Why is CCR not DIR?

[Scubakevdm]

What it really comes down to is : Needed equipment for the task at hand.

A SCR is nothing more than a gas extender. It allows you to use a bottom mix, and not have to worry about po2 tox issues UNLESS you exceed your MOD. With twin hp 120's on your back, you could actually run out of scrubber duration and have a co2 breakthrough before you run out of gas (depending on depth). The scruber Limitations are based on your metabolic rate, and how much co2 you produce. Some folks can push a scrubber far, some cannot. The only worry is having a hypoxic mix in your loop, due to not enough "clean gas" being inserted on the constant feed. That is for me, the main reason that an o2 sensor should be on the unit. You need to know your po2, even if you won't tox, you can still pass out.

So in answer to your questions:

1: NO, SCR's have not reached the end of the line, nor should they. They are great tools.

2: CCR's are MORE APPROPRIATE in certain situations where carrying huge tanks is not optimal. They also allow you to go deeper and run your deco straight off the loop. Yes, SCR's can do that too, but they need other gear (Tanks, travel gas, etc...)

3: Do CCR's have more failure points than SCR's... Yes. Does the task outweigh the risk? Depends on the task. In some explorations, CCR is the only way to go. Alot of sites do not have picnic tables, drive up lanes, a sandwich shop, and a compressor.

IMHO, SCR's and CCR's both have their place. Some archaeological sites that I have been to WILL NOT ALLOW bubbles below the anoxic halocline. If you need to do that job, you need a CCR. For long duration, task loaded big cave exploration, a SCR is perfect. When I want lobster, I use an AL80. Just match the equipment to the job at hand.

Cheers

Though the reply in its totality may not be DIR it contains good information concerning the original post, and why CCR's are a riskier choice, without benefit. Especially convincing is the fact that with a decent sac one can run out of scrubber before they run out of gas. If a CCR is going to be more efficient with the gas, but the scrubber still only gives you six hours, what good is the extra gas? You just get a poop-load of complications in trade. Or did I miss something?

 

[rjack321]

So.............. TSandM as usual a concise comment. All I have seen here in this thread is comments along the lines of: GUE doesn't use them hence not DIR. No-one has been able to specify WHY they are not DIR or GUE approved. I am not sure anyone knows on this thread. One or two posts seemed plausible, but not definite. So I guess this is going to go on for 200 posts with regurgitation and then fizzle out.....without answering the question in the title.

Personally I find DIR is defined by the larger group of DIR divers, not by one or two individuals in GUE. GUE may codify the rationale and package it for distribution (via classes). But those of us doing dives in DIR teams should know the basic rationale behind the decisions and choices - becaue ultimately we are the ones who have chosen to avoid CCRs.

If you look over the bulk of these posts, there are consistent messages about why OC is chosen first, the RB80 is selected when OC doesn't work, and a CCR is (to date) an unnecessary complication.

 

[lamont]

Well then you are in posession of facts that those of us who actually understand and dive CCRs seem to have not had access to.

Dr. Richard Dunford who is charge of Hyperbaric Medicine at Virginia Mason gave a talk at the PNWTDC on rebreather incidents and the classification of what contributing factors occured during those incidences with a parallel analysis of OC accidents. If you contact him he might be able to give you the slides. I'm really not making this up to try to bash rebreathers, it really is based on statistical analysis, and he wasn't out to bash rebreathers, in fact he repeatedly made statements over and over that the results of studying incidents were not statistically valid to extrapolate outside of that population.

I also listened very closely to Mel Clarke talking about how to dive a rebreather during her presentation. She was the one hammering on pre-dive and post-dive checks, hammering on constantly checking your ppO2 every minute, hammering on diving eCCRs like they're mCCRs, and hammering on bailing out if there was any question of hyperoxia/hypercapnia, including anxiety. I listened very closely to someone who was very pro-rebreather, and it didn't sound like a very attractive way to dive to me. I'm not anywhere near OCD enough.