In surface-supplied mixed-gas diving, specific procedures are used in emergency
situations. The following paragraphs detail these procedures. Other medical/physiological
factors that surface-supplied mixed-gas divers need to consider are
covered in detail in Volume 5. The U.S. Navy Treatment Tables are also presented
in Volume 5.
In the rare instance of diver entrapment or
umbilical fouling, bottom times may exceed 120 minutes, the longest value shown
in the table. When it is foreseen that bottom time will exceed 120 minutes, immediately
contact the Navy Experimental Diving Unit for advice on which
decompression procedure to follow. If advice cannot be obtained in time:
1. Decompress the diver using the 120-minute schedule for the deepest depth
attained.
2. Surface the diver after completing 30 minutes on oxygen at 40 fsw.
3. Quickly recompress the diver to 60 fsw in the chamber.
4. Treat the diver on Treatment Table 6 (Figure 21-8).
Certain emergencies may interrupt or prevent required
decompression. Unexpected surfacing, exhausted gas supply and bodily injury are
examples of such emergencies. Table 14-5 shows the initial management steps to
be taken when the diver has uncontrolled ascent..
Blowup from a depth greater than 50
fsw when more than 60 minutes of decompression is missed is an extreme emergency.
The diver shall be returned as rapidly as possible to the full depth of the
dive or the deepest depth of which the chamber is capable, whichever is shallower.
For saturation systems, initial rapid compression on air
to 60 fsw, followed by compression on pure helium to the full depth of the dive (or
deeper if symptom onset warrants) is indicated. The diver shall breathe 84-percent
helium/16-percent oxygen by mask during the compression (if possible) to avoid
the possibility of hypoxia as a result of gas pocketing in the chamber. Once at the
saturation depth, the length of time spent can be dictated by the circumstances of
the diver, but should not be less than 2 hours. During this 2 hours, treatment gas
should be administered to the diver as outlined in Chapter 15, Chapter 15-23.8.2.
The chamber oxygen partial pressure should be allowed to fall passively to 0.44-
0.48 ata. Saturation decompression is begun without an upward excursion
For nonsaturation systems, the diver shall be
rapidly compressed on air to the depth of the dive or to 225 feet, whichever is shallower.
For compressions deeper than 165 feet, remain at depth for 30 minutes. For
compressions to 165 feet and shallower, remain at depth for a minimum of two
hours. Decompress on USN Treatment Table 8 for Deep Blowup (Table 14-6).
While deeper than 165 feet, a helium-oxygen mixture with 16-percent oxygen to
21-percent oxygen, if available, may be breathed by mask to reduce narcosis.
If the diver develops symptoms of decompression sickness or gas embolism
before recompression for omitted decompression can be accomplished, immediate
treatment using the appropriate oxygen or air recompression table is essential.
Guidance for table selection and use is given in Chapter 21. If the depth of the deepest stop omitted was greater than 50 fsw and more than 60 minutes of decompression
have been missed, use of Treatment Table 8 for Deep Blowup or
saturation treatment is indicated. On Treatment Tables 4 and 8, a 60-percent
helium/40-percent oxygen or 60-percent nitrogen/40-percent oxygen mixture may
be breathed as treatment gas at 165 fsw and shallower. At 60 fsw and shallower,
pure oxygen may be given to the diver as treatment gas. For all treatment gases
(HeO2, N2O2, and O2) a schedule of 25 minutes on gas and 5 minutes on chamber air should be followed for four cycles. Additional oxygen may be given at 60 fsw
and shallower after a 2-hour interval of chamber air. See USN Treatment Tables 4
and 7 (Chapter 21) for guidance on additional oxygen breathing.
In all cases of deep blowup, the services of a Diving Medical Officer shall be
sought at the earliest possible moment.
table 14-6 .U.S. Navy Treatment Table 8 for Deep Blowup.
