Benthic Canada

Semi-Closed Circuit Rebreather Course
by Pedro Nunes (December 29, 2005)

Two Thousand and Five was a year full of scuba adventures and learning opportunities. December was no exception when John and I completed Technical Diving International's Semi-Closed Circuit Rebreather (SCR) Course. Our instructor was Sherri Golbeck; she did a wonderful job in the classroom and the ocean.

The theory we covered was interesting and some of it was a rehash of information we already knew. It all began with a short history lesson. Did you know that the first true rebreather was invented in 1878 by an Englishman named Henry A. Fleuss? That's 65 years before Emile Gagnan and Jacques-Yves Cousteau would refine the 1865 idea of a demand valve into the scuba devices that we know today. Rebreathers improved over time and would be adopted by most navies during World War II. Over the years there were many attempts at bringing rebreathers to the mainstream recreational market but it wasn't until 1995 when Drager and Uwatec brought the Atlantis I rebreather to the US that rebreathers really took off.

Our lesson went on to cover the concepts of a rebreather and how they work. As an example of the basic principle, you exhale into your mouthpiece and the gas travels past a check valve and through a hose over your right shoulder into an exhaust bag where some moisture and spittle (more on that later) is collected. The gas then passes into a scrubber canister tightly packed with calcium hydroxide (soda lime) where carbon dioxide is removed prior to entering the breathing bag, where a constant incoming flow of nitrox replenishes the gas with oxygen. You then inhale and the gas in the breathing bag flows through a hose over your left shoulder, past a check valve and in through the mouthpiece. It really is simple, just a continuous loop with several stages along the way.

We then returned to material that we are very familiar with in the "Rebreather Physiology" module. This was closely followed by the "Gas Consumption and Decompression" and "Dive Planning Considerations" modules where we applied previous knowledge in dive planning plus rebreather concepts to determine maximum depth and dive times.

The most important incident prevention measures for rebreather diving are taken before you even hit the water when you perform your equipment checks and tests. We learned these safety tests are done before every dive. Sherri provided Drager Dolphin SCRs as equipment for our ocean dives and we had an opportunity to assemble and disassemble them in the classroom. The Dolphin truly is a simple unit with few parts and easy assembly.

As we reviewed rebreather dive procedures I knew that the excitement was building because I could almost taste the salt water. Then again, maybe that was just residue on the mouthpiece. Talking about which, there is a valve that you keep closed when the mouthpiece is not in your mouth. If it weren't for this valve the scrubber canister would flood resulting in a caustic liquid that is very unpleasant. Our lesson was over for the evening after we covered emergency procedures where the most common procedure was to switch to your bail-out cylinder and end the dive.

The weekend couldn't arrive soon enough. With all this new found knowledge I was eager to put it into practice. We had postponed our knowledge reviews and exam for the weekend so it was promising to be a relatively long weekend. Our dive weekend started on Saturday morning at the dive shop where we completed our knowledge reviews, filled the scrubber canisters, filled the rebreather and bail-out cylinders, set up the rebreathers and performed most tests. It was then on to lunch before heading to the dive site.

We went to Cates Park in North Vancouver for dives one and two. Although it had been cold, we were fortunate to have good weather with more of it forecast for the next day as well. We were pleasantly surprised finding warm, clean, fresh smelling facilities when it was time to use them; the North Vancouver Parks folks obviously take pride in what they do.

It was time to focus on the task at hand. We completed the rebreather assembly and performed all tests. The first test was a flow check to ensure that we were using the correct orifice for the nitrox mix in our cylinder, then an oxygauge check to verify accurate reading of oxygen exposure, a canister check to verify that there are no leaks with the canister, and two final tests (negative and positive pressure) to verify that there are no leaks in the entire system. It was time to suit up and get to it.

As we walked down to the beach I was a little nervous as this would be the first time that I would knowingly breathe recirculated gas for basic survival. It was easy carrying the lightweight rebreather as I thought about the future prospect of diving with these for as long, and sometimes longer, than my heavy set of double 80s. After donning my fins I noticed that somehow I had opened the mouthpiece valve and a bit of water made it in. I was a bit concerned about this and after discussing the situation with Sherri I decided to proceed with the dive.

Once we were underwater I heard water gurgling on each exhale - so much for a silent dive - but things would be fine as long as the gurgling wasn't on the inhale. Some people say that using a rebreather for them is like using a snorkel; at this point I agree with that assertion. We went into slightly deeper water and did bubble checks on each other by rolling ourselves. Well, I got a mouthful of water and voila, the gurgling was over. As you do the turtle roll, you can definitely feel increased resistance on the exhale when you're upside down and the rebreather unit is deeper than your lungs.

