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US Navy Decompression
Tables and Procedures,
Part One
Presented by the NOAA Diving Center
Seattle, Washington

Table development
Definitions
Rules
No-decompression limits
and Repetitive Group
Designation table
Global View View
Residual nitrogen
timetables
Diagramming dives

What are decompression tables?
Introduction-1
Introduction
– Depth and time limits used to plan and conduct dives in
such a manner as to reduce the probability of
decompression sickness.
– Decompression tables take into consideration the amount
of nitrogen absorbed by the body at various depths and
times.
– Other considerations are the allowable pressure gradients
which can exist without excessive bubble formation and
different gas elimination rates associated with various
body tissues.

Introduction-2
Introduction
Development of the USN Decompression tables
– 1915: First set of decompression tables developed by French
and Stillson for the USN Bureau of Construction and
Repair
– 1935: Second generation tables developed by Hawkins,
Shillings, and Hanson
– 1937: Third generation tables developed by Yarborough
– 1951: Fourth generation developed by Van Der Aue
– 1956: Fifth generation tables developed by Des Granger,
Dwyer, and Workman developed with a UNIVAC
computer and tested with approximately 600 man-dives
at the USN EDU

Introduction-3
Introduction
Development of the USN Decompression tables Con’t.
– 1993: New probabilistic (versus deterministic)
tables developed, but rejected by Naval Sea
System Command (too conservative)
– 1999: Latest version of USN Air Decompression
Tables released. Includes new tables for
traveling to altitude following dives
– Future: New Nitrox Tables are being developed

Table Definitions-1
Definitions
Depth: Maximum depth attained during a dive
Actual Bottom Time (ABT): Time from leaving surface until
beginning a direct ascent to the surface
Decompression: Process of eliminating nitrogen from the body
during ascent
– Linear: One continuous ascent without stopping
– Staged: Stops for specific times at specific depths during
ascent
No-Decompression limits: Maximum time that can be spent at a
given depth without requiring staged decompression

Table Definitions-2
Definitions
Decompression schedule: List of decompression stops for a
particular max. depth and bottom time, e. g., 100’/25
Single dive: Any dive conducted more than 12 hours after a
previous dive
Surface Interval Time (SIT): Time spent at the surface
between dives.
Residual nitrogen: Amount of nitrogen gas remaining in a
diver’s tissues following a dive
Repetitive dive: Any dive conducted less than 12 hours after
a previous dive.

Table Definitions-3
Definitions
Repetitive Group Designation (RGD): A letter that designates
the amount of nitrogen remaining in a diver’s body during a
12-hour period following a dive
Residual Nitrogen Time (RNT): Time (minutes) that must be
considered when calculating the bottom time of a repetitive
dive to compensate for nitrogen remaining in a diver’s tissues
from a previous dive.
Equivalent Single Dive Time (ESDT): Time (minutes) used to
select a schedule for a single repetitive dive. Equal to the
bottom time of the planned repetitive dive plus the diver’s
residual nitrogen time (ABT + RNT)

Dive Table Rules
All dive schedules not specifically listed are covered in
the tables by the next deeper and longer schedule
Enter tables at the listed depth that is exactly equal to,
or is the next greater depth than the maximum depth
attained during a dive
Select the bottom time that is exactly equal to, or is
next greater than the bottom time of the dive
The rate of ascent from the bottom to the surface and
between decompression stops is 30 fpm

The U. S. Navy No-
Decompression Limits
and Repetitive Group
Designation Table
Summarizes all depth
and bottom time
combinations that do not
require staged decompression
Provides repetitive group designation
(RGD) for each no-decompression
dive
USN No-Deco No Deco Tables-1 Tables
FSW MAX A B C D E F
10 60 120 210 300 797 *
15 35 70 110 160 225 350
20 25 50 75 100 135 180
25 595 20 35 55 75 100 125
30 405 15 30 45 60 75 95
35 310 5 15 25 40 50 60

