Saturation diving

Saturation diving is a diving technique that allows divers to remain at great depth for long periods of time.^[1][2]

"Saturation" refers to the fact that the diver's tissues have absorbed the maximum partial pressure of gas possible for that depth due to the diver being exposed to breathing gas at that pressure for prolonged periods. This is significant because once the tissues become saturated, the time to ascend from depth, to decompress safely, will not increase with further exposure.

Operating method

Commonly, saturation diving allows professional divers to live and work at depths greater than 50 meters / 165 feet for days or weeks at a time. This type of diving allows for greater economy of work and enhanced safety for the divers.^[1] After working in the water, they rest and live in a dry pressurized habitat on or connected to a diving support vessel, oil platform or other floating work station, at the same pressure as the work depth.^[1] The diving team is compressed to the working pressure only once, and decompressed to surface pressure once, over the entire work period of days or weeks.

Equipment

The "Saturation System" typically comprises a living chamber, transfer chamber and submersible decompression chamber, which is commonly referred to in commercial diving and military diving as the diving bell^[3], PTC (Personnel Transfer Capsule) or SDC (Submersible Decompression Chamber).^[1] The system can be permanently placed on a ship or ocean platform, but is more commonly capable of being moved from one vessel to another by crane. The entire system is managed from a control room (van), where depth, chamber atmosphere and other system parameters are monitored and controlled. The diving bell is the elevator or lift that transfers divers from the system to the work site. Typically, it is mated to the system utilizing a removable clamp and is separated from the system tankage bulkhead by a trunking space, a kind of tunnel, through which the divers transfer to and from the bell. At the completion of work or a mission, the saturation diving team is decompressed gradually back to atmospheric pressure by the slow venting of system pressure, at an average of 15 meters/47 feet per day, traveling 24 hours a day (schedules vary). Thus the process involves only one ascent, thereby mitigating the time-consuming and comparatively risky process of in-water, staged decompression normally associated with non-saturation ("mixed gas diving or sur-D O2") operations.^[2]

The divers use surface supplied umbilical diving equipment, utilizing deep diving breathing gas, such as helium and oxygen mixtures, stored in large capacity, high pressure cylinders.^[2] The gas supplies are plumbed to the control room, where they are routed to supply the system components. The bell is fed via a large, multi-part umbilical that supplies breathing gas, electricity, communications and hot water. The bell also is fitted with exterior mounted breathing gas cylinders for emergency use.

While in the water the divers will use a hot water suit to protect against the cold.^[4] The hot water comes from boilers on the surface and is pumped down to the diver via the bell's umbilical and then through the diver's umbilical.

Medical aspects

Saturation diving (or more precisely, long term exposure to high pressure) can potentially cause aseptic bone necrosis, although it is not yet known if all divers are affected or only especially sensitive ones. The joints are most vulnerable to osteonecrosis.^[5][6][7] The connection between high-pressure exposure and osteonecrosis is not fully understood.

Extreme depth effects

The breathing gas mixtures, of oxygen, helium and hydrogen, for extreme depth use are designed to reduce the effects of high pressure on the central nervous system. Between 1978 and 1984, a team of divers from Duke University in North Carolina conducted the Atlantis series of on shore hyperbaric chamber deep scientific test dives. In 1981, during an extreme depth test dive to 686 metres they breathed the conventional mixture of oxygen and helium with difficulty and suffered trembling and memory lapses.^[8]

A hydrogen-helium-oxygen (hydreliox) gas mixture was used during a similar on shore scientific test dive by three divers involved in an experiment for the French Comex S.A. industrial deep-sea diving company in 1992. On 18 November 1992, Comex decided to stop the experiment at an equivalent of 675 meters of sea water (MSW) because the divers were suffering from insomnia and fatigue. All three divers wanted to push on but the company decided to decompress the chamber to 650 MSW. On 20 November 1992, Comex diver Theo Mavrostomos was given the go-ahead to continue but spent only two hours at 701 MSW (2300 ft). Comex had planned for the divers to spend four and a half days at this depth and carry out tasks.^[8]

Increased use of underwater remotely operated vehicles (ROV's) and autonomous underwater vehicles (AUV's) for routine or planned tasks means that saturation dives are becoming less common, though complicated underwater tasks requiring complex manual actions remain the preserve of the deep-sea saturation diver.

Saturation diving depth records

The diving depth record for off shore diving was achieved in 1988 by a team of professional divers of the Comex S.A. industrial deep-sea diving company performing pipe line connection exercises at a depth of 534 meters (1752 ft) of sea water (MSW) in the Mediterranean Sea during a record scientific dive.

In 1992 Comex diver Theo Mavrostomos [1] achieved a record of 701 MSW (2300 ft) in an on shore hyperbaric chamber. He took 43 days to complete the scientific record dive, where a hydrogen-helium-oxygen gas mixture was used as breathing gas^[8][9][10]

The complexity, medical problems and accompanying high costs of professional diving to such extreme depths and the development of deep water atmospheric diving suits and ROVs in offshore oilfield drilling and production have effectively prevented non-atmospheric manned intervention in the ocean at extreme depths.

Saturation diving in fiction

For saturation diving in fiction, see The Abyss (1989), or Sphere (1987).

See also

• Surface supplied diving
• Diving chamber

References

Saturation Dive Forum

Additional Reading

• Subsea Manned Engineering by Gerhard Haux, Carson, California U.S.A., Best Publishing Company, 1982, ISBN 0-941332-00-4
• Saturation Diving on www.divingheritage.com
• Saturation Divers Forum at www.satsystemforum.com
• Saturation Diving Resource Further Reading on Sat Diving and Commercial Diving in general]

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