Saturation Diving
"Saturation diving" is a technique developed by the U.S. Navy in the late 1950s that permits divers to remain at high pressures for weeks or months without having to often undergo decompression and waste the diver's time. Researchers discovered that when a diver is underwater for a long time -- days or weeks, for example - the time needed to decompress reaches a maximum and stable point. The diver becomes "saturated" and no longer accumulates additional gas such as nitrogen or helium. In other words, decompression time for a diver who has been underwater for one day may be the same as for a diver who has been down for a week.

Divers operating in the saturation mode live underwater and work out of a pressurized facility, such as a diving bell or underwater habitat, typically for a week or more, as in NOAA's Aquarius habitat at Key Largo, Florida, or in the North Sea oil fields. These facilities are maintained at the pressure of the depth at which the diver will be working. Today, a great deal of underwater work is done using remotely operated vehicles (ROVs) that are controlled from the surface. Still, there are some underwater jobs only a human diver can accomplish.

 During deep diving, a diver breathes a mixture of gases (compressed air or a combination of helium and oxygen; or helium, oxygen and nitrogen) at a pressure higher than that of air at the surface. As the diver breathes, a certain amount of nitrogen from compressed air is dissolved in the lungs. From the lungs, the blood carries this additional nitrogen to all the body's tissues. This condition can become potentially dangerous. Researchers discovered that in order to release nitrogen from the body safely, a deep-sea diver has to come to the surface slowly, a process known as "decompression." In general, the deeper or longer a diver is underwater, the longer it takes for the diver to decompress safely.