What is "recreational" rebreather, and any recommendations?

[taimen]

I’ve jumped in the water with my gas off several times, and each time I noticed that I had done so, either because I could not get a breath off my inhale/dil CL or because my PO2 was not rising, and quickly opened the valves.

Hmm. Jumping in with gas off several times sounds like something is lacking in your training after all. If you can do that kind of a mistake repeatedly, it is already a proof that eventually you can make two mistakes in a row. That is is typical for fatalities.

 

[silent running]

Hmm. Jumping in with gas off several times sounds like something is lacking in your training after all. If you can do that kind of a mistake repeatedly, it is already a proof that eventually you can make two mistakes in a row. That is is typical for fatalities.

No, and the snarky, holier than thou stuff is not helpful to this discussion. Nobody is perfect, and the idea that training can make a perfect diver is unrealistic and beside the point. Training is very important, but fault tolerant CCR design is even more important.

 

[taimen]

Nobody is perfect, and the idea that training can make a perfect diver is unrealistic and beside the point.

Must have really misunderstood your earlier post with emphasis on training and awareness.
I dive a (relatively) simplified eccr (JJ), and feel that my training is on par with others who dive at my level. To be honest, I would not mind some additional active safety features to back up my human behaviour.

 

[rjack321]

Must have really misunderstood your earlier post with emphasis on training and awareness.
I dive a (relatively) simplified eccr (JJ), and feel that my training is on par with others who dive at my level. To be honest, I would not mind some additional active safety features to back up my human behaviour.

I dive a Meg and a Kiss and I agree with you. There's room for "something" that addresses hypoxia and/or Co2 I think. But that layers on complexity and creates almost as many issues as it solves.

 

[rjack321]

Brian Bugge was on a tmix training dive, additionally task loaded with a camera, did not have his electronics in dive mode and his O2 was off.

Not paying attention to your PO2 and whether or not you have your gas turned on is at the top of the list of things you are supposed to do.

This could happen to any CCR diver, "recreational" or not. He was dead practically on the surface. And you admitted to jumping in with your gases off as well. There's a long laundry list of things CCR divers are "supposed to do" to avoid dying. No matter what the depth or the unit or the dive plan forgetting, getting distracted, task loaded, having dog hairs in orings during assembly etc etc (the OP is talking about CCRs photography afterall) you can die potentially before your head is even fully wet.

 

[silent running]

I can't give you a number, but the point is that there are two ways of developing hypercapnea - scrubber bypass (e.g. an improperly packed scrubber), and CO2 overproduction (e.g. suddenly having to do a lot more work, like someone caught in a downcurrent, as you mentioned upthread). If the problem is overbreathing, that means that the scrubber itself was not the problem. The fact that you personally were able to avoid hypercapnea with sudden unanticipated extra exertion in that specific instance doesn't mean that overbreathing isn't a thing.




No idea, I was just thinking of that duckweed report that I read a while ago (foreign object got into the downstream valve, keeping it from sealing).



Well, there you go. Survivor bias.

In my small sample of people that I actually know, I have lost two well trained and experienced friends who were diving CCR. In both cases, it was never clear what the exact sequence of events was, but people who have had CO2 hits describe being barely able to bail out (the argument for BOVs).

Look, you have a lot more experience than I do. And I'm not one of those people who know nothing about CCRs but go on and on about how they involve completely unacceptable risk. I also understand that CCR removes some OC risks. And I love my JJ.

I just don't think that you should imply that it is impossible to have a CCR catastrophe if you always do the right thing, because the point is that human beings - even really skilled and well trained ones - occasionally don't do the right thing. That's why I have been pushing to change rebreather culture about checklists. The point is that even the most well trained and experienced diver is running on human brain software, and we all can have occasional failures of that system. If you are sick, hungry, angry, dealing with an emergency, or whatever.

So yes, if you never make a mistake, it's pretty unlikely that your rebreather itself will do you in. I just don't think that your position is a good one to promote to OC divers considering making the switch to CCR.

I too have lost a friend, a very experienced, smart, methodical professional. His cause of death while diving tmix in warm water was unknown, which is scary in and of itself. That is one reason I said above that continuing education is mandatory for CCR diving, there are things we don’t yet know about the human body and the stresses on it from mixed gas CCR, like CO2 retention and it’s variance between individuals.

The key word you used is catastrophe, and that’s what I don’t see happening in most accident reports; catastrophic failures under normal conditions with well trained divers are not a regular occurrence. And by the way, when I say well trained, I mean someone who takes their time at each level and gains the experience and hours necessary to proceed to the next level. I have enjoyed every hour I spent on the loop and was in no hurry to move past mod 1 for a few years. The 2 fatalities mentioned to me above were both people pushing the envelope hard, both time and skill wise.

