Surface decompression is a technique for fulfilling all or a portion of a diver’s
decompression obligation in a recompression chamber instead of in the water,
significantly reducing the time that a diver must spend in the water. Also,
breathing oxygen in the recompression chamber reduces the diver’s total decompression
time. Other variations will be handled in accordance with paragraph
9-6.2.
Surface decompression offers many advantages that enhance the divers’ safety.
Shorter exposure time in the water keeps divers from chilling to a dangerous level.
Inside the recompression chamber, the divers can be maintained at a constant pressure,
unaffected by surface conditions of the sea. Divers shall be observed
constantly by either the inside tender or topside personnel, and monitored for
decompression sickness and oxygen toxicity. Using an inside tender when two
divers undergo surface decompression is at the discretion of the dive supervisor. If
an inside tender is not used, both divers will carefully monitor each other in addition
to being closely observed by topside personnel.
If an oxygen breathing system is installed in the recompression chamber, conduct
surface decompression according to the Surface Decompression Table Using
Oxygen (Table 9-6). If air is the only breathing medium available, use the Surface
Decompression Table Using Air (Table 9-10).
Residual Nitrogen Timetables have not been developed for Surface Decompression
Repetitive Dives. Repetitive surface decompression dives may be
accomplished in accordance with paragraph 9-10.1.5.
TABLE 9-6 Unlimited/No-Decompression Limits and Repetitive Group Designation Table for Unlimited/No-
Decompression Air Dives.
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TABLE 9-10 Surface Decompression Table Using Air.
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TABLE 9-10A Surface Decompression Table Using Air.
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TABLE 9-10B Surface Decompression Table Using Air.
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TABLE 9-10C Surface Decompression Table Using Air.
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Using the Surface Decompression
Table Using Oxygen (referred to as Sur D O2) requires an approved double-lock
recompression chamber with an oxygen breathing system as described in Chapter
22. With Sur D O2, divers ascend at a constant rate of 30 fpm. The divers are
decompressed to the first decompression stop (or to the surface if there are no
water stops required) at an ascent rate of 30 fpm. The travel rate between stops and
from 30 fsw to the surface is also 30 fpm (::20 per 10 fsw). Minor variations in the
rate of travel between 20 and 40 fpm are acceptable.
9-6.2.
Once the divers are on the surface, the tenders have three and a half (:03::30)
minutes to remove the breathing apparatus and diving dress and assist the divers
into the recompression chamber.
Pressurizing the recompression chamber with air to 40 fsw should take approximately
30 seconds (descent rate not to exceed 80 fpm). The total elapsed time
from when the divers leave the 30-foot stop to when they reach the 40-foot recompression
chamber stop must not exceed 5 minutes with the following exception:
If no in-water stops are required, the time from reaching the surface to arrival at 40
feet in the chamber must not exceed 4 minutes. During descent in the recompression
chamber, if a diver cannot clear and the chamber is at a depth of at least 20
fsw, stop, then breathe oxygen at 20 fsw for twice the 40 fsw chamber stop time.
Ascend to 10 fsw and breathe oxygen again for twice the 40 fsw chamber stop
time. Then ascend to the surface. This “safe way out” procedure is not intended to
be used in place of normal Sur D O2 procedure
If the prescribed surface interval is exceeded and the divers are asymptomatic,
treat them as if they have Type I decompression sickness (Treatment Table 5,
Chapter 21). If the divers are symptomatic, they are treated as if they have Type II
decompression sickness (Treatment Table 6, Chapter 21), even if they are only
displaying Type I symptoms. Symptoms occurring during the chamber stops are
treated as recurrences (Chapter 21).
Upon arrival at 40 fsw in the recompression chamber, the divers are placed on the
Built-in Breathing System (BIBS) mask breathing pure oxygen. The designated
40-foot stop time commences once the divers are breathing oxygen. The divers
breathe oxygen throughout the 40-foot stop, interrupting oxygen breathing after
each 30 minutes with a 5-minute period of breathing chamber air (referred to as an
“air break”). Count the air breaks as “dead time” and not part of the oxygen stop
time. If the air break interval falls on time to travel, remove oxygen and
commence traveling to the surface at 30 fpm. This procedure simplifies time
keeping and should be used whenever using the Surface Decompression Table
Using Oxygen. Remove the O2 mask prior to leaving the 40 fsw stop for the
surface.
