Mixed Gas EP's

Question 1

BOTTOM TIME IN EXCESS OF THE TABLE

Answer 1

Bottom time will exceed 120 minutes, contact NEDU for advice.
If advice cannot be obtained:
1. Decompress using the 120 minute schedule for the deepest depth.

2. Shift to 100 percent oxygen at 40 fsw.
3. Complete 30 minutes on oxygen at 40 fsw Sur D.
4. Compress to 60 fsw in the chamber not to exceed 100 fsw/min.
5. Treat the diver on an extended Treatment Table 6.

Extend treatment table 6 for two oxygen breathing period at 60 fsw (20 minutes on O2 , 5 minutes on air, then 20 minutes on O2) and two oxygen breathing periods at 30 fsw (60 minutes on O2, 15 minutes on air, then 60 minutes on O2)

Question 2

LOSS OF HELIUM-OXYGEN SUPPLY ON THE BOTTOM

Answer 2

1. Shift to EGS.
2. Abort the dive.
3. Remain on EGS until arrival at 90 fsw.
4. At 90 fsw, shift to 50/50, complete decompression as planned.
   If EGS exhausted before 90 fsw, shift to air, complete decompression to 90 fsw, shift to 50/50 decompress as planned.

Question 3

LOSS OF 50/50 SUPPLY DURING IN WATER DECOMPRESSION

Answer 3

1. Shift to air continue decompression as planned while trying to correct the problem.
2. Shift to 50/50 once problem is corrected. Time on air counts toward decompression.
3. If problem cannot be corrected:
    Continue planned decompression on air.

 Shift from air to oxygen at 50 fsw stop.

 Breathe oxygen at 50 and 40 fsw for the decompression times indicated, but not to exceed 16 minutes at 50 fsw. Oxygen time at 50 fsw starts when divers are confirmed on oxygen.

 If the 50 fsw stop exceeds 16 minutes, travel to 40 fsw and add remaining 50 fsw stop time to the 40 fsw stop time on oxygen.

 Surface decompress following completion of 40 fsw stop.

Question 4

LOSS OF OXYGEN SUPPLY DURING IN-WATER DECOMPRESSION

Answer 4

1. Switch to 50/50. If switch to 50/50 not possible, switch to air.
2. If problem can be remedied quickly, reventilate with oxygen and resume the schedule at point of interruption. Any time on 50/50 or air as dead time.
3. If problem cannot be remedied, initiate surface decompression. Ignore time already spent on oxygen. The five minute surface interval begins upon leaving the 30 or 20 fsw stop.
4. If the problem cannot be remedied and surface decompression is not feasible, complete decompression on 50/50 or air.

For 50/50 double the remaining oxygen time at each water stop.

For air, triple the remaining oxygen time.

Question 5

LOSS OF OXYGEN SUPPLY IN THE CHAMBER DURING SURFACE DECOMPRESSION

Answer 5

1. Breathe chamber air.
2. Temporary Loss. Return to oxygen breathing. Any time on air is dead time.
3. Permanent Loss. Multiply remaining oxygen time by three to obtain equivalent chamber decompression time on air.
    if 50/50 is available multiply remaining oxygen time by two.
4. If loss occurred at 50 or 40 fsw allocate 10% to the 40 fsw stop, 20% to the 30 fsw stop and 70% to the 20 fsw stop.
   • If at 50 fsw ascend to 40 fsw then begin stop time.
5. If loss occurred at 30 fsw allocate 30% to the 30 fsw stop and 70% to the 20 fsw stop.
6. Round the stop times to the nearest whole minute.
7. Surface upon completion of the 20 fsw stop.

Question 6

DECOMPRESSION GAS SUPPLY CONTAMINATION

Answer 6

If the decompression gas supply becomes contaminated with bottom mix, 50/50, air, or oxygen:
1. Find the source of the contamination and correct. Probable sources include.
• Improper valve line-up on the console. This can be verified by checking O2 percentage on console oxygen analyzer.
• Accidental opening of the EGS valve.

