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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.[2] This is different from scuba diving, where the diver's breathing equipment is completely self-contained and there is no 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made commercial diving a viable occupation, and although still used in some regions, this heavy equipment has been superseded by lighter free-flow helmets, and to a large extent, lightweight demand helmets, band masks and full-face diving masks.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.

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.[34]

Underwater tending point

For some operations it is necessary to control the umbilic

A rescue tether 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.

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.[34]

Underwater tending point

For some operations it is necessary to control the umbilical at a point underwater. This is known as an under

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.[34]

Occupational health and safety issues