The byproduct of our breathing is carbon dioxide. Carbon dioxide (CO2) is a poisonous gas that in high concentrations can cause unconsciousness and even death. In a closed breathing loop the removal of CO2 is very important. The scrubber is therefore also one of the key rebreather components in any system. The scrubber is simply a form of soda-lime that acts as a CO2 absorbent. As the exhaled breath moves up through the scrubber the CO2 binds with the soda-lime in an exothermic (heat-producing) reaction. Oxygen and other gases in the loop pass through to be rebreathed. The duration of the scrubber depends on the size of the scrubber canister, the granule size of the CO2 absorbent, temperature, and rebreather design. Improper packing of the CO2 absorbent can lead to channelling that allows CO2 to reenter the breathing loop.
An air-tight loop is the next rebreather component that allows the gas mixture to circulate from the divers’ lungs, in through the scrubber and back to the diver. The loop has breathing hoses that connect a mouthpiece to the counterlungs and also to the scrubber canister. The design of the loop is to allow gas to pass in only one direction (clock-wise or counter clock-wise) to ensure CO2 is removed from the exhaled gas by the scrubber. Special mushroom valves near the mouthpiece must be checked before every use to ensure the loop functions properly.