Navy Diving Manual Rev 6 Chapter 9 Air Decompression

Front 1

Deviations from established decompression procedures are not permitted except in an emergency and with the guidance and recommendation of _________________________ and with the approval of ___________________________________

Back 1

Diving Medical Officer (DMO), Commanding Officer or Officer-in-Charge

Front 2

What is descent time?

Back 2

The total elapsed time from the time the diver leaves the surface to the time he reaches the bottom. Descent time is rounded up to the next whole minute for charting purposes.

Front 3

What is bottom time?

Back 3

The total elapsed time from the time the diver leaves the surface to the time he leaves the bottom. Bottom time is measured in minutes and is rounded up to the next whole minute.

Front 4

What is total decompression time?

Back 4

The total elapsed time from the time the diver leaves the bottom to the time he arrives on the surface. This time is also frequently called the total ascent time. The two terms are synonymous and can be used interchangeably.

Front 5

What is total time of dive?

Back 5

The total elapsed time from the time the diver leaves the surface to the time he arrives back on the surface.

Front 6

What is deepest depth?

Back 6

The deepest depth recorded on the depth gauge during a dive.

Front 7

What is maximum depth?

Back 7

The deepest depth obtained by the diver after correction of the depth gauge reading for error. When conducting SCUBA operations, the diver’s depth gauge is considered error free. The diver’s maximum depth is the deepest depth gauge reading. When conducting surface-supplied diving operations using a pneumofathometer to measure depth, maximum depth is the deepest reading on the pneumofathometer gauge plus the pneumofathometer correction factor (Table 9-1). Maximum depth is the depth used to enter the decompression tables.

Front 8

What is stage depth?

Back 8

The pneumofathometer reading taken when the divers are on the stage just prior to leaving the bottom. Stage depth is used to compute the distance and travel time to the first stop, or to the surface if no stops are required.

Front 9

What is a decompression table?

Back 9

A structured set of decompression schedules, or limits, usually organized in order of increasing bottom times and depths.

Front 10

What is a decompression schedule?

Back 10

A specific decompression procedure for a given combination of depth and bottom time as listed in a decompression table. It is normally indicated as feet/minutes.

Front 11

What is a decompression stop?

Back 11

A specified depth where a diver must remain for a specified length of time (stop time) during ascent.

Front 12

What is No-Decompression (No “D”) Limit?

Back 12

The maximum time a diver can spend at a given depth and still ascend directly to the surface at the prescribed travel rate without taking decompression stops.

Front 13

What is a No-Decompression Dive?

Back 13

A dive that does not require a diver to take decompression stops during ascent to the surface.

Front 14

What is a Decompression Dive?

Back 14

A dive that does require a diver to take decompression stops during ascent to the surface.

Front 15

What is Surface Interval?

Back 15

In the context of repetitive diving, the surface interval is the time a diver spends on the surface between dives. It begins as soon as the diver surfaces and ends as soon as he starts his next descent. In the context of surface decompression, the surface interval is the total elapsed time from when the diver leaves the 40 fsw water stop to the time he arrives at 50 fsw in the recompression chamber.

Front 16

What is Residual Nitrogen?

Back 16

Residual nitrogen is the excess nitrogen gas still dissolved in a diver’s tissues after surfacing. This excess nitrogen is gradually eliminated during the surface interval. If a second dive is performed before all the residual nitrogen has been eliminated, the residual nitrogen must be considered in computing the decompression requirements of the second dive.

Front 17

What is a Single Dive?

Back 17

A single dive is any dive conducted after all the residual nitrogen from prior dives has been eliminated from the tissues.

Front 18

What is a Repetitive Dive?

Back 18

A repetitive dive is any dive conducted while the diver still has some residual nitrogen in his tissues from a prior dive.

Front 19

What is a Repetitive Group Designator?

Back 19

The repetitive group designator is a letter used to indicate the amount of residual nitrogen remaining in the diver’s body following a previous dive.

Front 20

What is Residual Nitrogen Time?

Back 20

Residual nitrogen time is the time that must be added to the bottom time of a repetitive dive to compensate for the nitrogen still in solution in a diver’s tissues from a previous dive. Residual nitrogen time is expressed in minutes.

Front 21

What is an Equivalent Single Dive?

Back 21

A repetitive dive is converted to its single dive equivalent before entering the decompression tables to determine the decompression requirement. The depth of the equivalent single dive is equal to the depth of the repetitive dive. The bottom time of the equivalent single dive is equal to the sum of the residual nitrogen time and the actual bottom time of the repetitive dive.

Front 22

What is Equivalent Single Dive Time?

Back 22

The equivalent single dive time is the sum of the residual nitrogen time and the bottom time of a repetitive dive. Equivalent single dive time is used to select the decompression schedule for a repetitive dive. This time is expressed in minutes.

Front 23

What is Surface Decompression?

Back 23

Surface decompression is a technique where some of the decompression stops in the water are skipped. These stops are made up by compressing the diver back to depth in a recompression chamber on the surface.

Front 24

What is an Exceptional Exposure Dive?

Back 24

An exceptional exposure dive is one in which the risk of decompression sickness, oxygen toxicity, and/or exposure to the elements is substantially greater than on a normal working dive. Planned exceptional exposure dives require CNO approval.

Front 25

What are the six tables used to perform the full spectrum of air dives?

Back 25

1. No-Decompression Limits and Repetitive Group Designation Table for No-Decompression Air Dives. This Table gives the no-decompression limits and the repetitive group designators for dives that do not require decompression stops.
2. Air Decompression Table. This Table gives the decompression schedules and repetitive group designators for dives that require decompression stops.
3. Residual Nitrogen Timetable for Repetitive Air Dives. This Table allows the diver to determine his Residual Nitrogen Time when performing a repetitive dive.
4. Sea Level Equivalent Depth Table. This Table allows the diver to correct the sea level decompression tables for use at altitude.
5. Repetitive Groups Associated with Initial Ascent to Altitude Table. This Table allows the diver to adjust his decompression if he is not fully equilibrated at altitude.
6. Required Surface Interval Before Ascent to Altitude After Diving. This Table tells the diver when it is safe to fly or ascend to higher altitude after a dive.

Front 26

Where should the pneumofathometer be located on a diver?

Back 26

At mid-chest level

Front 27

What are the pneumofathometer correction factors?

Back 27

0-100 fsw = +1 fsw
101-200 fsw = +2 fsw
201-300 fsw = +4 fsw
301-400 fsw = +7 fsw

Front 28

The descent rate on an air dive is not critical, but in general it should not exceed _________.

Back 28

75 fsw/min

Front 29

The ascent rate from the bottom to the first decompression stop, between decompression stops, and from the last decompression stop to the surface what?

