Diving (underwater).

Diving (underwater). I INTRODUCTION Diving (underwater), act of entering water and remaining below the surface to explore, to work, or simply to have fun. Diving is popular all over the world. It is usually done in the ocean, but divers also explore other bodies of water, including lakes, rivers, and ponds. Snorkeling on the surface (or just below) is a common form of diving, but many people use scuba, which stands for self-contained u nderwater b reathing apparatus. Scuba divers carry a tank of air that allows them to breathe while deep underwater. Throughout history, people have been fascinated by life underwater, and the Professional Association of Dive Instructors (PADI) estimates that there are now 6 million active divers worldwide. They engage in many different types of diving, of which wreck, cave, commercial, and military diving are just a few. The most common form of diving is sport diving, or recreational diving, which is practiced at depths of less than 130 ft (39 m). From these depths, divers can make a straight ascent to the surface. Diving beyond this limit requires advanced training. II SPORT DIVING FUNDAMENTALS Because popular dive sites such as coral reefs and wrecks are typically not near land, most diving is done from boats. In some locations, however, divers can enter the water from shore. On a typical outing, the divers decide beforehand how long they will remain underwater and how deep they will descend. While the divers are underwater, at least one person serves as a spotter by remaining on the boat or on shore. All groups, whether diving from a boat or from shore, are required to fly a diver down flag (a red flag with a white diagonal slash) to alert boaters that people are underwater. After divers put on their gear and double-check their equipment, they enter the water and descend. As they descend, the surrounding water pressure increases, causing a slight discomfort, or squeeze, in their ears and sinuses. Divers relieve this discomfort by holding their noses and blowing gently. This technique is called equalization, as it equalizes the pressure within the divers' bodies with that of the surrounding water, allowing them to proceed safely. The amount of time a diver can remain underwater depends on several elements. The deeper the descent, the more rapidly the diver consumes air. Thus, shallow dives can last longer than deeper ones. In addition, some people consume air at a quicker rate than others. Several factors influence how efficiently a diver uses air, including diving experience, physical fitness, general relaxation, and a healthy lifestyle that limits tobacco and alcohol intake. Most divers can spend 45 minutes to an hour at 40 ft (12 m) below the surface--the level of a medium-depth dive. A diver completes the dive by ascending slowly to the surface. Most experts recommend rising at a rate of no more than 60 ft (18 m) per minute in order to avoid such risks as air embolisms and decompression sickness (for more information, see the Hazards and Safety Measures section of this article). A Training and Certification Before taking a dive, enthusiasts must gain certification by passing a course offered by a certifying scuba diving agency. The largest agency worldwide is PADI, but there are many others, including the National Association of Underwater Instructors (NAUI) and the National Association of Scuba Diving Schools (NASDS). These agencies sponsor courses throughout the world, especially in places where diving is particularly popular, such as the Caribbean and Hawaii. All agencies require that participants be proficient swimmers, in reasonably good health, and at least 12 years old. The course typically consists of classroom work, practice in a pool or other confined body of water, and dives in the open water, usually in a large lake or the ocean. In the course, students learn to use diving equipment, to equalize air pressure as they descend, to swim efficiently underwater, to clear the mask if water leaks in, and to ascend safely. Because divers cannot talk to each other underwater, they also learn how to communicate underwater with hand signals. Scuba diving should always be practiced with at least one other person, and partners should remain together throughout the dive. Certification courses teach divers the rules and advantages of the buddy system. Diving partners learn to double-check each other's equipment, share a single air supply, and assist one another should a problem occur. Another important skill taught in certification courses is how to achieve neutral buoyancy--a state in which the individual neither sinks nor floats. In this weightless state, a diver conserves energy and air and keeps diving equipment off the bottom where it could be damaged. Controlling breathing rate is also important. During exercises in water, diving students practice breathing in a slow, continuous manner. To become certified, diving students must pass a written exam and a swimming proficiency test, and successfully demonstrate newly mastered skills in four open-water dives. Proficient divers then receive a certification card that allows them to make unsupervised dives, refill air tanks, and buy diving equipment worldwide. Stores that sell diving equipment and businesses that operate diving tours require this proof of certification. B Equipment Diving equipment depends on the location of the dive, but whether scuba diving or snorkeling, recreational divers need several basic items: a mask, a snorkel, fins, and, when necessary, an exposure suit to remain warm. Scuba divers wear special equipment to breathe underwater and to