USN No-Deco No Deco Tables-2 Tables
No-Decompression Limits and Repetitive Group Designation Table For No-
Decompression Air Dives - 1999
Depth Max A B C D E F G H I J K L M N O
10 60 120 210 300 797 *
15 35 70 110 160 225 350 452 *
20 25 50 75 100 135 180 240 325 390 917 *
25 595 20 35 55 75 100 125 160 195 245 315 361 540 595
30 405 15 30 45 60 75 95 120 145 170 205 250 310 344 405
35 310 5 15 25 40 50 60 80 100 120 140 160 190 220 270 310
40 200 5 15 25 30 40 50 70 80 100 110 130 150 170 200
50 100 10 15 25 30 40 50 60 70 80 90 100
60 60 10 15 20 25 30 40 50 55 60
70 50 5 10 15 20 30 35 40 45 50
80 40 5 10 15 20 25 30 35 40
90 30 5 10 12 15 20 25 30
100 25 5 7 10 15 20 22 25
110 20 5 10 13 15 20
120 15 5 10 12 15
130 10 5 8 10

Description:
USN No-Deco No Deco Tables-3
Tables
– First vertical column on far left lists various depths from 10
to 190 fsw
– Second vertical column from the left lists depths from 3 to
59.9 meters
– Third vertical column from the left indicates the maximum
No-decompression Limits in minutes for each depth
– Remaining vertical columns list specific bottom times
ranging from 5 minutes To 917 minutes
– Horizontal top row lists the repetitive group designation from
A to O

Description, cont.
USN No-Deco No Deco Tables-4 Tables
FSW MAX A B C D E F G H I J K L M N O
10 60 120 210 300 797 *
15 35 70 110 160 225 350 452 *
20 25 50 75 100 135 180 240 325 390 917 *
25 595 20 35 55 75 100 125 160 195 245 315 361 540 595
30 405 15 30 45 60 75 95 120 145 170 205 250 310 344 405
35 310 5 15 25 40 50 60 80 100 120 140 160 190 220 270 310
– Depths shallower than 20 feet do not have a specific nodecompression
limit. The USN determined that times listed were
sufficient for any operational tasks required
– Dives with times that exceed those listed on the table must use
the USN Standard Air Table

Application:
– Locate exact or next greater
depth from vertical column on
far left
– Move horizontally to locate
exact or next greater bottom
time
– Move vertically to the top of
the page and read the
repetitive group designation
(RGD) letter
USN No-Deco No Deco Tables-5
Tables
FSW MAX A B C D E F
10 60 120 210 300 797 *
15 35 70 110 160 225 350
20 25 50 75 100 135 180
25 595 20 35 55 75 100 125
30 405 15 30 45 60 75 95
35 310 5 15 25 40 50 60
40 200 5 15 25 30 40 50
50 100 10 15 25 30 40
60 60 10 15 20 25 30

Questions 1 and 2:
USN No-Deco No Deco Tables-6
Tables
– What is the max. no-decompression limit for a dive to 60
feet?
– What is the RGD for the 60’/:60 dive?
FSW MAX A B C D E F G H I J K
10 60 120 210 300 797 *
15 35 70 110 160 225 350 452 *
20 25 50 75 100 135 180 240 325 390 917 *
25 595 20 35 55 75 100 125 160 195 245 315 361
30 405 15 30 45 60 75 95 120 145 170 205 250
35 310 5 15 25 40 50 60 80 100 120 140 160
40 200 5 15 25 30 40 50 70 80 100 110 130
50 100 10 15 25 30 40 50 60 70 80 90
60 60 10 15 20 25 30 40 50 55 60

Answers to questions 1 and 2:
Question #1: 60 minutes
Question #1: 60 minutes
USN No-Deco No Deco Tables-7 Tables
FSW MAX A B C D E F G H I J K
10 60 120 210 300 797 *
15 35 70 110 160 225 350 452 *
20 25 50 75 100 135 180 240 325 390 917 *
25 595 20 35 55 75 100 125 160 195 245 315 361
30 405 15 30 45 60 75 95 120 145 170 205 250
35 310 5 15 25 40 50 60 80 100 120 140 160
40 200 5 15 25 30 40 50 70 80 100 110 130
50 100 10 15 25 30 40 50 60 70 80 90
60 60 10 15 20 25 30 40 50 55 60
Question #2: RGD = J
Question #2: RGD = J

