To Nitrox or not to Nitrox: that is the question

[Prostar]

Quite often, after I've finished a dive on air, my body feels like it was beat with a bag of potatoes. I never get that feeling with nitrox.

 

[DandyDon]

Quite often, after I've finished a dive on air, my body feels like it was beat with a bag of potatoes. I never get that feeling with nitrox.

That's subclinical DCS. And you Instructors go thru a lot of pressure changes with your students. :11:

 

[mthirsc]

Dude,

Take the class and filter the noise on here. Get the knowledge, then dive it or not. I'll dive it if it is available, but typically on boat dives. Fatigue? Less, but I still get the munchies.

Shark out.

I agree with this. Personally I have found 2 situations where Nitrox makes sense. More than 2 dives in a day, and more than 80-100CF of gas. With a lot of gas at the right depth nitrox is great. Otherwise I am more often limited by my air consumption.

For me, on a 45-50 min dive with avg depth 80ft (max 110) with 2x80CF, I will usually do 15 mins of deco to save $15 on two EAN32 80CF, that's $60/hour.

 

[Buoyant1]

From some of the reports I've read, larger people (like me) and people over 40 (yup, that too) purportedly have a bit more risk at DCS...whether those risks are legitimate due to research and test cases, or just projected based upon other factors, I still like the "reported" benefits so that's why I took the course. I ALSO like the increased bottom time. I compared my tables based on square profiles and it was significant between air and Nitrox!

But I like it for the taste!

(btw..Dandy Don..that's a "sporty" hat you got there!)

 

[ianr33]

You have to be a member to get the DAN info. Here are some other articles that reference the findings mentioned. I also included a link to the much debated scubadiving magazine article from a few months ago that I personally think is dead on, many disagree.

http://www.scubadiving.com/article4545

http://www.techdiver.ws/nitrox_eng.shtml

http://www.si.edu/dive/library_nitrox.htm

Thanks for the links.
As I thought DAN may be comparing apples to kumquats. From the second link:

<< Let's take a look at the diving accident statistics! DAN (Divers Alert Network) has statistics of DCS cases in the USA, which is based on DEMA/NUADC and PADI New Diver Benchmark reports. According to them, the probability to get DCS by air diving is about 0.004% (1 to 25000). Based on this number, and on the PADI Undersea Journal 3/97 magazine, the probability to get DCS by air diving even once during 500 dives is 1.98% (1 to 50). The risk is 1.49% in nitrox diving in same amount of dives. So... so far the difference is marginal, even though nitrox seems to be a bit safer.>>

Looking at the incidence of DCS per dive is meaningless if you dont know anything about the dives and all dives are not the same.I suspect that the average nitrox dive is deeper and longer than the average air dive. (not many people will use nitrox on a 30 foot dive) The implication of the quote above is just sloppy science.

I suspect the percentage of DCI cases is higher for Trimix dives (due to many of these dives being long and deep) does that mean I would be safer to use air on a 200 foot dive because it is known to have a lower incidence of DCS??

 

[mmex4wdauto]

I got my nitrox certification with the original intent to try a Discover Rebreather experience, but nitrox certification makes perfect sense for the majority of the diving that I do. I usually go cave diving in Mexico's Yucatan peninsula which involves a lot of sawtooth (a lot of ups and downs) depth profiles. In a majority of the places that I've been, you will get a maximum depth of 40-50 ft. which may not sound like a lot for excess nitrogen loading, but it is always good to err on the side of caution when ascending and descending according to the natural configuration of the cave. With that said, EAN40 is usually in my tanks for cave diving (I go with EAN40 because I can top them off with air). Anything that you can do to mitigate decompression stress is usually a good thing.

That said, this next bit may sound strange. In open-water situations, I'm much more likely to use air because once I start ascending to shallower depths, it's almost guaranteed that I'm not going deeper again. Although, for someone who makes many ascents and descents in open-water (like an instructor) throughout a given dive, it would make much more sense for them to use nitrox.

To sort of parrot an earlier posting, take the class and learn the skills. At that point, it's up to you if you want to use them or not.

 

[DandyDon]

I got my nitrox certification with the original intent to try a Discover Rebreather experience, but nitrox certification makes perfect sense for the majority of the diving that I do. I usually go cave diving in Mexico's Yucatan peninsula which involves a lot of sawtooth (a lot of ups and downs) depth profiles. In a majority of the places that I've been, you will get a maximum depth of 40-50 ft. which may not sound like a lot for excess nitrogen loading, but it is always good to err on the side of caution when ascending and descending according to the natural configuration of the cave. With that said, EAN40 is usually in my tanks for cave diving (I go with EAN40 because I can top them off with air). Anything that you can do to mitigate decompression stress is usually a good thing.

That said, this next bit may sound strange. In open-water situations, I'm much more likely to use air because once I start ascending to shallower depths, it's almost guaranteed that I'm not going deeper again. Although, for someone who makes many ascents and descents in open-water (like an instructor) throughout a given dive, it would make much more sense for them to use nitrox.

