Potential Safety Improvements in Rebreather Design

[gianaameri]

Reading that boring manual could be enlightening.

I'll do a cross-over course on the HP2.

In all likelihood I will learn something new and become a better diver and person.

It seems a machine with a lot of interesting features.

 

[boulderjohn]

John I get it.. I really do. Im busting your balls.

Sometimes you have to let the topic wander a bit to prove someone's point though. The MEG/EVO/Inspo comments were in direct relation to the fact that any rebreather can be put together FUBAR.

Like I said, no hard feelings.

The problem we have on ScubaBoard is that there is a history of discussions of rebreather incidents wandering off to generic rebreather discussions and never returning. Moderators were thus on high alert as soon as this one started.

You know, some of the moderators were remarking lately about how easy the last few months have been. Almost nothing to do. I guess this is payback.

 

[Akimbo]

… A manufacturer can key the loop hoses so they can only be attached in the proper orientation but that doesn't stop me from cross threading them, leaving off an o-ring, or failing to tighten them down all the way. How is a manufacturer supposed to prevent someone from failing to screw down their loop hose all the way?...

Keyed quick disconnects would be a good start, expensive to do well though. Screwed connections with piston seals also work since it is harder for O-rings to fall out and you can feel reduced insertion force when they do.

We always pressure-tested rebreathers on the bench. Isn’t that included in all pre-dive procedures? They find a lot of errors and faults. All it takes is a shop-made manometer and a stop watch.

… The answer is the implementation of standardized assembly procedures via checklists that incorporate steps to verify proper assembly (i.e. step one: install loop, step two: negative check). Just like every CCR manufacturer already provides...

The root problem is complacency due to repetition and checklists don’t solve that without a lot of discipline and preferably somebody else looking on. It is not unique to rebreathers.

 

[Dr. Lecter]

I built my Prism 2 before I even put it on in the swimming pool. Granted, it took longer than it does now, and my instructor was keeping any eye on me, but I assembled it myself, and on every subsequent dive too.

Yeah, I tore apart and rebuilt and checked my revo about a month before my class (picked up a used unit) and wound up correcting a small leak at one of the loop attachment ports (the revo II uses Drager p-ports) that was causing it to fail a positive test. Then I got to build it from scratch under the relatively watchful eyes of my instructors a couple times before I ever so much as got in the pool with it, though the process of completely disassembling it to find and repair the leak before class was probably the most eye-opening education I received on how it works.

But if an instructor built a student's unit (ideally in front of the student) during class and then had the student pool dive it...I'd at least say there's an argument that the student isn't insane. I still wouldn't dive it myself, but there's at least an argument that it's within the scope of what a student can trust an instructor to do.

 

[Bailout]

Reading these post - very interesting. Why would anyone knowingly dive knowing the O2 sensors are not reading .21 on the surface - and how could it be calibrated ?I'm pretty sure if I crisscrossed my top hoses and put my Bov and loop upside down I could improperly assemble and i could put the counter lungs on backwards and put the O2 where the dil goes and vice versa. There's more but guys come on - we are supposed to be above average achievers I am assuming I am not alone when I say I spend hours getting ready for a dive and am 100 percent confident in my assembly and calibration Before Even a pre breath excercise never mind a splash

 

[Akimbo]

... Why would anyone knowingly dive knowing the O2 sensors are not reading .21 on the surface - and how could it be calibrated? …

Not sure about all the current models but it was very common on the second-gen eCCRs to calibrate sensors against a certified cal-gas (on deep sat dives), just like an O2 analyzer. Galvanic Oxygen sensors generate a very low-current voltage in proportion to the PPO2. Manufacturing tolerances and age cause them to vary a little so they rarely match perfectly or for long. You can manually calibrate sensors with small potentiometers or through software in the computer. The software option is much easier to use and automate.

 

[ScoobaChef]

That’s a pretty high bar given that we haven’t achieved that level of reliability on open circuit Scuba in the last 70 years.



A lot of work needs to be done on the whole sensor, electronics, and software system to make a significant impact. That represents a considerable amount of R&D which is hard to amortize over so few units.