Question #3:
USN No-Deco No Deco Tables-8
Tables
– What is the maximum no-decompression limit for a dive to 33
feet?
FSW MAX A B C D E F G H I J K L M N O
10 60 120 210 300 797 *
15 35 70 110 160 225 350 452 *
20 25 50 75 100 135 180 240 325 390 917 *
25 595 20 35 55 75 100 125 160 195 245 315 361 540 595
30 405 15 30 45 60 75 95 120 145 170 205 250 310 344 405
35 310 5 15 25 40 50 60 80 100 120 140 160 190 220 270 310
40 200 5 15 25 30 40 50 70 80 100 110 130 150 170 200

Answer to question #3:
USN No-Deco No Deco Tables-9
Tables
FSW MAX A B C D E F G H I J K L M N O
10 60 120 210 300 797 *
15 35 70 110 160 225 350 452 *
20 25 50 75 100 135 180 240 325 390 917 *
25 595 20 35 55 75 100 125 160 195 245 315 361 540 595
30 405 15 30 45 60 75 95 120 145 170 205 250 310 344 405
35 310 5 15 25 40 50 60 80 100 120 140 160 190 220 270 310
40 200 5 15 25 30 40 50 70 80 100 110 130 150 170 200
– The maximum no-decompression limit for a dive to 33 fsw is
310 minutes.

Question #4:
USN No-Deco No Deco Tables-10
Tables 10
– What would be the RGD for a dive to 115 fsw for 14 minutes?
FSW MAX A B C D E F G H I J K L M N O
100 25 5 7 10 15 20 22 25
110 20 5 10 13 15 20
120 15 5 10 12 15
130 10 5 8 10

Answer to question #4:
USN No-Deco No Deco Tables-11
Tables 11
FSW MAX A B C D E F G H I J K L M N O
100 25 5 7 10 15 20 22 25
110 20 5 10 13 15 20
120 15 5 10 12 15
130 10 5 8 10
– The RGD for a dive to 115 fsw for 14 minutes is F

USN Repetitive Dive Tables-1
Tables
Residual nitrogen timetable for repetitive air dive
– Surface Interval Table
– Residual Nitrogen Table
Purpose: To provide a means to determine the
amount of nitrogen remaining in a diver’s body when
planning a repetitive dive

Surface Interval Credit Table
– Credits time that a diver at the
surface off-gasses nitrogen
– Minimum SIT must be 10
minutes
– A dive started less than 10
minutes after a previous dive is
considered part of the same
dive
USN Repetitive Dive Tables-2 Tables
– Dives 12 hours or more after
a previous dive are not repetitive
dives and do not require RNT A
calculation
B
F
E 0:10
0:54
0:10
0:45
C
D 0:10
1:09
0:46
1:29
0:55
1:57
1:30
2:28
0:10
1:39
1:10
2:38
1:58
3:24
2:29
3:57
0:10
3:20
1:40
4:49
2:39
5:48
3:25
6:34
3:58
7:05
F E D C B A
0:10
12:00
3:21
12:00
4:50
12:00
5:49
12:00
6:35
12:00
7:06
12:00

