Rebreathers

[Shotmaster]

Open circuit problems make themselves known, rebreather problems are silent killers. Big difference. Like I said, if you want to play astronaut, be my guest, until the sensors become fool proof, I won't be diving one.

 

[PfcAJ]

Depends I have had a regulator fail at 100ft, air stopped flowing. That tank was lost, I had another tank and was able to breath off of it, but due to a faulty second stage I could receive no air from that tank and my dive is significantly shorter. Say I had an complete failure in my O2 reg where no gas would flow from that. I can still breath off my dil and I have hoses on my bail out. I still have working scrubbers so though I will still have to abort a dive I still have the same amount of time to deal with getting out of an overhead environment, deco, and what ever else I need. Now back to the diligent diver when the 2nd stage failed it was very apparent, breath in and nothing comes out. An O2 failure requires the rebreather diver to watch his PPO2 to see there is a problem. Rebreathers do add complexity to a dive, but they do give more options as well. It is about mitigating what the risks are that pose the biggest problems. If I am only going 70 or 80 feet for an hour a rebreather may not be the best tool, I am adding complexity to a dive that does not require it. If I am doing a 200ft trimix dive to penetrate a large ship to get to a specific room something like a 2nd stage reg failure would be a much bigger problem open circuit than on a rebreather. In that example if the rebreather completely fails then I am still an open circuit diver. Still a problem on a rebreather will sneak up on you and catch you off guard if you are careless or not diligent.

See this is exactly what I'm talking about.

Two sentences in and you've described a dive with what appears to be two failures of oc regulators on the same dive. And we're having a conversation about being diligent with gear?

 

[abscuba]

There is nothing fool proof. I fly multi million dollar aircraft and things have happened that when I landed engineers said "aren't supposed to happen". Just like flying diving is dangerous and there is no way to change that. The rebreather diver who expects the computer and cells to keep him alive is a fool, but the diver thinks her is perfectly safe OC will meet the same fate. There is no life support on the planet that is fool proof its not possible to happen something will always happen. On top of that the more you push the limits of what has been done the more unexpected problems can occur. CCR is not the answer for everything often it add way more complexity to out weigh the benefits of it. How ever as you push deeper and go to more places its nice to have 6 hours to solve many problems outside of a complete rebreather failure. Then I am still where I am when I put a set of doubles on and dive open circuit. It is a tool in my tool box some times I use it other times I throw my tanks on and go OC. The best way to be safe is to be well trained, know the equipment you are using be it open circuit or ccr, plan your dive, and dive your plan.

 

[abscuba]

The failure of the 2nd stage was improper milling of the center shaft in the 2nd stage reg. The reg ended up getting replaced by apex. Failures will happen no matter what you dive.

 

[Shotmaster]

There is nothing fool proof. I fly multi million dollar aircraft and things have happened that when I landed engineers said "aren't supposed to happen". Just like flying diving is dangerous and there is no way to change that. The rebreather diver who expects the computer and cells to keep him alive is a fool, but the diver thinks her is perfectly safe OC will meet the same fate. There is no life support on the planet that is fool proof its not possible to happen something will always happen. On top of that the more you push the limits of what has been done the more unexpected problems can occur. CCR is not the answer for everything often it add way more complexity to out weigh the benefits of it. How ever as you push deeper and go to more places its nice to have 6 hours to solve many problems outside of a complete rebreather failure. Then I am still where I am when I put a set of doubles on and dive open circuit. It is a tool in my tool box some times I use it other times I throw my tanks on and go OC. The best way to be safe is to be well trained, know the equipment you are using be it open circuit or ccr, plan your dive, and dive your plan.

Yea, except the billions of miles flown per accident ratio is very different than the rediculously high death rate for rebreathers. If planes had the same death rate, nobody would be flying.

