why hasnt nitrox replaced compressed air completely?

[packrat12]

On my last vacation, we were diving typically deep, 100+ on every dive. We were also on Nitrox every dive. I carried both a computer set to my mix and an air computer that I used as a redundant timer. Out of 5 days of diving, I bent the air computer 3 of them.

What did nitrox do for me? Allowed longer dives with shorter surface intervals. Rather than bobbing around waiting for the next dive, we were able to do them and get back for lunch.

Without nitrox either the SI would have needed to be increased or the 2^nd+ dive shortened. That was worth the money for me.
On a normal dive, I like having the extra buffer for NDL gained by using nitrox.
As for the cost for me: Travel to site - $80 - $200 (real cost of driving in addition to gas), Boat: $100, Food: $20 – Total: $200 - $300+. Air: $15 - $20, Nitrox: $20 - $30 Difference: $10 out of by $200 trip. I just do not see nitrox as being a big part of my cost.

 

[EFX]

...If, however, you seek out the world's most learned scholars on the subject of decompression and decompression sickness, the top 5 or 6 most knowledgeable and experienced individuals on the subject, the ones who really know what they are talking about; the answer to the question of what causes decompression sickness will invariably be: "I don't know".... Bob (Grateful Diver)

And to think after all these years and all those dives that I thought that DCS was caused by an excess rate of inert gas leaving the tissues on ascent exceeding the rate at which it is exhaled from the body. Geeez..... what was I thinking?

 

[Bob DBF]

Read this;
http://archive.rubicon-foundation.o.../123456789/8005/AAUS_2008_1-11.pdf?sequence=1

Obviously this test was better than the previous study on Nitrox, may be the next study...

Eleven male participants
completed pre- and post-dive fatigue assessment using the Multidimensional Fatigue
Inventory and a Visual Analogue Scale, while general health was assessed using the Diver
Health Survey. Divers did tend to be more fatigued after diving; however, breathing gas
mixture exhibited no statistically significant effect. Participants did have significantly lower
Diver Health Survey scores upon the conclusion of EAN36 test sessions, possibly indicative
of reduced decompression stress.

As read it you are fatigued after diving but have a better health survey because of reduced decompression stress, which will exhibit itself on me as fatigue. Its nice they want a distinction between work fatigue and decompression stress (fatigue) but it is lost on me as think that less fatigue is better. I suppose I could sit out a few dives instead, but who are kidding.




Bob
-----------------------------------
I honestly feel I'm a better diver now. I learned to respect the ocean the hard way. One swallow at a time. Mark Derail

 

[EFX]

... As read it you are fatigued after diving but have a better health survey because of reduced decompression stress, which will exhibit itself on me as fatigue. Its nice they want a distinction between work fatigue and decompression stress (fatigue) but it is lost on me as think that less fatigue is better. I suppose I could sit out a few dives instead, but who are kidding.

I quickly read the study and came away from it thinking it was flawed in several ways. First, when I think about fatigue it's not just "I'm really tired" but I'm near exhaustion. The test was not designed to provide this level of what they call decompression stress. Doing 2 dives for 25 mintes at 60 feet with what was it 2 hours of surface interval doesn't even get you close. If your control group on air cannot get stressed how are you going to prove that nitrox is better? What the test really tried to show was that nitrox made you feel better than air -- and it failed. We're not talking about feeling a litttle less tired on nitrox than air. We're talking about feeling OK on nitrox vs. fatigued on air. Another problem is they took away all the predisposing factors that can lead to fatigue like alcohol consumption, caffeine, lack of sleep, etc. So, the deck was stacked in favor of air. Still another problem was using professionals. You take away stressors that could push otherwise not so experiencved divers into decompression stress. Still again they used "scuba studs" 18-25 year olds again eliminating pre-fatigue stressors. These yougsters are more likely to under report fatigue and blame it on too much "activity" the day before.

 

[chillyinCanada]

I've been so disappointed since I started using nitrox, to have found no benefit of more energy. I'm still tired after a good day. When I was younger and diving air, I was most often invigorated and ready to party. Perhaps I should go back to air? (Or the time machine)

 

[beanojones]

Do you know that from experience or do you have a computer that provides that level of planning information? If the latter, what is the computer?

