Normally when diving, we breath compressed air, which is 20.9% oxygen, 78.1% nitrogen, 0.9% argon, 0.04% carbon dioxide, and 0.06% a variety of other trace gases. The gases beyond oxygen and nitrogen really don’t matter, so we tend to focus on the oxygen and nitrogen content.
What is Nitrox
Enriched air, or nitrox, is compressed air that has extra oxygen added to bring it to a higher level of oxygen and a lower level of nitrogen. Standard amounts used are 32%, 36%, and 40%. The standard recreational nitrox class limits the diver to no more than 40% nitrox. Technical divers get certified to use higher amounts but that also requires some special treatment of the equipment and no titanium in the regulators (titanium and higher amounts of oxygen don’t mix without some very unpleasant consequences).
Once again, I did my class with Punkfish Academy. Their YouTube videos in addition to the SSI material were excellent instruction. I did find that while most O2 analyzers are pretty standard in how they work, a couple of brands are slightly different. I fumbled a bit the first time I picked up a tank in the shop because they had one of those odd ones.
Benefits of Nitrox
There are two major reasons for a recreational diver to use nitrox. The first is that it allows you an extended bottom time and minimize the surface interval you need to take between dives. This means more time seeing what you want to see.
The second major reason is safety. Because you’ve reduced the amount of nitrogen in your breathing mix, you won’t absorb as much into your tissues, which means less to off gas as you ascend and on the surface. Less nitrogen = less likely to experience any form of decompression sickness.
There is a 3rd reason to dive with nitrox. I don’t count it as a major reason because there’s, so far, only anecdotal evidence of the advantage. You don’t feel as tired or fatigued after a dive. Again, it’s anecdotal, but I can verify from my own personal experience that I’m far less tired after diving with nitrox than without. It was noticeable on my first dive with nitrox.
Risk of Nitrox
There is one major drawback to using nitrox. A risk that most recreational divers do not see is of oxygen toxicity. It is possible, under pressure, to get too much oxygen. At pressure, it saturates your tissues and does things more than just your respiration. At high enough levels, you can experience a central nervous system seizure. If you were on the surface when this happened, it’d be like any seizure and once you were in a normal oxygen range, you’d return to normal, probably with minimal negative impacts. When diving, however, a seizure can be fatal because of the drowning risk.
To minimize this risk, divers try to keep the partial pressure of oxygen below 1.4. At sea level (1 atmosphere of pressure), this is 0.21. As we descend underwater, it slowly increases. At 33 feet (10 meters or 2 atmospheres of pressure), compressed air has a partial pressure of oxygen of .42. The deeper you go, the higher it gets.
For a diver using compressed air, the maximum depth with a 1.4 level ends up being around 187 feet (far outside of the recreational range). For a diver using 32% nitrox (the most common level), the maximum depth is at around 110 feet. Between partial pressure of oxygen of 1.4 and 1.6, there is a greatly increased risk of a seizure. Above 1.6, you’re basically playing Russian Roulette. A diver right here in Missouri died in 2022 from what was likely oxygen toxicity.
O₂ Analyzers
When you pick up a tank with nitrox, you don’t just grab it and go. The dive shop will put a sticker on it and you (the diver that will be using the tank) use the analyzer (theirs or your own if you have one) and check the percent oxygen. You then write it on a sticker on the tank and initial it as the one who checked it. Finally, you calculate the maximum operating depth and write that on the sticker on the tank as well. Why? Any time you dive with anything other than compressed air, you check it yourself. Your life may depend on it.
After some minor problems with the analyzer at one shop (well, both of their analyzers) and at least once with a truly inaccurate reading, I’m going to get my own and take it with me when I travel. Truthfully, I’ve been considering getting a carbon monoxide detector and checking my compressed air tanks too, as a precaution.
Final Thoughts
In conclusion, dive with nitrox but be sure you stick to the depth limits for the mix you are using. It’s a little more costly than compressed air but the benefits are worth the few extra bucks, especially if you are going to have consecutive multiple dive days like you would on a trip.