2. When the problem is corrected.
   • Ventilate each diver for 20 seconds and confirm divers are on decompression gas.
   • Continue decompression as planned. DO NOT lengthen stop times to compensate for the time spent correcting the problem.

Question 7

CNS OXYGEN TOXICITY SYMPTOMS (NONCONVULSIVE) AT THE 90-60 FSW WATER STOPS

Answer 7

1. Up 10 feet and shift to air. Shift during travel.
2. Vent both divers at the shallower stop. Vent the stricken diver first.
3. Remain at shallower stop until missed time at previous stop is made up.
4. Resume planned decompression on air.
5. Upon arrival at next shallower stop, Back on 50/50. Ignore any 50/50 missed time.

Question 8

OXYGEN CONVULSION AT THE 90-60 FSW WATER STOP

Answer 8

If symptoms of oxygen toxicity progress to an oxygen convulsion at 90-60 fsw a serious emergency has developed. Topside supervisory personnel must take whatever action they deem necessary to bring the casualty under control.
1. Shift to air.

2. Have unaffected diver ventilate himself then vent the stricken diver.
    If only 1 diver is in the water, launch standby immediately and have him ventilate the stricken diver
3. Hold divers at depth until the tonic-clonic phase has subsided.
    The tonic-clonic phase generally lasts 1 to 2 minutes
4. At the end of tonic-clonic phase, ascertain whether the diver is breathing.
    The presence or absence of breath sounds will be audible over the comms.

If the affected diver is breathing, have the diver partner or standby diver tend the stricken diver and decompress both on air following the original schedule. Shift divers to 50/50 upon arrival at 50 fsw. Surface decompress upon completion of the 40 fsw stop.

If the affected diver appears not to be breathing, reposition the head to open the airway.
 Airway obstruction will be the most common reason why an unconscious diver fails to breathe.

If it is not possible to verify that the affected diver is breathing, leave the unaffected diver at the stop to complete decompression, and surface the affected diver and standby diver at 30 fsw/min.

5. Shift the unaffected diver back to 50/50 for completion of decompression. Standby should maintain an open airway on the stricken diver during ascent. On the surface the affected diver should receive any necessary airway support and be immediately recompressed and treated for arterial gas embolism and missed decompression.

Question 9

CNS TOXICITY SYMPTOMS (NONCONVULSIVE) AT 50 AND 40 FSW WATER STOPS

Answer 9

1. Up 10 feet and shift to air.
    Shift the console as the divers are traveling to the shallower stop
2. Vent both divers upon arrival at the shallower stop.
    Vent stricken diver first
3. Remain on air at the shallower depth for double the missed time from 50 and 40 fsw water stops, then surface decompress the diver.
    If on 100% oxygen triple the missed time from the 50 and 40 fsw stops, then surface decompress.
4. If surface decompression is not feasible, continue decompression in the water on either air or oxygen depending on the diver’s condition.

 To continue on oxygen, ascend to 30 fsw (or remain at 30 if already there)

 Take a 10 minute period on air
(time on air does not count toward decompression)
 Shift to oxygen and complete decompression in the water according to the schedule.

 Surface upon completion of the 20 fsw stop

 To continue on air, ascend to 30 fsw (or remain at 30 if already there)

 Compute the remaining 30 and 20 fsw air stop times by tripling the oxygen time given in the original schedule.

 Surface upon completion of the 20 fsw stop

Question 10

OXYGEN CONVULSION AT THE 50 – 40 FSW WATER STOP

Answer 10

1. Shift to air. Vent unaffected then stricken diver.
2. Stabilize the stricken diver and determine whether he is breathing. If the diver is breathing, hold him at current depth until stable, then:

 If the diver missed decompression time at 50 fsw, hold the diver at depth until the total elapsed time on air is at least double the missed time on helium-oxygen, then surface decompress.

 If the diver was on 100% oxygen remain at depth until the total elapsed time on air is at least triple the missed time on oxygen, then surface decompress.

 Add the 40 fsw water stop time to the 50 fsw chamber oxygen stop time.

 If the diver did not miss any decompression time at 50 fsw, surface decompress.

