Diving (underwater)

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.

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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.

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