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A diving bell is a rigid chamber used to transport divers from the surface to depth and back in open water, usually for the purpose of performing underwater work. The most common types are the open-bottomed wet bell and the closed bell, which can maintain an internal pressure greater than the external ambient. Diving bells are usually suspended by a cable, and lifted and lowered by a winch from a surface support platform. Unlike a
submersible A submersible is a small watercraft designed to operate underwater. The term "submersible" is often used to differentiate from other underwater vessels known as submarines, in that a submarine is a fully self-sufficient craft, capable of ind ...
, the diving bell is not designed to move under the control of its occupants, nor to operate independently of its launch and recovery system. The wet bell is a structure with an airtight chamber which is open to the water at the bottom, that is lowered underwater to operate as a base or a means of transport for a small number of divers. Air is trapped inside the bell by pressure of the water at the interface. These were the first type of
diving chamber A diving chamber is a vessel for human occupation, which may have an entrance that can be sealed to hold an internal pressure significantly higher than ambient pressure, a pressurised gas system to control the internal pressure, and a supply of ...
, and are still in use in modified form. The closed bell is a pressure vessel for human occupation, which may be used for bounce diving or
saturation diving Saturation diving is diving for periods long enough to bring all tissues into equilibrium with the partial pressures of the inert components of the breathing gas used. It is a diving mode that reduces the number of decompressions divers working ...
, with access to the water through a hatch at the bottom. The hatch is sealed before ascent to retain internal pressure. At the surface, this type of bell can lock on to a hyperbaric chamber where the divers live under saturation or are decompressed. The bell is mated with the chamber system via the bottom hatchway or a side hatchway, and the trunking in between is pressurized to enable the divers to transfer through to the chamber under pressure. In saturation diving the bell is merely the ride to and from the job, and the chamber system is the living quarters. If the dive is relatively short (a bounce dive), decompression can be done in the bell in exactly the same way it would be done in the chamber. A third type is the rescue bell, used for the rescue of personnel from sunk submarines which have maintained structural integrity. These bells may operate at atmospheric internal pressure and must withstand the ambient water pressure.