Back 29

30 fsw/min (20 seconds per 10 fsw)

Front 30

Explain the variations in rate of ascent rule.

Back 30

Minor variations in the rate of ascent between 20 and 40 fsw/min are acceptable. For surface decompression, the ascent rate from the 40 fsw water stop to the surface is 40 fsw/min.

Front 31

For in-water decompression on air, the time at the first decompression stop begins and ends when?

Back 31

When the diver arrives at the stop and ends when he leaves the stop.

Front 32

For in-water decompression on air, for all subsequent stops, after the first stop, the stop time begins and ends when?

Back 32

When the diver leaves the previous stop and ends when he leaves the stop. In other words, ascent time between stops is included in the subsequent stop time.

Front 33

For in-water decompression on air/oxygen, when does the time at the first oxygen stop begin and end?

Back 33

When all divers are confirmed on oxygen and ends when the divers leave the stop.

Front 34

What depth is the last water stop for all in-water decompressions?

Back 34

20 fsw

Front 35

When is a diver is considered eligible for surface decompression?

Back 35

Upon completion of the 40 fsw water stop. If a 40 fsw stop is not required by the decompression schedule, the diver may ascend directly to the surface without decompression stops and begin surface decompression.

Front 36

At depths of ____ fsw and shallower, there is no limit on the amount of time that can be spent at depth.

Back 36

20 fsw

Front 37

The optional shallow water No-Decompression Table can be used for depths between ______ and ______ fsw.

Back 37

30 and 50 fsw

Front 38

What factor must be accurately known to effectively use the optional shallow water No-Decompression Table?

Back 38

The diver’s maximum depth beginning of the dive, for example in ballast tank dives, or when continuous depth recording is available, for example with a decompression computer.

Front 39

The Air Decompression Table combines three modes of decompression into one table. What are they?

Back 39

1. In-water decompression on air
2. In-water decompression on air and oxygen
3. Surface decompression on oxygen

Front 40

What does it mean if the Air Decompression Table does not list a repetitive group designator for a dive?

Back 40

No repetitive dives deeper than 20 fsw are permitted following this dive. The diver must have an 18-hour surface interval before making another dive deeper than 20 fsw.

Front 41

How are the oxygen stops annotated on the decompression tables?

Back 41

They are in bold

Front 42

What are the air break rules during in-water decompression using oxygen?

Back 42

If more than 30 minutes must be spent on oxygen, a 5 min air break is required every 30 minutes.

Front 43

At what depth do decompression stops on oxygen commence?

Back 43

At 20 or 30 fsw

Front 44

What are the procedures for shifting to 100% Oxygen at 30 or 20 fsw?

Back 44

1. Upon arrival at the first oxygen stop, align the ORCA or FMGS to supply 100% oxygen to the diver.
2. Ventilate each diver for 20 seconds. Divers may be vented simultaneously or sequentially.
3. Verify that the oxygen monitoring device on the ORCA or FMGS, if one is present, shows 100% oxygen being delivered to the diver.

Front 45

True or False. At the 30 fsw and 20 fsw oxygen water decompression stops, the air breaks do not count toward required decompression time.

Back 45

True

Front 46

True or False. When an air break is required at the 30 fsw and 20 fsw oxygen water decompression stops, ventilation of the divers is not required.

Back 46

True

Front 47

What is your last in-water decompression stop during a Sur “D” O2?

Back 47

40 fsw

Front 48

When do you start timing your surface interval for a Sur “D” O2?

Back 48

When the diver leaves the 40 fsw

Front 49

How long is one (1) O2 period in the chamber for a Sur “D” O2?

Back 49

30 Minutes

Front 50

How long is a half (.5) an O2 period in the chamber for a Sur “D” O2?

Back 50

15 Minutes

Front 51

What is the ascent rate in the chamber during a Sur “D” O2?

Back 51

30 fsw/min

Front 52

To decompress the diver using the Surface Decompression on Oxygen mode, what table do you follow through the end of the 40 fsw water stop?

Back 52

The in-water air decompression schedule (top row)

Front 53

Upon completion of the 40 fsw stop, what is the ascent rate to the surface for a Sur “D” O2?

Back 53

40 fsw/min

Front 54

What is the ascent rate if a 40 fsw water stop is not required during a Sur “D” O2?

Back 54

Bring the diver from the bottom to 40 fsw at 30 fsw/min and then from 40 fsw to the surface at 40 fsw/min.

Front 55

Once the diver is on the surface, tenders have approximately how long to remove the breathing apparatus and diving dress and assist the diver into the recompression chamber during a Sur “D” O2?

Back 55

3::30

Front 56

True or False. When two divers undergo surface decompression simultaneously, the dive supervisor may elect not to use an inside tender.

Back 56

True. In this case, both divers will carefully monitor each other in addition to being closely observed by topside personnel.

Front 57

During the chamber phase of a Sur “D” O2, what is the maximum descent rate in the chamber?

Back 57

100 fsw/min

Front 58

During the chamber phase of a Sur “D” O2, what is the depth of the first stop in the chamber?

Back 58

50 fsw

Front 59

The surface interval of a Sur “D” O2 should not exceed how long?

Back 59

5 minutes

Front 60

When do you place the diver on 100 percent oxygen by mask during the chamber phase of a Sur “D” O2?

Back 60

Upon arrival at 50 fsw

Front 61

When does oxygen time begin during the chamber phase of a Sur “D” O2?

Back 61

When the diver is confirmed to be on oxygen at 50 fsw

Front 62

At what depth in the chamber is the first required O2 periods spent at during a Sur “D” O2?

Back 62

The first period consists of 15 minutes on oxygen at 50 fsw followed by 15 minutes on oxygen at 40 fsw

Front 63

During a Sur “D” O2, at what depth in the chamber is O2 periods 2–4 spent at during a Sur “D” O2?

Back 63

40 fsw

Front 64

During a Sur “D” O2, if more than 4 O2 periods are required, at what depth are they spent at?

Back 64

30 fsw

Front 65

During a Sur “D” O2, ascent from 50 fsw to 40 fsw and from 40 fsw to 30 fsw is at what rate?

Back 65

30 fsw/min

Front 66

True or False. During a Sur “D” O2, ascent time from 50 to 40 fsw is included in the first oxygen period. Ascent from 40 to 30 fsw, if required, should take place during an air break.

Back 66

True

Front 67

Except during an emergency, when does a diver come off O2 during a Sur “D” O2?

Back 67

During air breaks and when the last O2 period is complete during ascent to the surface

Front 68

The diving supervisor can initiate surface decompression at any point during in-water decompression at what depths?

Back 68

30 or 20 fsw

Front 69

What are the procedures for switching from an in-water decompression using O2 to a Sur “D” O2 after you have already shifted to O2 in the water?

