Dive Theory: Decompression Theory and the Recreational Dive Planner Flashcards
(126 cards)
1
Q
actual bottom time (abt)
A
Used in repetitive diving. ABT is added to residual nitrogen time, the sum gives you the total bottom time.
In essence it is the total time actually spent underwater from the beginning of descent until leaving the bottom for a direct continuous ascent to the surface or safety stop.
2
Q
adjusted no decompression limit
A
The time limit for a repetitive dive that accounts for residual nitrogen. Your actual bottom time should never exceed the adjusted no decompression limit.
3
Q
ascent rate
A
The proper speed for ascending, which is no faster than 18 meters/60 feet per minute. A slower rate is acceptable and appropriate.
4
Q
bottom time
A
Time from the beginning of descent until beginning a direct, continuous ascent to the surface or safety stop.
5
Q
decompression diving
A
Diving that requires planning stops during ascent to avoid decompression sickness.
In rec diving, a decom stop is considered an emergency procedure only, and never an intentional part of the dive plan.
6
Q
multilevel diving
A
tbd
7
Q
dive profile
A
A drawing of your dive plan including depth, time at depth, before and after pressure groups, surface intervals, etc.
8
Q
multilevel limit (ML)
A
Max allowable no decom time you have on each level of a multilevel dive.
9
Q
no decompression limit (NDL)
A
Max time that can be spent at a depth before decompression stops are required. Also called “no-stop time”
10
Q
no stop dive
A
A dive made within no decompression limits because you don’t have any required emergency decompression stops. Also called a “no decompression dive”
11
Q
pressure group
A
A letter used on the recreational Dive Planner to designate the amount of theoretical residual nitrogen in your body.
12
Q
repetitive dive
A
A dive that follows another while there’s still a significant amount of residual nitrogen in your body.
Using the Recreational Dive Planner, generally this is a dive made within 6 hours of a previous dive.
13
Q
residual nitrogen
A
The higher than normal amount of nitrogen remaining in your body after a dive.
14
Q
residual nitrogen time (RNT)
A
An amount of nitrogen, expressed in minutes, for a specific depth added to the actual bottom time of a dive to account for residual nitrogen from a previous dive.
15
Q
safety stop
A
A stop usually at 5 meters/15 feet for three or more minutes at the end of a dive for additional safety. Recommended after all dives.
Required for dives below 30m/100ft and those coming within 3 pressure groups of the no decompression limit.
16
Q
surface interval (SI)
A
The time spent on the surface between two dives - usually recorded in hours:minutes.
17
Q
total bottom time (TBT)
A
The sum of Residual Nitrogen Time and Actual Bottom Time of a repetitive dive used on Table 1 of the RDP Table to determine the pressure group following the repetitive dive.
You don’t use TBT eRDPML because it does the addition and displays the new pressure group automatically.
18
Q
Who is credited in coming up with the basic decompression model we use today?
A
John Haldane
19
Q
What are the seven basic decompression concepts developed by Haldane?
A
- Upon descent, nitrogen dissolves from the air - higher pressure - into body tissues - lower pressure
- Nitrogen continues to dissolve into the until the body saturates and absorbs no more nitrogen at that depth.
- Upon ascent, nitrogen dissolved in the body - tissue pressure - is now higher than surrounding pressure. Nitrogen dissolves out of the tissue into the breathing air and is exhaled from the body
- The difference between the dissolved nitrogen pressure and the surrounding pressure - whether ascending or descending - is called the pressure gradient.
- On ascent, tissues can tolerate some gradient of high tissue pressure without DCS occurring. Nitrogen in solution dissolves harmlessly out of tissues.
- If the pressure gradient exceeds acceptable limits, then dissolved nitrogen comes out of solution faster than the body can eliminate it through respiration and circulation. If acceptable limits are exceeded, nitrogen bubbles form, causing DCS.
- DCS can be avoided by keeping the gradient within acceptable limits. Gradient too great, decompression stops needed or slower ascent.
20
Q
What is meant by “compartment” in relation to Haldanean decompression model.
A
Different parts of the body absorb and release dissolved nitrogen at different rates.
