swapping 1st stages while at depth; emergency only

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It's one thing to talk about doing this in theory, reality is something else.

The intent is not to pick on anyone but rather to evaluate what was done, why, and wether there were better options by looking at the extant examples:
I know somebody who was on a tech dive when one of his buddy's deco regs blew up -- the diver calmly switched regs off the other deco bottle.
I know a diver who was on a dive with someone who tried this with their first deco gas at 130' bottle. It worked, but it took a lot longer than planned with the result that one of the divers on the team surfaced with only 300 psi. The take away from that was that it is an action that once started may quickly place you in a position where you need to complete it to safely end the dive.

In your example, the diver had two deco bottles and had a failure on one of them, using a single deco reg to access the contents of both deco bottles. I am assuming that he had succesfully used the first bottle and was switching to the second deco gas. In this case, had the swap failed, he still had his back gas reserve and could fall back on a lost gas contingency plan to safely end the dive.

This is an important point to make as if it was the first deco gas and the swap failed, the odds are good that his reserve back gas would not have been adequate to allow the much longer deco on back gas alone if the dive were deep enough and long enough to truly warrant two deco gasses.

In this case, the diver would have to rely on the deco gas reserves of other team members and may now be doing this in a situation where the team is now outside the original plan due to the effort to switch regs (in the case of the switch occurring with a low percentage deco gas at depth).

That's a very poor position to put the team in. Consequently, I might consider a reg swap but only if it can be done without risking both deco gasses, and only if it can be done after transitioning to a lost gas scenario and does not further delay the dive plan and team. In the event of a reg failure on the first deco gas, that criteria will not be met, unless it's a five bottle dive with an empty bottom mix stage that can donate a reg.

I found the article I was referring to here. The regulator switch is described toward the end.
It's an advanced sidemount cave diving class and that implies several things about the entry skill level. It still took the student 5 attempts over 2 days to successfully swap regs from one sidemount tank to the other.

It's also not stated but it is a last ditch "the gas planning wet seriously wrong due to serious dealys in the exit, and I've also had a reg failure" scenario. One of the positives of sidemount diving is that you are in essence diving independent doubles and, properly managed, there is enough gas in either tank to get you out of the cave or at a minimum back to your first deco gas, stage, etc so it virtually eliminates the possibility of total gas loss.

The qualifier here is that sidemount entries usually result in low viz or no viz exits that are much slower, so "thirds" gas management is not enough in terms of conservatism. In other words, a low viz exit is not an "emergency" but rather the norm, and one that should not require you to use your reserve gas. Consequently, if a reg failure poses a problem, the problem is not the reg failure but rather a lack of sufficiently conservative gas planning.

Planning to swap your sole remaining sidemount reg from one tank to the other in anything otther than a dire last ditch situation, would again just be adding one error in judgment/planning on top of others.

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In either case you need to think long and hard about the logic of switching a reg and you need to consider the systemic impact of the attempt on the dive and on the team, as well as on other options that while they might lengthen the deco, are much more of a sure thing and represent a far better contingency plan.
 
Swapping underwater will work fine, certainly on that dive to get you out of trouble. Yes the regs need a service after and ideally completely flooded in FRESH water as soon as possible and you MAY damage the SPG. But for a short time emergency it'll get you out of jail.
 
DAA, good points. I am absolutely not sure of the details of the reg swap -- where in the dive, or which gases. I just know it was done.

Given the amount of swearing and fussing I do putting ANY regulator on a tank (I HATE 300 bar valves) if I had a reg blow up, I'd go to my lost deco gas schedule.
 
if I had a reg blow up, I'd go to my lost deco gas schedule.
Assuming that's even an option. I can think of a couple of situations that may not be the viable solution.
 
Such as? ....................

Such as a situation where you don't have deco gas. Sidemount penetration diving could mean you only have two tanks, no deco gas.
 
Well, CD, isn't part of the gas planning for sidemount, the idea that you always have enough gas in EITHER tank for your exit? I thought one of the big arguments for sidemount is that, although you CAN lose all the gas in ONE tank, you can't lose all the gas in both tanks. So a need to swap regulators when sidemount ought to be vanishingly rare (only if you are seriously delayed with one tank down).

BTW, my comment was specifically for deco bottles.
 
The way I like to plan dives the easiest way to deal with a failed reg is just ignore it and go to the backup gas plan.
The one time I had a reg failure it was a 50% bottle on a 2 deco gas trimix dive. Just did the deco on backgas until I got to 20 feet and the O2 switch.
Similarly on a sidemount cave dive just head for the exit in the event of a tank failure. Share air from a buddy if you want. (And if you don't have a buddy don't dive to 1/3rds! )

Realistically a lot of things need to go wrong before you would ever need to switch a reg underwater,but its certainly something to bear in mind.
 
Well, CD, isn't part of the gas planning for sidemount, the idea that you always have enough gas in EITHER tank for your exit? I thought one of the big arguments for sidemount is that, although you CAN lose all the gas in ONE tank, you can't lose all the gas in both tanks. So a need to swap regulators when sidemount ought to be vanishingly rare (only if you are seriously delayed with one tank down).

BTW, my comment was specifically for deco bottles.

Agreed, but the basis for this discussion came from a question about sidemounted bottles so I tried to keep my thought process along that line without introducing additional bottles.

IMO, the problem is much less severe if you have deco gas, because that means you should have three regs. One on each primary bottle (whether sidemount or backmount) and at least one deco reg. So if one reg craps out, you still have one working reg to breathe off of while you swap the non working reg out. That seems much less stressful than trying to swap the only two regs between the only two bottles.
 
Agreed, but the basis for this discussion came from a question about sidemounted bottles so I tried to keep my thought process along that line without introducing additional bottles.

IMO, the problem is much less severe if you have deco gas, because that means you should have three regs. One on each primary bottle (whether sidemount or backmount) and at least one deco reg. So if one reg craps out, you still have one working reg to breathe off of while you swap the non working reg out. That seems much less stressful than trying to swap the only two regs between the only two bottles.
There is nothing wrong with the "limit it to two bottles" thought process.

However, even if it is *only* a two bottle side mount dive the principle is exactly the same as it is on a bigger dive where you plan for the loss of any single deco gas, its just that in a 2 bottle sidemount dive, you only have the 2 sidemount bottles to do the deco with, so you need to ensure you can still survive the loss of one tank.

Consequently, you absolutely *need* to manage the gas so that the gas remaining in either tank is enough to get you out of the cave, and that includes the deco.

If you can't do that then you have seriously &%$*ed up the gas planning.

Even if you take along a deco bottle and stash it near the intended deco stop, you still need to plan for a deco gas failure (or some idiot OW diver removing it if you are at Ginnie) and ensure there is enough reserve gas between the two sidemount tanks to handle a deco on back gas.

Thats just deco gas management 101. Which perhpas begs the question of how much of that is included in the average full cave class where a diver may or may not have taken AN/DP and/or a trimix course first.
 
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