How a Rebreather Works
Many frogmen of some of the world’s elite armed forces along with professional divers who monitor free-diving athletes for safety during training and competition use closed-circuit rebreathers with their scuba equipment. This is an apparatus that allows air exhaled by the diver to be recycled back to oxygen.
There are two types of this equipment: the one-way system and the pendulum system. The former involves one-way valves that direct gas through a loop. The second type uses a single tube where both the inhaled and exhaled gasses go back and forth. In both types, clean oxygen is supplied from a canister. The diver inhales the oxygen from his regulator and releases carbon dioxide as he breathes out. Instead of being released into the water as bubbles, the exhaled air passes through a scrubber, a canister that is full of soda lime. The substance removes the carbon molecules from the exhaled gas, making the gas fit to be re-inhaled. Because 80 percent or more of the oxygen remains in exhaled gas, this device therefore uses breathable air very economically, making it possible for people to stay longer underwater.
Rebreather design has advanced considerably thanks to new technology and materials. Innovations include the use of electro-galvanic fuel cells and other electronics to monitor oxygen concentration. There are also designs that incorporate gas-sensing cells and interpretive electronic that continuously monitors the presence of carbon dioxide in the loop, alerting the diver if the gas reaches alarming levels. When alerted, he can just rise up to the surface and replace the carbon-congested cover with a fresh one. Some models also incorporate integrated decompression computers, which allow divers to monitor the oxygen content of their air mixture. This gives them the capability to produce a schedule of free-floating decompression stops.