CHAPTER 17 Closed-Circuit Mixed-Gas UBA Diving
Change A 17-23
The last stop may be taken at 20 fsw if desired. After completing the
prescribed 20-fsw stop, remain at any depth between 10 fsw and 20 fsw
inclusive for the 10-fsw stop time as noted in the appropriate
Always use the appropriate decompression table when surfacing even if
UBA malfunction has significantly altered ppO2.
In emergency situations (e.g., UBA flood-out or failure), immediately ascend
to the first decompression stop according to the original decompression sched-
ule if deeper than the first stop, and shift to the Emergency Breathing System
(EBS). The subsequent decompression is modified according to the diluent gas
Helium-Oxygen Diluent. Follow the original HeO2 decompression
schedule without modification while breathing air.
Nitrogen-Oxygen (Air) Diluent. Double all remaining decompression
stops while breathing air. If the switch to emergency air is made
while at a decompression stop, then double the remaining time at that
stop and all shallower stops. If the dive falls within the no-decom-
pression limit and a switch to EBS has occurred, a mandatory 10-
minute stop at 20 fsw is required.
If either of these procedures is used, the diver should be closely observed for
signs of decompression sickness for 2 hours following the dive, but need not be
treated unless symptoms arise.
When selecting the proper decompression table, all dives within the past 12
hours must be considered. Repetitive dives are allowed. Repetitive diving
decompression procedures vary depending on the breathing medium(s)
selected for past dives and for the current dive. If a dive resulted in breathing
from the EBS then no repetitive dives shall be made within the next 12 hours.
Refer to the following tables:
Table 17-8a for Repetitive Dive Procedures for Various Gas Medi-
Figure 17-7 for the Dive Worksheet for Repetitive 0.7 ata Constant
Partial Pressure Oxygen in Nitrogen Dives.
Table 17-9 for the No-Decompression Limits and Repetitive Group
Designation Table for No-Decompression 0.7 ata Constant Partial
Pressure Oxygen in Nitrogen Dives.
Table 17-10 for the Residual Nitrogen Timetable for Repetitive 0.7
ata Constant Partial Pressure Oxygen in Nitrogen Dives.
PPO2 Variances. The ppO2 in the MK 16 UBAs is expected to vary slightly from
0.6 - 0.9 ata for irregular brief intervals. This does not constitute a malfunction.