History

The diving bell is one of the earliest types of equipment for underwater work and exploration. Its use was first described by Aristotle in the 4th century BC: "they enable the divers to respire equally well by letting down a cauldron, for this does not fill with water, but retains the air, for it is forced straight down into the water." Recurring legends about
Alexander the Great Alexander III of Macedon ( grc, Ἀλέξανδρος, Alexandros; 20/21 July 356 BC – 10/11 June 323 BC), commonly known as Alexander the Great, was a king of the ancient Greek kingdom of Macedon. He succeeded his father Philip II to ...
(including some versions of the '' Alexander Romance'') tell he explored the sea in some closed vessel, lowered from his ships. Their origin is hard to determine, but some of the earliest dated works are from the early middle ages. In 1535, Guglielmo de Lorena created and used what is considered to be the first modern diving bell. In 1616, Franz Kessler built an improved diving bell. In 1642,
John Winthrop John Winthrop (January 12, 1587/88 – March 26, 1649) was an English Puritan lawyer and one of the leading figures in founding the Massachusetts Bay Colony, the second major settlement in New England following Plymouth Colony. Winthrop led ...
reports one Edward Bendall building two large wooden barrels, weighted with lead and open at their bottoms, to salvage a ship ''Mary Rose'' which had exploded and sunk, blocking the harbor of
Charlestown, Boston Charlestown is the oldest neighborhood in Boston, Massachusetts, in the United States. Originally called Mishawum by the Massachusett tribe, it is located on a peninsula north of the Charles River, across from downtown Boston, and also adjoins ...
. Bendall undertook the work on condition that he be awarded all the value of the salvage should he succeed in unblocking the harbor, or half the value he could salvage if he could not. In 1658, Albrecht von Treileben was permitted to salvage the warship '' Vasa'', which sank in Stockholm harbor on its maiden voyage in 1628. Between 1663 and 1665 von Treileben's divers were successful in raising most of the cannon, working from a diving bell. A diving bell is mentioned in the 1663 Ballad of Gresham College (stanza 16): In late 1686, Sir William Phipps convinced investors to fund an expedition to what is now
Haiti Haiti (; ht, Ayiti ; French: ), officially the Republic of Haiti (); ) and formerly known as Hayti, is a country located on the island of Hispaniola in the Greater Antilles archipelago of the Caribbean Sea, east of Cuba and Jamaica, and s ...
and the
Dominican Republic The Dominican Republic ( ; es, República Dominicana, ) is a country located on the island of Hispaniola in the Greater Antilles archipelago of the Caribbean region. It occupies the eastern five-eighths of the island, which it shares with ...
to find sunken treasure, despite the location of the shipwreck being based entirely on rumor and speculation. In January 1687, Phipps found the wreck of the Spanish galleon ''Nuestra Señora de la Concepción'' off the coast of
Santo Domingo , total_type = Total , population_density_km2 = auto , timezone = AST (UTC −4) , area_code_type = Area codes , area_code = 809, 829, 849 , postal_code_type = Postal codes , postal_code = 10100–10699 (Distrito Nacional) , websi ...
. Some sources say they used an inverted container for the salvage operation while others say the crew was assisted by Indian divers in the shallow waters. The operation lasted from February to April 1687 during which time they salvaged jewels, some gold and 30 tons of silver which, at the time, was worth over £200,000. In 1689,
Denis Papin Denis Papin FRS (; 22 August 1647 – 26 August 1713) was a French physicist, mathematician and inventor, best known for his pioneering invention of the steam digester, the forerunner of the pressure cooker and of the steam engine. Early l ...
suggested that the pressure and fresh air inside a diving bell could be maintained by a force pump or bellows. Engineer
John Smeaton John Smeaton (8 June 1724 – 28 October 1792) was a British civil engineer responsible for the design of bridges, canals, harbours and lighthouses. He was also a capable mechanical engineer and an eminent physicist. Smeaton was the firs ...
utilized this concept in 1789. In 1691, Dr.
Edmond Halley Edmond (or Edmund) Halley (; – ) was an English astronomer, mathematician and physicist. He was the second Astronomer Royal in Britain, succeeding John Flamsteed in 1720. From an observatory he constructed on Saint Helena in 1676–77, Hal ...
completed plans for a diving bell capable of remaining submerged for extended periods of time, and fitted with a window for the purpose of undersea exploration. In Halley's design, atmosphere is replenished by sending weighted barrels of air down from the surface. In 1775,
Charles Spalding Charles Spalding (29 October 1738 – 2 June 1783) was an Edinburgh confectioner and amateur engineer who made improvements to the diving bell. He died while diving to the Shipwreck, wreck of the ''Belgioso'' in Dublin Bay using a diving bell ...
, an Edinburgh confectioner, improved on Halley's design by adding a system of balance-weights to ease the raising and lowering of the bell, along with a series of ropes for signaling the surface crew. Spalding and his nephew, Ebenezer Watson, later suffocated off the coast of Dublin in 1783 doing salvage work in a diving bell of Spalding's design.


