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What is a Rebreather?

By Lori Kilchermann
Updated May 23, 2024
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A rebreather is an apparatus also known as a Closed Circuit Underwater Breathing Apparatus, or CCUBA. This device scrubs or removes carbon dioxide from a diver's exhaled breath; a small amount of oxygen or an oxygen-gas mixture is added to the remaining breath to allow for a longer dive with less reserve oxygen and smaller tanks. There are many fewer bubbles emitted from a diver using a rebreather as compared to a one using traditional diving equipment. The oxygen in the escaping bubbles is filtered through the rebreather and used by the diver's body instead of being wasted in the water. By utilizing a rebreather, the diver is able to remain at depth much longer than with traditional diving tanks.

There are many advantages to using a rebreather as compared to traditional tanks, both to the diver and the underwater surroundings. By producing fewer bubbles, the diver is able to maintain a much stealthier position in the water, making the rebreather a very good military or tactical device. By inhaling the scrubbed gases through the rebreather, the breathing mixture is much warmer and more pleasant on extended duration dives, which makes the dive less physically demanding. Divers also suffer fewer effects of the bends when using a rebreather, making this a safer method of diving and ascending from the depths.

When using traditional diving gear, divers exploring dangerous shipwrecks are subject to the emitted bubbles disturbing objects within the wreck. The bubbles have the power to ignite unexploded armaments from sunken warships and can disturb dirt and silt, making vision and escape from the inner clutches of a wreck difficult. More dangerous than this, however, is the tendency for the diver's exhaled oxygen to be trapped in the inner compartments and form large air pockets. This trapped oxygenated air aids in the formation of rust and deterioration of the wreck.

Divers require specialized training in the use of a rebreather, and the feel of breathing the scrubbed gas requires some getting used to. In the event of two or more divers encountering a problem at depth, the ability to simply switch back and forth with the other's oxygen hose is not possible. This single factor convinces many divers to forgo the technology and remain equipped with the traditional diving equipment. This breathing apparatus has been tested at height by mountain climbers with little success. The equipment has not yet been designed to withstand extremely cold conditions.

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Discussion Comments

By anon242312 — On Jan 23, 2012

@Whiteplane (Post 4): You have asked about breathing “scrubbed” gas as opposed to “unscrubbed” gas. In terms of this article, scrubbed gas relates to the process of soda lime removing the CO2 that the diver exhales in the loop of a closed circuit rebreather system. Every exhaled breath is pushed through the scrubber and CO2 is effectively removed. The diver then is able “rebreathe” the exhaled gas via the upstream side of the loop without fear of taking in a mix that contains excessive amounts of CO2 -- a rebreather divers nightmare and essentially their death warrant.

The unit either automatically (or with manual intervention) increases the oxygen levels of the rebreather gas in order to sustain life as the diver metabolizes the oxygen in the loop. Not only is oxygen involved, but also the diluent (or inert) gas. This can either be air, nitrox, or a tri-mix and this is also injected by the system as well. In terms of your direct question, the feeling of breathing scrubbed or unscrubbed gas (the air you breathe on the surface), there is little difference from a life supporting perspective. Both work. What makes a rebreather feel different is the fact that the scrubbing process creates a chemical reaction that warms the breathed gas. This is beneficial for a rebreather diver as they typically stay at depth longer so the warmer gas they breathe can directly relate to overall comfort. That is, they don't begin to feel as cold as quickly.

Open Circuit divers exhale into the water with every breath they take, so the gas they inhale never warms up and the gas they breathe becomes colder at depth as well. Breathing gas on an open circuit system also means the air is much drier, too. Diving with a rebreather results in moister air which adds to comfort levels, as well.

What makes diving a rebreather feel very different from an open circuit system (and indeed from breathing air normally within the atmosphere) is what is called loop volume. The volume of gas within a closed circuit loop varies from type to type. Some literally feel harder to breathe from than others based purely on this. The fact that the inhaled gas is capable of supporting life doesn't change (assuming the system is functioning normally); it's the design of the rebreather system that determines how different it feels. So in a nutshell, breathing on a rebreather from type to type feels different and regardless (usually) of the system, it is a more conscious effort to breathe through a closed circuit rebreather than what is required on the surface. It's one reason why you'll often hear rebreather divers suggest you test dive a system you might be interested in to ensure you feel comfortable while breathing.

Personally, I dive a Poseidon Discovery MkVI eGR system. Hope this helps anyone wondering about closed circuit rebreathers and breathing through them.

By SuperJD — On Jul 05, 2011

I love scuba diving. It is very relaxing to me. I do not get to go that often, so I do not keep myself updated on all of the different and new types of equipment. I have never heard of a rebreather, but from what I read, I think I will give it a try.

The most important benefit for me is being able to stay under water longer with a rebreather. When I am diving, time seems to fly by. Before I know it, I have to return above water to change my tank. With a rebreather, I am hoping that I can stay submerged for a longer period of time.

Thanks for writing this article. I have learned a lot and I will look more into using a rebreather for my next diving excursion.

By drhs07 — On Jul 04, 2011

I go scuba diving at least twice a year. I started using a rebreather instead of other traditional equipment about a year ago. I must say, using a rebreather has definitely enhanced my diving experiences.

The best thing about using a rebreather is less bubbles. When I used my old equipment, there would be a lot of bubbles forming in the water when I exhaled. Not only did those bubbles make it harder to see, but it also scared off whatever fish I was trying to observe. I could not get as close as I wanted to the fish without the bubbles disturbing them and them swimming off.

Now, with the rebreather, I can get up close and personal with all sorts of exotic fish. I am glad that I upgraded my equipment, and I encourage all other divers to do the same.

By whiteplane — On Jul 03, 2011

It says that it takes some getting used to to be able to breathe scrubbed gas. Can anyone tell me what this feels like? I guess I have really only ever breather unscrubbed air, or whatever you would call the air that is just floating around us. I don't have anything to compare it to. I would almost want to go scuba diving just so I could try out the scrubbed air.

By backdraft — On Jul 03, 2011

I find it really interesting that the rebreather heats up the air the diver is breathing at this makes the diver able to stay under longer. I would never have thought of something like that but it makes a lot of sense.

Think of when you go outside on a really bitter cold day and you take those first few deep breaths. It kind of shocks you lungs and you almost struggle to take the next breath. It makes sense that this would be a struggle for a diver over the course of a long dive. If you go just 10 feet below the surface of the water it is usually much colder. Rebreathers are a really cool technology that works in lots of unexpected ways

By chivebasil — On Jul 02, 2011

There is so much talk these days about carbon dioxide being harmful for the atmosphere. I wonder if there is a way to adapt the technology in a rebreather for some kind of industrial purpose. Maybe we could put this technology on the top of smokestacks or at the end of tailpipes to scrub out some of the carbon dioxide. It is a small and maybe silly idea but if we are going to really prepare for a future with climate change we need to start thinking outside of the box.

By summing — On Jul 01, 2011

I got to go scuba diving on a vacation to the Caribbean last year. It was my first time and it was so much fun. The feeling of being able to breathe underwater is so foreign but also so exciting. It takes some getting used to but it starts to feel natural very quickly.

When I was under the water I got to see exotic fish, colorful plants and the ruins of a ship that sank decades ago. It was probably the best part of my vacation. I owe it all to the rebreather.

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