Rebreather Question from a non-rebreather user

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Tony, have you put substantial hours on an mCCR? Where do you get your conclusion that they are more dangerous at the surface in current, swimming back to a boat, etc. than an eCCR?

I think it's fair to say that both eCCR's and mCCR's are potentially "very dangerous", but I don't see how you can support that eCCR's are safer. I suspect the tendency to think an eCCR is more safe may be at the crux of the higher number of fatal mistakes associated with them. So far, there is no data that supports that eCCR's are safer than mCCR's, the body count even seems to suggest the contrary, and even that is debatable.

G

I know in circle of RB divers I dive with many of them feel the manual ccr's with hypoxic dil are quite dangerous at the surface. To the point, that I know several who will turn off the dil at 20 feet to avoid a hypoxic incident. On a eccr you have the solenoid to maintain the ppo2 at the surface despite your dil. Just my guess. I for one do not turn my dil off until I am on the boat. But that's just me and i am a not an expert by any means.
 
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I know in circle of RB divers I dive with many of them feel the manual ccr's with hypoxic dil are quite dangerous at the surface. To the point, that I know several who will turn off the dil at 20 feet to avoid a hypoxic incident. On a eccr you have the solenoid to maintain the ppo2 at the surface despite your dil. Just my guess. I for one do not turn my dil off until I am on the boat. But that's just me and i am a not an expert by any means.

whether a particular design of rebreather results in a fatality has mostly to do with how it's used, I think we can all agree with that. How it's used has a lot to do with training and practice, we can probably agree on that to, but also, beyond training, how it's used is also reflective of design, IMHO.

Against common sense (I admit), the dangers of diving an mCCR appear to be outweighed by the users tendency to compensate for those dangers. We'd expect to see more shallow water black outs, more spacing out and passing out, but so far, the users appear to find the threats both predictable and adequately compelling. The risks appear to be remarkably consistent and manageable.

The way I manage hypoxic dill near the surface is pretty simple, I begin and end each dive on pure 02, I dive with two po2 HUD's. Mostly, I assume I can kill myself at any depth on any reabreather. I would not bat an eye at diving an eCCR though, I just wouldn't "expect" it to work.

I was very convinced that eCCR's were safer, till I owned one that worked intermittently and until I put considerable hours on an mCCR and found my brain was remarkably reliable. Now I know mCCR's and eCCR's are just as dangerous. there is no gaget or gizmo or combination of them that can take the place of one's own awareness. I simply prefer mCCR's because they are more field serviceable and because they reinforce good habits by design and I need that to pay adequate attention... not everyone does.
g
 
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whether a particular design of rebreather results in a fatality has mostly to do with how it's used, I think we can all agree with that. How it's used has a lot to do with training and practice, we can probably agree on that to, but also, beyond training, how it's use is also reflective of design, IMHO.

Against common sense (I admit), the dangers of diving an mCCR appear to be outweighed by the users tendency to compensate for those dangers. We'd expect to see more shallow water black outs, more spacing out and passing out, but so far, the users appear to find the threats both predictable and adequately compelling. The risks appear to be remarkably consistent and manageable.

The way I manage hypoxic dill near the surface is pretty simple, I begin and end each dive on pure 02, I dive with two po2 HUD's. Mostly, I assume I can kill myself at any depth on any reabreather. I would not bat an eye at diving an eCCR though, I just wouldn't "expect" it to work.

I was very convinced that eCCR's were safer, till I owned one that worked intermittently and until I put considerable hours on an mCCR and found my brain was remarkably reliable. Now I know mCCR's and eCCR's are just as dangerous. there is no gaget or gizmo or combination of them that can take the place of one's own awareness. I simply prefer mCCR's because they reinforce good habits by design and I need that to pay adequate attention... not everyone does.
g

I agree that any rebreather can kill some one just as easy as the next. I was merely hypothesizing as to his logic.

I have a hybrid but dive it manual all the time. For me the manual is no more work and like you said it "reinforces good habits" I think (or hope) that a manual combats complacency.
 
To the OP: I'm going to preface my comments with the fact that I am NOT a rebreather diver and have never played one on television. My knowledge - such as it is - is obtained from my other half, who is a rebreather diver. It's amazing what you can pick up from watching and listening to someone progress through the learning curve, but as I said: this is my own understanding only, and as such, is woefully deficient compared to that of a rebreather diver.

