What is a Rebreather?

Titan Schematic

"Normal" scuba is an open circuit system. Combining a high pressure cylinder and a demand regulator, you inhale gas at ambient pressure, use a little of the oxygen in the gas, and exhale. When you exhale the gas, it bubbles to the surface, carrying as much as 98% of the original oxygen it contained. The "open circuit" comes from the fact that the exhaled gas is released on every breath.

A rebreather recirculates the gas a diver is breathing, allowing the diver to breath the same gas over and over again. The system removes the carbon dioxide generated by human metabolism, and adds oxygen and other gases to make up what is consumed. Because the gas is breathed over and over again, instead of being "thrown away" with every breath, a diver can remain underwater far longer on much less gas. In fact, for some dives, rebreathers can be as much as fifty times more efficient on gas consumption than standard scuba.

CLOSED CIRCUIT REBREATHERS (CCR) close the loop, so to speak, by recirculating all of the gas the diver is breathing. Oxygen from an oxygen cylinder is added to replace that which is metabolically utilized by the diver. As the diver descends, a diluents gas, typically air or trimix, is added to maintain the proper breathing volume.

Oxygen sensors monitor the oxygen partial pressure, allowing the diver to stay within safe limits. Some CCRs are computer controlled, automatically adding oxygen as necessary, and may also incorporate a dive computer to calculate inert gas status of the diver.

With rebreathers, "bigger" does not necessarily mean "better." As with any piece of equipment, the user must determine what the desired objective is, and select the gear accordingly. This is especially true with rebreathers, where the difference between units may involve a difference in 40-50 hours of training, and a price differential of over $10,000. In fact, for many objectives, traditional open circuit scuba is still the system of choice. However, if your objective necessitates it, nothing can beat the use of the appropriate rebreather.