Saturation diving
Saturation diving is a diving technique that allows divers to reduce the risk of decompression sickness
Decompression sickness
Decompression sickness describes a condition arising from dissolved gases coming out of solution into bubbles inside the body on depressurization...

 ("the bends") when they work at great depth for long periods of time.

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
Decompression (diving)
Decompression in the context of diving derives from the reduction in ambient pressure experienced by the diver during the ascent at the end of a dive or hyperbaric exposure and refers to both the reduction in pressure and the process of allowing dissolved inert gases to be eliminated from the...

, 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
Partial pressure
In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. The total pressure of a gas mixture is the sum of the partial pressures of each individual gas in the mixture....

 of gas possible for that depth due to the diver being exposed to breathing gas
Breathing gas
Breathing gas is a mixture of gaseous chemical elements and compounds used for respiration.Air is the most common and only natural breathing gas...

 at that pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...

 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 under pressure in a Saturation system or "saturation spread", a hyperbaric environment on the surface, or an ambient pressure underwater habitat, for the duration of the project or several day to weeks, as appropriate, and are decompressed to surface pressure only once, at the end of their tour of duty. This is usually done in a decompression chamber which is part of the saturation system, and the risk of decompression sickness is significantly reduced by limiting the number of decompressions, and by decompressing at a very conservative rate.


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
Milwaukee, Wisconsin
Milwaukee is the largest city in the U.S. state of Wisconsin, the 28th most populous city in the United States and 39th most populous region in the United States. It is the county seat of Milwaukee County and is located on the southwestern shore of Lake Michigan. According to 2010 census data, the...

. Their decompression lasted five hours leaving Nohl with a mild case of decompression sickness that resolved with recompression.

Albert R. Behnke
Albert R. Behnke
Captain Albert Richard Behnke Jr. USN was an American physician, who was principally responsible for developing the U.S. Naval Medical Research Institute...

 proposed the idea of exposing humans to increased ambient pressures long enough for the blood and tissues to become saturated
Saturation (chemistry)
In chemistry, saturation has six different meanings, all based on reaching a maximum capacity...

 with inert gases in 1942. In 1957, George F. Bond
George F. Bond
Capt. George Foote Bond USN was an American physician who was known as a leader in the field of undersea and hyperbaric medicine and the "Father of Saturation Diving".-Early life:...

 began the Genesis project at the Naval Submarine Medical Research Laboratory
Naval Submarine Medical Research Laboratory
The Naval Submarine Medical Research Laboratory is located on the New London Submarine Base in Groton, Connecticut. The laboratory's mission is to protect the health and enhance the performance of United States War Fighters through focused submarine, diving, and surface research solutions.-History...

 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.

The first commercial saturation dives were performed in 1965 by Westinghouse
Westinghouse Electric (1886)
Westinghouse Electric was an American manufacturing company. It was founded in 1886 as Westinghouse Electric Company and later renamed Westinghouse Electric Corporation by George Westinghouse. The company purchased CBS in 1995 and became CBS Corporation in 1997...

 to replace faulty trash racks at 200 feet on the Smith Mountain Dam
Smith Mountain Dam
Smith Mountain Dam is concrete arch dam located on the Roanoke River in Virginia, creating Smith Mountain Lake. The dam was built by Appalachian Power between 1960 and 1963 for the purposes of hydroelectricity via pumped-storage hydroelectricity...


Peter B. Bennett
Peter B. Bennett
Peter B. Bennett is the founder and former president and CEO of the Divers Alert Network , a non-profit organization devoted to assisting scuba divers in need. He is a professor of anesthesiology at Duke University Medical Center, and is currently the Senior Director of the Center for Hyperbaric...

 is credited with the invention of trimix breathing gas as a method to eliminate High Pressure Nervous Syndrome
High pressure nervous syndrome
High-pressure nervous syndrome is a neurological and physiological diving disorder that results when a commercial diver or scuba diver descends below about while breathing a helium–oxygen mixture. The effects depend on the rate of descent and the depth...

. 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 meters), and slowly decompressing them to the surface over a period of 31-plus days, setting an early world record for depth in the process.

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
Decompression (diving)
Decompression in the context of diving derives from the reduction in ambient pressure experienced by the diver during the ascent at the end of a dive or hyperbaric exposure and refers to both the reduction in pressure and the process of allowing dissolved inert gases to be eliminated from the...

