How great is the risk (in your perception)?

[RainPilot]

Agreed

Disagree. There are some people who should never be allowed to use a CCR even though they may be very good OC divers, like I should not be allowed to ride motorcycles.

Others will be absolutely fine with them. Mindset and attitude play a much bigger part in safe CCR diving than in general OC diving.

 

[tbone1004]

@CAPTAIN SINBAD CCR is a very simple unit. It is actually more more simple than OC gear as a base unit.
The difference is OC is a passive experience, inhale-exhale-repeat as necessary. As long as you are breathing a gas that is safe at the depth you are at, there isn't a whole lot that can go wrong.
CCR is an active experience where you are continuously blending the gas mix and the mix changes all the time. That mixing process is what will kill you. It's not complex, it just requires active participation from the operator and that active participation is what is lacking in most people. @RainPilot 's example of hypoxia is just that

 

[KenGordon]

It sort of makes sense but leads one to conclude that CCR is an enormously complex unit requiring such a high level of expertise that even after getting all the training that is possible, most divers are still inadequately trained to the point where fatalities are significantly higher than OC.

The fact that deaths were a result of user error does not mean the technology is totally forgiven. It just means that CCR is user unfriendly to the point where the level of expertise required to stay alive on those things is beyond the capacity of most people certified to use it.

Agreed?

If that were true half the people diving them would be dead.

 

[Schwob]

...There are CCR Instructor Trainers that don't know how rebreathers work, many of them....

That right there sounds really scary... Most of the other stuff I can wrap my head around I think... That I really struggle with...

 

[tbone1004]

That right there sounds really scary... Most of the other stuff I can wrap my head around I think... That I really struggle with...

an important differentiation is understanding that just because you know how to work something doesn't mean you know how it works

Most of those instructors don't get that differentiation so they make it sound like it is more complex than it is to validate their teaching. Note, this is a horribly contentious subject, but it is what it is. I have no problem calling people out for it

 

[Schwob]

an important differentiation is understanding that just because you know how to work something doesn't mean you know how it works

Most of those instructors don't get that differentiation so they make it sound like it is more complex than it is to validate their teaching

Yep, I got that, that's why it's really scary.
My OW instructor could go through the mechanics of explaining simple dive physiology, but was obviously struggling with true understanding as he struggled with questions coming his way and precluded answers with "PADI teaches that..."

Somehow I naivley thought that goes away with the tech-folks... I thought it just has to be such that true understanding is "obligatory", otherwise if people just blindly follow recipies it's scary sh.t.

Based on what I am reading, I think it is scary...
On that level I sure don't want to deal with an instructor who does not truly know and understand why he's (she's) doing what he/she is doing..., should be doing could be doing, shall not do... and why along the entire dive, at any moment, due to any change, anticipated or at least prepared for for in case, ... or not... That at least is my naive kind of expectation for anything tech.
Fully prepared, full understanding, no surprises, period... Still needing to perfect a skill (things can always be more perfect) is OK, but being clueless in subject matter relevant to a save dive is not OK... not with me...

 

[CAPTAIN SINBAD]

@CAPTAIN SINBAD CCR is a very simple unit. It is actually more more simple than OC gear as a base unit.
The difference is OC is a passive experience, inhale-exhale-repeat as necessary. As long as you are breathing a gas that is safe at the depth you are at, there isn't a whole lot that can go wrong.
CCR is an active experience where you are continuously blending the gas mix and the mix changes all the time. That mixing process is what will kill you. It's not complex, it just requires active participation from the operator and that active participation is what is lacking in most people. @RainPilot 's example of hypoxia is just that

I understand that but let us just say that when it comes to CCR there are only two things that can kill you.

1) Equipment malfunction: This suggests that even if you do things 100% by the book you are still assuming a risk greater than open water. As someone switching from OC to rebreather you then have to make the decision that no matter how well trained you are or how well you understand the unit, the technology up until this point is inherently riskier.

2) User error: This suggests that the technology is not any more risky (or prone to malfunction) than open circuit but in the hands of humans it becomes riskier because it is less "monkey proof." Since more people have died using CCR (within the same depth parameters as OC) it should beg the question how come human, the same specie who is surviving OC with a higher success rate is not surviving CCR with the same success rate?

I totally understand the point that CCR is being used for more extreme dives so data collected from CCR accidents is reflective of the dive being riskier rather than the unit being less reliable (either due to point 1 or point 2) but we are now talking about CCR responsible for more fatalities within the 40 meter depth.

I am sure I am missing something in this conversation. As it progresses I will be able to nail what it is.

 

[tbone1004]

@CAPTAIN SINBAD your two points are a bit conflicting. The technology is not inherently riskier, it's just very different because it requires active participation vs. passive participation. The equipment malfunctions that happen in a rebreather aren't the ones that are going to kill you, it's how you react to those equipment malfunctions, if you even identify them that will determine whether you live or die. Failure to identify that there is an equipment malfunction is dangerous *see verifying current limit of O2 sensor above as well as adding the point of verifying linearity *most CCR instructors and quite a few instructor trainers don't understand cell linearity* and failure to identify an issue with the O2 sensor because it isn't functioning properly is going to off you.
This is especially important in eCCR's because there is a possibility that the voting logic will vote out the one good cell. Yes this has happened before, and I believe it has killed someone due to the unit going hyperoxic due to current limited cells being voted "in" and the one properly functioning cell being voted "out". In mCCR's or eCCR's when operated in parachute mode, it requires the diver to identify that the cells are not behaving properly and through dil flush and linearity verification of the mv's they have to determine which cell to trust, or to bailout to OC or SCR mode.

In OC we have to worry about freeflows and that's about it. In CCR they can still freeflow, but you add in the variables of gas mixing and the components used to check that the mix is right. Are they inherently more risky? The cells themselves are, but the rest of the unit isn't. The problems circle back to the grey matter between the ears and if that is functioning properly. Sadly it all too often doesn't

 

[KenGordon]

I understand that but let us just say that when it comes to CCR there are only two things that can kill you.

1) Equipment malfunction: This suggests that even if you do things 100% by the book you are still assuming a risk greater than open water. As someone switching from OC to rebreather you then have to make the decision that no matter how well trained you are or how well you understand the unit, the technology up until this point is inherently riskier.

2) User error: This suggests that the technology is not any more risky (or prone to malfunction) than open circuit but in the hands of humans it becomes riskier because it is less "monkey proof." Since more people have died using CCR (within the same depth parameters as OC) it should beg the question how come human, the same specie who is surviving OC with a higher success rate is not surviving CCR with the same success rate?

I totally understand the point that CCR is being used for more extreme dives so data collected from CCR accidents is reflective of the dive being riskier rather than the unit being less reliable (either due to point 1 or point 2) but we are now talking about CCR responsible for more fatalities within the 40 meter depth.

I am sure I am missing something in this conversation. As it progresses I will be able to nail what it is.

Ignoring unrelated medical events, all RB deaths are user error. The dives are planned such that if the unit failed at the worst possible time there is enough bailout gas to surface. If the user is unable to use that gas they failed to properly monitor the unit and so failed to bailout (or otherwise deal with the issue). Or perhaps the error was not taking adequate bailout.

Read the incident reports. Very often they reveal really shoddy behaviour.

BTW it sounds like you are treating the Fock paper as gospel. You should read it. He identifies issues with the data he used. Also this is a few years ago now.

 

[Johnoly]

How risky are rebreathers .

I'd love to be able to use one, but they are illegal for us spearos to use.