Diving: Selecting the right rebreather

There's lots of CCRs (closed circuit rebreathers) on offer, many intended for the recreational market. Some have limits that are vital to understand.

September 20, 2022
Selecting the right rebreather is vital to safely achieve the goals you may have in mind.
Selecting the right rebreather is vital to safely achieve the goals you may have in mind.
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A technical CCR can be dived within and beyond recreational limits, a recreational CCR cannot.  You need to choose one that will allow you to do the depths and times you want.

Ok,  you have been diving for a while and thinking of buying a rebreather. They look complex and expensive, but are they really? The answer is: anyone can learn to dive using a rebreather and you may be surprised at how cost effective they are. The key is to select one that suits you, and to become well trained on it.

eCCR or mCCR?

There are two types of CCR: electronic (eCCR), and mechanical (mCCR). The difference between the eCCR and the mCCR is the reliance on electronics. All types of CCR have oxygen sensors which continually react with the oxygen concentration in the CCR breathing loop and produce a tiny electrical current which is displayed as a partial pressure of oxygen, or PO2. Most eCCRs have an electromagnetic device or solenoid that obeys the instructions you programme into it. It injects oxygen to maintain a pre-set loop PO2. The solenoid controls your PO2 and therefore your dive. If this electronic ‘brain’ should fail, and go unnoticed, the consequences could be catastrophic.

With the KISS type of mCCR, oxygen is supplied to the loop continuously through a constant bleed at about the metabolic rate you consume it. No electronics. It’s all mechanical.

If the PO2 drops, the diver pushes the manual ‘add’ button. At depth, the PO2 is very stable and does not distract from the dive. An mCCR is certainly less prone to failure.
Analysis of dive accidents shows complacency to be the main cause of CCR related diver deaths but divers know they must pay attention so complacency does not become an issue.

Regardless of the CCR type, divers are always urged to check their PO2s every 1-4 minutes, which is very simple if the diver is using a Shearwater NERD as a heads-up display.

Considering cost

Some CCRs are far more expensive than others for little or no advantage. All man-made items will eventually fail so look at what options the CCR offers if there is a failure. Whatever you do, research the market. Ask CCR divers you respect.
Many CCRs these days, like the KISS mCCR, have successfully undergone internationally recognised, third-party testing. Consider the weight, the manufacturer’s recommended underwater duration, simplicity, ease of maintenance on a trip, and the running costs.

Learning to dive with a CCR is like learning to dive all over again. Reputable CCRs have training programmes offered by the major diver certification agencies such as TDI and PADI. Agency CCR Standards do differ but are largely based on accepted international standards.

Where to be selective

Where you should be very selective is in choosing your Instructor. Get the best you can afford. You need them to guide you during the course and also to be available after your training, when you are at your most vulnerable.
Reliability is critical. Electronics and sea water don’t mix well. Certainly the electronics in my first CCR failed several times, including once underwater. I am pleased to say my KISS Classic mCCR has not failed me yet. When I go on a trip I take a few spares but have never had to use them. The simple and robust design has proven so very reliable.

It's a good idea to look at the operating cost of the CCR. What is the manufacturers recommended sorb duration (how long you can stay underwater safely).

The KISS Classic offers 5 hours in 18 degrees C and above. This is quite extraordinary considering there are no electronic devices involved in trying to track the invisible exothermic front. The CO2 absorbent duration affects the running cost of your CCR. If you are getting good scrubber times, the cost of running a CCR, at recreational depth, is about the same as twin tanks on nitrox at the same depth.

However that is where the comparison ends.

If you want to dive deeper wrecks and stay long enough to enjoy them, you need a trimix
capable CCR and a trimix CCR Diver qualification and in some places trimix can cost you about US$360.00 per 11L cylinder. If you are on twins or sidemount, multiply by two, plus deco gas, per dive.

In Truk Lagoon we do about 22-24 dives per trip. Because I use my KISS Classic mCCR, I buy one cylinder of trimix and might get it topped up once. That is enough for all my dives plus an emergency bailout if required. Low operating cost is a big reason for owning a CCR.

My preference

My preference, after being trained on, and diving both the mCCR and the eCCR, is the mCCR. But not all CCRs are equal. I bought my eCCR in 2007 and from then until 2009 I had all sorts of issues with the solenoid and control handsets, all electronic issues.  In 2009 I decided to give the KISS Classic mCCR a ‘go’ and that was a great decision which has allowed me fantastic trouble-free CCR wreck diving in many places around the world.

Tony Howell is a KISS mCCR Instructor Trainer.

Further information is available from:
Dive Centre Ltd -
09 444 7698 or
dive.centre.ltd@xtra.co.nz; and

NZ Sea Adventures Ltd
04 233-8238 or
tony@scubadiving.co.nz

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