help control their position underwater. A diving mask that covers the nose and eyes enables the diver to see while underwater. A snorkel is a tube that allows the diver to breathe while floating at the water's surface. One end fits in the diver's mouth and the other end extends above the water. Much like the flippers of a seal and the webbed feet of a duck, fins that are worn on the feet let divers propel themselves through the water with a smooth, energy-efficient motion. Divers lose body heat 60 times faster underwater than on land, because water conducts heat much more efficiently than air does. To stay warm, scuba divers wear either a wet suit or a dry suit, depending on water temperature. Wet suits are usually worn in warm-water climates, such as the Caribbean Sea. A wet suit is made of neoprene rubber and absorbs and traps a thin layer of water, which the diver's body quickly heats. In areas such as the North Atlantic or Pacific oceans, where water temperature drops below 10° C (50° F), divers wear dry suits to keep from freezing. A dry suit is made of waterproof materials that keep a diver completely dry. If water temperatures are extremely low, divers wear extra clothing underneath the suit. C Specialized Scuba Equipment To breathe underwater, scuba divers wear a metal tank filled with compressed air, and a regulator that attaches to the tank. The regulator reduces the pressure of the air to match the surrounding water pressure, so that the diver can breathe the air comfortably. The regulator also distributes the air among four hoses. One hose delivers air to a mouthpiece, through which the diver inhales and exhales. Another hose from the regulator attaches to an adjustable air bladder called a buoyancy compensator (or control) device (BCD or BC), which the diver wears as a vest. By adding air to the BCD, the diver becomes more buoyant and rises. By releasing air, the diver becomes less buoyant and sinks. With minor adjustments of air, the diver can achieve neutral buoyancy. A third hose attaches to pressure gauges that divers use to monitor how much air remains in the tank. A fourth hose attaches to a backup breathing device called an alternate air source, or octopus. Divers also wear a belt with lead weights to help them descend and stay underwater. The weights are spaced evenly around the belt for balance. Most divers carry from 5 to 20 lb (2.3 to 4 kg) of weight, depending on their body weight, the suit they are wearing, and where they are diving (buoyancy is greater in saltwater than in fresh water). A quick-release buckle enables the diver to shed the belt and rise to the surface in an emergency. Emergency equipment includes a dive knife, in case the diver becomes entangled in fishing line or marine plants, and whistles, lights, or signaling devices, in case the diver is lost or swept out in a current. Divers should also have a tank of oxygen onboard, along with a marine radio and a first aid kit. D Hazards and Safety Measures Hazards associated with recreational diving stem chiefly from breathing air under pressure, though a few marine animals also pose hazards. Most hazards can be avoided if divers follow the safety procedures taught in certification courses and do not attempt dives beyond their ability and experience. The single largest risk scuba divers face is pressure-related injury. Decompression sickness, also called the bends, is an injury that occurs when a diver ascends too quickly, or dives too deeply for too long. Throughout a dive, the body absorbs nitrogen (an element of air) from breathing compressed air. The deeper a diver descends, the denser the air that is breathed and the more nitrogen absorbed. This nitrogen forms tiny bubbles in the diver's tissues and bloodstream. If a diver ascends to the surface too quickly, these bubbles remain trapped inside the body and can cause extreme pain in joints and organs. Severe cases of decompression sickness can be fatal. For this reason, all divers attempt to ascend slowly from every dive, to allow excess nitrogen to escape the body gradually. Divers who suspect they are suffering from decompression sickness should seek medical attention immediately. Another pressure-related injury is an air embolism. It occurs when a diver ascends too rapidly and the gases in the diver's bloodstream form a large bubble. If large enough, the bubble can block the flow of blood to the brain and be fatal. To avoid these injuries, divers calculate how long it is safe to stay at certain depths and how long they should spend on the surface before diving again. Divers must also wait at least 12 hours, and sometimes 24 hours, after a dive before flying on a plane. Because air pressure changes rapidly when a plane increases its altitude, flying too soon after diving can result in decompression sickness. Most marine animals pose no threat to divers. In fact, divers pose far more threat to the animals. Coral, for example, can be killed by a diver's single touch. However, a few forms of marine life can injure divers. Jellyfish, fire coral, stinging coral, and sea urchins are the most common threats. In rare cases, poisonous fish and sharks can also injure people. In general, animals only attack humans when they are provoked. Scuba diving should be a visual experience, and divers should avoid touching anything--plant, animal, or object. Other risks inherent in recreational diving include running out of air, breathing contaminated air, or being injured by a boat. Certification courses not only teach divers how to avoid these problems, but also how to treat a fellow diver should an injury occur. E Sport Diving Sites In