A dive is planned to approximately 160 fsw for 40 minutes. The dive is
to be conducted using Sur D O2 procedures. Figure 9-12 shows this dive profile.
In the event of oxygen system failure, it is important to be familiar with the appropriate
air decompression schedules. If the oxygen system fails while the divers are
in the water, the divers are shifted to the Standard Air Decompression Table or the
Surface Decompression Table Using Air. During the chamber phase, use the
procedures listed below in the event of oxygen system failure or CNS oxygen
toxicity.
FIGURE 9-12 Dive Profile.
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Follow this procedure when
there is an oxygen system failure at the 40 fsw chamber stop:
1. Complete remainder of 40-fsw stop on air.
2. Ascend to 20 fsw. Repeat the 40-fsw chamber stop time.
3. Ascend to 10 fsw. Stay there for twice the 40-fsw chamber stop time.
Follow this procedure when a
diver displays symptoms of CNS O2 toxicity at the 40 fsw chamber stop:
1. Remove the BIBS masks from the divers.
2. Wait for all symptoms to completely subside, then wait an additional 15
minutes.
3. Place the divers back on oxygen and resume the decompression at the point of
interruption. The period the divers are not breathing oxygen is considered
“dead time” and is not counted toward the total stop time. This procedure can
be repeated as many times as the Dive Supervisor considers prudent until all
the required time spent breathing oxygen at 40 fsw is met.
If the Dive Supervisor decides that the diver cannot tolerate oxygen:
1. Complete remainder of 40-fsw stop on air. Count all the time at 40 fsw toward
stop time. If all time at 40 fsw already meets or exceeds the 40-fsw stop time,
then ascend to 20 fsw.
2. Ascend to 20 fsw. Repeat the 40-fsw chamber stop time.
3. Ascend to 10 fsw. Stay there for twice the 40-fsw stop chamber time.
Divers make a planned dive to 152 fsw for 40 minutes using the Surface
Decompression Table Using Oxygen. From the appropriate schedule (160/40),
there is a 3-minute water stop at 50 fsw, a 5-minute water stop at 40 fsw, an 8-
minute water stop at 30 fsw, and a 32-minute chamber stop at 40 fsw breathing
oxygen. After 12 minutes of breathing oxygen at the 40-foot chamber stop, a diver
develops an oxygen toxicity symptom that completely subsides in 5 minutes.
Following the procedures for handling an oxygen toxicity symptom,
remove the BIBS from the diver. The diver breathes chamber air until all symptoms
completely subside. After an additional 15 minutes, place the diver back on
oxygen and continue the decompression schedule from the point of interruption.
Figure 9-13 is a profile of this dive.
FIGURE 9-13 Dive Profile.
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NOTE If the first symptom of CNS O2 toxicity at the 40-fsw stop is a convulsion,
oxygen must not be restarted.
Follow this procedure when a diver convulses at the 40-fsw chamber stop:
1. Remove the BIBS mask.
2. Keep the chamber depth constant at 40 fsw. Wait for the convulsion to stop,
ensuring the diver is breathing. The diver breathes air until regaining consciousness
and all symptoms resolve.
3. Complete remainder of 40-fsw stop on air. Count all the time at 40 fsw toward
stop time. If all time at 40 fsw already meets or exceeds the 40-fsw stop time,
then ascend to 20 fsw.
4. Ascend to 20 fsw. Repeat the 40-fsw chamber stop time.
5. Ascend to 10 fsw. Stay there for twice the 40-fsw stop chamber time.
Divers make a planned dive to 152 fsw for 44 minutes using the Surface
Decompression Table Using Oxygen. From the appropriate schedule (160/45),
there is a 3-minute water stop at 60 fsw, a 4-minute water stop at 50 fsw, an 8-
minute water stop at 40 fsw, a 6-minute stop at 30 fsw, and a 38-minute chamber
stop at 40 fsw breathing oxygen. After 12 minutes of breathing oxygen at the 40-
foot chamber stop, a diver suffers a convulsion. The convulsion completely
subsides in 5 minutes and the diver regains consciousness.
Following the procedures for handling an oxygen toxicity convulsion,
remove the BIBS from the diver. The diver breathes chamber air until all symptoms
completely subside and he regains consciousness.
