Importance of being able to dewater?

[stuartv]

At least one CCR on the market gets criticized because if it gets water in it during a dive, you can't get it out.

I don't want a brand/model debate, so I'd like to avoid discussing brands/models if we can.

What I would like to know is what ways a CCR can get water in it, that make dewatering important?

For example, you could get water in by getting a big rip in a loop hose. I think the ability to dewater in that case is irrelevant, because if that happens, you're going to HAVE to get off the loop and onto BO, no matter what CCR you're using.

On the other hand, if you take the DSV out of your mouth without closing it, then you could get water in the loop and being able to dewater the loop would be useful. If you get that water out, you can likely continue your dive without any change in plans.

So, what are the various ways you can partly flood a CCR, where you could dewater and continue? Ways I can think of:

- Take DSV/BOV out of your mouth without closing it.
- loop hose/connector comes apart, but you can put it back together. E.g. you didn't screw it together all the way and it comes undone.

I started to add "got a very small leak in the loop" to the list, with the thought that, if it's slow enough, you could dewater periodically, but stay on the loop and continue the dive. I decided not to because, while you might be able to stay on the loop, my thought is that if you know you're getting water in from somewhere, you would have to thumb the dive (even though you MAY stay on the loop) on the basis that you wouldn't know for sure where the water was coming from, so must assume that it could change from a very slow leak to a catastrophic flood at any moment.

As I said, I am not interested in a debate on brands or models of CCR. I'm trying to educate myself on the specific things (or kinds of things) that can happen where an ability to dewater the unit is really useful, and HOW it's useful.

It seems like, if we presume the diver is carrying the right, and right amount of, bail out, then the ability to dewater should always be nothing more than a nice convenience, right? Still, I want to understand what can happen that would result in benefiting from that convenience.

Thanks.

 

[rddvet]

My wife recently closed her ADV for some reason on a rapid descent on dpvs. It caused the diaphragm of the adv to suck down hard and get a rip in it. It caused a severe flood. Our units are very very flood tolerant. She had probably a little less than half a gallon in there and could still breathe (though the WOB went up like crazy) and also didn't get a caustic. After the dive when we opened the loop you could taste the very early starts of a caustic but her body position was head up and head down at times exiting the cave. She obviously bailed out to her bov since there was no caustic taste in the reg at that point. There's no way to really dewater when that happens, but I would say that flood tolerance is exceptionally high on my list of things I want out of a unit. Though she had to bail out, she had time to think and figure out what was happening and act appropriately. Our units allow you to dewater the counterlung, but obviously with that much water in the can there's no way to get it out.

 

[kierentec]

Usually "dewatering" and "water tolerance" go hand in hand (the units on the market that do not have flood recovery are also very high risk of caustic hit with minimal water in them). So it's not just the unit's ability to dump water out of the loop, but also the ability to stay on the loop safely without risk of a caustic hit.

There's plenty of ways to flood a rebreather. I've done most of them. Getting the mouthpiece knocked out of your mouth, mouthpiece separating from the DSV/BOV (either completely or just enough to cause water ingress), torn/delaminated counterlung, OPV sticking open/pulling out of the counterlung, improper assembly, etc. Many of these are minor annoyances on most units as A) they are easy to notice right away when you hear the gurgle or WOB increases, and B) they don't result in a slug of caustic as the first indication there is a problem.

Most units that are advertised as being able to "de-water" are able to "mostly" de-water. meaning you can recover from a massive flood and get back on the loop, but there will still be an annoying gurgle.

Why is it important? Options (and not aspirating caustic fluid, of course). Yes, carrying adequate bailout is important, but is not always an option. CCR dives are often done in harsh environments where if **** happens and you get hung up, a planned 3 hour dive can quickly turn into 5 or 6. It's hard to plan for that much reserve gas. Knowing you can get back on the loop gives you not only options, but peace of mind. When you're stuck in a restriction 300' deep, it could likely mean the difference between rushing and making things worse, or realizing you're just going to have a long day, settling down, and solving the problem.

