Scuba Diving

December 4, 2010

Posted by David Haberthür

When not working in numismatics, Mr. Lee Minshull is an active scuba diver. The term “scuba” was not applied to the sport until World War II, when divers commonly used it as an acronym for “Self-Contained Underwater Breathing Apparatus,” which referred to the oxygen rebreathers used for underwater espionage and warfare. Today, individuals worldwide regularly refer to any type of underwater breathing system as a scuba apparatus. Modern scuba sets use one of two methods to supply divers with oxygen. The most common system, the open circuit, provides divers with a single hose controlled by a diving regulator and linked to a pressurized gas cylinder. A modernization of the “Aqua-Lung” developed by Emile Gagnan and Jacques Cousteau in 1943, the contemporary system utilizes a two-stage regulator to bring oxygen to the correct level for the diver’s lungs. As a diver travels deeper in the water, water exerts more pressure on the chest and lungs, requiring that the pressure of inhaled gas counter the ambient pressure. This necessity explains why early air-tank divers were unable to breathe mere feet under the water: The Gagnan and Cousteau Aqua-Lung pressurized the gas in the tank rather than through a regulator. Now, the first stage of the regulator significantly pressurizes the gas, allowing the second stage to bring the oxygen to the exact ambient pressure. The other system, a closed circuit or semi-closed circuit, also known as a rebreather, recycles the diver’s breath, processing each exhale. After removing carbon dioxide and adding oxygen, the diver inhales the same gas. As a result, the system requires much less oxygen and releases gas bubbles, making it ideal for researchers and photographers because they can dive for much longer periods and do not disturb their surroundings. Divers, however, must seek extensive training before trying rebreathers, which are much more expensive than open-circuit systems.



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