Doing Tech+Cave on a RB?

[lamont]

Here's some info on CCR design issues that I got off RBW:

http://www.deeplife.co.uk/files/How_Rebreathers_Kill_People.pdf
http://www.deeplife.co.uk/or_files/FMECA_OR_Faults_060807.pdf

 

[caveseeker7]

Yeah but you still rely on the electronics to tell you the ppO2.

There are quite some variations on how much electronics you need to rely on.
There are CCRs that use analog gauges that directly off the three sensors requiring no battery power or computers to monitor the pO2. And they have been around for over 30 years.

Vs. with a draeger or and RB80 if you've got the right mix and you hear the solenoid firing you can be pretty sure you're not on the verge of toxing

The Dräger (active gas addition) and RB80 (passive gas addition) are very different units in operation, size and price. In my opinion it is foolish to dive the Dräger without a pO2 monitor as the variations of the mix in the loop tend to be larger than on the RB80. Although in shallow water it has like problems.

Neither has a solenoid (electronic, battery powered valve) to add gas, so you won't hear it on either unit. The Dolphin has constant mass flow through orifices to be matched with a handfull of notrox mixes, the RB80 has dual manual injectors that are triggered via levers by the counterlung bottoming out. Those you should be able to hear unless your scooter makes a racket (and you will be using one if you're using the RB80 and DIR).

The "manual" method of changing setpoints by plugging in different gases seems like alot of switching to me.

There is no setpoint or changing setpoints on the RB80. There are gas switches as there are on OC, the RB80 solely extends the duration of diving for a given volume of gas.

Regarding scrubber life and/or failure that seems unavoidable. Although the Cis membranes can at least tolerate being wet (right?) without making a toxic cocktail.

Actually, the Cis had a waterproof membrane thus keeping the water from the absorbant. But a loop complete loop flood means you got water coming into your rig. A waterproof scrubber only solves that one problem. You'll still need to fix the leak and drain the the loop. What about the sensors, they were not protected by said membrane?

There are other, more likely problems that can occur causing hypercapnia. Channeling, malfunctioning one-way valves, that sort of thing. Including on SCRs, and the RB80. The ExtendAir cartridges all but eliminate channeling and caustic cocktails, by the way. Used in the Optima CCRs, and optional on Classic Inspo, Megs, Drägers and Azimuth.

A simple little one-way valve by the way failed on one of the RB80 clones, thus not dumping used or adding fresh gas. Fatal failure in what, less than 20 ft of water. Mind you, the guy was solo, IIRC on mix, and not particulary well trained. Goes right back to what MrX said about training and attitude. No rebreather (or dive gear for that matter) is fail safe. Never mind how good the design is.

 

[Mr.X]

My point is -- what if the HUD gives you bad info? The O2 sensor goes? With a CCR you are essentially reliant on a computer that can fail.

With OC, generally when something goes wrong you get a cloud of bubbles or no gas delivered -- very easy to tell. From my (very limited) understanding of the RB80 I think you get a similar thing (no pure O2 injected, fails to deliver gas if PPo2 too low?) The main failure mode that's hard to detect on the RB80 seems to be scrubber issue.

it seems to me that the CCR is inherently less safe than the other two methods (given current technology anyway), and no kind of "attitude" can really fix that.

Jeez...not to drag this out further. Have you ever tried a CCR with a HUD and independent controller - like the Meg just for the heck of it? Or a CIS? Boris? If everything dogs out on a dive you are remarkably unlucky, as would a guy in OC who cracks his manifold UW. Or catheter peels off. With CCR you revert to bailout procedures or semi-closed protocols.

Scrubber is not a huge issue with the RB 80. Unless you're doing major penetration/duration, the can has incredible duration since you are not asking it do to as much scrubbing as a CCR. Also, the RB dumps water as a natural part of it's venting function -very cool.