USN Repetitive Dive Tables-3
Tables
Description--Surface Interval Credit Table:
– Diagonal = Beginning RGD
– 16 columns in hours : minutes
– Bottom horizontal = Ending RGD
Z 0:10
0:22
O 0:10
0:23
E 0:10
0:54
Repetitive group at the beginning of the surface interval
N 0:10
0:24
0:23
0:34
M 0:10
0:25
0:24
0:36
0:35
0:48
L 0:10
0:26
0:25
0:39
0:37
0:51
0:49
1:02
J
K 0:10
0:28
0:26
0:42
0:40
0:54
0:52
1:07
1:03
1:18
0:27
0:45
0:43
0:59
0:55
1:11
1:08
1:24
1:19
1:36
I
0:10
0:31
0:29
0:49
0:46
1:04
1:00
1:18
1:12
1:30
1:25
1:43
1:37
1.55
H 0:10
0:36
0:10
0:33
0:32
0:54
0:50
1:11
1:05
1:25
1:19
1:35
1:31
1:53
1:44
2:04
1:56
2:17
F
G 0:10
0:40
0:34
0:59
0:55
1:19
1:12
1:35
1:26
1:49
1:40
2:05
1:54
2:18
2:05
2:29
2:18
2:42
0:37
1:06
1:00
1:29
1:20
1:47
1:36
2:03
1:50
2:19
2:06
2:34
2:19
2:47
2:30
2:59
2:43
3:10
0:10
0:45
0:41
1:15
1:07
1:41
1:30
2:02
1:48
2:20
2:04
2:38
2:20
2:53
2:35
3:08
2:48
3:22
3:00
3:33
3:11
3:45
C
D 0:10
1:09
0:46
1:29
1:16
1:59
1:42
2:23
2:03
2:44
2:21
3:04
2:39
3:21
2:54
3:36
3:09
3:52
3:23
4:04
3:34
4:17
3:46
4:29
0:55
1:57
1:30
2:28
2:00
2:58
2:24
3:20
2:45
3:43
3:05
4:02
3:22
4:19
3:37
4:35
3:53
4:49
4:05
5:03
4:18
5:16
4:30
5:27
B
0:10
1:39
1:10
2:38
1:58
3:24
2:29
3:57
2:59
4:25
3:21
4:49
3:44
5:12
4:03
5:40
4:20
5:48
4:36
6:02
4:50
6:18
5:04
6:32
5:17
6:44
5:28
6:56
A
0:10
3:20
1:40
4:49
2:39
5:48
3:25
6:34
3:58
7:05
4:26
7:35
4:50
7:59
5:13
8:21
5:41
8:50
5:49
8:58
6:03
9:12
6:19
9:28
6:33
9:43
6:45
9:54
6:57
10:05
Z O N M L K J I H G F E D C B A
0:10
12:00
3:21
12:00
4:50
12:00
5:49
12:00
6:35
12:00
7:06
12:00
7:36
12.00
8:00
12:00
8:22
12:00
8:51
12:00
8:59
12:00
9:13
12:00
9:29
12:00
9:44
12:00
9:55
12:00
10:06
12:00

Application--SIT:
– Enter the schedule on the
diagonal slope using the
RGD from the previous dive
– Read horizontally until the
surface interval is equal to,
or between, the times
shown in the schedule
– Read the new RGD at the
bottom of the column
USN Repetitive Dive Tables-4 Tables
IN
F 0:10
0:45
E 0:10
0:54
C
D 0:10
1:09
0:46
1:29
0:55
1:57
1:30
2:28
B
0:10
1:39
1:10
2:38
1:58
3:24
2:29
3:57
A
0:10
3:20
1:40
4:49
2:39
5:48
3:25
6:34
3:58
7:05
0:10
12:00
3:21
12:00
4:50
12:00
5:49
12:00
6:35
12:00
7:06
12:00
F E D C B A
OUT

USN Repetitive Dive Tables-5
Tables
Residual Nitrogen Timetable
– Used to determine the amount of nitrogen (RNT) that must be
considered for repetitive dives
– RNT is considered time that the diver has already spent at
depth for the planned repetitive dive
– When the SIT is less than 10 minutes, the RNT for a repetitive
dive is the same as the ABT from the previous dive
Z O N M L K J I H G F E D C B A
10 ** ** ** ** ** ** ** ** ** ** ** 797 279 159 88 39
20 ** ** ** ** ** ** 917 399 279 208 159 120 88 62 39 18
30 † † † 349 279 229 190 159 132 109 88 70 54 39 25 12
40 257 241 213 187 161 138 116 101 87 73 61 49 37 25 17 7
50 169 160 142 124 111 99 87 76 66 56 47 38 29 21 13 6

