Rebreather Discussion from Brockville Incident

[mathauck0814]

Is the "inability to dive it without a scrubber" really a necessary feature? If you're so stupid that you don't basically prep your unit and die, I say we're better off without you.

 

[gianaameri]

Is the "inability to dive it without a scrubber" really a necessary feature? If you're so stupid that you don't basically prep your unit and die, I say we're better off without you.

Have you ever forgotten your keys somewhere or your mobile in the car?

Is that being soooo stupid?

We all make mistakes. If a rebreather can be designed such that it is as easy to assemble as a SCUBA regulator, then you would remove the risk of getting a complex Checklist wrong (and die).

It is indeed a very useful safety feature.

Kevin Gurr (the leading design scientist) is one of the few manufacturers who has tried the hardest towards Functional Safety and actually delivered electronic rebreathers (sadly Functional Safety to EN14143:2003 cannot be achieved on rebreathers due to technological constraints).

 

[Superlyte27]

Is the "inability to dive it without a scrubber" really a necessary feature? If you're so stupid that you don't basically prep your unit and die, I say we're better off without you.

Dude, if YOU forget to put in a scrubber, and you die, this is CLEARLY the rebreathers fault.
HAHAHAHAHAHAHAHA!!! I hope you can read into my sarcasm.


-edit
Isn't it just as likely that I jump into the water and accidentally forget to attach the 1st stage reg to the tank on OC. Actually, truth be told, it's more likely. I've forgotten to attach a 1st stage to a tank after I removed the 1st stage to analyze gas content, however I've NEVER forgotten to put a scrubber in. You know why? Because that an item on my check list that got checked off with the blue dry erase market right after I put it the scrubber into my rEvo. The other reason is because I do a 5 minute pre-breathe and I know that I get a screaming headache without canisters in my rEvo during pre-breathe.

 

[gianaameri]

Dude, if YOU forget to put in a scrubber, and you die, this is CLEARLY the rebreathers fault.
HAHAHAHAHAHAHAHA!!! I hope you can read into my sarcasm.

No, it is the user fault.

Human Factor (i.e. Human Error).

"Functional Safety" for "life-support" equipment requires that human factors be taken into account in the design of the apparatus.

A rebreather is not a bicycle.

You fall off a bicycle, you scrape your knees.

Human Error or Machine Failure on a rebreather and you do not just scrape your knees - you are highly likely to pass-out and drown.

You are treating a rebreather as if it were a bicycle. It is "life-support" equipment (the "make a mistake and pass-out and die type").

---------- Post added July 12th, 2013 at 03:44 PM ----------

How many OC dives have you made? I've made less than 150 this year, but I can tell you that of those 150 there's been more than one failure. Dude, if you want to win an argument, you really gotta employ some common sense.

I have been diving OC since 1984.

I cannot recall ever witnessing a 1st and/or 2nd stage regulator failure in a buddy and never had one myself.

However,

a. On one occasion, on the first day of diving after a regulator was serviced, the Service Technician must have forgotten to tighten the LP inflator hose to the 1st stage port, and it started leaking during the dive.

b. On another occasion, the 2nd stage LP hose after a service was not tightened properly (only hand tightened) and the 2nd stage separated from the LP hose (40 bar of gas lost from an 18 liter cylinder in the time I closed the cylinder valve, fortunately this happened de-kitting at the end of a cave dive).

c. I had one button SPG explode (don't use any button SPGs any more).

d. I had a few minor leaks from the HP hose swivel a handful of times.

e. Received new from manufacturer an O2 1st stage supplying the rebreather solenoid with a slowly leaking HP seat.

Conversely, on rebreathers (diving rebreathers since 2006), I can confirm the failure rates I experienced are in the region of 5% to 35% in a year, depending on model, and some failures were life-threatening.

The USN report citing 5% failures ("The UBA failed in 4.9% of the 61 dives analyzed") on the best rebreather currently available is here:

http://www.dtic.mil/dtic/tr/fulltext/u2/a549996.pdf

 

[Larry7895]

Why don't rebreather a have full face masks or a way of securing the mouth piece. It seems to me if this were done and you did pass out, at least you may have a chance, especially if your buddy is alert? Or am barking completely up the wrong tree?