Back 69

Compute the number of chamber oxygen periods required by multiplying the remaining oxygen time at the stops by 1.1, dividing the total by 30 minutes, then rounding the result up to the next highest half period. One half period (15 minutes at 50 fsw) is the minimum requirement.

Example: The supervisor elects to surface decompress when the diver has a remaining oxygen time of 5 minutes at 30 fsw and 33 minutes at 20 fsw. The total remaining oxygen time is 38 minutes. The number of 30-min SurDO2 periods required is (1.1 × 38) / 30 = 1.39. This number is rounded up to 1.5.

Front 70

What are the procedures for switching from an in-water decompression using air to a Sur”D” O2 if the diver is at 30fsw?

Back 70

First convert the remaining air time at the stops to the equivalent remaining oxygen time at the stops, then convert this remaining oxygen time to the number of chamber oxygen periods required as shown above.
First compute the air/oxygen trading ratio at 30 fsw by dividing the 30 fsw air stop time listed in the table by the 30-fsw oxygen time. Next divide the remaining air time at 30 fsw by the air/oxygen trading ratio to determine the equivalent remaining oxygen time at 30 fsw. Add the oxygen time shown in the table at 20 fsw to the equivalent remaining oxygen time at 30 fsw to obtain the total remaining oxygen time. Compute the number of chamber oxygen periods required by multiplying the remaining oxygen time at the stops by 1.1, dividing the total by 30 minutes, then rounding the result up to the next highest half period. One half period (15 minutes at 50 fsw) is the minimum requirement.

Front 71

What are the procedures for switching from an in-water decompression using air to a Sur”D” O2 if the diver is at 20fsw?

Back 71

For a diver at 20 fsw: Compute the air/oxygen trading ratio at 20 fsw by dividing the 20 fsw air stop time listed in the table by the 20-fsw oxygen time. Divide the remaining air time at 20 fsw by the air/oxygen trading ratio to obtain the equivalent remaining oxygen time. Compute the number of chamber oxygen periods required by multiplying the remaining oxygen time at the stops by 1.1, dividing the total by 30 minutes, then rounding the result up to the next highest half period. One half period (15 minutes at 50 fsw) is the minimum requirement.

Example: A diver is decompressing on a schedule that calls for a single 50 min stop on air at 20 fsw. The corresponding 20-fsw oxygen stop time is 27 min. After 20 minutes on air at 20 fsw, the diving supervisor elects to surface decompress the diver. The air/oxygen trading ratio at 20 fsw is 50/27 = 1.85, i.e., every 1.85 minutes spent air at 20 fsw is the equivalent of 1 minute spent on oxygen at 20 fsw. The remaining time on air at 20 fsw is 50 – 20 = 30 minutes. The equivalent remaining oxygen time at 20 fsw is 30/1.85 = 16.2 minutes. This remaining oxygen time is rounded up to the next whole minute, 17 min. The number of 30-min SurDO2 periods required is (1.1 × 17) / 30 = 0.62. This number is rounded up to 1.0.

Front 72

In-water decompression on air is the most suitable mode for dives that do not require more than ______ min of total decompression stop time

Back 72

15 min

Front 73

In-water decompression on air and oxygen is strongly recommended whenever the total decompression stop time on air exceeds _____ min and surface decompression on oxygen is not a viable alternative.

Back 73

15 min

Front 74

In-water decompression on air and oxygen is most suitable for dives that do not require more than ______ min of total air and oxygen time in the water. Why is it not suitable for longer times?

Back 74

90 min, longer times increase the risk of CNS oxygen toxicity and exposure to the elements.

Front 75

If the total air/oxygen decompression time in the water is greater than _____ min, use of what decompression table is required?

Back 75

90 min, surface decompression on oxygen is required

Front 76

If the surface interval between dives is less than ______ minutes, add the bottom time of the two dives and enter the decompression table at the deeper of the two depths.

Back 76

10 min

Front 77

What two times are added together to get the Equivalent Single Dive Time (ESDT) for a repet dive?

Back 77

The residual nitrogen time and the actual bottom time of the repetitive dive

Front 78

At depths of 10, 15, and 20 fsw on the Residual Nitrogen Time Table, some of the higher repetitive groups do not have a defined residual nitrogen time. These groups are marked with a double asterisk in the lower half. What does this mean?

Back 78

The RNT is undefined because the tissue nitrogen loading associated with those repetitive groups is higher than the nitrogen loading that could be achieved even if the diver were to remain at those depths for an infinite period of time. A diver entering the dive in one of those higher groups marked by a double asterisk can still perform a repetitive dive at 10, 15 or 20 fsw because the no-decompression time at those depths is unlimited. An RNT time is not required to make the dive.

Front 79

If a repetitive group is not shown in the no decompression schedule, repetitive dives deeper than 20 fsw are not allowed following a dive on that schedule. The diver must remain on the surface for at least ______ hours before making another dive deeper than 20 fsw.

Back 79

18 hours

Front 80

What is the RNT Exception Rule?

Back 80

If you are diving to the same or greater depth as a previous dive and your RNT time is greater than the actual bottom time of your previous dive, use the actual bottom time of your previous dive and your repet dives bottom time to compute your equivalent single dive time.

Front 81

At what depths are the no-decompression times unlimited?

Back 81

10, 15, 20

Front 82

Is possible to perform a repetitive dive on air following either a MK 16 MOD 0 or a MK 16 MOD 1 nitrogen-oxygen dive using the existing tables.

Back 82

Yes

Front 83

You want to make an air repet dive following a MK-16 dive. What must you do first in order to figure your RNT?

Back 83

First compute the Equivalent Air Depth of the MK 16 dive

Front 84

How do you figure the equivalent Air Depth for a MOD 0 dive?

Back 84

(Depth of MOD 0 dive – 18 fsw)/0.79

Front 85

How do you figure the equivalent Air Depth for a MOD 1 dive?

Back 85

(Depth of MOD 1 dive – 36 fsw)/0.79

Front 86

From the decompression standpoint, the most efficient way to perform repetitive dives is to perform the deepest dive first or the shallowest dive first.

Back 86

Perform the deepest dive first and the shallowest dive last

Front 87

Why is an exceptional exposure dives dangerous?

Back 87

The risk of decompression sickness, oxygen toxicity, and/or exposure to the elements is substantially greater than on normal working dives.

Front 88

What air dives are considered exceptional exposure?

Back 88

1. Any dive deeper than 190 fsw.
2. Any in-water decompression dive with a total decompression time on air or air/oxygen greater than 90 minutes.
3. Any SurDO2 dive with a chamber oxygen time greater than 120 minutes (4 oxygen periods).

Front 89

Minor variations in the rate of travel between _____ and _____ fsw/min are acceptable and do not require correction.