Akimbo, I think you misunderstood me slightly. I DON'T believe that a breather could be built that is 100% foolproof no matter how much time and money is thrown at it. They've made planes that can fly themselves practically, but there's still a trained pilot at the controls watching.

the point I was making, rather simplistically, is that I'd rather see R+D focusing on making CCR less likely to kill you without warning as opposed to trying to make it not kill you at all.

Either way, Isn't making your gear is functioning and assembled correctly every divers responsibility? OC or CCR?

 

[Dr. Lecter]

I'd rather see R+D focusing on making CCR less likely to kill you without warning as opposed to trying to make it not kill you at all

This is a nice thought but as you admitted above, implementation gets tricky. I wouldn't dive a unit that forced me off the loop all by itself any time my O2 sensors voted for .15...that's just never going to be something I trust a machine to handle. Ditto for crap design improvements like vibrating HUDs and blinking buddy lights on the back of CCRs, which lead to false negative alarm complacency (no buzzing or light show does not mean everything's good).

I prefer to instead rely on carefully building and testing the unit, and then monitoring myself and the unit during the dive while verifying the what the instruments are telling me. That approach is easiest when the unit and its systems are simple, not overloaded with alarms and safeguards...which means that R&D focusing on making it less likely to kill me without warning is pretty much the same as making it less likely to kill me at all.

 

[gobfish1]

Low O2 and HIGH CO2 make you fall asleep (and there is no "happy ending" because high CO2 causes unpleasant and horrible psychosis, still looking for the link to the research).

For the uninitiated:

CO2: The rebreather incident

PCO2: The Dark Matter of Rebreather Diving | DIVER magazine

DO WATCH THIS: http://www.hse.gov.uk/diving/video/hse_diving_shell.swf

The crazy thing is that all these rebreather gurus could not find a solution, but I did in my garage long ago.

In any event, that is not enough.
Poor equipment and poor systems, procedures, and control inevitably lead to fatalities. The whole thing is f-up at the moment as exemplified by this fatality which demonstrates a whole chain of errors from design and manufacturing, to certification, to training, and to use and prior product delivery.

It don't get more f-up than this (take it from the guy who has two high power rifles recalled in the U.S., but not in the U.K.).

Yes seen the hse/gov video , and think its crap , lol bunch of duckeges in the water,
id like to see the units keyed so it v hard to feek it up ,
but some divers should not be diving a breather ,

someone said the lady dont,nt put her own breather togher , now iv seen this happen in my old diving club with man and wife teams , one all ways seem,s to take the lead , the man for the most part and the wife sits on her ar$e and lets him ,

as DO id split them up till both were good divers then and only then would i let them dive as a team ,
i dont mine guys helping girls lift / carry kit but it i see them setting ket up for them id give them a kick up tha ar$e ,
its bad for training good divers , if one of them allways takes the lead , as the uther just get lazy and stupid

 

[Akimbo]

Akimbo, I think you misunderstood me slightly. I DON'T believe that a breather could be built that is 100% foolproof no matter how much time and money is thrown at it…

Fair enough. The problem isn’t really a choice of where to put R&D money because the minute market size puts rebreather manufacturers at the mercy of outside technologies for breakthroughs. A reliable, robust, compact, and cost-effective CO2 sensor isn’t likely to be developed at a rebreather manufacturer. Same with a better CO2 absorbent (converter really) that resists channeling, has a much longer life per unit volume, is cost effective, and does not deliver a caustic cocktail when it get wet. Same with O2 sensors that don’t die with a few drops of salt water.

Sure, manufacturers can make electronics housings that are less likely to flood. But they can’t make a major rebreather flood recoverable with today’s technology. They also don’t have the resources to make the investments required to develop that kind of technology. If they did, they would probably get out of the rebreather business to sell the discovery to much larger industries.

What that leaves is incremental refinements which include usability and reliability. Sometimes they are one and the same. In any case I don’t think it is a situation where rebreather manufacturers are forced to make major compromises between reducing user errors and providing advance warning. They do their best to provide both within the market constraints that all businesses operate in.