MIXED gas Flashcards
What is the normal operational limit for surface supplied mixed gas diving?
300 fsw for 30 min.
What is the maximum working limit for surface supplied mixed gas diving?
380 fsw
When can you do exceptional exposure dives in mixed gas diving?
- CO’s discretion in an emergency
- Planned exceptional exposure dives require CNO approval
Is repetitive diving allowed in surface supplied helium-oxygen diving?
- No
- Yes, if the dive was aborted at 100fsw and shallower
How along after making a mixed gas decompression / no decompression dive, how long must a diver wait to make another dive?
No decompression: 12 hrs.
Decompression dive: 18 hrs.
How long of a break should a diver take after 4 consecutive days of mixed gas diving to avoid Pulmonary Oxygen Toxicity?
1 day break
How long must a diver wait to make an ascent to altitude following a mixed gas decompression/ no decompression dive?
Decompression: 24 hours
No decompression: 12 hours
What is the minimum personnel requirement on a mixed gas diving side?
1 Diver: 12 personnel
2 Divers: 14 Personnel
What positions on a surface supplied mixed gas dive side must be held by formally trained mixed gas divers?
- Diving officer
- Master diver
- Surface supplied Divers
What positions on a surface supplied mixed gas dive side shall be manned by formally trained surface supplied divers?
- Diver
- Standby diver
- Rack operator
- Console operator
- Time keeper / recorder
When can the Master Diver fill the position of the Diving Officer?
-If designated in writing by the Commanding Officer; however, he may not serve in more than one position.
Is a Diving Officer required on station for all mixed gas dives?
-No; when conducting no-decompression dives for training a Diving Officer is not required
What should be set-up when diving mixed gas in water below 40 degrees Fahrenheit as life support consideration?
Two water heaters to supply a common manifold that allows shifting between a primary and a backup water heater (salvage air manifold works well).
When should a diver who has been exposed to adverse environmental conditions be considered for mixed gas diving?
Not until normal core temperature has returned
What does fatigue predispose a diver to?
- Decompression Sickness
- Not being mentally alert
The Diving Supervisor must ensure that all mixed gas divers have slept how many hours within the last 24 hours before diving?
-8 Hours
What are the 4 gas mixtures used in mixed gas diving, and at what depths?
- Bottom Mix: 90% helium 10% oxygen or 60% helium 40% oxygen
- 50/50 (Helium /Oxygen mix): Used from 90 to 40fsw during decompression. Oxygen concentration ranges from 49% to 51%
- 100% Oxygen: Used at 30/20fsw for in water decompression. 50/40/30fsw for Sur “d” O2
- Air: Used in emergencies and to give air breaks
The FADS III Mixed Gas System (FMGS) is a portable, self-contained, surface supplied diver life support system designed to support mixed gas dive missions to what depth?
300fsw
The FMGS consists of what five gas rack assemblies?
- (1) Air Supply Rack Assembly (ASRA)
- (1) Oxygen Supply Rack Assembly (OSRA)
- (3) Helium-Oxygen Supply Rack Assemblies (HOSRA)
The FMGS consists of what other components in addition to the gas rack assemblies?
- 5000 psi air compressor assembly
- Mixed Gas Control Console Assembly (MGCCA)
- (2) Gas Boosters
Set-up and operating procedures for the FMGS are found in what publication?
-Operating and Maintenance Technical Manual for Fly Away Dive System (FADS) III Mixed Gas System: S9592-B2-OMI-010.
How must Helium-Oxygen mixtures be analyzed for oxygen content?
-Instrument having an accuracy of +/- 0.5 percent
What will be the EGS gas mixture during mixed gas diving operations?
-Same as the bottom mixture unless the bottom mixture contains less than 16 percent
If the bottom mixture has less than 16% oxygen, what is the allowable range of the EGS oxygen content?
-15 to 17 percent
What is the maximum PPO2 allowed in mixed gas diving operations?
1.3 ata PPO2
What is the minimum allowable oxygen content in a mixture for dives up to 200 fsw and in excess of 200 fsw?
- 14% : 200FT. and shallower
- 10% : Excess of 200FT.
During a mixed gas decompression dive what breathing gas will the diver breathe at certain depths?
- Bottom mix: 91ft and deeper
- 50/50: 90ft to 40 ft
- 100% oxygen: 30ft and shallower
Why is diving with a mixture near maximum oxygen percentage encouraged?
