Mixed buddies (air/Nitrox)

[SATurner]

Thanks, this gets me to about where I was going in my head, but wanted some confirmation.

It also isn't a topic that I have seen discussed so thought it might be worth getting out.

In reality, it probably isn't "normal" to have this type of pairing (air/Nitrox buddies), but an upcoming trip was headed down this path and I wanted to sort it out dry.

 

[formernuke]

Thanks, this gets me to about where I was going in my head, but wanted some confirmation.

It also isn't a topic that I have seen discussed so thought it might be worth getting out.

In reality, it probably isn't "normal" to have this type of pairing (air/Nitrox buddies), but an upcoming trip was headed down this path and I wanted to sort it out dry.

Not as uncommon as you would think for us single people.

 

[L13]

The rules are simple for a Nitrox / Air buddy pair.

The Air diver MUST respect the MOD of the Nitrox diver, and understand that this must never be broken.
The Nitrox diver MUST follow the air divers decompression schedule (either NDL or decompression).

@SATurner , it isn't that uncommon, I've done it many times. Just follow what @Gareth J said, and you are good.

The NDL thing applies not just to Nitrox/Air but also to dive computer algorithms, conservativeness settings/GF's, previous dives, etc. The most limiting NDL of any buddy of a buddy team is the limiting NDL of the whole team, regardless of the reason. He is not your buddy if you are not limited by his NDL as well as yours, and vice versa.

 

[ChrisDee]

@Tracy, thank you. I didn't intend to suggest a continuance of the dive after the incident, but was instead trying to "stack" the deck to potentially cause the Nitrox diver to rethink the 4th dive due to the "air" contamination.

Your answer drags me back to k.i.s.s. keep it simple Seth! The Nitrox diver was well below Nitrox NDL so the 4th dive is possible.

Do any adjustments need to be made when planning the fourth dive by the Nitrox diver or is it just a shortened bottom time going into the next dive planning?

What size tanks, age, temperature, stress / rested, surface interval, fitness, how hard are you working, all factors to consider. Yes lots of adjustments need to be made for 4th dive. DCS is correlated with all of these factors. IMO people need to reconsider that 4th dive. Frequently that 3rd dive as well. A dive computer like the Scubapro G2, and many others, will factor in varying gasses as long as you remember to change the settings.

More concerened with worrying abut running out air. Simple do not run out of air.

Take Nitrox class, or at least get good book on Nitrox. Easy.

 

[Doc]

If “no”…. The alternative would be?

Share the air, wait to discuss on surface while breathing Oxygen.

It’s an esoteric question best suited for Socratic teaching methodology. We all will learn something but maybe not pertaining to the original question.

 

[BlueTrin]

Is there an issue if two divers are using different gases in their tanks on a dive? For example one has air, one has Nitrox and an out of air event or some other catastrophic failure requiring shared air.

Going a step farther if the answer above is no, what if there are 4 dives planned for the day, two have been successful. On the third dive, the Nitrox diver has the failure and goes over to air. Failure occurs close to air NDL, but we'll short of Nitrox NDL. Should the 4th dive be scrubbed by the Nitrox diver?

Are there any times you can think of where pairing a person on air with a person on Nitrox should or shouldn't be paired together?

I also struggled with whether to put this in basic or advanced...

I doubt it would have a serious impact on the planning unless you do a deep dive and stay a ridiculous amount of time doing your switch and crossing NDL.

But if m you do recreational dives and have an incident and cross NDL by a large margin (like it took you 5/10 minutes to switch/argue and start to ascend slowly), wouldn’t you skip the dives for the rest of the day?

 

[MB NZ]

The Air diver MUST respect the MOD of the Nitrox diver, and understand that this must never be broken.
The Nitrox diver MUST follow the air divers decompression schedule (either NDL or decompression).

That's a good summary.

 

[Adamastor]

Is there an issue if two divers are using different gases in their tanks on a dive?

The only "issue" would be different desaturation procedures. Nothing that can't be solved during dive planning.

 

[BlueTrin]

I mean in theory you could switch to Air on your computer after taking your buddy reg to get the correct tissue info … (if your computer supports it)

But who’s gonna do this on a rec dive after an OOA and taking a buddy reg?

 

[Umpman]

Are there any times you can think of where pairing a person on air with a person on Nitrox should or shouldn't be paired together

I generally always dive nitrox and try to avoid diving with people who are on air (unless they are students). When with students, I’m on nitrox for the safety side of it and increased conservatism (diving Nitrox using Air tables). When I am fun diving, the problem with being paired with an AIR diver is they are going to shorten my dive. Depending on depth, their NDL is going to be much shorter than mine and they are going to need a longer surface interval. It is a mismatch. There have been times when I‘be been Instabuddy with someone on a drift dive and they are at NDL after 30 minutes and I still have plenty of time and more than half a tank. If I pay for a dive, I want my full dive, which is generally about an hour.

Going a step farther if the answer above is no, what if there are 4 dives planned for the day, two have been successful. On the third dive, the Nitrox diver has the failure and goes over to air. Failure occurs close to air NDL, but we'll short of Nitrox NDL. Should the 4th dive be scrubbed by the Nitrox diver?

Assuming the diver had to share air because of a catastrophic failure, I would have no problem ending dive 3, safely ascending, repairing the problem and then moving on to Dive 4. The diver spent most of his/her dive on Nitrox and would only be on air for the ascent so even the AIR ndl would increase during the ascent

Now, it the diver had to share air because he/she just ran out of air, then IMO the 4th dive should be scrubbed. If I am working on the dive boat and I see you ascend sharing air for any reason other than an equipment failure, I wouldnt let you dive. If you are my buddy and ran out of air (because you were just not checking/being honest about your air supply). I would not dive with you again.