Nitrox computer diving air profiles

[boulderjohn]

I am not sure which dive computer that you are using, but the Uwatec Aladin 2G, the OP is using ( along w/ all the other Uwatec dive computers sold under the Scubapro/SubGear name ), requires that you set a Nitrox mix from 21% - 100%. !00% is O2; a 21% Nitrox mix is referred to as air.

That is correct, and I believe that many and perhaps most modern computers to not have a specific air setting but rather just have you set the O2 level for whatever you are breathing. I used to use a Suunto Cobra, and I discovered the day I had to do my nitrox certification dives (they were required back then) that if you did a dive in the air mode within a certain time (I think 24 hours) of your intended dive, you could not switch it to nitrox. Whichever mode you were in, nitrox or air, you could not switch from one to the other for the second dive of a 2 tank dive. It would be interesting to meet the genius who came up with that plan and find out why. I quickly learned to leave it in nitrox mode permanently so I couldn't get locked out of using a particular mix. There is no reason to have two modes like that, and I think most people have figured that out by now.

 

[Sir-Dive-A-Lot]

You are diving nitrox on an air profile to decrease the risk of DCS. So what is the risk of DCS on recreational dives when diving with air? I don't recall exactly, but it is something like 0.01%. By diving nitrox on an air profile, you might be improving that possiblity to, what, 0.007%? Congratulations! You have just spent a bunch of extra money to make a statistically insignificant improvement in the odds that you will prevent something that is already overwhelmingly unlikely.

Why not dive nitrox instead for its intended purposes of increasing bottom time and lessening surface intervals?

What I just wrote is usually included in nitrox instruction.

Unfortunately the stats aren't covered in the SSI manuals. However, that exact point was made in the DAN Nitrox workshop document I've been reading as bedtime material

Also of interest was the mention that there's "no empirical evidence" to suggest you're less tired from diving Nitrox vs air on repetitive dives. But again, i'm sure that's a discussion for another day.

I used to use a Suunto Cobra, and I discovered the day I had to do my nitrox certification dives (they were required back then) that if you did a dive in the air mode within a certain time (I think 24 hours) of your intended dive, you could not switch it to nitrox. Whichever mode you were in, nitrox or air, you could not switch from one to the other for the second dive of a 2 tank dive.

Incidentally my dive partner has this same computer, so it will be good to let her know of this before we start the actual dives for the course. My computer is easy, I just have to dial in the mix and be done with it, apparently.

 

[Superlyte27]

Also of interest was the mention that there's "no empirical evidence" to suggest you're less tired from diving Nitrox vs air on repetitive dives. But again, i'm sure that's a discussion for another day.

I can prove that you are less tired diving Nitrox than Air. Spend two hours diving with me. When we're done you'll agree 100%. I'm absolutely certain of it.

 

[Sevenrider860]

Sir-Dive-A-Lot,

I think all three of your ideas would work. Many (most??) people just enter the O2 percentage and use the computer in Nitrox mode as it is designed to operate. If the computer provides a method for setting a conservative level you can use it, or just do it yourself by not getting close to the limits that are shown.

Diving air profiles using Nitrox is not that unusual and does add some conservatism. PADI outlines an option using air profiles while diving enriched air in the Nitrox manual: Use no higher than EANx32, Limit dives to 30 meters, Stay within the air NDL limits, Limit total dive time for the day to 160. This is a very conservative recommendation, but would you expect anything else from PADI? You analyzed the cylinder and wrote your name, the mix and the MOD on it. You should not need a computer alarm to remind you about your max depth limits.

While diving two computers would work, and a backup computer on a 4 or 5 day live-aboard is not a bad idea at all, I think you would be better off setting them both on Nitrox or both on Air. Even PADI makes the statement that "your far more likely to approach your nitrogen limits than any oxygen limit" when recreational diving. and a number of people have pointed that out on this thread.

If it were me? I would bring two computers on the live-aboard and I would set them both to Nitrox.

I am in the group that does feel less tired after a day of diving when using Nitrox. Might all be in my mind...but it is my mind, so I will go with it! Have a great time on the live-aboard!

 

[boulderjohn]

I can prove that you are less tired diving Nitrox than Air. Spend two hours diving with me. When we're done you'll agree 100%. I'm absolutely certain of it.

As a nitrox instructor, I can tell you that the party line is that there is no good evidence showing a difference in ow tired you will feel. As a nitrox user, I am pretty darn sure there is a difference--and a significant one at that.

The only studies I have seen are almost laughable in their process. They are something like take two divers to 60 feet for 25 minutes, one with nitrox and one with air, and see if there is any difference in how they feel afterwards. Seriously? If you want to test something like that, you have to go to the limits. For me, the difference is in the liveaboard trips I have done, with 4-5 dives a day for a week. On air--I'm in bed after dinner after the third day, sleeping nearly 12 hours until the next day. On nitrox, I'm up until late enjoying the party every night for six nights. Now, I won't pretend that what I just described is scientific, but neither are the studies I have read.

 

[Tigerman]

Which is why the PC answer is "there is no evidence".. cause really.. there isnt..
On the other hand, if a placebo works, dont tell the user its a placebo..

Personally though I feel no difference whatsoever diving air or nitrox other than the gutwrenching feeling of "ffs I have plenty of gas but Im out of NDL"..
Yeah, sure I can go 5 feet shallower and get more NDL, but that dont help when that manta is 10 feet DEEPER, now does it?

 

[Tortuga68]

That is correct, and I believe that many and perhaps most modern computers to not have a specific air setting but rather just have you set the O2 level for whatever you are breathing. I used to use a Suunto Cobra, and I discovered the day I had to do my nitrox certification dives (they were required back then) that if you did a dive in the air mode within a certain time (I think 24 hours) of your intended dive, you could not switch it to nitrox. Whichever mode you were in, nitrox or air, you could not switch from one to the other for the second dive of a 2 tank dive. It would be interesting to meet the genius who came up with that plan and find out why

(Speaking for Suunto computers) In Nitrox mode the computer tracks the OLF (a combination of CNS & OTU) of a dive series. In Air mode it doesn't. So if you switch from one to the other, the OLF won't be accurate. Personally I leave mine in Nitrox 21% for air dives, as was mentioned.