Rebreather Diving – SISAC 0833


Rebreather Diving

Rebreather divers are a more common sight at dive locations than in previous years. If you’ve been diving recently you will have noticed just how many divers are using a rebreather. From the rather rare item of a few years ago to the plethora of types and manufacturers available now. Some will also have been modified by adding to the system or maybe replacing the case or frame.

So what’s the deal.

The upsides are:

One of the most significant advantages of fully closed circuit diving is the massive increase in gas efficiency. Using smaller cylinders, less visits to the filling station and cheaper fills (particularly when using Trimix)… Open circuit SCUBA (air or mixed gas) is extremely wasteful of gas.

Much greater bottom time (dependent on depth). With a closed-circuit rebreather, bottom times are probably more limited by your endurance than the gas you are carrying. Typicall three hours at 20mtrs and no deco required.

A closed-circuit rebreather doesn’t make bubbles. The fish feel more comfortable around you and you can more clearly hear the subtle sounds of the sea. You are more at one with the underwater environment.

With a closed-circuit system, you can go deeper and stay down longer. The system monitors and manages the gas mixture that you are breathing at any given depth. Ensuring you are getting the optimum oxygen at the current pressure. Also mixing in nitrogen and inert gasses (helium, neon, xenon, etc.) for everything else. These advantages deminish with greater depths but are again advantageous in the decompression phase.

Since you are re-breathing the gas that has already been through your lungs (with a tiny amount of O2 added) your breath is a moister, warmer mixture so you are much less likely to get the typical ‘dry mouth’ that maybe an issue when breathing air directly from the tank.

That said, there some significant disadvantages to Rebreathers

Rebreathers are technical gear, and require special training to use safely,training beyond that experienced during traditional SCUBA qualification. Expect to pay around £750 for the initial qualification. A further cost is required for each of the subsequent Nitrox, Trimix etc. Courses……….yep, expensive. On successful completion of your training you will be given a unique RB number. This number will be required prior to purchasing any RB or for spares associated with it.

A rebreather unit is also expensive, typically around £5000 to £8000 and like buying a car the extras can add up to several thousand more, and I would regard some of these “extras” as essentials.

Since rebreathers are complex pieces of equipment. They require careful maintenance and setup, this can extend on site prep time.

The gases used in technical diving are often more expensive than standard air or Nitrox mixes, and can be impossible to find in remote locations.

In addition to gasses, rebreathers require a ‘scrubber’ chemical, normally know as sofnolime, (or kitty litter due to its appearance). Sofnolime removes the excess CO2 from the breathing loop and must be replaced after a few hours of use. The scubber duration may be extended when diving in warmer waters and/or using a scrubber monitor.

Unlike open circuit, boyancy can’t be fine tuned by adjusting the content of air/gas in the lungs as on a rebreather the breathing gas is merely moved from the lungs to the counterlungs so no change in boyancy, something that can take a bit of getting used to when first getting to grips with a RB.

Because rebreathers have limited gas (usually 2 or 3 litre bottles) a bailout cylinder(s) maybe carried and are expected for deeper Trimix dives.


Rebreathers have in the past had a bad reputation, phrases like “yellow box of death” however I have been using a rebreather for a serious number of years and it has never let me down, in short it’s cleverer than I am. Just like anything in diving, you need to know what you are doing and look after the equipment you use.

Rebreathers come in various guises, manual or Kiss ( keep it simple stupid ), semi closed active and passive, oxygen and of course full electronic. Whilst most choose the full electronic version, it is important to understand the different characteristics and costs before making a final decision.

With the application of common sense, diving (sometimes call flying) a rebreather is a fantastic way to dive and I recommend it.

Keith Cairey

Find out more by contacting the Training Officer and reviewing the following information.

Rebreather Try Dives available for qualified divers.

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