We went on to practice our bail-out skills and then proceeded deeper for some buoyancy acclimatization. Sherri cut the first dive short by bailing out due to a possible leak in her rebreather. In a way this was good as we observed real world troubleshooting taking place on the beach. While this was going on I was thinking about the dive we had completed; I would rate it a 2 or possibly 3 out of 10. My breathing and buoyancy techniques were not compatible with rebreathers. So what they say is true - many experienced divers have to re-learn some of the basic skills when they start using rebreathers.

I had some ideas on things I could do differently by the time we returned to the water for dive two. Without the hindrance of skills I was able to focus on different breathing and buoyancy techniques. Eureka! What a magnificent difference when you make even subtle changes. From this experience I realized that taking double breaths doesn't work very well with rebreathers and also found that I use my lungs for buoyancy adjustment far more often than I thought. This turned out to be an 8 out of 10 dive.

At the end of the first dive day I had to leave as soon as possible due to family commitments. Sherri and John graciously offered to take my rebreather and disinfect it for the next day. It turned out that Sherri later decided to clean all of our units herself as it was late and we were going to have a relatively early start the next day. Thank you Sherri!

The Three Amigos

Alithea was able to join us for day two. This time we went to Porteau Cove to get a bit more depth and some interesting scenery too. It was an extra chilly day but we were bound to get plenty of sunshine in the afternoon. After being spoiled with cozy facilities at Cates Park, it was back to long walks and cold washrooms at Porteau.

Sherri brought her Drager Ray along because she knew Alithea may join us today and thought that it would be nice for her to have an intro to rebreathers. As you might guess, there was no way that Alithea would say no! Alithea had an intro to the Drager Dolphin and then prepped for the dive.

This morning there was a large contingent of divers from the Underwater Archaeological Society of British Columbia doing surveys on the Nakaya and Porteau's other treasures. Needless to say there was much interest in the rebreathers and Sherri could have sold an Inspiration right there if she had one!

We were all at the water's edge ready to go when Sherri had some problems with the first stage on the Drager Ray cylinder. This was not good as the Ray's cylinder also serves as the bail-out, so Sherri went to Plan B and switched to open circuit. With Sherri back in the water we did our bubble checks and bail-out skills before proceeding on.

We went on to have a wonderful dive exploring the man made objects scattered throughout the dive site. I felt exceptionally comfortable, almost as if I have been diving with a rebreather for some time. I have always found scuba diving to be relaxing but it seems that much better with the silence. By the end of the dive my mouth was somewhat uncomfortable as the mouthpiece seemed to push up; I made a mental note to investigate this during the surface interval.

Alithea and Sherri at Porteau Cove

John and Alithea, the lucky bums, had recently returned home from a wonderful two week dive trip to Chuuk Lagoon in Micronesia. While away they had their drysuits serviced and hadn't yet replaced the dryglove rings. Needless to say their hands suffered bitterly from the cold and yielded schoolgirl-like screams. Can you hear the world's smallest violin playing? Alithea opted out of the second dive.

Before dive two, I removed the breathing hose to sort out the mouthpiece issue and just happened to peak in the exhaust bag. Oh no, liquid! I removed the exhaust bag to inspect and found that it had a bunch of spittle. Now I know what the term means - it's this clear goo that builds up as a result of the moisture in your breath and it sure grossed everyone out. I drained the spittle and checked the canister and completed the rest of the checks.

There was one more skill to complete. Once in the water we completed a hose recovery without closing the mouthpiece, remembering to lean back to grab the hose before water can get in. The adjustments to the hose paid off making the mouthpiece comfortable to wear. We were all pretty cold so the final dive was quite short.

We were nearly there with two more tasks to complete. When we arrived at the shop it was time to disinfect the rebreathers and write the exam. I loved the last question in the exam but I'll keep it to myself for obvious reasons. This turned out to be a very enjoyable course and I look forward to future rebreather dives. The mechanics of rebreathers are easy to understand, even more so if you are nitrox certified. For those without nitrox certification, you are able to obtain the certification in conjunction with this course.

If you are interested in taking the TDI Semi-Closed Circuit Rebreather course in the Vancouver Lower Mainland area, I do recommend Sherri Golbeck as an instructor. Our experience was definitely positive, thanks again Sherri. I would also like to thank Silent World in Bellevue, Washington for providing rental Drager Dolphin rebreathers.

Resources

Drager Dolphin Manual

Silent World Diving Systems

Technical Diving International (TDI)