breathing apparatus

A scuba set is any breathing set that is carried entirely by an underwater diver and provides the diver with breathing gas at the ambient pressure. (Scuba is an acronym for self-contained underwater breathing apparatus). Although strictly speaking the scuba set is only the diving equipment which is required for providing breathing gas to the diver, general usage includes the harness by which it is carried, and those accessories which are integral parts of the harness and breathing apparatus assembly, such as a jacket or wing style buoyancy compensator and instruments mounted in a combined housing with the pressure gauge, and in the looser sense it is used to refer to any diving equipment used by the scuba diver, though this would more commonly be termed scuba equipment. Scuba is overwhelmingly the most common underwater breathing equipment used by recreational divers. A scuba set is also used in professional diving when it provides advantages, usually of mobility and range, over surface supplied systems. Two basic configurations of scuba are in general use: Open-circuit-demand scuba expels exhaled air to the environment, and requires each breath be delivered to the diver on demand by a diving regulator, which reduces the pressure from the storage cylinder and supplies it through the demand valve when the diver reduces the pressure in the demand valve slightly during inhalation. Rebreather scuba recycles the exhaled gas, removes carbon dioxide, and compensates for the used oxygen before the diver is supplied with gas from the breathing circuit. The amount of gas lost from the circuit during each breathing cycle depends on the design of the rebreather and depth change during the breathing cycle. Gas in the breathing circuit is at ambient pressure, and stored gas is provided through regulators or injectors, depending on design.