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Dizziness is a common term used to
describe a number of feelings, including light-headedness, unsteadiness, vertigo (a
sense of spinning), or the feeling that one might pass out. There are a number of
potential causes of dizziness in surface-supplied diving, including hypoxia, a gas
supply contaminated with toxic gases such as methylchloroform, and trauma to the
inner ear caused by difficult clearing of the ear. At the low levels of oxygen
percentage specified for surface-supplied diving, oxygen toxicity is an unlikely
cause unless the wrong gas has been supplied to the diver.
The first step to take is to have the diver stop work and ventilate
the rig while topside checks the oxygen content of the supply gas. These actions
should eliminate hypoxia as a cause. If ventilation does not improve symptoms,
the cause may be a contaminated gas supply. Shift banks to the standby heliumoxygen
supply and continue ventilation. If the condition clears, isolate the contaminated
bank for future analysis and abort the dive on the standby gas supply. If the
entire gas supply is suspect, place the diver on the EGS and abort the dive. Follow
the guidance of paragraph 14-4.2 for ascents.
Vertigo due to inner ear problems will not respond to ventilation and in
fact may worsen. One form of vertigo, however, alternobaric vertigo, may be so
short-lived that it will disappear during ventilation. Alternobaric vertigo will
usually occur just as the diver arrives on the bottom and often can be related to a
difficult clearing of the ear. It would be unusual for alternobaric vertigo to occur
after the diver has been on the bottom for more than a few minutes. Longer lasting
vertigo due to inner ear barotrauma will not respond to ventilation and will be
accompanied by an intense sensation of spinning and marked nausea. Also, it is
usually accompanied by a history of difficult clearing during the descent. These
characteristic symptoms may allow the diagnosis to be made. A wide variety of
ordinary medical conditions may also lead to dizziness. These conditions may
occur while the diver is on the bottom. If symptoms of dizziness are not cleared by
ventilation and/or shifting to alternate gas supplies, have the dive partner or
standby diver assist the diver(s) and abort the dive.
An unconscious diver on the bottom constitutes
a serious emergency. Only general guidance can be given here. Management
decisions must be made on site, taking into account all known factors. The advice
of a Diving Medical Officer shall be obtained at the earliest possible moment.
If the diver becomes unconscious on the bottom:
1. Make sure that the breathing medium is adequate and that the diver is breathing.
2. Check the status of any other divers.
3. If there is any reason to suspect gas contamination, shift to the standby
helium-oxygen supply.
4. Have the dive partner or standby diver ventilate the afflicted diver to remove
accumulated carbon dioxide in the helmet and ensure the correct oxygen
concentration.
5. When ventilation is complete, have the dive partner or standby diver ascertain
whether the diver is breathing. In the MK 21, the presence or absence of breath
sounds will be audible over the intercom.
6. If the diver appears not to be breathing, the dive partner/standby diver should
attempt to reposition the diver’s head to open the airway. Airway obstruction
will be the most common reason why an unconscious diver fails to breathe.
7. Check afflicted diver for signs of consciousness:
-
If the diver has regained consciousness, allow a short period for stabilization
and then abort the dive.
-
If the diver appears not to be breathing, make further attempts to open
the airway while moving the diver rapidly to the stage.
8. Once the diver is on the stage, observe again briefly for the return of
consciousness.
-
If consciousness returns, allow a period for stabilization, then begin
decompression.
-
If consciousness does not return, bring the diver to the first decompression
stop at a rate of 30 fsw/min (or to the surface if the diver is in a nodecompression
status).
9. At the first decompression stop:
-
If consciousness returns, decompress the diver on the standard decompression
schedule using normal surface decompression.
-
If the diver remains unconscious but is breathing, decompress on the
standard decompression schedule and plan on emergency surface
decompression from 40 fsw. If consciousness returns during ascent, use
normal surface decompression.
-
If the diver remains unconscious and breathing cannot be detected in
spite of repeated attempts to position the head and open the airway, an extreme emergency exists. One must weigh the risk of catastrophic,
even fatal, decompression sickness if the diver is brought to the surface,
versus the risk of asphyxiation if the diver remains in the water.
