Variations
There are two basic modes of surface-supplied diving, and several variations for supplying breathing gas to divers from the surface.Surface oriented diving
Surface oriented diving, with or without a stage or open bell, is where the diver starts and ends the dive at surface pressure. The diver is decompressed during the ascent or by surface decompression in a decompression chamber. In addition to the standard system of surface-supplied diving using a diver's umbilical and diving helmet or full-face diving mask to provide the diver with compressed atmospheric air from a low-pressure diving compressor, there are other configurations in use for surface oriented diving:Scuba replacement
Scuba replacement is a surface-supplied diving mode where both the primary and reserve breathing gas supplies are from high-pressure storage cylinders. The rest of the system is identical to the standard surface supply configuration, and the full umbilical system, bailout cylinder, communications and surface gas panel are used. This is more portable than most compressors and is used by commercial diving contractors as a substitute for scuba with most of the advantages and disadvantages of a regular compressor fed surface air supply. It is also used where the ambient air is contaminated and unsuitable for use as a breathing gas when compressed, such as some situations in hazmat diving.Standard diving dress
Standard, or heavy gear is the historical copper helmet, waterproofed canvas suit, and weighted boots. The original system used a manually powered diver's pump to supply air, and no reserve gas or bailout cylinder was provided. As the technology became available, voice communication was added, and mechanically driven compressors were used.Air-line diving
Air-line diving uses an air line hose in place of a full diver's umbilical to supply breathing air from the surface. If any of the required components of a diver's umbilical are absent this term applies. There are subcatgories of air-line diving: * Hookah diving – A basic form of surface-supplied diving in which the air supply is via a single hose is often referred to as air line or Hookah (occasionally Hooka) diving. This often uses a standard scuba second stage as the delivery unit, but is also used with light full-face masks. Bailout gas may be carried, but this is not always the case. Commercial diamond divers working in the shallow zone off the west coast of South Africa under the codes of practice of the Department of Minerals and Energy use half mask and demand valve hookah. Their safety record is relatively poor, as a bailout cylinder is seldom carried. When done using a diving compressor with suitable breathing air quality and an appropriate emergency gas supply, there is no obvious reason why hookah diving should be more dangerous than scuba diving in the same conditions. A concern is that if the diver is supplied from a compressor in a boat, the intake must be clear of any exhaust fumes, which is also the case for surface supplied diving using a full umbilical. * Snuba and SASUBA – A system used to supply air from a cylinder mounted on a float to a recreational diver tethered by a short (approximately 6 m) hose through a scuba regulator. * Compressor diving – An even more basic system is the "Compressor diving" arrangement used in the Philippines and Caribbean for fishing. This rudimentary and highly hazardous system uses a large number of small bore plastic tubes connected to a single compressor to supply a large number of divers simultaneously. The delivery end of the hose is unencumbered by any mechanism or mouthpiece, and is simply held by the diver's teeth. Air supply is free flow and often unfiltered, and varies with depth and number of divers drawing off the system, with greater flow going to divers with a shorter hose and at shallower depth. A kink or restriction in a hose can cut off a diver's air supply without warning.Bell bounce diving
Bell bounce diving, also known as transfer under pressure diving, is where the divers are transported vertically through the water in a closed bell and transferred under pressure into a surface decompression chamber for decompression, or decompressed in the bell. This mode of diving is most likely to be used when the dive is relatively deep, and the decompression is likely to be long, but neither deep enough nor long enough to justify the costs of setting up for saturation diving. The mode was often used with mixed breathing gases. but is also used for long air dives shallower than 50 m. A development of this system uses a set of decompression chambers mounted in a lifeboat for the routine surface decompression of the divers. The lifeboat is positioned between the transfer chamber and the side of the deck, and can be launched by the davits included in the package. This avoids the necessity for an additional hyperbaric evacuation system.Saturation diving
In saturation diving, the diver is transferred under pressure from the pressurised accommodation to the underwater worksite, which is at a similar pressure, and back in a closed bell, only decompressing once at the end of the contract.Alternatives
