How to switch with 2 deco bottles?

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Originally Posted by Randall

If you follow your verification procedures correctly it would be very difficult to switch to the wrong bottle.

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Not to pick on you, but it's not the first time for someone to say something to the extent of, "as long as you do everything right, nothing can go wrong". There's nothing incorrect in your statement and I'm just using it as an example, but this is a dangerous train of thought. Risk management is about minimizing risks when things do go wrong (if they haven't, you haven't dove enough). Protocol will (and does) get broken all the time and our procedures should account for this as much as reasonably possible. The first time a real emergency happens, our brain shuts down and we react. I'd rather not have 3 regs to choose from if my buddy is OOG and I need to donate one...hell I've seen people try to donate their necklace in an "emergency" instead of their long hose and that's just with 2 regs and a 50/50 chance of getting it right. I've seen instructors stop whatever they're doing (including gas switches) because someone dropped their spool or light, it happens, it's instinctual for some.

I'm always going to screw something up, so let me reduce the amount of things I can possibly screw up as much as reasonably possible. Everyone has their own risk tolerance.

I think this all sounds very reasonable if your back gas is 32... but what if you're doing a dive at eagles nest, and your back gas is a high percentage helium mix?

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Originally Posted by Randall

Personally i feel if you switch to back gas you would be adding a bit of risk, as it would be possible for you to not have your next deco gas in you hand at all times after the verification with your buddy. To do it safely you would have to reach your next stop depth, switch to BG, stow the lean mix, verify the rich mix, deploy the rich mix, then stow the BG reg.

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Yes you're right you come off the deep deco gas and get on back gas, stow your hose before you even begin with the deployment. The idea is to have all the other tasks done so that when you switch to the shallow deco gas it's the same procedure you always always use. A lot of people get stuck on the how many hoses are around the neck, but the other aspect is that my mechanical movement to keep my left hand on the valve, and the right hand on the reg, and then swapping with the reg in my mouth and clipping off that reg stays constant.

Two fine points I would offer for this method that you can take or leave, is that I will typically come off my deep gas at the end of the previous deco stop. So for instance I would come off of 50% after having completed my 30 ft stop, I would ascend from 30 to 20 with my BG reg in my mouth. That way when I get to 20 to perform the gas switch it's a very familiar and consistent series of actions. Second, I keep my left hand on the valve and right hand on the reg after I verify the bottle I'm switching to because I can do one last dummy check. Right before I breath from the reg I'll purge the reg to see pressure drop on the SPG I have on the bottle my left hands on (not depressurize, just a tap so the needle deflects). Then when I turn the bottle on the SPG goes back to full pressure and I can check the bottle one more time and start breathing.

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Originally Posted by TotDoc

I think this all sounds very reasonable if your back gas is 32... but what if you're doing a dive at eagles nest, and your back gas is a high percentage helium mix?

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what are you worried about with the high helium mix?

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Originally Posted by tbone1004

what are you worried about with the high helium mix?

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Isobaric counter diffusion, particularly as it relates to the inner ear.

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Originally Posted by TotDoc

Isobaric counter diffusion, particularly as it relates to the inner ear.

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not relevant for O2 gas breaks

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Originally Posted by TraviTheDiver

Not to pick on you, but it's not the first time for someone to say something to the extent of, "as long as you do everything right, nothing can go wrong". There's nothing incorrect in your statement and I'm just using it as an example, but this is a dangerous train of thought. Risk management is about minimizing risks when things do go wrong (if they haven't, you haven't dove enough). Protocol will (and does) get broken all the time and our procedures should account for this as much as reasonably possible. The first time a real emergency happens, our brain shuts down and we react. I'd rather not have 3 regs to choose from if my buddy is OOG and I need to donate one...hell I've seen people try to donate their necklace in an "emergency" instead of their long hose and that's just with 2 regs and a 50/50 chance of getting it right. I've seen instructors stop whatever they're doing (including gas switches) because someone dropped their spool or light, it happens, it's instinctual for some.

I'm always going to screw something up, so let me reduce the amount of things I can possibly screw up as much as reasonably possible. Everyone has their own risk tolerance.

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Na you are not picking on me at all. I get it, every one has a different opinion of the best way to do something. It is definitely good to discuss these things, hopefully that's how we learn. I don't necessarily disagree with the point you are making. I generally keep an open mind as far as different ways to do something is concerned. The point I was making is, it seems more complicated to me to make two gas switches instead of one. Not saying it is wrong at all. Just not how I like to do things.



The idea of having 3 regs to choose from in a OOG situation, I understand. But you donate what you are breathing. I've been in situations where it has hit the fan. Fortunately for all involved training and practice kicked in, and everything was fine. I know that is not always the case.


I think the biggest issue with gas switches, and switching to the wrong gas, is not enough people practice theses skills when they are not actively using them. It comes back to the point you were making of, "Whelp I'm certified to do this now, now we just go do it". Too many times people get complacent with what they consider "mundane" skills. That leads to major issues when you brain shorts out.


There are always multiple ways to do something. When it boils down to it use the method that you and your team is most familiar with.

Even if you switch directly from one deco mix to the other, you still stow the first regulator immediately afterwards. Technically you don't even need to have 3 regs around your neck at any point in time, because you can take the reg out of your mouth and from around your neck at the same time, then immediately wrap the next hose around your neck and put it in your mouth.

Yes, protocols get broken, but they can get broken with either option. What grounds are there to claim, that putting a confirmed reg into your mouth has different levels of risk, depending on the reg you're taking out?

If you've confirmed the reg, both options are "safe". If you have not (or you've gone and fetched a reel in the middle of the switch), both are dangerous. You can't take a general risk and apply it to one situation only.

I think the best solution would be to dive CCR. None of those dangerous and apparently very complicated gas switches.

Now someone can chime in about stepping down your high He diluent as you ascend and then the required discussion about nitrogen uptake w/He outgassing and the benefits of one vs the other.....

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Originally Posted by floridabob

I think the best solution would be to dive CCR. None of those dangerous and apparently very complicated gas switches.

Now someone can chime in about stepping down your high He diluent as you ascend and then the required discussion about nitrogen uptake w/He outgassing and the benefits of one vs the other.....

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What Bob said... LOL