Operational Characteristics of SSDS Surfacesupplied diving systems can be

divided into two major categories: lightweight full face mask (MK 20), and deep-sea (MK 21) gear.

6-7.3.1 Mobility. Surface-supplied gear allows the diver almost as much mobility as scuba. The primary use for deep-sea gear is bottom work in depths up to 190 fsw.

6-7.3.2 Buoyancy. The buoyancy associated with SSDS varies with the diving dress selected. Variable Volume Dry Suit (VVDS) provides the greatest buoyancy control (see paragraph 7-3.1.2), making it a desirable technique for working on muddy bottoms, conducting jetting or tunneling, or working where the reaction forces of tools are high.

6-7.3.3 Operational Limitations. Divers using surface supplied gear are restricted to the operational limitations described in Figure 6-14. Additional limitations of using surface-supplied gear includes additional topside support personnel and lengthy predive and postdive procedures.

6-7.3.4 Environmental Protection. Surface-supplied diving systems can offer the diver increased thermal protection when used with a Hot Water or VVDS. The MK 21 helmet can increase protection of the diver's head. Because the diver's negative buoyancy is easily controlled, an SSDS allows diving in areas with strong currents.

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