* Scuba diving, which is commonly used for recreational diving, is the main alternative to surface-supplied diving. Scuba is available in open circuit and rebreather configurations. * Atmospheric diving suits such as the JIM suit and the Newtsuit, and manned submersibles with manipulator arms, isolate the occupant from the ambient pressure, but are bulky, expensive, and allow limited dexterity and agility. * Unmanned submersibles ( ROVs and AUVs) which can operate deeper and avoid exposing a diver to underwater hazards, have their applications, but lack the dexterity of a diver at present (2011). * Freediving, or breathhold diving, is extremely limited in duration and exposes the diver to relatively high risk.Application
Surface-supplied diving equipment and techniques are mainly used in professional diving due to the greater cost and complexity of owning and operating the equipment. This type of equipment is used in saturation diving, as the gas supply is relatively secure, and the diver can not bail out to the surface, and for diving in contaminated water, where the diver must be protected from the environment, and helmets are generally used for environmental isolation. There has been development of low-cost airline systems for shallow recreational diving, where limited training is offset by physically limiting the depth accessible.History
Equipment
Breathing apparatus
The definitive equipment for surface-supplied diving is the breathing apparatus which is supplied with primary breathing gas from the surface via a hose, which is usually part of a diver's umbilical connecting the surface supply systems with the diver, sometimes directly, otherwise via a bell umbilical and bell panel.Helmets
Band mask
A band mask is a heavy duty full-face mask with many of the characteristics of a lightweight demand helmet. In structure it is the front section of a lightweight helmet from above the faceplate to below the demand valve and exhaust ports, including the bailout block and communications connections on the sides. This rigid frame is attached to a neoprene hood by a metal clamping band, hence the name. It is provided with a padded sealing surface around the frame edge which is held firmly against the diver's face by a rubber "spider", a multiple strap arrangement with a pad behind the diver's head, and usually five straps which hook onto pins on the band. The straps have several holes so the tension can be adjusted to get a comfortable seal. A band mask is heavier than other full face masks, but lighter than a helmet, and can be donned more quickly than a helmet. They are often used by the standby diver for this reason.Full-face mask
A full-face mask encloses both mouth and nose, which reduces the risk of the diver losing the air supply compared to a half mask and demand valve. Some models require a bailout block to provide alternative breathing gas supply from the umbilical and bailout cylinder, but are not suitable for accepting an alternative air supply from a rescue diver, while a few models accept a secondary demand valve which can be plugged into an accessory port (Draeger, Apeks and Ocean Reef). The unique Kirby Morgan 48 SuperMask has a removable DV pod which can be unclipped to allow the diver to breathe from a standard scuba demand valve with mouthpiece. Despite the improvement in diver safety provided by the more secure attachment of the breathing apparatus to the diver's face, some models of full face mask can fail catastrophically if the faceplate is broken or detached from the skirt, as there is then no way to breathe from the mask. This can be mitigated by carrying a standard secondary second stage, and preferably also a spare half mask. A full face mask is lighter and more comfortable for swimming than a helmet or band mask, and usually provides an improved field of vision, but it is not as secure, and does not provide the same level of protection as the heavier and more sturdily constructed equipment. The two types of equipment have different ranges of application. Most full face masks are adaptable for use with scuba or surface supply. The full face mask does not usually have a bailout block fitted, and this is usually attached to the diver's harness, with a single hose to supply the mask from main or bailout gas which is selected at the block. The strap arrangement for full face masks is usually quite secure, but not as secure as a bandmask or helmet, and it is possible for it to be dislodged in the water. However it is also quite practicable for a trained diver to replace and clear a full face mask under water without assistance, so this is more an inconvenience than a disaster unless the diver is rendered unconscious at the same time.Breathing gas supply
Diver's umbilical
Air-line
Gas panel
= Pneumofathometer
= A '' pneumofathometer'' is a device used to measure the depth of a diver by displaying the back-pressure on a gas supply hose with an open end at the diver, and a flow rate with negligible resistance in the hose. The pressure indicated is the hydrostic pressure at the depth of the open end, and is usually displayed in units of metres or feet of seawater, the same units used for decompression calculations. The pneumo line is usually a bore hose in the diver's umbilical, supplied with breathing gas from the gas panel via a supply valve. Downstream from the valve there is a branch to a high resolution pressure gauge, a restriction to flow to the gauge, and an overpressure relief valve to protect the gauge from full panel supply pressure in case the pneumo line is used for emergency breathing gas supply. Each diver has an independent pneumofathometer, and if there is a bell, it will also have an independent pneumofathometer.Low-pressure breathing air compressor
High pressure main gas supply