 

[Akimbo]

What I would like to know is what ways a CCR can get water in it, that make dewatering important?

It can get REALLY heavy and jettisoning it is a pretty expensive option. Allowing it to flood enough to soak sensors isn't cheap either. That's reason enough to master dewatering even if it's already a caustic cocktail.

 

[stuartv]

My wife recently closed her ADV for some reason on a rapid descent on dpvs. It caused the diaphragm of the adv to suck down hard and get a rip in it. It caused a severe flood. Our units are very very flood tolerant. She had probably a little less than half a gallon in there and could still breathe (though the WOB went up like crazy) and also didn't get a caustic. After the dive when we opened the loop you could taste the very early starts of a caustic but her body position was head up and head down at times exiting the cave. She obviously bailed out to her bov since there was no caustic taste in the reg at that point. There's no way to really dewater when that happens, but I would say that flood tolerance is exceptionally high on my list of things I want out of a unit. Though she had to bail out, she had time to think and figure out what was happening and act appropriately. Our units allow you to dewater the counterlung, but obviously with that much water in the can there's no way to get it out.

First, I'm glad to hear that y'all got out safely!

Second, I'm unclear on when she bailed to BOV and what prompted her to do so.

Third, she did not get a caustic. But, if she had not bailed, is there some way that she COULD have? I.e. if she had still been on the loop after getting all that water in there, is there some maneuver she might have done underwater that would/could have resulted in getting a caustic? Some series of head up/down, roll to one side or the other, etc, that would/could have channeled some caustic through the system and into her mouth?

Fourth, I think this example is one that is not example of what I'm looking for. I.e. it's not an example where an ability to de-water was particularly important. Her flood was the result of something that meant the dive was over, regardless, right?

 

[stuartv]

Usually "dewatering" and "water tolerance" go hand in hand (the units on the market that do not have flood recovery are also very high risk of caustic hit with minimal water in them). So it's not just the unit's ability to dump water out of the loop, but also the ability to stay on the loop safely without risk of a caustic hit.

There's plenty of ways to flood a rebreather. I've done most of them. Getting the mouthpiece knocked out of your mouth, mouthpiece separating from the DSV/BOV (either completely or just enough to cause water ingress), torn/delaminated counterlung, OPV sticking open/pulling out of the counterlung, improper assembly, etc. Many of these are minor annoyances on most units as A) they are easy to notice right away when you hear the gurgle or WOB increases, and B) they don't result in a slug of caustic as the first indication there is a problem.

Most units that are advertised as being able to "de-water" are able to "mostly" de-water. meaning you can recover from a massive flood and get back on the loop, but there will still be an annoying gurgle.

I'm trying to distill out a list of specifics cases where being able to de-water is genuinely useful. You mentioned:

- Mouthpiece out of mouth. I think I would include all those examples under the same heading I already mentioned. "DSV out without closing it"
- improper assembly. I also mentioned that in my initial list.

Those are cases where being able to de-water could be useful.

Torn CL, and OPV sticking or pulling out of CL seem like examples where de-watering is not that useful. I.e. in those cases, the dive is over, right?

As for "flood tolerance", that is not a subject I thought about when I wrote my OP, but it is definitely worthy of thought.

So, how do you quantify or at least rate flood tolerance? Amount of water the loop will hold before it affects the sensors? Amount of water before it creates a caustic solution? Amount of water before WOB is affected by some (pick a number) percentage? Those all seem rather simplistic.

And then how do you factor changes in trim/pitch/yaw into the evaluation of flood tolerance? What if 1 unit can hold 4 liters of water with no effect on sensors or WOB, and no caustic, but only if you stay within +/- 10 degrees of horizontal trim. But, another unit can only hold 1 liter of water, but it will hold that with no negative effects, no matter how the diver orients him/herself? Which one is "more flood tolerant"?

