RB80 Course Report

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PfcAJ

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I've debated even writing this course report for about two weeks now, but here it is:

For well over a year I had kicked around the idea of moving to the RB80. Dives have gotten longer, deeper, farther from the door, and more and more stages were needed to pull them off. 3-4 stage dives + 2-3 deco gases were becoming somewhat commonplace. But still, the transition to a rebreather seemed like a REALLY big jump in my mind. I've always been very suspicious of both SCRs and especially CCRs, but I'm also suspicious of deep cave diving on OC. Now seemed like the best time to take the class since everything we've been working on in the Tallahassee area (insert shameless plug for GUE Quest 13.3) is blown out due to the rains (dark water in the cave).

So why the RB80? For me, there were a few reasons. #1 its quite similar in procedure to open circuit. Gas switches are procedurally similar, the gases are the same, and the configuration is the same as what I've had since 2005 when I took Fundamentals. The only difference is the doubles are spread apart a bit, a rebreather is put in the middle, and there's now a switchblock on the right hand side (more about all that stuff later) with a feed from the left post, and an extra hose from the right post that goes to the OC bailout valve. #2 the RB80 is really a simple machine. I've had a lot of exposure to the RB80 over the years and I had a pretty good understanding of how it all worked going into the class, and how it compared to other RB technologies. To me, the advantages of a slightly less efficient mechanical RB outweigh the efficiency advantages of a CCR #3 is that its what the rest of the WKPP uses. This was something I pondered long about. Just because 'everyone else is doing it' is NOT a valid reason when it comes to something like this. #1 and #2 were enough to solidify the decision, with #3 being kind of an added bonus.

Flash forward to RB80 class -2 days. The two other WKPP members who are on the course with me (who prefer not to be named) met at Extreme Exposure in High Springs. We decided to head up to Peacock for a leisurely single stage dive up the Distance Tunnel to spend some in-water time together right before class and knock off any rust. Back in the basin we went through our usual valve drills, s-drills, and bottle rotations in 20ft of water to ensure we were all on the same page (we were) and to help build some confidence pre-class. We had all dived together in the past, but not as a trio. These are top notch guys (I can't emphasize enough how much I lucked out with these two as team mates), and we got along perfectly in the water. Day -1 was a rest day/ gear checkout where we went through and made sure everything was as it should be before David Rhea showed up on Monday morning.

Class kicked off with David asking point blank why we were here. This isn't a class they want you to take. You have to want it, and you have to need it, or David just won't teach you. We were all cave 2/ tech 2 divers with a respectable amount of deep+cave experience, and our motivations were nearly all the same: To have a tool that allows us to get more done on a dive. Whether exploration or support, the RB would open doors that would be a logistical circus to pull off on open circuit. We went through some powerpoints about GUE, the history of rebreathers and the RB80, pros and cons of each type of system, and the risks involved with rebreather diving. Then we headed to Halcyon to pick up our RB80s and associated accouterments, signed some paperwork, then back to the classroom for a complete teardown of the unit. David has a rebreather that's only purpose is to show the students how the entire thing works, and David cut no corners. Literally every. Single. Part. of the thing was disassembled so we came away with a thorough understanding of how it all worked.

The mouthpiece houses a bailout valve is a simple rotating valve with a Scubapro r190 at the bottom that serves as open circuit bailout, and the two one way valves on the sides. Any problem with RB and its incredibly simple to rotate the lever on the front of the BOV and boom - Open Circuit.

The RB80 is a passive semiclosed rebreather and the design of the unit is quite elegant. There's no diluent. No o2 injection. No solenoid. No computer control. When the diver exhales, the counterlungs (inner and outer bellows) fills up, and when the diver inhales, 1/10th of the previously exhaled gas is vented from the inner bellows to the water, 9/10ths is drawn up through the scrubber from the outer bellows, and fresh gas is injected to make up the difference via two modified r190 regulators, which make a little 'psshh' noise you come to hear and pay attention to every 2nd or 3rd breath (give or take). Its *really* simple. Whatever gas you have plugged into the switchblock (which feeds those two modified r190s) is what gets injected into the unit as you breath. In practice, this equates to an ~8x advantage over OC

We were taught the assembly checks to make sure everything is sealed up correctly (which are also simple and don't take much time) and got time to practice on the demo rebreather. More powerpoints followed going over the oxygen drop and decompression/dive planning followed.