USN Repetitive Dive Tables-6
Tables
Description--Residual Nitrogen Timetable:
– Far left column lists depth of the repetitive dive from 10 to 190 fsw
– 16 columns of residual nitrogen times for specific depths
Z O N M L K J I H G F E D C B A
10 ** ** ** ** ** ** ** ** ** ** ** 797 279 159 88 39
20 ** ** ** ** ** ** 917 399 279 208 159 120 88 62 39 18
30 † † † 349 279 229 190 159 132 109 88 70 54 39 25 12
40 257 241 213 187 161 138 116 101 87 73 61 49 37 25 17 7
50 169 160 142 124 111 99 87 76 66 56 47 38 29 21 13 6
60 122 117 107 97 88 79 70 61 52 44 36 30 24 17 11 5
70 100 96 87 80 72 64 57 50 43 37 31 26 20 15 9 4

Application--RNT:
USN Repetitive Dive Tables-7 Tables
– Enter the timetable vertically with the RGD from the SIT table
– Read directly the bottom time to be added to the repetitive
dive in the depth row for the dive
Z O N M L K J I H G F E D C B A
10 ** ** ** ** ** ** ** ** ** ** ** 797 279 159 88 39
20 ** ** ** ** ** ** 917 399 279 208 159 120 88 62 39 18
30 † † † 349 279 229 190 159 132 109 88 70 54 39 25 12
40 257 241 213 187 161 138 116 101 87 73 61 49 37 25 17 7
50 169 160 142 124 111 99 87 76 66 56 47 38 29 21 13 6
60 122 117 107 97 88 79 70 61 52 44 36 30 24 17 11 5
70 100 96 87 80 72 64 57 50 43 37 31 26 20 15 9 4
80 84 80 73 68 61 54 48 43 38 32 28 23 18 13 8 4

Question #1:
USN Repetitive Dive Tables-8
Tables
– What is the Residual Nitrogen Time (RNT) for a Group G
diver planning a repetitive dive to 75 fsw after a Surface
Interval (SIT) of 2½ hours?

USN Repetitive Dive Tables-9
Tables
Answer to question #1:
– RNT = 18 mins.
I
60
70
80
90
H 0:10
0:36
0:10
0:33
G 0:10
0:40
0:34
0:59
F 0:10
0:45
0:37
1:06
1:00
1:29
E 0:10
0:54
0:41
1:15
1:07
1:41
1:30
2:02
0:46
1:29
1:16
1:59
1:42
2:23
2:03
2:44
0:55
1:57
1:30
2:28
2:00
2:58
2:24
3:20
2:45
3:43
1:58
3:24
2:29
3:57
2:59
4:25
3:21
4:49
3:44
5:12
3:25
6:34
3:58
7:05
4:26
7:35
4:50
7:59
5:13
8:21
I H G F E D C B
61 52 44 36 30 24 17 11
50 43 37 31 26 20 15 9
43 38 32 28 23 18 13 8
38 33 29 24 20 16 11 7

Question #2:
USN Repetitive Dive Tables-10
Tables 10
– What is the RNT for a Group C diver planning a
repetitive dive to 65 fsw after an SIT of 1 hour and :05
minutes?

USN Repetitive Dive Tables-11
Tables 11
Answer to question #2:
– RNT = 15 mins.
E 0:10
0:54
50
60
70
80
C
D 0:10
1:09
0:55
1:57
B
0:10
1:39
1:10
2:38
1:58
3:24
A 0:10
12:00
0:10
3:20
1:40
4:49
2:39
5:48
3:25
6:34
3:21
12:00
4:50
12:00
5:49
12:00
6:35
12:00
E D C B A
38 29 21 13 6
30 24 17 11 5
26 20 15 9 4
23 18 13 8 4

Question #3:
USN Repetitive Dive Tables-12
Tables 12
– A diver makes a dive to 95 fsw for 20 minutes. After a
surface interval of 2½ hours, the diver wants to make a
second dive to 90 fsw. What’s the maximum nodecompression
time allowed on the second dive?

