Let's discuss open-circuit (OC) SCUBA diving before we discuss closed- circuit rebreather (CCR) SCUBA diving. SCUBA stands for “Self Contained Underwater Breathing Apparatus.” The first SCUBA system consisted of a high-pressure cylinder filled with a breathable gas mix connected to a regulator. The regulator serves two functions: the first stage decreases the air pressure in the tank, and the second stage lowers the pressure to ambient, or atmospheric, pressure. The second stage also has a mouthpiece, allowing the diver to breathe “on demand.” Jacques Cousteau is credited for introducing OC scuba to recreational divers.
With OC diving, the diver’s exhaust gas, which contains approximately 75% oxygen, is released into the atmosphere as bubbles when the diver exhales. CCR divers are able to recapture the oxygen that is released into the atmosphere. This helps decease the amount of gas they carry, and aids in allowing longer dive times.
A rebreather has a “breathing loop” which consists of a mouthpiece, hoses, a “scrubber” canister filled with carbon dioxide absorbent, and “counterlungs,” The counterlungs inflate when the diver exhales, and deflate when the diver inhales. The absorbent in the canister prevents the diver from re-breathing carbon dioxide (CO2).
THE FOLLOWING SECTIONS ARE COURTESY OF IANTD. Unlike open circuit divers, the rebreather diver’s gas supply maintains a constant oxygen pressure at depth. The pressure is set by the diver. Possibly the most significant advantage closed-circuit rebreather diving offers is greatly increased gas efficiency.
Moreover, with rebreathers, the non-oxygen portion of the breathing gas (the part that determines decompression obligations) is kept at a minimum. This allows the CCR diver to stay longer at depth without incurring as much decompression obligation as the OC diver, and also helps speed up the decompression process whenever an obligation is incurred.
Last but far from least, CCR units do not produce bubbles, which makes them the pride and joy of many an underwater photographer or videographer. Fish and other marine life respond to bubbles. Without bubble production, photographic and videographic capabilities increase tremendously!
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Thank you!
Peri
Thank you!
Peri
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CCR Diving 