general, divers seek locations where the water is clear, the temperatures warm, and the marine life plentiful. Divers often choose to visit areas with coral reefs because they are colorful and dense with life, and provide shelter for many types of fish. The Caribbean is the most popular destination in the world. Parts of the region are designated as marine parks or sanctuaries. Because they are protected from fishing and other human activity, these locations boast abundant aquatic plant and animal life. Similar protected areas exist throughout the world, and the South Pacific, the Indian Ocean, and the Red Sea are common dive destinations. F Related Activities As divers become more proficient, they usually want to take up related activities. Underwater photography and videography are the most common. Spearfishing, also called underwater hunting, is popular with some people. And divers can also choose specialized forms of diving. Many people engage in wreck diving. Shipwrecks provide a so-called artificial reef where marine life prospers, and some wrecks offer a unique look at a historical event. Divers can take special wreck-diving courses to learn how to explore a shipwreck safely. Going inside a shipwreck without proper training can be extremely dangerous, because divers can get lost and not find their way out. Cave diving offers an opportunity to explore the geological wonders of underwater caves. It is far more dangerous than diving in open water because, once inside a cave, the diver cannot return directly to the surface for air. Cave divers use multiple tanks, backup systems, and other specialized equipment (including lights) to travel safely in the complete darkness of caves. They also carry a reel of strong, lightweight line, which they attach to a solid object outside the cave. A diver who becomes lost can retrace his or her path by following the line to the mouth of the cave. III OTHER PURPOSES OF UNDERWATER DIVING People who dive for recreation do so to enjoy aquatic life and observe the underwater world, but others carry out work underwater. Commercial divers are highly trained men and women who work on offshore oil rigs, pipelines, and barges, and inshore on civil engineering sites such as hydroelectric plants and harbors. At oildrilling platforms, for example, they may perform such tasks as welding at depths below 200 ft (61 m). These tasks can require that they spend extended time underwater. Commercial divers use special equipment to stay underwater for long periods. Surface-supplied diving, also called hard-hat or helmet diving, affords commercial divers an unlimited air supply; a compressor connected to a surface reservoir provides the air to the diver's mask or helmet through a long, flexible tube. The diver also wears bailout tanks in case of a malfunction with the air supply. The equipment used in hard-hat diving is cumbersome and hampers mobility, making it difficult to perform tasks with the arms, such as moving heavy equipment underwater. Because commercial divers work for extended periods at depths below the recreational limit, they need to go through long decompression periods before surfacing. As in sport diving, failure to decompress properly can lead to decompression sickness and other long-term illnesses. A Submersibles Submersibles are pressurized vehicles that maintain surface air pressure inside while they descend deep into the ocean. The most common type of submersible is a submarine. Smaller submersibles are used in deep diving to transport hard-hat divers to and from workstations. Submersibles such as the bathyscaphe are used in deep-sea exploration, scientific studies, and military operations. Researchers continue to work on developing submersibles that could take scientists to the deepest parts of the ocean. B Living and Working Underwater In addition to commercial operations, other types of work are performed by divers with specialized training. Police divers perform search-and-recovery missions. Military divers engage in combat and surveillance. Treasure hunters and salvagers recover valuables by diving in areas where ships lie on the bottom. Marine biologists, geologists, and archaeologists use diving to gather valuable scientific information. Marine biologists collect data about plants and animals. Geologists learn about the formation of the earth by observing the insides of underwater caves and by studying the topography of the ocean floor. And nautical archaeologists find clues to history by surveying shipwrecks and sunken civilizations. C Saturation Diving In some cases, commercial and scientific divers live in an underwater habitat, or pressurized chamber, for extended periods. In a type of diving called saturation diving, the diver's body becomes saturated with gas mixtures corresponding to the working depth. Divers can therefore remain under a constant pressure for weeks or months, rather than go through a lengthy decompression during and after each dive. After early attempts in the 1950s, the first commercial application of saturation diving occurred in the 1960s on the Smith Mountain Dam project in Virginia. One of the most famous habitats was the Hydrolab of the National Oceanic and Atmospheric Administration (NOAA), which was based in the Bahamas and Caribbean from 1972 to 1985. During that time, Hydrolab was used by more than 600 researchers from nine countries. The hazards in saturation diving are much like the hazards of living in a space station. Inhabitants depend on life support systems for their air and power supply. Should medical or mechanical difficulties occur, a risky evacuation procedure that requires a