The total decompression requirements for a long task can be reduced by allowing the diver(s) to stay at depth until the task is finished, and then decompress slowly in a chamber. Thus, only one decompression is required. This procedure - called saturation diving - was first demonstrated by Dr George Bond of the United States Navy, who was exploiting a suggestion made by Behnke in 1942, as a method of increasing the duration of exposure in caisson workers.
Although these men were instrumental in applying the concept of saturation diving, they were predated by Dr Cunningham (Kansas City, USA in 1927) who used air under pressure for several days, followed by a slow decompression, as a form of hyperbaric therapy.
The main value of saturation diving is that a diver needs the same decompression time for a dive lasting either two days or two months. Once the body has equilibrated with the gases in the environment at any pressure, it will not take up any more gas, so the amount of decompression will not increase.
Bond tested this concept with animals and then with men in compression chambers. In 1964 he had a group of four men in a cylindrical underwater house for nine days at a depth of nearly 60 metres. Other early dives based on underwater houses, or habitats, were conducted by Link and Cousteau.
Instead of permanent underwater habitats, saturation dives can be conducted by the use of transportable chambers. The first commercial work in saturation diving was conducted by Westinghouse Inc. The men lived in a pressurized chamber on the surface called a deck decompression chamber (DDC) and were lowered to work in a capsule called a submersible decompression chamber (SDC), often called a 'bell'. This allowed their transfer in the chamber to the working depth without anyalteration in pressure. In 1965 this procedure was used for a series of dives to repair a dam in the USA. Four men at a time were pressurized, and they performed 800 hours of work in 12 weeks. With surface diving the men could have performed only about 160 hours of work during the same period.
The main need for saturation diving is in the offshore oil industry, which relies on saturation divers to carry out many tasks underwater. These include observations, welding joins in pipes, cleaning, anti- fouling and repairing damaged components (technical diving). Military saturation dives have been conducted for a variety of purposes, but most have been for the recovery of valuable, dangerous or strategic items from the sea bed.
The recovery of the components from crashed aircraft is a common task, and salvage divers and treasure hunters have also used this technique. The recovery of a large amount of gold from the wreck of HMS Edinburgh in over 200 metres of water is one example. Oceanographers often find the submersible decompression chambers too restrictive, and have found fixed underwater habitats, with direct access to the surrounding terrain, to be a useful alternative as these allow direct observation and prolonged data collection. At the end of their period on the seabed they use a SDC to transfer to a DDC for decompression.