Rebreather Overview
Rebreathers are diving systems that recycle your breathing gas. It is a machine that recycles your exhaled gas so that it can be used again. Your body processes oxygen when you inhale and gives of carbon dioxide (CO2) when you exhale. Rebreathers remove the CO2 from your exhaled gas so that what is left can be recycled and used again. There are two categories of rebreathers, semi-closed circuit rebreathers (SCR) and closed-circuit rebreathers (CCR), which differ in their design functionality. SCRs are designed to vent small amounts of gas into the water during use and CCRs are designed to retain all gas during use (no bubbles).
Rebreathers, whether SCR or CCR, do much the same thing; they recycle either part of all of the gas you exhale. This is one of the attractions to rebreathers because you get greater gas efficiency and economy, meaning you can dive much longer with much less gas. Before you can re-breathe your exhaled gas, as mentioned above, it must be cleansed of the CO2. This is done by the scrubbing system built in the rebreather. A chemical is used to remove the CO2 and pass along the oxygen and inert gas for reuse. In addition, as you consume oxygen metabolically, additional oxygen must be added to the system to replenish what is used and this addition of oxygen must be maintained within the oxygen partial pressure limits set in the system. Rebreathers perform these basic functions: recycle exhaled gas, conserve oxygen and inert gas, remove CO2 from the exhaled gas, maintain a safe oxygen partial pressure (PO2), and provide a reasonable breathing volume.