Rebreather diving, CCR diving, silent diving—call it what you like, but rebreather diving remains a bit of a mystery to many divers, especially those in the beginning stages.
If you’ve always wanted to know a little more about how rebreathers work and why divers choose them, read on. Quick disclaimer, though: there is much more to learn about rebreather diving—and we could have easily written a much longer piece—so use this information as a starting point if you’re interested in the topic.
Let’s dive into the world of rebreather diving!
For the uninitiated: How rebreathers work
In a nutshell, rebreathers clean and recycle your breathing gas during the dive. They also monitor the gas you’re breathing with the help of sensors, just as you’d find in a nitrox analyzer.
To clean and recycle your gas, rebreathers have one or two scrubber canisters filled with soda lime. Through a chemical reaction, the soda lime granules bind the carbon dioxide you exhale to ‘clean’ the gas that’s circulating through the machine, aka “the loop.”
As your body uses some of the oxygen in the breathing gas, it’s replenished either automatically or mechanically, depending on the type of rebreather.
Very (very) basically speaking, there are two classes of rebreathers—semi-closed circuit rebreathers (SCR) and closed-circuit rebreathers (CCR). SCRs extend the duration of the gas you carry but you still exhale your loop content regularly and replace it completely.
CCRs are more efficient because they recycle the gas divers breathe rather than letting it be exhaled into the water. As you metabolize oxygen, a small cylinder of pure oxygen replenishes the O2 on CCRs, whereas SCRs rely on nitrox.
While all rebreathers adhere to these basic principles, makes and models are sufficiently different to warrant unit-specific courses. Once you’re trained and have some experience on one of them, you still need a crossover (think of it as about 50% of a full course) if you would like to dive another.
For the undecided: Top 10 reasons to choose rebreather diving
1. Silent diving
Diving on a CCR is almost silent. You may feel that you descend into the silent world whenever you dive, but try rebreather diving and you’ll find out just how much quieter diving can be. You’ll only hear yourself breathe.
In fact, whenever there are open circuit (bubble-making) divers around, many rebreather divers do a quick bubble check just to be extra sure that none of their gear is leaking.
2. No more dry mouth
The chemical reaction used to bind your exhaled CO2 to the scrubber materials creates moisture and heat. In practice, that means two things. First, the gas you’re breathing is not as dry as you’re used to from open-circuit diving and your mouth won’t feel dry at the end of a dive.
Second, as you’re breathing, the gas not only feels warmer but also keeps you a little warmer throughout the dive. That’s great news for those of us who always feel chilly underwater.
3. Getting closer to marine life
Just as rebreather divers think of bubbles as noisy and distracting, so too do fish and other marine life. Even in areas where fish are used to divers, they tend to keep a bit of distance.
When you’re diving on CCR, one of the first things you’ll notice is that the fish come much closer. That makes for better pictures and videos and overall more memorable marine life encounters.
4. Not disturbing wrecks and caves less
Have you ever noticed that divers’ bubbles in wrecks and caves can disturb silt, sediment, and loose rust on ceilings? Depending on where you dive, this can seriously limit visibility. Not making bubbles in the first place means you have less of an impact on your environment, and preserve visibility for those behind you and for your return.
5. Optimal gas mix at every depth
Think of rebreathers as a gas-mixing machine you take with you underwater. When you dive open-circuit, you breathe the same gas at every depth and you choose your oxygen content depending on your maximum depth.
When you dive a rebreather, you choose what gas you want to breathe at a given depth and adjust your settings accordingly. As you change depths, you change your gas mixture. This allows you to maximize no-stop times and minimize potential decompression obligations.
6. Longer Dives
On many CCR dives, your real time limit becomes the number of hours for which your scrubber will work efficiently to bind carbon dioxide. That means dives can be longer without the fear of running out of gas.
How long your scrubber lasts depends on a few factors, such as your workload, depth, and water temperature. Each manufacturer makes a conservative recommendation for scrubber duration, and some rebreathers also have measuring tools.
Because you’re breathing the ideal gas for a certain depth (see No. 5), you can also often spend more time at depths where you would have been limited by the decompression obligation and deco gas on open-circuit. In short, rebreathers have the potential to transform the way you dive.
Of course, you still need to plan your dive so you understand where you have flexibility and where you have limits. The flexibility is really great on wreck dives, for example, where you may be changing depths a few times to dip in and out of cargo holds.
7. More options for problem solving
Anyone who has done technical diving training with open-circuit gear will recognize this scenario: you discover a leak from somewhere, contain it as best as possible, and now must end your dive with limited resources.
