Breathing mixed gasses

[DarinMartell]

I pretty sure I know what the answer to this is but I was wondering if it is an issue for a person who was not trained in mixed gasses to breathe from a mixed tank? My thoughts are about an Out of Air situation when one buddy has mixed gas and the other does not. I know any air is better then no air, my question was more about if any different precautions are needed after breathing it.

[Scubastud16]

Well if your buddy is on EANx, the only thing you want to worry about is being below MOD (maximum operating depth), but if he's past it, you're both probably going to take an ox-tox hit.

Trimix is a whole different story, but tech divers rely much more on themselves than others. (total generalization as to not get into the specifics )

[CompuDude]

Originally Posted by Scubastud16

Well if your buddy is on EANx, the only thing you want to worry about is being below MOD (maximum operating depth), but if he's past it, you're both probably going to take an ox-tox hit.

Trimix is a whole different story, but tech divers rely much more on themselves than others. (total generalization as to not get into the specifics )

A little over-simplified, but a decent summary nonetheless.

[cummings66]

As a Nitrox diver I don't worry about donating the mix to my buddy, after all I won't be below my mod and so he won't either.

The important knowledge a Nitrox class teaches is how to safely dive with Nitrox, you can assume your buddy using it is safe and thus you are if you share it. It's a trust me situation, but really, what other option do you have?

[rox@ucf11]

If you take the class you can figure our or at least be familiar with the mods of a certain mix that way if your buddies diving it you can still know 32% a pretty standard mix and the mod(maximum operating depth) is around ~111 (thats 1.4 ppo2)

I would suggest taking the class as it is imo a very good class to help you learn about nitrox but to also help you better understand some of the theories behind diving.

[texdiveguy]

A basic nitrox class is fun and fairly informative....not alot of $ or time.

[Miked]

Originally Posted by rox@ucf11

If you take the class you can figure our or at least be familiar with the mods of a certain mix that way if your buddies diving it you can still know 32% a pretty standard mix and the mod(maximum operating depth) is around ~111 (thats 1.4 ppo2) the equation is ATM+1*PPO2%=MOD

I would suggest taking the class as it is imo a very good class to help you learn about nitrox but to also help you better understand some of the theories behind diving.

Rox, no offense intended, but while your MOD for a 32% mix is correct, I think the formula you showed is for the one for calculating the partial pressure, rather than the MOD.
IIRC, to get the mod, we would do a 2 stage calculation:

1) [(max "safe" ppo2) /(% mix as a decimal)]= ata (absolute pressure, in atmospheres)

2) (ata -1) * 33= MOD

to illustrate: if you wanted to use the 1.4 as your max safe ppo, for a 32% mix, the calculations would go something like:
1) (1.4/.32)= 4.375= ata
2) 4.375-1= 3.375; 3.375 *33= 111.375'= MOD

IIRC, from nitrox class, they created a single formula that combined these 2 steps:

{[33* "safe" ppo]/[mix ]} -33 = MOD

but the instructor said that the 2 -step process is simpler to keep track of.

To Darinmartell, sorry for the detour in your thread for all this Math stuff.

[rox@ucf11]

oops I think your right my bad also the equation for pp02 is still wrong lmao I deleted it anyways but it should have read (atm +1)*mix=PPO2 but dont mind my equation lol can I blame it on the 3 hrs of sleep last night??? stupid roommate

It is a good idea though to know your buddys mod of the mix he is using.

[MSilvia]

It's generally a bad practice to buddy with someone using a different mix than you are, as it will almost certainly mean you're diving different profiles. If it's time for you to surface, and your buddy still has additional bottom time alloted (or vice versa), you're put in the position of either being a bad buddy and separating, or wasting the money and advantage inherent in diving mixed gas.

Rather than wonder if it's safe to use the gas your buddy is using, get a buddy diving the same gas you are, so there isn't any misunderstanding or confusion. At the very least, make it part of your pre-dive buddy check. That said, if the only gas available is from a diver using a different gas, what choice do you have but to breathe what they give you? So long as you let the donor donate, and don't just grab the first regulator you see, you should be okay. If you do get grabby with a mixed gas diver, you might indeed get a mix you shouldn't be using, and central nervous system toxicity convulsions may result. That, as they say, "will learn ya".

If you want to understand the dangers, benefits, and other implications of what you breath, txdiveguy's right... take a nitrox class and find out. They're easy to find and usually short money.

[Rockhound76]

Originally Posted by MSilvia

It's generally a bad practice to buddy with someone using a different mix than you are, as it will almost certainly mean you're diving different profiles......

What he said...Never dive in "mixed pairs".

( just deleted the rest of this, as it is a repeat of most of what MSilvia said. I should have read his post more closely.)