Diving (underwater)

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.

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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 oil-drilling 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.