Not that I would trust it to make an early flight but most computers have "desat" time as well as a "No-fly" time. Using Nitrox makes the desat time much much shorter.

For people who live at altitude and dive at sea level(not at all uncommmon in Hawaii), there is no practical way to wait out a no-fly time to go back to altitude, so Nitrox makes a lot of sense because it minimizes nitrogen loading. Since most computers auto shut off unless they are dove to 3 m, it's not easy to do it properly*** and have the computer actually do the proper calculations.

Part of why my 'rule of thumb' is always load the minumum nitrogen on any dive if using Nitrox, which is different than a lot of people do.

(Personally, I never dive Nitrox (money), but I do use 100 o2 for deco/safety whenever possible. In many senses, the best of both worlds: no depth restrictions, and reduced Nitrogen loading.)


*** Can you set Shearwaters to not shut off and properly do these calculations for people living at altitude, and diving at sea level?

 

[KeithG]

Not that I would trust it to make an early flight but most computers have "desat" time as well as a "No-fly" time. Using Nitrox makes the desat time much much shorter.

In theory, all things being equal. but this generally does not happen in the real world.

IF you dove the same profile on ean as air, then you would have less loading. Ean wins!

But what really happens is the ean divers stay down deeper and longer (because that is why they are using ean!) and get just as close to NDLs as the air divers that got out of the water sooner. So they have the same loading. Actually, the air divers will have a head start at off gassing. Air wins?

or am I missing something?

 

[boulderjohn]

I quickly read the study and came away from it thinking it was flawed in several ways. First, when I think about fatigue it's not just "I'm really tired" but I'm near exhaustion. The test was not designed to provide this level of what they call decompression stress. Doing 2 dives for 25 mintes at 60 feet with what was it 2 hours of surface interval doesn't even get you close. If your control group on air cannot get stressed how are you going to prove that nitrox is better? What the test really tried to show was that nitrox made you feel better than air -- and it failed. We're not talking about feeling a litttle less tired on nitrox than air. We're talking about feeling OK on nitrox vs. fatigued on air. Another problem is they took away all the predisposing factors that can lead to fatigue like alcohol consumption, caffeine, lack of sleep, etc. So, the deck was stacked in favor of air. Still another problem was using professionals. You take away stressors that could push otherwise not so experiencved divers into decompression stress. Still again they used "scuba studs" 18-25 year olds again eliminating pre-fatigue stressors. These yougsters are more likely to under report fatigue and blame it on too much "activity" the day before.

My analogy to this study would be to see whether a good strong alcoholic beer is more intoxicating than root beer. For this study, we will give a handful of test subjects either a 6 ounce glass of beer or a 6 ounce glass of root beer and tell them to sip it slowly over an hour. After that we will ask them how drunk they feel. If they both report that they don't feel drunk, we will assume that beer with alcohol is no more intoxicating than root beer.

 

[beanojones]

In theory, all things being equal. but this generally does not happen in the real world.

IF you dove the same profile on ean as air, then you would have less loading. Ean wins!

But what really happens is the ean divers stay down deeper and longer (because that is why they are using ean!) and get just as close to NDLs as the air divers that got out of the water sooner. So they have the same loading. Actually, the air divers will have a head start at off gassing. Air wins?

or am I missing something?

As you say, Nitrox only has an advantage if used for tha same profile as air.

I only dive anywhere near deco limits when I am doing specific deep dives　with deco　(And those are always air with 02 deco), and almost all my dives are done guiding/teaching so if I used Nitrox it would be in the unusual case of diving air profiles with Nitrox.

But though that's not how most people dive, it is how all the customers I dive with use Nitrox. They dive Air profiles on Nitrox for less tiredness and flying safer, since they are all flying out the next day.

People who dive near limits regardles of gas of course wouldn't see any out of water benefits of Nitrox.

 

[Bob DBF]

My analogy to this study would be to see whether a good strong alcoholic beer is more intoxicating than root beer. For this study, we will give a handful of test subjects either a 6 ounce glass of beer or a 6 ounce glass of root beer and tell them to sip it slowly over an hour. After that we will ask them how drunk they feel. If they both report that they don't feel drunk, we will assume that beer with alcohol is no more intoxicating than root beer.

Yeah, and if only the subjects on beer can't walk a straight line to the bathroom it's because of an uneven floor.


Bob