When you dive a rebreather, you have both your rebreather and a supply of open-circuit bailout (emergency) gas at your disposal. During your training, you learn that it is often possible to troubleshoot your rebreather. Consequently, when a problem happens, you have a toolbox of options to deal with it.
8. Minimal gas use (defeat that helium bill)
Rebreather divers use less gas than open-circuit divers simply because they recirculate the same breath through the rebreather, with a few variations. That makes your diving cheaper on a day-to-day basis, especially if you’re thinking of diving depths that require trimix.
Of course, there is the cost of buying and training on a rebreather unit as well as oxygen fills and soda lime. However, if you’re planning a series of technical or trimix dives over a week or 10 days, you’ll notice a significant difference in your gas bill.
9. Flexible dive planning
Rebreather divers need to plan their dives just like open-circuit divers. However, with a greater choice of which gas to breathe at each depth, dive planning can be more flexible. To do this, CCR divers adjust the amount of oxygen they have in their mix at a certain depth. This is called changing their set point—a target amount of O2 in the gas.
Typically, dives start on a low set point, such as an oxygen partial pressure of 0.7 ata. As you reach your target depth, you typically change your set point to something richer in O2, like 1.2 or 1.3 ata.
On most rebreathers, divers choose when those changes happen, and they can adapt their plan as circumstances change. This flexibility is ideal when you need to react to adverse conditions or when you find that there is far more to see at 100 feet (30 m) than at 130 feet (40 m).
There are more considerations to rebreather dive planning such as tracking oxygen exposure, but those would reach far beyond this top 10 list.
10. A whole new level of diving skills
There’s no denying that rebreather training is challenging. Basic courses tend to take a week and give divers their license to practice. Fine-tuning buoyancy without your lungs tends to take a little longer for most.
When you dive a rebreather, inhaling and exhaling doesn’t change your buoyancy for the majority of the dive. You exhale into a part of your rebreather, the counterlung, and inhale from that same counterlung. Depending on the make, your trim might change, but your buoyancy doesn’t.
Divers qualify for their chosen unit only and need to complete a crossover course if they would like to dive another rebreather. Because course work differs depending on which unit you choose, many rebreather instructors offer try dives on specific rebreathers, allowing you to test out a rebreather before committing to it.
Once you go through the training, you’ll find your diving skills reach a whole new level. Managing buoyancy without your lungs, diving your rebreather, and handling various emergencies becomes second nature.
This type of diving can seriously transform your underwater experience thanks to the silence and the flexibility. Most divers also find that they start to prefer one longer dive to several short ones.
Any Downsides?
We’d be lying if we said there were no potential downsides to CCR diving. For starters, it is expensive to get started, and renting a rebreather is rarely a long-term option.
Perhaps more importantly, rebreather diving is more complex—not complicated—than open-circuit diving. There are more things to consider when you prepare and check your gear, so you need to be conscientious and focused during the process. You also need to keep your skills fresh, ideally by making your rebreather your first choice of diving configuration.
None of these steps are necessarily difficult, but it’s even more important than on open-circuit not to skip anything or become complacent. Preparing your rebreather isn’t something you’d leave to the crew on a liveaboard, for example. Diving regularly, practicing skills, and being open to new knowledge are some of the key factors to successful rebreather diving for years to come.
How to start rebreather diving
As we mentioned above, if you’re not sure about which rebreather is right for you, consider trying several of them. Think about the type of diving you would like to do and narrow down your choices with those criteria in mind.
Some rebreathers are well-suited to cave diving while others are easier to handle when you’re on a boat in big waves.That doesn’t mean one rebreather can only do one thing but, just like different types of cars are suited to different tasks, not every rebreather excels at every type of diving.
Check out your local rebreather diving community to see which CCRs people are diving near you. Plus, don’t be afraid to talk to different instructors to get a feel for the rebreathers they’re teaching and why they chose those.
You may also be able to complete an entry-level rebreather class on a rental unit. That’s a great way to figure out whether you like this kind of diving before committing to the biggest part of the investment.
Initial rebreather qualifications are usually referred to as “Mod 1” (think of it as Module 1) and take about a week to complete. This is where it gets a little complicated. Mod 1 courses come in different “flavors,” depending on manufacturers and training agencies.
The most basic level would allow you to dive your rebreather to 100 feet (30 m) without mandatory decompression stops. Under the standards of TDI, you would need to be a nitrox diver and have at least 20 dives under your belt to start the training. Many instructors will recommend more experience.