Haldane constructed a mathematical model consisting of multiple theoretical tissues.
Theoretical tissues don’t correspond to any particular body tissues, they simply model that the body doesn’t absorb and release nitrogen on a singular time scale.
21
Q
What is the relationship between the human body and Haldane decompression model and how far can you rely on the model?
A
There is no direct relationship between the model and the body. Actual dive data imply and support the relationship but like all models, decompression models have limits of reliability.
22
Q
pressure gradient
A
Difference between the dissolved nitrogen pressure and the surrounding pressure.
23
Q
What is ‘halftime’ in relation to Haldanean decompression model?
A
Time in minutes for a particular compartment to go halfway from its beginning tissue pressure to equilibrium - saturation - at a new depth.
50% equilibrated after one halftime, 75 after two, 87.5 after 3, etc.
After six, the compartment is considered 100 percent equalized.
24
Q
Haldanean Half-time ranges.
A
Haldanean’s original model had half times ranging from 5min to 75min.
Modern models 3min to 600min.
Often called slow (600min) and fast (3min) compartments.
25
What is 'M-Values' in relation to Haldanean decompression model?
Maximum tissue pressure allowed in the compartment when the diver surfaces, so as to prevent exceeding the maximum acceptable gradient.
26
Exceeding the M-value
Unacceptable risk of decompression sickness
27
M-Value and no decompression diving.
Only concerned with the surfacing M-Value (M0-value).
28
M-Value relationship to compartments?
The faster the compartment (halftime length) the higher its M-Value. With slower compartments having lower M-Values.
29
Haldanean model consists of several _______, each with a _______ in minutes that represent how fast is absorbs and releases nitrogen, and a(n) ________ that sets the max nitrogen pressure it can have when a diver surfaces.
compartments
halftime
M-Value
30
A 60-minute tissue compartment requires _______ to fill or empty completely, while a 120-minute compartment requires _______.
6 hours
12 hours
60 min x 6 = 6 hours
120 min x 6 = 12 hours
halftime repeated 6 times, compartment considered 100% full or empty.
31
There is _______ relationship between the Haldanean model and the human body; you can rely on it only as far as it is supported by _______.
no direct
| test and field data
32
The time limit for a repetitive dive that accounts for residual nitrogen remaining in your body from a previous dive.
Adjusted no decompression limit.
33
Used in repetitive diving and added to the Residual Nitrogen Time to equal the Total Bottom Time.
Actual Bottom Time
34
The time from the beginning of descent until beginning of a direct, continuous ascent to the surface or safety stop.
Bottom Time
35
The time spent on the surface between two dives - usually recorded in hours:minutes.
Surface Interval
36
An amount of nitrogen expressed in minutes, for a specific depth added to the actual bottom time of a dive to account for the residual nitrogen from a previous dive.
Residual nitrogen time
37
The sum of the Residual Nitrogen Time and the Actual Bottom Time of a repetitive dive used on Table 1 of the RDP table to determine the Pressure Group (PG) following repetitive dives.
Total Bottom Time (TBT)
38
A stop usually at 5m/15ft for three or more minutes at the end of a dive for additional safety
safety stop
39
The higher-than-normal amount of nitrogen remaining in your body after a dive
Residual nitrogen
40
A letter used on a rec dive planner (RDP) to designate the amount of theoretical residual nitrogen in your body
Pressure Group (PG)
41
Non rec diving that requires planning stops during ascent to avoid decompression sickness
Decompression Diving
42
A dive made within no decom limits because you don't have any required emergency decom stops
No stop dive
43
The proper speed for ascending, which is no faster than 18m/60ft per minute
Ascent rate
44
The max time that can be spent at a depth before decompression stops are required.
No decompression limit (ndl)
45
A dive that follows another while there is still residual nitrogen in your body.
Repetitive dive
46
Why was the 1950's version of the US Navy table at one time the standard for rec diving?
Developing a table was tedious.
Many early divers and instructors came from the military.
The tables were widely available.
47
What is basis for the US navy table's repetitive diving surface interval credit?
