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.