Back 89

20, 40

Front 90

If the rate of ascent is greater than 40 fsw/min, what are your actions?

Back 90

Stop the ascent, allow the watches to catch up, and then continue ascent.

Front 91

If the divers arrive early at the first decompression stop what are your actions?

Back 91

1. If the first stop is an air stop, begin timing the first stop when the required travel time has been completed.
2. If the first stop is an oxygen stop, shift the divers to oxygen upon arrival at the stop. Begin stop time when the divers are confirmed on oxygen and the required travel time has been completed.

Front 92

What are the procedures for handling delays in arriving at the first decompression stop?

Back 92

1. Delay up to 1 minute: A delay of up to one minute in reaching the first decompression stop can be ignored.
2. Delay greater than 1 minute, deeper than 50 fsw: Round up the delay time to the next whole minute and add it to the bottom time. Recompute the decompression schedule. If no change in schedule is required, continue on the planned decompression. If a change in schedule is required and the new schedule calls for a decompression stop deeper than the diver’s current depth, perform any missed deeper stops at the diver’s current depth. Do not go deeper.
3. Delay greater than 1 minute, shallower than 50 fsw: If a delay in ascent greater than 1 minute occurs shallower than 50 fsw, round the delay time up to the next whole minute and add the delay time to the diver’s first decompression stop.

Front 93

What are the procedures for handling delays when leaving a stop and between decompression stops during air decompression dives?

Back 93

1. Delay less than 1 minute leaving an air stop. When the delay in leaving an air stop is less than 1 minute, disregard the delay. Resume the normal decompression when the delay is over.
2. Delay less than 1 minute between air stops. If the delay between stops is less than 1 minute, disregard the delay.
3. Delay greater than 1 minute leaving an air stop or between air stops deeper than 50 fsw. Add the delay to the bottom time and recalculate the required decompression. If a new schedule is required, pick up the new schedule at the present stop or subsequent stop if delay occurs between stops. Ignore any missed stops or time deeper than the depth at which the delay occurred.
4. Delay greater than 1 minute leaving an air stop or between air stops shallower than 50 fsw. Ignore the delay. Resume the normal schedule upon completion of the delay.

Front 94

What are the procedures for handling delays in leaving an oxygen stop at 30 fsw or delay between oxygen stops at 30 and 20 fsw?

Back 94

Subtract any delay in leaving the 30 fsw oxygen stop or any delay during travel from 30 to 20 fsw on oxygen from the subsequent 20-fsw oxygen stop time. If the delay causes the total time on oxygen deeper than 20 fsw to exceed 30 minutes, shift the diver to air at the 30-minute mark. When the problem has been resolved, shift the diver back to oxygen and resume decompression. Ignore any time spent on air.

Front 95

What are the procedures for handling delays in leaving the 20-fsw oxygen stop?

Back 95

Delays leaving the 20-fsw oxygen stop can be ignored. However, do not leave divers on oxygen longer than 30 minutes as. Shift the divers to air and remain on air until travel to the surface is possible.

Front 96

What are the procedures for handling delays in travel from 40 fsw to the surface for Surface Decompression?

Back 96

Disregard any delays in travel from 40 fsw to the surface during surface decompression unless the diver exceeds the allowed 5-minute surface interval

Front 97

In the rare instance of diver entrapment or umbilical fouling, bottom time may exceed the longest bottom time listed in the table for the diver’s depth. When it is foreseen the bottom time will exceed the longest listed value, what should you do?

Back 97

Immediately contact the Navy Experimental Diving Unit for advice on how to decompress. If the Navy Experimental Diving Unit cannot be contacted in time, take the following action:
1. If available, use the U.S. Navy Thalmann Algorithm Dive Planner to compute the decompression requirement.
2. Read down to deeper depths in the Air Decompression Table until a depth is found that has a schedule that is equal to or longer than the bottom time. The Air Decompression Table contains longer schedules at various depths especially for this purpose.

Front 98

What are your actions if the diver cannot be shifted to oxygen at 30 or 20 fsw?

Back 98

1. Have the diver continue to breathe air while the problem is investigated.
2. If the problem can be corrected quickly, ventilate the diver with oxygen as soon as the gas supply is restored. Consider any time spent on air as dead time. Remain on oxygen at the stop for the full stop time listed in the table.
3. If the problem cannot be corrected, initiate surface decompression or continue decompression in the water on air. In this situation, the surface interval for surface decompression is the time from leaving the in-water stop to reaching the 50-fsw stop in the recompression chamber.

Front 99

What are your actions if the oxygen supply is lost during the 30 or 20-fsw water stops after the diver has shifted to oxygen?

Back 99

1. Shift the diver back to air.
2. If the problem can be corrected quickly, re-ventilate the diver with oxygen and resume the schedule at the point of interruption. Consider any time spent on air as dead time.
3. If the problem cannot be corrected and a recompression chamber is available on the dive station, initiate surface decompression. Compute the number of chamber oxygen periods required by multiplying the remaining oxygen time at the stops by 1.1, dividing the total by 30 minutes, then rounding the result up to the next highest half period. One half period (15 minutes at 50 fsw) is the minimum requirement.
4. If the problem cannot be corrected and a recompression chamber is not available on the dive station, continue decompression on air in the water. Compute the remaining stop time on air at the depth of the loss by multiplying the remaining stop time on oxygen at that depth by the ratio of the air stop time to the oxygen time at that depth.
If the shift to air occurs at 30 fsw, compute the remaining stop time on air at 30 fsw as shown above, then take the full 20-fsw air stop as prescribed in the Air Decompression Table.

Front 100

Why is it difficult to detect mixing of air with the oxygen supply during oxygen decompression in the water?

Back 100

No voice change will occur as it does in helium-oxygen diving

Front 101

What are your actions if the console operator discovers that the ORCA is improperly lined up, and it is detected that air is being mixed with the oxygen supply during oxygen decompression in the water?

Back 101

1. Align the ORCA properly
2. Re-ventilate each diver with oxygen for 20 seconds
3. Restart oxygen time. Consider any time spent on contaminated oxygen as dead time

Front 102

During in-water decompression using oxygen, CNS oxygen toxicity symptoms, if they do develop, are most likely to occur at what point and what is the most likely symptom?

Back 102

Near the end of the 20-fsw oxygen stop. Nausea is the most likely symptom.

Front 103

What are your actions for CNS Oxygen Toxicity Symptoms (Non-convulsive) at 30 or 20 fsw water stop? You have a chamber station.

Back 103

If a recompression chamber is available on the dive station, initiate surface decompression. Shift the console to air during travel to the surface. Compute the number of chamber oxygen periods required by multiplying the remaining oxygen time at the stops by 1.1, dividing the total by 30 minutes, then rounding the result up to the next highest half period. One half period (15 minutes at 50 fsw) is the minimum requirement.