Military O2 rebreathers have been touched upon by multiple posters, and are obviously depth-restricted owing to oxygen toxicity concerns. Recreational rebreathers, like the Poseidon Mk VI, are also specifically meant for recreational (>130 feet) depths, so your fiance is right there. Where is gets a little trickier is the long list of manual, electronic and hybrid rebreathers. Once you get into that area, it's a matter of picking the rebreather that's 'right' for you and your purposes. Some manual rebreathers, like the Sport KISS (which I believe was marketed more as a sport rebreather) and the Classic KISS, are depth-restricted...I believe the Sport has a ~150-feet maximum operating depth, while the Classic is rated to 250-ish feet. It's possible to dive the KISS Classic deeper, if modifications are made - I believe veteran cave explorer Brett Hemphill has taken his unit to much deeper than that, although he's tweaked his rebreather pretty significantly to enable him to do so. Divers that know they're likely to see some depth would obviously look to a unit that's not so restrictive - the Ouroboros, for example, is an electronic control unit will full manual override capabilities, and has been used by explorers visiting the Britannic, which rests in water over 300-feet deep. But there's many others out there that are capable of handling such depths, and that's where zillions of other considerations are weighed to arrive at the individual diver's final choice of unit. Some 'considerations' are a question of personal preference; others may be dictated by the diver's chosen environment. These include profile (big unit = not necessarily advantageous for cave exploration, for example); counter-lung positioning (back-mounted vs over-the-shoulder; positioning can affect work of breathing); scrubber (radial vs axial; sorb vs cartridges); cost; ease of servicing; instructor availability in a given locale; and on, and on...

One thing seems for sure: a single rebreather doesn't seem to be enough. My fiance only has the one, and he's already identified his next two fantasy purchases. Anyone know where we can get a money-tree?
 
Tony, have you put substantial hours on an mCCR? Where do you get your conclusion that they are more dangerous at the surface in current, swimming back to a boat, etc. than an eCCR?

I think it's fair to say that both eCCR's and mCCR's are potentially "very dangerous", but I don't see how you can support that eCCR's are safer. I suspect the tendency to think an eCCR is more safe may be at the crux of the higher number of fatal mistakes associated with them. So far, there is no data that supports that eCCR's are safer than mCCR's, the body count even seems to suggest the contrary, and even that is debatable.

G


The statement was that any rebreather at the surface could be dangerous. The paragraph formatting was to separate the answers to the OP 's questions.

I hope this helps to clarify the post.

Sent from my iPad using Tapatalk
 
To the OP: I'm going to preface my comments with the fact that I am NOT a rebreather diver and have never played one on television. My knowledge - such as it is - is obtained from my other half, who is a rebreather diver. It's amazing what you can pick up from watching and listening to someone progress through the learning curve, but as I said: this is my own understanding only, and as such, is woefully deficient compared to that of a rebreather diver.

Military O2 rebreathers have been touched upon by multiple posters, and are obviously depth-restricted owing to oxygen toxicity concerns. Recreational rebreathers, like the Poseidon Mk VI, are also specifically meant for recreational (>130 feet) depths, so your fiance is right there. Where is gets a little trickier is the long list of manual, electronic and hybrid rebreathers. Once you get into that area, it's a matter of picking the rebreather that's 'right' for you and your purposes. Some manual rebreathers, like the Sport KISS (which I believe was marketed more as a sport rebreather) and the Classic KISS, are depth-restricted...I believe the Sport has a ~150-feet maximum operating depth, while the Classic is rated to 250-ish feet. It's possible to dive the KISS Classic deeper, if modifications are made - I believe veteran cave explorer Brett Hemphill has taken his unit to much deeper than that, although he's tweaked his rebreather pretty significantly to enable him to do so. Divers that know they're likely to see some depth would obviously look to a unit that's not so restrictive - the Ouroboros, for example, is an electronic control unit will full manual override capabilities, and has been used by explorers visiting the Britannic, which rests in water over 300-feet deep. But there's many others out there that are capable of handling such depths, and that's where zillions of other considerations are weighed to arrive at the individual diver's final choice of unit. Some 'considerations' are a question of personal preference; others may be dictated by the diver's chosen environment. These include profile (big unit = not necessarily advantageous for cave exploration, for example); counter-lung positioning (back-mounted vs over-the-shoulder; positioning can affect work of breathing); scrubber (radial vs axial; sorb vs cartridges); cost; ease of servicing; instructor availability in a given locale; and on, and on...

One thing seems for sure: a single rebreather doesn't seem to be enough. My fiance only has the one, and he's already identified his next two fantasy purchases. Anyone know where we can get a money-tree?

HA! Great post, thanks for sticking your next out and throwing in a little humor as well.

Just as a point of clarification, the modification necessary to go deeper on many of the mCCR's out there is a simple as adding a second o2 bottle with a non-depth compinsating first stage or the use of the appropriate BO mix, either can be imployed to maintain po2 during the deep part of the dive where the IP is maxed out on the primary o2 reg, it requires good planning, but is not a big deal. Also, a smaller orifice and higher IP's can be used to extend the depth ability of the primary reg as well. I would consider these relatively minor modifications. Some models (both E and M) lack truly independent and redundant po2 monitors and I feel that true independence/redundancy is a vital at any depth, but especially on deep dives. The depth rating on many rebreathers can be misleading, IMHO.

Kind Regards,
George
 
I know in circle of RB divers I dive with many of them feel the manual ccr's with hypoxic dil are quite dangerous at the surface. To the point, that I know several who will turn off the dil at 20 feet to avoid a hypoxic incident.

