Open and closed design of SCUBA sets Modern scuba sets can be classified into two types: there is an "open" SCUBA design and a "closed" one. The "open" scuba design allows the diver to breath and the exhaled air goes into the water, producing some bubbles that then rise to the surface of the water. Thus the exhaled gas goes to waste. This type is cheap and very reliable. The diver must return to the surface before or when the supply of air runs out.
The "closed" scuba set design, often referred to as a rebreather, allows a diver to reuse the same gas. A diver's exhaled breath is passed through a chemical in one of the cylinders to be stored between breaths in a "counterlung". The carbon dioxide is being chemically restored and the diver then breathes it over again, with some of new oxygen being added automatically to compensate the consumed portion. This type of system allows the diver to remain underwater longer with no bubbles emerging to the surface. The rebreather's economic use of gas is typically 1.6 litres of oxygen per minute.
In fact, the closed scuba is an improved version of open scuba.
Follows soon: A comparison of open-circuit scuba diving to closed-circuit (rebreather) diving in regards to extreme diving in complicated or adverse environment