IT’S NEARLY 20 YEARS since I first met Dave Thompson. He was then known as “Mr B&Q”, because his knowledge of plumbing had allowed him to make a rudimentary closed-circuit rebreather.

Dave is a practical man. He approached the manufacture of a viable rebreather from the point of view of an ex-scaffolder rather than that of a theorist. He wanted something that was simple but worked.Martin Parker, the CEO of the company that made Buddy BCs, tried Dave’s rebreather and decided that he wanted one, so he applied the expertise readily available to him at his factory to make a better version of Dave’s idea.

I was invited to go with Martin and Dave for a couple of days out into the English Channel to try out the prototypes of what would later become the Ambient Pressure Diving Inspiration Classic. The rest is history.
Developments of that prototype represent the majority of leisure rebreathers in use in the world today. They did a great deal to popularise this method of diving.
In the meantime, Dave concentrated on training CCR divers and CCR-diver instructors, and in the process accumulated a lot of in-water practical knowledge about rebreather design.
When two keen Danish divers, one of whom was an engineer, decided to make their own open-circuit bail-out valve, they went to Dave for advice. His verdict on their device was one they probably didn’t want to hear. They were Jan Jorgensen and Jan Pedersen.
Undeterred, the Danes went on to design and make their own CCR, though asking Dave for design advice along the way. It was Jan Jorgensen’s concept, and Jan Pedersen, the engineer, made it happen. Dave Thompson was mainly responsible for perfecting the work of breathing (WOB) and the design of the manual oxygen-addition control.
The result became known as the JJ-CCR, and in 2011 it was finally produced in a CE-marked form, which allows us to review it here.
Jan Pedersen primarily made a CCR for his own use, so it is made up to a standard rather than down to a price.
That’s all very well, but the UK delivered price of around £7000 makes this one of the most expensive CE-marked rebreathers currently available.
It was a privilege for me to accompany Dave for a week on the liveaboard Mistral in the Egyptian Red Sea to get familiar with and review the JJ-CCR.
We chose Mistral because it has the technical support a CCR diver needs. Naturally, I had to go through all the routines under water that any trainee or anyone else crossing over from another type of CCR would need to do.

When the JJ-CCR arrived, I thought it looked very simple but strongly engineered. It had a stainless-steel frame that allowed it to free-stand, which was very convenient. A lot of precisely machined Delrin was in evidence, but all the hoses and fittings looked to be
of standard scuba issue, and the type that could be easily replaced if needs be, anywhere in the diving world.
In fact, all parts appeared to be machined rather than moulded, which means small production runs and perhaps a little waiting time for anyone who wants to buy one, but everything screwed together in a very satisfying way.
Dave was quick to point out that the model gained its reliability from simplicity rather than complicated automation, although of course it is an electronically controlled unit (eCCR).
Most of those who have bought a JJ-CCR so far have progressed from other rebreathers.
It’s as though you need to understand the subtleties of CCR design to appreciate what you get, as with a Rolex watch.
The downside was its weight. Not as heavy as some, but in its standard plastic crate and without the corrugated hose and mouthpiece that I packed separately, it still weighed in at 25kg.
I was a little worried at the Monarch check-in, where no item of more than 20kg would be accepted according to its excess-baggage rules. Scuba Travel staff were there to smooth the way.

As a photographer, I was also a little concerned that the back-mounted counter-lungs might make this rebreather difficult to breathe from in some attitudes.
There is an inhalation and an exhalation bag, and these are positioned carefully, by adjusting the harness, so that the tops come just up to and over the top of the wearer’s shoulders.
In use I found that there was no drawback to any position I took while under water, and I was able to lie on my back to take photographs upwards without incurring any WOB penalty, although at this time I was extremely relaxed and not breathing very hard.
Back-mounted counter-lungs give the benefit of an uncluttered chest area.

The harness looks at first glance like a one-piece, but it isn’t. It is easily tightened by pulling down on the two D-rings where the free ends terminate, and when it comes to taking the unit
off (in the water, for example) it’s easy to lift two fixed pre-bent D-rings to slacken it off.
There is also a waist-strap fastened by a conventional weightbelt-type buckle, and the 3kg of lead I needed to balance my steel bail-out cylinder on my left side was slipped onto the webbing and secured with an H-clip on the right.

The mouthpiece I used was the straightforward dive/surface valve (DSV), with which the unit has been CE-certified. Dave had a unit with a bail-out valve (BOV) that would switch from closed-circuit to open-circuit in the event of a CCR problem that was insurmountable, and this would allow him to breathe directly from his diluent cylinder without removing the mouthpiece.
I was comfortable with the standard DSV because it was exactly like the Dräger DSV with which I started using rebreathers almost 22 years ago.
It was extremely positive to open and close, as one would do when bailing-out to open-circuit (or simulating that) and when it’s time to pass your unit up from the water to a RIB. It uses a single lever.
The BOV should be CE-certified soon, I’m told.
The corrugated hoses are connected to the T-pieces of the rebreather via large threaded collars. These are left-hand-threaded on the exhale side, so there is no chance of connecting up the hose and finding yourself breathing in the wrong direction, as I once did with an early version of another make of rebreather.
The exhale T-piece employs a water-trap. This resists small amounts of water that might result from moist breath condensing in the breathing hoses and entering the counter-lung.

