My Conversion to a Rebreather Diver

In the very distant past when I was doing my Ocean Diver course, the only question I recall asking was “Isn’t there a more efficient way of using the air in the bottles on our backs?” after being told that we only actually utilise 4% of the air that we carry. In my mind, before I had even gone into open water I couldn’t understand why a system I was being taught that was so inefficient. At that time, rebreathers were very much in their infancy and so little was known about them.

Over the years as I progressed from a single 12 Ltr, to a 15ltr with pony then on to twin 10s I started learning more about Closed Circuit Rebreathers (CCR) and Semi-Closed circuit rebreathers (SCR). The former seemed like voodoo to me and very complicated with most of them using sophisticated electronics. The thought of sophisticated electronics and salt water made me unduly nervous. I’d seen CCR dive buddies tinkering with the sensors in their units in-between dives and this made them look prone to failure; the real problem was that AP Diving had produced a bad batch of sensors so this tinkering was not normal behaviour.

SCRs were a different kettle of fish. I loved the idea of a system that had reduced bubbles, warm air, more efficiently utilized the chosen gas I carried and yet had no electronics. This combination excited me and my research led me to the Draeger Dolphin. A beautifully simple constant injection SCR using Nitrox. In September 2015 I eventually bought one of these units with the aims to learn to dive it.

Draeger Dolphin

Late in 2015 I started to look for someone to train me on the SCR and I came across Ian Reid of Northern Technical Diving. Ian had a similar interest in the Dolphin as I and was willing to train me. However, before we could start training he offered to buy my Dolphin from me and train me on the AP Inspiration Classic. What could I say? I jumped and the chance and bought myself an AP Inspiration Classic with integrated Shearwater Predator computer that monitors my 3 cells. This is a beautiful piece of equipment.

AP Inspiration Classic (CCR)

My training was completed by Ian with Gavin Anderson as my buddy during the two weeks over Christmas and leading in to 2016. You are probably thinking “Was this not when we had all the severe storms and flooding?” Well, yeah, it was. We were hit by Storm Eva and Frank. They were a pleasure to drive through on my way to the West coast and I came across flooded roads on my way but with my masterful driving and with my car that is absolutely suitable for the conditions (a Mazda 3 Sport) I made it the dive sites.

Floods at Loch Earn #stormfrank

Only one day was cancelled due to a large landslide at the Rest and be Thankful. Needless to say that the diving conditions and overall visibility of all training dives were what could only be classed as zero visibility night dives.

Coming into the CCR course, everyone who had been before said that my buoyancy would be all over the place due to a CCR having a fixed volume of air in the system and therefore taking a deep breath or exhaling doesn’t change the volume of air. Therefore, fine buoyancy control is entirely different to when you are using open-circuit. Secondly, my weighting would be out too.

Prior to starting the course I had read through the AP Inspiration Classic manual a couple of times and it prepared me with a lot of useful information. Subtle things such as your aim is to preserve the air in the system and be as efficient as possible. If you come across a big rock, swim around it rather than over it so save adding and removing air from your closed system. Other tit bits included putting some lead in the pocket at the top of the rebreather case and an indication that people can find it useful to initially do a duck dive to get underwater initially.

For our first dive, we went to the A-Frames, a place that is will known for its excellent visibility even when Storm Frank isn’t battering it. I setup my CCR with the help of Grant. He taught me how to do a negative test; this involves squeezing the hoses so they are tiny and sucking the air out of the system and closing the mouthpiece. It’s quite an art trying to get the hang of this! The system is left in this way for many minutes to see if the hoses are still compressed afterwards. If they are then the system has no leak.

As is the case when you get a new unit (I came from a twinset with lots of hoses), and especially one with lots of hoses, you spend a reasonable amount of time routing all the hoses to places where they are comfortable for you and then figuring out where all the straps go. With my Inspiration I have front mounted lungs that need to be clipped down so there’s another couple of new straps to fit. It takes a few dives before you figure our the best arrangement for all the new hoses and straps and I ended up using coloured cable ties to colour code my different straps so I knew which ones matches where.