To sort of parrot an earlier posting, take the class and learn the skills. At that point, it's up to you if you want to use them or not.

Yeah I can see it. With no more depth than you get on your caves, good mix - and takes the edge off of all that bouncing up and down.

 

[boulderjohn]

You have to be a member to get the DAN info. Here are some other articles that reference the findings mentioned. I also included a link to the much debated scubadiving magazine article from a few months ago that I personally think is dead on, many disagree.

http://www.scubadiving.com/article4545

http://www.techdiver.ws/nitrox_eng.shtml

http://www.si.edu/dive/library_nitrox.htm

The DAN article specifically says what Dandy Don said: if you dive with Nitrox to air limits, you get a safety benefit. If you dive to the Nitrox limits, you will get no benefits other than the increased bottom time. That is not a safety benefit, but it is a benefit.

Here is a quote from another section of the DAN article:

What Is Nitrox Good For?
The real value of nitrox is that it gives you more minutes before you have to ascend to avoid decompression stops, often a lot more. Compare no-decompression limits: at 100 feet, tables issued by NOAA give 25 minutes on air, 30 minutes on 32 percent nitrox and 40 minutes on 36 percent nitrox. In some cases, nitrox can double your permitted no-deco time, and the difference can be even more dramatic on repetitive dives.

They also say that is not much of a benefit if you are running out of air anyway, or if you are doing a time-restricted dive. Well enough. On a typical dive for me, though, if I am on air, it is the NDL that is limiting my bottom time, not my air supply, even if I am just diving with an aluminum 80.

 

[highlandfarmwv]

With less nitrogen in the air you breathe, you have less nitrogen in your blood to form bubbles and therefore DCS. So the benefit is not necessarily more oxygen, but less nitrogen. ...supposedly....

From experience, I have found I even breathe more slowly (and use less gas) with nitrox, perhaps I need less breaths to oxygenate with more O2 in the mix? However, could less breaths prevent blowing off excess nitrogen quickly?

I wouldn't force nitrox on anyone, but I like it. Plus, it kind of adds to the technical aspects of diving, which is interesting.

My usual time in the Keys on air 63s last year was an hour, and I'm looking forward to extending that bottom time in Bonaire without having to lug around 80s.

 

[scubadobadoo]

The DAN article specifically says what Dandy Don said: if you dive with Nitrox to air limits, you get a safety benefit. If you dive to the Nitrox limits, you will get no benefits other than the increased bottom time. That is not a safety benefit, but it is a benefit.

Here is a quote from another section of the DAN article:

What Is Nitrox Good For?
The real value of nitrox is that it gives you more minutes before you have to ascend to avoid decompression stops, often a lot more. Compare no-decompression limits: at 100 feet, tables issued by NOAA give 25 minutes on air, 30 minutes on 32 percent nitrox and 40 minutes on 36 percent nitrox. In some cases, nitrox can double your permitted no-deco time, and the difference can be even more dramatic on repetitive dives.

They also say that is not much of a benefit if you are running out of air anyway, or if you are doing a time-restricted dive. Well enough. On a typical dive for me, though, if I am on air, it is the NDL that is limiting my bottom time, not my air supply, even if I am just diving with an aluminum 80.

Actually you are quoting articles that reference the DAN research, not the DAN articles themselves right? I just don't want to put words in DAN's mouth here, not trying to be picky.

This is my favorite quote from one of the above articles(again NOT DAN's words)...If you're one of those who likes a belt with suspenders for a "tremendous margin of safety, you're going to love diving nitrox to air limits."

We are really splitting hairs here and I think we all basically agree with each other. My only point is that the words "great, significant, many, and large" shouldn't be used in association with the SAFETY margin/benefit in regards to decrease in DCS hits of Nitrox VS. air. "Minimal, insignificant, miniscule," these are more fitting words only because the chances of of a DCS hit are already so low, when diving with common sense, that simply adding Nitrox to the mix doesn't decrease the number of hits. That is what the DAN research has shown. Does it have MANY other benefits that I will take advantage of in Cozumel? Heck yeah!

Increased safety is a benefit, but insignificant statistically unless you are that one guy more out of 10,000 that the study showed took the hit and maybe he was a knuckle head. Being in better shape, hydration, proper sleep, slower ascents, safety stops, common sense, diving within limits...these are the things that the DAN research says will play a more significant role in decreasing DCS hits. I think the nitrox class and others should focus more on these things instead of claiming a HUGE margin of safety just because one is using nitrox, as some shops do. "Get your geezer gas here!" "Be a safer diver!" ""Feel less tired, use Nitrox!" I have seen all of this written on LDS windows. That isn't a very clear and honest message to send. Nitrox is only a tool to decrease bottom time, the rest is icing on the cake, but hey, icing is better than no icing I guess.