Front 104

What are your actions for CNS Oxygen Toxicity Symptoms (Non-convulsive) at 30 fsw water stop? You have no chamber available.

Back 104

Bring the divers up 10 fsw and shift to air to reduce the partial pressure of oxygen. Shift the console as the divers are traveling to 20 fsw. Ventilate both divers with air upon arrival at 20 fsw. Ventilate the affected diver first. Complete the decompression on air at 20 fsw. Compute the 20-fsw stop time as follows: Multiply the missed stop time on oxygen at 30 fsw by the ratio of the air to oxygen stop time at 30 fsw to obtain the equivalent missed air time at 30 fsw. Add this time to the 20-fsw air stop time shown in the Air Decompression Table.

Example: After 10 minutes on oxygen at 30 fsw, a diver has a non-convulsive CNS oxygen toxicity symptom. A recompression chamber is not available on the dive station. The diver is immediately brought up to 20 fsw and ventilated with air. His decompression schedule calls for 28 minutes on air at 30 fsw and 175 minutes on air at 20 fsw. The oxygen stop time at 30 fsw is 14 minutes. The missed oxygen time at 30 fsw is 4 minutes (14 – 10). The ratio of air to oxygen time at 30 fsw is 28/14 = 2.0. The missed air time at 30 fsw therefore is 4 × 2.0 = 8 minutes. The required air decompression time at 20 fsw is 183 minutes (8 + 175).

Front 105

What are your actions for CNS Oxygen Toxicity Symptoms (Non-convulsive) at 20 fsw water stop? You have no chamber available.

Back 105

Shift the console to air, ventilate both divers, affected diver first, and complete the decompression in the water at 20 fsw on air. Compute the remaining stop time on air at 20 fsw by multiplying the remaining stop time on oxygen at 20 fsw by the ratio of the air stop time to the oxygen time at 20 fsw.

Example: After 24 minutes on oxygen at 20 fsw, a diver has a non-convulsive CNS oxygen toxicity symptom. A recompression chamber is not available on the dive station. The diver is shifted to air with 10 min of oxygen time remaining at 20 fsw. His decompression schedule calls for either 140 minutes on air at 20 fsw or 31 minutes on oxygen at 20 fsw. The ratio of air stop time to oxygen time at the 20-fsw stop is 140/31 = 4.52. His remaining time on air at 20 fsw is 10 × 4.52 = 45.2 minutes. Round this time up to 46 minutes.

Front 106

If CNS O2 toxicity symptoms progress to an oxygen convulsion, during an in-water decompression dive using oxygen, despite taking actions for non-convulsive symptoms, or if a convulsion occurs suddenly without warning, what are your actions?

Back 106

1. Shift both divers to air if this action has not already been taken.
2. Have the unaffected diver ventilate himself and then ventilate the stricken diver.
3. If only one diver is in the water, launch the standby diver immediately and have him ventilate the stricken diver.
4. Hold the divers at depth until the tonic-clonic phase of the convulsion has subsided. The tonic-clonic phase of a convulsion generally lasts 1–2 minutes.
5. At the end of the tonic-clonic phase, have the dive partner or standby diver ascertain whether the diver is breathing. The presence or absence of breath sounds will usually be audible over the diver communication system.
6. If the diver appears not to be breathing, have the dive partner or standby diver attempt to reposition the head to open the airway. Airway obstruction will be the most common reason why an unconscious diver fails to breathe.
7. If the diver is breathing, hold him at depth until he is stable, then surface decompress. Compute the number of chamber oxygen periods required by multiplying the remaining oxygen time at the stops by 1.1, dividing the total by 30 min, then rounding the result up to the next highest half period. One half period (15 minutes at 50 fsw) is the minimum requirement.
8. If surface decompression is not feasible, continue decompression on air in the water. Compute the remaining stop time on air at the depth of the incident by multiplying the remaining stop time on oxygen at that depth by the ratio of the air stop time to the oxygen time at that depth. If the shift to air occurs at 30 fsw, compute the remaining stop time on air at 30 fsw, then take the full 20-fsw air stop as prescribed in the Air Decompression Table.
9. 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 the standby diver at 30 fsw/min. The standby diver should attempt to 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.

Front 107

If the time from leaving 40 fsw in the water to the time of arrival at 50 fsw in the chamber during surface decompression exceeds 5 minutes but less than or equal to 7 minutes, what are your actions?

Back 107

If less than or equal to 7 minutes, increase the time on oxygen at 50 fsw from 15 to 30 minutes, i.e., add one-half oxygen period to the 50 fsw chamber stop. Ascend to 40 fsw during the subsequent air break. The 15-min penalty is considered a part of the normal surface decompression procedure, not an emergency procedure.
Example: Divers are decompressing on a SurDO2 schedule that requires 1.5 oxygen breathing periods. It took 6 minutes and 20 seconds to travel from 40 fsw to the surface, undress the diver, and recompress to 50 fsw in the chamber. The divers are placed on oxygen at 50 fsw in the chamber. They will breathe oxygen at 50 fsw for the 15 minutes (one-half period) required by the original schedule plus an additional 15 minutes to compensate for exceeding the normal 5-min surface interval. Upon completion of 30 minutes on oxygen at 50 fsw, they will remove the BIBS to initiate a 5-minute air break and ascend from 50 fsw to 40 fsw at 30 fsw/min while breathing air. After 5 minutes on air, the divers will breathe oxygen for 30 minutes to complete the oxygen time required at 40 fsw on the original schedule. After 30 minutes on oxygen at 40 fsw, the divers will remove the BIBS and ascend to the surface at 30 fsw/min breathing air. Because the divers exceeded the normal 5-minute surface interval, the total number of oxygen periods is increased from 1.5 to 2.0.

Front 108

If the time from leaving 40 fsw in the water to the time of arrival at 50 fsw in the chamber during surface decompression exceeds 7 minutes, what are your actions?

Back 108

Continue compression to a depth of 60 fsw. Treat the divers on Treatment Table 5 if the original schedule required 2 or fewer oxygen periods in the chamber. Treat the divers on Treatment Table 6 if the original schedule required 2.5 or more oxygen periods in the chamber.

Front 109

What are your actions if the diver is unable to reach 50 fsw in the chamber because of difficulty equalizing middle ear pressure during a Sur “D” dive.

Back 109

Use the “Safe Way Out”. Compress the diver to the deepest depth he can attain initially. This will usually be less than 20 fsw. Begin oxygen breathing at that depth. Continue attempts to gradually compress the diver deeper. If the in-water air or air/oxygen decompression schedule required only a 20-fsw water stop, attempt to compress the diver to 20 fsw. If the in-water air or air/oxygen decompression schedule required a 30-fsw water stop, attempt to compress the diver to 30 fsw. In either case, double the number of chamber oxygen periods indicated in the table and have the diver take these periods at whatever depth he 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. Upon completion of the oxygen breathing periods, surface the diver at 30 fsw/min. Carefully observe the diver post-dive for the onset of decompression sickness. This “safe way out” procedure is not intended to be used in place of normal surface decompression procedures. Repetitive diving is not allowed following a dive in which the “safe way out” procedure is used.

