Surface-supplied diving is a mode of underwater diving using equipment supplied with breathing gas through a diver's umbilical from the surface, either from the shore or from a diving support vessel, sometimes indirectly via a diving bell.^[2] This is different from scuba diving, where the diver's breathing equipment is completely self-contained and there is no essential link to the surface. The primary advantages of conventional surface supplied diving are lower risk of drowning and considerably larger breathing gas supply than scuba, allowing longer working periods and safer decompression. Disadvantages are the absolute limitation on diver mobility imposed by the length of the umbilical, encumbrance by the umbilical, and high logistical and equipment costs compared with scuba. The disadvantages restrict use of this mode of diving to applications where the diver operates within a small area, which is common in commercial diving work.

The copper helmeted free-flow standard diving dress is the version which made commercial diving a viable occupation, and although still used in some regions, this heavy equipment has been superseded by lighter free-flow helmets, and to a large extent, lightweight demand helmets, band masks and full-face diving masks. Breathing gases used include air, heliox, nitrox and trimix.

Saturation diving is a mode of surface supplied diving in which the divers live under pressure in a saturation system or underwater habitat and are decompressed only at the end of a tour of duty.

Airline, or hookah diving, and "compressor diving" are lower technology variants also using a breathing air supply from the surface.

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.^[3]

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.^[4]: 149 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, 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.^[5]

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.^[6]: 29 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. ^{[citation needed]} 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.^[7]
• 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.^[8]
• 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 divers' teeth. Air supply is free flow and often unfiltered, and varies with depth and number of divers drawing off the system.^[9]

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.^[3] but is also used for long air dives shallower than 50 m.^[10]

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.^[11]

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.^[3]

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.^[3][12] 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,^[3] and for diving in contaminated water, where the diver must be protected from the environment, and helmets are generally used for environmental isolation.^[13]

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

The first successful surface-supplied diving equipment was produced by the brothers Charles and John Deane in the 1820s.^[14] Inspired by a fire accident he witnessed in a stable in England,^[15] he^{[clarification needed]} designed and patented a "Smoke Helmet" to be used by firemen in smoke-filled areas in 1823. The apparatus comprised a copper helmet with an attached flexible collar and jacket. A long leather hose attached to the rear of the helmet was to be used to supply air - the original concept being that it would be pumped using a double bellows. A continuous airflow passed through the helmet, and the user breathed from it and exhaled back into it. A short pipe allowed excess air to escape. The garment was constructed from leather or airtight cloth, secured by straps.^[16]

The brothers had insufficient funds to build the equipment themselves, so they sold the patent to their employer, Edward Barnard. It was not until 1827 that the first smoke helmets were built, by German-born British engineer Augustus Siebe. In 1828 they decided to find another application for their device and converted it into a diving helmet. They marketed the helmet with a loosely attached "diving suit" so that a diver could perform salvage work but only in a vertical position, otherwise water entered the suit.^[16]

In 1829 the Deane brothers sailed from Whitstable for trials of their new underwater apparatus, establishing the diving industry in the town. In 1834 Charles used his diving helmet and suit in a successful attempt on the wreck of HMS Royal George at Spithead, during which he recovered 28 of the ship's cannon.^[17] In 1836, John Deane recovered timbers, guns, longbows, and other items from the rediscovered Mary Rose shipwreck.^[18] By 1836 the Deane brothers had produced the world's first diving manual, Method of Using Deane's Patent Diving Apparatus which explained in detail the workings of the apparatus and pump, plus safety precautions.^[19]

In the 1830s the Deane brothers asked Siebe to apply his skill to improve their underwater helmet design.^[20] Expanding on improvements already made by another engineer, George Edwards, Siebe produced his own design; a helmet fitted to a full-length watertight canvas diving suit.^[21] The real success of the equipment was a exhaust non-return valve in the helmet, which prevented flooding through the exhaust port.^{[citation needed][clarification needed]}

Siebe introduced various modifications on his diving dress design to accommodate the requirements of the salvage team on the wreck of HMS Royal George, including making the helmet be detachable from the corselet; his improved design gave rise to the typical standard diving dress which revolutionised underwater civil engineering, underwater salvage, commercial diving and naval diving.^[20]