 Add any missed time at 40 fsw to the 50 fsw chamber oxygen period time.

3. If SurD is not feasible, complete decompression in the water on air.
    Compute the remaining stop times on air by doubling the remaining helium-oxygen time, or tripling the remaining oxygen time at each stop.
4. If the diver is not breathing, surface the diver at 30 fsw/min while maintaining an open airway. Treat the diver for arterial gas embolism.

Question 11

CNS OXYGEN TOXICITY SYMPTOMS (NONCONVULSIVE) AT 30 and 20 FSW WATER STOPS

Answer 11

If a recompression chamber is available on dive station.

1. Initiate surface decompression
2. Shift the console to air during travel to the surface
3. Once in the chamber, take the full number of chamber oxygen periods prescribed by the tables.
    No credit is allowed for time spent on oxygen in the water.

If a recompression chamber is not available on the dive station and the event occurs at 30 fsw.

1. Bring the divers up 10 fsw and shift to air
2. Shift the console as the divers are traveling to 20 fsw.
3. Ventilate both divers with air upon arrival at 20 fsw, ventilate the affected first.
4. Complete the decompression on air in the water at 20 fsw.
5. Compute the required air time at 20 fsw by tripling the sum of the missed oxygen time at 30 and 20 fsw.

If a recompression chamber is not available on the dive station and the event occurs at 20 fsw.

1. Shift the console to air
2. Ventilate both divers, affected diver first.
3. Complete the decompression in the water at 20 fsw on air.
4. Compute the required air time at 20 fsw by tripling the missed oxygen time at 20 fsw.

Question 12

OXYGEN CONVULSION AT THE 30 AND 20 FSW WATER STOPS

Answer 12

1. Shift both divers to air
2. Stabilize the affected diver and determine whether he is breathing.

 If the diver is breathing, hold him at depth until he is stable, then surface decompress.

 If surface decompression is not feasible, ventilate both divers with air and complete decompression in the water on air. Compute the remaining stop times on air by tripling the remaining oxygen time at each stop.

 If the diver is not breathing, surface the diver at 30 fsw/min while maintaining an open airway and treat the diver for arterial gas embolism.

Question 13

OXYGEN TOXICITY SYMPTOMS IN THE CHAMBER

Answer 13

At the first sign of CNS oxygen toxicity, remove from oxygen and breathe chamber air.

Fifteen minutes after all symptoms have completely subsided; resume oxygen breathing at the point of interruption.

If symptoms of CNS toxicity develop again or if the first symptom is a convulsion:

1. Remove the mask
2. After all symptoms have completely subsided, decompress 10 feet at 1 fsw/min
    for a convulsion, begin travel when the patient is fully relaxed and breathing normally
3. resume oxygen breathing at the shallower depth at the point of interruption
4. if another oxygen symptom occurs, complete decompression on chamber air.
    Follow the guidance given for permanent loss of chamber oxygen supply

Question 14

SURFACE INTERVAL GREATER THAN 5 MINUTES

Answer 14

1. If the surface interval is less than or equal to 7 minutes, add one-half oxygen period to the total number of chamber periods required by increasing the time on oxygen at 50 fsw from 15 to 30 minutes. Ascend to 40 fsw during the subsequent air break. The 15-min penalty is not an emergency procedure.
2. If the surface interval is greater than 7 minutes, continue compression to 60 fsw. Treat the divers on Treatment Table 5 if the original schedule required 2 or fewer periods. Treat on a Treatment Table 6 if the original schedule required 3 or more periods in the chamber.

Question 15

SAFE WAY OUT PROCEDURE

Answer 15

Begin oxygen breathing at the initially attained depth

If surface decompression was initiated while the diver was decompression on oxygen in the water at 20 fsw, attempt to gradually compress the diver to 20 fsw.

If surface decompression was initiated from deeper than 20 fsw, attempt to gradually compress the diver to 30 fsw.

In either case, double the number of chamber periods indicated and take these periods at the deepest depth the diver is able to attain. Oxygen time starts when the diver initially goes on oxygen.

Interrupt oxygen breathing every 60 minutes with a 15 min air break. The air break does not count toward the total oxygen time.