The main gas supply for surface-supplied diving can be from high pressure bulk storage cylinders. When the storage cylinders are relatively portable this is known as a ''scuba replacement'' system in the commercial diving industry. The application is versatile and can ensure high quality breathing gas in places where atmospheric air is too contaminated to use through a normal low pressure compressor filter system, and is easily adaptable to a mixed gas supply and oxygen decompression provided that the breathing apparatus and gas supply system are compatible with the mixtures to be used. Scuba replacement is often used from smaller diving support vessels, for emergency work, and for hazmat diving. Mixed breathing gases are provided from high pressure bulk storage systems for saturation diving, but these are less portable, and generally involve manifolded racks of cylinders of approximately 50 litres water capacity arranged as ''quads'' and even larger racks of high pressure ''tubes''. If gas reclaim systems are used, the reclaimed gas is scrubbed of carbon dioxide, filtered of other contaminants, and recompressed into high pressure cylinders for interim storage, ans is generally blended with oxygen or helium to make up the required mix for the next dive before re-use.Decompression gas
Reducing the partial pressure of the inert gas component of the breathing mixture will accelerate decompression as the concentration gradient will be greater for a given depth. This is achieved by increasing the fraction of oxygen in the breathing gas used, whereas substitution of a different inert gas will not produce the desired effect. Any substitution may introduce counter-diffusion complications, owing to differing rates of diffusion of the inert gases, which can lead to a net gain in total dissolved gas tension in a tissue. This can lead to bubble formation and growth, with decompression sickness as a consequence. Partial pressure of oxygen is usually limited to 1.6 bar during in-water decompression for scuba divers, but can be up to 1.9 bar in-water and 2.2 bar in the chamber when using the US Navy tables for surface decompression,High-pressure reserve gas
An alternative to a low-pressure compressor for gas supply is high-pressure storage cylinders feeding through a pressure regulator which will be set to the required supply pressure for the depth and equipment in use. In practice HP storage may be used for either reserve gas supply or both main and reserve gas supplies to a gas panel. High-pressure bulk cylinders are quiet in operation and provide gas of known quality (if it has been tested). This allows the relatively simple and reliable use of nitrox mixtures in surface-supplied diving. Bulk cylinders are also quiet in operation compared to a low-pressure compressor, but have the obvious limitation of amount of gas available. The usual configurations for surface-supplied bulk gas storage are large single cylinders of around 50 litres water capacity, often referred to as "J"s or "bombs", " quads", which are a group (sometimes, but not necessarily four in number) of similar cylinders mounted on a frame and connected together to a common supply fitting, and "kellys" which are a group of "tubes" (long large volume pressure vessels) usually mounted in a container frame, and usually connected together to a common connection fitting.Bailout gas supply
Diver's harness
The diver's harness is an item of strong webbing, and sometimes cloth, which is fastened around a diver over the exposure suit, and allows the diver to be lifted without risk of falling out of the harness. Several types are in use.Jacket harness
Bell harness
A bell harness has the same function as a jacket harness, but lacks the cloth jacket component, and is made entirely of webbing, with a similar configuration of straps. It too may have a means of carrying a bailout cylinder, or the bailout cylinder may be carried on a separate backpack.Harness with buoyancy compensation
The AP Valves Mk4 Jump Jacket is a harness with integral buoyancy jacket specifically designed for commercial diving work with helmets and bells. There is a direct feed to the jacket from the main air supply, from the pneumo line and from bailout, and a system which allows the diver's pneumo to be directly connected to another diver's helmet as an emergency air supply.Buoyancy control
Surface-supplied divers may be required to work in mid-water or on the bottom. They must be able to stay down without effort, and this usually requires weighting. When working in mid-water the diver may wish to be neutrally buoyant or negative, and when working on the bottom he will usually want to be several kilos negative. The only time the diver may want to be positively buoyant is when on the surface or during a limited range of emergencies where uncontrolled ascent is less life-threatening than remaining under water. Surface-supplied divers generally have a secure supply of breathing gas, and there are very few occasions where weights should be jettisoned, so in most cases the surface-supplied diver weighting arrangement does not provide for quick release. On those occasions when surface supplied divers need variable buoyancy, it may be provided by inflation of the dry suit, if used, or by a buoyancy control device similar in principle to those used by scuba divers, or both.Weight systems
