Surface-supplied diving
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. 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-oriented surface-supplied diving are lower risk of drowning and considerably larger breathing gas supply than scuba, allowing longer working periods and safer decompression. It is also nearly impossible for the diver to get lost. 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made commercial diving a viable occupation, and although still used in some regions, this heavy equipment has been superseded by lighter free-flow helmets, and to a large extent, lightweight demand helmets, band masks and full-face diving masks.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.
Air-line, 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. It may also be referred to as bounce diving, an ambiguous term.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:
Technically, atmospheric suit diving, scuba diving and freediving are also "surface oriented", but are not "surface-supplied".
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. The assembled combination of equipment is called a scuba replacement package. Scuba replacement equipment is used where compact, portable surface supplied equipment is needed for rapid deployment by small craft or road vehicle. 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 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 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
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.Open, closed, and semi-closed circuit systems
The surface-supplied diving mode can be further qualified by the management of exhaled and bypassed breathing gas. In open-circuit mode it is discharged directly into the ambient environment. In semi-closed or gas-extender mode, it is partly recirculated and scrubbed to remove carbon dioxide, and partly replenished to maintain an acceptable oxygen partial pressure., with the balance discharged to the ambient environment. In closed circuit and gas reclaim systems, most to all of the gas is scrubbed, re-oxygenated, and made available for either immediate or later re-use. Full or partial recycling is usually used to make more economical use of helium based gases due to the high cost of helium and the large quantities used at the depths where it is needed.Alternatives
Alternative modes of diving may be used to attain the objectives of a surface-supplied dive in some circumstances:- Scuba diving, which is commonly used for recreational diving and scientific 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 which can operate deeper and avoid exposing a diver to underwater hazards, have their applications, but lack the dexterity of a diver at present.
- Freediving, or breathhold diving, is extremely limited in duration and exposes the diver to relatively high risk.
Application
A major limitation of surface-supplied diving is the presence of an umbilical between the surface control point and the diver, which encumbers the diver's mobility, restricts their range of access to the environment, and requires an attendant to manage the umbilical, which can get snagged on underwater obstructions even when correctly tended. Where this limitation is acceptable, the connection with the diver provides some advantages, in that the diver can find their way back to the control point by following the umbilical, and a standby diver can reach the diver by following the umbilical.
There has been development of low-cost airline systems for shallow recreational diving, where limited training is offset by physically limiting the depth accessible.
There are two major advantaged to surface supplied diving: The breathing gas supply is not limited to the ability of the diver to carry it, and is monitored from the surface, reducing the task load on the diver, and the diver is in continuous communication with the surface control point, so their safety can be monitored effectively. The physical constraint of the umbulical is sometimes a limitation on mobility and radius of activity, and at other times a safety feature, preventing access to known hazards and identifying the route back to a place of safety.