CHAPTER 17 — Closed-Circuit Mixed-Gas UBA Diving
Change A 17-13
requires the addition of diluent gas to the breathing loop either automatically
through the diluent add valve or manually through the diluent bypass valve to
make up lost volume. Excessive gas loss caused by face mask leaks, frequent
depth changes, or improper UBA assembly will deplete the diluent gas supply
rapidly.
17-4.1.3
Canister Duration. Canister duration is estimated by using a working diver
scenario. This allows an adequate safety margin for the diver in any situation.
Table 17-4 shows the canister duration limits and approved absorbents for the MK
16 UBA.
17-4.1.4
Thermal Protection. Divers must be equipped with adequate thermal protection
to perform effectively and safely. A cold diver will either begin to shiver or
increase his exercise rate, both of which will increase oxygen consumption and
decrease oxygen supply duration and canister duration. Refer to Chapter 11 for
guidance on thermal protection.
17-4.2
Equipment Requirements. Equipment requirements for closed-circuit mixed-gas
UBA training dives are provided in Table 17-5. Two equipment items merit
special comment:
Safety Boat. A minimum of one motorized safety boat must be present for all
open-water dives. A safety boat is also recommended for tended pier dives or
diving from shore. Safe diving practice in many situations, however, will
require the presence of more than one safety boat. The Diving Supervisor must
Table 17-4. MK 16 Canister Duration Limits.
Canister Duration with HeO2
Temperature (°F)
Depth (fsw)
Time (minutes)
40 and above
0-300
300
29-39
0-100
300
35-39
101-300
240
29-34
101-300
120
Canister Duration with N202
Temperature (°F)
Depth (fsw)
Time (minutes)
29 and above
0-50
300
40 and above
51-150
200
29-39
51-150
100
NAVSEA-Approved Sodalime CO2 Absorbents
Name
Vendor
NSN
High Performance Sodasorb, Regular
W.R. Grace
6810-01-113-0110
Sofnolime 4-8 Mesh NI, L Grade
O.C. Lugo
6810-01-113-0110
Sofnolime 8-12 Mesh NI, D Grade
O.C. Lugo
6810-01-412-0637
