Diving chamber

"Hyperbaric chamber" redirects here. It is not to be confused with Hypobaric chamber.
The decompression chamber at the Neutral Buoyancy Lab

A diving chamber has two main functions:

Basic types of diving chamber

There are two basic types of submersible diving chamber differentiated by the way in which the pressure in the diving chamber is produced and controlled.

Open diving bell

Main article: Diving bell

The historically older open diving chamber, open diving bell or wet bell is in effect a large diving bell, utilising an open bottom, the equivalent of a moon pool, to equalise internal air pressure and external water pressure automatically without the need, necessarily, to measure and control it. An air compressor or bottled compressed air is required to maintain the volume of the air as it becomes compressed with increasing depth, or to make up for oxygen depleted by the occupants' breathing and for carbon dioxide removed from exhaled air by a carbon dioxide scrubber system. This type of diving chamber can only be used underwater, as the internal air pressure is directly proportional to the depth underwater and raising or lowering the chamber is the only way to adjust the pressure.

Hyperbaric chamber

A sealable diving chamber, closed bell or dry bell is a pressure vessel with hatches large enough for people to enter and exit, and a compressed breathing gas supply to raise the internal air pressure. Such chambers provide a supply of oxygen for the user, and are usually called hyperbaric chambers whether used underwater or at the water surface or on land to produce underwater pressures. However, some use submersible chamber to refer to those used underwater and hyperbaric chamber for those used out of water. There are two related terms which reflect particular usages rather than technically different types:

When used underwater there are two ways to prevent water flooding in when the submersible hyperbaric chamber's hatch is opened. The hatch could open into a moon pool chamber, and then its internal pressure must first be equalised to that of the moon pool chamber. More commonly the hatch opens into an underwater airlock, in which case the main chamber's pressure can stay constant, while it is the airlock pressure which shifts. This common design is called a lock-out chamber, and is used in submarines, submersibles, and underwater habitats as well as diving chambers.

Another arrangement utilises a dry airlock between a sealable hyperbaric compartment and an open diving bell compartment (so that effectively the whole structure is a mixture of the two types of diving chamber).

When used underwater all types of diving chamber are attached to a diving support vessel by a strong cable for raising and lowering and an umbilical cable delivering, at a minimum, compressed breathing gas, power, and communications, and all need weights attached or built in to overcome their buoyancy. The greatest depth reached using a cable-suspended chamber is about 1500 m; beyond this the cable becomes unmanageable.

Related equipment

In addition to the diving bell and hyperbaric chamber, related diving equipment includes the following.

Underwater use

As well as transporting divers, a diving chamber carries tools and equipment, breathing gas cylinders to replenish scuba tanks, and communications and emergency equipment. It provides a temporary dry air environment during extended dives for rest, eating meals, carrying out tasks which can't be done underwater, and for emergencies. Diving chambers also act as an underwater base for surface supplied diving operations, with the divers' umbilicals (air supply, etc.) attached to the diving chamber rather than to the diving support vessel.

Diving bells

Diving bells and open diving chambers of the same principle were more common in the past owing to their simplicity, since they do not necessarily need to monitor, control and mechanically adjust the internal pressure. Secondly since internal air pressure and external water pressure on the bell wall are almost balanced, the chamber does not have to be as strong as a pressurised diving chamber (dry bell). (Actually if h is the distance between a point on the side of the bell and the air/water interface at the bottom, the air pressure at that point is higher than the water on the other side by a water head pressure equivalent to h, but this is a small and constant amount, and is not a structural problem).

A wet diving bell or open diving chamber must be raised slowly to the surface with decompression stops appropriate to the dive profile so that the occupants can avoid decompression sickness. This may take hours, and so limits its use.

Submersible hyperbaric chambers

Submersible hyperbaric chambers can be brought to the surface without delay to allow divers to decompress since they can maintain the same pressure at which the divers were working. The divers can stay in the chamber on the support vessel to decompress. This flexibility makes them safer to use and more useful in an accident or emergency, including problems affecting the dive support vessel, such as sudden bad weather. They are used to support saturation diving for which the decompression times are very long.

A diving chamber based on a pressure vessel is more expensive to construct since it has to withstand very high pressure differentials. These may be both crushing pressures when the chamber is lowered into the sea and the internal pressure is kept less than ambient water pressure, or it may be an outwards pressure when it is out of the water and its internal pressure is set the same as water pressure at a certain depth.

Hyperbaric chambers also require more sophisticated systems to set and control internal gas pressure. However modern manufacturing techniques and control systems have reduced the cost and this type of diving chamber is now more common than the older dive bell type.

