Saturation decompression may be initiated by an upward excursion as long as the
excursion remains within the limits permitted by the Unlimited Duration Excursion
Tables. The alternative is to begin travel at the appropriate decompression
rate without the upward excursion. Decompression travel rates are found on Table
15-9.
TABLE 15-9 Saturation Decompression Rates.
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The minimum depth to which the upward excursion
may be made is found by entering Table 15-8 with the deepest depth attained by
any diver in the preceding 48 hours. The total upward excursion actually chosen is
determined by the Diving Officer and Master Diver, and approved by the
Commanding Officer, taking into consideration environmental factors, the diver’s
workload, and the diver’s physical condition.
The travel rate for the upward excursion is 2 fsw/min. Beginning
decompression with an upward excursion will save considerable time and may be
used whenever practical.
15-9.
Due to the increased risk of decompression sickness
following an upward excursion for dives with a storage depth of 200 fsw or less, a
2-hour post-excursion hold should be utilized. The 2-hour hold begins upon arrival
at upward excursion depth.
During decompression, traveling stops for a total of 8 hours out of
every 24 hours. The 8 hours should be divided into at least two periods known as “Rest Stops.” At what hours these rest stops occur are determined by the daily
routine and operations schedule. The 2-hour post-excursion hold may be considered
as one of the rest stops.
Table 15-9 shows saturation decompression
rates. In practice, saturation decompression is executed by decompressing the
DDC in 1-foot or 2-foot increments when indicated in the dive protocol. For
example, using a travel rate of 6 feet per hour will decompress the chamber 1 foot
every 10 minutes. The last decompression stop before surfacing may be taken at 4
fsw to ensure early surfacing does not occur and that gas flow to atmosphere
monitoring instruments remains adequate. This last stop would be 80 minutes,
followed by direct ascent to the surface at 1 fsw/min.
Traveling is conducted for 16 hours in each 24-hour period. A 16-hour daily
travel/rest outline example consistent with a normal day/night cycle is:
Daily Routine Schedule
2400–0600 Rest Stop
0600–1400 Travel
1400–1600 Rest Stop
1600–2400 Travel
This schedule minimizes travel when the divers are normally sleeping. Such a
daily routine is not, however, mandatory. Other 16-hour periods of travel per 24-
hour routines are acceptable, although they shall include at least two stop periods
dispersed throughout the 24-hour period and travel may continue while the divers
sleep. An example of an alternate schedule is:
Alternate Sample Schedule
2300–0500 Travel
0500–0700 Rest Stop
0700–0900 Travel
0900–1500 Rest Stop
1500–2300 Travel
The timing of the stop is dependent upon operational requirements. The travel rate
between stops should not exceed 1 fsw per minute.
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TABLE 15-9 Saturation Decompression Rates.
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As previously stated, the partial pressure
of oxygen in the chamber shall be maintained between 0.44 and 0.48 ata, with
two exceptions. The first is just before making the initial Upward Excursion and
the second during the terminal portion of saturation decompression. Approximately
1 hour before beginning an Upward Excursion, the chamber ppO2 may be
increased up to a maximum of 0.6 ata to ensure that the ppO2 after excursion does
not fall excessively. The ppO2 should be raised just enough so the post-excursion
ppO2 does not exceed 0.48 ata. However, when excursions begin from depths of 200 fsw or shallower, a pre-excursion ppO2 of 0.6 ata will result in a post-excursion
ppO2 of less than 0.44 ata. In these cases, the pre-excursion ppO2 should not
exceed 0.6 ata, but the post-excursion ppO2 should be increased as rapidly as
possible.
The second exception is at shallow chamber depth. As chamber depth decreases,
the fractional concentration of oxygen necessary to maintain a given partial pressure
increases. If the chamber ppO2 were maintained at 0.44–0.48 ata all the way
to the surface, the chamber oxygen percentage would rise to 44–48 percent.
Accordingly, for the terminal portion of saturation decompression, the allowable
oxygen percentage is between 19 and 23 percent. The maximum oxygen
percentage for the terminal portion of the decompression shall not exceed 23
percent, based upon fire-risk considerations.