Navy designed an easy to use surface interval credit table based on the worst-case scenario - a repetitive dive preceded by a decompression dive.
At the time of the original development, the navy based repetitive credit on the slowest compartment, the 120 minute halftime.
The newest version of the U.S.N tables (2008rev) uses even longer halftimes.
Testing based upon all male, fit and in their 20s and 30s. Test criteria = DCS or no DCS. Doppler checking for bubbles didn't exist then.
Based on Decompression Diving. Might be to conservative for recreational diving, because rec diving is no decom diving.
48
The early version of the US Navy tables were the standard for rec diving because?
Before the rise of computers, it was beyond the practical abilities of most people to develop a table.
They were widely available.
Many early divers were former military divers used to them already.
49
The basis of surface interval credit with the 1950s version of the US Navy tables is the ________ minute compartment.
120
50
Why does the recreational dive planner use a different basis for repetitive dive credit from that used by the 1950s US Navy table?
1) 120 minute halftime for calculating washout is overly conservative for exclusively no decom diving. US Navy tables developed for decompression diving. Rec diving is no decom or no stop diving.
2) Test group used by Navy (20s and 30s fit male) doesn't represent rec diving population.
3) Doppler ultrasound flow meters came into being. This tech found "silent" asymptomatic bubbles in test subjects diving to US Navy table limits. Made clear tables could be overly conservative or insufficiently conservative, depending on the circumstances.
Note: surface interval credit can be less conservative when limited to no decom diving.
51
The US Navy selected the 120-minute tissue compartment to control their "surface interval credit table" because?
They were designing the tables that enabled decompression diving.
52
The RDP uses a different basis for repetitive diving from that used by the 950s US Navy tables because?
Surface interval credit can be less restrictive when limited to no decompression diving.
53
What effect does the RDP's repetitive diving surface interval credit ahve compared to the 1950s version of the US Navy Tables?
Uses 60-minute halftime compartment for repetitive diving, instead of 120.
RDP gives about twice as much credit for a given surface interval.
Residual nitrogen time for a repetitive dive i roughly cut in half compared to the US Navy Tables.
54
RDP Table WX Rule
If planning 3 or more dives, beginning with the first dive of the day, if your ending pressure group is W or X, the minimum surface interval between all subsequent dives is 1 hour.
55
RDP Table YZ Rule
If your ending pressure group after any dive is Y or Z, the minimum surface interval between all subsequent dives is 3 hours.
56
The 60 minute halftime surface interval credit of the RDP gives approximately _______ the surface interval credit of the 1950s version of the US Navy Tables.
Double
57
Why were the WX and YZ rules created for the RDP?
Analysis found that a compartment slower than 60 minutes could control a repetitive dive for a small portion of no stop dives involving long shallow multiple dive profiles.
58
What are the various forms of the Recreational Dive Planner?
Traditional RDP Tabl
eRDPml
Enriched Air RDP Tables
59
The RDP was developed for _______divers. Its tests included _______ divers, a wider range of _______ and _______ type.
(Note: in contrast to 1950's US Navy Tables)
Recreational
Female
Age
Physical
60
Why can't pressure groups from the RDP be used on the US Navy tables or any other tables?
The tables are based on different decompression models.
61
How do modern dive computers apply decom models to provide more no decom dive time?
Eliminates unnecessary rounding by calculating the dive exactly.
62
A dive computer
Follows the same theoretical basis as dive tables.
Calls for following the same general recommendations as when diving with tables.
Should not be shared by two or more divers on a dive.
63
Which decompression model(s) are commonly used in dive computers?
Buhlmann Limits - EE Washout
Spencer Limits - 60 Minute washout
64
Basic idea behind "Bubble" models
Prevent bubbles from forming, or if they do form to dissolve gas out of the bubbles and back into tissues.
This should leave the venous circulation and lungs less restricted by microbubbles, making off-gassing more efficient at the time dissolved gas decompression stops.
65
Some dive computers have added adjustments that reduce dive time or mandate safety/decompression stops:
If you exceed a safe ascent rate
If the water is cold
If you make short surface intervals.