Hyperbaric lifeboats are specialized diving chambers or submersibles able to retrieve divers or occupants of diving chambers or underwater habitats in an emergency and to keep them in the required decompression phase. They have airlocks for underwater entry or to form a watertight seal with hatches on the target structure to effect a dry transfer of personnel. Rescuing occupants of submarines or submersibles with internal air pressure of one atmosphere requires being able to withstand the huge pressure differential to effect a dry transfer, and has the advantage of not requiring decompression measures on returning to the surface.

Out of water use

Hyperbaric chambers are also used on land and at the ocean surface

Hyperbaric chambers designed only for use out of water do not have to resist inward crushing forces, only outward expansion forces. Those for medical applications typically only operate up to two or three atmospheres, while those for diving applications may have to go to six atmospheres and above.

Lightweight portable hyperbaric chambers which can be lifted by helicopter are used by commercial diving operators and rescue services to carry one or more divers requiring hospitalisation.

Decompression chamber

A decompression chamber is a pressure vessel used in surface supplied diving to allow the divers to complete their decompression stops at the end of a dive on the surface rather than underwater. This eliminates many of the risks of long decompressions underwater, in cold or dangerous conditions.

Hyperbaric treatment chamber

Hyperbaric oxygen therapy chamber

Monoplace chamber for clinical hyperbaric oxygen treatment

A hyperbaric oxygen therapy chamber is used to treat patients, including divers, whose condition might improve through hyperbaric oxygen treatment. Hyperbaric chambers capable of admitting more than one patient (multiplace) and an inside attendant have advantages for the treatment of decompression sickness (DCS). Divers with serious complications or injuries may be attended to in this manner during treatment. Multiplace chambers are capable of greater depth of recompression than soft chambers which are unsuitable for treating DCS.

Recompression chamber

Recompression chamber

A recompression chamber is a hyperbaric treatment chamber used to treat divers suffering from certain diving disorders such as decompression sickness.[2]

Treatment is ordered by the treating physician (medical diving officer), and is often in accordance with the U.S. Navy Diving Tables.[3] Other treatment tables have been developed, including the Catalina Tables, and others, including proprietary tables.

When hyperbaric oxygen is used it is generally administered by built-in breathing systems (BIBS), which reduce contamination of the chamber gas by excessive oxygen.[4]

Test of pressure

If the diagnosis of decompression illness is considered questionable, the diving officer may order a test of pressure. This typically consists of a recompression to 60 feet (18 m) for up to 20 minutes. If the diver notes significant improvement in symptoms, or the attendant can detect changes in a physical examination, a treatment table is followed.

Representative treatment tables
Further information: Hyperbaric treatment schedules

U.S. Navy Table 6 consists of compression to the depth of 60 feet (18 m) with the patient on oxygen. The diver is later decompressed to 30 feet (9.1 m) on oxygen, then slowly returned to surface pressure. This table typically takes 4 hours 45 minutes. It may be extended further. It is the most common treatment for type 2 decompression illness.

U.S. Navy Table 5 is similar to Table 6 above, but is shorter in duration. It may be used in divers with less severe complaints (type 1 decompression illness).

U.S. Navy Table 9 consists of compression to 45 feet (14 m) with the patient on oxygen, with later decompression to surface pressure. This table may be used by lower-pressure monoplace hyperbaric chambers, or as a follow-up treatment in multiplace chambers.

Saturation diving life support systems

Main article: Saturation diving
Schematic plan of a simple saturation system showing the main pressure vessels for human occupation
DDC - Living chamber
DTC - Transfer chamber
PTC - Personnel transfer chamber (bell)
RC - Recompression chamber
SL - Supply lock
Personnel transfer capsule.

A hyperbaric environment on the surface comprising a set of linked pressure chambers is used in saturation diving to house divers under pressure for the duration of the project or several days to weeks, as appropriate. The occupants 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. The risk of decompression sickness is significantly reduced by minimizing the number of decompressions, and by decompressing at a very conservative rate.

The saturation system typically comprises a complex made up of a living chamber, transfer chamber and submersible decompression chamber,[5] which is commonly referred to in commercial diving and military diving as the diving bell,[6] PTC (personnel transfer capsule) or SDC (submersible decompression chamber).[4] The system can be permanently installed on a ship or ocean platform, but is usually capable of being transferred between vessels. The system is managed from a control room, where depth, chamber atmosphere and other system parameters are monitored and controlled. The diving bell is used to transfer 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 by a trunking space, through which the divers transfer to and from the bell.

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. The divers operate from the bell using surface supplied umbilical diving equipment.

