Request for comments on article - mixed OC / CCR teams

[doctormike]

I guess we may be asking two different questions. And don't get me wrong, I appreciate your experience and your willingness to help me on this.

But I think that you are asking: "What needs to be done to make me reasonably sure that my OC buddy can rescue me?" The answer to that is certainly more than "read Mike's article." In fact, rescuing a CCR diver is such a challenge (as you mentioned) that even full CCR certification isn't always enough. So if that's the requirement, then yes, it's unlikely that this (or any) article will reach that goal.

I'm asking the question "Given that my OC buddy isn't going to get full CCR certification to improve my safety, what can I do to make things safer, assuming that I am still going to dive in a mixed team?".

So while yeah, it's obviously very hard to manage 5 air spaces on an ascent, that doesn't mean that it's not worth showing your OC buddy how to hold your loop in place and flip the BOV, since that might make a full rescue ascent unnecessary.

And the article isn't just about rescuing people in dire emergencies - there's a lot more to it. I think that it's important that the OC diver know not to do a sawtooth profile, not to do very fast descents, not to talk do you during your prebreathe, to know where to get gas if THEY need it, and not to be freaked out when they see bubbles on ascent, etc...

 

[KenGordon]

It is ok, I am not trying to dismiss your efforts. It is certainly worth a think about where the line lies between two much information and as much as possible. Of course that depends on the OC person in question.

 

[doctormike]

It is ok, I am not trying to dismiss your efforts. It is certainly worth a think about where the line lies between two much information and as much as possible. Of course that depends on the OC person in question.

Sure, and I really do appreciate your help and insight... thanks again!

 

[Brett Hatch]

Hi Mike,

I read the article, liked it, and learned a few things. For context, I am an OC diver who occasionally lurks in the rebreather forum and places like it. I have a vague interest in diving one some day, am currently just starting to dive OC doubles, and have never been in an OC/CCR buddy pair. Here's some feedback, hope it helps.

* I like the Bill/Tony anecdote, and agree that placing the cliffhanger at the top does provide a decent hook. However by the time I got to the story's conclusion, I had forgotten the details of the predicament. You might consider moving the conclusion up, perhaps the top of the "EMERGENCY" section, rather than the bottom. Or maybe revisiting the story in the middle of the article, say, the "DURING THE DIVE" section. Or both.

* The Bill/Tony story sounds fictional. If there is a real-life story of an OC diver helping out or even saving a CCR diver like this, you might consider retelling that story instead, or keeping your fictional one and linking to an article covering a real-life event. There's nothing wrong with using a fictional anecdote to illustrate your point, but historical ones lend a sense of both credibility and seriousness.

* The point comes across quite clearly that this is meant as an overview, not a replacement for proper training, and does not attempt to exhaustively cover all types of CCR builds (and doesn't cover hypoxic dil at all). However you might be able to ax a sentence or two on this from the opening paragraphs, while still making that point crystal clear.

And a question. You mentioned flooding the loop several times in the article, how to avoid it (switch BOV to OC / close DSV once on OC), and the consequences of it (super negative rig). I get that the entire loop contains space for a large volume of gas and that the non-loop part of the breather is mostly metal, so it would be quite negative if most of the gas were swapped out for water. But, you will never catch me diving steel doubles with a 20lb wing, because then a drysuit failure could make me catastrophically negative.

If rebreather pilots take loop flood into account when choosing wing size, then why is this a problem? Or, if they don't do that, well, why don't they?

Thanks!

 

[doctormike]

Hi Mike,

I read the article, liked it, and learned a few things. For context, I am an OC diver who occasionally lurks in the rebreather forum and places like it. I have a vague interest in diving one some day, am currently just starting to dive OC doubles, and have never been in an OC/CCR buddy pair. Here's some feedback, hope it helps.

I really appreciate your taking the time to help!

