CHAPTER 17 — Closed-Circuit Mixed-Gas UBA Diving
Change A 17-25
Table 17-8b. Repetitive Dive Procedures for Various Gas Mediums.
Notes:
A.
(1)
Use the Worksheet (Figure 17-7) for calculations.
(2)
Determine the repetitive group letter for depth and time of dive conducted from Table 17-9 for no-decompression
dives or from the Closed-Circuit Mixed-Gas UBA Decompression Tables (Table 17-14 and Table 17-15) for
decompression dives. If the exact time or depth is not found, go to the next longer time or the next deeper depth.
(3)
Locate the repetitive group letter in Table 17-10. Move across the table to the correct surface interval time. Move
down to the bottom of the column for the new group designation.
(4)
Move down the column of the new group designation to the depth of the planned dive. This is the residual nitrogen
time (RNT). Add this to the planned bottom time of the next dive to find the decompression schedule and the new
group designation.
(5)
RNT Exception Rule: If the repetitive dive is to the same depth or deeper than the depth of the previous dive, and
the RNT is longer than the original bottom time, use the original bottom time.
B.
Use the repetitive group designation from the standard air decompression table or the no-decompression limits and
repetitive group designation table for no-decompression air dives to enter Table 17-10. Compute the RNT as in
procedure A. Do not use the residual nitrogen timetable for repetitive air dives to find the RNT.
C.
(1)
Determine the repetitive group designation for depth and time of dive conducted from Table 17-9 or Table 17-14. If
the exact time or depth is not found, go to the next longer time or the next deeper depth.
(2) Locate the repetitive group letter in Table 17-10. Move across the table to the correct surface-interval time. Move
down to the bottom of the column for the new group designation.
(3) Use the repetitive group designation from Table 17-10 as the new group designation in the residual nitrogen
timetable for repetitive air dives (Chapter 10) to find the RNT.
D.
Add the bottom time of the current dive to the sum of the bottom times for all dives within the past 12 hours to get the
adjusted bottom time. Use the maximum depth attained within the past 12 hours and the adjusted bottom time to select
the appropriate profile from Table 17-15.
E.
Add the bottom times of all dives within the past 12 hours to get an adjusted bottom time. Using the standard air
decompression table, find the maximum depth attained during the past 12 hours and the adjusted bottom time. The
repetitive group from this air table may then be used as the surfacing repetitive group from the last dive. The residual
nitrogen timetable for repetitive air dives is used to find the repetitive group at the end of the current surface interval and
the appropriate residual nitrogen time for the current air dive.
F.
Compute the RNT from the residual nitrogen timetable for repetitive air dives using the depth of the planned dive. Add
the RNT to the planned bottom time to get the adjusted bottom time. Use Table 17-15 for the adjusted bottom time at
the planned depth.
G.
Add the bottom times of all dives within the past 12 hours to get an adjusted bottom time. Using Table 17-14, find the
maximum depth attained during the past 12 hours and the adjusted bottom time. The repetitive group from the table
may then be used as the surfacing repetitive group from the last dive. Table 17-10 is used to find the repetitive group at
the end of the current surface interval and the appropriate RNT for the current dive.
H.
Compute the RNT from Table 17-10 using the depth of the previous dive. Add the RNT to the planned bottom time to
get the adjusted bottom time. Use Table 17-15 for the adjusted bottom time at the planned depth.
