What Is a Rebreather?
A rebreather is an apparatus also known as a Closed Circuit Underwater Breathing Apparatus, or CCUBA. This device scrubs or removes carbon dioxide from a diver's exhaled breath; a small amount of oxygen or an oxygen-gas mixture is added to the remaining breath to allow for a longer dive with less reserve oxygen and smaller tanks. There are many fewer bubbles emitted from a diver using a rebreather as compared to a one using traditional diving equipment. The oxygen in the escaping bubbles is filtered through the rebreather and used by the diver's body instead of being wasted in the water. By utilizing a rebreather , the diver is able to remain at depth much longer than with traditional diving tanks.
Semi-closed circuit rebreather
Military and recreational divers use these because they provide good underwater duration with fairly simple and cheap equipment. Semi-closed circuit equipment generally supplies one breathing gas such as air or nitrox or trimix. The gas is injected at a constant rate. Excess gas is constantly vented from the loop in small volumes.
The diver must fill the cylinders with gas mix that has a maximum operating depth that is safe for the depth of the dive being planned. As the amount of oxygen required by the diver increases with work rate, the oxygen injection rate must be carefully chosen and controlled to prevent either oxygen toxicity or unconsciousness in the diver due to hypoxia.
Fully closed circuit rebreather
Military, photographic and recreational divers use these because they allow long dives and produce no bubbles. Closed circuit rebreathers generally supply two breathing gases to the loop: one is pure oxygen and the other is a diluent or diluting gas such as air, nitrox or trimix.
The major task of the fully closed circuit rebreather is to control the oxygen concentration, known as the oxygen partial pressure, in the loop and to warn the diver if it is becoming dangerously low or high. The concentration of oxygen in the loop depends on two factors: depth and the proportion of oxygen in the mix. Too low a concentration of oxygen results in hypoxia leading to sudden unconsciousness and ultimately death when the oxygen is exhausted.Too high a concentration of oxygen results in oxygen toxicity, a condition causing convulsions, which make the diver, spit his regulator out when they occur underwater and can lead to drowning.