These tables are designed to be used with MK 16 UBA (or any other constant ppO2 closed-circuit UBA) with an oxygen setpoint of 0.7 ata or higher.
When using helium as the inert gas, the amount of nitrogen must be minimized in the breathing loop. Flush the UBA well with helium-oxygen using proper purge procedure in the MK 16 UBA O&M manual.
Tables are grouped by depth and within each depth group is a limit line. These tables are designed to be dived to the limit line. Schedules below the limit line provide for unforeseen circumstances when a diver might experience an inadvertent downward excursion or for an unforeseen reason overstay the planned bottom time.
Tables/schedules are selected according to the maximum depth obtained during the dive and the bottom time (time from leaving the surface to leaving the bottom).
■ General rules for using these tables are the same as for standard air tables:
1. Enter the table at the listed depth that is exactly equal to or is next greater than the maximum depth attained during the dive.
2. Select the bottom time from those listed for the selected depth that is exactly equal to or is next greater than the bottom time of the dive.
3. Never attempt to interpolate between decompression schedules.
4. Use the decompression stops listed for the selected bottom time.
5. Ensure that the diver's chest is maintained as close as possible to each decompression depth for the number of minutes listed.
7. Begin timing each stop on arrival at the decompression stop depth and resume ascent when the specified time has elapsed. Do not include ascent time as part of stop time.
8. 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 decompression table.
■ In emergency situations (e.g., UBA flood-out or failure), immediately ascend to the first decompression stop according to the original decompression schedule if deeper than the first stop, and shift to the Emergency Breathing System (EBS). The subsequent decompression is modified according to the diluent gas originally breathed.
— 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 a planned decompression dive falls within a no-decompression 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 Mediums.
— 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.
17-10.4 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. The decompression tables were calculated and tested using functioning or prototype MK 16 UBAs. When addition of oxygen to the UBA is manually controlled,
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