Nitrox – When to take the plunge…

A question that comes up quite regularly, but what is the right answer?

To give a proper thought, we must first look at the history and current events of Nitrox.

Used in a commercial setting for as long as there have been divers, nitrox didn’t come into mainstream use until the early 90’s and even then is was only really supported by “fringe” technical diving agencies such as TDI. In fact the British Sub Aqua Club (BSAC), the “governing body” of UK diving didn’t accept it’s use officially until 1994, after outright banning its use in 1992!*

Put simply, it’s the practice of using more oxygen in your breathing mix which in turn lowers the amount of nitrogen available to be absorbed into your bodies tissues while at depth. The result of this is longer no-decompression limits, shorter decompression times or the perceived safety factor if diving to air limits and a more energetic post-dive feeling. I say perceived, because when it comes to safety, it’s statistically null and as for the lack of lethargy, that’s subjective and difficult to measure. Mainly because if you dive enough to notice a difference, then it may be improved dive fitness rather than any benefit from the nitrox.

The downside of this higher oxygen, is far shallower depth limits than air and a requirement to track your cumulative dose of oxygen. For example: Air is 56m, Nitrox 32 is 32m and Nitrox 100 is 4, yes 4m!

Sounds simple, but is it…

Well, yes and no. While it is very simple to implement, it depends on your use as to how easy it is for the diver to manage.

If you are only diving on holiday with a guide, then it really is just a case of plugging the mix into your computer, then following the guide and any instruction from your computer during the dive.

Diving locally though is a different story. For one, you’ll likely be autonomous and not have a “higher being” watching your every move, leaving you free to make your own decisions about depth and time.

Diving on air, this isn’t such a problem as you are very unlikely to reach any of it’s physical limitations, due to your own decisions or not – tide for example.

On nitrox though, to get the benefit of using it, you need to have a mix that is as “strong” as possible for the maximum depth of the dive. This means that you have an absolute depth limit which lies inside recreational depths, that you must adhere to or face the risk of very nasty consequences.

A scenario that comes to mind, which has actually happened. You dive at Anfre post with north running tide. You pull up to a bobber and check the tide and notice a nice trickle. You know that because it’s half tide up, that the tide will continue in that direction. So you select a start depth of 20m, knowing that if you run north, the maximum depth will prove no more than 25m. After getting in the water, you notice that it’s getting slightly deeper, so you angle yourself into the tide slightly to make your way shallower, at this point you reach a steep slope and wooooosh – you’re in 40m!

On air, this isn’t a problem. You’ll either make your way up the line, or deploy your smb and head for the surface. Either way, provided you have the gas, there is no immediate danger.  On nitrox, you’ve just exceeded your depth limit by some margin! Alongside the danger of the nitrox itself, you now have an added danger of panic, due to knowing that you have exceeded this limit. Neither are good for your health, or an issue on air.

So straight away, we have 2 extra things that you need to think about before and during the dive. How deep am i going? (before) and How deep can i go?(during).

You’ll also need to need to make sure the mix in the tank is what you think it is, by religiously analysing it before every dive. Another step and thing to remember.

This is why nitrox was always considered a semi-advanced qualification, until it’s mainstream use got high enough to where the agencies could start to make money out of it without too much fear of it being dangerous. Now for example, you can use nitrox from pretty much day one, even on your Open Water course!

So to be a safe nitrox diver, you need to:

  • Have the knowledge of the dive sites to be able to know how deep they are, and once in the water be able to navigate a route that keeps you inside the limits
  • Have comfort around the methods of calculating the depth limits and tracking your cumulative exposure to the elevated  oxygen.
  • Have the confidence and skills to be able to control your environment and equipment while underwater. To make sure that you don’t get pushed around by the tide.
  • Finally, you’ll need to have a good comfort level whilst underwater, this will enable you to have a clear enough mind to make sure that you are thinking about these new limits.

So why use it at all?

For dives of 30-45 meters, you can nearly double your no-decompression time. That makes a big difference to your dive times, especially on multiple dives. Diving up the Platte scalloping in the summer would be almost impossible without nitrox, as by the 3rd dive of the day in nearly 40m the no-deco limits are just a few minutes.

Are you going to benefit?

Simply, if you are ending most dives because of low gas, then nitrox will be of little benefit. If however, you are frequently ending dives with plenty of gas left because you have hit a no-decompression limit, then absolutely nitrox is for you.

One final note, the nitrox courses offered by all agencies are “theory only” with dives being optional. I personally believe that this is a bad example of “bare-minimum” teaching, and will always make sure that my students get a dive in as part of the course. That way, we all go diving which is the whole point of learning, secondly, we can all make sure that we are happy with actually using nitrox. Also, be sure to pick an instructor that actually uses the stuff, the number of instructors teaching nitrox with no experience in using it is pretty scary!

As always, i’m keen to hear your thoughts on this. You can either comment below, send me a message or pop in for a chat.

Cheers and i hope to see you in the water soon! #nobullshitjustdiving


*from wikipedia, so probably wrong dates, but the gist is correct

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