series of decompression stops is the only way to bring divers to the surface safely. IV HISTORY The earliest reference to underwater diving techniques occurs in the manuscripts of the Greek philosopher Aristotle, which refer to a diving bell used by forces of Alexander the Great to clear the harbor at Tyre in 332 BC. This contraption, shaped like a bell, was actually a large wooden barrel that a diver could place over the head and upper body while walking on the bottom of the sea. Underwater, the pressure of the air trapped inside the barrel displaced any water that might enter. This displacement created an airspace where the diver could breathe and see. Few advances in underwater diving equipment occurred from the 4th century BC to the 1600s, but since the 1600s inventors have devised several methods for working underwater. In 1616 German inventor Franz Kessler built a diving bell that extended to the diver's ankles. His design created a larger air pocket for divers to breathe, and the lowered water level made it easier to see the ocean floor. In 1716 English astronomer Edmond Halley invented a bell that allowed divers to stay at about 60 ft (18 m) for an hour and a half. His bell consisted of a wooden shell with windows to admit light from the surface. Air was supplied to divers through leather tubes connected to air casks that could be lowered into the water as needed. As the casks were lowered below the bell, increasing water pressure forced air up through the tubes into the upper part of the diving bell where the divers could inhale it. These early inventions led to the development of more sophisticated diving bells that are used today. Modern diving bells are constructed of materials such as steel that can withstand extreme water pressure at lower depths. They also have communication systems that link them to the surface, and lighting and heating systems that provide divers with a comfortable working environment. These bells are a means of working on the underwater portions of bridges, piers, and jetties. Diving bells are also used to transport commercial divers to their underwater workstations. Equipment now used for scuba diving began to appear in the 1800s. In 1819 German inventor August Siebe developed the first diving suit--a copper helmet attached to a canvas and leather suit. Hoses supplied air to the diver by a surface pump. The hoses were attached to the helmet, and the pressure the air provided kept the water level below the diver's chin. Weights worn around the chest kept the diver from rising to the surface when more air was supplied to the helmet. Siebe's suit freed divers to explore the bottom of the sea on foot, and windows in the helmet increased what divers could see. Whereas a bell only permitted divers to see what was below the bell's opening, Siebe's suit allowed them to see in all directions, including the surface above. Later variations of Siebe's invention included a rubberized suit to keep the diver dry, valves to control buoyancy, and communication lines that provided contact with those on the surface. Each of these additions marked an important advance in underwater diving. The invention of a self-contained breathing apparatus (scuba), which provided divers with a portable air supply, was a breakthrough that freed divers from dependence on surface-supplied air. In 1865 French inventors Benoit Rouquayrol and Auguste Denayrouze developed a system consisting of a helmet with surface-supported hoses that attached to a durable canvas suit. An additional reservoir of pressurized air carried on the back enabled the diver to move about without relying upon the surface supply of air. The system was inefficient, however, because compressed gas cylinders of that period were of poor quality. Over time, gas cylinders improved. The two pioneers who receive most credit for inventing the modern scuba system are Frenchmen Jacques Cousteau and Emil Gagnon. Their invention, called the Aqua-Lung, was first successfully used in 1943. It allowed divers to breathe underwater without a cumbersome diving suit. The Aqua-Lung consisted of a valve-operated hose connecting the diver's mouth to a high-pressure cylinder worn on the back. For the first time, anyone in reasonable physical condition could don the equipment and explore the underwater environment. And for the first time, people could dive for recreation, not just as a means of accomplishing work. V RECENT DEVELOPMENTS Shortly after the invention of the Aqua-Lung, dive shops in Europe and North America began supplying basic scuba diving equipment for recreational use. Today, diving technology progresses rapidly. Advances in technology enable divers to explore places once thought inaccessible to humans. One advance is the rebreather, a device to recycle the air exhaled by the diver, thus increasing the air supply underwater. The air supply of such units lasts from about 45 minutes to 2 hours. Exhaled air passes through a regeneration chamber; carbon dioxide is removed; the air is then combined with oxygen and air from the cylinder; and then it is rebreathed. Because the rebreather does not emit bubbles the way open-circuit scuba does, divers are quieter and can interact more freely with marine life. Innovators are also developing mini-submersibles that will enable scientists and researchers to explore the bottom of the ocean at a fraction of previous costs. Most of these units are small, highly maneuverable, and extremely safe. They have windows for viewing and mechanical arms for working and gathering scientific samples. Contributed By: Katie Schickel Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.