Mechanics

The bell is lowered into the water by cables from a crane, gantry or A-frame attached to a floating platform or shore structure. The bell is
ballast Ballast is material that is used to provide stability to a vehicle or structure. Ballast, other than cargo, may be placed in a vehicle, often a ship or the gondola of a balloon or airship, to provide stability. A compartment within a boat, ship ...
ed so as to remain upright in the water and to be negatively
buoyant Buoyancy (), or upthrust, is an upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the pr ...
, so that it will sink even when full of air. Hoses, supplied by
gas compressor A compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor. Compressors are similar to pumps: both increase the pressure on a fluid and both can tran ...
s or banks of
high pressure storage cylinder A gas cylinder is a pressure vessel for storage and containment of gases at above atmospheric pressure. High-pressure gas cylinders are also called ''bottles''. Inside the cylinder the stored contents may be in a state of compressed gas, vapo ...
s at the surface, provide
breathing gas A breathing gas is a mixture of gaseous chemical elements and compounds used for respiration. Air is the most common and only natural breathing gas, but other mixtures of gases, or pure oxygen, are also used in breathing equipment and enclosed h ...
to the bell, serving two functions: * Fresh gas is available for breathing by the occupants. * Volume reduction of the air in an open bell due to increasing hydrostatic pressure as the bell is lowered is compensated. Adding pressurized gas ensures that the gas space within the bell remains at constant volume as the bell descends in the water. Otherwise the bell would partially fill with water as the gas was compressed. The physics of the diving bell applies also to an
underwater habitat Underwater habitats are underwater structures in which people can live for extended periods and carry out most of the basic human functions of a 24-hour day, such as working, resting, eating, attending to personal hygiene, and sleeping. In thi ...
equipped with a
moon pool A moon pool is a feature of marine drilling platforms, drillships and diving support vessels, some marine research and underwater exploration or research vessels, and underwater habitats, in which it is also known as a wet porch. It is an o ...
, which is like a diving bell enlarged to the size of a room or two, and with the water–air interface at the bottom confined to a section rather than forming the entire bottom of the structure.


Wet bell

A wet bell is a platform for lowering and lifting divers to and from the underwater workplace, which has an air filled space, open at the bottom, where the divers can stand or sit with their heads out of the water. The air space is at ambient pressure at all times, so there are no great pressure differences, and the greatest structural loads are usually self weight and the buoyancy of the air space. A fairly heavy ballast is often required to counteract the buoyancy of the airspace, and this is usually set low at the bottom of the bell, which helps with stability. The base of the bell is usually a grating or deck which the divers can stand on, and folding seats may be fitted for the divers' comfort during ascent, as in-water decompression may be long. Other equipment that is carried on the bell include cylinders with the emergency gas supply, and racks or boxes for tools and equipment to be used on the job. There may be a tackle for hoisting and supporting a disabled diver so that their head projects into the air space.


Type 1 wet bell

The type 1 wet bell does not have an umbilical supplying the bell, because diver's umbilicals supply the divers directly from the surface, similar to a
diving stage There are several categories of decompression equipment used to help divers decompress, which is the process required to allow divers to return to the surface safely after spending time underwater at higher ambient pressures. Decompression o ...
. Divers deploying from a type 1 bell will exit on the opposite side to where the umbilicals enter the bell so that the umbilicals pass through the bell and the divers can find their way back to the bell at all times by following the umbilical. Bailout from a type 1 bell is done by exiting the bell on the side that the umbilicals enter the bell so they no longer pass through the bell, leaving the divers free to surface.


Type 2 wet bell

A gas panel inside the bell is supplied by the bell umbilical and the emergency gas cylinders, and supplies the divers' umbilicals and sometimes BIBS sets. There will be racks to hang the divers' excursion umbilicals, which for this application must not be buoyant. Abandonment of a type 2 wet bell requires the divers to manage their own umbilicals as they ascend along a remaining connection to the surface.