A hyperbaric lifeboat or rescue chamber may be provided for emergency evacuation of saturation divers from a saturation system.[5] This would be used if the platform is at immediate risk due to fire or sinking to get the occupants clear of the immediate danger. A hyperbaric lifeboat is self-contained and self-sufficient for several days at sea, and can be operated from the inside by the occupants while under pressure.

Transfer under pressure

The process of transferring personnel from one hyperbaric system to another is called transfer under pressure (TUP). This is used to transfer personnel from portable recompression chambers to multi-person chambers for treatment, and between saturation life support systems and personnel transfer capsules (closed bells) for transport to and from the worksite, and for evacuation of saturation divers to a hyperbaric lifeboat.

History

Early decompression (recompression) chamber in the park at Broome, Western Australia. The chamber is now located in the Broome Museum.

Experimental compression chambers have been used since about 1860.[7]

In 1904, submarine engineers Siebe and Gorman, together with physiologist Leonard Hill, designed a device to allow a diver to enter a closed chamber at depth, then have the chamber – still pressurised – raised and brought aboard a boat. The chamber pressure was then reduced gradually. This preventative measure allowed divers to safely work at greater depths for longer times without developing decompression sickness.[8]

In 1906, Hill and another English scientist M Greenwood subjected themselves to high pressure environments, in a pressure chamber built by Siebe and Gorman, to investigate the effects. Their conclusions were that an adult could safely endure seven atmospheres, provided that decompression was sufficiently gradual.[9]

A recompression chamber intended for treatment of divers with decompression sickness was built by CE Heinke and company in 1913, for delivery to Broome, Western Australia in 1914,[10] where it was successfully used to treat a diver in 1915.[11] That chamber is now in the Broome Historical Museum.[12]

Structure and layout

The construction and layout of a hyperbaric diving chamber depends on its intended use, but there are several features common to most chambers.

Operation

Details will vary depending on the application. A generalised sequence for a stand-alone chamber is described. The operator of a commercial diving decompression chamber is generally called a Chamber operator, and the operator of a saturation system is called a life support technician (LST).

Working pressure

A large range of working pressures are used, depending on the application of the chamber. Hyperbaric oxygen therapy is usually done at pressures not exceeding 18msw, or an absolute internal pressure of 2.8 bar. Decompression chambers are usually rated for depths similar to the depths that the divers will encounter during planned operations. Chambers using air as the chamber atmosphere are frequently rated to depths in the range of 50 to 90 msw, and chambers, closed bells and other components of saturation systems must be rated for at least the planned operational depth. The US Navy has Heliox saturation decompression schedules for depths up to 480 msw (1600 fsw).[4] Experimental chambers may be rated for deeper depths. An experimental dive has been done to 701 msw (2300 fsw), so at least one chamber has been rated to at least this depth.[13]

See also

References

  1. ↑ Zamboni, WA; Riseman, JA; Kucan, JO (1990). "Management of Fournier's Gangrene and the role of Hyperbaric Oxygen". Journal of Hyperbaric Medicine 5 (3): 177–186. Retrieved 19 October 2014.
  2. ↑ "NOAA Ocean Explorer: Monitor Expedition 2002: decompression chamber". National Oceanic and Atmospheric Administration. 2002. Retrieved 3 July 2010.
  3. ↑ http://www.supsalv.org/00c3_publications.asp
  4. 1 2 3 US Navy Diving Manual, 6th revision. United States: US Naval Sea Systems Command. 2006. Retrieved 2008-04-24.
  5. 1 2 Lettnin, Heinz (1999). International textbook of Mixed Gas Diving. Flagstaff, AZ: Best Publishing. ISBN 0941332500.
  6. ↑ 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.
  7. ↑ Hyperbaric chamber, Encyclopaedia Britannica, retrieved 2 March 2015
  8. ↑ "Ocean Treasure". The Daily News (Perth, Western Australia). 25 July 1904. p. 6. Retrieved 2 March 2015.
  9. ↑ "The Dangers to Divers. Scientists' pressure test". The World's News. 2 June 1906. p. 21. Retrieved 2 March 2015.
  10. ↑ "untitled". Sunday Times (Sunday Times, Perth, WA.). 1 March 1914. p. 23. Retrieved 2 March 2015.
  11. ↑ "Divers' paralysis. Interesting case at Broome. Success of the recompression method". The West Australian. 15 March 1915. p. 8. Retrieved 2 March 2015.
  12. ↑ Jones, Natalie (1 March 2015). "Pearling industry marks 100 years of treating the bends". Australian Broadcasting Corporation. Retrieved 2 March 2015.
  13. ↑ staff (1992-11-28). "Technology: Dry run for deepest dive" (1849). NewScientist. Retrieved 2009-02-22.

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