We all learn to dive on Open Circuit scuba equipment (OC) This means that the gas we breathe from our cylinders is inhaled through the first and second stage regulators, processed in our lungs, and exhaled through our second stage into the water and up to the atmosphere – an open circuit.
The other way is by use of a rebreather unit. Simplified, this is where we breathe gas from smaller cylinders in a closed circuit (CCR) The gas is breathed in through a one-way regulator in a loop system, processed in our lungs and exhaled through the regulator back to the unit, where it passes through a dry chemical to remove the toxic, waste gases. It is analysed electronically and oxygen is added automatically to replace that which has been used, at a level to suit the depth at which the diver is at. This gas is then re-breathed in the closed circuit. Other gases such as Helium can also be added. Re-breathers have been around for many years, but with modern technology and manufacturing methods are becoming more efficient and reliable – although, as in open-circuit, they also carry risks.
It is a big commitment, both financially and training-wise, to purchase one of these units, and again, advice and research should be undertaken before taking the step.