It offers a decompression advantage to the diver
During a mixed gas decompression dive what gas will a diver surface on if a Sur “D” O2 is elected?
-50/50
At what depth in the water column does a diver start breathing a gas mixture with less than 16% oxygen content?
-20 FSW
How long do you ventilate divers at 20 fsw when switching to mixed gas?
- 20 seconds
If diving a gas mixture with less than 16% oxygen content, how long does a diver have to descent to 20 fsw and shift to bottom mix and perform equipment checks?
- 5 minutes
When does the bottom time start when a diver is breathing a gas with less than 16% oxygen content?
- When diver has been at 20 fsw for 5 minutes or more
- When diver leaves 20 fsw
What is required if a diver is at 20ft on bottom mix and a problem that requires you to surface the divers occur?
- Shift the diver back to air
- When diver re-enters the water, bottom time starts over along with the 5 minute grace period.
What actions are required when aborting a mixed gas dive shallower than 100 fsw with less than/greater than 16% oxygen content?
- Less than: ascend to 20 fsw, shift diver to air, complete ascent to the surface
- Greater than: ascend directly to the surface at 30 fsw/min
What is required if another dive is desired following a dive aborted 100 fsw and shallower?
- Add bottom time of all dives to the bottom time of the new dive
- Use the deepest depth when calculating the table and schedule for the new dive
What actions are required when aborting a mixed gas deeper than 100 fsw?
- Follow normal decompression schedule to the surface
Is a repetitive dive allowed if aborting a dive deeper than 100 fsw?
- No
What dives require a shift to 50/50 at 90 fsw?
- Mixed gas decompression dives only
If conducting a mixed gas decompression dive, when will you shift the divers to 50/50 if there is no 90 fsw decompression stop?
- You will shift to 50/50 at 90 fsw
- The next shallower stop you will vent the divers
On mixed gas decompression dives when shifting to 50/50, is the shift time included in the stop time?
- Yes
When is it required to shift the divers to 100% oxygen at the 30 fsw stop?
- All in water decompression dives
When shifting to 100% oxygen at 30 fsw, what is an indication that the diver is on oxygen instead of bottom mix?
- Voice change
Does an air break count toward a diver’s decompression time?
- No
Do you have to ventilate the divers with oxygen following a 5 minute air break?
- No
When is a 5 minute air break not required when breathing 100% oxygen?
- If the total oxygen time is :35 or less
- If the final oxygen period is :35 or less
Is the use of an inside tender required when conducting Sur D O2 diving operations?
- It is at the discretion of the diving supervisor
Where are O2 periods 5, 6 and 7 spent in the chamber?
- 30 fsw
What actions are taken if a diver arrives early at his first decompression stop and it requires a gas shift?
- Initiate the gas shift and ventilation upon arrival at the stop.
- Begin the stop time only when the required travel time has been completed.
What are the required actions if you have a delay greater than a minute on ascent to the first decompression stop?
- Add delay to BT; Recomputed table and schedule
- If a new schedule is required pick it up at current or subsequent stop
- Fulfill any deeper decompression requirements at the diver’s current depth.
What are the required actions when you have a delay greater than a minute deeper than 90 fsw on mixed gas?
- Add delay to BT; Recomputed table and schedule
- If a new schedule is required pick it up at current or subsequent stop
- Ignore any deeper decompression
What are the required actions when you have a delay greater than a minute shallower than 90 fsw on mixed gas?
- No special action required
- Resume normal decompression at the completion of the delay
- If delay occurred between stops, restart subsequent stop time at completion of delay.
If a delay greater than 5 minutes occur between 90 and 70 feet on mixed gas what are the required actions?
- Shift to air to avoid CNS O2 toxicity
- Shift back to 50/50 after completion of delay
- Add the time on air to the bottom time
- Recalculate the required decompression
- If new schedule is required pick it up at current or subsequent stop
- Ignore any deeper decompression
What is the maximum allowed bottom time on all mixed gas dives?
- 120 minutes
What are the required actions if a diver is in excess of the table on a mixed gas dive and EDU cannot be contacted?
- Decompress using 120 min schedule for the deepest depth obtained
- Shift to oxygen at 40 fsw
- Surface decompress after competing 30 min of O2 @ 40 ft
- Complete Treatment table 6 w/ max extensions at 60 and 30 ft.
What are the required actions if Primary helium-oxygen supply is lost on the bottom?
