Scuba Diving
The underwater exploration of the sea has been a desire and a fascination for humankind since the earliest times. Divers are mentioned in Homer's Illiad; Xerxes of Persia used divers to recover treasure in 475 B.C., and divers breathing through tubes are mentioned by Aristotle in 355 B.C. Early attempts at underwater exploration made use of the diving bell and special rigid suits supplied with air from surface pumps. In 1889, Jules Verne (1828-1905), in Twenty Thousand Leagues Under the Sea, describes divers moving freely to hunt in underwater forests while breathing air from iron tanks "fastened to their backs with straps." Verne claimed that the equipment had been invented by two French men.
In 1943, two French men, Jacques Cousteau and Emile Gagnan did, in fact, invent the aqualung, a Self-Contained U nderwater Breathing Apparatus (SCUBA) and gave birth to a new sport and a new profession. The key element of the invention was the demand regulator. The regulator delivered air to the diver's breathing mouthpiece at the same pressure as the diver's underwater surroundings allowing the diver to breath in a normal and comfortable manner. It is called a demand regulator because air only flows in response to the diver's inhalation effort, rather than free flowing. The scuba diver now was free to move underwater without dependence on a supply of air from the surface.
Since 1943, innovations in scuba equipment design have improved the safety and comfort of the sport. In addition to the mask, fins and snorkel used in skin diving, a scuba diver utilizes a broad array of equipment specialized for the underwater environment. Compressed air is carried in a steel or aluminum tank and two pressure regulators (the first and second stages) are mounted on the tank. The first stage reduces the air pressure to an intermediate level and the second includes the breathing mouthpiece and reduces the pressure further so that it matches the diver's surrounding pressure. An additional second stage regulator is frequently carried as a backup against equipment failure. A weight belt and an inflatable vest called a buoyancy compensator are worn to control underwater buoyancy. In water that is below about 75°F (24°C), most divers wear a protective body suit to keep warm.
Two types of suits, wet and dry, are in common use. The wet suit is made of neoprene foam rubber and includes jacket, pants, hood, gloves and boots. The neoprene is a thermal insulator as is the thin layer of water trapped between the suit and the skin. The dry suit has water-tight seals at the neck and wrists and uses a heavy insulating undergarment to keep the diver warm. While somewhat more difficult to use and prone to the occasional leak, the dry suit is substantially more effective than the wet suit.
A diver carries a watch and a depth gauge to monitor the duration and depth of the dive. Underwater computers are available that continuously monitor depth and calculate how long and how deep the diver may safely remain underwater. The amount of air remaining in the tank is monitored with a pressure gauge and the diver carries a knife to free himself from underwater entanglements.
Knowledge and training are required to avoid the risks associated with the underwater environment. While underwater, nitrogen gas accumulates in the diver's body tissues. If a diver remains too deep for too long and surfaces too quickly, the nitrogen gas will form bubbles within the body. This condition is called decompression sickness (DCS) or the bends. Depending on their location, these bubbles may cause joint pain, choking, blindness, seizures, unconsciousness, or death. The cause of these effects was first identified in 1878 by Paul Bert (1833-1886) and in 1907, John Scott Haldane (1860-1936) developed the first decompression tables to limit time under pressure and, thus, avoid the bends. The most effective treatment of decompression sickness is immediate recompression in a recompression chamber. This chamber was invented by Edwin Link and uses elevated pressure to reduce the size of the nitrogen bubbles. The diver can then be decompressed very slowly without the formation of new bubbles.
Nitrogen is normally an inert gas but, at depth, the increased pressure of the nitrogen causes it to become a narcotic and effect the thinking process. Nitrogen narcosis or rapture of the deep can cause divers to take illogical and unsafe actions. This effect may occur at depths as shallow as 60 feet and is treated by simply moving into shallower water.
Oxygen toxicity is another potential diving problem related to the gases breathed. Toxic effects may begin to appear in as little as 33 ft (10 m) of water when breathing pure oxygen. Onset of toxicity may occur with air at depths of 265 ft (80 m) or so. To avoid or reduce the risk of decompression sickness, nitrogen narcosis, and oxygen toxicity, many commercial divers, as well as a few recreational divers, breath mixed gases when deep diving. These consist of various mixtures of nitrogen, oxygen and in some cases, helium, designed to circumvent these diving maladies.
The increased mobility and safety of scuba diving permits a wide range of new underwater activities for hobbyists, scientists, and entrepreneurs. These include activites as varied as nautical archaeology, shipwreck exploration, studies of marine and freshwater ecology, dredging for gold, and treasure hunting.
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