Scuba Set

A scuba set, acronym for self-contained underwater breathing apparatus, is any breathing set which is carried entirely by an underwater diver and provides the diver with breathing gas at the ambient pressure. 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 exhausts exhaled air to the environment, and requires each breath to 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, dependent on design.

The word SCUBA was coined in 1952 by Major Christian Lambertsen who served in the U.S. Army Medical Corps from 1944 to 1946 as a physician. Lambertsen's invention (patented by himself several times from 1940 to 1989) was a rebreather and is different from the open circuit diving regulator and diving cylinder assemblies also commonly referred to as scuba. Open circuit demand scuba is a 1943 invention by the Frenchmen Émile Gagnan and Jacques-Yves Cousteau, but in the English language Lambertsen's acronym has become common usage and the name Aqua-Lung, (often spelled "aqualung"), coined by Cousteau for use in English-speaking countries, has fallen into secondary use. As with radar, the acronym scuba has become so familiar that it is generally not capitalized and is treated as an ordinary noun. For example, it has been translated into the Welsh language as sgwba.