Operation of a wet bell

The bell with divers on board is deployed from the working platform (usually a vessel) by a crane,
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, or other mechanism with a
man-rated Human-rating certification, also known as man-rating or crew-rating, is the certification of a spacecraft or launch vehicle as capable of safely transporting humans. There is no one particular standard for human-rating a spacecraft or launch veh ...
winch. The bell is lowered into the water and to the working depth at a rate recommended by the decompression schedule, and which allows the divers to
equalize ''Equalize'' is the third album by the UK band Swami, released on 24 September 2007. Track listing # "Hey Hey" (featuring Boostylz) # "Electro Jugni" # "Intoxicated" (featuring Lady Ru) # "Ching" (featuring Spee) # "Pushin'" (featuring Pras ...
comfortably. Wet bells with an air space will have the air space topped up as the bell descends and the air is compressed by increasing
hydrostatic pressure Fluid statics or hydrostatics is the branch of fluid mechanics that studies the condition of the equilibrium of a floating body and submerged body "fluids at hydrostatic equilibrium and the pressure in a fluid, or exerted by a fluid, on an imme ...
. The air will also be refreshed as required to keep the carbon dioxide level acceptable to the occupants. The
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as well ...
content is also replenished, but this is not the limiting factor, as the oxygen
partial pressure In a mixture of gases, each constituent gas has a partial pressure which is the notional pressure of that constituent gas as if it alone occupied the entire volume of the original mixture at the same temperature. The total pressure of an ideal gas ...
will be higher than in surface air due to the depth. When the bell is raised, the pressure will drop and excess air due to expansion will automatically spill under the edges. If the divers are breathing from the bell airspace at the time, it may need to be vented with additional air to maintain a low carbon dioxide level. The decrease in pressure is proportional to the depth as the airspace is at ambient pressure, and the ascent must be conducted according to the planned decompression schedule appropriate to the depth and duration of the diving operation. File:Campana húmeda.JPG, Wet bell exterior view File:Campan húmeda6.JPG, Wet bell interior showing bell gas panel File:Campana húmeda9.JPG, Wet bell hoisting winch File:Campana húmeda10.JPG, Wet bell supply gas panel (left) File:Campana húmeda11.JPG, Wet bell supply gas panel (right) File:Campana húmeda8.JPG, Wet bell umbilical deck storage File:Campana húmeda7.JPG, Wet bell bailout gas cylinders


Closed bell

A closed or dry bell is a pressure vessel for human occupation which is lowered into the sea to the workplace, equalised in pressure to the environment, and opened to allow the divers in and out. These functional requirements dictate the structure and arrangement. The internal pressure requires a strong structure, and a sphere or spherically ended cylinder is most efficient for this purpose. When the bell is underwater, it must be possible for the occupants to get in or out without flooding the entire interior. This requires a pressure hatch at the bottom. The requirement that the bell retain its internal pressure when the external pressure is lowered dictates that the hatch open inward, so that internal pressure will hold it closed. The bell sinks through the water to working depth, so must be negatively buoyant. This may require additional ballast, which may be attached by a system that can be released from inside the bell in an emergency, without losing pressure, to allow the bell to float back to the surface. Locking onto a decompression chamber at the surface is possible either from the bottom or the side. Using the bell bottom hatch for this purpose has the advantage of only needing one hatch, and the disadvantage of having to lift the bell up and place it over a vertical entry to the chamber. A bell used in this way may be called a personnel transfer capsule. If decompression is done inside the bell, it may be referred to as a submersible decompression chamber. The bell bottom hatch must be wide enough for a large diver fully kitted with appropriate
bailout cylinder A bailout bottle (BoB) or, more formally, bailout cylinder is a scuba cylinder carried by an underwater diver for use as an emergency supply of breathing gas in the event of a primary gas supply failure. A bailout cylinder may be carried by a sc ...
