Diving shallow on Nitrox.

[mainedvr]

LOL exactly I had no idea what he was talking about. I'm not advanced or a tec diver. AND was hoping that someone who actually does beach and spring dives on Nitrox would actually answer. I have asked a few people why nitrox... One agreed with the placebo effect, the other didn't really give me a straight answer he just said because he gets longer bottom time. But dude, we're diving together, I not at a max of 25' and you're only doing a 1 tank dive.

I keep my tanks filled with 32%ish due to the fact that I may do a shallow shore dive or a deeper boat dives or shore dives so I just like to have what I need for the deepest dive I am certified to do (rec). Now, I cant say I feel better diving the nitrox but I dive air too on some of the same dives I dive nitrox and on repetive dive days I do seem to feel better, but that could also be I am drinking more water, eating better or whatever. One thing that I did not think about in the beginning when I dove nitrox was that while the EAN gives you more bottom time compared to Air at a certain depth, I am still limited to my consumption and it does not to seem to less with EAN than air.

That may not answer your question directly, also air and EAN for me cost wise is about 3 bucks more a fill so I am good with that but when I have to pay $16 for a nitrox fill on a boat or something I may dive air so in my mind the benefit of feeling better is not a huge part of my decision.

 

[mi000ke]

One thing that I did not think about in the beginning when I dove nitrox was that while the EAN gives you more bottom time compared to Air at a certain depth, I am still limited to my consumption and it does not to seem to less with EAN than air.

Gas consumption being the limiting factor was the premise of the OP's question - and at 20' depth, gas consumption in most cases is going to be the limiting factor. I am about to do my EAN cert course and had the same question, so I computed my consumption (based on my SAC of 0.5 cf/min, and a 3000 psi AL80 tank consumed down to 500 psi) and compared it to NDL for air vs EAN32 from dive tables for different depths.

I found that down to 50' my gas consumption is still the limiting factor vs NDL for either air or 32, so I would probably use air if much cheaper. At 66' its essentially a toss-up. I would theoretically have a couple of minutes more consumption time vs my air NDL, so EAN32 would let me stay down a minute or two longer - not really significant on a practical level. So again could just use air. At 82' my air NDL is about 5-6 minutes less than my consumption time, so I theoretically gain about 5-6 minutes more bottom time with 32 vs air. Again, not sure how significant this really is. It's not until 99' that the NDL of 32 vs air becomes a significant factor. At that depth, my gas consumption would give me about 10 more minutes than my air NDL, and is about the same as the 32 NDL, So EAN32 would give me about another 10 minutes.

Now I realize that this is all theoretical, and depends on my actual dive profile and various factors that affect gas consumption. But as any profile would probably be more conservative (e.g.., I would not be spending my entire dive at 99'), my sac rate might be higher (I computed mine based on data from several 40' - 50' warm -water low-stress dives), and I would certainly begin surfacing with more that 500 psi, the bottom time effects of 32 vs air would probably be even less significant.

I am looking forward to testing all of this with real data on my next few dives after getting certified. But this all suggests to me that until I get my SAC rate much lower (and from other posts I read it's already pretty low - benefits of being a sax player), the primary benefits to EAN seem to be conservatism re DCS, possibly better energy, and lower SI. But not increased bottom time.

 

[RainPilot]

Gas consumption being the limiting factor was the premise of the OP's question - and at 20' depth, gas consumption in most cases is going to be the limiting factor. I am about to do my EAN cert course and had the same question, so I computed my consumption (based on my SAC of 0.5 cf/min, and a 3000 psi AL80 tank consumed down to 500 psi) and compared it to NDL for air vs EAN32 from dive tables for different depths.