Ian discussed the plan for the first dive. It was a simple plan, get in the water, duck dive to get under if necessary and swim around to get comfortable with the unit before doing some initial exercises.

Remove and replace mouthpiece / Clear water from loop using exhalation

Because you have a closed loop with a rebreather that circulates your breathing air, you can’t simply remove the loop from your mouth as you want to prevent water getting into the system as it could eventually work its way to the electronics and that would be bad. Therefore, when you remove the mouthpiece you need to close it first before removing and then when putting it back in you breathe into the mouthpiece as you open it up to prevent water getting in.

Remove loop and stretch over head to drain water from loop into counter lung

The rebreather can take water on board and still function but if you have water in the loop you can hear it sloshing or making you feel uncomfortable when breathing. To resolve this you can remove the loop from your mouth and hold above your head to encourage the water to flow down into your unit’s counter lungs.

Recovery of loss of loop from mouth

This is similar to the technique we do for open-circuit where we recover a lost regulator.

When we all got into the water I initially struggled to get under. Due to the nature of a rebreather, you have more sources of air in the system that need to be emptied before you get under. For open-circuit your two main buoyancy sources are dry suit and BCD. With a rebreather you have those two plus two counter lungs strapped to the front of your chest. Therefore on your first dive, you are trying to expel air from all these places and do a duck dive!! Fun.

Once under we went for a little swim through the murk. The trickiest part here was keeping someone within view as the visibility was so limited. My buoyancy at this point was so bad because of this new way of doing things that my dive profile probably looked like the flight profile of the Wright brothers on their first few attempt at flight.

The next couple of training dives were at St Catherines (Loch Fyne) and the weather was suitably miserable again with doses of sleet and snow. This training session involved learning how to fill my scrubber. The scrubber is the part of the system that removes the CO2 from the air you expel by using lime. Packing the scrubber is very important as it needs to work efficiently to be able to remove the CO2. Packing it involve carefully filling it with lime bit by bit and to a particular level and so the lime is packed to a certain firmness. After a dive, if you put your hand on the scrubber you can feel a lot of heat from the exothermic chemical reaction.

The third and fourth dives introduced the fact that my weighting was all wrong and really struggled to get underwater. Once there,  we went to sufficient depths and tested the alarms on our rebreather handsets and computers. We tested the low and high oxygen alarms. The later needs to be done at a few metres as on the surface you can’t get sufficient concentration to trigger the alarm. It was an interesting experience triggering these alarms under the supervision of our instructor and listening to the alarms going off and the computers telling you everything was wrong!

We also got taught the most important of techniques; the Diluent Flush. If you are ever in doubt that your system isn’t reporting the true state of the content of your loop you do a diluent flush to get rid of the air / o2 currently in the system and to replace with new air and o2. It’s an odd technique, as you tilt to the side and then pull the dump valve on one counterlung while putting dilutent (air) into the other counterlung.

The final training dive was at The Slates and involved techniques relating to continuing to dive with a unit that has failed due to various scenarios. We covered the following:

  • solenoid stuck open so the unit has o2 constantly streaming in – here you manually open and close the valve while monitoring the setpoint on your handset
  • solenoid stuck closed – manually add o2 using the counterlung manual addition valve
  • Simulate no oxygen by closing tank valve
  • Unconscious ccr diver rescue

After all these training routines we had about 30 minutes to enjoy a simple dive with no training routines. This was the first time since using the rebreather that I actually felt really comfortable and had full control of my buoyancy; my days of doing impressions of bouncing bombs were behind me. When you choose a depth on a rebreather and get your buoyancy set for that depth, life is fairly easy as the volume of air stays the same so you stay level. While enjoying this dive at around 28-30 meters I had the realization that I no longer need to acutely monitor my air usage with respect to my depth as with a rebreather no matter what depth you are at you are using up the same amount of diluent and O2 – cool or what?

One of the other things my buddy and I found during my course was that we saw a lot more critters as we finned around and we were able to get right up close to them without them flinching. I’m guessing the lack of bubbles really helps with finding the underwater life.

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