CHAPTER 13 — Mixed Gas Operational Planning
Change A 13-3
13-3.1
Mixed Gas Diving Methods. Mixed gas diving methods are defined by the type of
mixed gas diving equipment that will be used. The three types of mixed gas diving
equipment are:
Surface supplied gear (MK 21 MOD 1, EXO BR MS)
Semiclosed circuit and closed circuit UBAs
Saturation deep dive systems
For deep dives (190-300 fsw) of short duration, or for shallower dives where
nitrogen narcosis reduces mental acuity and physical dexterity, helium-oxygen
diving methods should be employed.
Because of the unusual hazards incurred by long exposures to extreme environ-
mental conditions, extended excursions away from topside support, and great
decompression obligations, semiclosed circuit and closed circuit diving should
only be undertaken by specially trained divers. Semiclosed circuit and closed
circuit diving operations are covered in depth in Volume 4.
Saturation diving is the preferred method for dives deeper than 300 fsw or for
shallow dives where extensive in-water times are required. Disadvantages of satu-
ration diving include the requirement for extensive logistic support and the
inability of the support ship to easily shift position once the mooring is set. For
this reason, it is very important that the ship be moored as closely over the work
site as possible. Using side-scan sonar, remotely operated vehicles (ROVs) or
precision navigation systems will greatly aid in the successful completion of the
operation. Saturation diving is discussed in Chapter 15.
13-3.2
Method Considerations. In mixed gas diving, the principle factors influencing the
choice of a particular method are:
Depth and planned duration of the dive
Equipment availability
Quantities of gas mixtures available
Qualifications and number of personnel available
Type of work and degree of mobility required
Environmental considerations such as temperature, visibility, type of bottom,
current, and pollution levels
Communication requirements
Need for special operations procedures
13-3.3
Depth. Equipment depth limitations are contained in Table 13-2. The limitations
are based on a number of interrelated factors such as decompression obligations,