s, to get in and out without undue difficulty, and it can not be closed while the diver is outside as the umbilical is tended through the hatch by the bellman. It must also be possible for the bellman to lift the working diver in through the hatch if he is unconscious, and close the hatch after him, so that the bell can be raised and pressurised for the ascent. A lifting tackle is usually fitted inside the bell for this purpose, and the bell may be partially flooded to assist the procedure. The internal space must be large enough for a fully kitted diver and bellman (the
stand-by diver Surface-supplied diving is diving 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. This is different from scub ...
responsible for manning the bell while the working diver is locked out) to sit, and for their umbilicals to be stowed neatly on racks, and the hatch to be opened inwards while they are inside. Anything bigger will make the bell heavier than it really needs to be, so all equipment that does not need to be inside is mounted outside. This includes a framework to support the ancillary equipment and protect the bell from impact and snagging on obstacles, and the emergency gas and power supplies, which are usually racked around the framework. The emergency gas supply (EGS) is connected via manifolds to the internal gas panel. The part of the framework that keeps the lower hatch off the bottom is called the bell stage. It may be removable, which can facilitate connection to a vertical access chamber lock. The bell umbilical is connected to the bell via through hull fittings (hull penetrations), which must withstand all operating pressures without leaking. The internal gas panel connects to the hull penetrations and the diver's umbilicals. The umbilicals will carry main breathing gas supply, a communications cable, a
pneumofathometer Surface-supplied diving is diving 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. This is different from ...
hose, hot water supply for suit heating, power for helmet mounted lights, and possibly gas reclaim hose and video cable. The bell umbilical will usually also carry a power cable for internal and external bell lighting. Hydraulic power lines for tools do not have to pass into the interior of the bell as they will never be used there, and tools can also be stored outside. There may be an emergency through-water communications system with a battery power supply, and a location transponder working on the international standard 37.5 kHz. The bell may also have viewports and a medical lock. A closed bell may be fitted with an umbilical cutter, a mechanism which allows the occupants to sever the bell umbilical from inside the sealed and pressurised bell in the event of an umbilical snag that prevents bell recovery. The device is typically hydraulically operated using a hand pump inside the bell, and can shear the umbilical at or just above the point where it is fastened to the top of the bell. Once cut, the bell can be raised and if the umbilical can then be recovered, it can be reconnected with only a short length lost. An external connection known as a ''hot stab unit'' which allows an emergency umbilical to be connected to maintain life support in the bell during a rescue operation may be fitted. The divers in the bell may also be monitored from the diving control point by closed circuit video, and the bell atmosphere can be monitored for volatile hydrocarbon contamination by a hyperbaric hydrocarbon analyser which can be linked to a topside repeater and set to give an alarm if the hydrocarbon levels exceed 10% of the anaesthetic level. The bell may be fitted with an external emergency battery power pack, carbon dioxide scrubber for the internal atmosphere, and air conditioner for temperature control. Power supply is typically 12 or 24V DC. A bell will be provided with equipment to rescue and treat an injured diver. This will normally include a small tackle to lift the disabled diver into the bell through the bottom hatch and secure them in an upright position if needed. A bell flooding valve, also known as a flood-up valve may be available to partially flood the interior to aid in lifting a disabled diver into the bell, once inside and secure, the bell is cleared of water using the blow-down valve to fill the interior with breathing gas at ambient pressure and displace the water out through the hatch. A first aid kit will be carried.


