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 underwater breathing 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.

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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.

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