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Scuba diving is the term used to describe the use of a Self Contained Underwater Breathing Apparatus to stay Underwater for periods of time greater than the average individual can breath-hold. The diver self-propels underwater using manufactured-fins attached to the feet. Some divers also move around with the assistance of a DPV Diver Propulsion Vehicle or surface-tethered devices called sleds, which are pulled by a boat. Divers are not limited to the use of scuba equipment in their sojourns underwater. While the Aqua-lung , developed by Emile Gagnan with assistance from Jacques-Yves Cousteau , is an "open-circuit" unit, Rebreather s (both open circuit and closed-circuit) and Surface-supplied systems are used depeding on the needs of the diver. Although Scuba Diving is still evolving, general classifications have grown up to describe the pursuits a diver might follow. These classifications include, but are not limited to: Recreational Diving , Public Safety Diving, Technical Diving Military Diving and Commercial Diving . Within Recreational Diving there are those whom are considered Professional Divers , because they maintain a Professional standard of training and skills. Some consider Technical Diving to be a subset of Recreational Diving while others separate it out due to the extensively different training equipment and knowledge required to execute Technical Dives. Public Safety Diving and Military Diving might likewise be classified as Commercial Diving because the practitioners make a living from their pursuit of diving. However, Public Safety Diver (Police/Rescue) and Military Divers have a different mission than the typical Commercial Diver. The word ' SCUBA ' is an Acronym for "Self Contained Underwater Breathing Apparatus", but it is grammatically acceptable to refer to ' Scuba Equipment ' or 'scuba apparatus' in conversation. HISTORY OF DIVING '']] Men and women have practiced Breath-hold Diving for centuries. Indirect evidence comes from ancient artifacts of undersea origin found on land (e.g. Mother-of-pearl ornaments), and depictions of divers in ancient drawings. In Ancient Greece , breath-hold divers are known to have hunted for Sponge s and engaged in military exploits. Of the latter, the story of Scyllis (sometimes spelled Scyllias; about 500 B.C.) is perhaps the most famous, as told by the 5th century B.C. Greek historian Herodotus (and quoted in numerous modern texts). During a naval campaign the Greek Scyllis was taken aboard ship as prisoner by the Persian King Xerxes I. When Scyllis learned that Xerxes was to attack a Greek flotilla, he seized a knife and jumped overboard. The Persians could not find him in the water and presumed he had drowned. Scyllis surfaced at night and made his way among all the ships in Xerxes's fleet, cutting each ship loose from its moorings; he used a hollow reed as snorkel to remain unobserved. Then he swam nine miles (15 kilometers) to rejoin the Greeks off Cape Artemisium . The desire to go under water has probably always existed: to hunt for food, uncover artifacts, repair ships (or sink them), and perhaps just to observe marine life. Until humans found a way to breathe underwater, however, each dive was necessarily short and frantic. One of the major hurdles of diving is to stay under water for a longer period of time. Breathing through a hollow reed allows the body to be submerged, but reeds more than two feet long do not work well; difficulty inhaling against water pressure effectively limits Snorkel length. Breathing from an air-filled bag brought under water was also tried, but it failed due to rebreathing of carbon dioxide. In the 16th Century people began to use Diving Bell s supplied with air from the surface, the first effective means of staying under water for any length of time. The bell was held stationary a few feet from the surface, its bottom open to water and its top portion containing air compressed by the water pressure. A diver standing upright would have his head in the air. He could leave the bell for a minute or two to collect Sponge s or explore the bottom, then return for a short while until air in the bell was no longer breathable. In 16th century England and France, full diving suits made of leather were used to depths of 60 feet. Air was pumped down from the surface with the aid of manual pumps. Soon helmets were made of metal to withstand even greater water pressure and divers went deeper. By the 1830s the Surface-supplied Air Helmet was perfected well enough to allow extensive salvage work. Starting in the 19th century, two main avenues of investigation - one scientific, the other technological - greatly accelerated underwater exploration. Scientific research was advanced by the work of Paul Bert and John Scott Haldane , from France and Scotland, respectively. Their studies helped explain effects of water Pressure on the body, and also define safe limits for compressed air diving. At the same time, improvements in technology - compressed air Pump s, Carbon Dioxide Scrubbers , Regulators , etc., - made it possible for people to stay Underwater for long periods. ''See also: Timeline Of Underwater Technology '' DIVING ISSUES This section looks at some of the Physiological issues posed by diving. See Diving Hazards And Precautions . Breathing underwater The two most common types of equipment are:
Injuries due to changes in water pressure The diver must avoid injury caused by changes in water pressure. Pressure injuries are called Barotrauma . They are caused by pressure differences between the outside and trapped air spaces inside the diver or the diver's equipment. To avoid them, the diver "equalises" the pressure in all air spaces with the surrounding water pressure when changing depth. Decompression sickness The diver must avoid Decompression Sickness by Decompression Stops and a slow ascent using Dive Computer s or Decompression Tables for guidance. Need to see underwater Diving Mask s and Diving Helmet s solve this problem. Controlling buoyancy underwater Control is needed to descend and ascend safely and at will. Diving Weighting System s, Diving Suit s, BCs ( Buoyancy Compensator s), and Slight Adjustments In One's Lung Volume all contribute to the diver's buoyancy. Avoiding losing body heat Water ''. In the case of a wet suit, the suit is designed to trap a thin layer of water between the diver's skin and the suit itself. Body heat then heats the trapped water and therefore keeps the diver warm. In the case of a dry suit, it does exactly that... keeps a diver dry. The suit is sealed so that frigid water cannot penetrate the suit. Breathing mixes There is no single optimal Breathing Gas mix for every type of dive. Each mix must contain sufficient Oxygen to sustain life and consciousness. Mixes may contain other gases such as Nitrogen and Helium . As the concentration of gases increases with the depth of the dive, and some gases are toxic at high concentrations, the design of breathing gas mixes depends on the depth of the dive. Avoiding skin cuts and grazes Diving Suit s also help prevent the diver's skin being damaged by rough or sharp underwater objects and marine animals and coral. Diving longer and deeper safely There are a number of techniques to increase the diver's ability dive deeper and longer:
Being mobile underwater
SEE ALSO .]]
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