Rebreathers are, to many divers, something of a mythical beast. Most divers will know that they somehow recycle your breathing mixture, and that some tech divers prefer them. That’s usually about as far as it goes though. I was one of those divers, albeit one who knew that rebreather technology was based on older concepts, and so when I had the chance to do a few Discover Rebreather dives, I leapt on it! Rebreathers have always been fascinating to me, and I’d seen them in action before. I knew that they made for easier underwater photography, and that they were allowed to be used for some commercial and scientific applications (with permission). The prospect of finally trying one of these systems out was a can’t miss chance as a diver.
In the Intro to Tech Diving course, there is a section on rebreathers that greatly expanded my knowledge on the subject. This was followed up by some great instruction by Dave Tomblin, who I mentioned previously, a top rebreather instructor for North America. In addition to the review of the course materials, he demonstrated, via two basic rebreathers he made the previous night, how they worked. Naturally, I volunteered to be his demo guy, and it was a very cool and informative experience. One thing that I learned was that the canister containing the scrubber material that removes CO2 heats up. It was surprising, and only added more to my interest in how rebreathers work. The next morning, I was pumped up and was ready to dive!
The rebreather units we had were Innerspace Systems Corp (ISC) ones, and I was going to dive the Megalodon model. It was a close circuit rebreather (CCR), and clearly designed with hard use and simplicity in mind. Dave put us through the basic start up and systems checks, then the checks to ensure the system was working and that our desired Partial Pressure of oxygen (PPO) was set correctly. Our diluent was 21% oxygen breathing mixture, as we were only on discover dives, not planning to go to the extreme depths of Lake Okanagan. He also explained how the counter-lungs work, and what to expect on the dive itself. Once we were strapped in, it was time to hit the water. We were diving at The Dog Beach, in the same location as the Intro to Tech Course. The dives were happening concurrently, which made for a good experience. We maxed out at around 18m, and enjoyed the vis.
The first thing I’ll say about rebreather diving is that it is not for everyone. At all. It is a very, very different feeling, familiar, but still different. For one thing, your buoyancy is much more consistent. Because you’re effectively breathing the same breath over and over again, there is very little to change your buoyancy once you’ve adjusted your BCD or drysuit. I was using drysuit inflation, and had pony bottle for that task. As the dive progressed and we went deeper, I found that I had to give the system a burst of 21% to keep the volume in my lungs and the counter-lungs at the right level. Gas physics can’t be denied after all! Probably the single biggest difference I immediately noticed (aside from how creepy quiet it was) was that my breathing mixture was warm. This made the dive more comfortable, especially given that it was, like so many of my dives, a cold water one! This did lead to some condensation in the breathing hose assembly, and a wet knocking sound on the left side. It was easy enough to clear out though, the procedure Dave had shown previously worked like a charm. Aside from that, it also left me feeling less dehydrated than when I dive on an open circuit scuba system.
By lucky chance, I got two dives on on this unit, so I had a good chance to really see what rebreather diving was all about. And at the end of the day? I loved it. Using a bio-mechanical diving apparatus not only sounds cool, it is cool. What was also cool was how the information was presented. Again, there was no emphasis on pushing the envelope. It was all about getting the best experience out of your dive. Which is exactly what I did!