Why CCR?

[wedivebc]

Time (if you need it)?

I'm been away for a bit and have really enjoyed reading this thread. Thanks all.

Time to do twice as much deco as you would on OC bailout?
I teach SCR to trimix students as last resort only.
Deco on a gas containing a higher fN2 than air takes a really looooong time

 

[rjack321]

Really? I was under the impression that when diving an scr you can approximate with reasonable accuracy what your average fo2 will be.

The RB80 SCR guys know, but it takes alot of no deco practice to derive their personal ppO2 drops. Going SCR as a fallback from a wonky CCR seems like a deco disaster to me. Without diving SCR alot to develop the baseline drop, there is no way to predict what is going on in the loop.

 

[Doppler]

I think many/most RB deaths would have been prevented if all RB users wore full face masks and didn't dive solo.

I agree on the solo issue but have to disagree strongly on FFM as a means to prevent CCR death. If you have time or a fault tree analysis diagram kicking around please explain the logic. Thanks.

 

[wedivebc]

Really? I was under the impression that when diving an scr you can approximate with reasonable accuracy what your average fo2 will be.

I see from your profile you are not RB trained so I better clarify:
A rebreather designed as an SCR can with the right gas selection maintain a fairly tight PO2 range. A CCR being used in emergency circumstances as a SCR will support life but PO2 range is far from optimal. You also mentioned minimal loop volume which is also a less than optimal operation mode. It can work but the best insurance of surviving a rebreather failure is carrying enough bailout gas and making sure you know how to use it. There are some RB failures that require the diver to get off the loop so you have to carry the bailout anyway.

 

[marchand]

Maybe I should update that...

 

[netmage]

I see from your profile you are not RB trained so I better clarify:
A rebreather designed as an SCR can with the right gas selection maintain a fairly tight PO2 range. A CCR being used in emergency circumstances as a SCR will support life but PO2 range is far from optimal. You also mentioned minimal loop volume which is also a less than optimal operation mode. It can work but the best insurance of surviving a rebreather failure is carrying enough bailout gas and making sure you know how to use it. There are some RB failures that require the diver to get off the loop so you have to carry the bailout anyway.

Maybe I should update that...

Probably something to chime in here... I don't plan for SCR, I know its there - its one of the options in the toolkit.

Marchand lives in cave country. As such - I can certainly see a typical N. Florida siege approach being put into play when all other options have been exhausted. I'm using SCR mode to get me to the big stash of O2 awaiting me at 10-20' in the cavern and figure it out from there.

 

[ucfdiver]

Probably something to chime in here... I don't plan for SCR, I know its there - its one of the options in the toolkit.

Marchand lives in cave country. As such - I can certainly see a typical N. Florida siege approach being put into play when all other options have been exhausted. I'm using SCR mode to get me to the big stash of O2 awaiting me at 10-20' in the cavern and figure it out from there.

Not breather trained here...I don't do dives that require one, all my dives are shorter than 4 hours including deco, so forgive my stupidity.

If you've got enough bailout gas to get you to the exit, and your buddy has enough gas for him as well, why would you screw with a broken piece of gear rather than going OC and getting out of the cave?

Sorry to put you on the spot Tim, it's just been something I've never understood, since you really have 2x or 3x (depending on team size) of the gas you need to exit.

 

[netmage]

If you've got enough bailout gas to get you to the exit, and your buddy has enough gas for him as well, why would you screw with a broken piece of gear rather than going OC and getting out of the cave?

Sorry to put you on the spot Tim, it's just been something I've never understood, since you really have 2x or 3x (depending on team size) of the gas you need to exit.

It's an option, and generally considered last ditch... When some people subscribe to the team bailout principle - you would have 1.5x... Not 2x or 3x...

 

[Tienuts]

Here's an issue with SCR which I think people fail to think about....

Why do you bail off the loop? Hyperoxic loop? Hypoxic loop? No, since once you are at the level of incurring deco while on a rebreather, you should have the ability to correct either of these 2 conditions. If you're not incurring deco, SCR is a non issue.

So that leaves hypercapnia or flooded loop. In either of these situations, you're not going to be able to perform SCR. Not very well, or for very long anyway.

So the only real reason IMHO to go SCR is if you completely loose your ability to know your PO2. Either by total electronics failure, or by total simultaneous failure of all 3 cells. Either scenario is quite remote if you're on a modern rebreather, and you have a good cell regimen.

 

[rookers]

So the only real reason IMHO to go SCR is if you completely loose your ability to know your PO2. Either by total electronics failure, or by total simultaneous failure of all 3 cells. Either scenario is quite remote if you're on a modern rebreather, and you have a good cell regimen.

Yes, electronics loss and doubts about your bailout gas supply combined would be the only reasons I could think of. Of course, I still teach people to buddy breathe, and will show the interested how to breath from a wing, a tank and a free hose. All extremely unlikely, but in the end, having something appropriate to breathe is pretty important. Having had some training and a bit of practice, I know the procedure, and can execute it if needed.