66
Dive planning Special Rules, rule one dives in cold water or strenuous dives.
Plan the dive assuming the depth is 4m/10ft deeper than it actually is.
With a computer - make sure that you stay well within no decom limits at all times.
67
Dive planning Special Rules, rule two repetitive dives.
Plan repetitive dives so each successive dive is to the same or a shallower depth.
68
Dive planning Special Rules, rule three Depth and Experience
Limit max depths in consideration of training and experience.
- Scuba Diverr: 12m/40ft
- Open Water: 18m/60ft
- Greater training and experience: 30m/100ft
69
Dive planning Special Rules, rule four multiple repetitive dives.
If after making multiple repetitive dives:
A. If the ending pressure group after any dive W or X, the minimum surface interval between all subsequent dives is 1 hour.
B. If the ending pressure group after any dive is Y or Z, the minimum surface interval between all subsequent dives is 3 hours.
70
Dive planning Special Rules, rule five repetitive dive depth limitation
Limit repetitive dives to 30m/100ft or shallower.
Deep repetitive dives seem to be associated disproportionately with DCS incidence.
71
Dive planning Special Rules, rule six 42m/140ft designation
42m/140ft designation on the RDP is for emergency purpose only; do not dive deeper than 40m/130ft.
72
Dive planning Special Rules, rule seven accidental deep dive
If you discover you have accidentally descended below 40m/130ft, immediately ascend to 5m/15ft, and make an emergency decom stop for 8 minutes.
* Use this rule only if the no decompression limit for 40m/140ft is NOT exceeded by more than 5 minutes.
* Do not dive again for 6 hours.
73
When does RDP require a safety stop.
On any dive to 30m/100ft.
On any dive that comes within three Pressure Groups of a no decompression limit
On any dive that reaches any RDP limit.
74
When is an emergency decompression stop required?
When a diver exceeds any limit on the RDP.
75
Emergency decompression vs safety stop
Emergency decompression stop required when the model limits may have been exceeded.
76
Two Emergency Decompression Rules?
1)
No Decom Limit is accidentally exceeded by 5 minutes or less:
- Make an emergency decom stop for 8 minutes at 5m/15ft
- Remain out of the water at least 6 hours
2)
No Decom limit is accidentally exceeded by more than 5 minutes:
- Make an emergency decom stop at 5m/15ft for no less than 15 minutes - air supply permitting.
- Remain out of the water at least 24 hours.
77
Why do the two emergency decompression rules exist?
Required surface intervals are necessary to assure the diver's body releases sufficient nitrogen to return within model limits before diving again.
78
If Emergency Decompression stop is omitted.
- Diver should not re-enter the water for 24 hours.
- Diver should rest and remain alert for signs and symptoms of DCS
- Breathing pure oxygen may reduce the possibility of DCS
If DCS signs and symptoms occur:
- Contact medical assistance
- In water re-compression should not be attempted.
79
Most RDP special rules, recommendations and considerations come entirely from _______.
What diving has found to work, whether they have any basis in a decompression model or not.
80
An in-depth understanding of all the special rules, recommendations, and considerations can help you _______.
Avoid decompression sickness
81
Which of the following are recommendations or rules for RDP use?
Make deeper dives before shallower dives
Make safety stops at the end of all dives
Plan cold/stenuous dives as if they are 4m/10ft deeper than actual
Allow at least 12 hours after a single dive before flying
Allow at least 18 hours after multiple dives for several days
82
When diving with a computer (Check all that apply):
Follow the recommendations that apply to dive tables
don't share it with a buddy
follow all manufacturer recommendations
83
With the RDP, if you are planning 3 or more dives in a day, beginning with the first dive, if your ending pressure group after any dive is W or X, the minimum surface interval between all subsequent dives is _______.
1 hour
84
When using the RDP, limit repetitive dives to:
Review question answer is:
None of the above.
The actual answer, which is not provided in the review multiple choice is 30m/100ft.
85
The 42m/140ft designation on the Recreational Dive Planner is for _______.
Emergency purposed only.