D
e
p
t
h
RGD
SIT
Diagramming Dives
Depth = Vertical axis Time = Horizontal axis
Time
____ ABT
RGD RGD SIT RGD
____ RNT
+____ ABT
____ ESDT
RGD
____ RNT
+____ ABT
____ ESDT

USN Repetitive Dive Tables-13
Tables 13
Answer to question #3: Maximum of 19 minutes
F 2:30 C H
95’ 100’/:20 90’ 90’/:30
20 ABT
11 RNT
19 ABT
30 ESDT

Know the dive table terms and abbreviations
Always follow the dive table rules--DO NOT
INTERPOLATE
Learn when to use which dive table
Always diagram dives
Ascend no faster than 30 fpm
Good table use requires frequent practice
Key Key Points

US Navy Decompression
Tables and Procedures,
Part Two
Presented by the NOAA Diving Center
Seattle, Washington

Standard air decompression tables
Minimum surface interval
Surface interval special rule
Dive sequencing
Global View View

USN Decompression Tables-1 Tables
Purpose: Provides decompression schedule information for dives
that require staged decompression
60
U. S. Navy Air Decompression Table - 1999
Bottom Time Time 1 st Stop 20’ Stop 10’ Stop Total Time Repet. Group
60 Mins. 0 2:00 *
70 Mins. (1:40) 2 4:00 K
80 Mins. (1:40) 7 9:00 L
100 Mins. (1:40) 14 16:00 M
120 Mins. (1:40) 26 28:00 N
140 Mins. (1:40) 39 41:00 O
160 Mins. (1:40) 48 50:00 Z
180 Mins. (1:40) 56 58:00 Z
200 Mins. (1:20) 1 69 72:00 Z
240 Mins. (1:20) 2 79 83:00 **
360 Mins. (1:20) 20 119 141:00 **
480 Mins. (1:20) 44 148 194:00 **
720 Mins. (1:20) 78 187 267:00 **

Description:
USN Decompression Tables-2 Tables
– Dives

60
USN Decompression Tables-3
Tables
Description, cont.
– Far left column lists depths from 40 to 300 fsw
– Next column to right is the bottom time in minutes that range
from 5 to 270 minutes depending on the depth
– Next column to right is the time (minutes) to reach the first
decompression stop from depth
Bottom Time Time 1 st Stop 20’ Stop 10’ Stop Total Time Repet. Group
60 Mins. 0 2:00 *
70 Mins. (1:40) 2 4:00 K
80 Mins. (1:40) 7 9:00 L

60
USN Decompression Tables-4 Tables
Description, cont.
– Next set of columns to right are depths of decompression
stops that range from 10 to 200 fsw, and decompression
times that range from 1 to 187 minutes.
Bottom Time Time 1 st Stop 20’ Stop 10’ Stop Total Time Repet. Group
60 Mins. 0 2:00 *
70 Mins. (1:40) 2 4:00 K
80 Mins. (1:40) 7 9:00 L

Description, cont.
USN Decompression Tables-5
Tables
– Next column to right is the total decompression time (time from
leaving bottom until reaching surface) in minutes and seconds
– The far right column is the RGD, which ranges from C to Z
Bottom Time Time 1 st Stop 20’ Stop 10’ Stop Total Time Repet. Group
60 Mins. 0 2:00 *
70 Mins. (1:40) 2 4:00 K
80 Mins. (1:40) 7 9:00 L

60
USN Decompression Tables- Tables 6
Application: (60 foot table)
Bottom Time Time 1 st Stop 20’ Stop 10’ Stop Total Time Repet. Group
60 Mins. 0 2:00 *
70 Mins. (1:40) 2 4:00 K
80 Mins. (1:40) 7 9:00 L
100 Mins. (1:40) 14 16:00 M
120 Mins. (1:40) 26 28:00 N
– Locate exact or next greater depth of dive from vertical
column on far left
– Move horizontally to locate exact or next greater bottom time
– Move horizontally on the same line, and read RGD from the
far right column

60
Question #1 :
USN Decompression Tables-7 Tables
– What is the schedule, decompression requirement, and RGD
for a dive to 60 fsw for 80 minutes?
Bottom Time Time 1 st Stop 20’ Stop 10’ Stop Total Time Repet. Group
60 Mins. 0 2:00 *
70 Mins. (1:40) 2 4:00 K
80 Mins. (1:40) 7 9:00 L
100 Mins. (1:40) 14 16:00 M