Part of the reason the RB80 looks so insanely large when compared to other rebreathers is the OC bailout. Most pics of the thing are sandwiched between two lp120s, which are massive, and the breather is driven off of al80 stage bottles. The unit itself is only about the size of an al80 tank. It seems like most CCR guys have diluent and o2 on their back and sidemount their bailout while RB80 uses backmounted bailout (no o2 or dil, remember). Cubic foot for cubic foot, its really about the same size. You can use whatever size bailout you want, and I've even seen al40s used for ocean diving and as deco rebreathers in the WKPP.

Tuesday was an off day. One of the team members had an important meeting (since he works at a nuclear powerplant, if he says its important, its probably important), and David had some errands to run around town.

Wednesday morning we all met at 8am at Blue Grotto. David went over how to pack the scrubber, and one by one we all prep our breathers, working as a team making sure everything is proper. Regs, hoses, wings, and plates are all installed, and we made our way down to the water. The dive was simple. Open circuit to 20ft. Switch to rebreather, take 4 laps around a line course David set up, then all the fundamental skills at 30ft. We dropped down, followed the course to 20ft, and I signaled the team to switch to RB. I went first. I rotated the lever on the BOV, the bubbles stopped, and I just hung out for a minute feeling what was happening. The gas was warm, buoyancy was stable, and the effort to breath was minimal to nonexistent. Cool. The other guys switched and had the same result.

Off we went around and around. OC shallower than 20ft, RB deeper than 20. Over and over. Fundamentals practice was similar. The RB has a bit more mass, but its not ridiculous. We went through valve drills (the valves are in outer space compared to a regular set of doubles) which includes checking the switchblock and o2 meter, S-drills are a bit more complicated requiring a switch to OC on the BOV, unclipping of the hose, and removal of the loop. Its a tad slower, but once again, not terribly ridiculous. We finished up with the basic 5, I shot an SMB, and our first RB80 dive was over. After lunch and a debrief on what we needed to work on, we went back down and did a mask off swim around the line course in touch contact, more laps, more skills. Pretty much Fundamentals days 1-4 in 1 day. We headed back to EE for video debrief as usual, then hit the sack.

I'll spare you the novel and keep it quick, but day 2 was like cave 1 in blue grotto cavern with failures of all sorts. The RB portion is easy. Its all the peripherals that get ya. Backup reg, primary reg, OC bailout, the rebreather, lights, reel, switchblock, RB drive hose, valves on the switchblock. The challenge is keeping it all straight in your mind, and any weakness in the fundamentals becomes super obvious.

Day 3 introduced stages at Orange Grove Sink. Switching is nearly exactly the same as on OC. The drive hose is added to the stage reg in addition to the normal OC reg, and you walk through the procedure with that hose vs the OC reg. Its routed through the crotch strap, under the long hose, and into the switchblock. Verification is the same, spg needle drop is the same. I appreciate how similar it is. But now you've got 2 things that *can* drive the RB (stage and backgas), plus all the other stuff. Now a left post failure doesn't render the RB inoperable. A right post failure doesn't either, but the OC bailout no longer works. See what I mean about keeping it all straight? All the variables are what I think make GUE's RB80 the hardest course I've ever taken, but those variables are what give you options in the water.

David's teaching method, however, is specifically designed to work your brain. Genuine learning occurs. He "got me" at one point and failed a combination of things (David will shut off gas supply to the RB via the switchblock), and my right post was failed, so the OC reg on the BOV wasn't an option) that resulted in me ditching the loop and going for my backup reg. In my haste, I didn't close the BOV. Its my understanding that with some rebreather designs, this would be very bad. With the RB80, however, its no big deal. The gas path diverts any water in the loop to the inner bellows out its ejected out of the unit. My scrubber was completely dry after that dive.

Day 4 was like Tech 2. We simulated a hypoxic backgas, requiring descent on the OC stage reg, dropping o2, switching to RB through the stage and stowing the OC stage reg, into the cavern, and all the failures associated with that. We each carried a spare "cheater" (a swagelock qc6 quick disconnect, which goes on all the stage regs and the left post) which we could use to turn any reg into something that can drive the rebreather. This plus a wrench can solve a lot of problems. Missing deco bottle? No prob, spin off the 2nd stage, slap on a cheater, and now you can run 2 rebreathers off 1 bottle. Pretty neat. But once again, keeping all this stuff straight upstairs is the challenge. David failed enough things that we had to really get creative and utilize our resources efficiently.

