Scuba, the common acronym for Self-Contained Underwater Breathing Apparatus, or S.C.U.B.A., has opened up the underwater realms of Earth as territory for exploration, exploitation and recreation. Scuba developers have advanced the technology so humans can take a breathable atmosphere hundreds of meters under the ocean nearly anywhere in the world.
True Scuba
Until 1825, prolonged underwater activities could not be called "self-contained." They required air pumps or snorkels to supply air from the surface. In 1825, English scientist William James invented the first true, workable scuba system with a cylindrical air-reservoir belt worn around the diver's trunk, pressurized to 450 psi. In 1865 French inventors Benoit Rouquayrol and Auguste Denayrouse patented the Aerophore, a steel air tank compressed to 350 psi worn on a diver's back, connected to a mouthpiece that delivered air only when a diver inhaled. This was the first underwater, pressure-sensitive, demand regulator. The tank can be replenished from the surface but holds enough air for brief, independent activities.
Recycling Systems
Early scuba systems suffered from drawbacks. Air contains only a limited supply of oxygen, about 21 percent. The diver's exhaled carbon dioxide, CO2, would accumulate to toxic levels if the system simply provided an air reservoir to breathe in and out of. Also, if the exhaled air was vented into the water to eliminate CO2, telltale bubbles rose to the surface exposing clandestine military divers to detection. In 1876, an English merchant seaman, Henry A. Fleuss, used compressed oxygen and recycled the diver's exhaled breath through caustic potash to absorb carbon dioxide. This was the first self-contained, closed system, clearing CO2 and leaving no bubbles to rise to the surface. It provided three hours of bottom time. Fleuss's scuba system became the forerunner of all modern military systems.
Safer Scuba
Fleuss's advanced scuba equipment still left some problems unresolved. Laurence Martin, author of "Scuba Diving Explained," notes that oxygen becomes highly toxic under pressure, with the safe duration of use decreasing as the depth -- and therefore the pressure -- increased. Also, when air, which is 80 percent nitrogen, was used instead of pure oxygen, a dangerous condition, decompression sickness, "the bends," resulted when nitrogen bubbles formed in a deep-diver's blood on surfacing. Later research revealed that replacing some of the nitrogen with helium prevented both bends and oxygen toxicity. Modern scuba divers can now select among various gas mixtures best suited to their diving practices.
Aqua Lungs
By 1952, advanced systems that included highly efficient CO2 absorbers, tailored gas mixtures, improved pressure regulators for easier breathing and stronger tanks and gear, were developed by Jacques Cousteau and his underwater exploration partners as the "Aqua Lung," a brand name which has since become common usage for popular scuba gear. These were marketed commercially in France, Britain, Canada and the United States. Not only is the modern equipment highly advanced, but diving competence requires in-depth training in underwater gas physics. At the beginning of the 21st century, nearly 1 million new scuba diving competency certifications are issued every year worldwide.
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