If it is necessary to terminate a saturation dive
after exceeding the abort limits (see paragraph 15-20.4), standard saturation
decompression procedures shall be followed.
In exceptional cases it could be necessary to execute a
mission abort and not be able to adhere to standard saturation decompression
procedures. The emergency abort procedures should only be conducted for grave,
unforeseen casualties that require deviation from the standard decompression
procedures such as
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An unrepairable failure of key primary and related backup equipment in the
dive system that would prevent following standard decompression procedures.
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Unrepairable damage to the diving support vessel or diving support facility.
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A life-threatening medical emergency where the risk of not getting the patient
to a more specialized medical care facility outweighs the increased risk of pulmonary
oxygen toxicity and increased risk of decompression sickness
imposed upon the patient by not following standard saturation decompression
procedures.
An Emergency Abort Procedure was developed and has received limited testing. It
enables the divers to surface earlier than would be allowed normally. However,
the time saved may be insignificant to the total decompression time still required,
especially if the divers have been under pressure for 12 hours or more. In addition,
executing the Emergency Abort Procedure increases the diver’s risk for decompression
sickness and complications from pulmonary oxygen toxicity.
Before executing a mission abort procedure that does not follow standard decompression
procedures or the abort procedures contained in paragraph 15-20.4, the
Commanding Officer must carefully weigh the risk of the action, relying on the
advice and recommendations of the Master Diver, Diving Officer, and Saturation
Diving Medical Officer. Specifically, it must be determined if the time saved will
benefit the diver’s life despite the increased risks, and whether the Emergency
Abort Procedure can be supported logistically.
NOTE USN dive system design incorporates separate primary, secondary, and
treatment gas supplies and redundancy of key equipment. It is neither
the intent of this section nor a requirement that saturation dive systems
be configured with additional gas stores specifically dedicated to execution
of an emergency abort procedure. Augmentation gas supplies if
required will be gained by returning to port or receiving additional supplies
on site.
Except in situations where the nature or time sensitivity of the emergency does not
allow, technical and medical assistance should be sought from the Navy Experimental
Diving Unit prior to deviating from standard saturation decompression
procedures.
Emergency Abort Procedures should only be
conducted for grave casualties that are time critical. Decompression times and
chamber oxygen partial pressures for emergency aborts from helium-oxygen saturation
are shown in Table 15-10.
Emergency Abort decompression is begun by making the maximum Upward
Excursion allowed by Table 15-8. Rate of travel should not exceed 2 fsw/min. The
upward excursion includes a 2-hour hold at the upward excursion limit. Travel
time is included as part of the 2-hour hold. Following the Upward Excursion, the
chamber oxygen partial pressure is raised to the value shown in Table 15-10.
Decompression is begun in 1-foot increments using the times indicated in Table
15-10. Rate of travel between stops is not to exceed 1 fsw/min. Travel time is
included in the next stop time. The partial pressure of oxygen is controlled at the
value indicated until the chamber oxygen concentration reaches 23 percent. The
oxygen concentration is then controlled between 19 and 23 percent for the
remainder of the decompression. Stop travel at 4 fsw until total decompression
time has elapsed and then travel to the surface at 1 fsw/min.
For example, the maximum depth of the diver in the last 48 hours was 400 fsw,
and the Commanding Officer approves using the Emergency Abort Procedure.
From the Upward Excursion Table, the complex travels to 307 fsw at a rate not to
exceed 2 fsw/min. It takes 46.5 minutes to travel. This time is part of a 2-hour hold
requirement as part of the upward excursion for emergency aborts.
Because the post-excursion depth is between 273–1,000 fsw, the chamber oxygen
partial pressure is raised to 0.6 ata. Once the atmosphere is established and the
remainder of the 2-hour hold completed, begin decompression in 1-foot increments
with stop times of 12 minutes from 307 to 200 fsw. The travel rate between
stops should not exceed 1 fsw/min. Travel time is included in the stop time. It will
take 21.4 hours to arrive at 200 fsw.
At 200 fsw the 1-foot stop time changes to 21 minutes. It will take 70 hours to
reach the surface. The total decompression time is 93.4 hours (3 days, 21 hours, 21
minutes, 36 seconds). By contrast, standard saturation decompression would take
approximately 4 days and 3 hours to complete.