Surface the diver at 30 fsw/min upon completion of the oxygen breathing periods and carefully observe the diver for the onset of decompression sickness.

“Safe Way Out” is not intended to be used in place of normal surface decompression procedures.

Divers that experience ear difficulty on descent in the water column may not be good candidates for surface decompression.

Question 16

MANAGEMENT OF ASYMPTOMATIC OMITTED DECOMPRESSION:

NO Stops Omitted

Answer 16

Observe on surface for one hour

Question 17

MANAGEMENT OF ASYMPTOMATIC OMITTED DECOMPRESSION:

20 or 30 Foot stops missed
Surface Interval less than 1 minute

Answer 17

Return to depth of stop. Increase stop time by 1 min. Resume decompression according to original schedule

Question 18

MANAGEMENT OF ASYMPTOMATIC OMITTED DECOMPRESSION:

20 or 30 Foot stops missed
Surface Interval 1 - 7 minutes

Answer 18

Use Surface Decompression Procedure

Question 19

MANAGEMENT OF ASYMPTOMATIC OMITTED DECOMPRESSION:

20 or 30 Foot stops missed
Surface Interval greater than 7 minutes

Answer 19

Treatment Table 5 if 2 or fewer SurDO2 periods

Treatment Table 6 if 3 or more SurDO2 periods

Question 20

MANAGEMENT OF ASYMPTOMATIC OMITTED DECOMPRESSION:

40 or 50 Foot stops missed

Answer 20

Treatment Table 6

Question 21

MANAGEMENT OF ASYMPTOMATIC OMITTED DECOMPRESSION:

Deeper than 50 foot stops missed requiring less than 60 minutes of decompression

Answer 21

Treatment Table 6A

Question 22

MANAGEMENT OF ASYMPTOMATIC OMITTED DECOMPRESSION:

Deeper than 50 foot stops missed requiring more than 60 minutes of decompression

Answer 22

Compress to depth of dive not to exceed 225 fsw. Use Treatment Table 8

Question 23

OMITED DECOMPRESSION STOP DEEPER THAN 50 FSW

Answer 23

An omitted decompression stop deeper than 50 fsw when more than 60 minutes of decompression is missed is an extreme emergency.

The diver shall be rapidly compressed on air to the depth of the diver or 225 feet, whichever is shallower.

For compressions deeper than 165 feet, remain at depth for 30 minutes.

For compression to 165 feet and shallower, remain at depth for a minimum of two hours.

Decompress on USN Treatment Table 8.

While deeper than 165 feet, a helium-oxygen mixture of 16% percent to 21% oxygen, if available may be breathed by mask to reduce narcosis.

Question 24

SYMPTOMATIC OMITTED DECOMPRESSION

Answer 24

If the diver develops symptoms of decompression sickness or gas embolism before recompression for omitted decompression can be accomplished, immediate treatment using the appropriate table is essential.

If the depth of the deepest stop omitted was greater than 50 fsw and more than 60 minutes of decompression have been missed, use Treatment Table 8.

In all cases of deep blowup, the services of a Diving Medical Officer SHALL be sought at the earliest possible moment.

Question 25

LIGHT HEADED OR DIZZY DIVER ON THE BOTTOM

Answer 25

Initial Management:
1. Stop work and ventilate the rig while topside checks the oxygen content of the gas supply.

These actions should eliminate hypoxia and hypercapnia as the cause

2. If ventilation does not improve symptoms, the cause may be a contaminated gas supply. Shift to secondary and ventilate.

If condition clears isolate the contaminated bank and abort the dive

3. If the entire gas supply is suspect, place the diver on EGS and abort the dive.
4. Shift diver to 50/50 at 90 FSW and continue normal decompression.

Question 26

VERTIGO

Answer 26

Vertigo due to inner ear problems will not respond to ventilation and may worsen.

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.

Longer lasting vertigo due to inner ear barotraumas will not respond to ventilation and will be accompanied by an intense sensation of spinning and marked nausea.

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 and abort the dive.

