03 December 2008

Aqualung

The invention: A device that allows divers to descend hundreds of meters below the surface of the ocean by enabling them to carry the oxygen they breathe with them. The people behind the invention: Jacques-Yves Cousteau (1910-1997), a French navy officer, undersea explorer, inventor, and author. Émile Gagnan, a French engineer who invented an automatic air-regulating device. The Limitations of Early Diving Undersea dives have been made since ancient times for the purposes of spying, recovering lost treasures from wrecks, and obtaining natural treasures (such as pearls). Many attempts have been made since then to prolong the amount of time divers could remain underwater. The first device, described by the Greek philosopher Aristotle in 335 b.c.e., was probably the ancestor of the modern snorkel. It was a bent reed placed in the mouth, with one end above the water. In addition to depth limitations set by the length of the reed, pressure considerations also presented a problem. The pressure on a diver’s body increases by about one-half pound per square centimeter for every meter ventured below the surface. After descending about 0.9 meter, inhaling surface air through a snorkel becomes difficult because the human chest muscles are no longer strong enough to inflate the chest. In order to breathe at or below this depth, a diver must breathe air that has been pressurized; moreover, that pressure must be able to vary as the diver descends or ascends. Few changes were possible in the technology of diving until air compressors were invented during the early nineteenth century. Fresh, pressurized air could then be supplied to divers. At first, the divers who used this method had to wear diving suits, complete with fishbowl-like helmets. This “tethered” diving made divers relatively immobile but allowed them to search for sunken treasure or do other complex jobs at great depths. The Development of Scuba Diving The invention of scuba gear gave divers more freedom to move about and made them less dependent on heavy equipment. (“Scuba” stands for self-contained underwater breathing apparatus.) Its development occurred in several stages. In 1880, Henry Fleuss of England developed an outfit that used a belt containing pure oxygen. Belt and diver were connected, and the diver breathed the oxygen over and over. Aversion of this system was used by the U.S. Navy in World War II spying efforts. Nevertheless, it had serious drawbacks: Pure oxygen was toxic to divers at depths greater than 9 meters, and divers could carry only enough oxygen for relatively short dives. It did have an advantage for spies, namely, that the oxygen—breathed over and over in a closed system—did not reach the surface in the form of telltale bubbles. The next stage of scuba development occurred with the design of metal tanks that were able to hold highly compressed air. This enabled divers to use air rather than the potentially toxic pure oxygen. More important, being hooked up to a greater supply of air meant that divers could stay under water longer. Initially, the main problem with the system was that the air flowed continuously through a mask that covered the diver’s entire face. This process wasted air, and the scuba divers expelled a continual stream of air bubbles that made spying difficult. The solution, according to Axel Madsen’s Cousteau (1986), was “a valve that would allow inhaling and exhaling through the same mouthpiece.” Jacques-Yves Cousteau’s father was an executive for Air Liquide— France’s main producer of industrial gases. He was able to direct Cousteau to Émile Gagnan, an engineer at thecompany’s Paris laboratory who had been developing an automatic gas shutoff valve for Air Liquide. This valve became the Cousteau-Gagnan regulator, a breathing device that fed air to the diver at just the right pressure whenever he or she inhaled.With this valve—and funding from Air Liquide—Cousteau and Gagnan set out to design what would become the Aqualung. The first Aqualungs could be used at depths of up to 68.5 meters. During testing, however, the dangers of Aqualung diving became apparent. For example, unless divers ascended and descended in slow stages, it was likely that they would get “the bends” (decompression sickness), the feared disease of earlier, tethered deep-sea divers. Another problem was that, below 42.6 meters, divers encountered nitrogen narcosis. (This can lead to impaired judgment that may cause fatal actions, including removing a mouthpiece or developing an overpowering desire to continue diving downward, to dangerous depths.)Cousteau believed that the Aqualung had tremendous military potential. DuringWorldWar II, he traveled to London soon after the Normandy invasion, hoping to persuade the Allied Powers of its usefulness. He was not successful. So Cousteau returned to Paris and convinced France’s new government to use Aqualungs to locate and neutralize underwater mines laid along the French coast by the German navy. Cousteau was commissioned to combine minesweeping with the study of the physiology of scuba diving. Further research revealed that the use of helium-oxygen mixtures increased to 76 meters the depth to which a scuba diver could go without suffering nitrogen narcosis. Impact One way to describe the effects of the development of the Aqualung is to summarize Cousteau’s continued efforts to the present. In 1946, he and Philippe Tailliez established the Undersea Research Group of Toulon to study diving techniques and various aspects of life in the oceans. They studied marine life in the Red Sea from 1951 to 1952. From 1952 to 1956, they engaged in an expedition supported by the National Geographic Society. By that time, the Research Group had developed many techniques that enabled them to identify life-forms and conditions at great depths. Throughout their undersea studies, Cousteau and his coworkers continued to develop better techniques for scuba diving, for recording observations by means of still and television photography, and for collecting plant and animal specimens. In addition, Cousteau participated (with Swiss physicist Auguste Piccard) in the construction of the deep-submergence research vehicle, or bathyscaphe. In the 1960’s, he directed a program called Conshelf, which tested a human’s ability to live in a specially built underwater habitat. He also wrote and produced films on underwater exploration that attracted, entertained, and educated millions of people. Cousteau has won numerous medals and scientific distinctions. These include the Gold Medal of the National Geographic Society (1963), the United Nations International Environment Prize (1977), membership in the American and Indian academies of science (1968 and 1978, respectively), and honorary doctor of science degrees from the University of California, Berkeley (1970), Harvard University (1979), and Rensselaer Polytechnical Institute (1979).

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