Nitrox computer diving air profiles

[Sir-Dive-A-Lot]

Hello,

Just doing my Nitrox course now and they were talking about diving air profiles with Nitrox. I can see a few issues with this idea. One being the CNS clock won't be calculated properly and 2, the MOD will be different for air to your actual Nitrox mix. I'm planning on going on a liveaboard with up to 4 dives a day over four or five days.

I have an Aladin 2g by the way.

So, I was thinking I could do a few things:

1. Dive Nitrox profile, entering the PPO2 and correct mix, and maybe up the conseravite factor
2. Dive the air profile, and put a manual depth alarm for the correct MOD for the mix
3. Get a second computer, dive one on air and the other on Nitrox.

Wouldn't it be great if a specific computer already has the functionality to dive air profiles but allow you to track actual O2 loading of the mix you're diving? Anyone know if any computer on the market that actually has this?

 

[Insta-Gator]

Best plan, diving nitrox, use a nitrox compatible computer.

Air profiles are more conservative on than nitrox profiles, so you should be fine following an air profile, just stay above 100' to be sure you not violate MOD.

We used air-only computers for years using nitrox and just followed the normal profile. Getting older we wanted any marginal benefit the nitrox would afford even if we weren't taking full advantage of the extra down time or shorter SI. We've since gotten better computers.

 

[beaverdivers]

Dive your Scubapro Aladin 2G set on the mix that you just analyzed.

If you want it to be more conservative use the level stop feature. Simple!

 

[dfx]

So, I was thinking I could do a few things:

1. Dive Nitrox profile, entering the PPO2 and correct mix, and maybe up the conseravite factor
2. Dive the air profile, and put a manual depth alarm for the correct MOD for the mix
3. Get a second computer, dive one on air and the other on Nitrox.

4. Dive an air profile, and just don't go deeper than the MOD! What you need an alarm for?

 

[NAM001]

I am not sure what you are trying to get at. It appears that what is being suggested is that you use the nitrox mix to get mod. dive your nitrox with the air table. if the air table says you have 24 min then come up in 24 min. by doing that you are shortening the required SIIE say from an hour to 45 in. by doing so youcan get back in the water sooner or by doing the full hour that air calls for you are getting more benifit from the SI. In short if you use air tables on a nitrox dive then you get the benifit of more off gassing. The chance of getting hurt is minute so long as you plan useing a table based on O2 that is = or less than what you are breathing. To use say air and plan using a ean32 table you would exceed you ndl. If air gives you a botton time of 24 and nitrox allows 32 than you are taking on 25% less and the (air) SI is off gassing longer.

Remember nitrox gives you
1. more bottom time OR 2. shorter SI but not both if you maximize the benifit of one or the other. That is why they covered equivilant air depth to reconcile this. There is a give and take in play. Your choice of which benifit to use depends on your dive schedule. 5 dives a day 2 dives a day shallow/ deep ect. Just like nitrox reduces the nitrogen issues in exchange for depth limits drivin by O2 issues.

Next i am saying this without the benifit of having a calculator with me. If you are going to do several dives to 80 ft. the bext mix may not be 40% (OK per PPO2 limits only) as taught if you are going to be doing 4 hours at that depth over several dives in a day. You could very well exceed your otu's or cns limits. In respect to normal rec diving of say 2 dives to 80' , then 40% would be acceptable ( PPO2,CNS&OTU driven) as taught in the course.

 

[Superlyte27]

I'd be interested in hearing about a day when you thought you could exceed or even approach your O2 clock.
It's next to impossible unless you are doing very technical dives, and pretty stinkin hard without a rebreather with a constant PPO2.

But, that's for another class.
At any rate... You can either calculate your MOD and don't dive deeper than the MOD with your computer set on air. Or you can set your computer on the mix you are using and not dive it to its limits. Or, best case, dive two computers one set on air, one set on nitrox. But, don't overthink it.

 

[ianr33]

Hello,

Just doing my Nitrox course now and they were talking about diving air profiles with Nitrox. I can see a few issues with this idea. One being the CNS clock won't be calculated properly and 2, the MOD will be different for air to your actual Nitrox mix.

Assuming you are using 32%: Stay shallower than 110 feet. Don't go into deco. Forget about CNS toxicity. Simple.

(I have run the numbers on this and it does work)

 

[Sir-Dive-A-Lot]

4. Dive an air profile, and just don't go deeper than the MOD! What you need an alarm for?

Yeah I don't need an alarm, I know when not to go too deep, and on 32% wouldn't go below 100ft/30m anyway.

I am not sure what you are trying to get at. It appears that what is being suggested is that you use the nitrox mix to get mod. dive your nitrox with the air table. if the air table says you have 24 min then come up in 24 min. by doing that you are shortening the required SIIE say from an hour to 45 in. by doing so youcan get back in the water sooner or by doing the full hour that air calls for you are getting more benifit from the SI. In short if you use air tables on a nitrox dive then you get the benifit of more off gassing. The chance of getting hurt is minute so long as you plan useing a table based on O2 that is = or less than what you are breathing. To use say air and plan using a ean32 table you would exceed you ndl. If air gives you a botton time of 24 and nitrox allows 32 than you are taking on 25% less and the (air) SI is off gassing longer.

Pretty much what I was trying to get at. Setting the nitrox mix will get you MOD and CNS O2 exposure. Diving 32% I would be unlikely to go below 100ft/30m anyway - so I guess that just leaves the CNS exposure factor if you're setting your computer to 21% while diving 32%.

I think I've answered my own question anyway. I think i'll do what beaverdivers suggests by setting the computer to the actual mix and turn the conservative factor up, and maybe up the safety stop duration.

I'd be interested in hearing about a day when you thought you could exceed or even approach your O2 clock.

It's next to impossible unless you are doing very technical dives, and pretty stinkin hard without a rebreather with a constant PPO2.

Well, if i'm doing 4x dives a day, I usually go for 60+ minutes on my local shore dives. I see from my book the NOAA tables give me for 24 hr limits 180 minutes at 1.4. I guess i'd have to be diving a fairly rich mix and/or consistently hitting the MOD to get that. Not having dived Nitrox before, I'm just theorising at the moment and not sure what to expect on the liveaboard either.

Thanks for all the replies. It's been a good learning experience.

 

[Tigerman]

Yes, you have the MOD limit not showing and warning properly if you dont set the computer, but you should know what the MOD for the mix is without relying on the computer anyways and you should also keep track of your depth, so this is a minor inconvenience.

With regards to the o2 clock that is in practice only theoretical for recreational single tank profiles. I dont think Ive ever seen it go above 20% even on 4-dive days with hour long and 30m deep dives. You wont be able to stay down for long enough and deep enough without doing something with the ammount of gas you carry.

That said, I always set my computer (2g predecessor - Prime) to the correct mix - cause I dive nitrox to extend my bottomn times

 

[ajduplessis]

CNS clock on rec dives with Nitrox will never be an issue. The important factor will be PPO2, make sure you stay within limit. Set you computer to the correct mix and dive it as such. If you want to be more conservative rather control your ascent, extend your safety stop and make sure your SI is at least 2 hours.

Have fun and be safe.