If you’re already a technical diver, you may be allowed to qualify to dive to deeper depths and use limited amounts of helium. Having said that, it’s important to progress slowly and don’t rush your rebreather diving journey.
Rebreather training costs vary widely depending on your location, availability of consumables like scrubber material and oxygen, and other overhead costs. Remember that your instructor has invested (tens of) thousands of dollars and considerable amounts of time in their training. Their course price will surely reflect that.
Ready to get started? Rebreather try dives are a great way of getting to know models and instructors first-hand before making a bigger commitment. Don’t hesitate to ask lots of questions, and enjoy the journey!
What is the best rebreather?
Hand on heart, there are few questions that more quickly start an argument in a room full of technical divers. After all, the best rebreather for you is the one that allows you to do the kind of diving you want to do.
That was our guiding principle for the selections below—this list is not meant to be complete, but rather a sample of several worthy rebreathers, and it’s certainly not a judgement on the other fantastic models on the market today. With that said, here are a few of our favorites:
Best rebreather for classic simplicity
Ever since its launch in 2010, the JJ-CCR has grown its fan base around the world. This rebreather is sometimes also called the Land Rover of rebreathers for its simplicity and indestructibility.
The JJ is a classic backmount rebreather, featuring oxygen and diluent tanks on either side of its scrubber canister. The canister is made from tough, anodized aluminium with space for up to four diving tanks, ready for the moment you move from entry-level CCR dives to bigger adventures in demanding environments.
The JJ is an electronic CCR that features a Shearwater Petrel computer and a heads-up display mounted to the loop. It weighs about 77 pounds (35 kg) ready to dive.
Best rebreather for small caves
Not every cave is small, but if you’re thinking about exploring smaller caves or those with difficult access, you can’t really go wrong with the KISS Sidewinder.
Think of it as a simple rebreather added on top of your sidemount configuration. There is no need to change your existing setup—you simply add connectors for the rebreather. The Sidewinder is a mechanical CCR, giving divers control over the addition of oxygen during their dives. A Shearwater computer helps monitor oxygen content and calculates decompression time.
It also has a relatively small internal volume, making it easy to dive in shallow waters. Plus, you can disassemble it into parts that are small enough to travel in an airplane cabin.
Best rebreather for diving from large boats
Even if they love sidemount diving, most rebreather divers would admit that it poses challenges on boats in heavy seas. That’s even truer if the plan is to dive deeper and use several bailout cylinders.
If that’s what most of your diving looks like, check out the Hollis Prism2. This electronic rebreather features a transparent scrubber canister, making it easy for divers to verify that their scrubber has been packed and fitted. It’s also been fitted with Shearwater electronics and weighs about 66 pounds (30 kg) ready to dive.
Best rebreather for travel
Any technical diver will admit that technical diving and traveling light are mutually exclusive. Still, some rebreathers are easier to travel with than others.
In the back-mount category, the rEvo rebreather is one of the lighter choices you could make. This rebreather combines electronic and mechanical oxygen addition. It also benefits from one of the longest lasting scrubbers in the market and redundant PO2 displays through Shearwater electronics backed up by two rEvo dream displays.
In the sidemount category, aside from the Sidewinder or the Fathom Gemini, which shares some design features, it’s worth looking at cylinder-style models like the Flex CCR. As a rule, rebreathers that can be broken down into individual components are easier to pack than others.
Best rebreather for versatility
Mention rebreathers, and many non-CCR divers picture classic back-mount models. Over the past few years, though, chest-mount or front-mount rebreathers have grown in popularity.
Previously associated primarily with military diving, the versatility of small rebreathers—great for travel— means they can be used with back-mount, side-mount, and even single-tank configurations. The Triton is a mechanical chest-mount CCR, while Dive Rite’s O2ptima CM offers an electronic version.
Which rebreather is right for you? Talk to rebreather divers around you, try a few different units, and don’t be afraid to ask a lot of questions before you commit. The good news is that even though many rebreathers are best suited to a specific kind of diving, few are one-trick ponies.
Poor choice. I’ve been diving an Inspiration for more than 20 years. There is one thing you have forgotten about, and that is the percentage of successful dives, or the numbver of dives lost to problems once on the boat and away from land.
I’ve lost count of the number of dives that have been called off for technical problems with buddies RBs. The Inspiration just gets the job done in a very uneventful way. Triton? never see them, JJ? great when they work. Hollis? always having niggly problems. Liberty? you’re right, way over priced for what it is, you will have to sell a kidney.
You might not like the APD machines, but from my experience, there are far more of them out there than the others, and they’re about the most reliable that there are available, they’re there, getting the job done.