- Shift to secondary bottom mix (if available)
- Shift the diver to EGS ( if no secondary supply is available)
- Abort dive
- Remain on EGS until arrival at 90 fsw
- Shift to 50/50 at 90 fsw
- Complete decompression as planned
What is done if the EGS becomes exhausted before 90 fsw is reached?
- Shift to air
- Continue decompression on air
- Shift to 50/50 upon arrival at 90fsw
What actions will you take if you cannot shift at 90 fsw or 50/50 is lost during decompression?
- Continue decompression on air
- Shift to 50/50 once corrected
- Time on air counts toward decompression
- Continue decompression as normal
What actions are taken if 50/50 cannot be restored?
- Continue decompression on air
- At 50 fsw shift to 100% O2
- Do not spend more than :16 at 50 fsw
- After completing your 40ft. stop, surface decompress
What actions are taken if the oxygen stop time at 50 fsw exceeds 16 minutes?
- Bring divers to 40 fsw
- Add remaining oxygen time at 50 fsw to the 40 fsw stop time
What action is taken if 100% O2 is lost at your 20/30fsw decompression stop and the problem can be quickly remedied?
- Switch to 50/50 or air
- Re-ventilate Divers with oxygen once it is restored
- Resume schedule at point of interruption
- Any time spent on 50/50 or air is counted as dead time
What actions are taken if 100% O2 is lost at your 20/30fsw decompression stop, oxygen cannot be restored and a chamber is available?
- Switch to 50/50 or air
- Initiate surface decompression
What actions are taken if oxygen is lost at your 20/30fsw decompression stop, it cannot be restored and a chamber is not available?
- Shift the Divers to 50/50
- Shift to air if 50/50 is not available
What is done to the remaining oxygen stop time if decompressing on 50/50 or air?
- 50/50: Double the time at each stop
- Air: Triple the time at each stop
What is done for a temporary loss of oxygen is the chamber during a Sur D O2?
- Have divers breathe chamber air
- Return divers to oxygen breathing once it is restored
- Consider any time on air as dead time
What are your actions if oxygen is lost in the chamber at 40/50 fsw?
- Ascend to 40 fsw in the chamber
- Multiply remaining oxygen time by 2 if 50/50 is available
- Multiply remaining oxygen time by 3 if finishing decompression on air
- Fulfill 10% at 40 fsw, 20% at 30 fsw, and 70% at 20 fsw
How do you allocate the required 50/50 or air time if oxygen is lost in the chamber at 30 fsw?
- Do 30% at 30 fsw, and 70% at 20 fsw
What are some possible sources of decompression gas contamination?
- Improper valve line-up
- Accidental opening of the EGS valve
What is the primary way you can verify whether you have an improper valve lin-up?
- By checking the oxygen percentage on the console Analox
What happens if your decompression gas is contaminated with bottom mix, 50/50, air of oxygen?
- Find the source of contamination
- Correct the problem
- Ventilate each diver for 20 seconds
- Confirm Divers are on bottom mix
- Continue decompression
- No lengthening is required
What actions are taken if a diver has CNS O2 toxicity symptoms at the 90-60 fsw water stops?
- Bring divers up 10 fsw
- Shift to air while traveling
- Have both divers ventilate for 20 seconds (stricken diver first)
- Remain at the shallower depth on air until all decompression time has been fulfilled from the previous and current depth
- Resume decompression on air
- Shift back to 50/50 at the next shallower stop
What actions are taken for an oxygen convulsion at the 90-60 fsw water stop?
- Shift to air
- Ventilate both Divers ( un-stricken then the stricken Diver)
- Launch standby if a single diver is in the water
- Hold at current depth until the tonic-clonic phase of the convulsion has subsided
- Check the stricken diver for breathing
Breathing
- Decompress the divers on air following the original schedule
- Shift to 50/50 once at 50 fsw
- Surface decompress upon completion of the 40 fsw stop
Can’t determine if the diver is breathing
- Have the un-stricken diver or standby diver maintain an open airway
- Surface standby Diver and the stricken diver @ 30 fpm
- Have the un-stricken diver complete decompression in the water
- Shift the unaffected diver back to 50/50 to finish decompression
Why is it important to maintain an open air on a Diver that appears not to be breathing?
- Air way obstruction is the most common reason why an unconscious Diver fails to breath.
What diver ventilates first following a CNS O2 toxicity convulsion?