The way I manage hypoxic dill near the surface is pretty simple, I begin and end each dive on pure 02, I dive with two po2 HUD's. Mostly, I assume I can kill myself at any depth on any reabreather. I would not bat an eye at diving an eCCR though, I just wouldn't "expect" it to work.

That's how I dive every time - I begin and end on pure O2.

I'm one of the ones Kim is referring to, who shuts their dil down at the 20 foot stop. The reason is because many times I am yo-yo-ing around taking shots of diver decompressing. In my bouncing around, I've been known to vent gas from the loop. When I drop back down, I like to have the dil off so the ADV doesn't kick in and drop my PO2.

To the OP, I would say that theoretically a CCR is more dangerous at the surface due to the fact that the PO2 can drop quicker at the surface than at depth, simply through metabolism. Jeff Bozanik even suggests in his book Mastering Rebreathers, that you should consider diving with a snorkel for this reason.

I would think theoretically a mCCR can be safer than an eCCR. In either unit the most likely failure is probably something in your electronics, or multiple current limited cells. Electronics on a mCCR simply just monitor the PO2. If they fail, no big deal - the orifice will continue to feed O2 as normal, and that will sustain you for a long time. If the electronics on an eCCR fail - these control the solenoid, which controls your PO2. Without the solenoid, the unit can't add o2 to the loop, and the PO2 could drop hypoxic. If you look at Curt Bowen's article here, you can see the difference of having an orifice or not is quite substantial.

That being said, for the above scenario to happen, you'd have to be ignoring your electronics for some time, at least 6 minutes, which is unacceptable. Either that, or you'd have to have 3 cells fail low simultaneously, which as Paul Raymaekers demonstrated, is the closest thing to mathematically impossible.

To the op: Rule 1 - know your PO2 at all times. Stick with rule 1, and it's a non-issue.
 
That's how I dive every time - I begin and end on pure O2.

I'm one of the ones Kim is referring to, who shuts their dil down at the 20 foot stop. The reason is because many times I am yo-yo-ing around taking shots of diver decompressing. In my bouncing around, I've been known to vent gas from the loop. When I drop back down, I like to have the dil off so the ADV doesn't kick in and drop my PO2.

To the OP, I would say that theoretically a CCR is more dangerous at the surface due to the fact that the PO2 can drop quicker at the surface than at depth, simply through metabolism. Jeff Bozanik even suggests in his book Mastering Rebreathers, that you should consider diving with a snorkel for this reason.

I would think theoretically a mCCR can be safer than an eCCR. In either unit the most likely failure is probably something in your electronics, or multiple current limited cells. Electronics on a mCCR simply just monitor the PO2. If they fail, no big deal - the orifice will continue to feed O2 as normal, and that will sustain you for a long time. If the electronics on an eCCR fail - these control the solenoid, which controls your PO2. Without the solenoid, the unit can't add o2 to the loop, and the PO2 could drop hypoxic. If you look at Curt Bowen's article here, you can see the difference of having an orifice or not is quite substantial.

That being said, for the above scenario to happen, you'd have to be ignoring your electronics for some time, at least 6 minutes, which is unacceptable. Either that, or you'd have to have 3 cells fail low simultaneously, which as Paul Raymaekers demonstrated, is the closest thing to mathematically impossible.

To the op: Rule 1 - know your PO2 at all times. Stick with rule 1, and it's a non-issue.

That is the most accurate and intelligent post that you have ever made.

I really hate to agree with you, but I must.
 
That's how I dive every time - I begin and end on pure O2.

I'm one of the ones Kim is referring to, who shuts their dil down at the 20 foot stop. The reason is because many times I am yo-yo-ing around taking shots of diver decompressing. In my bouncing around, I've been known to vent gas from the loop. When I drop back down, I like to have the dil off so the ADV doesn't kick in and drop my PO2.

...

I'm thinking, "why do these folks turn off their dill?" and then I realized, Oh, right, I forgot to mention (ha!), I have disabled the ADV altogether, on all dives for that very reason. All dill get's added manually on my set up, I have two manual add options, one on the right and one of the left.

I find it strangely amusing how I started out not trusting myself and wanting everything to be automatic and gradually over the years migrated to wanting total control, accept for the orifice, which throws a little uncertainly into the mix, which only serves to makes me want to keep an eye on my po2 even more.

the gadgets and gizmo's are great for convenience, but they don't appear to improve outcomes the way we'd all like, ultimately there is a reason why conventional wisdom boils down to "know your po2", there's just no substitute for good monitoring habits, on any rebreather, at any depth.

are rebreathers safe? no way! Is the risk manageable? with careful study and practice, I do believe it is!

g
 
I'm thinking, "why do these folks turn off their dill?" and then I realized, Oh, right, I forgot to mention (ha!), I have disabled the ADV altogether, on all dives for that very reason. All dill get's added manually on my set up, I have two manual add options, one on the right and one of the left.

I agree 100%, also as someone who started out on an eCCR and moved to an mCCR. The only reason I haven't disabled the ADV completely, is because many dives I have a dSLR camera rig in my hands, and sometimes I have to use the ADV on my decent.
 
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