86
RDP procedures REQUIRE a safety stop:
On any dive to 30m/100ft or deeper
On any dive that comes within three Pressure Groups of a no decompression limit
On any dive that reaches any RDP limit
87
If you discover you have accidentally descended below 40m/130ft, immediately _______.
Ascend to 5m/15ft, make an emergency decom stop for 8 minutes and do not dive again for 6 hours.
88
If while at depth, you discover that you have exceeded a no decompression limit on the RDP by 5 minutes or less you should _______.
Make an emergency decom stop for 8 minutes at 5m/15ft prior to surfacing, then remain out of the water at least 6 hours prior to making another dive.
89
You need to follow special dive table and computer procedures at altitude (where there is _______ atmospheric pressure) because decompression models were developed for _______.
Less
Sea Level
90
Using the RDP above _______ requires the use of special procedures including the conversion of actual depth to theoretical depth. To use theoretical depth tables, you must know the _______.
300m/1000ft
altitude of the dive
91
At about _______ above sea level, atmospheric pressure drops enough to question the accuracy of calculations intended for sea level. Diving _______ this altitude without following proper altitude procedures increases the risk of decompression sickness.
300m/1000ft
above
92
At no time should you use the RDP to plan dives at altitudes above _______.
3000m/10,000ft
93
When making an altitude dive, the ascent rate is _______ per minute slower.
9m/30ft
94
Making no more than _______ dives per day while altitude diving, and don't mix altitudes by making the repetitive dive at a _______ altitude than the first dive.
two
higher
95
A diver plans an altitude dive at 2286m/7500ft. What is the pressure group upon arrival at the dive site altitude?
P
Count two PG's for every 300m/1000ft. 2286m/7500ft is rounded up to 2400m/8000ft. So count 16 PG's down Table one.
96
A diver plans to dive at an altitiude of 2150m/7053ft to an actual depth of 25m/65ft. What is the depth used on the RDP for planning this dive?
35m/94ft
97
If you make a single no decompression dive at sea level, it is suggested that your minimum preflight surface interval be _______.
Review question answer is:
None of the above
Actual answer is:
12 hours
98
Use RDP
A dive to 13 metres for one hour yields what pressure group?
Q
99
Use RDP
A dive to 9 metres for 70min yields what pressure group?
M
100
Use RDP
A dive to 18 metres for 40min yields what pressure group?
P
101
Use RDP
After a dive, Table 1 shows you are in pressure group J. What will your new pressure group be after a 32-minute surface interval?
E
102
Use RDP
A diver in pressure group P will be in what new pressure group after a 55-minute surface interval?
F
103
Use RDP
A diver in pressure group I will be in what new pressure group after a surface interval of 4 hours?
A
104
Use RDP
If you are in pressure group K after your surface interval, and you are planning a dive to 18 metres, what is your adjusted no decompression limit?
26 minutes
105
Use RDP
After a surface interval, you are in pressure group P and planning a dive to 16 metres. What is your adjusted no decompression limit for this dive?
24 minutes
106
Use RDP
If you're in pressure group M after a surface interval, what is the residual nitrogen time if you're planning a repetitive dive to 18 metres?
34 minutes
107
Use RDP
Following a surface interval, you're in pressure group T. What would be your RNT for a repetitive dive planned to 16 metres?
60 minutes
108
Use RDP
Indicate the final pressure group upon surfacing after the following series of dives.
First Dive: 15m/40min
Surface Interval: 1:00
Second Dive: 12m/60min
S
109
Use RDP
Indicate the final pressure group upon surfacing after the following series of dives.
First Dive: 18m/30min
Surface Interval: 30mins
Second Dive: 15m/30min
R
110
Use RDP
Indicate the final pressure group upon surfacing after the following series of dives.
First Dive: 17m/50min
Surface Interval: 24mins
Second Dive: 16m/30min
X
111
Use RDP
What is the min surface interval required between a dive to 18m/40min and a second dive to 18m/40min?
1:08
112
Use RDP
What is the min surface interval required between a dive to 16m/60min and a second dive to 14m/70min?
1:07
113
Use RDP
What is the min surface interval required between a dive to 18m/50min and a second dive to 14m/60min?