Front 110

What are your actions if symptoms of Type I decompression sickness occur during travel from 40 fsw to the surface during surface decompression or during the surface undress phase?

Back 110

Compress the diver to 50 fsw following normal surface decompression procedures. Delay neurological exam until the diver reaches the 50-fsw stop and is on oxygen. If Type I symptoms resolve during the 15 minute 50-fsw stop, the surface interval was 5 minutes or less, and no neurological signs are found, increase the 50 fsw oxygen time from 15 to 30 minutes as outlined above, then continue normal decompression for the schedule of the dive. Ascend from 50 to 40 fsw during the subsequent air break.

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 the diver on Treatment Table 5 if the original schedule required 2 or fewer oxygen periods in the chamber. Treat the diver on Treatment Table 6 if the original schedule required 2.5 or more oxygen periods in the chamber. Treatment table time starts upon arrival at 60 fsw. Follow the guidelines for treatment of decompression sickness given in Chapter 20, Volume 5.

Front 111

What are your actions if symptoms of Type II decompression sickness occur during travel from 40 fsw to the surface, during the surface undress phase, or the neurological examination at 50 fsw is abnormal?

Back 111

Compress the diver to 60 fsw on oxygen. Treat the diver on Treatment Table 6. Treatment table time starts upon arrival at 60 fsw.

Front 112

What are your actions for permanent loss of the oxygen supply in the chamber during a Sur “D” O2 dive?

Back 112

Complete decompression in the chamber on 50% nitrogen 50% oxygen (preferred) or on air. If 50% nitrogen 50% oxygen is available, multiply the remaining oxygen time by two to obtain the equivalent chamber decompression time on 50/50. Air breaks are not required when breathing 50/50. Diver may remove mask briefly (e.g., for drinking fluids). Consider any time spent on air as dead time. If chamber air is the only gas available, multiply the remaining chamber time on oxygen by the ratio of the water stop times on air at 30 and 20 fsw to the oxygen time at those depths to obtain the equivalent chamber decompression time on air. Allocate 10% of the equivalent air or 50/50 nitrogen-oxygen time to the 40-fsw stop, 20% to the 30-fsw stop, and 70% to the 20-fsw stop. If the diver is at 50 fsw when the loss occurs, ascend to 40 fsw and begin the stop time. If the loss occurred at 30 fsw, allocate 30% of the equivalent air or nitrogen-oxygen time to the 30-fsw stop and 70% to the 20-fsw stop. Round the stop times to the nearest whole minute. Surface the divers upon completion of the 20-fsw stop.

Example: A SurDO2 schedule calls for two 30-min oxygen periods in the chamber. The chamber oxygen supply is lost permanently after 28 minutes on oxygen at 50 and 40 fsw. Chamber air is the only gas available. The remaining oxygen time is (2 × 30) – 28 = 32 minutes. The original decompression schedule calls for 52 and 140 minute in-water air decompression stops at 30 and 20 fsw for a total air stop time of 192 minutes. The corresponding oxygen stop times are 13 and 34 minutes, for a total of oxygen stop time of 47 min. The ratio of air stop time to oxygen stop time is 192/47 = 4.08. The remaining chamber air time is 32 × 4.08 = 131 minutes. This time is allocated as follows: 13 min at 40 fsw (131 × 0.1), 26 min at 30 fsw (131 × 0.2), and 92 min at 20 fsw (131 × 0.7).

Front 113

What are your actions for temporary loss of oxygen supply in the chamber during a Sur “D” O2 dive?

Back 113

Have the diver breathe chamber air. If the loss is temporary, return the diver to oxygen breathing. Consider any time spent on air as dead time.

Front 114

What are your actions for CNS oxygen toxicity in the chamber during a Sur “D” O2 dive?

Back 114

1st symptom:
Off O2. Fifteen minutes after all symptoms have completely subsided, resume oxygen breathing at the point of interruption.

2nd symptom or if the first symptom is a convulsion:
1. Off O2
2. After all symptoms have completely subsided, decompress 10 feet at a rate of 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 schedule interruption.

3rd symptom:
If another oxygen symptom occurs after ascending 10 fsw, complete decompression on chamber air. If the diver is at 40 fsw, allocate 10% of the remaining air time to the 40-fsw stop, 20% to the 30-fsw stop, and 70% to the 20-fsw stop. If the diver is at 30 fsw, allocate 30% of the remaining time to the 30-fsw stop and 70% to the 20-fsw stop. Round the stop times to the nearest whole minute. Surface the divers upon completion of the 20-fsw stop.

Front 115

What are your actions for if a diver makes an uncontrolled ascent to the surface at a rate greater than 30 fsw/min, but the dive itself is within no-decompression limits?

Back 115

The diver should be observed on the surface for one hour to ensure that symptoms of decompression sickness or arterial gas embolism do not develop.

Front 116

An asymptomatic diver appears on the surface omitting his 30 and 20 fsw decompression stops. You are able to get him back to 30 fsw within one minute. What are your actions?

Back 116

Increase that stop time by one minute. Resume decompression according to the original schedule

Front 117

An asymptomatic diver appears on the surface omitting his 30 and 20 fsw decompression stops. You have a chamber available and choose to do a Sur “D” O2 and get him to 50’ in the chamber within 4 minutes and 45 seconds. What are your actions?

Back 117

If the diver is on the surface for 1 to 5 minutes and a recompression chamber is available on dive station, place the diver in the recompression chamber and complete the decompression using surface decompression. If the diver was on oxygen at the time of the omission, compute the number of chamber oxygen periods required by multiplying the remaining oxygen time at the stops by 1.1, dividing the total by 30 min, then rounding the result up to the next highest half period. If the diver was on air at the time of the omission, first compute the equivalent remaining oxygen time at the stop as shown in paragraph 9-8.3.2. If the omission occurred at 20 fsw, use this remaining oxygen time to compute the number of oxygen periods as shown above. If the omission occurred at 30 fsw, compute the remaining oxygen time at 30 fsw, then add the oxygen time shown in the decompression table at 20 fsw to get the total remaining oxygen time. Use the total remaining oxygen time to compute the number of oxygen periods. In all instances, one half period (15 minutes at 50 fsw) is the minimum requirement.

Front 118

An asymptomatic diver appears on the surface omitting his 30 and 20 fsw decompression stops. You have a chamber available and choose to do a Sur “D” O2 and get him to 50’ in the chamber within 6 minutes and 15 seconds. What are your actions?

