Decompression sickness occurs when a diver with a large amount of inert gas dissolved in the body tissues is decompressed to a pressure where the gas forms bubbles which may block blood vessels or physically damage surrounding cells. This is a risk on every decompression, and limiting the number of decompressions can reduce the risk.
"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.
In saturation diving, the divers live in a pressurized environment, which can be a saturation system or "saturation spread", a hyperbaric environment on the surface, or an ambient pressure underwater habitat. This may be maintained for up to several weeks, and they are decompressed to surface pressure only once, at the end of their tour of duty. By limiting the number of decompressions in this way, the risk of decompression sickness is significantly reduced.
On December 22, 1938, Edgar End and Max Nohl made the first intentional saturation dive by spending 27 hours breathing air at 101 feet in the County Emergency Hospital recompression facility in Milwaukee, Wisconsin. Their decompression lasted five hours leaving Nohl with a mild case of decompression sickness that resolved with recompression.
Albert R. Behnke proposed the idea of exposing humans to increased ambient pressures long enough for the blood and tissues to become saturated with inert gases in 1942. In 1957, George F. Bond began the Genesis project at the Naval Submarine Medical Research Laboratory proving that humans could in fact withstand prolonged exposure to different breathing gases and increased environmental pressures. Once saturation is achieved, the amount of time needed for decompression depends on the depth and gases breathed. This was the beginning of saturation diving and the US Navy's Man-in-the-Sea Program.
Peter B. Bennett is credited with the invention of trimix breathing gas as a method to eliminate High Pressure Nervous Syndrome. In 1981, at Duke University Medical Center, Bennett conducted an experiment called Atlantis III, which involved taking divers to a depth of 2,250 feet (685.8 metres), and slowly decompressing them to the surface over a period of 31-plus days, setting an early world record for depth in the process.
Medical aspects 
Decompression sickness 
Decompression sickness (DCS) is a potentially fatal condition caused by bubbles of inert gas, which can occur in divers' bodies following the pressure reduction as they ascend. To prevent DCS, divers have to limit their rate of ascent, and pause at regular intervals to allow the pressure of gases in their body to approach equilibrium. This protocol, known as decompression, can last for many hours for dives in excess of 50 metres (160 ft) when divers spend more than a few minutes at these depths. The longer divers remain at depth, the more inert gas is absorbed into their body tissues, and the time required for decompression increases rapidly. This presents a problem for operations that require divers to work for extended periods at depth. However, after several hours under pressure, divers' bodies become saturated with inert gas, and no further uptake occurs. From that point onward, no increase in decompression time is necessary. The idea of saturation diving takes advantage of this by providing a means for divers to remain at depth for days. At the end of that period, divers need to carry out a single decompression, which is much more efficient and a lower risk than making multiple short dives, each of which requires a lengthy decompression time. By making the single decompression slower and longer, in the relative comfort of the saturation habitat or decompression chamber, the risk of decompression sickness during the single exposure is further reduced.
High Pressure Nervous Syndrome 
High Pressure Nervous Syndrome is a neurological and physiological diving disorder that results when a diver descends below about 500 feet (150 m) while breathing a helium–oxygen mixture. The effects depend on the rate of descent and the depth. HPNS is a limiting factor in future deep diving. HPNS can be reduced by using a small percentage of Nitrogen in the gas mixture.
Dysbaric osteonecrosis 
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. The connection between high-pressure exposure and osteonecrosis is not fully understood.
Extreme depth effects 
A breathing gas mixture of oxygen, helium and hydrogen was developed for use at extreme depths 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.
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.
Operating method 
Commonly, saturation diving allows professional divers to live and work at pressures greater than 50msw (160fsw) for days or weeks at a time. This type of diving allows for greater economy of work and enhanced safety for the divers. 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 approximately the same pressure as the work depth. The diving team is compressed to the working pressure only once, at the beginning of the work period, and decompressed to surface pressure once, after the entire work period of days or weeks.
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.
The "Saturation System" typically comprises either an underwater habitat or a surface complex made up of a living chamber, transfer chamber and submersible decompression chamber, which is commonly referred to in commercial diving and military diving as the diving bell, PTC (Personnel Transfer Capsule) or SDC (Submersible Decompression Chamber). 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 metres (49 ft) 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.
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. 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. 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.
A helium reclaim system (or push-pull system) is used to recover helium based breathing gas after use by the divers as this is more economical than losing it to the environment in open circuit systems. The recovered gas is passed through a scrubber system to remove carbon dioxide, filtered to remove odours, and pressurised into storage containers, where it may be mixed with oxygen to the required composition.
A hyperbaric lifeboat or rescue chamber may be provided for emergency evacuation of saturation divers from a saturation system. This would be used if the platform is at immediate risk due to fire or sinking, and allows the divers under saturation to get clear of the immediate danger. A hyperbaric lifeboat is self-contained and can be operated from the inside by the occupants while under pressure. It must be self-sufficient for several days at sea, in case of a delay in rescue due to sea conditions. The occupants would normally start decompression immediately after launching.
