Nitrox vs Air

[HowardE]

For most divers... Spending time underwater is a precious short time that they can be down there to enjoy the underwater world. For most divers... I would expect that if you could spend as much as 25% more time underwater on a single dive, wouldn't you pay more for that gas (if it actually cost more.)?

Look at a simple safe dive to 60' on EAN 36 vs Air. Now do a 2 tank dive on a similar profile. The Nitrox divers can spend a LOT more time under the water than the air divers. So even if there is more cost involved, isn't nitrox worth that (to most recreational divers)?

The fatigue thing aside... Nitrox is safe, and lets you get more No Decompression time at most recreational depths.

 

[SilverNU]

I originally ask this questions because I was planning a dive for a wreck that was 75-110 ft.

I am AOW certified (supposedly for a recommended 100 ft). I doubt the extra 10 ft will bother me in this case (or I will just stay above it).. but the divemaster told me if I could before I came back (months away) to get my nitrox cert. to extend my bottom times a little.

thanks for all the info so far..

this is one reason.

another is that my instructor recommended it in conjunction with our rescue diver class.

 

[MauiScubaSteve]

Do you really need a reference source for people using nitrox to increase their safety margin? If you make a dive on air, you would have an increased margin of safety if the same dive were made on an appropriate mix of nitrox for the same amount of time as you would have on-gassed less nitrogen. What sort of reference were you looking for?

So, let us say that for the last decade, for all dives 80' deep or shallower that were conducted within NDL's, there were <2% undeserved DCS cases. Let's say that for that same decade, not just all 32% Nitrox dives 80' deep or shallower "that were dove to air tables", but even including dives to Nitrox NDL's, resulted in <1.8% undeserved DCS.

The margin of error would be greater than the difference in safety so the difference is statistically insignificant; air is not statistically more dangerous than EAN, even on air tables.

So far as I know, there is no documented evidence that there are less undeserved DCS hits diving EAN to air tables than there are diving air to air tables.

 

[mbram]

Actually, it is a true statement. If you said you were abducted by aliens and I said it wasn't true, I would not have to prove you weren't abducted. Most reasonable people would not believe you. You can believe anything you want about nitrox, but unless you have some solid evidence that it reduces fatigue or lowers DCS risk significantly, I'll continue to believe known facts.

Pure hyperbole. There are 2 competing hypotheses, one saying nitrox with >21% oxygen reduces post-dive fatigue and one saying it doesn't. Neither have been proved conclusively, both are equally invalid until one has been proved. Hope that's easier for you to understand. I never said it reduces DCS risk at all, it obviously doesn't. FWIW, I feel exactly the same after diving air as I do nitrox, neither leaves me fatigued.

The status quo remains until proven otherwise. Its how standard scientific method and peer review works.

Otherwise i could quite happily state "I have pink fairies living at the bottom of my garden that only i can see and talk to" and pass it off as true unless you can prove otherwise.

FWIW there have been some small scale studies and all have failed to find any reduction in fatigue (however you attempt to quantify that) over a placebo. But that isn't relevant to the above. Its a very difficult thing to test and measure but there is currently no evidence supporting a reduction in fatigue nor in fact is there any postulated mechanism as to why it would that stands up to any scrutiny. However placebo effect is known to and scientifically proven to have a physical effect on a person.

More hyperbole, you're still wrong, see above. Your hypothesis that it is a placebo effect is just that, a hypothesis. Surely you can see that, right? Some people report less fatigue on EAN, some report no difference. Neither has been proved. Hope I kept that on your level.

 

[DandyDon]

These Why Nitrox threads are so much fun. I haven't been on one in a while that I remember.

Why does the 25% more time suggestion keep coming up? I figure 50% more safe NDL time overall + a few minutes at various depths. On 80 cf tanks maybe not as I am such a air hog, but I generally can find 100 to 130 cf tanks at various destinations.

My bud who travels with me some is as bad as I am on gas. Last trip we were diving 100 cf air tanks on Cozumel multi-level dives and while we were ending much shallower on each, and relaxing with only 2 tanks a day, we were having to do some lonnng SSs on the second tanks to get our Oceanic computers back into the green. My trip before, I could not find anything larger than 80s at FIBR but with the Nitrox discount package on 3/day, clearing yellow was so easy. The air divers didn't seem to be taking long SSs, but

Thinking about the trips where boats altered plans for air divers on board: I remember a liveaboard with free Nitrox and only one air diver. There was an Inst giving classes onboard so they baptized him Discover Nitrox for the weekend after a quickie course. Safe? Maybe, except he didn't bother to tell them of his history of seizures - something I knew about from past trips with that group. I swore I'd never go on a trip with him along but he showed up after I did.