At the end of the day, we dumped our scrubbers, reassembled the units, and one at a time we got into the water. Flanked by our buddies, we were to get onto the RB (driven by o2 which has no o2 drop) and kick as hard as we could against the stairs in like 6inches of water. This was to show what a co2 hit could feel like, since there was no scrubber. It was...less than fun. I ended my run after about 3mins and had an extreme case of the jitters, was weak, tunnel vision, and felt starved for air. Not cool. My buddies hauled me up the stairs, then it was their turn. Everyone had a different response and a different time. The lesson was important. A co2 hit is NOT something you want in the water and must be avoided. Don't push the scrubber (esp over multiple days), pack it correctly, don't over work while on the RB.

The next morning, we went for our 500yd swim and 75ft breathold, went over the test, and received our cards. We all passed woo! With that pass came a responsibility to progress slowly on the unit. The RB80 kind of a magic carpet that makes a single al80 last as long as 8 al80s, but it also has the potential to murder. I have a very healthy respect for the unit. Its not a toy, and there is no room at ALL for complacency. We came out of the class with roughly 16hrs on the unit. My mission now is to gain more hours and experience.

So about the o2 drop. Due to how the unit works (and its a long drawn out explanation), the inspired oxygen percentage decays and ends up being less than the gas driving the unit. In the shallows, its serious. Like 20% less o2. 32% nitrox becomes hypoxic above about 20ft. But at depth, the % is way less. 32% becomes more like 26% at 100ft after ~20mins (and it stabilizes at that point). Deeper still, the drop % is less. In practice, it doesn't add much deco time, its extremely predictable, but the hypoxia risk in the shallows is a very very real risk. If I took away one key point after the week of training, its to remain ALWAYS vigilant about the hypoxia risk on the unit.

We trained with a po2 meter, and I'm on the fence about the necessity of it. I lost a good friend to hyperoxia a few years ago, and almost lost another friend to hypoxia a few years before that. At present, I believe that improper procedure is what caused those two accidents, and proper fundamental procedure would have prevented them. I will continue to dive with the po2 meter until I feel confident that the mathematical prediction lines up with reality, and I will reevaluate my use of it at that time.

I think I can speak for everyone who took the class that we got our asses kicked in it. It was hard. The learning curve was steep and the complexity is a lot higher than on OC, but our previous GUE training laid a solid foundation, and we would have been up the creek if we didn't have that going into the class. David made sure we understood the unit through and through (and after t1 and c2 with him, I knew what to expect), and that we are all competent to go out and begin to learn how to use the RB80. It was one of the most memorable weeks I've had in diving. I learned a ton in those 5 days, and really cemented friendships with my other two class mates.
 
Nice report. Congrats!

So about these bolt snap thingies.
 
Very good write up. The last paragraph about shallow water hypoxia is interesting. Can you share some detail there? Why the O2 drop? Not that I want to nor quality for this kind of diving, as engineer, I like technical detail.
 
Very good write up. The last paragraph about shallow water hypoxia is interesting. Can you share some detail there? Why the O2 drop? Not that I want to nor quality for this kind of diving, as engineer, I like technical detail.

In a nutshell, there are less oxygen molecules per unit of volume when shallow. As you get deeper, there are more molecules of o2/unit volume, but you metabolize the same amount as when you're shallow. Therefore, the oxygen drop % is less when deep.

The gas is replenished based on your respiratory cycle, so even a high workload doesn't affect the end % drop, it just shortens the time it takes to reach that %. So with each breath, you're replenishing some of the oxygen, but not enough to bring it back up to the fo2 in the supply gas. Eventually, what you metabolize and what's being put back in the loop equalizes and the o2 % levels off.

It takes a bit of time for the o2 drop to level off and fully stabilize. Maybe 20mins, maybe less if you're huffin' and puffin'. It can be a bit different for person to person, but I'm pretty much 'average' in that department. The software allows you to adjust its parameters so you can match it up pretty closely with reality. For me, the default parameters line up well with what I've seen displayed on the po2 monitor.
 
Can't believe I missed this the first time around! Thank you for writing up an account of a very infrequently-taught class.

I remember doing S-drills with Steve White when he was practicing with his RB80. It's a clumsy procedure, but it does work -- and how likely would a complete out of air be with an entire rebreather team, anyway?
 
For sure about the OOG thing. It takes a LOT of broken stuff for a RB diver to be out of gas, and if you're headed in that direction you'll be able to see it coming and prepare accordingly.
 
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