I found that down to 50' my gas consumption is still the limiting factor vs NDL for either air or 32, so I would probably use air if much cheaper. At 66' its essentially a toss-up. I would theoretically have a couple of minutes more consumption time vs my air NDL, so EAN32 would let me stay down a minute or two longer - not really significant on a practical level. So again could just use air. At 82' my air NDL is about 5-6 minutes less than my consumption time, so I theoretically gain about 5-6 minutes more bottom time with 32 vs air. Again, not sure how significant this really is. It's not until 99' that the NDL of 32 vs air becomes a significant factor. At that depth, my gas consumption would give me about 10 more minutes than my air NDL, and is about the same as the 32 NDL, So EAN32 would give me about another 10 minutes.

Now I realize that this is all theoretical, and depends on my actual dive profile and various factors that affect gas consumption. But as any profile would probably be more conservative (e.g.., I would not be spending my entire dive at 99'), my sac rate might be higher (I computed mine based on data from several 40' - 50' warm -water low-stress dives), and I would certainly begin surfacing with more that 500 psi, the bottom time effects of 32 vs air would probably be even less significant.

I am looking forward to testing all of this with real data on my next few dives after getting certified. But this all suggests to me that until I get my SAC rate much lower (and from other posts I read it's already pretty low - benefits of being a sax player), the primary benefits to EAN seem to be conservatism re DCS, possibly better energy, and lower SI. But not increased bottom time.

Where I find it really helps is when I'm diving 2 tank side mount. Then the break-even depth gets a lot shallower.

Even in your scenario, run the numbers on a 3 dive trip with 1 hour SIT. I suspect that the next few dives will end up NDL limited faster on air.

 

[MXGratefulDiver]

Several have hit on the point of tanks with nitrox bands. I have a site that will not fill air in a nitrox tank without charging for nitrox. IE any tank is 8 for air and 16 for nitrox. If the tank has a nitrox sticker that is what they charge. Another site will scrape the sticker if they put air in the tank so you get nitrox or pay the nitrox processing to simplify the process. One site I go to says they do not know if they have air that is e or hyp e. They just get a pass or no pass on the air testing. Since the shop does not deal in nitrox they have no idea, when the air analysis comes back, if it meets hyp e or not. Another site claims that their liability ins does not cover filling nitrox tanks. There are shops that say nitrox is nitrox so 23% is the same as 32% when pricing. Others say banked is one price and custom is another. Nitrox is a hassel in many cases, especially if you own your own tanks.

A final kicker a site with 25' water does nitrox fills. Why cause you cant put air in a nitrox tank. Go figure....................

Sounds like you got a lot of sh!tty shops in your part of Texas ... or a lot of gullible customers willing to put up with their unethical business practices. If a shop tried any of those tactics in my area, they wouldn't long remain in business, because people simply wouldn't go there.

... Bob (Grateful Diver)

 

[DaleC]

I don't believe there is any practical benefit in 20' unless you are doing exceptionally long repetitive dives. While theoretical nitrogen uptake might be lessened on those long dives, in cold water at least, the risk of temperature stress and its effect on DCS suceptibility would mitigate that benefit IMO. I also think the placebo effect is real in that EAN probably reduces the incidence of sub acute DCS stress which manifests as fatigue but for reasonable dives at 20' that should not be an issue.

If you normally fill 32% as GUE proscribes then it is practically more convenient but not really more beneficial.

 

[sealark]

I fill all my tanks and if I PLAN a dive less than 50 ft I just pack an air tank. If all I have is Nitrox it will get used. Don't really see much difference with Nitrox. But then again I have been diving for 60 years and would rather have a regulator in my mouth than walking around on land.

 

[MasterChief D]

There might be one more reason why one may do a very shallow dive on high Nx % - unless the operator offers O2 service compatible air, one might have to get a Nx fill to avoid invalidating the equipment's O2 service rating.

 

[Diverman68]

I did 30 dives in a week in Roatan using 32% did it make me less fatigued of course.

 

[MaxBottomtime]

 

[Basking Ridge Diver]

I've been on a few beach and shallow spring dives over the summer and have seen this. Just asking!

I have friends that leave the sticker on the tank and dive air or 21%. Did you ask if they were diving Nitrox or you saw the sticker that said Ntirox and assumed they were diving Nitrox?