As a general rule, if there is any doubt about the diver’s breathing
status, assume he is breathing and continue normal decompression in
the water. If it is absolutely certain that the diver is not breathing, leave
the unaffected diver at his first decompression stop to complete decompression
and surface the affected diver at 30 fsw/minute, deploying the
standby diver as required. Recompress immediately and treat for
omitted decompression according to Table 14-5.
table 14-5 . Management of Asymptomatic Omitted Decompression.
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Decompression sickness may develop in
the water during surface-supplied diving. This possibility is one of the prime
reasons for limiting dives to 300 fsw and allowing exceptional exposures only
under emergency circumstances. The symptoms of decompression sickness may
be joint pain or more serious manifestations such as numbness, loss of muscular
function, or vertigo.
Management of decompression sickness in the water will be difficult
under the best of circumstances. Only general guidance can be presented here.
Management decisions must be made on site taking into account all known
factors. The advice of a Diving Medical Officer shall be obtained at the earliest
possible moment.
If symptoms of decompression sickness occur deeper than
50 fsw, recompress the diver 10 fsw. Shift to a 60 percent helium/40 percent
oxygen mixture if the diver is not already on that mixture. Remain at the deeper
stop for 1.5 times the stop time called for in the decompression table. If no stop
time is indicated in the table, use the next shallower stop time to make the calculation.
If symptoms resolve or stabilize at an acceptable level, decompress the diver
to the 50 fsw water stop by multiplying each intervening stop time by 1.5 or more
as needed to control the symptoms. Shift to 100 percent oxygen at 50 fsw and take
the standard 50-fsw stop. Ascend to 40 fsw and take a 30-minute stop on oxygen,
then surface decompress and treat on Treatment Table 6. If during this scenario,
symptoms worsen to the point that it is no longer practical for the diver to remain
in the water, surface the diver and follow the guidelines for symptomatic omitted
decompression outlined in Chapter 21 of Volume 5.
Symptoms developing at the 50-fsw and 40-fsw oxygen
breathing stops can represent either decompression sickness or oxygen toxicity.
Oxygen toxicity will be a much more common occurrence. To avoid potential
error in diagnosis, all symptoms with the exception of joint pain shall initially be
considered oxygen toxicity and be treated accordingly. If the case is clearly
decompression sickness, remain at the stop. Resolution of symptoms may occur as
oxygen breathing continues.
If resolution occurs, resume the decompression, use
normal surface decompression and treat on Treatment Table 6. If symptoms are not resolved within 20 minutes at 50 fsw or within 30 minutes at 40 fsw, or have
worsened to the point it is no longer practical for the diver to remain in the water,
surface the diver and treat on Treatment Table 6. If symptoms originally thought
to be oxygen toxicity persist or worsen following an “up ten and shift” procedure
and are now felt to be decompression sickness, shift the diver to 100 percent
oxygen, recompress 10 fsw and repeat the missed stop. Follow the guidance for
resolution/nonresolution of symptoms as previously outlined.
Follow this procedure if the
umbilical helium-oxygen supply is lost on the bottom:
1. Shift the diver to the emergency gas system (EGS).
2. Unless the loss is momentary, abort the dive.
3. Remain on the EGS until arrival at the first water stop.
-
If the first water stop is an oxygen stop, shift to oxygen and complete
the decompression.
If the first stop is a helium-oxygen stop shallower than 160 fsw, shift to
air at the first stop and continue on the original decompression schedule
to 50 fsw.
-
If 60 percent helium/40 percent oxygen is available, upon reaching
100-fsw shift the divers to this mixture and continue on the original
decompression schedule to 50 fsw. Shift to oxygen at 50 fsw and complete
the decompression.
-
If the first stop is 160 fsw or deeper, delay the air shift to 150 fsw.
4. If the EGS becomes exhausted before the first stop can be reached, shift the
diver to air, ascend to the first stop and continue as outlined above.
If the
diver cannot be shifted to 60 percent helium/40 percent oxygen at 100 fsw during
decompression:
1. Shift the diver to air.
2. Follow the stops of the original decompression schedule to 50 fsw.
3. Shift to oxygen at 50 fsw and complete the decompression as originally
planned.
