Nitrox – When to Dive It

by Cris Merz:

Nitrox Diver

The fantastic stories about voodoo gas seem to have mellowed out a little in the last 20 years. From, “It’ll kill you” to “You will have soooo much energy after the dive”, it never ceases to amaze how nitrox, as a topic for discussion, has always been a leader in misconceptions.

With many reasons in favor of diving nitrox, the reasons for doing so may hold a little more scientific value today than they did 20 years ago.

Few advances in the realm of diving have had a more profound impact during the past two decades than the widespread availability of Enriched Air Nitrox. And nothing has made the switch from diving air to diving nitrox more straightforward or more enjoyable than nitrox programmable dive computers.

Simply put, nitrox – air with additional oxygen content – allows divers to enjoy longer bottom times (and shorter surface intervals) than their air-breathing dive buddies, while staying within the limits that were stressed in their open water training.

Nitrox makes this possible because it contains reduced levels of nitrogen compared to air and less nitrogen translates into more bottom time! But of course there is a price to pay. Diving nitrox does present risks that are not present while diving air and these risks require divers to take additional steps during their pre-dive planning and then adhere to that dive plan.

The number one reason for diving nitrox is safety. When diving with a greater amount of oxygen (32% or 36%) in the mix, rather than air (21%), you decrease the risk of decompression sickness because you’ve lowered the amount of nitrogen you are breathing in at depth – and as we know, nitrogen is the number one culprit associated with decompression sickness.

When should we dive nitrox? Well, whenever the opportunity presents itself. It may not make a great difference but it certainly will not hurt. Unless you go diving beyond the Maximum Operating Depth (MOD) of the mix in your tank, it is beneficial to you every time, though sometimes those benefits are much greater than others based on your diving profile.

The moments when nitrox will make the greatest difference is when you are doing multiple dives over multiple days and are getting close to some of the no-decompression limits your personal dive computer is telling you about.

As stated, when you dive using nitrox you can take advantage of increasing your maximum allowable bottom time. This happens because the extra oxygen added to your breathing gas when it was filled has displaced nitrogen. Because there is less nitrogen in the mix to be absorbed by your body you can spend longer at depth before you reach the nitrogen limit – which is the decompression limit. Secondly, since you are absorbing less nitrogen on a given dive, your surface intervals can usually be shortened.

Being on a live-aboard, hundreds of miles from home where you are doing 3 to 4 dives a day will allow you to see a huge difference if you can compare yourself to those diving on regular air. You have paid a lot of money to get there and you want to make each and every dive count. You do not want to get back in the water for the fourth dive so you can zip about at 50ft/15 meters just because you have reached your no-deco limits for the day – especially when the schooling hammerheads are hanging out around 70ft/21 meters. That is where you want to be… for as long as possible.

Despite having depth limits to be aware of due to the risk of oxygen toxicity, and perhaps some additional costs for the fills, the benefits of nitrox will play a role in your steps to keeping your dives within safer limits than if you were on air.

If you are not yet nitrox certified, find out more about diving with enriched air from your local SDI or TDI instructor.

You will discover that diving nitrox is not rocket science. The concepts are straightforward and easy to understand. Of course, like most things relating to diving, the subject does have another side and if the science and technology behind the basic concepts of nitrox interest you or if you find yourself wondering how nitrox with higher levels of oxygen than 40 percent would affect your diving, you may want to consider continuing on to Technical Diving International’s (TDI’s) Advanced Nitrox Diver course.

16 replies
  1. Ian Robertson
    Ian Robertson says:

    I heartily agree with the content of your article, however, as a frequent Nitrox user, I hoped for a little bit more…. like a discussion of the fatigue issue or some tabulated examples of where it is most efficient.
    By the way (re article title) you don’t ‘Dive Nitrox’, vou ‘Dive with Nitrox’.

    Ian Robertson

  2. Craig
    Craig says:

    G’day! Why does TDI/SDI still use imperial measurements in it’s news letters? I can think of no dive operators (or divers) who use the imperial system for measuring depth, temperature, tank pressure, amount of dive weight used or any other measurements. It can be confusing because one might read about a certain feature, (shipwreck, cave entrance, etc.) at “70 ft.” and later remember it as “70m”, concluding “Well, I can’t dive that feature as it is beyond my depth limit”. I heard one diver tell the story of ordering a camera housing online and upon receiving it realising that the stated depth was of 100ft., not 100 as he had concluded when ordering, possibly assuming that 100′ meant 100 metres. If nothing else, it disrupts your flow of reading as you have to stop and think of the conversion. More recently, I have read statements that dive schools and freelance dive instructors are now more frequently encountering new students who don’t continue diving after completing their open water course, (apparently this is not an uncommon occurrence) or want more simplified training. So perhaps pop culture, stressing instant gratification, is the main contributing factor, ……. so could this be the reason for the imperial measurements appearing in dive related material, ……… there is a “new breed” of diver unwilling to learn something new?, …….. as dive culture’s standard of metric measurement? Cheers! -Craig

  3. warren hastings
    warren hastings says:

    After 4500 dives I suffered a bend, due to a PFO, in 2006 DDRC recommended to use Nitrox on all dives, using the biggest mix possible on all dives. So 5200 and all is well, Note of caution using any Nitrox mix to its no stop time is the same risk as using Air.

