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.

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.