Again, I stress attitude is everything. Your current perspective is that CCR's are unsafe, or not where they should be. Mine is "whatever the job calls for". Given that range, I use the tool best suited/safest for the job and get the best training available. Simple as that.

x

 

[rjack321]

There are CCRs that use analog gauges that directly off the three sensors requiring no battery power or computers to monitor the pO2. And they have been around for over 30 years.

Help an RB noob out here what are these?

 

[limeyx]

Jeez...not to drag this out further. Have you ever tried a CCR with a HUD and independent controller - like the Meg just for the heck of it? Or a CIS? Boris? If everything dogs out on a dive you are remarkably unlucky, as would a guy in OC who cracks his manifold UW. Or catheter peels off. With CCR you revert to bailout procedures or semi-closed protocols.

Scrubber is not a huge issue with the RB 80. Unless you're doing major penetration/duration, the can has incredible duration since you are not asking it do to as much scrubbing as a CCR. Also, the RB dumps water as a natural part of it's venting function -very cool.

Again, I stress attitude is everything. Your current perspective is that CCR's are unsafe, or not where they should be. Mine is "whatever the job calls for". Given that range, I use the tool best suited/safest for the job and get the best training available. Simple as that.

x

No, I have not used a CCR in any form, and so I am just going by my understanding which may be inaccurate and/or incomplete.

I also do not do the kind of diving that requires any kind of rebreather. Such dives are way beyond my experience/training.

Generally I would always try to a dive on OC whenever possible, using a Rebreather as option of last resort.

However, here you find a lot of RB divers will use them on dives that are easily doable on OC. Obviously part of this is practice, training and building skills on the RB also.

My big concern (or one of) with CCR is that (from what I have heard/read) by the time you are able to detect a lot of the problems, you have already likely passed out or toxed (at least compared to open circuit or a SCR). However, that is obviously just based on what I have read/heard. I am by no means an expert on a CCR or SCR.

I still have plenty far to go before I would even consider any kind of rebreather, and I think that's a good thing, rather than considering a rebreather as something like a separate training path that once could embark on say right out of Open Water class.

 

[caveseeker7]

So you think the WKPP would have better results with less hassle on CCR-type rebreathers? Also, I believe GUE uses RB80's down to 400+ on OW wreck dives (Britannic, and S/S Maidan)

I for one don't think so. The RB80 (and probably some of the units "inspired" by it) are, IMHO, the best of their breed. Deep and long dives were the design goal, and the unit has succeded in that.

But it is by no means the only tool for the job. No matter if you look in the US, in Europe or elsewhere in the world, CCR have been used succesfully in cave and wreck exploration.

And how many "user errors" have to happen on CCR's before someone considers that maybe there is some kind of usability problem, or that *maybe* current CCR's are too dangerous for most divers who just are not able/willing to put in the time/money into gear, training and continual practice to be "safe"

And how many errors have to happen on OC before someone considers that there's a problem, or *maybe* current OC diving is too dangerous. Have a look in accident forums, plenty of OC accidents and sadly enough, fatalities.

To err is human, CCR divers are not immune to that.

My point is -- what if the HUD gives you bad info?

A good HUD lets you know there's a problem with the electronics, either way the gauges will let you know. The HUD is there to alert you to a problem (even multiple problems), the gauges need to be checked anyway.

The O2 sensor goes?

Use the other two, that's what tripple redundancy is for.

With a CCR you are essentially reliant on a computer that can fail.

As mentioned before, that depends very much on the CCR model.

For me the scary part of CCR is that the worst failure modes (Hypoxia, Hyperoxia) etc. can happen without the user of the unit really knowing about it or getting a reliable indication that it's happening. With OC (and from my understanding to an extent the RB80), you get some indication/prevention of those issues.

There are three sensors for tripple redundancy. Depending on the RB no electronics or power sources are needed to either monitor or verify them. If one or even two fail, the third can still be monitored and verified. A CCR can be used as a SCR if two or all fail, and last but not least there is OC bailout. How much of that is carried depends on the diver or team, same as on OC or SCR. What bailout volume do you use? One third? Separate tank(s)? So, carry the same third when using a CCR.