So, let us say that for the last decade, for all dives 80' deep or shallower that were conducted within NDL's, there were <2% undeserved DCS cases. Let's say that for that same decade, not just all 32% Nitrox dives 80' deep or shallower "that were dove to air tables", but even including dives to Nitrox NDL's, resulted in <1.8% undeserved DCS.

The margin of error would be greater than the difference in safety so the difference is statistically insignificant; air is not statistically more dangerous than EAN, even on air tables.

So far as I know, there is no documented evidence that there are less undeserved DCS hits diving EAN to air tables than there are diving air to air tables.

No, DAN does not support Nitrox as a safer gas. One would think that diving Nitrox on air tables would yield greater safety margins but DCS is more complicated than that I think. Then there are those nice folks who do use that approach: I've seen them dive tanks without analyzing, then go down to 110-120 or more ft with the rest on air. :shocked2:

 

[vladimir]

You can believe anything you want about nitrox, but unless you have some solid evidence that it...lowers DCS risk significantly, I'll continue to believe known facts.

We can't be slaves to data that doesn't exist; we're allowed to use a little common sense. Are 50-minute dives to 60 feet safer than 70-minute dives to 60 feet? Safer than 80-minute dives? Why? Because there is less nitrogen uptake on shorter dives using the same gas. Well, there is less nitrogen uptake on 32% nitrox dives of the same depth and duration as one using air. Why is there no evidence of reduced DCS risk? Because divers, as a group, are not taking much risk. They use conservative NDLs to reduce the DCS risk to a negligible level. What if we had no ethical or financial constraints and we did some experimentation. Group A does a thousand dives on air to 60 feet for 60 minutes. Group B does the same dives on 32% nitrox. Still no difference in DCS incidence? Repeat the experiment, doing 65-minute dives, then 70-minute dives. Which group do you want to be in?

 

[DaleC]

Lot's of theories are just supposition until someone does the work to prove or disprove the hypothesis: evolution, quantum mechanics, e=mc2. None of those had the proof in hand when the theory was first introduced.
Proving or disproving the placebo effect will probably not happen (except as a purely acedemic exercise) because there is no financial impetus to do so. Nitrox is accepted and widely accessable in sport diving and proving/disproving the effect would probably have no effect on sales.

 

[MaxBottomtime]

We can't be slaves to data that doesn't exist; we're allowed to use a little common sense. Are 50-minute dives to 60 feet safer than 70-minute dives to 60 feet? Safer than 80-minute dives? Why? Because there is less nitrogen uptake on shorter dives using the same gas. Well, there is less nitrogen uptake on 32% nitrox dives of the same depth and duration as one using air. Why is there no evidence of reduced DCS risk? Because divers, as a group, are not taking much risk. They use conservative NDLs to reduce the DCS risk to a negligible level. What if we had no ethical or financial constraints and we did some experimentation. Group A does a thousand dives on air to 60 feet for 60 minutes. Group B does the same dives on 32% nitrox. Still no difference in DCS incidence? Repeat the experiment, doing 65-minute dives, then 70-minute dives. Which group do you want to be in?

It would not matter. There have been millions of dives to 60 feet on air and several hundred thousand dives or more on nitrox. There is still no lower incidence of dcs hits per capita.

 

[vladimir]

It would not matter. There have been millions of dives to 60 feet on air and several hundred thousand dives or more on nitrox. There is still no lower incidence of dcs hits per capita.

Most of which were for 60 minutes or less. Which is why subsequent iterations of my experiment moved the duration to a point where it would matter. If your only contention is that the DCS risk of NDL dives is minimal whether using air or 32%, say, then I agree. But it is easy to see that you could choose values for "NDL" where it would matter.

 

[Thalassamania]

So, let us say that for the last decade, for all dives 80' deep or shallower that were conducted within NDL's, there were <2% undeserved DCS cases. Let's say that for that same decade, not just all 32% Nitrox dives 80' deep or shallower "that were dove to air tables", but even including dives to Nitrox NDL's, resulted in <1.8% undeserved DCS.

The margin of error would be greater than the difference in safety so the difference is statistically insignificant; air is not statistically more dangerous than EAN, even on air tables.

So far as I know, there is no documented evidence that there are less undeserved DCS hits diving EAN to air tables than there are diving air to air tables.

It would not matter. There have been millions of dives to 60 feet on air and several hundred thousand dives or more on nitrox. There is still no lower incidence of dcs hits per capita.

Your posts might have more meaning if you guys would cease making up data and inventing statistics.