxygen in our tanks. Once we understand what nitrox is, and how nitrox works, we can take full advantage of using nitrox on most of our dives. In fact, I always try to dive with nitrox on every one of my dives except when I’m teaching the open water course, or when nitrox is unavailable.
What exactly is nitrox?
Basically the word nitrox was coined by combining the words nitrogen (N2) and oxygen (O2). And that’s exactly what nitrox is: any gas blend containing nitrogen and oxygen as the major constituents of the mixture. The air we breathe every day from the atmosphere contains approximately 21% O2, and 79% N2, so air is considered a nitrox mixture according to the definition given above (we exclude any trace gases, and other inert gases, such as Argon (Ar)) The trace gases in a nitrox mixture are present in such minimal concentrations that for the purpose of recreational scuba diving, we can safely ignore them.
A nitrox blend could contain less than 21% O2, which would be considered hypoxic, and is sometimes used by technical divers, in commercial deep diving applications, and by military divers under certain circumstances. A hyperoxic mixture, also known as Enriched Air Nitrox (EAN) is one that contains more than 21% O2, or an “enriched” gas blend. We might end up with a gas blend containing from 22% to 99% O2. Since this article concerns recreational nitrox diving, and no-decompression diving, I will be talking about diving with enriched air containing between 22% and 40% oxygen.
Although diving with enriched air means having a gas blend with more than 21% oxygen in the mix, the most common blends are 32% and 36% oxygen, while the remaining 68% and 64%, respectively, is nitrogen. Enriched Air Nitrox is also abbreviated EANx. The x in EANx tells us the oxygen percentage present in the mix, for example, EAN32, and EAN36.
As you can see now, we end up with a gas blend containing less nitrogen. As you may remember from your open water course, nitrogen is the gas component in air, or nitrox for that matter, which causes decompression sickness (DCS), narcosis, and is our limiting gas which dictates our bottom time.
Benefits of diving with Enriched Air Nitrox (EAN)
Since there is less nitrogen in our gas blend, we have certain benefits when scuba diving with nitrox. Nitrogen limits our bottom time. By having less nitrogen in the mix, your body absorbs less of it than you would when breathing normal air. This translates into two benefits. First, you can significantly extend your bottom time beyond the duration you would have with air. Second, if you dive with nitrox within air table limits, you will see a reduction in your exposure to nitrogen, and this gives you an extra margin of safety. For example, if you use nitrox in this way, you can have a bottom time close to the limits of, let’s say, an air computer, but still be well within the actual no-decompression limit.
In addition, if you dive with nitrox using an air profile, you can also reduce your surface interval times between repetitive dives. Nitrogen also affects the nervous system at depths below 100 feet (33 m) causing nitrogen narcosis, an anesthetic effect that intensifies as you go deeper. Although, some nitrox divers say they experience a slight decrease in narcosis and consider it a benefit, many diving physiologists believe there is no such reduction in narcosis effects. So when you dive with nitrox, it is always smart to assume that the risk of nitrogen narcosis is the same, and be prepared for it.
Since Enriched Air Nitrox has less nitrogen than air, and nitrogen is “the gas you don’t want in your body,” you can use nitrox for safety reasons by reducing your exposure to nitrogen, and reducing the potential risk of DCS. Or nitrox can offer you a time advantage by increasing your bottom time, or reducing your surface interval time, when compared to dives using air. Either way, nitrox can benefit any diver in a number of different ways.
Next: Nitrox for the Recreational Diver Part II