CHAPTER 17 — Closed-Circuit Mixed-Gas UBA Diving
Change A 17-1
C H A P T E R 1 7
Closed-Circuit Mixed-Gas UBA Diving
17-1
INTRODUCTION
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. When using
HeO2 as a diluent, dives to 200 fsw can be made using 84/16 and to 300 fsw using
88/12. 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 man-
ual SS600-AH-MMA-010 (MK 16).
17-1.2
Scope. This chapter covers MK 16 UBA princi-
ples of operations, operational planning, dive pro-
cedures, and medical aspects of mixed-gas closed-
circuit diving. Refer to Chapter 16 for procedures
for mixing divers’ breathing gas.
17-2
PRINCIPLES OF OPERATION
The U.S. Navy closed-circuit mixed-gas UBA is a
constant partial-pressure-of-oxygen rebreather. To
conserve the gas supply and extend underwater
duration, the efficiency of gas use is improved by:
Removing carbon dioxide produced by meta-
bolic action of the body.
Adding pure oxygen to the breathing gas to
replace the oxygen consumed.
Recirculating the breathing gas for reuse.
Figure 17-1. MK 16
MOD 0 Closed-Circuit
Mixed-Gas UBA.