 

[nadwidny]

I have been diving OC since 1984.

I cannot recall ever witnessing a 1st and/or 2nd stage regulator failure in a buddy and never had one myself.

1980. Seen more than a few.

Just because you haven't seen it doesn't mean it doesn't happen.

---------- Post added July 12th, 2013 at 09:42 PM ----------

Why don't rebreather a have full face masks or a way of securing the mouth piece. It seems to me if this were done and you did pass out, at least you may have a chance, especially if your buddy is alert? Or am barking completely up the wrong tree?

Some people dive with FFM. I think it's stupid because it makes bailout ridiculously complicated.

The rEvo mouthpiece has a gag strap for mouthpiece retention. Others may but I don't know about them all.

 

[TSandM]

Well, Brian, if your team took better care of its gear . . .

 

[gianaameri]

Why don't rebreather a have full face masks or a way of securing the mouth piece. It seems to me if this were done and you did pass out, at least you may have a chance, especially if your buddy is alert? Or am barking completely up the wrong tree?

EN14143:2003 requires some form of protection for the mouthpiece like a Draeger (top company) mouth-strap or a FFM.

It is yet another requirement which manufacturers chose to ignore from their Checklist (the rebreather standard EN14143:2003).

FFM are complex, require training, and could cause more problems than they try to resolve.

Mouth-straps are useful and give your buddy a tiny/miniscule better chance to intervene if you go unconscious underwater, but "self-help" forget about it.

Go unconscious underwater and the odds are you drown. Recovering an unconscious diver and keeping him alive at the same time is nearly impossible.

Reality is that the solution is to avoid going unconscious, but anybody with experience and integrity will tell you that the rebreather technology is just not available yet to protect the diver from hypercapnia, hypoxia, and hyperoxia (certainly to a Probability of Failure which is acceptable in this modern world as we have with airplanes. ships, medical devices, cars...).

You can read more about it here:

Marketing Rebreathers | Diver Magazine

OC does have its risks, but it it safer and fully meets the EN250 standard without legal loopholes or trickery.

 

[nadwidny]

Well, Brian, if your team took better care of its gear . . .

Maintenance, shmaintenance. It's highly over-rated.

 

[Dr Simon Mitchell]

Hi, Claudia…

The one problem that you mention with the Fock paper is the phrase "fatality rates … ranging from one in ten users", implying that the authors are suggesting that the fatality rate for CCR is 10%. That sentence fragment is taken from the discussion section of the paper, where authors review the background literature about the topic at hand. It seems totally reasonable to set the stage by stating the range of previous conjecture in the discussion, since this is not actually used to support the conclusions of the paper. Their actual relative risk numbers are drawn from other published data.

THANK YOU. Not just "totally reasonable" but "normal scientific writing practice". It would appear that it is you who is much more familiar with critically appraising papers than the original poster.

I also know enough about study design to know that you would never be able to accurately answer the question about relative fatality rates, because of the very nature of the question. Your study would be tainted by inclusion bias, inadequate datasets and design issues. To accurately answer the question of relative risk of OC and CCR, and to screen out the dive profile variable, you would need to have matched cohorts of divers, randomly assigned to dive OC or CCR on matched dives, and you would need a VERY large number of dives to achieve statistical significance. Obviously, you can't do such a study. So we are stuck with a review of fatality databases and necessary assumptions, with all the unavoidable data reporting contamination. There will always be insufficient data to answer this question. But that doesn't mean that the paper is useless… Like any published paper, it doesn't exist in a vacuum, but is one piece of a larger puzzle.

And again, thank you. This paper is limited methodologically and is based on weak data (facts which the author freely admits), but it is the best data we currently have and, as you point out, are likely to have. The previous poster's suggestion that a randomized controlled trial is a pragmatic means of solving the question of relative safety of CCRs and OC is ludicrous. Under circumstances in which better data is unlikely to appear, papers like this do get published from time to time. It just needs to be interpreted in the context of all the caveats the author discusses.

Simon M



---------- Post added July 4th, 2013 at 11:51 PM ----------