British mini-bell system

A variant of this system used in the North Sea oilfields between early 1986 and the early 90s was the Oceantech Minibell system, which was used for bell-bounce dives, and was operated as an open bell for the descent, and as a closed bell for the ascent. The divers would climb into the bell after stowing their umbilicals on outside racks, remove their helmets for outside storage, seal the bell, and return to the surface, venting to the depth of the first decompression stop. The bell would then be locked onto a deck decompression chamber, the divers transferred under pressure to complete decompression in the chamber, and the bell would be available for use for another dive.


Deployment of a modern diving bell

Diving bells are deployed over the side of the vessel or platform using a gantry or A-frame from which the clump weight and the bell are suspended. On
dive support vessel A diving support vessel is a ship that is used as a floating base for professional diving projects. Basic requirements are the ability to keep station accurately and reliably throughout a diving operation, often in close proximity to drilling or ...
s with in-built saturation systems the bell may be deployed through a
moon pool A moon pool is a feature of marine drilling platforms, drillships and diving support vessels, some marine research and underwater exploration or research vessels, and underwater habitats, in which it is also known as a wet porch. It is an o ...
. The bell handling system is also known as the launch and recovery system (LARS). The bell umbilical supplies gas to the bell gas panel, and is separate from the divers' excursion umbilicals, which are connected to the gas panel on the inside of the bell. The bell umbilical is deployed from a large drum or umbilical basket and care is taken to keep the tension in the umbilical low but sufficient to remain near vertical in use and to roll up neatly during recovery, as this reduces the risk of the umbilical snagging on underwater obstructions. Wet bell handling differs from closed bell handling in that there is no requirement to transfer the bell to and from the chamber system to make a pressure-tight connection, and that a wet bell will be required to maintain a finely controlled speed of descent and ascent and remain at a fixed depth within fairly close tolerances for the occupants to decompress at a specific ambient pressure, whereas a closed bell can be removed from the water without delay and the speed of ascent and descent is not critical. A bell diving team will usually include two divers in the bell, designated the working diver and bellman, though they may alternate these roles during the dive. The bellman is a
stand-by diver Surface-supplied diving is diving 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. This is different from scub ...
and umbilical tender from the bell to the working diver, the operator of the on-board gas distribution panel, and has an umbilical about 2 m longer than the working diver to ensure that the working diver can be reached in an emergency. This can be adjusted by tying off the umbilicals inside the bell to limit deployment length, which must often be done in any case, to prevent the divers from approaching known hazards in the water. Depending on circumstances, there may also be a surface stand-by diver, with attendant in case there is an emergency where the surface diver could assist. The team be under the direct control of the
diving supervisor The diving supervisor is the professional diving team member who is directly responsible for the diving operation's safety and the management of any incidents or accidents that may occur during the operation; the supervisor is required to be ava ...
and will also include a winch operator, and may include a dedicated surface gas panel operator. Clump weight Deployment usually starts by lowering the clump weight, which is a large ballast weight suspended from a cable which runs down from one side of the gantry, through a pair of sheaves on the sides of the weight, and up the other side back to the gantry, where it is fastened. The weight hangs freely between the two parts of the cable, and due to its weight, hangs horizontally and keeps the cable under tension. The bell hangs between the parts of the cable, and has a fairlead on each side which slides along the cable as it is lowered or lifted. Deployment of the bell is by a cable attached to the top. As the bell is lowered, the fairleads prevent it from rotating on the deployment cable, which would put twist into the umbilical and risk loops or snagging. The clump weight cables therefore act as guidelines or rails along which the bell is lowered to the workplace, and raised back to the platform. If the lifting winch or cable fails, and the bell ballast is released, a positively buoyant bell can float up and the cables will guide it to the surface to a position where it can be recovered relatively easily. The clump weight cable can also be used as an emergency recovery system, in which case both bell and weight are lifted together. An alternative system for preventing rotation on the lifting cable is the use of a cross-haul system, which may also be used as a means of adjusting the lateral position of the bell at working depth, and as an emergency recovery system. Bell handling system A closed bell handling system is used to move the bell from the position where it is locked on to the chamber system into the water, lower it to the working depth and hold it in position without excessive movement, and recover it to the chamber system. The system used to transfer the bell on deck may be a deck trolley system, an overhead gantry or a swinging A-frame. The system must constrain movement of the supported bell sufficiently to allow accurate location on the chamber trunking even in bad weather. A bell cursor may be used to control movement through and above the splash zone, and heave compensation gear may be used to limit vertical movement when in the water and clear of the cursor, particularly at working depth when the diver may be locked out and the bell is open to ambient pressure. Bell cursor A bell cursor is a device used to guide and control the motion of the bell through the air and the splash zone near the surface, where waves can move the bell significantly. It can either be a passive system which relies on additional ballast weight or an active system which uses a controlled drive system to provide vertical motion. The cursor has a cradle which locks onto the bell and which moves vertically on rails to constrain lateral movement. The bell is released and locked onto the cursor in the relatively still water below the splash zone. Heave compensation Heave compensation equipment is used to stabilise the depth of the bell by counteracting vertical movement of the handling system caused by movements of the platform, and usually also maintains correct tension on the guide wires. It is not usually essential, depending on the stability of the platform. Cross-hauling Cross-hauling systems are cables from an independent lifting device which are intended to be used to move the bell laterally from a point directly below the LARS, and may also be used to limit rotation and as an emergency bell recovery system.