  4. The Pro
    The Pro says:

    Craig, sadly the people of the USA are stuck in time with their insistence on remaining the last country on Earth that has not switched to the metric system or to DIN. Most Americans that I talk to are rather ignorant about the metric units. I have been yelled at by immigration officers and ridiculed by commoners when traveling in the USA for my use of metric and my inability to comprehend Fahrenheit. It’s a sad state for an otherwise advanced and progressive country.

    This said… Love it or hate it, the imperial system is still kicking in the USA. Thus, it is to be expected from an American author to express himself in imperial units. It’s a free world, so there is nothing wrong with that. Still, you have a point that TDI/SDI, being an international organization (at least by name), should make sure that their blog posts state the units in BOTH metric and imperial (metric preferred) so that they can be read outside the USA without the need to keep converting in Google.

    • Paul s
      Paul s says:

      I guess the real problem isn’t then unit of measure that’s being used its having the same units everywhere.
      Think of aviation, height is in ft, speed in miles, communication in English etc and its the same everywhere so no confusion.

      • JJ
        JJ says:

        It’s referred to as air speed or ground speed speed depending on which speed is being calculated. It’s also measured in knots vs
        mph. Also, metrics vs imperial argument is a non issue. Doesn’t everyone in the world learn both systems? We do in the USA!!!

  5. Tim St.Clair
    Tim St.Clair says:

    To add to what Warren points out…

    Not only is diving to no-stop limits on nitrox NOT ‘safer’ in terms of DCS risk than doing so on air, reaching a no-stop limit on nitrox will also NOT result in shorter surface intervals than when diving on air. If you are diving to the point where your table/computer’s controlling tissue compartment(s) is/are maximally loaded while still allowing a direct ascent to the surface, it will take the SAME amount of time to eliminate that excess N2 at the surface after the dive, regardless of how (fast) it got in there during the dive.

    TDI/SDI is a US-based training agency. The Yanks still routinely use Imperial measures for diving, even though the rest of the diving world has long since gone metric (even the UK, where Imperial measures were invented!).

  6. Darryl
    Darryl says:

    I worry that the article says “Unless you go diving beyond the Maximum Operating Depth (MOD) of the mix in your tank, it is beneficial to you every time”. I disagree with this, especially when the very next paragraph goes on about doing multiple dives over multiple days. This is exactly when Nitrox can cause new issues as you start to push the CNS clock. You get the benefit of longer dives but it is important to also weigh that against the increased risk from CNS oxygen toxicity as you increase both your individual dive O2 exposure and your 24 hour O2 exposure.

  7. Coley M.
    Coley M. says:

    I love the article but I have a question about Nitrox. As a new diver, I was informed that I should take a nitrox class as soon as I finish my Open Water, my one huge concern is that when I am underwater I tend to have a few moments of panic because I am still getting used to the feeling of being underwater, if I want to finish a dive early, will this affect me at all? In other words is it dangerous to finish diving with nitrox early? Also, is there a difference in taste or thickness of the air? For example, the tanks I have used have like a rubbery taste when I first breath it in and the air is pretty much the same as breathing in normal air, how does Nitrox compare? And, if I only wanted to do like a 30 foot dive (as I am still not completely comfortable underwater yet) is Nitrox okay to use or should I stick to the regular air? As a smoker, does Nitrox have a negative affect on a pack a day smoker? I know these are questions I can ask my instructor but I am not going to take a course I am not ready for so I thought this is a perfect opportunity to get some answers prior to beginning my eLearning with SDI Computer Nitrox. Thank you! 🙂

    • Paul s
      Paul s says:

      Finishing a dive earlier than planned will make no difference on EAN to air.
      As an example: let’s say we were making a 15m (45ft) dive and planning on a bottom time of 30mins.
      With air you would end up in group E whilst with EAN36 it’d be D. Meaning you’d have less nitrogen and could therefore have a shorter surface interval.
      Now if you aborted the dive after say 15mins bottom time then the only difference would be the group the fall into (air C EAN36 B).
      As for taste it’s no different, and the rubber taste will simply be the mouth piece or hose.

    SDI/TDI/ERDI says:

    Thank you, Coley.
    Yes, you may finish your dives as early as you’d like with Nitrox but you may not want to bother with diving Enriched Air if you are not planning on going beyond 30ft/10m. You may want to get a few dives under your belt until you are ready to go a little deeper. Like air, it is odorless and should not have any taste and as a smoker, you are still able to dive it


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