Equipment

The essential aspect of surface-supplied diving is that breathing gas is supplied from the surface, either from a specialized diving compressor, high-pressure cylinders, or both. In commercial and military surface-supplied diving, a backup source of surface-supplied breathing gas should always be present in case the primary supply fails. The diver may also wear a bailout cylinder which can provide self-contained breathing gas in an emergency. Thus, the surface-supplied diver is less likely to have an "out-of-air" emergency than a scuba diver using a single gas supply, as there are normally two alternative breathing gas sources available. Surface-supplied diving equipment usually includes communication capability with the surface, which adds to the safety and efficiency of the working diver.^[22]

The equipment needed for surface supplied diving can be broadly grouped as diving and support equipment, but the distinction is not always clear. Diving support equipment is the equipment used to facilitate a diving operation. It is either not taken into the water during the dive, such as the gas panel and compressor, or is not integral to the actual diving, being there to make the dive easier or safer, such as a surface decompression chamber. Some equipment, like a diving stage, is not easily categorised as diving or support equipment, and may be considered as either.

Surface-supplied diving equipment is required for a large proportion of the commercial diving operations conducted in many countries, either by direct legislation, or by authorised codes of practice, as in the case of IMCA operations.^[23] Surface-supplied equipment is also required under the US Navy operational guidance for diving in harsh contaminated environments which was drawn up by the Navy Experimental Diving Unit.^[24]

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

Lightweight demand helmets are rigid structures which fully enclose the head of the diver and supply breathing gas "on demand". The flow of gas from the supply line is activated by inhalation reducing the pressure in the helmet to slightly below ambient, and a diaphragm in the demand valve uses this pressure difference to open the valve allowing breathing gas to flow into the helmet until the pressure inside the helmet again balances the ambient pressure and the lever returns to the shut position. This is exactly the same principle as used for scuba demand valves, and in some cases the same components are used. Sensitivity of the lever can often be adjusted by the diver by turning a knob on the side of the demand valve.

Lightweight demand helmets are available in open circuit systems which exhaust to the surrounding water, used when breathing standard air or nitrox,^[25]: Ch4 and closed circuit (reclaim) systems used to reduce costs when breathing mixed gas with a large helium fraction. the exhaled gas is returned to the surface through a reclaim valve, a type of back-pressure regulator in the helmet, via the umbilical, scrubbed of carbon dioxide, filtered of odour and micro-organisms, re-oxygenated, and recompressed to storage.^{[26][27][28][29]}

The helmet shell may be of metal^[30] or reinforced plastic composite (GRP), and is either connected to a neck dam or clamped directly to a drysuit. The neck dam is on the lower part of the helmet, which seals around the neck of the diver in the same way as the neck seal of a dry suit. Attachment to the neck dam is critical to diver safety and a reliable locking mechanism is needed to ensure that it is not inadvertently released during a dive.^[13]

Demand breathing systems reduce the amount of gas required to adequately ventilate the diver, as gas is only supplied when the diver inhales, but the slightly increased work of breathing caused by this system is a disadvantage at extreme levels of exertion, where free-flow systems may be better. The demand system is also quieter than free-flow, particularly during the non-inhalation phase of breathing. This can make voice communication more effective. The breathing of the diver is also audible to the surface team over the communications system, and this helps to monitor the condition of the diver and is a valuable safety feature.^[26]

A free flow diving helmet supplies a continuous flow of air to the diver, who breathes it as it flows past. Mechanical work of breathing is minimal, but flow rate must be high if the diver works hard, and this is noisy, affecting communications and requiring hearing protection to avoid damage to the ears. This type of helmet is popular where divers have to work hard in relatively shallow water for long periods. It is also useful when diving in contaminated environments, where the helmet is sealed onto a dry suit, and the entire system is kept at a slight positive pressure by adjusting the back-pressure of the exhaust valve, to ensure that there is no leakage into the helmet. This type of helmet is often large in volume, and if it is attached to the suit, it does not move with the head. The diver must move their body to face anything they want to see. For this reason the faceplate is large and there is often an upper window or side windows to improve the field of vision.^[31]