Don't get me wrong, there are a whole lot things that can go south on a rebreather. The more stuff is on it, the more can go wrong. But it also means that more often than not there is more time to solve problems, and more options to solve them.

The pO2 related problems worry me considerably less than CO2 in the loop.
While there is at least one working CO2 monitor, it hasn't found its way into civilian rebreathers. So there is still very little warning (solely the body's reaction, which varies from diver to diver and dive to dive) of hypercapnia. Even if the RB is working perfectly it can occur. Even on OC. Even freediving. CO2 is scary.

 

[caveseeker7]

Help an RB noob out here what are these?

Biomarinne CCR1000 since 1969, the military version of it is the MK15.
Later the MK15.5, both from various manufacturers like Rexnold, Carleton,
Innerspace, Steam Machines and still today Colkan in Australia (though the
latter come with a digital gauge these days I believe).

Also the Steam Machines PRISM Topaz, links to some info below.

http://www.therebreathersite.nl/sm1600.htm
http://www.rebreatherworld.com/prism-rebreather-articles/1972-prism-topaz.html

 

[caveseeker7]

However, here you find a lot of RB divers will use them on dives that are easily doable on OC. Obviously part of this is practice, training and building skills on the RB also.

Yes, I'm one of those. To be honest, practice, skills, proficiency are part of it and of course make a perfect excuse. But I started diving because I enjoy it. I started diving rebreathers because I enjoy it more. It did have the nice side effect that I appreciate OC (lil' 72 shorty on an alu bp) a bit more for its simplicity and streamlining ... still have more fun on a RB, though.

And if joy and fun qualifies as a reason to dive in the first place, IMHO it also qualifies as a reason to dive CC.
It does for me, anyway. But I certainly understand and respect people that think differently.

 

[rjack321]

I agree that CO2 is scary. But the thing that's scaring us OC tech divers off are design issues.

From the pdfs Lamont posted, last page...

Preventing the Deaths
1.Popular rebreathers are nowhere near the standard expected of other life critical systems.
2.No eCCR appears to meet EN61508, therefore none actually meet EN14143:2003. 3.Most manufacturers have no staff with formal training in the design of life critical systems.
4.Open review and adopting better safety systems could have prevented all of the incidents reported here.
5.Technologies are available that would have prevented every one of the incidents cited here, at reasonable cost
6.The fact is people are dying because equipment is designed badly, with inadequate safeguards.

Lack of safegaurds to prevent or mitigate human error being the biggest issue.

OC has some distinct benefits on maintaining ppO2s in a safe range or at least having a less than infinite capability to vary for a given depth. RBs appear to us (Limeyx and myself, RB noobs that we are) to have extra failure points / potential for an accident chain to start with the primary safeguard being only the operator, not the machine itself.

 

[jkaterenchuk]

First, I apologize in advance in case I sound stupid.

So, I was sort of thinking of skipping the whole doubles tech setup step for monetary reasons and go straight to a rebreather, then go on from there. I would have to buy my own doubles wing, manifold, backup reg, etc etc. Now this costs a lot of money, and since I'm planning to dive RB in the end run anyways, is there a way I could skip this and go straight to the RB and do courses from there?

I went directly from OC to eCCR. I used ANDI for my certification on the CCR. The first certification allows for only recreational diving...130ft max and no deco. You will need to get dive time on the unit before taking additional courses.

I had alot of OC rec dive experience but still approached the CCR course with alot of caution. In fact even after the course I utilize caution as I continue to build skills and comfort with all the new things that come with using a new piece of equipment. I now have about 40 hrs of dive time on the unit and feel I am still a beginner just like when I had 40 hrs on OC. So far I am happy with my decision to skip doubles and go directly to CCR.

As otheres have suggested I would agree that you should go to www.rebreatherworld.com and spend a considerable amount of time reading. If nothing else it will help you to know what questions you should ask a potential instructor while making your decision Hope this helps.