Back 118

If the diver is on the surface for more than 5 minutes but less than or equal to 7 minutes and a recompression chamber is available on the dive station, place the diver in the recompression chamber and complete the decompression using surface decompression. If the diver was on oxygen at the time of the omission, compute the number of chamber oxygen periods required by multiplying the remaining oxygen time at the stops by 1.1, dividing the total by 30 min, then rounding the result up to the next highest half period. If the diver was on air at the time of the omission, first compute the equivalent remaining oxygen time at the stop as shown in paragraph 9-8.3.2. If the omission occurred at 20 fsw, use this remaining oxygen time to compute the number of oxygen periods as shown above. If the omission occurred at 30 fsw, compute the remaining oxygen time at 30 fsw, then add the oxygen time shown in the decompression table at 20 fsw to get the total remaining oxygen time. Use the total remaining oxygen time to compute the number of oxygen periods. In all instances, one half period (15 minutes at 50 fsw) is the minimum requirement. This is the same procedure for surface intervals of less than 5 minutes except you will increase the time on oxygen at 50 fsw from 15 to 30 minutes.

Front 119

An asymptomatic diver appears on the surface omitting his 30 and 20 fsw decompression stops. You have a chamber available and choose to do a Sur “D” O2 and get him to 50’ in the chamber within 7 minutes and 15 seconds. What are your actions?

Back 119

If the diver is on the surface for more than 7 minutes and a recompression chamber is available on site, treat the diver with Treatment Table 5 if the surface decompression schedule for that dive required two or fewer oxygen periods in the chamber. Treat on Treatment Table 6 if the surface decompression schedule for that dive required 2.5 or more oxygen periods in the chamber.

Front 120

An asymptomatic diver appears on the surface omitting his 30 and 20 fsw decompression stops. You have no chamber available but and are able to get him back to 30 fsw in 1 minute and 45 seconds. What are your actions?

Back 120

If the diver is on the surface for more than 1 minute and a recompression chamber is not available, return the diver to the depth of the omitted stop. Complete decompression in the water by multiplying the 30- and/or 20-fsw air or oxygen stops by 1.5.

Front 121

If the diver omits part or all of a decompression stop at 40 fsw or deeper and a recompression chamber is available on site, what are your actions?

Back 121

Treat the diver with Treatment Table 6.

Front 122

If the diver omits part or all of a decompression stop at 40 fsw or deeper and no recompression chamber is available on site, what are your actions?

Back 122

Return the diver to the depth of the first decompression stop. Follow the original decompression schedule to 30 fsw. At 30 fsw, shift the diver to oxygen if it is available. Complete decompression from 30 fsw by multiplying the 30- and 20-fsw air or oxygen stops by 1.5.

Front 123

When decompression sickness occurs in the water during prolonged decompression on air or air/oxygen, what is the predominant symptom?

Back 123

It will usually be joint pain but more serious manifestations such as numbness, weakness, hearing loss, and vertigo may also occur.

Front 124

When decompression sickness occurs in the water during prolonged decompression on air or air/oxygen, when is it most likely to occur?

Back 124

Decompression sickness is most likely to appear at the shallow stops just prior to surfacing. Some cases, however, have occurred during ascent to the first stop or shortly thereafter.

Front 125

If the diver indicates that he has pain in his elbow at his 20 fsw during in-water decompression stop but feels he can remain in the water, what are your actions? You have O2 available to the divers in the water and no recompression chamber immediately available.

Back 125

1. Dispatch the standby diver to assist. Continue to decompress the other divers according to the original schedule.
2. Switch the diver to 100% oxygen if available.
3. Have the diver descend 10 fsw. If significant relief of symptoms is not obtained, have the diver descend an additional 10 fsw, but no deeper than 40 fsw if the diver is on oxygen.
4. Remain at treatment depth for at least 30 minutes.
5. If the diver is undergoing treatment on oxygen at 40 fsw, return to the surface by multiplying the 30 and 20-fsw oxygen stop times by 1.5. If the original schedule did not call for a 30-fsw oxygen stop, insert a 30-fsw oxygen stop with a stop time equal to the 20-fsw stop time.
7. If the diver is undergoing treatment on oxygen at 30 fsw, return to the surface by multiplying the 20-fsw oxygen stop time by 1.5.
8. If the diver is symptom-free upon surfacing, place the diver on oxygen, transport to the nearest recompression chamber, and treat on Treatment Table 5. This requirement may be waived for dives conducted in remote locations that do not have recompression chambers within a reasonable travel distance. If the diver is not symptom-free upon surfacing, transport the diver to the nearest chamber and treat on Treatment Table 6.
9. After completing recompression treatment, observe the diver for at least 6 hours. If any symptoms recur, treat as a recurrence of Type II symptoms.

Front 126

If the diver indicates that he has pain in his elbow at his 20 fsw during in-water decompression stop but feels he can remain in the water, what are your actions? You have no O2 available to the divers in the water and no recompression chamber immediately available.

Back 126

1. Dispatch the standby diver to assist. Continue to decompress the other divers according to the original schedule.
2. Have the diver descend 10 fsw. If significant relief of symptoms is not obtained, have the diver descend an additional 10 fsw.
4. Remain at treatment depth for at least 30 minutes.
5. Resume decompression from treatment depth by multiplying subsequent air stop times in the Air Decompression Table by 1.5. If recompression went deeper than the depth of the first stop on the original air decompression schedule, insert intervening stops in 10 fsw increments between the treatment depth and the original first stop depth equal to 1.5 times the original first stop time.
6. If the diver is symptom-free upon surfacing, place the diver on oxygen, transport to the nearest recompression chamber, and treat on Treatment Table 5. This requirement may be waived for dives conducted in remote locations that do not have recompression chambers within a reasonable travel distance. If the diver is not symptom-free upon surfacing, transport the diver to the nearest chamber and treat on Treatment Table 6.
9. After completing recompression treatment, observe the diver for at least 6 hours. If any symptoms recur, treat as a recurrence of Type II symptoms.

Front 127

If the diver indicates that he has pain in his elbow at his 30 fsw during in-water decompression stop but feels he can remain in the water, what are your available treatment procedures? You have O2 available to the divers in the water and a recompression chamber immediately available.