, can last for many hours for dives in excess of 50 metres (164 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 commercial diver or scuba diver descends below about 500 feet (152.4 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
Dysbaric osteonecrosis
Dysbaric osteonecrosis or DON is a form of avascular necrosis where there is death of a portion of the bone that is thought to be caused by nitrogen embolism in divers...

. 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.

A hydrogen–helium–oxygen (hydreliox
Hydreliox is an exotic breathing gas mixture of helium, oxygen and hydrogen.It is used primarily for research and scientific deep diving, usually below . Below this depth, extended breathing of heliox gas mixtures may cause high pressure nervous syndrome . Two gas mixtures exist that attempt to...

) 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
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...

 habitat on or connected to a diving support vessel
Diving support vessel
A diving support vessel is a ship that is used as a floating base for professional diving projects.Commercial Diving Support Vessels emerged during the 1960s and 1970s when the need arose for diving operations to be performed below and around oil production platforms and associated installations in...

, oil platform
Oil platform
An oil platform, also referred to as an offshore platform or, somewhat incorrectly, oil rig, is a lаrge structure with facilities to drill wells, to extract and process oil and natural gas, and to temporarily store product until it can be brought to shore for refining and marketing...

 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 vehicle
Remotely operated vehicle
A remotely operated vehicle is a tethered underwater vehicle. They are common in deepwater industries such as offshore hydrocarbon extraction. An ROV may sometimes be called a remotely operated underwater vehicle to distinguish it from remote control vehicles operating on land or in the air. ROVs...

s (ROV's) and autonomous underwater vehicle
Autonomous Underwater Vehicle
An autonomous underwater vehicle is a robot which travels underwater without requiring input from an operator. AUVs constitute part of a larger group of undersea systems known as unmanned underwater vehicles, a classification that includes non-autonomous remotely operated underwater vehicles...

s (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 a living chamber, transfer chamber and submersible decompression chamber , which is commonly referred to in commercial diving
Commercial Diving
Professional diving is a type of diving where the divers are paid for their work. There are several branches of professional diving, the most well known of which is probably commercial diving...

 and military diving as the diving bell
Diving bell
A diving bell is a rigid chamber used to transport divers to depth in the ocean. The most common types are the wet bell and the closed 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 decompress
Decompression has several meanings:* Decompression , the release of pressure and the opposition of physical compression* Decompression sickness, a condition arising from the precipitation of dissolved gases into bubbles inside the body on depressurization* Decompression , a procedure used to treat...

ed gradually back to atmospheric pressure
Atmospheric pressure
Atmospheric pressure is the force per unit area exerted into a surface by the weight of air above that surface in the atmosphere of Earth . In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point...

 by the slow venting of system pressure, at an average of 15 metres (49.2 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
Surface supplied diving
Surface supplied diving refers to divers using equipment supplied with breathing gas using a diver's umbilical from the surface, either from the shore or from a diving support vessel sometimes indirectly via a diving bell...

 umbilical diving equipment, utilizing deep diving breathing gas
Breathing gas
Breathing gas is a mixture of gaseous chemical elements and compounds used for respiration.Air is the most common and only natural breathing gas...

, such as helium and oxygen mixtures, stored in large capacity, high pressure cylinders
Diving cylinder
A diving cylinder, scuba tank or diving tank is a gas cylinder used to store and transport high pressure breathing gas as a component of a scuba set. It provides gas to the scuba diver through the demand valve of a diving regulator....

. 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.

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
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...

 during a record scientific dive.

In 1992 Comex diver Theo 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
Breathing gas
Breathing gas is a mixture of gaseous chemical elements and compounds used for respiration.Air is the most common and only natural 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 suit
Atmospheric diving suit
An atmospheric diving suit or ADS is a small one-man articulated submersible of anthropomorphic form which resembles a suit of armour, with elaborate pressure joints to allow articulation while maintaining an internal pressure of one atmosphere...

s 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
The Abyss
The Abyss is a 1989 science fiction film written and directed by James Cameron. It stars Ed Harris, Mary Elizabeth Mastrantonio, and Michael Biehn. The original musical score was composed by Alan Silvestri...

(1989), Sphere
Sphere (novel)
Sphere is a science fiction novel written by Michael Crichton and published in 1987. It was made into the film Sphere in 1998.The novel follows Norman Johnson as a psychologist who is engaged by the United States Navy to join a team of scientists assembled by the U.S. Government to examine an...

(1987), or Dykket (The Dive) (1989)

Additional reading

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