Scuba Diving
The development of self-contained underwater breathing apparatus, or scuba, provided the free-moving diver with a portable air supply which, although finite in comparison with the unlimited air supply available to the helmet diver, allowed for better mobility. Scuba diving is the most frequently used mode in recreational diving and is also widely used to perform underwater work for military, scientific and commercial purposes.

What are the two types of scuba?
The two types of scuba designs include the "open" scuba design, where the diver breathes air from a cylinder or canister and the exhaled air goes into the water and rises to the surface as bubbles. The diver must return to the surface before or when the supply of air runs out.

The "closed" scuba rig design allows a diver to reuse the same gas. A diver's exhaled breath is passed through a chemical in one of the cylinders to remove the carbon dioxide and the diver then breathes the "cleaned" gases over and over again. New oxygen is added automatically as consumed. Using this system, the diver can stay underwater longer and no bubbles come to the surface.