The JJ-CCR can be mated to virtually any cylinders with standard DIN connections. It uses any size of cylinder, even as big as 12 litres, though usually 3-, 5- or 7-litre units are employed.
We used 3-litre steel cylinders of the type commonly used with the popular Inspiration, because these were what was available on Mistral.
I even alternated between one of these and a standard 12-litre aluminium cylinder for use as open-circuit bail-out, side-slung according to the intended depth of any particular dive.

Unplugging the O2 feed, disconnecting the breathing hoses and unclipping the Head-up Display (HUD), you press a large spring-loaded button at the back of the scrubber bucket and lift out the electronic head together with the scrubber canister to which it is screwed. A loop of webbing allows this to be done very easily.
The bottom of the canister bears a base piece mounted on three large springs. The head is easily unscrewed, revealing access to the CO2 absorbent scrubber material. A scrubber load (about 2.3kg) is good for three hours’ diving in UK coldwater conditions.
There is a layer of hydrophobic material at the base and, after packing the Sofnolime 797 (1-2mm) appropriately tightly, another layer of hydrophobic material is placed on top.
The whole lot is held tightly in place by a spider frame that fits a central spindle and is secured by an over-sized threaded knob screwed down onto it.

The underside of the electronic scrubber head reveals the three sensors that control the oxygen levels. These are hard-wired to short leads connected to co-axial plugs. The oxygen-controlled solenoid valve is adjacent to the sensors.
Two flexible leads run from out of here to the wrist unit and the HUD attached to the mouthpiece.
Although the HUD gets its information from the three sensors, it runs entirely independently of the wrist unit, which is basically a Shearwater Predator computer.

The Shearwater Predator is turned on and off and set up by means of two buttons (Mode/Adjust/Confirm).
It has a colourful OLED display that is extremely clear in dark and murky conditions and is still readable in the shallows of a brightly sunlit Egyptian Red Sea.
It displays the pO2 read-outs from the three sensors, plus remaining no-stop time, depth and dive time. It also confirms that you are in CCR mode, the mix of your diluent and the safe ascent time (TTS). This is all displayed in green (green is good).
Once you get down to four minutes of no-stop time remaining, this figure changes to yellow. Once stop times and stop depths are displayed, this information is displayed elsewhere
in red. It’s all very simple and clear. Naturally, there is a fast-ascent warning.
If you need to change to open-circuit bail-out under water, a press on the left-hand button offers the change and you confirm this by a press on the right-hand side. In this way your mandated decompression is continually tracked. The buttons are piezo-type.
Although you can predetermine the unit to switch set-points automatically, you also have the option to change set-points on the fly. This is especially useful when doing training simulations, such as driving the unit on the HUD alone.
I had it set to 0.7bar pO2 for a descent until 12m, where it changed to 1.2bar pO2 and back to 0.7 pO2 at 3m on the way back up. There is total diver intervention capability during diving.
You can also change diluent gas mixes and bail-out gas mixes to a variety of different gases of your choice. And you have the option to change the preset gradient factors if you wish.
I pre-set gradient factors appropriate to my level of fitness, together with my advancing years.

Initially, I found the HUD confusing to understand. It displays an LED connected to each of the three sensors. These flash red or green. Both can be good.
You have to get your head around the fact that for each of one-tenth of a pO2 set-point below or above 1bar, an LED flashes red or green in quick succession.
There is an LED for each of the three sensors. For example, at 0.7bar you will see three rapid flashes from the three LEDs in red followed by a pause.
At a set-point of 1.2 bar, you will see two flashes in quick succession, repeated
in green.
At 1.3 bar, you will see three green flashes in quick succession, repeated. If all the sensors are reading the same, you will see the three LEDs flash together.
Sometimes one will be different by less than one-tenth of a point, and it won’t flash. You need to wait a moment for it to catch up, and you then see the three flash together in unison. Got it
It sounds very complicated, but in fact it’s quite straightforward once you get your head around it. Eventually I could drive the unit on the HUD display alone.
This would be important in the event of failure of the wrist unit during a dive.
You need to remember to switch on the HUD using its piezo button on top of the scrubber unit before diving, and to calibrate the HUD independently after the wrist unit, but as soon as the wrist unit’s calibration is complete.

Unlike with early rebreathers, you can simply top up the gas volume of the counter-lung as you descend, inhaling and allowing the ADV to do its work.
When it comes to diluent flushes, you have to reach up to this valve and manually press it while turning on your side to position the dump-valve of the counter-lung to release gas.

