You might be considering switching to a rebreather from diving with an open-circuit-scuba tank. If you are, then this article will help you decide if rebreathers are a good idea. Rebreathers are a totally different way of breathing when scuba diving, which is why it’s important to understand what does a rebreather do and how long you can dive on a rebreather.
You can dive on a rebreather for 2-3 hours, and your dive time whilst using a rebreather is limited by the CNS oxygen toxicity clock, the gas supply and the scrubber duration. Rebreathers are a closed-circuit breathing apparatus for scuba diving as an alternative to a scuba tank and apparatus.
One of the great benefits of diving on a rebreather is how the unit doesn’t produce noisy bubbles. Bubbles frighten fish and other sea creatures, which includes sharks, so if you dive with a rebreather you are more likely to be approached by sharks and other animals.
How long can you dive on a rebreather?
You can usually dive for 2-3 hours on a rebreather, depending on the scrubber duration and the CNS oxygen toxicity clock. Scrubbers remove carbon dioxide from the recycled air and are normally rated for either two or three hours, depending on the type of scrubber.
The other limiting factor for how long you can dive on a rebreather is the gas supply. A gas cylinder with a 3 litre capacity will give up to 10 hours of dive time vs a cylinder of 2 litres that will last around 6 1/2 hours. But these time limits will depend on how hard you work during the dive.
In a test of a Dreger LAR V Close-Circuit Oxygen Rebreather, the following times were recorded:
- CO2 canister duration in unmanned test was 48 minutes in cold water at 39°F (4°C).
- CO2 canister duration in unmanned test was 3 hours 15 minutes in warm water at 70°F (21°C).
- The mean cannister duration in 25 FSW* (7.6 metres) with a manned test was 124 minutes (+ or – 9 minutes) at 40°F (4°C).
- The mean cannister duration in 25 FSW (7.6 metres) with a manned test was 226 minutes (+ or – 23 minutes) at 70°F (21°C).
* FSW = Foot sea water. Above source – Research Gate.
How does a rebreather work and what does it do?
A rebreather is a closed circuit breathing apparatus which has a CO2 scrubber to absorb the carbon dioxide in the exhaled breath of the user. The exhaled breath is recycled and the unused oxygen is topped-up from the gas cannister so it can be breathed again.
The amount of oxygen replenished will be equal to the amount that’s been metabolised by the user. But the percentage of oxygen added to the gas is optimised to keep the partial pressure of oxygen safe for the diver’s depth.
What is the longest rebreather dive?
The longest rebreather dive was nine hours 40 minutes and was set by Australian diver David Shaw. This longest rebreather dive was dived in the Boesmansgat Cave and reached a depth of 270 metres (886 feet).
A Navy Seal can stay underwater with a rebreather for up to four hours in warm water and two hours in cold water, but the length of time is also affected by Navy Seal work rates whilst underwater and how much carbon dioxide they generate.
Navy Seals use Dräger Rebreathers, and the length of underwater time is limited by the scrubber unit inside their rebreathers.
Navy Seals use rebreathers because of the closed circuit mode which eliminates bubbles and is therefore ideal for clandestine operations. The Navy Seals use Dräger rebreathers because with this rebreather they can choose between front and back carry.
If you choose to dive with a rebreather, there are liveaboards that cater to rebreather divers and offer support. For example, if you like diving in the Red Sea, there are 29 Red Sea liveaboards with rebreather support. Plus in the Maldives there are 7 Maldives liveaboards with rebreather support.
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