During and following the dive, the divers should be monitored closely for signs of
decompression sickness and for signs of pulmonary oxygen toxicity. The latter
includes burning chest pain and coughing. The divers should be kept under close
observation for at least 24 hours following the dive.
If the emergency ceases to exist during the decompression, hold for a minimum of
2 hours, revert to standard decompression rates, and allow the oxygen partial pressure
to fall to normal control values as divers consume the oxygen. Venting to
reduce the oxygen level is not necessary.
TABLE 15-10 Emergency Abort Decompression Times and Oxygen Partial Pressures.
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Decompression sickness may occur during a
saturation dive as a result of an Upward Excursion or as a result of standard saturation
decompression. The decompression sickness may manifest itself as
musculoskeletal pain (Type I) or as involvement of the central nervous system and
organs of special sense (Type II). Due to the subtleness of decompression sickness
pain, all divers should be questioned about symptoms when it is determined that
one diver is suffering from decompression sickness. For treatment, refer to Figure
15-9.
Type I Decompression Sickness may result
from an Upward Excursion or as the result of standard saturation decompression.
It is usually manifested as the gradual onset of musculoskeletal pain most often
involving the knee. Divers report that it begins as knee stiffness that is relieved by
motion but which increases to pain over a period of several hours. Care must be
taken to distinguish knee pain arising from compression arthralgia or injury
incurred during the dive from pain due to decompression sickness. This can
usually be done by obtaining a clear history of the onset of symptoms and their
progression. Pain or soreness present prior to decompression and unchanged after
ascent is unlikely to be decompression sickness. Type I Decompression Sickness
that occurs during an Upward Excursion or within 60 minutes immediately after
an Upward Excursion shall be treated in the same manner as Type II Decompression
Sickness, as it may herald the onset of more severe symptoms. Type I
Decompression Sickness occurring more than 60 minutes after an Upward Excursion
or during saturation decompression should be treated by recompressing in
increments of 5 fsw at 5 fsw/min until distinct improvement of symptoms is indicated.
Recompression of more than 30 fsw is usually unnecessary. Once treatment depth is reached, the stricken diver is given a treatment gas, by BIBS mask, with
an oxygen partial pressure between 1.5 and 2.8 ata. Interrupt treatment gas
breathing every 25 minutes with 5 minutes of breathing chamber atmosphere.
Divers should remain at treatment depth for at least 2 hours on treatment gas
following resolution of symptoms. Decompression can then be resumed using
standard saturation decompression rates. Further Upward Excursions are not
permitted.
Type II Decompression Sickness in saturation
diving most often occurs as a result of an Upward Excursion. The onset of symptoms
is usually rapid, occurring during the Upward Excursion or within the first
hour following an excursion ascent. Inner ear decompression sickness manifests
itself as nausea and vomiting, vertigo, loss of equilibrium, ringing in the ears and
hearing loss. Central nervous system (CNS) decompression sickness may present
itself as weakness, muscular paralysis, or loss of mental alertness and memory.
Type II Decompression Sickness resulting from an Upward Excursion is a medical
emergency and shall be treated by immediate recompression at 30 fsw/min to the
depth from which the Upward Excursion originated. When Type II Decompression
Sickness symptoms do not occur in association with an Upward Excursion,
compression at 5 fsw/min to the depth where distinct improvement is noted should
take place. Upon reaching treatment depth, symptoms usually begin to abate
rapidly. If symptoms are not significantly improved within 5 to 10 minutes at the
initial treatment depth, deeper recompression at the recommendation of a Saturation
Diving Medical Officer should be started until significant relief is obtained.
After reaching the final treatment depth, treatment gas having an oxygen partial
pressure of 1.5 to 2.8 ata shall be administered to the stricken diver for 25-minute
periods interspersed with 5 minutes of breathing chamber atmosphere. Treatment
gas shall be administered for at least 2 hours and the divers shall remain at the
final treatment depth for at least 12 hours following resolution of symptoms.
Decompression can then be resumed using standard saturation decompression
using rates shown in Table 15-9. Further Upward Excursions are not permitted.
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TABLE 15-9 Saturation Decompression Rates.
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