Why is CCR not DIR?

[rjack321]

At what point will SCRs reach the end of the line and CCRs then become the better solution? Can we expect to just throw bigger and more SCRs at the problem without increasing the risk? Are the scrubber limitations identical between SCR and CCR? I'm really asking, I don't know the details to come up with the answers.

Its not a question of scrubber capacity since both remove the same mass of CO2. You just have to haul vasty more gas into the cave to drive a RB80. The CCR would not have that much drive gas but then you'd be hauling in OC bailout anyway. Notice that this starts to breakdown in OW.

But in OW diving GUE/DIR limits overall exposure/deco because the environment's variable. So having the (CCR) capability to do a 5 hour ocean deco dive is "too risky" to utilize.

 

[jkaterenchuk]

there's a few equipment issues which make CCRs look a little sketchy:

- the O2 cells work best when not exposed to water, which is somewhat problematic when you've got a loop of air you are rebreathing with high humidity and you're diving under water.

- even with voting logic you could have 2 or more cells go bad similarly (e.g. both get wet, both are from the same batch). the voting logic itself is still a single point of failure.

- electronics don't particularly like water and should be approached a little skeptically in critical life-support underwater.

then there's the procedural issues:

- your pre-dive equipment checks must be extremely good and rigorous. screw up with equipment checks on open circuit and you usually either get no gas or lose gas. screw up on a rebreather and you go unconscious (the exception to this obvious is gas analysis in technical diving, which is why that needs to get done religiously). equipment failure is second only to buoyancy issues in rebreather fatalities and occurs at a much higher relative rate than in open circuit fatalities because rebreathers are more complicated devices than OC.

- during the dive you have to be constantly aware of your ppO2 and readouts on CCR, you can't get task loaded or space-out underwater. again, spacing out on OC is bad, spacing out on CCR and you can go unconscious and have a fatality.

- the first awareness you have that something is going wrong and you need to bailout will probably be anxiety due to either hyperoxia or hypercapnia and with hypoxia you'll probably just pass out without noticing. if you've analyzed your gases properly on OC, you shouldn't see these issues.

then there's the fact that the positives of CCR aren't really as positive as all that:

- constant ppO2 decompression goes against the theories of push-pull deco at high/low ppO2s that GUE/WKPP have developed: no backgas breaks with CCR, no high/low ppO2 sections of the deco curve, no giving your lungs and your CNS clock a rest.

- typically CCR divers run with low setpoints and gain very little decompression time advantage over OC divers doing bumps to 1.6

- given sufficient OC bailout, the weight reduction from going to CCR is reduced unless you start doing team-bailout strategies.

So, "DIR CCR" would probably looks something like diving mCCR, or diving an eCCR like an mCCR, with a diver who is extremely detail oriented on pre-dive and post-dive checks and constantly watching their ppO2 and scanning their awareness for warning signs that they're going hyperoxic or hypercapnic. There's a whole lot of minuses there and not really enough plusses.

- don't know if that's exactly in line with DIR thought, but those are my heavily DIR-influenced thoughts.

Some good and valid points but as a CCR diver i would say not exactly complete or absolutely correct. Some of your points really are based upon how the diver(s) choose to handle their protocol before, during and after the dive. Some are very detail oriented and others are not. For every CCR issue there is a similar OC issue. You need to monitor Po2 on CCR....on OC you need to monitor gas usage. I think it would be true that you have more points of possible failure on CCR than OC and hence need to be prepared to handle them if they fail. But I guess you could also say the DIR tech diving has more points of failure than OC rec.

 

[Meng_Tze]

First flung poo closes the thread.

I like the way you think and operate.

 

[do it easy]

Its not a question of scrubber capacity since both remove the same mass of CO2. You just have to haul vasty more gas into the cave to drive a RB80. The CCR would not have that much drive gas but then you'd be hauling in OC bailout anyway. Notice that this starts to breakdown in OW.

But in OW diving GUE/DIR limits overall exposure/deco because the environment's variable. So having the (CCR) capability to do a 5 hour ocean deco dive is "too risky" to utilize.

When considering CCR as an exploration tool , the OW scenarios don't affect the decisions at the end of the line.

From your post, scrubbers and bailout seem even, so at what point does a cave dive become long enough and/or deep enough that taking enough drive gas is riskier and introduces more failure points than diving CCR? How much more efficient is CCR than SCR? 10x 1000X?? What order of magnitude are we talking about?

 

[Jeff Toorish]

equipment failure is second only to buoyancy issues in rebreather fatalities...

Lamont,

Do you know where I could find this data?

Jeff

(Great thread!)

 

[Sloth]

When considering CCR as an exploration tool , the OW scenarios don't affect the decisions at the end of the line.

From your post, scrubbers and bailout seem even, so at what point does a cave dive become long enough and/or deep enough that taking enough drive gas is riskier and introduces more failure points than diving CCR? How much more efficient is CCR than SCR? 10x 1000X?? What order of magnitude are we talking about?

Since this is the DIR forum then the current answer is a CCR is never part of the equation.

I know you mean will and arent looking to troll but can we please stay on topic.

 

[do it easy]

Since this is the DIR forum then the current answer is a CCR is never part of the equation.

I know you mean will and arent looking to troll but can we please stay on topic.

I was looking to see where the line was between risk and reward for CCRs so that I could better understand why they curently are not DIR. I thought that was germane to the question.

have fun storming the castle!
:fruit:

 

[dsteding]

have fun storming the castle!
:fruit:

Hilarious Tony, the best post of the day.

 

[Doc Intrepid]

Since this is the DIR forum then the current answer is a CCR is never part of the equation.

I know you mean will and arent looking to troll but can we please stay on topic.

Sloth, with the very greatest of respect,

If the phrase "DIR" and accompanying protocols that defined DIR were developed when George was the director of WKPP; and

If the WKPP used rebreathers during the push to run line in Wakulla for several years running; and

If WKPP protocols and rationale matching solutions to problems de facto met DIR criteria;

then

"never" is a strong word.

George himself has used rebreathers in Wakulla when they represent the most efficient/effective tool available to accomplish a specific objective.

At issue is where do the risk/ benefit curves cross on an X/Y axis? At which point in a given set of environmental parameters does Option A make more sense than Option B?

 

[wedivebc]

equipment failure is second only to buoyancy issues in rebreather fatalities and occurs at a much higher relative rate than in open circuit fatalities because rebreathers are more complicated devices than OC.
.

Sorry for posting in a DIR thread but this statement is absolute crap.