 

[abscuba]

Aviation is in a different place in its history than diving is. It takes substantially more training to become a pilot then a diver. It takes us a year to teach a person to fly when it is their only job that is because we teach them to fly the aircraft when all the systems that help them fail. How many diver deaths would there be if you needed 60 hours under water just to become an open water diver. To become a rebreather diver would be the equivalent of an ATP rated pilot equating to years of experience and training and an understanding that no matter what aircraft you are flying if you let it it will kill you. The dive community could learn a lot from the aviation community we had a rocky start and our rules are written in the blood because those before us found out the hard way that things fail and the only way to stay alive in the air is to be a good pilot. Even with all the training in aviation many people lose their life every year there is no fool proof way to keep things from failing. There was a point when planes had an even higher death rate than rebreathers will ever know it is in our past and we have learned how to mitigate the risks.

 

[Shotmaster]

Yea, aviation had a higher death rate when the Germans were shooting them down! As far training goes, when I went training for cert it was a lot more than 60 hours, and you had to demonstrate water skills and physically endurance during the first pool day or they told you to come back when you could. Which is a far cry from where it is today with 65 year old grandma's getting certified via the internet. I dont think rebreather training is sufficient either. My opinion about the current sensor failure rate is not going to change, all the training in the world will not change that. Posiedon is rumored to have a new sensor and is being tested by the Navy. I wish them luck with that, it might change things.

 

[abscuba]

O2 sensors are finicky, I will def not argue with that. My wife and I both dive rEvos each has 5 cells. It is not uncommon for one to be out to lunch. This goes back to the diligent diver, I do linearity checks on each unit, I put a new cell in every 4 months to ensure non are from the same batch. The unit has a great deal of redundancy with that many cells often to almost over kill. If in doubt a dill flush will identify a bad cell, and if not enough bail out to OC. That won't solve every problem and the is always the chance that 2 cells can go bad on the controller and it will dump O2 in the system when the controller thinks the good cell is bad due to voting logic. With rebreathers you have to pay attention every time that solenoid fires should be expected. If you hear that sound and you weren't expecting it should be a wakeup call. I am personally not a fan of the mrk 6 or 7 rebreathers, but I am excited about the solid state O2 cells and hope the technology progresses. And for the aviation part I am a flight instructor for naval aviators, during WW2 just in the great lakes when aviators were learning to land on an aircraft carrier they had 2 crashes a week. We as aviators have learned a lot since then and now we can teach some one to land on the boat and will have boats go years with out an accident. I do agree rebreather training should be more in-depth, all dive training should teach more. If we would put more into teaching operational risk management and pushing more experienced divers to mentor younger divers we would see a significant reduction in accidents both ccr and OC.

 

[PfcAJ]

Again with the diligent diver but it's not uncommon to have 1/10 of the cells between you and your wife "out to lunch."

Good grief.

 

[abscuba]

1/10th is a pretty good average, but long as it happens while the unit is on the work bench and not underwater its an easy fix. When it happens underwater dill flush is what shows the bad cell and there are 4 others giving you info. The unit only requires 2 to manually fly if the other 3 fail. We practice drills, plan our dives and always have ample bail out for the given dive we are doing. No it is not risk free, but we put a lot of time and effort into mitigating the risks. If everything goes wrong and both units fail we still have our OC units. We were OC tech divers before we moved to CCR and we still keep those skills current. I have only ever missed one dive because I had a failure in my unit before a dive and a hose burst one closed checks. It happened on the surface and I had OC gear so I was able to do a shorter dive. We plan the dive and dive the plan this includes building, closed, and pre-jump checks that included checkin millivolts to find the cells that might be out to lunch or in the one missed dive case the microcline that burst any issues that might arise. CCRs are less forgiving to negligence or skipping check list. We spend a lot of time deep 200+ and we spend a lot of time in wrecks which is why we are usually on CCR it is the best tool for what we are doing. There are exceptions, I have had to go to my side mount set more than once to fit through a port hole or door way that was to small for even a rEvo.