The diver needs to stay on the bottom to work some of the time, and may need to have neutral buoyancy some of the time. The diving suit is usually buoyant, so added weight is usually necessary. This can be provided in several ways. Unwanted positive buoyancy is dangerous to a diver who may need to spend significant time decompressing during the ascent, so the weights are usually attached securely to prevent accidental loss.Weight belts
Weight belts for surface supplied diving are usually provided with buckles which can not accidentally be released, and the weight belt is often worn under the jacket harness.Weight harnesses
When large amounts of weight are needed, a harness may be used to carry the load on the diver's shoulders, rather than around the waist, where it may tend to slip down into an uncomfortable position if the diver is working in a vertical posture, which is often the case. Sometimes this is a separate harness, worn under the safety harness, with pockets at the sides to carry the weights, and sometimes it is an integrated system, which carries the weight in pockets built into or externally attached to the safety harness.Trim weights
If the diver needs to adjust trim for greater comfort and efficiency while working, trim weights of various types may be added to the harness.Weighted boots
Weighted boots of several styles may be used if the diver will be working heavy. Some are in the form of clogs which strap on over the boots, and others use lead inner soles. Ankle weights are also an option, but less comfortable. These weights give the diver better stability when working upright on the bottom, which can significantly improve productivity for some kinds of work.Environmental protection
Wetsuits are economical and used where the water temperature is not too low - more than about , the diver will not be spending too long in the water, and the water is reasonably clean. Dry suits are better thermal protection than most wetsuits, and isolate the diver from the environment more effectively than other exposure suits. When diving in contaminated water, a drysuit with integral boots, sealed dry gloves and a helmet sealed directly to the suit provides the best environmental isolation. The suit material must be selected to be compatible with the expected contaminants. Thermal undersuits can be matched to the expected water temperature. Hot water suits provide active warming which is particularly suitable for use with helium based breathing gases. Heated water is provided from the surface through a hose in the umbilical, and water flow can be adjusted to suit the diver's needs. Heated water continuously flows into the suit and is distributed by perforated internal tubes down the front and back of the torso and along the limbs. The hot water supply hose of the umbilical is commonly bore, and is connected to a supply manifold at the right hip of the suit with a set of valves which allow the diver to control flow to the front and back of the torso, and to the arms and legs, and to dump the supply to the environment if the water is too hot or too cold. The manifold distributes the water through the suit through perforated tubes. The hot-water suit is normally a one-piece neoprene wetsuit, fairly loose fitting, to fit over a neoprene undersuit, which can protect the diver from scalding if the temperature control system fails, with a zipper on the front of the torso and on the lower part of each leg. Gloves and boots are worn which receive hot water from the ends of the arm and leg hoses. If a full-face mask is worn, the hood may be supplied by a tube at the neck of the suit. Helmets do not require heating. The heating water flows out at the neck and cuffs of the suit through the overlap with gloves, boots, or hood.Communications system
Diver's telephone
The communications equipment is relatively straightforward and may be of the two-wire or four-wire type. Two wire systems use the same wires for surface to diver and diver to surface messages, whereas four wire systems allow the diver's messages and the surface operator's messages to use separate wire pairs. In a two wire system the standard arrangement for diver communications is to have the diver's side normally on, so that the surface team can hear anything from the diver at all times except when the surface is sending a message. In a four-wire system the diver's side is always on, even when the surface operator is talking. This is considered an important safety feature, as the surface team can monitor the diver's breathing sounds, which can give early warning of problems developing, and confirms that the diver is alive. Helium divers may need a decoder system (unscrambler) which reduces the frequency of the sound to make it more intelligible.Video
Closed circuit video has also become popular, as this allows the surface personnel to see what the diver is doing, which is particularly useful for inspection work, as a non-diving specialist can see the underwater equipment in real time and direct the diver to look at particular features of interest.Wireless systems
Dry bells may have a through-water (wireless) communication system fitted as a backup. This is intended to provide communications in the event that the cable is damaged, or even if the bell is completely severed from the umbilical and deployment cables.Equipment maintenance and testing
All components of a surface supplied diving system are required to be maintained in good working condition for diver safety, and may be required to be tested or calibrated at specified intervals.Diving spread