0:42
114
Use RDP
A diver exits the water at 10:45am after a dive to 24m for 21 mins. At 11:15am he re-enters the water for a 36min dive to 18m. If he wishes to make a third dive after only a 2 min surface interval, what is the maximum depth to which he may dive and remain for at least 20 minutes?
The third dive cannot be made with such a short interval.
You'll notice after the second dive he's in pressure group W. This triggers one of the special rules.
The rule:
If planning 3 or more dives in one day: Beginning with the first dive, if your ending pressure group after any dive is W or X, the minimum surface interval between all subsequent dives is 1 hour. If your ending pressure group after any dive is Y or Z, the min surface interval between all subsequent dives is 3 hours.
115
Use RDP
A diver is planning a series of 3 dives. Assume he will use minimum surface intervals between EACH dive, follow all Recreational Dive Planner rules and dive the following exact profiles:
Dive 1: 24m/26min
Dive 2: 12m/85min
Dive 3: 11m/61min
In minutes, approximately how long will the entire dive profile take to complete-from start to finish?
362
Notes:
Both dives require 3 minute safety stop. And after dive 2, special rule related to pressure group Z is triggered, causing next interval to be min 3 hours.
116
Use eRDPml
A diver exits the water at 1:30pm after a dive to 19m/34min. he re-enters the water at 2:20pm for a dive to 17m/24min. how soon cold the diver re-enter the water for a diver to 15m/40min?
35 Min
Dive planning mode to get pressure group after dive two. Then surface interval mode, put in pressure group found and last dive numbers.
117
Use eRDPml
A diver exits the water at 10:40am after a dive to 28m/20min. he re-enters the water at 12:20pm for a dive to 19m/27min. how soon cold the diver re-enter the water for a diver to 17m/30min?
37 min
Dive planning mode to get pressure group after dive two. Then surface interval mode, put in pressure group found and last dive numbers.
118
The RDP Model is characterized by:
*Online assessment question
14 compartments and a 60 minute surface interval washout
119
Using RDP table, you plan to make two dives, the first to 40m and the second to 12m.
What is the no decompression limit for the first dive?
Assuming your first dive is for 9 minutes and you have a one hour, 30 minute surface interval, what is the no decompression limit for the second dive?
*Online assessment question
9min
130min
120
Using RDP Table, you plan to make three dives. The first will be to 29m for 15 minutes, followed by a one hour, 45 minute surface interval. The second will be to 21m for 20 minutes.
If this is followed by a 52 minute surface interval, what is the no decompression limit for a repetitive dive to 21m?
*Online assessment question
Metric: 22 min
121
Using the RDP Table, what is the minimum surface interval required between a dive to 16m for 60 minutes, followed by a second dive to 14m for 70 minutes?
*Online assessment question
Metric 1:07
122
Using eRDPml, what is the no decom limit for a dive to 28m?
*Online assessment question
23min
123
Using eRDPml, you plan to make two dives.
The first dive will be to 28m for 14 min, followed by a one hour, 30 minute surface interval. The second dive will be to 12m. What is the no decom limit for the second dive?
*Online assessment question
130min
124
Using the eRDPML, you’re planning a two-level multilevel dive. You plan to spend 18 minutes at your first level of 29 m/92 ft and then ascend to 20 m/65 ft for the remainder of the dive. What is the maximum time you can spend at your second depth level?
*Online assessment question
10min
125
Using the eRDPML, you plan to make three dives. The first will be to 19 m/63 ft for 30 minutes, followed by a 30 minute surface interval. The second will be to 15 m/54 ft for 27 minutes. If this is followed by a one hour, 40 minute surface interval, what is the no decompression limit for a repetitive dive to 14 m/48 ft?
*Online assessment question
79min
126
Using the eRDPML, you have just made two dives, the first to 29 m/98 ft for 12 minutes, and the second to 23 m/59 ft for 20 minutes, with a 42 minute surface interval between them. What is the minimum required surface interval for a third dive to 15 m/54 ft for 40 minutes?
*Online assessment question
35 min