The JJ-CCR is easy for anyone already familiar with closed-circuit diving techniques to use. You need to exhale through your nose to leave the surface, for example. I found it slightly difficult at first to dump air from the wing during a quick head-down descent, but that was because Jan likes to cut the toggles off the pull-cords of the dump-valves, and I was using his personal unit. I got used to finding it.
I can’t comment on the work of breathing, because unless you use two different units side by side, they are difficult to compare. However, Dave was quick to tell me that the JJ-CCR has the lowest WOB of any closed-circuit rebreather on the market.
I just got into the water and used it.
It also tolerates a minor flood well, because that water goes into the exhale counter-lung and can be drained out with a diluent flush and with the dump valve positioned downwards.

Dave gave me a taste of the course. I had to simulate bail-out to open-circuit, an oxygen solenoid failure both stuck open and stuck closed, driving it manually both by the wrist unit and by the HUD alone and, of course, I had to repack my scrubber after each three hours of diving and recalibrate both wrist unit and HUD every morning.
One point that Dave was keen to make is that nobody who has purchased a CE-certified JJ-CCR to date has found it necessary to modify the unit, so, even though less complicated than some others, one might call the JJ-CCR state of the art.
I liked its purity of design, with nothing unnecessary, nothing to add. No doubt a few oddballs will find ways to “improve” the one they buy and add potential failure points. Time will tell.

Big changes are afoot in the world of rebreather diving. PADI has introduced courses not only aimed at those who want to be technical divers but others who simply want to swim with the fish without having to worry about their gas consumption.
The revolution comes with the leisure closed-circuit rebreather course aimed at this second group, and CCR manufacturers are rushing to produce models that conform to the PADI specification.
This means keeping diver intervention to a minimum. The rebreather itself must have automatic activation on entering the water, and warn if anything is amiss, so that the diver simply switches from closed- to open-circuit without removing the mouthpiece, and heads for the surface.
There are two levels of PADI Recreational Rebreather Diver. The first is depth-limited to 18m and uses the on-board diluent cylinder for OC bail-out, whereas the Advanced Rebreather Diver trains to carry an off-board OC supply in the form of a sling-tank and can go to a maximum of 40m. Dives are no-deco and without penetration of overhead environments. The rebreather unit must still be prepared meticulously.
So far only the Poseidon Discovery Mk6 conforms to the PADI spec, but a version of an APD rebreather will be available with the simplified electronics. We presume other manufacturers will follow suit.
It all depends on whether there is popular uptake of the course but we hear that many PADI instructors are racing to get certified to be able to teach it.
The JJ-CCR reviewed here is not suitable for the recreational course, but coming is a PADI Technical Rebreather course, for which the VR Technology Sentinel and some other advanced rebreathers like it will comply.

WITH CONVENTIONAL open-circuit (OC) scuba, the diver inhales pre-mixed gas from a tank via a suitable valve and exhales into the water. This exhaled gas contains the poisonous carbon dioxide that is a by-product of metabolism, plus a lot of unused oxygen.
A closed-circuit rebreather (CCR) diver exhales back into a closed loop. This includes a chemical scrubber to remove the carbon dioxide, and a device, either manual, automatic or a combination of the two, that adds a little oxygen to replace that which has been used.
Far less gas is required for any dive than with open circuit. And at any given moment the rebreather diver is breathing the mix most appropriate for the current depth, so deco requirements are kept to a minimum.
Because of the small amount of gas used, CCRs have become popular with divers who like to go deep, though if they carry sufficient bail-out supplies, they will end up carrying lots of OC tanks too. Rebreathers are popular with wildlife film-makers and photographers, because they get plenty of in-water time without deco stops, and the lack of bubbles can allow them to be covert, though it is not a cloak of invisibility.
All good, but there are so many important considerations that the rebreather designer and user must never forget.

FIRSTLY, THE CARBON DIOXIDE must be totally removed as the gas passes round the fixed loop before the diver rebreathes it.
Secondly, the partial pressure of oxygen in the breathing mix must be within a breathable range at any given depth. If it is too high, oxygen toxicity might occur, causing muscle spasms leading to drowning. If it is too low, the diver becomes hypoxic without warning and dies as surely as if he had received a bullet in the brain.
So whereas the OC diver must be sure to be able to breathe, and to breathe from the right tank at any given moment during multiple-tank dives, the rebreather diver can always breathe but must be sure of what he is breathing.
That’s where the design of the scrubber unit and the oxygen management system that includes 02-sensing devices and the 02-addition solenoid comes in.
Buoyancy is also managed differently to OC diving. Lung volumes cannot be easily altered to fine-tune buoyancy, so the rebreather diver is circumspect about frequent depth changes, especially in the shallows, because this means constantly adjusting either the loop volume, by exhaling through the nose, or the BC (wing) volume to compensate.
You can’t just throw a set on your back and jump in, either. Rebreathers need to be set up precisely and correctly before diving.