What diving is? |
Diving (underwater), act of entering water and remaining below the surface for such purposes as working or exploring. Diving without mechanical aids has been practised since ancient times in the harvesting of pearls and sponges. Various devices to supply the diver with air and thus permit a prolonged stay under water have been tried since at least the 4th century BC. Alexander the Great supposedly made a descent in a machine that was probably a primitive form of diving bell; and Aristotle mentioned devices that enabled divers to breathe under water. Practical apparatus was not developed, however, until the 18th century.
Diving Bells
In 1717 the British astronomer Edmund Halley devised one of the first practical diving bells, an open-bottomed wooden chamber with glass windows in the top to admit light. Air was supplied to people inside the bell through leather tubes connected to air casks that could be lowered into the water as needed. As water entered the casks, the air in them was forced through the tubes into the upper part of the diving bell, which was kept clear of water by the pressure of the air. A modern steel version of this device, supplied with compressed air pumped through a hose, is used for such underwater work as building bridges, piers, and jetties. See Bathyscaphe; Bathysphere.
Underwater Habitats
Underwater habitats, or diving stations, enable scientists to conduct research on the sea floor at depths of up to 100 m (328 ft) for unlimited periods of time. Air pressure inside these stations is equalized with sea pressure outside, thereby keeping the station walls from collapsing. By means of a technique known as saturation diving, scientists are able to live in and work around such stations for extended periods without the risk of developing a disease known as the bends. Divers breathe compressed air mixed with light, inert gases, such as helium. When the diver's blood becomes saturated with helium, the time required for decompression, even if the diver returns to the surface after a period of weeks or months, is no greater than that required after a dive lasting just a few hours.
A 13-m (43-ft) habitat launched by the National Oceanic and Atmospheric Administration of the United States (NOAA) in the Caribbean in 1988 provides a crew of six with an underwater base from which they can work nine-hour days. The station, called Aquarius, is connected by umbilical cable to an unmanned surface support craft that delivers a steady flow of air and power. Such systems are not feasible for deep-sea exploration, where water pressures far exceed human endurance.
Diving Suits
From the 17th century onwards, efforts were made to perfect a helmet or suit to give divers maximum protection and freedom of movement. One of the first such successful devices was created in 1819 by the Anglo-German inventor Augustus Siebe. Based on the principle of the diving bell, it consisted of a leather jacket fitted to a metal helmet into which air was pumped from the surface through a flexible hose. The helmet was not watertight, but air pressure kept water below the diver's chin. The modern closed diving suit, essentially the same as one introduced by Siebe in 1830, is made of rubberized fabric. It covers the diver completely and is airtight. Valves on the helmet allow the diver to regulate air pressure inside the suit and thus to control buoyancy. Auxiliary equipment of modern diving dress includes weighted shoes to keep the diver upright and leaden plates for weight on back and chest. A rope containing telephone wires connects the diver with the surface and permits conversation. For deeper diving, jointed metal suits heavy enough to withstand great water pressures are used. In these suits air pressure can be kept normal, and the diver experiences less stress than when diving in shallower water with an ordinary suit.
A troublesome feature of ordinary diving dress is the unwieldy lengths of air hose and lifeline divers must drag with them. This problem has been met by the development of diving suits with a self-contained air supply consisting of a pressure cylinder of mixed oxygen and air and a regeneration chamber filled with caustic soda. Exhaled air is passed through the regeneration chamber, carbon dioxide is removed, and the air is then combined with oxygen and air from the cylinder and rebreathed. The air supply of such units lasts from about 45 minutes to 2 hours.
Self-contained underwater breathing apparatus (scuba), independent of diving suits, has been developed for skin diving. It differs from the conventional diving suit in that it is designed for swimming, whereas the more cumbersome type is suitable only for walking on ocean floors. One form of this apparatus, a lightweight breathing mask operating on the same principle as the self-contained diving suit, was used during World War II by underwater demolition teams to clear away mines and other obstacles before amphibious landings. At present, the most popular form is the aqualung designed in France during World War II by the French naval officer and underwater explorer Jacques Yves Cousteau. It consists of one, two, or three cylinders (carried on the back) of compressed air fed to the diver's mouthpiece through valves that assure a constant flow at a pressure automatically equalized with outside water pressure.
Diving Equipment
Because of the difficulty of working underwater with ordinary hand tools, divers usually employ pneumatic hammers, drills, wrenches, and other implements. Cutting and welding are carried out with standard torches. Because in many waters daylight penetrates only a few metres beneath the surface, it is necessary to supply artificial light by which divers can work. High-power incandescent electric lights are usually employed.
Depth of Working
For divers without mechanical aids, a depth of about 18 m (60 ft) is the practical limit of working. Pearl and sponge divers have been credited with reaching depths of 30.5 m (100 ft) in individual dives, but normally they remain submerged for from 50 to 80 seconds at depths of about 12 m (40 ft). With breathing apparatus using conventional mixtures of compressed air and oxygen, divers cannot safely go below 76 m (250 ft), but with special light breathing mixtures (such as oxygen with helium or hydrogen to replace nitrogen), dives to below 152 m (500 ft) have been made successfully by surface divers. Divers who are acclimatized to undersea pressures, through living in underwater stations established at a depth of more than 100 m (328 ft), are expected to dive from a station to a maximum depth of from 396 to 657 m (1,300 to 1,500 ft) in flexible suits.
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What diving is?