In the event that the diver cannot be shifted to
oxygen at 50 fsw or the oxygen supply is lost during the 50-fsw stop, take the
following action. If 60 percent helium/40 percent oxygen is available on the
console, shift the diver to that mixture. If 60 percent helium/40 percent oxygen is
not available, shift the diver to air. If the problem can be remedied quickly, reventilate
the diver with oxygen and resume the schedule at the point of interruption.
Consider any time on air or helium-oxygen as dead time. If the problem cannot be
remedied, keep the diver on air or helium-oxygen and use the Emergency Procedures
Decompression Table (Table 14-1) to complete the decompression. Any
time spent on oxygen at 50 fsw counts as decompression time on the Emergency
Procedures Decompression Table.
table 14-1 Emergency Procedures Decompression Table.
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If it is not possible to shift the diver back to 60 percent
helium/40 percent oxygen, or if the 60 percent helium/40 percent oxygen supply is
also lost during the subsequent decompression, shift the diver to air and complete
the dive using the Emergency Procedures Decompression Table. Any time spent
on oxygen or 60 percent helium/40 percent oxygen counts toward decompression
time on the Emergency Procedures Decompression Table.
The diver can be surface decompressed from the Emergency Procedures
Decompression Table when the 30-fsw in-water stop is completed. Surface the
diver at 30 fsw/minute and recompress in the chamber to 40 fsw. The time from
leaving 30 fsw in the water to arriving at 40 fsw in the chamber cannot exceed 5
minutes. The number of oxygen breathing periods in the chamber is determined
with the same method as for normal surface decompression on the original
schedule.
If the diver cannot be shifted to
oxygen at 40 fsw or the oxygen supply is lost during the 40-fsw stop, follow one
of the following procedures
If the loss occurs
before the diver is within emergency surface decompression limits, proceed as
follows:
1. If 60 percent helium/40 percent oxygen is available on the console, shift the
diver to that mixture.
2. If 60 percent helium/40 percent oxygen is not available, shift the diver to air.
3. If the loss of oxygen can be remedied quickly, reventilate the divers with oxygen
and resume the schedule at the point of interruption. Consider any time on
air or helium-oxygen as dead time.
4. If the loss of oxygen is permanent, have the divers remain on air or heliumoxygen
and use the Emergency Procedures Decompression Table to complete
the decompression. Time spent on oxygen at 40 fsw counts toward decompression
on the Emergency Procedures Decompression Table. Surface
decompression can be used after completing the 30-fsw stop.
If the diver is within Emergency SUR
D limits when the oxygen supply is lost, shift the diver to air, surface the diver,
and complete decompression in accordance with Emergency SUR D procedures.
If the diver is within Emergency SUR
D limits when the oxygen supply is lost, shift the diver to air, surface the diver,
and complete decompression in accordance with Emergency SUR D procedures.
If the loss occurs in the chamber, have the diver breathe
chamber air.
-
Temporary Loss. Return the diver to oxygen breathing. Consider any air time
as dead time.
-
Permanent Loss. Follow the Emergency Procedures Decompression Table to
the surface. Any time already spent on oxygen or air at 40 fsw counts toward
decompression time on the Emergency Procedures Decompression Table.
If the oxygen supply becomes
contaminated with helium-oxygen:
1. Shift the divers to helium-oxygen or air, whichever has the highest percentage
of oxygen.
2. Find the contamination source and correct the problem. Probable sources of
contamination include:
-
Accidental opening of the emergency gas supply (EGS) valve on the
MK 21 MOD 1
-
An improper valve line-up on the console.
3. When the problem is corrected:
-
Shift the divers back to oxygen.
-
Ventilate each diver and verify voice change.
— Ventilate each diver and listen for the gas-flow change over the
communications.
— Once a gas-flow change is heard, continue to vent for an additional
10 seconds. If a gas flow change cannot be heard, ventilate
for a minimum of 20 seconds.
-
Restart the stop time. Disregard all previous time spent at the stop, i.e.,
treat as dead time.