This seems a bit like evaluating motorcycle helmets. One might cushion you more in a 5 MPH impact, but split open and give no protection at 20 MPH, while another will give less cushion at 5 MPH, but stay together and still give very useful protection at 20. Which one is "safer"?

Why is it important? Options (and not aspirating caustic fluid, of course). Yes, carrying adequate bailout is important, but is not always an option. CCR dives are often done in harsh environments where if **** happens and you get hung up, a planned 3 hour dive can quickly turn into 5 or 6. It's hard to plan for that much reserve gas. Knowing you can get back on the loop gives you not only options, but peace of mind. When you're stuck in a restriction 300' deep, it could likely mean the difference between rushing and making things worse, or realizing you're just going to have a long day, settling down, and solving the problem.

I'm not sure if this is what you intended, but it sounds like you're saying that it is normal and acceptable to you to do dives where you know you don't have adequate bail out. I mean, you said "carrying adequate bailout is important, but is not always an option". I think what you are really saying here is that **** can happen to totally blow your dive plan, in a way that keeps you in the water much longer than planned and that is where being on a CCR can save your life, where being on OC would mean you would die.

But, for that example, at what point does our technical diving mantra of "we only plan for 1 failure" become a factor. I mean, what you're saying is that you could have a (recoverable) loop flood AND get stuck in a cave at the same time. Doesn't that just start us down the path of planning our way out of ever diving?

 

[stuartv]

It can get REALLY heavy and jettisoning it is a pretty expensive option. Allowing it to flood enough to soak sensors isn't cheap either. That's reason enough to master dewatering even if it's already a caustic cocktail.

If a unit floods that completely, how likely is it that will be able to de-water it and it not just flood again immediately?

Which really seems like I'm asking my original question again. How could it get so much water in it that it becomes REALLY heavy, and you be able to get the water out? I mean, it seems unlikely to flood THAT completely just from taking the DSV out without closing it. If you rip open a breathing hose or blow out a CL, de-watering it is pointless, right?

 

[PfcAJ]

I'm trying to distill out a list of specifics cases where being able to de-water is genuinely useful. You mentioned:

- Mouthpiece out of mouth. I think I would include all those examples under the same heading I already mentioned. "DSV out without closing it"
- improper assembly. I also mentioned that in my initial list.

Those are cases where being able to de-water could be useful.

Torn CL, and OPV sticking or pulling out of CL seem like examples where de-watering is not that useful. I.e. in those cases, the dive is over, right?

As for "flood tolerance", that is not a subject I thought about when I wrote my OP, but it is definitely worthy of thought.

So, how do you quantify or at least rate flood tolerance? Amount of water the loop will hold before it affects the sensors? Amount of water before it creates a caustic solution? Amount of water before WOB is affected by some (pick a number) percentage? Those all seem rather simplistic.

And then how do you factor changes in trim/pitch/yaw into the evaluation of flood tolerance? What if 1 unit can hold 4 liters of water with no effect on sensors or WOB, and no caustic, but only if you stay within +/- 10 degrees of horizontal trim. But, another unit can only hold 1 liter of water, but it will hold that with no negative effects, no matter how the diver orients him/herself? Which one is "more flood tolerant"?

This seems a bit like evaluating motorcycle helmets. One might cushion you more in a 5 MPH impact, but split open and give no protection at 20 MPH, while another will give less cushion at 5 MPH, but stay together and still give very useful protection at 20. Which one is "safer"?



I'm not sure if this is what you intended, but it sounds like you're saying that it is normal and acceptable to you to do dives where you know you don't have adequate bail out. I mean, you said "carrying adequate bailout is important, but is not always an option". I think what you are really saying here is that **** can happen to totally blow your dive plan, in a way that keeps you in the water much longer than planned and that is where being on a CCR can save your life, where being on OC would mean you would die.

