Can CCR's be safe?

[midway]

I disagree with you constantly about rebreathers trying to kill you, clearly they have no will of their own however there are several key ways a user can die that are worth being honest about. Obviously they aren't karmic agents or yours would have taken you out long ago.

You're right to be concerned about o2 cells, not exactly robust engineering meant for diving applications going on there.
While I am always suspicious of deep life data, they are doing some pretty cool research.

Turns out that water blocked cells will continue to output last measurement, how's that for warm and fuzzy comfort?
http://www.deeplife.co.uk/or_files/D..._E4_160415.pdf

Great reference. Thanks for sharing.

[PfcAJ]

[DA Aquamaster]

.../
To the actual units, WOB in all positions and CO2 remain a issue that leads to many issues, both unit related and also will provide tipping points for physiologically compromised divers that will be causative in stuff like heart attacks that wouldn't happen in younger/fitter certainly but are also not happening in anywhere near the incidence in OC technical divers who are often task loaded with equipment induced drag etc (compared to the diver in ccr with a single slung 40). It's easy to say a heart attack isn't the fault of the CCR but it also doesn't address that the unit can breed the conditions that lead to one for some compromised individuals in a manner that OC does NOT.
I also am not of the belief they are ALWAYS trying to kill you, but they do work on it if you aren't paying attention. Like flying in IFR in a GA aircraft in the soup.
yeah, water blocked cells are a scary truth.

Frozen sensor readings are something CCR divers are (or at least should be) trained to be wary of. This may be more of a concern on an eCCR where the diver might get lax and expect the electronics to maintain a stable set point, where a diver on an mCCR pays close attention and maintains a tolerance band around the target set point. Personally, if the sensor readings are not moving slightly on one or more cells, I'm inclined to either add a bit of diluent or a bit of O2 and see if the reading(s) move. If one cell stays frozen, then it's automatically suspect and if a dil flush won't clear the water and get it moving again, it needs to be ignored.

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I like the GA IFR analogy. I don't see cross checking the rebreather displays between themselves and with other sources of information (changes in depth, diluent percentage at depth, etc) on a rebreather as being substantially different than cross checking aircraft instruments against each other to ensure they are functioning properly, that you don't have a blocked or iced over pitot or static port, etc.

If there is a difference, it's that things on a rebreather fail much more frequently, and cross checking is both more essential and more often rewarded than is the case when flying a GA aircraft in IFR conditions.

[cerich]

Frozen sensor readings are something CCR divers are (or at least should be) trained to be wary of. This may be more of a concern on an eCCR where the diver might get lax and expect the electronics to maintain a stable set point, where a diver on an mCCR pays close attention and maintains a tolerance band around the target set point. Personally, if the sensor readings are not moving slightly on one or more cells, I'm inclined to either add a bit of diluent or a bit of O2 and see if the reading(s) move. If one cell stays frozen, then it's automatically suspect and if a dil flush won't clear the water and get it moving again, it needs to be ignored.

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I like the GA IFR analogy. I don't see cross checking the rebreather displays between themselves and with other sources of information (changes in depth, diluent percentage at depth, etc) on a rebreather as being substantially different than cross checking aircraft instruments against each other to ensure they are functioning properly, that you don't have a blocked or iced over pitot or static port, etc.

If there is a difference, it's that things on a rebreather fail much more frequently, and cross checking is both more essential and more often rewarded than is the case when flying a GA aircraft in IFR conditions.

the report on cells is interesting and is certainly food for thought. However the degree the report shows failures if uniform across platforms we would be having a much more in depth discussion

When the Sr20/22 came out, quite a few folks BRS'd and also just plain ole crashed because of trusting the technology more than trusting and cross checking.

Here is a summary of one that is interesting because of this conversation "On August 9, 2004, Jeff Ippoliti had his SR22 washed and some avionics maintenance performed. On August 10, 2004, Ippoliti departed into low IMC and began getting erratic readings from his pitot-static instruments. He pulled the parachute and walked away from the wreckage, which was examined by the FAA:

"Examination of the static system of the airplane revealed approximately 1 teaspoon of water was found between the static port openings and the alternate static air valve; the water was retained for analysis. ... Prior to the wash the pitot tube and two static ports were reportedly covered with yellow vinyl tape (Patco's #150-P 2). Testing of the water sample retained from the static system of the airplane, revealed it contained 3.2 mg/L of fluoride, which is common in tap water."" (http://philip.greenspun.com/flying/cirrus-sr20)

we do lack the CC equiv of a 'standard T" in crosschecking across units to reduce some human factor failures as well, but the prevalence of Shearwaters are starting to almost address it.

[cerich]

don't be shy, explain what parts of the discussion you think are stupid and lay it out. If I am wrong on things, show me where and why and I'll learn as will others.

[wingman]

With regard to relative extrema you labeled the maximum, may I suggest "Trough of Wisdom" for the minima? On another issue what about the relative contribution of solo CCR to risk? I have oft heard that a buddy may recognize your eratic behavior and help you to bail if you miss your own symptoms; nevertheless I notice many solo rebreather divers at the popular spots and have participated in that activity myself on several instances but quit doing it as a result have been diving my unit less as I do not like to mix platforms. Bill

[sea_ledford]

During my cave class one of my fellow students had a reverse block right as we turned for thirds. As two of us "worked on our buoyancy" while the third one worked on her ears for about 10 minutes on a dive with several more ups and downs between us and the surface, all I could think was "Man, cave diving on open circuit is STUPID!"

Turns out she was fine for the rest of the dive, and we still had plenty of air to do another series of mask off-lights out-air sharing drills on the way out. But given some minor situation changes it could have easily turned into a decision between barely making it out and rupturing an eardrum. CCRs add complexity and create additional failure points that you may have to deal with, but it takes away (or greatly diminishes) the primary stressor: lack of time/air.

-Chris

[Leandro]

Last year, an Adv. Trimix and Rebreather cave instructor diver, asked me if my family knew about the additional risks involved in taking the Trimix and Rebreather Diver course in the cave environment; as you know, having a beautiful family is priceless; so, it made me re-think about it and I chose not to advance further at this stage of my life, it is not worth it; this is just a hobby. I think, this decision makes me feel that rebreather divers are pushing too much their limits when in fact they feel pretty safe. The bottom line is: each person has different values, motivations, and needs that we all have to accept.

[Ben M]

yet OC tech divers are not buying the farm anywhere close due to "medical conditions" to that of CC tech divers... I would argue that OC they are often diving with more effort than CC (equipment induced drag). That oft heard argument ignores the facts

It would be interesting to see some data on this but I'd argue just the opposite.

Working even harder on OC is self defeating. A dive with poor technique, trim, and fitness adds a stage and doesn't really get much further into the cave before he gets spit out back out. Take the same diver and give him a CCR and he can go as far and as long as he wants, except now he is working hard on the loop.

[cerich]

It would be interesting to see some data on this but I'd argue just the opposite.

Working even harder on OC is self defeating. A dive with poor technique, trim, and fitness adds a stage and doesn't really get much further into the cave before he gets spit out back out. Take the same diver and give him a CCR and he can go as far and as long as he wants, except now he is working hard on the loop.

which makes my argument stronger, if you are correct they should be having heart attacks on OC more often than CCR, the stats presented at RF3 said otherwise. the again I observe more CCR divers with poor trim in caves than OC divers once you get past the first 1000 ft, regardless of the amount of bail out carried or not