Styles of Rebreathers
There are two styles of rebreathers: Closed Circuit (CCR) and semi-Closed Circuit (s-CCR), described below. Either of these styles can be electronic or manual, depending upon the individual model. When we’ve discussed rebreather benefits, we are describing the benefits from Closed Circuit and not semi-Closed (which produce bubbles).
Semi-Closed Circuit Rebreathers (SCR) only use one gas cylinder with an enriched air content. It usually pushes gas into the loop with a constant flow. The oxymoronically named semi-closed rebreather isn’t as efficient as the closed circuit rebreather and will need to let gas out from the system every other minute.
Electronic rebreathers (recreational rebreathers fall into this category) monitor the loop with the help of computers and other systems to make sure that the loop is breathable. They add oxygen to the loop automatically to keep the loop oxygen partial pressure in correlation to the setpoint. This takes away some of the task loading pressure from the diver, maintaining a breathable loop at all times. For a rebreather to become a recreational rebreather it needs to be monitored with electronics.
Manual rebreathers require the diver to manage the gas content of the loop. The rebreather still monitors the loop partial pressure but the diver needs to add gases manually. This opens up possibilities for the technical rebreather diver to dive deeper and longer, but also increases risk and requires significantly more skill and attention to maintain safety.
Closed Circuit Rebreather
Semi-Closed Circuit Rebreather