Why Rebreathers?

[caveseeker7]

The thing that frightens me, when you are talking about risk, is that hypoxia has few symptoms, and the ones it does have aren't likely to make you recognize what's happening to you. Unlike CO2 buildup, which causes anxiety and shortness of breath, hypoxia causes euphoria and then unconsciousness.

For me hypercapnia (CO2 poisening) is the bigger worry, as so far no way to monitor CO2 in the loop has been introduced for sport diving. The problem with the bodies reaction to gases at raised ambient pressure is that it varies from diver to diver, day to day, dive to dive. Just look at the reaction to raised partial pressure of nitrogen, and what a broad spectrum of narcosis is incurred. And a CO2 hit can incapacitate very fast judging by anecdotal evidence.

The partial pressure of O2 can be monitored reasonably well, usually with triple redundancy. It's for most part a matter of actually monitoring it, and improvements such as HUD and buddy displays help. To a lesser extend it's a matter of knowing if the data you're getting is correct, and new options are becoming available there, too. When you monitor the pO2 properly, you have a pretty good idea where the pO2 should be. There is the option of a loop flush to verify cells, and on most units the ability to track their reaction time as you raise the pO2 back to setpoint. One unit even tracks the cells output, monitoring pO2 changes due to ambient pressure and solenoid injection.

New stuff, from affordable cell checkers that allow the testing before the dive, to the new concept of continually checking cells during the diving with known gases as introduced by Bill Stone and his team.

O2 is manageable, well, enough anyway that I'm comfortable diving a CCR.
CO2, as well as a lack of data regarding elevated pCO2, worries me more.

BTW, there are rebreathers other than CCRs that use pre-mixed gas(es) and just extend their use. The pSCRs currently build are quite intuitive, Halcyon isn't kidding about that. Gas addition is based on the amount of gas dumped from the loop on each breath, and you'll know if fresh gas was added. There are reasons the safety conscious GUE people picked that technology.

But as on any rebreather, you'll need more discipline than on OC to dive safely.

 

[jepuskar]

What statistics are you basing this off of? Do you have figures you can point to?

Don't forget, Tom Mount is the one who first made the claim "for the diligent diver, CCR is safer than OC."

Tie, it is well known in the RB community that many divers have passed from simply not turning their unit on.

I think what wedivebc is saying is...you can do stupid things like forgetting to turn your air on while on OC and laugh it off as you pop to the surface...while on a RB if you forget to turn something on, like the unit or O2 than your chance of bodily harm is great.

I'm a little confused though because you both pretty much state the same point... Non-complacent vs diligent

The problem with thinking that a CCR is safer than OC for the diligent diver is that the diver must be diligent 100% of the time. Earlier this month Tom Mount told us a story at the RB Summit at the Florida dive show about how he was on a boat getting ready and got distracted...because his routine was messed up he missed a step in setting his unit up. He noticed it as he stood up with his gear on to get into the water...the unit felt lighter to him. What did he forget to do...mount/connect his scrubber.

I dont ever want to think that a rebreather is safer than OC, no matter how diligent I think I am.

J

 

[caveseeker7]

Andy, I think for most part you're right.

Rebreathers have many more parts than open circuit, mostly the rebreather itself.
At best, it runs pretty much of a complete OC setup. At worst it uses two more or less
complete OC setups and does its voodoo gas mixing ... . While most parts that make up
the loop are rather simple (there's a reason that they were around for decades before
OC gear) they can and have failed.

While most everything man-made is bound to fail at one point or another, it seems the
majority of failures on rebreathers have been due to the diver rather than the units.
Mind you, I'm aware of some design failures, as well as some manufacturing failures.

But the diver is likely the weakest link in most cases. Comes back to the discipline I
mentioned before, and the complacency that Dave mentioned. Complacency kills.
Then again, it has done so on OC many times over.

 

[Hoyden]

Top Ten reasons to dive a rebreather:
10. Air hog no more, you’ve got plenty of gas.
9. Warm moist air makes 40 degree water feel like 45 degree water.
8. Weighs less than Godzilla, unlike the doubles you used to dive.
7. Rebreathers have nifty nicknames like “yellow box of death.”
6. 8 cubic feet of helium costs a lot less than 80 cubic feet of helium, say 10 times less.
5. Fishes like you better when you are not making all of those distressing bubbles.
4. Longer bottom times, shorter deco hangs – get to the beer and stories part of your dive day sooner.
3. Get to say cool words like “diluent” and guess how W would mispronounce them.
2. Reduce, reuse, recycle, and rebreathe – new mantra to save the planet

And the #1 reason to dive a rebreather:
Dive gear for 3 days of wreck diving will fit in the trunk of your mid-life crisis sports car.

