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New Skills: Learning to Dive a Rebreather

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Image credit: Aaron Thomas (@ccr.doc)

James H reports on his recent rebreather training

If you ever go to a UK dive site, you are likely to see just as many rebreather divers as those on open circuit. The use of rebreathers has exploded in recent years, making long duration deep diving more practical than ever. AP rebreathers, typified by their distinctive yellow case, are one of the most popular on the market and BSAC has a dedicated certification course for them. After walking down the technical road on open circuit, I decided it was time for me to relearn diving on a fundamentally different machine.

For those wishing to get started on closed circuit diving, without sinking several thousand pounds into a unit, BSAC can provide members with one of their rental units for a small fee. These are packed with a surprising number of add-ons (e.g., BOV, tempstik) that make the experience a bit easier.

Technical skills instructor Andy B very kindly offered to run the course for me, even after my fellow student sadly had to drop out for personal reasons. After digesting the course manuals, I felt pretty confident in my ability to understand the rebreather, but that was the easy part.

Getting started

The practical introduction to the kit begins with the build-up workshop. After filling the scrubber with sofnalime, the substance that removes the carbon dioxide from the used breathing gas,  and assembling the rest of the unit, it was off to the local leisure centre for my introduction to the “silent world”.

No amount of research and preparation can prepare you for your first dive with a rebreather. At first, it feels like breathing from a sentient vacuum cleaner while simultaneously trying to regulate the gas in the wing and lungs (including yours…). It really feels more like the machine is taking you for a dive rather than the other way around at first.

With the first hour in the pool under my belt, it was off to Stoney Cove once again for four full days of diving and lectures.

On the first dive the added buoyancy from the drysuit really threw my buoyancy control. The simple act of descending became a mammoth task involving a lot of flapping around and desperate dumping. It must have been quite an amusing sight for onlookers. Eventually I realised that the ABS case was acting like an upturned bathtub and was trapping a lot of air after jumping in, and the correct way to descend is to lie on your back while dumping everything. Once on the bottom the unit trims out nicely with the back-mounted counterlungs and I didn’t have to shift any weight around.

One of the first habits you have to unlearn is using your lungs for buoyancy. You will quickly find this out when you exhale to stop an ascent and realise this has no effect other than shifting the gas into the bags behind your shoulders. You will also need to get accustomed to checking your handset regularly and altering your style of diving (going around instead of over tall things, for example).


The first few days are a real rollercoaster with endless drills that increase in complexity as the course and depth progresses. This was not without incident as during the second dive someone had forgotten to do their drysuit zip up and later I spectacularly bottled the bailout ascent drill and spent the safety stop holding onto a large rock to stay on the shelf.

The course culminates in a couple of deep dives on day four to ≈35m when the drills are stopped and you start to relax with the unit. By the last dive it all clicked, and despite the cool 7°C water it was very comfortable sipping on a helium cocktail in the 35m pit. After successfully redoing the bailout ascent from 15m it was time to pack up and head home.

A special thanks to Andy B for sacrificing his easter break to provide quality instruction and invaluable advice.

Want to find out more about the course James did?

MOD1 AP Vision CCR Diver: course details

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