Two divers critical - Hawaii

[Landlocked123]

Hopefully, as his wife stated, this can help other folks on rebreathers so we dont lose another good person to an accident. The only thing I would say is that it sounds like he died doing what he loved. There has to be some meaning in that at least. RIP.

 

[John the Pom]

I don’t think there are any issues with the Liberty here. I think it’s warning capabilities are better than every other rebreather I’ve encountered except maybe one. The Liberty or the folks at Dive Soft are not the ones to blame for this one. There’s are very precise things that must happen in order to dive. Failure to follow those procedures ends in death.
Where do we draw the line... When CCR detects that it’s removed from the trunk a computer signals a servo that opens the valve on the O2? Who turns on that computer that fires that servo? What computer tells you to fill the oxygen bottle? LOL.... Oh wait, your first and primary computer, your brain.

As I understand it, engineering of safety-critical systems is based on acknowledging human error as part of the system. In other words, you can have all the check lists, safety warning signs, and training you want, but it is 100% certain that people will still make mistakes, and ideally you want to engineer systems so that those mistakes will be caught before they lead to injury or death. That engineering approach is why for example air transport is so incredibly safe.

I'm just an old-time O/C SCUBA diver, and my most adventurous diving was wreck diving to 50 m on independent twin air tanks on Navy tables, but reading many of these accounts it seems to me that recreational CCR diving is still in the Stone Age when it comes to safety.

 

[Superlyte27]

but reading many of these accounts it seems to me that recreational CCR diving is still in the Stone Age when it comes to safety.

It’s really not.
Honestly man, a CCR removes so many possible fatalities. Get lost in a cave, lost a buddy, lost a line, total silt out, tied yourself in the reel, cave collapse, scooter dead, etc etc etc, the CCR gives you time to resolve all of it.

I tell my students: A CCR resolves 17 possible perils to cave diving, and introduces 3. Too much Oxygen, Too little oxygen or Too much CO2. That’s it.

CCRs are just like cave diving. In cave diving there’s 5 rules. You obey all 5 rules, you get to live every single time (unless you’re Parker). A rebreather is the same thing, except there are a few more rules to follow. The biggest of which is: Turn on your fuggin Oxygen and Computer

 

[JahJahwarrior]

I wouldn't call it the stone age...if the main mistake was failure to open a tank valve, there is no technology to catch that mistake on open circuit either. You have to do a breathe test in both cases.

I do wonder how difficult/expensive/functional it would be to have a gas flow sensor, so you could confirm using the computer that both o2 and dil gasses are flowing, which could alert you to a closed valve.

So often, we divers don't want anyone on the boat touching valves, but what if you had a DM confirm that they also believed all valves were open before you get in? I wonder if that would result in cases where a DM closes a valve on accident?

 

[doctormike]

Real tragedy. I don't dive a re breather but I am assuming when you are at the surface waiting for others you have inflated your BC and are positively buoyant. When he went unconscious would he not have floated at the top? what caused him to go down? If he was waiting for the other students and instructor then I don't see how he sank to the bottom unless he had already initiated the descent. So sad.

Rebreathers have a large interior gas space - the "loop", which includes the breathing hoses and mouthpiece, the counterlungs and the canister that contains the scrubber. A diver would be positively buoyant at the surface with gas in the wing (not part of the loop).

Normally, if a diver on the surface takes the mouthpiece out of their mouth, they close the "dive/surface valve" so that no water can get into the loop. If the diver loses consciousness on the surface, the mouthpiece would fall out of their mouth with the DSV open, and the entire loop would flood, making it very negative, and causing the diver to sink. This is a well known scenario in rebreather accidents.

 

[Superlyte27]

Rebreathers have a large interior gas space - the "loop", which includes the breathing hoses and mouthpiece, the counterlungs and the canister that contains the scrubber. A diver would be positively buoyant at the surface with gas in the wing (not part of the loop).

Normally, if a diver on the surface takes the mouthpiece out of their mouth, they close the "dive/surface valve" so that no water can get into the loop. If the diver loses consciousness on the surface, the mouthpiece would fall out of their mouth with the DSV open, and the entire loop would flood, making it very negative, and causing the diver to sink. This is a well known scenario in rebreather accidents.

Well, it’s also documented by Dive Soft’s findings that the loop was flooded with salt water. So that makes sense. No oxygen, passes out, DSV falls out of mouth with loop open, fills with water and he sinks.

 

[telemonster]

I do wonder how difficult/expensive/functional it would be to have a gas flow sensor, so you could confirm using the computer that both o2 and dil gasses are flowing, which could alert you to a closed valve.

I was thinking the same thing, but each way seems to add a lot more complexity breaking KISS rules.

I suppose the easiest way I can think of is to have a pressure sensor on the o2 hose between tank and solenoid, fire it quickly when splash detected and see if pressure drops a lot. But then what? It wouldn't have helped in this situation because the ppo2 has already been breathed down while on the boat (pre splash detector tripping.) The controllers weren't on so they weren't looking for low ppo2.

If the valves themselves could transmit their open/closed state that would be something, but now your tank valves need to have batteries to transmit data on HF radio frequencies or waterproof fischer-style connectors.

Maybe a fiber optic loop. That wouldn't be that complex to shoot LED or laser to the tank valve and look for it's return when valve open. No new off board electronics, but would need to read it on the control system. Slim chance of false "ok" status. Might be kind of physically fragile but wouldn't have to be.

As a "not a trained CCR diver yet" the whole o2-tank-off is related to so many incidents I would be paranoid of it being off pre-dive. I always make my oc buddies check their tank pre-dive due to knowledge of incidents of people on OC who jump in tank off then get in trouble.

I like elegant solutions and can't think of an elegant way to read the o2 or diluent cylinder valves easily.

What happens to your heart rate when you're about to pass out? Could this be detected? If so and the BOV is spring loaded/solenoid maybe that could be detected and then BOV fired into open circuit mode. Or controllers come online and see ppo2 too low to sustain life at current depth. That plus gag strap....

 

[Superlyte27]

You just fall asleep. No warning.
I don’t think we need to engineer a fix to forgetting to turn crap on. I think we need to overcome complacency.

 

[Shasta_man]

<<overcome complacency.>> So you're saying it's going to keep happening then. People forget to do things, large or small, all the time and that isn't going to change. The extent of my knowledge about CCR is what you just told me and I agree with your general point, but multiple people on this thread also said this was a common problem in rebreather accidents and it can drown you in 4 feet of water. Sounds like we are beyond testing whether people will always remember and need an engineering solution to this skills problem. Apparently you need to take the choice out of the users hands. Else we'll continue to see little innocent children losing their folks over simply forgetting something..

 

[Superlyte27]

That would be like engineering cars that don't speed.