The standard diving helmet (Copper hat) is made of two main parts: the bonnet, which covers the diver's head, and the corselet which supports the weight of the helmet on the diver's shoulders, and is clamped to the suit to create a watertight seal. The bonnet is attached and sealed to the corselet at the neck, either by bolts or an interrupted screw-thread, with some form of locking mechanism.^[32]

The bonnet is usually a copper shell with soldered brass fittings. It covers the diver's head and provides sufficient space to turn the head to look out of the glazed faceplate and other viewports (windows). The front port can usually be opened for ventilation and communication when the diver is on deck, by being screwed out or swung to the side on a hinge. The other viewports are generally fixed.^[32][33][34]

The corselet, also known as a breastplate or gorget, is an oval or rectangular collar-piece resting on the shoulders, chest and back, to support the helmet and seal it to the suit.^[35] The helmet is usually connected to the suit by clamping the rubberised collar of the suit to the rim of the corselet to make a water-tight seal. Most six and twelve bolt bonnets are joined to the corselet by 1/8th turn interrupted thread with a safety lock.^[32][34]

An alternative method is to bolt the bonnet to the corselet over a rubber collar seal bonded to the neck opening of the suit.^[35]

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.^[36]

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).^[37][38] 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.^[39]

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.^{[citation needed]}

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.^{[citation needed]}

Breathing gas supply

Diver's umbilical

The umbilical contains a hose to supply the breathing gas and usually several other components. These usually include a communications cable (comms wire), a pneumofathometer, and a strength member, which may be the breathing gas hose, communications cable, or a rope. When needed, a hot water supply line, helium reclaim line, video camera and lighting cables may be included. These components are neatly twisted into a multistrand cable, or taped together, and are deployed as a single unit. The diver's end has underwater connectors for the electrical cables, and the hoses are usually connected to the helmet, band mask, or bailout block by JIC fittings. A screw-gate carabiner or similar connector is provided on the strength member for attachment to the diver's harness, and may be used to lift the diver in an emergency. Similar connections are provided for attachment to the diving bell, if used, or to the surface gas panel and communications equipment. A diver's umbilical supplied from a bell gas panel is called an excursion umbilical, and the supply from the surface to the bell panel is the bell umbilical.^[40][41]

Air-line

Hookah, Sasuba and Snuba systems are categorised as "air-line" equipment, as they do not include the communication, lifeline and pneumofathometer hose characteristic of a full diver's umbilical. Most hookah diving uses a demand system based on a standard scuba second stage, but there have been special purpose free-flow full-face masks specifically intended for hookah diving (see photos). A bailout system, or emergency gas supply (EGS) is not an inherent part of an air-line diving system, though it may be required in some applications.^[42][7]

Their field of application is very different from full surface-supplied diving. Hookah is generally used for shallow water work in low-hazard applications, such as archaeology, aquaculture, and aquarium maintenance work, but is also sometimes used for open water hunting and gathering of seafood,^[42] shallow water mining of gold and diamonds in rivers and streams, and bottom cleaning and other underwater maintenance of boats.^[6]: 29 Sasuba and Snuba are mainly a shallow water recreational application for low-hazard sites. Sasuba and hookah diving equipment is also used for yacht or boat maintenance and hull cleaning, swimming pool maintenance, shallow underwater inspections.^{[citation needed]}

The systems used to supply air through the hose to a demand valve mouthpiece, are either 12-volt electrical air pumps, gasoline engine powered low-pressure compressors, or floating scuba cylinders with high pressure regulators. These hookah diving systems usually limit the hose length to allow less than 7 metres depth.^{[citation needed]} The exception is the gasoline engine powered unit, which requires a much higher level of training and topside supervision for safe use.^[42]

A notable exception to this trend are the inshore diamond diving operations on the west coast of South Africa, where hookah is still the standard equipment for diamondiferous gravel extraction in the hostile conditions of the surf zone, where the water temperature is usually around 8 to 10 °C, visibility is usually low, and surge is often strong. Divers work shifts of about two hours with a crowbar and a suction hose, are heavily weighted to stay in place while working, and the standard method of ascent is to ditch the weighted harness and regulator and make a free swimming ascent. The next diver will free dive down the air line, fit the regulator and wriggle into the harness before continuing with the job.^{[citation needed]} Until the South African abalone fishery was closed, hookah was the only mode of diving permitted for harvesting wild abalone, and several aspects of this practice were in direct contravention of the diving regulations at the time. Abalone divers were not allowed to have a standby diver on the boat.^{[citation needed]}

