Are rebreathers getting safer over time?

[The Chairman]

Is this user risk perception bias? Of course.

Like many subjects about diving, there are far more emotions presented as facts and not mere opinions. It's like having a discussion about GMOs with normally sane people and that's on both sides of the question. Are they safer? Certainly in my own mind. Many small improvements have contributed to a general improvement not only in the gear, but also in the training and end user expectations.

 

[kr2y5]

I have purposely stayed away from this whole discussion. But I find the whole "more technology is better" and "digital is safer than analog" type of arguments ridiculous. The weakest part of any rebreather always has been and always will be the nut behind the mouthpiece. No amount of technology can or should change that because it only substitutes one type of false reliance with another. Or to put it as usually stated, "nothing is idiot proof to a sufficiently talented idiot."

Well, this is actually the core aspect of the discussion that intrigues me, and that I've been trying to get at... if the system as a whole consists of components X and Y (X = the rebreather, Y = the diver connected to it), and component Y, as everyone on this thread admits, is that weak link (e.g., Y barely has enough bandwidth to process information coming from X without getting considerably task-loaded), then at least in theory, it makes good sense to reduce stress on Y, and have X do more of the work...

Perhaps in practice, it doesn't work this way... the reason I ask is so that I can better understand why.

It has been asserted on multiple occasions, but I never really heard a complete argument why the diver absolutely MUST be aware of all the information thrown at them, and why, as you say, it is ridiculous to even consider the possibility of relying on better technology to offload that admittedly weak link.

The only thing that comes to mind is that, those who are extremely experienced on rebreathers, just don't see the task loading as a problem in practice for someone who's sufficiently well trained, because their own experience tells them it works well enough. Still, maybe there's some inherent bias in thinking this way...

So, restating the question... is it really an absolute hard requirement for the diver to manually keep track of all the parameters (e.g., all individual sensor outputs, and so on)? If so, why?

 

[kensuf]

Eleven topics summarized. No HCI.

The field of human/machine interaction — human factors — never seems to get any serious attention in rebreather design threads. The closest we usually come is griping about task loading.

Yes, the machine assigns us homework. But why must the human perform so many tasks?


Imagine an ideal rebreather that comes with a single LED in the HUD. When it is green, you can dive without worry.

When the LED turns red, you must stop whatever else you are doing, close the dive/surface valve manually to prevent water from entering, spit out the mouthpiece, and then begin breathing from your bailout open circuit reg. If you do these steps correctly, you safety is assured.

So, the imaginary ideal rebreather has one indicator, and that thing has two states: green or red. Yet somehow we still have a four item ordered list of actions to perform in the event that the green LED changes to red. One single transition, four actions to perform, in order.

Here are the LED indicator states for the new CCR Liberty, built in the Czech Republic. It is an actual unit that you can purchase and dive right now. As you can see, it has more than one LED, and those LEDs can indicate many states.

View attachment 209103


Imagine we add a second LED to our hypothetical HUD.

Suppose you are in the middle of performing one set of required actions for the first indicator, and you see the other indicator change color. Now you need to consider two courses of action. Can you safely interleave the two chains of steps? How do you determine the correct order of operations?

When you receive multiple inputs from the monitoring hardware, how can you determine for certain what exactly your next action should be?

I spent some time playing with the JJ HUD on Friday and came to the same conclusion that a simple "green - go" / "red - no go" system would be so much simpler.

 

[descent]

So, ... is it really an absolute hard requirement for the diver to manually keep track of all the parameters (e.g., all individual sensor outputs, and so on)? If so, why?

Absolutely required? No, of course not.

For many decades, spearfisherman and military divers got lots of work done using simple oxygen rebreathers. Until recently, those systems had no sensors of any kind. The gas mix was described by myth and folklore.

For the same definition of 'recently', the huge majority of passenger cars needed reconfiguration during operation. All experienced drivers knew how to manually rearrange the gear ratios in the transmission while the vehicle was in motion. Many motorists found this complexity overwhelming, especially in dynamic situations: dense mixed traffic, snow & ice, the dreaded hill.

Can you drive a stick? Do you prefer it?

 

[TSandM]

I do prefer a stick . . . always have, still do, even though I drive an automatic.

It's interesting to me that, despite the fact that it's clear a lot of RB accidents are user error, and the diver is the weak link, most of the folks I know who have been diving RBs safely for a long time have opted for a RB which is as manual as possible. It's a clear lack of trust of electronics and computer processing of information, despite the fact that most of the complex machines we operate nowadays are heavily managed by computer systems (admittedly, not underwater!).

 

[PfcAJ]

I do prefer a stick . . . always have, still do, even though I drive an automatic.

It's interesting to me that, despite the fact that it's clear a lot of RB accidents are user error, and the diver is the weak link, most of the folks I know who have been diving RBs safely for a long time have opted for a RB which is as manual as possible. It's a clear lack of trust of electronics and computer processing of information, despite the fact that most of the complex machines we operate nowadays are heavily managed by computer systems (admittedly, not underwater!).

This is exactly why I went the pSCR route. Zero electronics, same procedures as OC.

 

[Akimbo]

… So, restating the question... is it really an absolute hard requirement for the diver to manually keep track of all the parameters (e.g., all individual sensor outputs, and so on)? If so, why?

Although I agree with descent, I think there are other factors at play. First is liability. The White Star Line learned more than a century ago it isn’t prudent to promote an unsinkable ship. Advertising and/or training divers that they don’t need to manually track/monitor their rebreather is a good way to give your company to a plaintiff. Second is the installed base of rebreather divers who have been trained for years to monitor everything and to doubt their systems.

 

[kafkaland]

What's the deal with the lack of innovation when it comes to O2 sensors? With the rapid improvement in integrated optics (fiber lasers etc.) over the last two decades one would think that some robust spectroscopic scheme to analyze gas content that doesn't rely on archaic fuel cells would be developed by now. Is it just the relatively small market that scares of any serious development, or are there other barriers?

 

[Akimbo]

What's the deal with the lack of innovation when it comes to O2 sensors?...

There's a much bigger market for a gas chromatograph on a chip (so to speak) than rebreathers.

 

[kwinter]

So, restating the question... is it really an absolute hard requirement for the diver to manually keep track of all the parameters (e.g., all individual sensor outputs, and so on)? If so, why?

You fly on a commercial airliner. I think you want a pilot that is not only paying attention to all the automated systems, but is trained, skilled and experienced enough to know when those systems are failing and what to do about it. Or to take another old adage from the aviation industry, "those who insist on flying by black boxes are destined to be buried in one."

What's the deal with the lack of innovation when it comes to O2 sensors? With the rapid improvement in integrated optics (fiber lasers etc.) over the last two decades one would think that some robust spectroscopic scheme to analyze gas content that doesn't rely on archaic fuel cells would be developed by now. Is it just the relatively small market that scares of any serious development, or are there other barriers?

SeaBear has been testing a prototype solid state sensor in their rebreather for a while. They are very hush hush about it, so I wouldn't expect anything for a few more years.


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