Why is CCR not DIR?

[Jimmer]

I'm not trolling here, just a serious DIR question. I've noticed a few times people mentioning that CCR is not DIR, can someone please clarify why? Is it because it's constant PPO2, and therefore not using GUE standard gases?

Thanks,
Jim

 

[Doc Intrepid]

Keep this one short and simple.

If you're not sure, give it a pass.

(George, who is not a GUE member, and who basically coined the phrase "DIR", dives a rebreather in Wakulla.)

It isn't all black and white.

First flung poo closes the thread.

 

[Sloth]

In the fundies class it was specificly brought up why a ccr isnt DIR but a scr is.

The answer Steve White gave was by first stating when a dive on a RB80 would be appropriate and hopefully I want screw his message up to bad.

Basicly what he said is that the only time you should consider an RB80 is when you are doing a dive profile that would require so many deco bottles that the risks of diving multiple deco bottles begin to out weigh the risks of an RB80.

In regards to the RB80 it is still consider a liability to the team due to the added complexites over open circuit and should only be considered for training dives or dives where it's risks are out shadowed by risks of diving open circuit.

So, from a DIR stand point, for most dives, an RB80 is not ideal even though it is consider a fairly safe rebreather and is "DIR" approved.

CCRs, requiring a computer to control your gas input, (and other points that were over my head) add to many additional risks to the team to make them an approprate tool for "DIR" diving when compared to open circuit or to a RB80.

Please keep in mind that I have no rebreather experince I am only trying to relay the answer my fundies instructor gave to this very question.

 

[rainman_02]

The big difference between eCCR/mCCR and the RB80 style SCR is the O2/diluent bottle setup.

With the RB80 style SCR, you're breathing all premixed "bottom mix" (or premixed deco mixes plumbed in). You are not custom mixing the gas in the rig during the dive by either electronic or manual addition of O2 and diluent.

The idea being that if you have to regulate the amount of O2 going into the mix...you can wind up with ppO2 out of limits (>1.6 or <.16).


Additionally, as Sloth says, the risk/benefit curve is very important. When the inherent risks and added complexities of the rebreather are outweighed by the risks associated with OC...then the rebreather starts to become the "better" solution.

 

[rjack321]

CCRs, requiring a computer to control your gas input, (add other points that were over my head) add to many additional risks to the team to make them an approprate tool for "DIR" diving when compared to open circuit or to a RB80.

Basically that's it. A computer adds alot of failure points and makes it very difficult/impossible for the team to monitor gas switches (since its essentially continuous). The RB80 relies on gases being "plugged in" at various times/points and those switches can be tracked across the team - there's no 'puter, no O2 sensors to fail, no voting logic to the O2 content like there is to a CCR.

If I have missed anything I hope Rtodd catches it and then someone closes this thread before the poo flinging starts

 

[Jimmer]

Thanks guys, I am very well informed on the workings of a CCR versus SCR. So I guess it just comes down to simply a matter of acceptable levels of risk, where a faulty computer could concievably put you into Ox Tox or hypoxic?

 

[rjack321]

Thanks guys, I am very well informed on the workings of a CCR versus SCR. So I guess it just comes down to simply a matter of acceptable levels of risk, where a faulty computer could concievably put you into Ox Tox or hypoxic?

Yes but its more than that. Can the dive be done without that risk? If you are very risk adverse and willing to put in a huge amount of logistical effort basically any dive can be done on OC. For those that can't there's the RB80. The DIR answer is that logistical reasons should not dictate the level of risk you take.

E.g. you don't choose deep air because He is too costly, you pay up or skip the dive. Similar reasoning has to date not been able to justify CCR risks.

 

[jkaterenchuk]

Thanks guys, I am very well informed on the workings of a CCR versus SCR. So I guess it just comes down to simply a matter of acceptable levels of risk, where a faulty computer could concievably put you into Ox Tox or hypoxic?

I cannot address the DIR reasons but I am not sure that the faulty computer is the answer. CCR's can have (and many do) redundacy in O2 cells (2, 3, 4) , batteries (1,2,3), computers (2,3). In addiiton the redundancy can be integrated or completely independent. The more redundancy the lower the risk similar to other OC concepts.

I suspect some of the DIR reasons might stem from the threat of Co2 overexposure.

 

[Sloth]

I cannot address the DIR reasons but........

Please remember this is a question looking for a specific DIR answer please don&#8217;t guess :no

 

[fweber]

Pardon the Hijack. But, it will be interesting to see what comes from this years GUE Conference Round Table on Rebreathers. Could O2 sensors directly driving analog gauges come out as the DIR way to CCR?

For those of you in the know. What issues of CCR design and procedures do you think will be discussed as they relate to DIR diving?