What do veteran divers think about Air vs Nitrox

[mccabejc]

The contention that since the overall risk of DCS is very low, then there is probably little additional benefit from EAN seems flawed to me. I read "overall risk" as the risk to the diving community in general. As others have alluded to, if 10 people in a total of 10,000 dives get DCS due to excess nitrogen (made-up numbers), then yes, the overall risk to the community is low (0.1%). But that's meaningless in terms of evaluating protective measures for those 10 people.

Sure, if EAN cuts that down from 10 to 8 incidences, in the overall scheme of things that's only going from 0.1% to 0.08%. No biggie. But that's actually a 20% reduction in the number of incidences. That's a biggie, especially for those two divers.

I'm guessing that the problem is that we can't prove the "if EAN cuts that down" part. There's no way to prove that the presence of EAN on a particular dive avoided DCS. All we can do is look at gross statistics. Maybe they look to see if there's a corresponding decrease in DCS cases in the general dive population as the popularity and use of EAN increases. Dunno.

I hope I'm interpreting it wrong, and it's not the case that PADI, et. al., are just looking at overall risk to the dive community and saying EAN wouldn't make a difference. Heck, nothing would make a difference using that logic.

 

[scubadobadoo]

If it doesn't recude the risk of DCS, how do you explain getting longer bottom times & shorter surface intervals? How can those things be possible if the risk hasn't been reduced?

I don't think ANYONE is saying that it DOESN'T reduce the risk. The discussion here (for me) is about HOW MUCH of a reduction and I am of the mind that the reduction is very miniscule. Some have argued that miniscule is the same as none and I disagree becasue we really are splitting hairs here. Like Jim said above, you can look at it from both ways. Miniscule or a 20% reduction for an already miniscule 10 people out of 10,000. That said, it clearly IS still a reduction in risk, but not nearly as much as MANY (not all) LDS's teach it to be.

 

[Wayward Son]

Plan a few repetive dives. Same profiles, do one set with air, the other with 32%. You're going to find that your allowable NDL times differ by far more than a fraction of a percent, as well as your SI times required.

Now, if you want to say that divers who run to the edge of NDL profiles on air & nitrox have about the same risk of getting bent, that's one thing, but it is not the complete picture. if there was not a substantial reduction in risk, there would be no appreciable gains in available NDL bottom times & reduction in required SI times between dives.

 

[Thalassamania]

Actually in the recreational community the numbers are about one case in ten thousand dives.

As far as the risks are concerened, bent is bent it's an either or. If you're bent it 100% if you're not it's 0%. The 1 in 10,000 is not a statistical prediction, it's a commentary on how people dive. In the commercial community its about 1 in a thousand and in the science community its about one in one hundred thousand.

 

[scubadobadoo]

Plan a few repetive dives.

We discussed this earlier and I agree with you completely.

As for diving nitrox within air limits, sure the increase is substantial but still fractional. Even DAN's #'s don't prove that diving nitrox within air limits means that less people get bent. Does the math make sense? Sure I agree, and I do it sometimes, but we still don't have enough data to 100% prove that diving nitrox with air tables equals fewer cases of DCS.

 

[TheRedHead]

...in the science community its about one in one hundred thousand.

Thal, which factors account for such a stellar record in the science community?

 

[HowardE]

I honestly can't believe that there is DEBATE over the validity and/or benefits of diving nitrox.

If you're afraid of nitrox, then don't dive it. It's only your loss.

Personally - I dive nitrox on 99.9% of my dives, and I don't pay a penny more for any recreational nitrox mix (22-40%) than I would for air.

I usually dive the richest possible mix, keeping my PPO2 to 1.5 or even possibly 1.6 ppo2 for a max depth.

I usually TRY to dive 40% on dives up to 90 FSW. This extends my bottom time greatly.

 

[TheRedHead]

Sure I agree, and I do it sometimes, but we still don't have enough data to 100% prove that diving nitrox with air tables equals fewer cases of DCS.

You can't prove anything in deco theory - that's the problem. They don't even know exactly how people get bent. All you can do is look at statistics and improve models.

 

[TheRedHead]

I usually dive the richest possible mix, keeping my PPO2 to 1.5 or even possibly 1.6 ppo2 for a max depth.

You're limiting yourself to 45 minutes at 1.6. 1.6 is generally reserved for deco gas where you are not exercising.

 

[scubadobadoo]

You can't prove anything in deco theory - that's the problem. They don't even know exactly how people get bent. All you can do is look at statistics and improve models.

I agree. I said exactly that three pages ago. I think the model is pretty good now and that is why I think diving nitrox over air only offers a minimal or miniscule advantage. We can't improve the model much more than we already have. The safety numbers are already pretty darn good and those numbers account for all the idots out there who don't dive in a safe manner. Like Thal said, the way you dive is far more important than the gas used in terms of adding a meaningful safety advantage. I think that is what he was saying in regard to the "comment on how we dive," comment.