The diving spread is a commercial diving term for the topside dive site infrastructure supporting the diving operations for a diving project. The diving contractor provides the diving and support equipment and sets it up on site, usually at a place provided for the purpose by the client, or on a diving support vessel. Two types of diving spread are in common use: Air spreads for surface oriented diving operations, where the divers are deployed from normal atmospheric pressure, and decompressed back to atmospheric pressure at the end of the dive, either in-water, or in a chamber for surface decompression, using compressed air as the primary breathing gas, and saturation spreads, where divers are deployed under pressure from the saturation accommodation via a closed diving bell to the underwater worksite, and returned under pressure in the bell to the saturation accommodation system, usually breathing a helium based gas mixture. At the end of their contract the divers are decompressed to surface pressure. The process of selecting, transporting, setting up and testing the equipment is the mobilisation stage of the project, and the demobilisation involves dismantling, transportation and return to storage of the spread components. Surface oriented mixed gas diving spreads may also be used, but are less common, and are likely to be associated with projects which are too deep for air but require only a short working time at depth.Air spread
An air spread will include the breathing air supply equipment, and often a deck decompression chamber. Where a chamber is present, facilities for hyperbaric oxygen treatment are usually required. If the planned decompression is to be long, a diving stage or bell and the associated handling equipment is likely to be included to allow better control of ascent rate and decompression depth. Equipment for in-water or surface decompression on oxygen (SurDO2) may be available. Equipment may be necessary to facilitate safe entry to and exit from the water, and may include extrication equipment in case the diver is injured. A basic offshore air diving spread will typically include a dive control unit with compressor and high pressure storage banks, a launch and recovery system with a wet bell, a deck decompression chamber and a hot water unit.Saturation spread
A saturation spread will include the closed bell and launch and recovery system, saturation habitat, breathing gas supplies and services, all the life support and control equipment, dive equipment stores and workshops, and may also include power supplies and other equipment not directly involved in the diving. It does not include the diving platform as such, for example a DP vessel, or offshore drilling rig, on which the spread is established, or other services such as catering and accommodation for the topside personnel, which would usually be provided to the dive team.Diving procedures
There are a large number of standard procedures associated with surface-supplied diving. Some of these have their equivalents in scuba, and others are very different. Many procedures are common to all surface-supplied diving, others are specific to stage and bell operations or to saturation diving. Details will vary depending on the equipment used, as manufacturers will specify some checks and procedures in detail, and the order may vary to some extent.The working diver
Preparation of the working diver for the dive is very much a routine, but details depend on the diving equipment and the task, and to some extent on the site, particularly aspects of accessibility.Preparation for diving
Before a diving operation it is usually necessary to set up the surface supply equipment. There are a number of components which must be connected in the correct order, with checks at various stages to ensure that there are no leaks and everything functions correctly. Most diving contractors will have comprehensive checklists that are used to ensure that the equipment is connected in the appropriate sequence and all checks are done. Some checks are critical to the safety of the diver. The compressor must be set up so that it gets uncontaminated air to the intake. Filters should be checked in case they need to be changed. Air supply hoses will be connected to the air panel and checked for leaks, umbilicals connected to the panels and helmets, and the communications equipment connected and tested. Before the umbilical is connected to the helmet or full face mask, the umbilical should be blown through to ensure there is no dirt inside, and the non return valve on the bailout block must be given a function test. This is important, as it is there to prevent backflow of air up the umbilical if the line is cut, and if it fails the diver may suffer a helmet squeeze, or a neck dam flood. Compared to scuba diving, dressing the diver in is a relatively laborious process, as the equipment is bulky and fairly heavy, and several components are connected together by hoses. This is more so with helmets, and less so with light full-face masks. It is not usual for the diver to do all the dressing in without the assistance of a diver's tender, who will also manage the umbilical during the dive. * Exposure suit – The diver will wear an exposure suit appropriate for the planned dive time, breathing gas and water temperature, and also influenced by the level of exertion expected during the dive. * Harness – After putting on the exposure suit and checking any seals and zips, the diver will put on the harness. The topside crew will usually help as