After selecting the applicable decompression schedule, it
is imperative that it be followed as closely as possible. Unless a Diving Medical
Officer recommends a deviation and the Commanding Officer concurs, decompression
must be completed according to the schedule selected.
Always ascend at a rate of 30 fpm (::20 per 10 fsw). Minor variations
in the rate of travel between 20 and 40 fsw/minute are acceptable. Any
variation in the rate of ascent must be corrected in accordance with the procedures
in paragraph 9-6.2. However, a delay of up to one minute in reaching the first
decompression stop can be ignored.
Decompression stop times, as specified in the
decompression schedule, begin as soon as the divers reach the stop depth. Upon completion of the specified stop time, the divers ascend to the next stop or to the
surface at the proper ascent rate. Ascent time is not included as part of stop time.
The following rules for correcting variations in rate
of ascent apply to Standard Air Decompression dives as well as Surface Decompression
Table dives. (For ease of illustration, the following examples address
Standard Air dives.)
-
Delay greater than 1 minute, deeper than 50 fsw.Add the total delay time
(rounded up to the next whole minute) to the bottom time, recompute a new
decompression schedule, and decompress accordingly.
Example: A dive was made to 113 fsw with a bottom time of 60 minutes.
According to the 120/60 decompression schedule of the Standard Air
Decompression Table, the first decompression stop is 30 fsw. During ascent,
the divers were delayed at 100 fsw for: 03::27 and it actually took 6 minutes 13
seconds to reach the 30-foot decompression stop. Determine the new
decompression schedule.
Solution:If the divers had maintained an ascent rate of 30 fpm, it would have
taken the divers 2 minutes 46 seconds to ascend from 113 fsw to 30 fsw. The
difference between what it should have taken and what it actually took is 3
minutes 27 seconds. Increase the bottom time from 60 minutes to 64 minutes
(3 minutes 27 seconds rounded up), recompute the decompression schedule
using a 70-minute bottom time and continue decompression according to the
new decompression schedule, 120/70. This dive is illustrated in Figure 9-3.
-
Delay greater than 1 minute, shallower than 50 fsw.If the rate of ascent is
less than 30 fpm, add the delay time to the diver’s first decompression stop. If
the delay is between stops, disregard the delay. The delay time is rounded up
to the next whole minute.
Example: A dive was made to 113 fsw with a bottom time of 60 minutes.
According to the Standard Air Decompression Table, the first decompression
stop is at 30 fsw. During ascent, the divers were delayed at 40 fsw and it
actually took 6 minutes 20 seconds to reach the 30-foot stop. Determine the
new decompression schedule.
Solution: If the divers had maintained an ascent rate of 30 fpm, the correct
ascent time should have been 2 minutes 46 seconds. Because it took 6 minutes
20 seconds to reach the 30-foot stop, there was a delay of 3 minutes 34 seconds
(6 minutes 20 seconds minus 2 minutes 46 seconds). Therefore, increase the
length of the 30-foot decompression stop by 3 minutes 34 seconds, rounded up
to 4 minutes. Instead of 2 minutes, the divers must spend 6 minutes at 30 fsw.
This dive is illustrated in Figure 9-4.
FIGURE 9-3 Completed Air Diving Chart.
|
FIGURE 9-4 Completed Air Diving Chart.
|
On a Standard Air Dive, if the rate of ascent is greater
than 30 fpm, STOP THE ASCENT, allow the watches to catch up, and then
continue ascent. If the stop is arrived at early, start the stop time after the watches
catch up.