* I like the Bill/Tony anecdote, and agree that placing the cliffhanger at the top does provide a decent hook. However by the time I got to the story's conclusion, I had forgotten the details of the predicament. You might consider moving the conclusion up, perhaps the top of the "EMERGENCY" section, rather than the bottom. Or maybe revisiting the story in the middle of the article, say, the "DURING THE DIVE" section. Or both.

That's a good idea! Let me play around with that

* The Bill/Tony story sounds fictional. If there is a real-life story of an OC diver helping out or even saving a CCR diver like this, you might consider retelling that story instead, or keeping your fictional one and linking to an article covering a real-life event. There's nothing wrong with using a fictional anecdote to illustrate your point, but historical ones lend a sense of both credibility and seriousness.

Eh, I don't know of anything remotely like that personally, and I'm not sure how it being a real story makes it more illustrative. With a fictional story, I can write it how I like to illustrate the point that I'm trying to make. Wheras for a real life story, I'm not going to have special access to the true details, and there are probably a lot of irrelevant externaities which might dilute the impact. I see what you mean, but these are pretty rare occurrences (OC rescuing a CCR diver), and not sure where I woudl find that.

* The point comes across quite clearly that this is meant as an overview, not a replacement for proper training, and does not attempt to exhaustively cover all types of CCR builds (and doesn't cover hypoxic dil at all). However you might be able to ax a sentence or two on this from the opening paragraphs, while still making that point crystal clear.

Good idea... move that point up in the discussion.

And a question. You mentioned flooding the loop several times in the article, how to avoid it (switch BOV to OC / close DSV once on OC), and the consequences of it (super negative rig). I get that the entire loop contains space for a large volume of gas and that the non-loop part of the breather is mostly metal, so it would be quite negative if most of the gas were swapped out for water. But, you will never catch me diving steel doubles with a 20lb wing, because then a drysuit failure could make me catastrophically negative.

If rebreather pilots take loop flood into account when choosing wing size, then why is this a problem? Or, if they don't do that, well, why don't they?

Thanks!

Maybe that could be explained better in the text, but that might be something that expands they article beyond the desired scope.

The "dead bug syndrome" refers to a diver that loses consciousness, drops the loop and sinks rapidly, making rescue unlikely - not something that would happen to an alert diver underwater. That would be a situation where inflating the wing isn't going to happen.

Someone diving a heavy unit in a wetsuit that tears a hose or something would be in that situation of possibly not being able to reduce negative buoyancy enough for an ascent. But I would think that in that situation - a conscious diver, bailed out and in a flooded rebreather - the wing would suffice to allow you to get off the bottom. And in most cases of a flood that's not associated with dropping an open loop or tearing a hose, it's not a complete flood. Probably some more experienced CCR divers than I can explain this better.

 

[Brett Hatch]

Eh, I don't know of anything remotely like that personally, and I'm not sure how it being a real story makes it more illustrative. With a fictional story, I can write it how I like to illustrate the point that I'm trying to make. Wheras for a real life story, I'm not going to have special access to the true details, and there are probably a lot of irrelevant externaities which might dilute the impact. I see what you mean, but these are pretty rare occurrences (OC rescuing a CCR diver), and not sure where I woudl find that.

Sure, point taken both on the utility of a fictional story, and if these events aren't all that common, then I wouldn't be surprised if there are few or no good articles to point to. If one comes along though, it might be a good pointer for some readers.

Maybe that could be explained better in the text, but that might be something that expands they article beyond the desired scope.

Yeah, I don't see a need to expand on this point in depth in your article, since it's kind of in the weeds. Just a question that your emphasis on avoiding flooding the loop brought up for me. I would expect that either flooded loops are extremely uncommon in the first place, or diving with a sufficiently large wing to handle a flooded loop is standard practice. If that premise holds true, then I didn't understand why it's so important to emphasize the possiblity of a flooded rig if the loop is left open after bailing out.

The "dead bug syndrome" refers to a diver that loses consciousness, drops the loop and sinks rapidly, making rescue unlikely - not something that would happen to an alert diver underwater. That would be a situation where inflating the wing isn't going to happen.