Should a BOV be mandatory? Maybe, they have gotten a lot better since my first one back in 2005. I’m getting another one after trying a few and disliking them. Maybe this one will suit me and the CO2 issue will then be further lessened. Personally, I think most ECCR designs are over complicated and do not involve the diver in the workings of the unit on a minute to minute basis. A bunch of automation is no substitute for situational awareness, like watching your sensors react to an O2 injection and seeing if any are lagging. The simpler the CCR the better, in my opinion, as the best chance to avert a catastrophe is for the diver to be maximally involved in the dive and focused on their PO2 and the workings of the basic parts of the CCR. Fully automated CCRs with lots of alarms and blinking displays are additional task loading of their own and may actually overload someone into doing the wrong thing. A well designed BOV may be the exception to the complexity rule for me.

Should we all approach CCR diving with caution? Of course. Can CCRs be made safer and more fault tolerant? Yes, but I’m not sure we are going in the right direction by adding more bells and whistles to CCRs, which is another topic...

 

[silent running]

Must have really misunderstood your earlier post with emphasis on training and awareness.
I dive a (relatively) simplified eccr (JJ), and feel that my training is on par with others who dive at my level. To be honest, I would not mind some additional active safety features to back up my human behaviour.

Understood, but at some point additional features ad more failure points and complexity with the capacity to also fail or distract. In my opinion the safest driver is the one who is maximally involved in the dive, not trusting a bunch of automation with code written by someone who doesn’t even dive...

 

[silent running]

This could happen to any CCR diver, "recreational" or not. He was dead practically on the surface. And you admitted to jumping in with your gases off as well. There's a long laundry list of things CCR divers are "supposed to do" to avoid dying. No matter what the depth or the unit or the dive plan forgetting, getting distracted, task loaded, having dog hairs in orings during assembly etc etc (the OP is talking about CCRs photography afterall) you can die potentially before your head is even fully wet.

It could happen to any CCR diver who was pushing the envelope of training and experience, and poorly instructed.

The laundry list is mostly survivable, all the more so on a simple, well designed, fault tolerant CCR. I had a pinched scrubber O ring and during my descent I saw a few bubbles above me. I surfaced fixed the problem and was back in the water in 15 minutes. My CCR has 2 O-rings so there was barely any water in the bottom of the scrubber. No big deal, and I probably could’ve done an hr or 2 without any adverse consequences on a regular recreational type dive. Could that situation have spiraled out of control? Yes, but it is very unlikely under normal mod 1 experience conditions.

You will notice that I emphasized to the OP keeping things simple if he is doing photography. On the topic of simplicity we agree more than not, but I would hardly call the 2 fatalities you mentioned simple, every day situations.

 

[taimen]

In my opinion the safest driver is the one who is maximally involved in the dive, not trusting a bunch of automation with code written by someone who doesn’t even dive...

This probably everybody agrees. Although someone could add that the safest diver is maximally involved also prior to dive and doesn't splash with gas off
The additional features I am looking for would (possibly) help when maximal involvement is already impaired. And that can happen due to hypoxia and hypercapnia, but also unexpected task loading.
I don't know how those features would be best implemented.
There could be some audible/vibrational warnings in addition to visual, but they must be very carefully reserved to most critical issues.
I like electronic pressure sensors with low pressure alarms for more awareness. They warn for closed O2 earlier than following pO2. Suddenly and unexpectedly depleted diluent has also caused panic with escalating problems.
Many people (including myself) like to hear the solenoid clicking. Problem is that the solenoid is sometimes difficult to hear. People with hearing loss can't hear the solenoid at all. It feels somewhat stupid to suggest an audible indicator of a perfectly working unit, but actually that is something we are currently using (if we can hear it).

 

[silent running]

This probably everybody agrees. Although someone could add that the safest diver is maximally involved also prior to dive and doesn't splash with gas off
The additional features I am looking for would (possibly) help when maximal involvement is already impaired. And that can happen due to hypoxia and hypercapnia, but also unexpected task loading.
I don't know how those features would be best implemented.
There could be some audible/vibrational warnings in addition to visual, but they must be very carefully reserved to most critical issues.
I like electronic pressure sensors with low pressure alarms for more awareness. They warn for closed O2 earlier than following pO2. Suddenly and unexpectedly depleted diluent has also caused panic with escalating problems.
Many people (including myself) like to hear the solenoid clicking. Problem is that the solenoid is sometimes difficult to hear. People with hearing loss can't hear the solenoid at all. It feels somewhat stupid to suggest an audible indicator of a perfectly working unit, but actually that is something we are currently using (if we can hear it).

All good thoughts above worth considering, and not to distract away from my stupid mistakes with the valves, but they were ultimately no big deal because of the fault tolerant design of having the valves easily accessible. Also, as part of my unit predive, the loop is full of O2 from calibration, so a hypoxic loop on entering is not even possible following this procedure. I personally don’t believe a PO2 spike on the bottom is so dangerous, and jumping in with a loop full of O2 is certainly a good way to avoid hypoxia. Trade offs are a big part of the CCR safety equation...