 

[jepuskar]

Not only that, but if im going to die in the water I think it would be way cooler to die on a rebreather than on OC.

 

[ScubaDadMiami]

I would urge anyone that is commenting on the safety of rebreathers to also include in your posts whether you have completed rebreather training. It is one thing to comment on something based off of what you have heard or read; it is another to have the experience base on which you rely to formulate your opinion.

Yes, rebreathers are more complex. That means there are more parts, and you have to put them together properly. It does take some more doing than does open circuit. However, once properly assembled, the rebreather can be even less risk than open circuit diving. Complexity does not mean higher risk; it just means more work in some respects.

Simplifying the situation, so long as your rebreather works as it is designed, staying on top of things is no more difficult than the equivalent of checking your SPG on open circuit. (With closed circuit, you hardly have to check the actual SPG on most dives since they use so little gas. Instead, you have another monitor to observe just to make sure that the unit is maintaining the proper levels of oxygen.)

Remember when all of those divers were dying because they switched to the wrong gas, toxed and died? This is a major risk of open circuit diving that you don't have with CCR. However, this does not mean that making gas switches itself is dangerous. It only means that the diver must make the switch following the proper protocol and using proper care.

On closed circuit, so long as you follow the proper protocol for operation, risks can be even lower than on open circuit. If you don't follow the protocol, then you can be in serious trouble just as you can be by not following protocol on open circuit.

Again, this is a very big simplification of the situation.

 

[H2Andy]

Yes, rebreathers are more complex. That means there are more parts, and you have to put them together properly. It does take some more doing than does open circuit. However, once properly assembled, the rebreather can be even less risk than open circuit diving. Complexity does not mean higher risk; it just means more work in some respects.

that is where i totally disagree

because if something can go wrong in two ways, whereas something else can go wrong in ten ways, the one that can go wrong in ten ways is riskier

rebreathers are more complex and thus have more potential ways to hurt you and are thus riskier

what is riskier, a life-support system with two possible failure points or a life-support system with ten possible failure points?

you basically have a lot vested in not admitting that rebreathers are, simply put, a riskier proposition

can they be managed safely? of course

can a diver dive a whole lifetime on a rebreather and be safe? of course

but please stop arguing that they are not riskier than a demand valve. of course they are. the very nature of the training and the extra vigilance and care needed to dive rebreathers safely are proof that they are riskier and need to be managed accordingly

But the diver is likely the weakest link in most cases.

true, but since scuba is more forgiving than a rebreather, the point is moot

(why? think about it ... rebreathers stress the weakest link more, and can break a weak link that scuba would not break -- which system puts more stress on the weakest link? rebreathers, of course)

 

[jepuskar]

Andy, you're a lawyer arent you?

 

[H2Andy]

Andy, you're a lawyer arent you?

ah ...

respondent neither confirms nor denies, nor in fact comments on, discusses, elucidates, or further addresses this issue; however, respondent reserve the right to amend this answer. failure to respond is not intended to establish any liability, direct or vicarious, on the part of the respondent.

sorry, what was the question again?

 

[wedivebc]

that is where i totally disagree

because if something can go wrong in two ways, whereas something else can go wrong in ten ways, the one that can go wrong in ten ways is riskier

rebreathers are more complex and thus have more potential ways to hurt you and are thus riskier

what is riskier, a life-support system with two possible failure points or a life-support system with ten possible failure points?

you basically have a lot vested in not admitting that rebreathers are, simply put, a riskier proposition

can they be managed safely? of course

can a diver dive a whole lifetime on a rebreather and be safe? of course

but please stop arguing that they are not riskier than a demand valve

Yes they have more failure points but they also have more recovery modes. We are trained when dealing with a RB failure to deal with it in steps. One; obtain something to breath, two; analyze situation and obtain optimal breathing gas (ie bailout, SCR mode, fix problem go back on loop).
An OC diver deals with failure one way, obtain breathing gas/ bailout. There is a story posted by Mike Gadd about silt that Uncle Ricky linked to here http://www.scubaboard.com/forums/3238497-post70.html
If that does not make you believe in the value of rebreathers I don't know what will.