Follow this procedure if a diver exhibits CNS oxygen toxicity
symptoms at the 50-fsw stop:
1. Bring the divers up 10 feet and shift to air to reduce the partial pressure of oxygen.
Shift the console as the divers are traveling.
2. Upon reaching the 40-fsw stop, maintain communications as the buddy or
standby diver monitors the stricken diver.
3. Ventilate both divers (the stricken diver first).
4. SUR D after completing the 30-fsw stop on the Emergency Procedures
Decompression Table.
5.Disregard the missed time at 50 fsw.
6. If the diver convulses at 40 fsw in spite of these measures, follow the procedures
outlined in paragraph 14-4.9.
If symptoms appear
before the diver is within emergency surface decompression limits:
1. Ascend to the 30-fsw stop and shift to air.
2. Surface decompress after completing the 30-fsw stop on the Emergency Procedures
Decompression Table.
3. Disregard missed time at 40 fsw.
4. SIf the diver convulses at 30 fsw in spite of these measures, follow the procedures
outlined in paragraph 14-4.9.
If symptoms occur
after the diver is within emergency surface decompression limits, surface decompress
the diver using emergency SUR D procedures.
If symptoms occur after
the diver is within normal surface decompression limits, surface decompress the
diver using normal SUR D procedures.
If symptoms occur during the chamber stop:
1. Remove the mask.
2. Fifteen minutes after all symptoms have completely subsided, resume oxygen
breathing at the point of interruption.
3. Complete all required oxygen breathing time. If the diver cannot tolerate oxygen
at all, complete decompression on chamber air using the stops of the
Emergency Procedures Decompression Table. All previous time on oxygen
and air at 40 fsw in the chamber counts toward decompression when a shift to
this table is made.
If oxygen symptoms
advance to convulsions, or if the diver is presumed to be convulsing at the
50-fsw stop or 40-fsw stop, a serious emergency has developed. Only general
management guidelines can be presented here. Topside supervisory personnel
must take whatever action they deem necessary to bring the casualty under
control.
Follow these procedures when a diver is convulsing at the 50-fsw stop or the 40-
fsw stop:
1. Shift the divers to air.
2. Have the unaffected diver ventilate himself and then ventilate the stricken
diver.
3. Hold the divers at depth until the tonic-clonic phase of the sequence has subsided.
The tonic-clonic phase of a convulsion generally lasts 1 to 2 minute
4.If only one diver is in the water, launch the standby diver immediately and
have him ventilate the stricken diver.
5. If consciousness is quickly regained and voice communication reestablished,
the stricken diver may be tended by the standby diver or the buddy diver and
decompressed according to one of two options:
-
If the diver was eligible for emergency or normal surface decompression
prior to the seizure, allow a short period for stabilization and then
decompress using emergency or normal surface decompression
procedures.
-
If the diver was not eligible for emergency or normal surface decompression,
conduct decompression on the Emergency Procedures
Decompression Table. Surface decompress upon completing the 30 fsw
water stop.
6. If communication is not reestablished when the tonic-clonic phase is presumed
past, but conditions are such that the standby diver or the buddy diver can verify
that the affected diver is breathing and stable, conduct decompression on
the Emergency Procedures Decompression Table using surface decompression
upon completion of the 30 fsw water stop.
7. If it is not possible to verify that the affected diver is breathing because he cannot
be reached quickly enough or visibility will not permit an assessment, the
diver shall be surfaced at 40 fsw/min. In this situation, airway obstruction cannot
be ruled out and to remain at depth may be fatal. As the diver has 100
percent oxygen in his lungs prior to the seizure, approximately 2 minutes may
be allowed to lapse after the tonic-clonic phase ends before surfacing is initiated.
Although blood carbon dioxide will be high, oxygenation should be
adequate. The diver will almost certainly be unconscious and arterial gas
embolism cannot be ruled out. Such a diver should receive any necessary airway
support, be recompressed to 60 fsw immediately and be treated for
arterial gas embolism in accordance with Figure 21-5.