Scientific saturation diving is usually conducted by researchers and technicians known as aquanauts living in an underwater habitat, a structure designed for people to live in for extended periods, where they can carry out most all basic human functions: working, resting, eating, attending to personal hygiene, and sleeping, all while remaining under pressure beneath the surface.
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 Greek diver Theodoros Mavrostomos  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.
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 
See also 
- US Navy Diving Manual, 6th revision. United States: US Naval Sea Systems Command. 2006. Retrieved 2008-04-24.
- Beyerstein, G (2006). Lang, MA; Smith, NE, eds. "Commercial Diving: Surface-Mixed Gas, Sur-D-O2, Bell Bounce, Saturation". Proceedings of Advanced Scientific Diving Workshop. Washington, DC. Retrieved 12 April 2010. More than one of
- Kindwall, Eric P. "A short history of diving and diving medicine.". In: Bove, Alfred A; Davis, Jefferson C. Diving Medicine. 2nd edition. WB Saunders Company.: 6–7. ISBN 0-7216-2934-2.
- Miller, James W; Koblick, Ian G (1984). Living and working in the sea. Best Publishing Company. p. 432. ISBN 1-886699-01-1.
- Behnke, Albert R (1942). "Effects of High Pressures; Prevention and Treatment of Compressed-air illness". Medical Clinics of North America 26: 1212–1237.
- Murray, John (2005). ""Papa Topside", Captain George F. Bond, MC, USN". Faceplate 9 (1): 8–9. Retrieved 2010-01-15.
- Shilling, Charles (1983). "Papa Topside". Pressure, newsletter of the Undersea and Hyperbaric Medical Society 12 (1): 1–2. ISSN 0889-0242.
- Camporesi, Enrico M (2007). "The Atlantis Series and Other Deep Dives". In: Moon RE, Piantadosi CA, Camporesi EM (eds.). Dr. Peter Bennett Symposium Proceedings. Held May 1, 2004. Durham, N.C.: (Divers Alert Network). Retrieved 2011-01-15.
- Tikuisis, Peter; Gerth, Wayne A (2003). "Decompression Theory". In Brubakk, Alf O; Neuman, Tom S. Bennett and Elliott's physiology and medicine of diving, 5th Rev ed. United States: Saunders. pp. 419–54. ISBN 0-7020-2571-2.
- Bennett, Peter B; Rostain, Jean Claude (2003). "The High Pressure Nervous Syndrome". In Brubakk, Alf O; Neuman, Tom S. Bennett and Elliott's physiology and medicine of diving, 5th Rev ed. United States: Saunders. pp. 323–57. ISBN 0-7020-2571-2.
- Smith EB, Halsey MJ (ed). (1980). "Techniques for Diving Deeper than 1,500 feet.". 23rd Undersea and Hyperbaric Medical Society Workshop. UHMS Publication Number 40WS(DD)6-30-80. (Undersea and Hyperbaric Medical Society). Retrieved 2011-11-09.
- Coulthard A, Pooley J, Reed J, Walder D (1996). "Pathophysiology of dysbaric osteonecrosis: a magnetic resonance imaging study". Undersea and Hyperbaric Medicine 23 (2): 119–20. ISSN 1066-2936. OCLC 26915585. PMID 8840481. Retrieved 2008-04-26.
- British Medical Research Council Decompression Sickness Central Registry and Radiological Panel (1981). "Aseptic bone necrosis in commercial divers. A report from the Decompression Sickness Central Registry and Radiological Panel". Lancet 2 (8243): 384–8. PMID 6115158.
- staff (1992-11-28). Technology: Dry run for deepest dive (1849). NewScientist. Retrieved 2009-02-22.
- Heinz Lettnin (1999); International textbook of Mixed Gas Diving, Best Publishing Company. Flagstaff, AZ, ISBN 0-941332--50-0
- Bevan, J. (1999). "Diving bells through the centuries". South Pacific Underwater Medicine Society Journal 29 (1). ISSN 0813-1988. OCLC 16986801. Retrieved 2008-04-25.
- Mekjavić B, Golden FS, Eglin M, Tipton MJ (2001). "Thermal status of saturation divers during operational dives in the North Sea". Undersea and Hyperbaric Medicine 28 (3): 149–55. PMID 12067151. Retrieved 2008-05-05.
- Lafay V, Barthelemy P, Comet B, Frances Y, Jammes Y (March 1995). "ECG changes during the experimental human dive HYDRA 10 (71 atm/7,200 kPa)". Undersea and Hyperbaric Medicine 22 (1): 51–60. PMID 7742710. Retrieved 2009-02-22.
- "HYDRA 8 and HYDRA 10 test projects". Comex S.A. Retrieved 2009-02-22.[dead link]
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]
- Saturation diving literature
- Extremely comprehensive commercial diving site - offshorediver.com