Someone diving a heavy unit in a wetsuit that tears a hose or something would be in that situation of possibly not being able to reduce negative buoyancy enough for an ascent. But I would think that in that situation - a conscious diver, bailed out and in a flooded rebreather - the wing would suffice to allow you to get off the bottom. And in most cases of a flood that's not associated with dropping an open loop or tearing a hose, it's not a complete flood. Probably some more experienced CCR divers than I can explain this better.

OK, I think this clears it up a bit. If partial floods are much more common than floods which turn the breather into an anchor, then worrying about wing size might be trying to solve a non-existent problem. It sounds like you are saying that when serious floods occur, the diver would have typically lost consciousness anyway, so they definitely can't save themselves, and others may not be able to either. Basically, floods that bad mainly come from passing out/convulsing and spitting the loop out, in which case the diver is pretty screwed. Is that about right, or have I misinterpreted your answer?

 

[doctormike]

OK, I think this clears it up a bit. If partial floods are much more common than floods which turn the breather into an anchor, then worrying about wing size might be trying to solve a non-existent problem. It sounds like you are saying that when serious floods occur, the diver would have typically lost consciousness anyway, so they definitely can't save themselves, and others may not be able to either. Basically, floods that bad mainly come from passing out/convulsing and spitting the loop out, in which case the diver is pretty screwed. Is that about right, or have I misinterpreted your answer?

Well, the term "flood" can really mean two different things. If your loop volume is completely replaced with water, that would either come from a torn hose or an unconscious diver losing an open mouthpiece. Even then, there might be gas trapped in portions of the loop that were above the opening. You can't get back on the loop if that happens, the rebreather is a useless anchor at that point.

On the other hand, it's certainly possible to have a leak that will result in the slow accumulation of water in a breathable loop. Eventually, the scrubber will flood and you will get CO2 buildup scrubber failure, but I have seen a number of cases where a diver with a good, flood-tolerant CCR finished a dive and was surprised to find a good bit of water in the can. Rebreathers differ in their ability to dewater the loop, and assuming that you haven't trashed your scrubber, you can often force water in the exhale hose out through the counterlung valve and stay on the loop. This can come from a small leak, loose lips, condensation, or just the humidity of exhaled gas (the very appetizing "lung butter" that you dump out of the exhale CL between dives!).

 

[rsingler]

I think both you guys are getting down in the weeds a bit. Mike had a good point in raising the loop flooding question, and you had a good question relating to wing buoyancy in response.

So here's my take on the reason why it's a CCR issue: speed of onset. A diver with a wetsuit flood gets an immediate warning re: the problem! Things get cold, fast! Maybe they have adequate compensatory wing buoyancy, maybe not. But they're conscious and aware. And there are other drysuit buoyancy advantages...e.g., trapping air in a leg.
The CCR diver who sustains a loop flood, on the other hand, either had a catastrophic issue like a torn hose, to which he can respond immediately (bail out, inflate wing), OR,
he's stupid (hypoxic) and can't. In the latter case, his adequate wing buoyancy is irrelevant. And the shift to negative buoyancy when his loop comes out of his mouth (for some rebreathers at least) is rapid.
As for the slow loop leak example? The diver is still cognizant of a growing problem, with a (hopefully) adequate wing.

Sooo...flooded loop for a hypoxic CCR diver? A problem!
Flooded drysuit for an OC diver? A real aggravation! But life threatening, given adequate forethought? Not so much.

My 2 psi...

 

[doctormike]

Thanks for all the help, everybody!

The article just came out in X-Ray magazine. Check it out...

 

[Scuba Client]

Rebeathers and Scientific Dive Proceedings 2015/16: from what I’ve read, the most useful contribution was the gas density calculations, gradient factors, and for potential CCR students to seek instructors limited to teaching a maximum of 2 Rebreathers. The implied suggestion for a CCR diver to hand over his bailout bottle to an OC diver would be met with skepticism. CCR divers have a slower rate of ascent compared to OC divers, therefore, OC divers do not control the dive when diving mixed teams. I also got the impression the scientists were more interest in funding than anything else.