The offshore industry is heavily dependant on diving operations. Air diving is used for the inspection and repair programmes carried out in shallow waters. For depths of more than 50m saturation diving is necessary. Safe diving operations require sophisticated support systems, such as large pressure chambers to allow the divers to remain under deep water pressure while on board.
Saturation divers live in an onboard accommodation chamber which is pressurised to several times atmospheric pressure for up to a month at a time, traveling to and from their work place at the sea bed in a similarly pressurised diving bell. At the end of their time on board they decompress slowly, allowing the absorbed gasses saturated within their tissues by the pressure, to gradually dissipate before exiting the chamber to normal atmosphere. Existing under pressure for extended periods negates the need for prolonged decompression at the end of each dive.This makes deep water diving practical, since it is not necessary to depressurize in between working spells. Diving support vessels are intended as a base for diving operations offshore and are fitted with all equipment necessary for safe deep water diving operations.
Further reading: “Offshore Engineering” by Angus Mather