But, for that example, at what point does our technical diving mantra of "we only plan for 1 failure" become a factor. I mean, what you're saying is that you could have a (recoverable) loop flood AND get stuck in a cave at the same time. Doesn't that just start us down the path of planning our way out of ever diving?

Getting stuck on a deep dive can invalidate just about any bailout plan.

A flooded RB that you can't recover FORCES you onto open circuit, and from that point on a serious delay (or even a modest one) = death. Staying on the breather affords you time to solve your immediate problems, and that's really one of the big advantages a rebreather has.

 

[kierentec]

I'm trying to distill out a list of specifics cases where being able to de-water is genuinely useful. You mentioned:

- Mouthpiece out of mouth. I think I would include all those examples under the same heading I already mentioned. "DSV out without closing it"
- improper assembly. I also mentioned that in my initial list.

Those are cases where being able to de-water could be useful.

Torn CL, and OPV sticking or pulling out of CL seem like examples where de-watering is not that useful. I.e. in those cases, the dive is over, right?

Depends on exactly what type of failure and which counterlung it happens on (reference Leon's "meg destruction" video from years ago). Most "water tolerant" units can suffer from catastrophic CL failure on the exhale lung if it's in the right spot (delamination or OPV failure). I've recovered from a complete OPV failure twice (once the OPV got jammed open, the other the OPV came off in my hand and I was able to re-instal it). Both instances I continued the dive after clearing the water out.

So, how do you quantify or at least rate flood tolerance? Amount of water the loop will hold before it affects the sensors? Amount of water before it creates a caustic solution? Amount of water before WOB is affected by some (pick a number) percentage? Those all seem rather simplistic.

And then how do you factor changes in trim/pitch/yaw into the evaluation of flood tolerance? What if 1 unit can hold 4 liters of water with no effect on sensors or WOB, and no caustic, but only if you stay within +/- 10 degrees of horizontal trim. But, another unit can only hold 1 liter of water, but it will hold that with no negative effects, no matter how the diver orients him/herself? Which one is "more flood tolerant"?

You're probably looking for more specific information here than will be available. However, there are loop designs that are inherently more tolerant to the failures mentioned above (the likely causes of water ingress which are recoverable), which flood the exhale side of the loop. In these scenarios on these units, the water is trapped in the exhalation counterlung and it is very difficult to migrate to the inhalation side of the loop. Keeping sorb and cells dry. Units which are inherently NOT water tolerant are those which use the scrubber itself as a water trap, or those which force water from the exhale lung through the scrubber and to the inhalation side when the CL collapses.

I'm not sure if this is what you intended, but it sounds like you're saying that it is normal and acceptable to you to do dives where you know you don't have adequate bail out. I mean, you said "carrying adequate bailout is important, but is not always an option". I think what you are really saying here is that **** can happen to totally blow your dive plan, in a way that keeps you in the water much longer than planned and that is where being on a CCR can save your life, where being on OC would mean you would die.

Right, I said it's not always possible to carry enough bailout, because you don't always know how long you'll be in the water.

At 300' every minute on the bottom is about 10 minutes of deco. When we start looking at dives in that range, we need to go into them with the assumption that if things get really dicey and we are hung up on the bottom for an extended period, there might not be enough OC gas to get us out. So we dive rebreathers which are fault-tolerant and have the ability to remain on the loop in all but VERY few failure modes (like a completely torn loop hose).

But, for that example, at what point does our technical diving mantra of "we only plan for 1 failure" become a factor. I mean, what you're saying is that you could have a (recoverable) loop flood AND get stuck in a cave at the same time. Doesn't that just start us down the path of planning our way out of ever diving?

That is not a mantra I believe in or teach. You plan for the most likely cascade of events. Like, a failure delaying your exit.

 

[Dsix36]

Flood tolerance is also extremely relevant to WHERE the leak is coming from. This can also make a big difference in the effectiveness of dewatering the unit. Almost any unit incorporating "T" pieces for the counterlung connections will offer better chances for both tolerence and recovery, but it still depends on where the leak is at.