the bailout cylinder will be already mounted, and usually also attached to the helmet, making this a cumbersome procedure, easiest if the diver is seated. * Weights – The weights will be put onto the diver at some time during the dressing procedure, but the stage where this is done depends on what weighting system is used. * Bailout – The bailout cylinder is usually strapped to the harness and connected to the helmet before the diver is dressed in. * Helmet – The helmet is usually put on last, as it is heavy and uncomfortable out of the water. Some divers can put on their own helmet, but it is usual for the topside crew to do most of the locking on to the neck dam, and check that there are no obvious faults with the seal. There are a series of pre-dive checks which are done after the diver is locked into the helmet, and before he is committed to the water. These should be done every time a diver is prepared for a dive. * Comms check – The diver and comms operator check that the voice communications system is working both ways and they can hear each other clearly. This also ensures that the operator is sure which comms channel connects to the specific diver. * Breathing checks – The diver breathes on main air supply to ensure that the demand valve is delivering gas at low work of breathing, without free flow, and that the umbilical is connected to the correct valve on the panel. * Bailout checks – The diver operates the bailout system to ensure that he can reach and operate the valve and it turns smoothly, the pressure in the cylinder is adequate for the planned dive profile and is ready for immediate use, and reports bailout readiness to the supervisor by "On at the tap, off at the hat, Pressure...bar" or equivalent. Surface checks are done after the diver enters the water, but before he is allowed to descend. They are checks which can not be done as effectively, or at all, in air. * Wet comms check – Once in the water, the comms should be checked again to make sure it is still working adequately. It is possible that water will cause the comms to fail or deteriorate when the contacts get wet. * Helmet seal – The helmet seals and neckdam should not allow water to enter the helmet. This can only be checked when in the water. * Pneumo bubbles – The diver calls for the air panel operator to open the pneumofathometer valve to check that the line is not blocked, and that it is connected to the correct place on the panel.Diving heavy
The traditional buoyancy condition of the working surface-supplied diver is "heavy", or negatively buoyant, with sufficient apparent weight to move around on the bottom by walking. This was more important with the standard diving dress, where inadvertent positive buoyancy could have fatal consequences if poorly managed and degraded to an uncontrolled buoyant ascent. Diving heavy has advantages for working when there is good footing, as the diver has more natural resistance to the reaction forces on tools used and to light currents, due to friction and ground reaction, so the technique remains popular for many tasks. The technique virtually eliminates the risk of uncontrolled buoyant ascent, and reduces task loading, but makes the diver dependent on umbilical management or a jackstay for depth control in midwater and introduces a risk of accidental descent to unplanned depths by falling off the substrate and sinking until the slack in the umbilical is taken up, but with an adequate gas supply the risk of serious squeeze injury is low.Emergency procedures
The diver must be able to deal with the following emergencies. Some are life-threatening, whereas others are more inconveniences. * Bailout to back gas, in the case of a failure of gas supply from the umbilical, or if the main air supply is contaminated. * Pneumo breathing, if the main air supply is cut, but the pneumo hose is intact. Pneumo gas can also be supplied by the standby diver * Voice communications failure is not usually an emergency, but can adversely affect work effectiveness and expose the diver to higher risk if anything else goes wrong. Ability to communicate with line signals can help here, particularly to assist in the decision whether the dive should be aborted, and if there are other more urgent problems. * Helmet flood. Depending on the severity of the flood, this can range from an annoyance to an emergency. A slow leak can be controlled by opening the free flow valve, which will drive a moderate flow of water out of the exhaust valve. A neck dam failure usually has this effect. * Broken faceplate. This is a real emergency, but very unlikely as the faceplate is usually a highly impact-resistant polymer and should not shatter. It can be mitigated by opening the free flow valve and holding the opening level, facing down, and breathing very carefully. a small hole or crack can be covered with a hand to slow the leak. * Demand valve failure. This is a minor problem if there is a free flow valve, but the dive will normally be terminated, as the bailout will not last long if needed. * Exhaust valve failure, like demand valve failure, can be dealt with by opening the free flow valve and ensuring a constant outflow of air. * Vomiting in the helmet. This can be a real emergency and life-threatening in a demand helmet with an orinasal mask if not handled effectively, as the diver can aspirate the vomit and asphyxiate. Once again, the action is to open the free flow valve, preferably before vomiting, and to inhale as carefully as possible. If there is no free flow valve, as on a full face mask, the purge button should clear the demand valve and orinasal mask, and the mask can be rinsed by lifting the bottom edge away from the face to let in some water, before purging again. With a free-flow helmet it is more a nuisance than an emergency. * Hot water supply failure. This can be life-threatening for deep heliox diving, and there is not much the diver can do but head back to the bell immediately.Wet bell and stage emergency procedures