Gas panel

A gas panel or gas manifold is the control equipment for supplying the breathing gas to the divers.^[31] Primary and reserve gas is supplied to the panel through shutoff valves from a low-pressure compressor or high-pressure storage cylinders ("bombs", "bundles", "quads", or "kellys"). The gas pressure may be controlled at the panel by an industrial pressure regulator, or it may already be regulated closer to the source (at the compressor, or at the storage cylinder outlet). The supply gas pressure is monitored on a gauge at the panel, and an over-pressure valve is fitted in case the supply pressure is too high. The gas panel may be operated by the diving supervisor if the breathing gas is air or a fixed ratio premix, but if the composition must be controlled or monitored during the dive it is usual for a dedicated gas panel operator, or "gas man" to do this work.^[40]

There is a set of valves and gauges for each diver to be supplied from the panel. These include:^[40]

• A main supply valve with non-return valve, which supplies gas to the main gas supply hose of the umbilical. This is usually a quarter-turn valve, as it must be quick to operate and obvious whether it is open or closed.^[40]
• A pneumofathometer supply valve, which supplies gas to the pneumofathometer for the diver. This valve is usually near the main supply valve but with a different handle. It is usually a needle type valve as it must be finely adjustable, but it must also be large enough to allow a fairly high flow rate, as the air may be used as an alternative breathing air source, or to fill small lift bags.^[40]
• A pneumofathometer gauge is connected to the pneumo line. This is a high resolution pressure gauge calibrated in feet sea water (fsw) and/or metres sea water (msw). and is used to measure the depth of the diver by allowing air to flow through the pneumo hose and out the end attached to the diver. When the air supply is shut off, and the flow stops, the gauge indicates the pressure at the open end at the diver.^[40]
• Each pneumofathometer gauge has an overpressure valve to protect it against gas supply at higher pressure than it is designed to take. This is essential as the main supply pressure is significantly higher than the maximum depth pressure on the pneumo gauge. There is also often a snubbing valve or orifice between the pneumo line and the gauge to restrict flow into the gauge and ensure that the overpressure valve can adequately relieve the pressure.^[40]
• Some gas panels have a separate supply gauge for each diver downstream of the supply valve, but this is not standard practice.^[40]

The gas panel may be fairly large and mounted on a board for convenience of use, or may be compact and mounted inside a portable box, for ease of transport. Gas panels are usually for one, two or three divers. In some countries, or under some codes of practice, the surface standby diver must be supplied from a separate panel to the working diver/s.^[43]

A wet or closed bell will be fitted with a bell gas panel to supply gas to the divers' excursion umbilicals. The bell gas panel is supplied with primary gas from the surface via a bell umbilical, and on-board emergency gas from high-pressure storage cylinders mounted on the frame of the bell.^[4][44]

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.^[40]

The pneumo line is usually a 0.25 inches (6.4 mm) 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.^[40]

Low-pressure breathing air compressor

A low-pressure compressor is often the air supply of choice for surface-supplied diving, as it is virtually unlimited in the amount of air it can supply, provided the delivery volume and pressure are adequate for the application. A low-pressure compressor can run for tens of hours, needing only refueling, periodical filter drainage and occasional running checks, and is therefore more convenient than high-pressure storage cylinders for primary air supply.^[40]

It is however, critical to diver safety that the compressor is suitable for breathing air delivery, uses a suitable oil, is adequately filtered, and takes in clean and uncontaminated air. Positioning of the intake opening is important, and may have to be changed if the relative wind direction changes, to ensure that no engine exhaust gas enters the intake. Various national standards for breathing air quality may apply.

Power for portable compressors is usually a 4-stroke petrol (gasoline) engine. Larger, trailer mounted compressors, may be diesel powered. Permanently installed compressors on dive support boats are likely to be powered by 3-phase electric motors.

The compressor should be provided with an accumulator and a relief valve. The accumulator functions as an additional water trap, but the main purpose is to provide a reserve volume of pressurised air. The relief valve allows any excess air to be released back to the atmosphere while retaining the appropriate supply pressure in the accumulator.^[40]

High pressure main gas supply

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