Nitrox class - no dives/dives?

[OceanEyes]

Maybe I should have given a bit more info.
It's not a deco dive. Depth won't be anywhere near MOD for 33%. My plan to swap regs is based on the fact that it's the procedure for diving SM.
It's not my desire to dive with unmatched mixes, it's just what happens to be in them. In this scenario I could just leave my computer set to air and enjoy the "buffer" so it's not a big deal.
Having said all that, I still think after the dive my nitrogen loading and O2 exposure would be the same, or that close it wouldn't matter, as doing the same dive with both tanks at 27%.
You're a PADI pro so you definitely know more than me about this stuff so I'm probably wrong, can you please give me something more than just because to support your opinion? Cheers

Hi Mike1967.

Please keep in mind that this thread is in the Basic Scuba Discussion forums, and that side mount diving itself is a technical approach that originated in, and is most popularly used amongst the cave diving community. (Though in recent years it is gaining some practitioners who choose to use the techniques for open water dives for a variety of personal reasons such as to relieve stress on their lower backs.) This puts side mount in a rather more advanced realm than those hosted in these forums.

You may recall that in your initial training you were taught to plan your dive, then dive your plan.

The multi gas scenario that you propose would require substantial guesswork in order to estimate your potential deco and O2 status. Rather than try and figure out the complicated adjustments that your proposed gas switching would require, or guesstimate the average fO2 of your two cylinders, I would suggest that it would be more prudent, (as you have already surmised), to simply set your computer to the fO2 of your lean gas, (air in the example that you propose), and adhere to the MOD of your rich gas, 33%. This approach would lead you to plan a dive with a reasonably conservative NDL for a single dive, but realize that your computer would not be calculating an accurate tally of your O2 exposure. Subsequent dives made within the next 24 hours would not be based on all of the information that might be important as regards your actual status. Alternatively, you could program both gasses into your computer, and select the active gas with each switch.

I trust that this reply is a touch more succinct than “just because.”
Cheers,
OceanEyes

 

[OceanEyes]

Of course the simplest course would be to beg, borrow, or steal a tank with the same gas as one of the pair that you’ve already got, or dump the contents of one, and fill it with the same mix as the other.

 

[Zef]

Maybe I should have given a bit more info.
It's not a deco dive. Depth won't be anywhere near MOD for 33%. My plan to swap regs is based on the fact that it's the procedure for diving SM.
It's not my desire to dive with unmatched mixes, it's just what happens to be in them. In this scenario I could just leave my computer set to air and enjoy the "buffer" so it's not a big deal.
Having said all that, I still think after the dive my nitrogen loading and O2 exposure would be the same, or that close it wouldn't matter, as doing the same dive with both tanks at 27%.
You're a PADI pro so you definitely know more than me about this stuff so I'm probably wrong, can you please give me something more than just because to support your opinion? Cheers

First, in general, just because someone is a "PADI Pro" does not mean they know much of anything at all, or conversely they can be the freaking einstein of the diving world, one should not make assumptions based on certification status of another diver. (No offense directed towards the person you were responding to).

Second, if you do you not plan on programming your computer for two gasses, or can't, and still plan to dive then the protocol would be to set your computer to the most limiting gas mix and use the MOD for that mix regardless of what is in the lower O2 concentration tank. This ensures that your computer will not direct you to a depth below the MOD for the highest concentration of O2 you are diving with and will guide you to dive a more conservative profile.

-Z

 

[Tribal]

Second, if you do you not plan on programming your computer for two gasses, or can't, and still plan to dive then the protocol would be to set your computer to the most limiting gas mix and use the MOD for that mix regardless of what is in the lower O2 concentration tank. This ensures that your computer will not direct you to a depth below the MOD for the highest concentration of O2 you are diving with and will guide you to dive a more conservative profile.

Isn’t it safer to put your computer on the mix with the lower o2 concentration? That way you only have to keep An Eye on your MOD but atleast you are safe with your NDL?

 

[Mike1967]

Basic Scuba Discussion

My bad.

set your computer to the most limiting gas mix

This is what I'll do.

I trust that this reply is a touch more succinct than “just because.”

Yes, thanks mate.