The R1P Almost Lives Up To Its Name

Originally published at Cave Diver

The R1P Almost Lives Up To Its Name
By Duncan Price


My latest creation, the "R1P" is a fully closed mixed gas (Nitrox) unit with a manual O2 and diluent addition. The design is continually evolving but I now have something that I'm happy with. It is very small and compact, with the scrubber being worn on the chest and the drive gases worn side-mounted. After an "interesting" experience with a sensor failure, I've put in two O2 sensors for redundancy. When I get around to building a bigger scrubber canister I'll fit three O2 sensors.


Anyway, my preferred test site is a large flooded pothole in the bed of a river. No caving is required to get to the entrance, which drops down vertically to 50ft to a gravel restriction (too small for backmounts) into a large tunnel, which heads upstream for 1800 ft at 60 ft depth. The visibility is typical for Britain - 3-6 ft.

On Friday July 26th I dived the site on open circuit for 40 minutes to dig open the gravel restriction. Having enlarged the route through and placed a fixed line to the surface. I went back to my car and fetched out my rebreather. Wearing a 50 cu ft tank of air as diluent and bailout with a 15 cu ft bottle of O2 I re-entered the water after an hour's surface interval. Apart from being a bit too light on the surface everything worked very well once underwater. I passed the restriction and swam upstream to 600 ft and back with no problems in a 30 minute dive. I would have gone further but this was the limit of my bailout.

Two days later I was back for a more extended test. This time I added another bailout and a bigger O2 cylinder. Mindful of how buoyant I was last time I also added more lead. The equipment was getting bulky and I required assistance to kit up. Once in the water everything fell into place. Dumping the air from my drysuit I soon found myself going into free fall down the shaft - passing a couple of my friends who were on their way up. Crash landing on the bottom, my helmet with lights on it almost fell off. Regaining composure, I realized I was far too heavy. Everything seemed to be OK though and I resolved to push on. I'd added diluent on my descent and as I was about to pass the awkward section I decided to hit the O2 addition to raise the ppO2 to 1.4 so that I wouldn't have to worry about it while I squeezed through into the larger passage beyond. Suddenly the O2 displays went off scale and I started to feel queasy. My legs started tingling. At that depth the ppO2 would be around 2.4 atm. Rather than hit the diluent injector - which feeds very close to the inhale side of the mouthpiece. I (foolishly) decided to breathe down the O2 level figuring that it was a mixing problem rather than having too much O2. This turned out to be the case and the displays came back online and dropped down to sensible levels quickly. Likewise, I was shaken but now OK. Having had more than enough, I decided to abort. However, inflating both my suit and counterlung (with air) did not lift me off the floor. There seemed to be a leak somewhere (suspect it was my neck seal on my drysuit). Instead, I opted to haul myself up the line and go "open circuit" still on my rebreather. This I achieved by manually adding air into the mouthpiece and breathing out though my nose. I was reluctant to switch to my OC bailout in order to keep the rebreather dry, as the provision for isolating the mouthpiece is rather rudimentary. Gaining the surface, I found my friends still in the water. They were able to support me and help me to land. I made another dive after this, without the rebreather, just on my bailouts. Before adjourning to the pub - it served to calm me down.

It is not appropriate here to go into the technicalities of the rebreather, design flaws and user error that contributed to this incident, but more general learning points are: * don't feel egged on by your audience. (On Friday I was solo, on Sunday, a crowd of people were watching and I felt that I had to put on a "show". My friends undoubtedly helped on the surface where I was having trouble staying afloat once I'd reached air - however, I could have got out unaided and I don't think I'd have got into the mess in the first place.)


* if in doubt, bailout. * complacency kills.



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