Are you looking for longer, quieter dives? Or perhaps you have a diving aficionado guest who wants to take exploring the sea to a new level? Either way, rebreather diving might be the answer you’re looking for.
Unlike scuba equipment, which has divers breathing on an open circuit,’ in which they breathe in gas from their cylinder(s) and exhale through their underwater environment, a rebreather retains the diver’s exhalation in a closed circuit, where that exhalation is “scrubbed” of CO2 by passing it through a chemical absorbent canister, explains John Chatterton, a professional diver for more than 35 years and trainer of technical divers. Essentially, the air breathed is recycled into a system in which CO2 is kept and O2 added.
Open circuit diving, Chatterton says, is relatively simple in that you just need gas and reliable regulators — divers need to manage their gas supply, and should one regulator fail, they go to a proper backup. However, as divers go deeper, it’s increasingly difficult to carry enough gas as increased ambient water pressure increases gas usage, posing serious limitations. This is when rebreather diving might be more suitable.
“That scrubbed gas is passed on to the diver for inhalation after electronic sensors determine the amount of oxygen the diver has metabolized, and a computer directs solenoids to deliver the exact amounts to keep oxygen at determined levels,” says Chatterton. The amount of O2 breathed can be adapted to your dive and depth, meaning those deep dives you’ve been craving are possible.
But are they safe? There are certainly concerns circulating regarding the safety of diving deep with mixed gas. While rebreather diving does bring alternative risks, it also has its benefits and is quite enjoyable when carried out safely. Here’s what you need to know.
First things first, any certified scuba diver can go rebreather diving, according to Christelle Holler of Tahiti Private Expeditions, which has trained crew on technical diving and has joined a few trained owners on their diving trips around the world. She maintains the minimum level required is the PADI Open Water. As an example, PADI requests that the student be at least 18 and has a minimum of 25 logged dives.
However, using the rebreather unit does require a proper learning process via renowned dive schools such as PADI and TDI. “Every brand or model of rebreather has its own training process adapted to the unit you are going to dive with,” says Holler. “Your certification will only allow you to dive with that specific brand or model. If you would like to dive with a different kind of rebreather, you will need to go through the training process adapted to it.”
If you’re a multi-skilled crewmember with scuba instructor credentials to your name, this also applies to you. You need to go through the instructorship process for every kind of rebreather you would like to teach with and justify beforehand a certain number of hours with the unit first, usually at least 100 hours.
“The training to become a rebreather diver usually involves about eight dives, theory, and a written exam,” says Holler, adding that once trained, it’s easy to use a rebreather unit. “[Training] takes about five days minimum in total. Students learn how the rebreather unit is made and how it works.”
She adds that there are several ways of diving with a rebreather, such as technical diving versus recreational diving. Technical diving, she explains, involves cave diving or decompression diving with a rebreather unit, which requires a certain level of expertise and number of dives performed as well as specific certifications. On the flip side, recreational diving doesn’t involve any deco stop, and there is always a way to reach the surface safely in case a problem arises. This still implies training, says Holler, but is more accessible to anyone than technical diving.
Once trained, longer dives aren’t the only benefits of moving from scuba to rebreather diving you’ll enjoy. While it allows a diver to dive longer for up to three hours, says Holler, it’s still a plus for those who don't want to do long dives as they can dive from two to three times per day without refilling tanks and preparing the dive gear again.
But the deeper you go, the more marine life you’ll be able to see — and the better you’ll be able to experience it. Since the unit doesn’t make bubbles, there is no noise underwater. “Observation of marine life is much better and closer and allows [the diver] to watch natural behaviors, such as breeding or hunt sessions,” says Holler, adding that this isn’t possible with scuba diving. “When a rebreather diver stops moving, the fish do not notice him anymore.” And for you photographers out there, since you can observe marine life without making noise, the potential for great underwater shots is much higher.
“For crew superyacht owners who are keen divers and who have dived basically all over the world, rebreather diving will make them feel like discovering all the areas they have visited before while scuba diving,” she says.
Holler adds that there is also much less nitrogen in the gas breathed than when scuba diving with regular equipment, meaning there are lessor limited deco stops. “The gas breathed is warm and humid as opposed to scuba, where the air is cold and dry,” she explains. “It avoids getting a dry throat but also getting cold quickly.”
Safety and Risks
But where there are advantages, there are also disadvantages— and in the case of rebreather diving, as with any water activity, it comes in the form of safety risks.
As simple as the rebreather diving system is, Chatterton points out that it’s dependent on electronics and computerization. “A rebreather will pretty much function, or fail, regardless if the diver is in fifty feet of water or five hundred feet of water,” he says. “While the diver may need to consider the depth and things like decompression, the rebreather just works or not.”
If an open circuit diver has an emergency situation relative to their life support, they just need something to breathe. Rebreathers, however, are more complicated and sensitive than this. As Chatterton explains, you can have too much or too little oxygen for a variety of reasons, and figuring it out is not always easy. A rebreather, he adds, can deliver you gas to breathe that will render you unconscious.
“Rebreathers can make deep dives possible, but with increased responsibilities and risks,” he says. “Open circuit is simple, but deeper dives can pose serious risks of inadequate gas supply. So, if you are diving deeper, or you just like the sophistication of rebreather technology, then it may lure you from open circuit to closed circuit. Like so many things in life, rebreathers are a compromise — greater capabilities for greater responsibilities.”
However, that’s not to say rebreather diving can’t be safe. “Rebreatherdiving, when rules are followed, is not more dangerous than any other recreational activity such as paragliding, kayaking, canoeing,” says Holler. “Itis of utmost importance to be trained and understand this way of diving as well as following the rules, especially since we are under the water.”