Stage Diving: What are you doing?

[LiteHedded]

well in that scenario I'd have about 100 cuft of gas on my back. between that and my buddy's long hose (assuming 2 man team) I think I'd be in ok shape. if I've done my math right, you're left with more than a third of your starting backgas pressure if you save half the gas during a failure at max penetration.
I'd probably go on the long hose for a big chunk of the trip back to the stages, saving my backgas for gas switches/whatever, then cash the stages and ditch them to get streamlined.

I'll just add that I think the far more likely failure is coming back to an empty stage. or a stage with a bad freeflow once you turn it on. i've had more stages go tits up on me than anything

[aainslie]

I agree that adding the buddy changes things. Personally I always plan solo - but as soon as you plan in teams of two or 3, gas planning definitely gets way the heck safer.

Solo, I'd prefer to distribute the gas rather than putting it all on my back. The extra carry achieves the same thing, while the gas distribution decreases gas lost in a worst case emergency.

Chris, thanks for blowing my cover!! I'm only an OW instructor, and rarely use those privileges. I did it mainly for the learning.

[LiteHedded]

I agree that adding the buddy changes things. Personally I always plan solo - but as soon as you plan in teams of two or 3, gas planning definitely gets way the heck safer.

Solo, I'd prefer to distribute the gas rather than putting it all on my back. The extra carry achieves the same thing, while the gas distribution decreases gas lost in a worst case emergency.

Chris, thanks for blowing my cover!! I'm only an OW instructor, and rarely use those privileges. I did it mainly for the learning.

oh I agree. I can't speak to solo diving. it's just not my cup-o-tea.
but with team diving I think the reserves make the most sense being on your back so you can ditch the stages as they become empty. and having access to that reserve with two regulators (one of which is on a long hose) is certainly preferable.

[atedeschi]

Here is my reasoning, and if you see something faulty I am open to change.

From my example I posted before:

On the way IN:
AL80 used 33.8 cu ft
LP85s used 64 cu ft

Lose Half BG I would only have 83.2 cu ft minus the 64 cu ft need to get back to stage, which leaves me 19.2 cu ft.

This should give me enough reserve incase of a slower exit, or lost line, or light failure.

OK but say I lost half my gas and made it back to the stage, turn it on, and its freeflowing. I have 44.2 cu ft but say by feathering I will waste half, which leaves me 22.1 cu ft to use out of the stage, plus the 19.2 cu ft left in my 85 which gives me 41.3 cu ft to exit when I only need 33.8 cu ft. Therefore I should still have a reserve of 7.5 cu ft.

Now I plan as a solo diver so a buddy will just give me more gas, also I dive SM so I should be able to feather the tank that is losing gas, if not a bursk disk, and I when i get to the stage i can always change the regs since i have reserve of 19.2 to keep breathing off while i swap regs.

You in a sense this is planning for 1.5 major failures. If you try to plan for everything you would need so much gas you would not go far or carry to many tanks. Just my thoughts.

[limeyx]

So it seems a common approach is to breathe the stage below 2/3 BUT reserve the extra in BG. I like it. Couple of questions:

Is this an official GUE and/or UTD approach? Does anyone else officially teach this?

Why do that rather than just go to 1/3 and then carry a bit further? Woudln't it make for identical redundancy plus easier planning?

As others have said, this is (currently what GUE teaches which is my only experience.

One benefit of not keeping the extra 1/3 in the stage but in BG is that in an emergency exit you dont have a bunch of 1/3 full stages you need to carry to get out of the cave so you can ditch empty stages earlier. You can also more easily share gas in your BG

You wouldnt really lose more of that reserve gas exactly if your BG goes, because you are *already* assuming loss of 1 BG at max penetration + total loss of 1 or more stages (depending on your planning)

Anything more than that going wrong, and I really should have taken up golf!

[rjack]

I understand why you want to carry it with you. But then if you lose 1/2 your BG, you lose 1/2 the "reserve" from the stage that you moved over there. Doesn't that worry you? Doesn't it make more sense to leave it in an independent tank (the stage), and just carry the stage a bit further instead?

The whole point of splitting reserves up is so that the loss of one tank doesn't take a disproportionate percentage of your gas with it.

The "problem" with the independent tank is that its all alone in the cave. And the gremlins like the cave police can screw with it. Any problem with that dropped stage and is likely going to vent until its dry. Unlike with backgas that you at least know what's going on. So the risk is balancing losing all of a stage vs. a portion of backgas (cause you can at least shut it down isolate etc)

I have "lost" stages in classes and getting out without them is trival. In a team of 2, I "lost" all backgas at maximum penetration (1/2+200 from the stage + 700psi of backgas in AL80s in MX) and my buddy lost his stage when we returned to it. I exited on his long hose back to the stage, and he had to remain on backgas all the way out. He still had 1000psi in AL80s at the O2. I had about 500psi in my stage and no backgas. So even with a fairly significant double failure and we had roughly ~65cf left and almost no stress. This was in Mayan Blue, essentially a no-flow system. Sure it was a class, but I think it illustrates the strength of "reserving the stage" from backgas when you're a long way from 1ATA.

[limeyx]

I have "lost" stages in classes and getting out without them is trival. In a team of 2, I "lost" all backgas at maximum penetration (1/2+200 from the stage + 700psi of backgas in AL80s in MX) and my buddy lost his stage when we returned to it. I exited on his long hose back to the stage, and he had to remain on backgas all the way out. He still had 1000psi in AL80s at the O2. I had about 500psi in my stage and no backgas. So even with a fairly significant double failure and we had roughly ~65cf left and almost no stress. This was in Mayan Blue, essentially a no-flow system. Sure it was a class, but I think it illustrates the strength of "reserving the stage" from backgas when you're a long way from 1ATA.

We did same with team of 3 (slightly more penetration gas) and with similar results. Over 1000 psi in all remaining doubles, still gas in both stages.

[Brian Kakuk]

The "problem" with the independent tank is that its all alone in the cave. And the gremlins like the cave police can screw with it. Any problem with that dropped stage and is likely going to vent until its dry. Unlike with backgas that you at least know what's going on. So the risk is balancing losing all of a stage vs. a portion of backgas (cause you can at least shut it down isolate etc)

I'm unsure how a stage could lose gas while unattended if it is shut down when dropped with 2/3 left in it. An independent cylinder (when used in conjunction with another cylinder) such as back mounted independents and side mounts) is much more safe that manifolded double cylinders any day.

If a burst disc goes on a stage tank you lose the gas. If a burst disc goes on a set of manifolded doubles (back gas), you lose the gas on that side, PLUS any gas that escapes from the "good side" up until the point of closing the isolator valve. Manifolded doubles are not redundant until the isolator is closed... IF you can close it fast enough...if you realize what is happening soon enough and which valve needs closing....if the cave configuration allows easy access and if you have continued with muscle memory training for your valve drills.

If you are planning your emergency gas thinking that all of the gas in the "good side" of a BG set of doubles will be there after a burst disc or even freeflow from the bad side, you will be fatally mistaken.

I see not a single "problem" with dropping an independent cylinder other that some idiot who may carry it away while unattended....at which point a 9mm should solve any reoccurance if you survive the dive.

Safe diving,

Brian

[LiteHedded]

has anyone ever had a doubled burst disk blow during a dive? ever?

[Jason B.]

has anyone ever had a doubled burst disk blow during a dive? ever?

I had a set that was double disked have one of the tank neck o-rings extrude. After 45 minutes of air spewing out, it was decided to open a valve and drain the tanks down as it was clear it was not going to be a quick process draining via the extruded o-ring (this was on land).
YMMV