Use with hyperbaric chambers

Commercial
diving contractor Professional diving is underwater diving where the divers are paid for their work. The procedures are often regulated by legislation and codes of practice as it is an inherently hazardous occupation and the diver works as a member of a team. D ...
s generally use a closed bell in conjunction with a surface
hyperbaric chamber A diving chamber is a vessel for human occupation, which may have an entrance that can be sealed to hold an internal pressure significantly higher than ambient pressure, a pressurised gas system to control the internal pressure, and a supply of ...
, These have safety and ergonomic advantages and allow decompression to be carried out after the bell has been raised to the surface and back on board the
diving support vessel A diving support vessel is a ship that is used as a floating base for professional diving projects. Basic requirements are the ability to keep station accurately and reliably throughout a diving operation, often in close proximity to drilling or ...
. Closed bells are often used in
saturation diving Saturation diving is diving for periods long enough to bring all tissues into equilibrium with the partial pressures of the inert components of the breathing gas used. It is a diving mode that reduces the number of decompressions divers working ...
and undersea rescue operations. The diving bell would be connected via the mating flange of an
airlock An airlock, air-lock or air lock, often abbreviated to just lock, is a compartment with doors which can be sealed against pressure which permits the passage of people and objects between environments of differing pressure or atmospheric compo ...
to the deck decompression chamber or
saturation system Saturation diving is diving for periods long enough to bring all tissues into equilibrium with the partial pressures of the inert components of the breathing gas used. It is a diving mode that reduces the number of decompressions divers working ...
for
transfer under pressure Surface supplied diving skills are the skills and procedures required for the safe operation and use of surface-supplied diving equipment. Besides these skills, which may be categorised as standard operating procedures, emergency procedures and r ...
of the occupants.


Air-lock diving bells

The
air lock diving-bell plant Port of Gibraltar, Gibraltar Harbour's air lock diving-bell plant, or caisson diving bell barge, was a purpose-built barge for the laying, examination and repair of moorings for battleships. It was designed by Siebe Gorman, Siebe Gorman & Company ...
was a purpose-built
barge Barge nowadays generally refers to a flat-bottomed inland waterway vessel which does not have its own means of mechanical propulsion. The first modern barges were pulled by tugs, but nowadays most are pushed by pusher boats, or other vessels. ...
for the laying, examination and repair of moorings for battleships at
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harbour. It was designed by
Siebe Gorman Siebe Gorman & Company Ltd was a British company that developed diving equipment and breathing equipment and worked on commercial diving and marine salvage projects. The company advertised itself as 'Submarine Engineers'. It was founded by A ...
of
Lambeth Lambeth () is a district in South London, England, in the London Borough of Lambeth, historically in the County of Surrey. It is situated south of Charing Cross. The population of the London Borough of Lambeth was 303,086 in 2011. The area e ...
and Forrestt & Co. Ltd of
Wivenhoe Wivenhoe ( ) is a town and civil parish in north-eastern Essex, England, approximately south-east of Colchester. Historically Wivenhoe village, on the banks of the River Colne, and Wivenhoe Cross, on the higher ground to the north, were two ...
in Essex, who built and supplied it in 1902 to the
British Admiralty The Admiralty was a department of the Government of the United Kingdom responsible for the command of the Royal Navy until 1964, historically under its titular head, the Lord High Admiral – one of the Great Officers of State. For much of i ...
. The vessel came about from the specific conditions at Gibraltar. The heavy harbour moorings have three chains extending out radially along the seabed from a central ring, each terminating in a large anchor. Most harbours have a soft seabed, and it is usual to lay down moorings by settling anchors in the mud, clay or sand but this could not be done in Gibraltar harbour, where the seabed is hard rock. In operation the barge would be towed over the work site, moored in place with anchors, and the bell would be lowered vertically to the bottom. and the water displaced by pumping. The work teams entered the bell through an
airlock An airlock, air-lock or air lock, often abbreviated to just lock, is a compartment with doors which can be sealed against pressure which permits the passage of people and objects between environments of differing pressure or atmospheric compo ...
in the central access shaft. Working in ordinary clothes they could dig out anchorings for the moorings. The German service barge '' Carl Straat'' is similar in concept, but the bell is lowered by swinging the access tube. ''Carl Straat'' was built in 1963 for the Waterways and Shipping Directorate West in Münster. The 6 m × 4 m × 2.5 m bell is accessible through a 2 m diameter tube and an airlock. A pantograph system keeps the bell and internal stairs level at all depths. Maximum working depth is 10 m. The vessel is used on those inland waterways which have locks large enough to accommodate its 52 m length overall, 11.8 m beam and 1.6 m draft.