Back 127

1. Dispatch the standby diver to assist. Continue to decompress the other divers according to the original schedule.
2. If the diver is decompressing on air, switch the diver to 100% oxygen if available.
3. Have the diver descend 10 fsw. If significant relief of symptoms is not obtained, have the diver descend an additional 10 fsw, but no deeper than 40 fsw if the diver is on oxygen.
4. Remain at treatment depth for at least 30 minutes.
5. If the diver is undergoing treatment on oxygen at 40 fsw, return to the surface by multiplying the 30 and 20-fsw oxygen stop times by 1.5. If the original schedule did not call for a 30-fsw oxygen stop, insert a 30-fsw oxygen stop with a stop time equal to the 20-fsw stop time.
7. If the diver is undergoing treatment on oxygen at 30 fsw, return to the surface by multiplying the 20-fsw oxygen stop time by 1.5.
8. If the diver is symptom-free upon surfacing, place the diver on oxygen, transport to the nearest recompression chamber, and treat on Treatment Table 5. This requirement may be waived for dives conducted in remote locations that do not have recompression chambers within a reasonable travel distance. If the diver is not symptom-free upon surfacing, transport the diver to the nearest chamber and treat on Treatment Table 6.
9. If a recompression chamber is available on the dive station, the diving supervisor may elect to forego treatment with in-water recompression and surface the diver for treatment in the recompression chamber or treat the diver in the water for 30 minutes to relieve symptoms, then surface the diver for further treatment in the recompression chamber. In either case, the surface interval should be 5 minutes or less, and the diver should be considered to have Type II decompression sickness, even if the symptoms are Type I. After completing recompression treatment, observe the diver for at least 6 hours. If any symptoms recur, treat as a recurrence of Type II symptoms.

Front 128

If the diver indicates that he has pain in his elbow at his 20 fsw during in-water decompression stop and feels he cannot safely remain in the water, what are your available treatment procedures? You have O2 available to the divers in the water and a recompression chamber immediately available.

Back 128

1. Surface the diver at a moderate rate (not to exceed 30 fsw/min).
2. If a recompression chamber is on site, recompress the diver immediately. Guidance for treatment table selection and use is given in Chapter 20.
3. If a recompression chamber is not on site, follow the management guidance given in Volume 5.

Front 129

Because of the reduced atmospheric pressure, dives conducted at altitude require more or less decompression than identical dives conducted at sea level?

Back 129

More

Front 130

What is the procedure commonly called to correct an altitude dive to obtain the equivalent sea level dive, then determine the decompression requirement using standard tables?

Back 130

This procedure is commonly known as the “Cross Correction” technique

Front 131

To apply the “Cross Correction” technique, what two corrections must be made for altitude diving?

Back 131

First, the actual dive depth must be corrected to determine the sea level equivalent depth. Second, the decompression stops in the sea level equivalent depth table must be corrected for use at altitude

Front 132

What is the formula for correction of dive depth at altitude?

Back 132

The depth of the sea level equivalent dive is determined by multiplying the depth of the dive at altitude by the ratio of the atmospheric pressure at sea level to the atmospheric pressure at altitude.

Front 133

What is the formula for correction of decompression stops?

Back 133

The depth of the corrected stop at altitude is calculated by multiplying the depth of a sea level equivalent stop by the ratio of the atmospheric pressure at altitude to the atmospheric pressure at sea level. [Note: this ratio is the inverse of the ratio for figuring correction of dive depth.]

Front 134

Table 9-4 (Sea Level Equivalent Depth Table) cannot be used when diving with equipment that maintains a constant partial pressure of oxygen such as the MK 16 MOD 0 and the MK 16 MOD 1. Who do you contact for guidance diving the MK 16 MOD 0 and the MK 16 MOD 1 at altitudes.

Back 134

Consult NAVSEA 00C for specific guidance when diving the MK 16 at altitudes greater than 1000 feet.

Front 135

State the rules for when correction for depth is required when diving at altitudes.

Back 135

1. Between sea level and 300 feet - No correction is required
2. At altitudes between 300 and 1000 feet, correction is required for dives deeper than 145 fsw (actual depth).
3. At altitudes above 1000 feet, correction is required for all dives

Front 136

What is the preferred method for measuring depth at altitude?

Back 136

A mechanical or electronic gauge that can be re-zeroed at the dive site. Once re-zeroed, no further correction of the reading is required.

Front 137

Most mechanical depth gauges carried by divers have a sealed one-atmosphere reference and cannot be adjusted for altitude; thus they will read low throughout a dive at altitude. What is the correction factor when using these types of gauges?

Back 137

A correction factor of 1 fsw for every 1000 feet of altitude should be added to the reading of a sealed reference gauge before entering Table 9-4.

Front 138

True or False: Add the pneumofathometer correction factor to the depth reading before entering Table 9-4 (Sea Level Equivalent Depth Table). The pneumofathometer correction factors are unchanged at altitude.

Back 138

True

Front 139

Upon ascent to altitude, two things happen. The body off-gases excess nitrogen to come into equilibrium with the lower partial pressure of nitrogen in the atmosphere. It also begins a series of complicated adjustments to the lower partial pressure of oxygen. The first process is called equilibration; the second is called acclimatization. Approximately ________ hours at altitude is required for equilibration. A longer period is required for full acclimatization.

Back 139

Twelve

Front 140

True or False: If a diver begins a dive at altitude within 12 hours of arrival, the residual nitrogen left over from sea level must be taken into account.

Back 140

True

Front 141

How do you figure residual nitrogen for a dive made at altitude within 12 hours of ascent to the dive altitude?

Back 141

Table 9-5 gives the repetitive group associated with an initial ascent to altitude. Using this group and time at altitude before diving, enter the Residual Nitrogen Timetable for Repetitive Air Dives (Table 9-8) to determine the new repetitive group designator associated with that period of equilibration. Determine the sea level equivalent depth for your planned dive using Table 9-4. From your new repetitive group and sea level equivalent depth, determine the residual nitrogen time associated with the dive. Add this time to the actual bottom time of the dive. If the diver has spent enough time at altitude to desaturate beyond repetitive group A in Table 9-8, no addition of residual nitrogen time to bottom time is needed. The diver is “clean.”

Front 142

For surface decompression dives on oxygen at altitude, the chamber stops are, or are not adjusted for altitude?

Back 142

Are not. Enter the same depths as at sea level. Keeping chamber stop depths the same as sea level provides an extra decompression benefit for the diver on oxygen.

Front 143

How do you figure how long you must wait to fly or ascend to a higher altitude after an air dive?

Back 143

Table 9-6 gives the surface interval (hours:minutes) required before making a further ascent to altitude. The surface interval depends on the planned increase in altitude and the highest repetitive group designator obtained in the previous 24-hour period. Enter the table with the highest repetitive group designator obtained in the previous 24-hour period. Read the required surface interval from the column for the planned change in altitude.

Front 144

What are most commercial airline flights pressurized to?

Back 144

8000 feet

Front 145

How do you figure how long you must wait to fly or ascend to a higher altitude after a non-saturation helium-oxygen dive?

Back 145

Wait 12 hours if the dive was a no-decompression dive. Wait 24 hours if the dive was a decompression dive.