In conventional scuba gear, when you breathe in through the mouthpiece you get a fresh lungful of air from the tank that you carry on your back. When you breathe out, the exhaled air goes out through the regulator into the water in the form of bubbles. A rebreather is a scuba device that allows you to breathe your own air over and over again and produce no bubbles. To allow you to rebreathe your air, the device must do the following:
- Remove your exhaled carbon dioxide. This is accomplished through the use of a canister of sodium hydroxide (Sofnolime). The carbon dioxide (gas) reacts with sodium hydroxide and calcium hydroxide to form calcium carbonate (solid).
- Replace oxygen that you have consumed. Small tanks of pure oxygen or mixed gases (nitrogen-oxygen or helium-oxygen) inject fresh oxygen into the breathing loop.
- Control the oxygen concentration in the breathing loop. Solid-state oxygen sensors monitor the partial pressure of oxygen in the breathing loop and send this information to a microprocessor that controls the oxygen-delivery system.
You’ll find three types of rebreathers: oxygen, semi-closed circuit and closed circuit. Oxygen rebreathers carry a cylinder of pure oxygen as the only gas supply. They’re limited to “no decompression” depths and carry a danger of oxygen toxicity. Semi-closed circuit rebreathers use gas mixtures as the gas supply. A diver using a semi-closed rebreather can go to greater depths without risking oxygen toxicity. Closed-circuit rebreathers carry both pure oxygen and mixed gases. They differ from semi-closed circuit rebreathers in the way that they maintain the oxygen concentration and allow you to go even deeper and stay longer.