- The unaffected diver
What should be evaluated after the tonic-clonic phase of a convulsion?
- Breathing
How long does the tonic clonic phase of a convulsion last?
- 1 to 2 minutes
When are you going to put divers that are experiencing a convulsive/non-convulsive CNS 02 hit at 90-60fsw back on 50/50?
- Non-convulsive: Next shallower depth
- Convulsive: 50 fsw
What actions are taken for a non-convulsive CNS O2 symptom at the 50/40fsw stop while breathing 50/50 or oxygen?
- Bring the divers up 10 ft
- Shift to air while traveling
- Ventilate both Divers (stricken then unstricken Diver)
- Double the decompression the missed time form the 50/40 fsw water stops if you were on 50/50
- Triple the decompression the missed time form the 50/40 fsw water stops if you were on 100% oxygen
- Surface Decompress
What actions are taken for a CNS O2 toxicity symptom at the 50/40 fsw stop when surface decompression is not feasible and in water decompression on oxygen is elected?
- Ascend to 30 fsw (stay if already there)
- Take a 10 min air break ( time on air does not count toward decompression)
- Shift to oxygen
- Complete decompression according to the schedule
What actions are taken for a CNS O2 toxicity symptom at the 50/40 fsw stop when surface decompression is not feasible and in water decompression on air is elected?
- Ascend to 30 fsw
- Compute air stop time by Tripling the required oxygen times required
What actions are taken for a CNS O2 toxicity symptom at the 50/40 fsw stop when surface decompression is not feasible and in water decompression on air and oxygen is elected?
- Ascend to 30 fsw (stay if already there)
- Compute air stop time by multiplying the 30 fsw oxygen time by 3
- Shift to oxygen at the 20 fsw stop
- Complete original 20 fsw stop on oxygen
What actions are taken if an oxygen convulsion occurs at the 50 fsw water stop and the diver is breathing?
- Shift to air
- Deploy standby if a single diver is in the water
- Vent divers ( unstricken then the stricken diver)
- Hold divers at current depth until the tonic-clonic phase of the convulsion has subsided
- If Divers were breathing 50/50 double any missed time
- If the divers were breathing oxygen triple any missed time
- Surface decompress
- Add the 40 fsw stop time in the water to the 50 fsw chamber stop time
What is done differently is the convulsion happened at 40 fsw instead of 50 fsw?
- Surface decompress the divers immediately
- Add the missed decompression time at 40 fsw to the 50 fsw chamber stop
What do you treat an unconscious diver that is not breathing for upon surfacing?
- AGE
- Omitted Decompression
What is done if a chamber is available and a diver experiences a CNS O2 toxicity symptom at the 30/20 fsw stop?
- Sift to air
- Surface decompress
What do you do to the diver’s decompression time if he experiences a CNS O2 symptom at the 30 fsw stop and a chamber is not available?
- Bring divers up 10 fsw while shifting to air
- Ventilate both divers at 20 fsw ( stricken then un-stricken Diver)
- Triple the missed 30 fsw and 20 fsw stop time
What do you do to the diver’s decompression time if he experiences a CNS O2 symptom/convulsion at the 20 fsw stop and a chamber is not available?
- Shift to air
- Ventilate both Divers ( Stricken Diver then un-stricken Diver)
- Multiple the remaining oxygen time by 3
What actions are taken for an oxygen convulsion at 30-20 fsw water stop?
- Shift to air
- Ventilate Divers (un-stricken then stricken)
- Hold diver at depth until the end of the tonic-clonic phase
- Check for breathing and stabilize the stricken diver
- Surface decompress
What actions are taken if a diver is not breathing following an oxygen convulsion?
- Maintain an open airway
- Surface the diver at 30 fsw a minute
- Treat for AGE
Do you take the full prescribed chamber O2 periods if oxygen is lost while decompressing in the water during a mixed gas dive?
- Yes
What is done in the chamber if a diver cannot breathe oxygen due to CNS O2 toxicity?
- Have the diver breathe chamber air
- If at 50 fsw in the chamber ascend to 40 fsw
- Multiply remaining oxygen stop time by three
- Allocate 10% to the 40 fsw stop time, 20 % to the 30 fsw stop time, and 70% to the 20 fsw stop time
Can you breathe 50/50 in the chamber if a diver cannot breathe oxygen due to CNS O2 toxicity?
- No
What is the penalty if a diver has a surface interval of greater than 7 minutes on a mixed gas surface decompression dive?
- TT5 if 2 or fewer oxygen periods were required
- TT6 if 3 or more oxygen periods were required
Is a repetitive dive allowed following a dive in which the safe way out procedure is used?
- No
What is required if a diver has asymptomatic decompression and omitted a stop between 40 and 50 fsw?
- TT6
What is required if a diver has asymptomatic decompression and missed less than/more than 60 min. of decompression at depths greater than 50 fsw?
- Less than: TT6A
- More than: compress to depth of relief not exceed 225fsw
What procedure is used when a non-saturation dive systems is used to treat a diver that has omitted a decompression stop deeper than 50 fsw where more than 60 minutes of decompression are missed?
- Compress to depth of dive or 225fsw (whichever is shallower)
- Stay at depth for 30 min (deeper than 165) and 2 hours minimum (shallower than 165)
- Decompress using TT8
What kind of treatment gas is breathed at depths greater than 165 fsw in the chamber?
- Deeper than 165 an HE-O2 mix w/ 16-21% oxygen may be used to reduce nitrogen narcosis
Saturation dive systems:
- Compress to 60ft on air
- Compress on full helium and to depth of dive or depth of relief if needed
- Diver shall breath 84% helium and 16% oxygen during compression to avoid hypoxia
- No less than 2 hours at depth
- PPO2 should be allowed to fall passively to 0.44-0.48 ataBegin saturation decompression without an upward excursion
What treatment table is used for omitted decompression occurred deeper than 50 fsw and more 60 minutes of decompression missed?
- TT8
What are some causes of a diver being dizzy or light headed on the bottom during a mixed gas dive?
- Hypoxia
- Gas supply contamination
- Trauma to the inner ear due to difficulty clearing
What actions are taken to manage a dizzy or light headed diver on the bottom during a mixed gas dive?
- Stop work and ventilate
- Topside needs to check oxygen content of gas via the Analox
- If ventilation does improve symptoms switch to your secondary bottom mix
- Continue ventilation
- If entire gas supply is suspect, place the Divers on EGS
- Abort the dive
What will vertigo due to inner ear problems not respond to?
- Ventilation
- May worsen the problem
What kind of vertigo responds to ventilation and when does it occur?
- Alternobaric Vertigo
- Just as the diver arrives on bottom
What is the first thing you do if you have an unconscious diver on the bottom?
- Make sure the breathing medium is adequate and the diver is breathing
- Verify manifold pressure and oxygen content
Why do you want to ventilate an unconscious diver?
- To remove any accumulated CO2 in the helmet
What are your actions if you cannot determine whether a diver is breathing at depth on a decompression dive?
- Assume he is breathing and continue with normal decompression
What are your actions if you know a diver is not breathing during a decompression dive?
- Diver will fulfill his first decompression stop and then surface at 30fsw/min
- Recompress immediately and treat for omitted decompression
What actions are taken if decompression sickness occurs on a mixed gas dive deeper than 30 fsw?
- Recompress 10 fsw
- Remain on 50/50 during recompression
- Remain at deeper stop for 1.5 times the decompression table called for (if no stop time was indicated use the next shallower stop time)
- Decompress to 40 fsw by multiplying each stop in-between by 1.5 or more if needed to control the symptoms
- Shift to 100% oxygen at 40 fsw
- Complete a :30 stop at 40 fsw
- Surface decompress after completion of :30 stop at 40 fsw
- Treat on TT6
What actions are taken if decompression sickness occurs on a mixed gas dive at 30 fsw or shallower?
- Remain on oxygen
- Recompress 10 fsw
- Remain at depth for :30
- Surface decompress
- Treat on TT6
What is done if the diver’s symptoms do not resolve after 30 minutes at the deeper depth?
- Decompress the diver on oxygen
- Multiply the intervening stop times by 1.5 or more as needed to control the symptoms
- Treat on TT6 once on the surface
How long do type 1 symptoms have to resolve at 50 fsw in the chamber to avoid a treatment?
- 15 minutes
- Neuro has to be normal
Can you do mixed gas diving at altitude?
- Yes
How long do you have to wait once at altitude to make a mixed gas dive?
- 12 hours
Are minimum and maximum oxygen percentages adjusted for mixed gas diving at altitude?
- No
- Use actual depth not the sea level equivalent depth
Are chamber stop depths adjusted when performing a surface decompression for a mixed gas dive at altitude?
- No