Emergency procedures for wet bell and diving stages include: * Loss of main gas supply to the bell * Recovery of a distressed diver to the bell * Abandonment of the bell or stage * Deployment of a surface standby diver * Loss of heated water supply for hot water suits * Voice communications failures * Dynamic positioning alarm and runout response for bell divers: Yellow and Red alerts.Standby diver
The standby diver will be prepared in the same way as the working diver, but will not enter the water until needed. He will usually be prepared to the stage of readiness to enter the water, and then will remove his mask, or have his helmet removed and will then sit in as comfortable a place as can be found, so that in case of an emergency he can be readied for action in as short a time as possible. This often means setting up some form of shelter from the weather, and heat and sunshine are usually more of a problem than cold and wet. It is frequently necessary to cool the standby diver to avoid overheating, and dehydration can also be a problem. When the working diver is using a helmet, the stand-by diver may use a full face mask or bandmask, as this makes it quicker to get into the water in an emergency. The stand-by diver's job is to wait until something goes wrong, and then be sent in to sort it out. For this reason a stand by diver should be one of the best divers on the team regarding diving skills and strength, but does not have to be expert at the work skills for the specific job. When deployed, the standby diver will normally follow the umbilical of the diver who is in trouble, as unless it has been severed, it will reliably lead to the correct diver. The standby diver must maintain communications with the supervisor throughout the dive and is expected to give a running commentary of progress so that the supervisor and surface crew know as much as possible what is happening and can plan accordingly, and must take the necessary steps to resolve incidents, which may involve supply of emergency air or locating and rescuing an injured or unconscious diver. In bell diving, the bellman is the primary standby diver, and may have to recover a distressed diver to the bell and give first aid if necessary and possible. There will generally also be a surface standby diver in a bell operation, as some types of assistance are provided from the surface. A rescue tether or rescue strop is a short length of rope or webbing with a clip at one or both ends, which the stand-by diver uses to clip the unresponsive diver to his harness to free up both hands during a recovery. This can be useful if he needs to climb a structure, shotline or topographical feature, and the umbilicals can not be safely used to lift the divers due to snags or sharp edges.Bellman
A bellman is a stand-by diver who tends the working diver's umbilical from a wet or closed bell, and is ready to go to the diver's assistance at all times. The bellman must be in effective voice communication with the supervisor.Underwater tending point
For some operations it is necessary to control the umbilical at a point underwater. This is known as an underwater tending point, and it may be done by another diver or by the diver passing through a closed fairlead placed in the required position. This is usually done to prevent inadvertent access to a known hazard by making the length of the umbilical extending beyond the tending point too short to let the diver get to the hazard. The fairlead must constrain the umbilical laterally and vertically, while allowing free passage away from and back to the bell or stage, and should not interfere with the bellman's ability to pay out or take up slack when the diver travels to the workplace and back. It may be held in position by suspending a weighted hoop from a crane, resting a frame on the bottom, or other methods as may suit the job. Underwater tending may also be used for penetrations of enclosed spaces, such as wrecks, caves, penstocks, sewers, culverts and the like. A diving stage or basket is a by default an underwater tending point, as the umbilical passes through it from the surface to the diver, which also serves as a guide line for the diver to get back to the stage. A diving bell is also an underwater tending point, as the excursion umbilical is tended from the bell by the bellman.Occupational health and safety issues
Divers face specific physical andCompressor diving
"Compressor diving" is a method of surface-supplied diving used in some tropical sea areas including theTraining and registration
Almost all surface-supplied diving is done by professional divers, and consequently the training is done by schools which specialise in the training of professional divers. Registration of professional divers is generally subject to national or state legislation, though international recognition is available for some qualifications.See also
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References
External links
Hookah: