Over the last ten years, recreational Scuba Diving has become one of the fastest growing sports in the world. The Scuba or “Open-Circuit” unit is currently the dominant underwater breathing apparatus. But did you know that rebreathers were among the first Scuba units? Rebreather units have always been the apparatus of choice for military diving and now they are making a comeback
A Closed Circuit Rebreather operates on the principle of recirculating the air that a diver breathes underwater. As most people know, our bodies do not use all the Oxygen we inhale with each breath, only part of it. Exhaled air also contains Carbon Dioxide, which is released by our bodies as a waste product. Early in the history of diving, it was determined that if there was a way to absorb this CO2, and replace the small amount of Oxygen absorbed by the body, a diver could continue to RE-breathe the same air over and over.
What a Closed Circuit Rebreather does is exactly that. The air exhaled by a diver passes through an air-permeable container called a “scrubber” which contains a chemical compound that absorbs Carbon Dioxide. The air then passes across 3 Oxygen sensors (most CCR systems use 3 sensors for redundancy). The sensors react to the presence of Oxygen by emitting voltage – in essence, they are like batteries – the more Oxygen present, the higher voltage they output.
If the Oxygen Sensors put out voltage lower than the user-definable “Set-Point” (meaning there is less Oxygen in the loop than the diver established through the initial set-up procedure) then a signal is sent to a Oxygen Solenoid, which will inject a metered amount of additional Oxygen into the loop.
Given the remarkably low Oxygen uptake of the average adult, this means that even a working diver can stay underwater for up to 8 hours with only 21 cu. ft. of Oxygen.