Question 27

UNCONSCIOUS DIVER ON THE BOTTOM

Answer 27

An unconscious diver on the bottom constitutes a serious emergency

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 the breathing medium is adequate and that the diver is breathing. Verify manifold pressure and oxygen percentage.
2. Check the status of any other divers.
3. Have the dive partner or standby diver ventilate the afflicted diver to remove any accumulated carbon dioxide in the helmet and ensure the correct oxygen concentration.
4. If there is any reason to suspect gas contamination, shift to secondary and ventilate both divers, vent the unaffected diver first.
5. When ventilation is complete, have the dive partner or standby diver ascertain whether the diver is breathing. 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 divers head to open the airway.
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 remains unresponsive but is breathing, have the dive partner or standby diver move the afflicted diver to the stage. This action need not be rushed.

If the diver appears not to be breathing, maintain an open 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 no-decompression status).

9. At the first decompression stop:

If consciousness returns, decompress the diver on the standard decompression schedule using surface decompression.

If the diver remains unconscious but is breathing, decompress on the standard decompression schedule using surface decompression.

If the diver remains unconscious and breathing cannot be detected 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/min, deploy standby as required.

Recompress the diver immediately and treat for omitted decompression.

Question 28

DECOMPRESSION SICKNESS IN THE WATER DEEPER THAN 30 FEET

Answer 28

1. Recompress the diver 10 fsw. The diver may remain on 50% helium 50% oxygen during recompression from 90 to 100 fsw.
2. Remain at the deeper stop for 1.5 times the stop time.

If no stop time is indicated in the table, use the next shallower stop time

3. If symptoms resolve or stabilize to an acceptable level, decompress to the 40 fsw stop by multiplying each stop time by 1.5 or more as need to control the symptoms.

shift to 50/50 at 90 fsw if the diver is not already on this mixture

4. Shift to 100% oxygen at 40 and complete a 30 minute stop.
5. Surface decompress and treat on a Treatment Table 6.

If symptoms worsen to the point it is no longer practical for the diver to remain in the water, surface the diver and treat for decompression sickness.

Question 29

DECOMPRESSION SICKNESS IN THE WATER 30 FEET AND SHALLOWER

Answer 29

1. Remain on oxygen and recompress 10 fsw.
2. Remain at the deeper stop for 30 minutes.

 If symptoms resolve surface decompress and treat on Treatment Table 6

 If symptoms do not resolve decompress the diver to the surface on O2 by multiplying each stop time by 1.5, treat on Treatment Table 6.

If symptoms worsen to the point it is no longer practical for the diver to remain in the water, surface the diver and treat for decompression sickness.

Question 30

DECOMPRESSION SICKNESS DURING THE SURFACE INTERVAL

Answer 30

Compress the diver to 50 fsw, delay neuro until the diver reaches 50 fsw and is on oxygen.

1. If Type I symptoms resolve during the 15 min 50 fsw stop, the surface interval was 5 minutes or less, and no neurological signs are found. Increase the oxygen time at 50 fsw from 15 to 30 minutes then continue normal decompression.
2. If Type I symptoms do not resolve during the 15 minute 50 fsw stop or symptoms resolve but the surface interval was greater than 5 minutes, compress the diver to 60 FSW on oxygen.

 Treat on Treatment Table 5 if the original schedule required 2 or fewer oxygen periods in the chamber.

 Treat on Treatment Table 6 if the original schedule required 3 or more periods.

3. If Type II symptoms occur or the neurological examination at 50 fsw is abnormal:

 Compress to 60FSW on oxygen, Treat on Treatment Table 6 following the guidelines for treatment of Decompression Sickness.

4. If DCS symptoms appear while the diver is undergoing decompression at 50,40 or 30 fsw in the chamber,

TREAT AS A RECURRENCE.
Compress diver on oxygen to 60 FSW
Complete three 20 min. oxygen breathing periods at 60FSW
Reassess

Question 31

DELAY TO 1ST STOP.

Answer 31

Less than 1 minute ignore.

Greater than 1 minute, round up to next whole minute and add to bottom time. Recompute table and schedule.

Perform any missed stops at current depth.