Closed-circuit mixed-gas underwater breathing apparatus (UBA) is primarily employed by Naval Explosive Ordnance Disposal (EOD) and Special Warfare (SPECWAR) forces. This equipment combines the mobility of a free-swimming diver with the depth advantages of mixed gas. UBAs in this category permit completely autonomous diver operations without an umbilical. The term closed-circuit refers to the recirculation of 100 percent of the mixed-gas breathing medium. This results in bubble-free operation, except during ascent or inadvertent gas release. This capability makes closed-circuit UBAs well-suited for special warfare operations and for operations requiring a low acoustic signature. The U.S. Navy's use of the mixed-gas closed-circuit UBA was developed to satisfy the operational requirements of SPECWAR combat swimmers and EOD divers. Improvements in gas usage, dive duration, and depth capabilities provided by the UBA greatly increase the effectiveness of these divers. Dives to 150 feet of seawater (fsw) can be made when N2O2 (air) is used as a diluent and to 300 fsw when HeO2 (84/16-82/18) is used as a diluent. Current certification limits the MK 16 UBA diving to 200 fsw.

17-1.1 Purpose. This chapter provides general guidelines for MK 16 UBA diving, operations and procedures (Figures 17-1 and 17-2). For detailed operation and maintenance instructions, see technical manual SS600-AH-MMA-010 (MK 16).

17-1.2 Scope. This chapter covers MK 16 UBA principles of operations, operational planning, dive procedures, and medical aspects of mixed-gas closed-circuit diving. Refer to Chapter 16 for procedures for mixing divers' breathing gas.

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