It’s hard to get into diving without hearing the word nitrox thrown around. So what’s the fuss about scuba diving with nitrox?
Many non-divers incorrectly believe that we dive with pure oxygen (I guess because it’s oxygen that keeps us alive).
Most divers dive with the same air we breathe on the surface… it’s just compressed to fit about 80 cubic feet worth of air into a cylinder that’s really only 0.39 cubic feet (for the standard “aluminum 80” cylinder). The air we breathe at the surface and in our tanks is approximately 21% oxygen, 78% nitrogen and 1% argon (with a very small percentage of other gasses). To simplify things, we usually lump together the argon and nitrogen and say air has 79% nitrogen.
In recreational diving, we avoid the need for decompression stops by limiting the amount of nitrogen that gets absorbed into our blood and body tissues by limiting depth and time underwater. The time we’re allowed to stay underwater is called the no-stop or no-decompression limit.
A relatively simple way to extend this time underwater is to dive with a breathing gas that contains less nitrogen.
What is nitrox?
Nitrox (or more formally Enriched Air Nitrox) is a breathing gas mixture that contains a higher proportion of oxygen than regular air. A common nitrox mix is 32% oxygen and 68% nitrogen, but most fill stations that offer nitrox can provide any mix upon request.
Why isn’t nitrox the default breathing gas for scuba?
Breathing oxygen under pressure can be toxic if the pressure is high enough. We’re talking seriously toxic… oxygen toxicity causes convulsions, which underwater usually results in the diver spitting out their regulator, which leads to drowning. That is why divers must be certified to use nitrox, so they understand the risks and learn how to dive safely with nitrox. If done properly, scuba diving with nitrox is perfectly safe.
The PADI Enriched Air certification is a relatively simple half-day training session that doesn’t require any dives. They key takeaway of this course is to understand how deep you can safely go with various nitrox mixes, and how to analyze a nitrox tank to ensure it actually contains the mix it says it does. For example, the common 32% nitrox mix is safe to depths of 34m/112ft (essentially the depth limit for recreational diving, which is why this is such a popular nitrox mix). For shallower dives, scuba diving with nitrox mixes with greater amounts of oxygen can be safely used.
Benefits of scuba diving with nitrox
Nitrox is useful on deeper dives from 18 metres (60 feet) to 30 metres (100 feet) to increase your no-decompression time. It will give you a few extra minutes at that depth. If your dives are fairly shallow, your no-stop limits are already plenty long, so nitrox doesn’t provide much benefit.
It’s also very useful when you’ll be doing repetitive dives. Even with appropriate surface intervals, if you’re doing 4 or 5 dives a day (like on a liveaboard trip), you’re not off-gassing all the absorbed nitrogen between dives. So scuba diving with nitrox will mean you accumulate less nitrogen over repetitive dives, and will therefore have significantly longer no-stop times on your latter dives.
And finally, while science can’t explain it, most divers say they feel less tired after dives when they breathe nitrox. I’ve experienced this first-hand, and will always dive nitrox if it’s available.
So go for it… get your nitrox certification and start enjoying the benefits of nitrox.