1. Complete remainder of 40-fsw stop on air.
2. Ascend to 20 fsw. Repeat the 40-fsw chamber stop time.
3. Ascend to 10 fsw. Stay there for twice the 40-fsw chamber stop time.
Figure 9-14 is a profile of this dive.
FIGURE 9-14 Dive Profile.
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There are no repetitive diving tables or surface interval tables
for surface decompression dives. If another surface decompression dive using
oxygen is planned within a 12-hour period, select the appropriate decompression
schedule by:
1. Adding the bottom times of all dives made in the previous 12 hours to get an
adjusted bottom time, and
2. Using the maximum depth obtained in the previous 12 hours.
3. The equivalent single dive shall not exceed 170/40 for Sur D O2 or 190/60 for
Sur D Air.
A dive is conducted to 165 fsw for 25 minutes, followed by a surface
interval of 3 hours 42 minutes, and a repetitive dive to 133 fsw for 15 minutes. The
Surface Decompression Table Using Oxygen is used for both dives. Determine the
correct decompression schedules.
The correct decompression schedule is 170/25 for the first dive and
170/40 for the second dive. Even though the second dive was to a maximum depth
of 138 fsw for 15 minutes, the divers must be decompressed for the maximum
depth attained in the previous 12 hours, which was 170 fsw, and a total of all
bottom times, which was 40 minutes. Figure 9-15, Figure 9-16, and Figure 9-17
chart this example.
Even if the second dive is to be a Standard Air dive, combine all bottom times in
the previous 12 hours to get an adjusted bottom time and decompression schedule
from the maximum depth attained in the previous 12 hours.
FIGURE 9-15 Dive Profile.
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FIGURE 9-16 Completed Repetitive Dive Worksheet.
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FIGURE 9-17 Dive Profile.
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The Surface Decompression Table
Using Air (referred to as Sur D Air) should be used for surface decompression
following an air dive when a recompression chamber without an oxygen breathing
system is all that is available.
The total ascent times of the Surface Decompression Table Using Air exceed
those of the Standard Air Decompression Table; the only advantages surface
decompression using air are getting the divers out of the water sooner and maintaining
the divers in a controlled, closely observed environment during
decompression.
When using the Sur D Air table, all ascents are made at 30 fpm. This includes the
ascent rate from the last water stop. The time spent on the surface should not
exceed 3˝ minutes and the rate of descent to the first recompression chamber stop
should not exceed 60 fpm. The total elapsed time for these three procedures must
not exceed 5 minutes.
If the prescribed surface interval is exceeded and the divers are asymptomatic,
they are treated as if they had Type I Decompression Sickness (Treatment Table 5
or 1A, Chapter 21). If the divers are symptomatic, they are treated as if they had
Type II Decompression Sickness (Treatment Table 6 or 2A, Chapter 21), even if
they are only displaying Type I symptoms. Symptoms occurring during the
chamber stops are treated as recurrences (Chapter 21).
A dive is conducted to 123 fsw for 48 minutes using the Surface
Decompression Table Using Air. Determine the correct decompression schedule.
The correct decompression schedule for a dive conducted to 123 fsw for
48 minutes is the 130/50 schedule. The decompression chart is shown in Figure
9-18.
FIGURE 9-18 Dive Profile.
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If a second surface decompression air dive is planned within a
12-hour period, the same rule applies as for making a second Sur D O2 dive (paragraph
9-10.1.5).
A repetitive Sur D Air dive is planned for 138 fsw for 20 minutes. The
previous dive was to 167 fsw for 30 minutes. The surface interval was 4 hours 27
minutes. Determine the correct decompression schedules.
The correct schedule for the first dive is 180/30. The correct schedule
for the second dive is 180/50. As explained in the Sur D O2 procedure, the correct
procedure is to decompress the divers on a schedule for the maximum depth
attained and the total of bottom times of all dives made in the previous 12 hours.
Figure 9-19 illustrate the first dive, the repetitive dive worksheet is shown in
Figure 9-20 and the repetitive dive for the example above is shown in Figure 9-21.
FIGURE 9-19 Dive Profile.
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FIGURE 9-20 Completed Repetitive Dive Worksheet.
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FIGURE 9-21 Dive Profile.
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