Rescue bell

Diving bells have been used for submarine rescue. The closed dry bell is designed to seal against the deck of the submarine above an escape hatch. Water in the space between the bell and the submarine is pumped out and the hatches can be opened to allow occupants to leave the submarine and enter the bell. The hatches are then closed, the bell skirt flooded to release it from the submarine, and the bell with its load of survivors is hoisted back to the surface, where the survivors exit and the bell may return for the next group. The internal pressure in the bell is usually kept at atmospheric pressure to minimise run time by eliminating the need for decompression, so the seal between the bell skirt and the submarine deck is critical to the safety of the operation. This seal is provided by using a flexible sealing material, usually a type of rubber, which is pressed firmly against the smooth hatch surround by the pressure differential when the skirt is pumped out.


Observation bell

A closed bell, generally operated with internal pressure at atmospheric pressure, which provides an observation platform that can be lowered to depth with one or more occupants who can observe the environment through viewports, but are generally not provided with a means of interacting physically with the outside environment. A
bathysphere The Bathysphere (Greek: , , "deep" and , , "sphere") was a unique spherical deep-sea submersible which was unpowered and lowered into the ocean on a cable, and was used to conduct a series of dives off the coast of Bermuda from 1930 to 1934. The ...
is a similar structure.


Diver training

Divers qualified to work from bells are trained in the skills and procedures relevant to the type of bell they will be expected to work from. Open bells are generally used for surface oriented surface-supplied deep air diving, and closed bells are used for saturation diving and surface oriented mixed gas diving. These skills include the standard procedures for the deployment of the working diver from the bell, the tending of the working diver from the bell by the bellman, and the emergency and rescue procedures for both working diver and bellman. There is considerable similarity and significant differences in these procedures between open and closed bell diving.


Underwater habitats

As noted above, further extension of the wet bell concept is the moon-pool-equipped underwater habitat, where divers may spend long periods in dry comfort while acclimated to the increased pressure experienced underwater. By not needing to return to the surface between excursions into the water, they can reduce the necessity for decompression (gradual reduction of pressure), after each excursion, required to avoid problems with nitrogen bubbles releasing from the bloodstream (the bends, also known as caisson disease). Such problems can occur at pressures greater than , corresponding to a depth of of water. Divers in an ambient pressure habitat will require decompression when they return to the surface. This is a form of
saturation diving Saturation diving is diving for periods long enough to bring all tissues into equilibrium with the partial pressures of the inert components of the breathing gas used. It is a diving mode that reduces the number of decompressions divers working ...
.


In nature

The diving bell spider, ''Argyroneta aquatica'', is a
spider Spiders (order Araneae) are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species ...
which lives entirely under water, even though it could survive on land. Since the spider must breathe air, it constructs from
silk Silk is a natural protein fiber, some forms of which can be woven into textiles. The protein fiber of silk is composed mainly of fibroin and is produced by certain insect larvae to form cocoons. The best-known silk is obtained from th ...
a habitat like an open diving bell which it attaches to an underwater
plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae excl ...
. The spider collects air in a thin layer around its body, trapped by dense hairs on its
abdomen The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the to ...
and legs. It transports this air to its diving bell to replenish the air supply in the bell. This allows the spider to remain in the bell for long periods, where it waits for its
prey Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill ...
.


See also

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References


External links


Historical Diving Society: The History of the Diving Bellclose call rapid depressurisation
{{Authority control Diving support equipment Protective gear