60
USN Decompression Tables-8
Tables
Answer to question #1:
Bottom Time Time 1 st Stop 20’ Stop 10’ Stop Total Time Repet. Group
60 Mins. 0 2:00 *
70 Mins. (1:40) 2 4:00 K
80 Mins. (1:40) 7 9:00 L
100 Mins. (1:40) 14 16:00 M
– 60’/80, 10’/7, Group L

Question #2:
USN Decompression Tables-9
Tables
– A diver makes a dive to 115 fsw for 24 minutes.
Following a 3 hour surface interval, the diver makes
another dive to 108’ for 42 minutes.
– What will be the diver’s RGD at the end of the second
dive?

USN Decompression Tables-10
Tables 10
Answer question #2:
115’ 108’
120’/:25 110’/:60
24 ABT
I 3 hrs. D
10’ :06
10 10’ 10 :36
:13 RNT
:42 ABT
N
20’ :18
:55 ESDT

Calculating Minimum SIT-1
SIT
Step 1: Determine RGD from previous dive
Step 2: Determine ABT for repetitive dive
Step 3: Subtract planned dive time (ABT) from maximum
ESDT for planned depth to find the maximum RNT
allowable for repetitive dive
Step 4: Find RNT # maximum RNT allowed for
dive and note RGD for that RNT at planned
depth
Step 5: Find minimum SIT to move from current RGD
to required RGD

Minimum SIT-2 SIT
Question: A diver plans to dive for 35 minutes to 60 fsw
after a 12 minute dive to 92 fsw. What is the minimum
SIT to make the second dive without stage
decompression?

Minimum SIT-3 SIT
Answer:
– Step 1: Find RGD for the first dive. 92’/12 = 100’/15 = E
– Step 2: Find NDL for repetitive dive depth. 60 fsw = 60 mins.
– Step 3: Subtract ABT from NDL to get maximum RNT allowed
– Step 4: Find RNT = or < 25 on 60’ line of RNT table = 24 mins.
– Step 5: Find new RGD at top of 24 mins. Column = D
15 18 22 25 28 31 34 37 40 GROUP
50 60 70 80 90 100 110 120 130 Letter
6 5 4 4 3 3 3 3 3
94 55 46 36 27 22 17 12 7 A
13 1 1 9 8 7 7 6 6 6
87 49 41 32 23 18 14 9 4
21 17 15 13 11 10 10 9 8
79 43 35 27 19 15 10 6 2
29 24 20 18 16 14 13 12
71 36 30 22 14 11 7 3
38 30 26 23 20 18 16
62 30 24 17 10 7 4
B
C
D
E

– Step 6: Use SIT Table
to determine minimum
time to change from
RGD “E” to RGD “D” =
55 minutes
GROUP
Letter
A
B
C
D
E
Minimum SIT-4 SIT
A B C D E F
12:00 12:00 12:00 12:00 12:00 12:00
0:10 3:21 4:50 5:49 6:35 7:06
3:20 4:49 5:48 6:34 7:05
0:10 1:40 2:39 3:25 3:58
1:39 2:38 3:24 3:57
0:10 1:10 1:58 2:29
1:09 1:57 2:28
0:10 0:55 1:30
0:54 1:29
0:10 0:46

Minimum SIT-5 SIT
Question #1: A diver wants to make three, 30
minute No-D dives to 55 fsw. What is the minimum
SIT between dives?
? ?
55’ 55’ 55’
30 ABT 30 ABT 30 ABT

Answer to question #1:
55’ 55’ 55’
30 ABT
30 RNT
+30 ABT
60 ESDT
Minimum SIT-6 SIT
F 0:46 E J 2:21 E J
30 RNT
+30 ABT
60 ESDT

Special table rule:
SI Special Rule-1 Rule
– If a repetitive dive is to the same or greater depth than the
previous dive and the RNT from the RNT timetable is
greater than the ABT or ESDT, you may compute the
repetitive dive using the ABT or ESDT time
– Example: 60’/30 = Group F. Up to 45 min. SIT = Group F.
Group F to 60’ before 46 minutes SIT = 36 minutes RNT.
Use 30 minutes for RNT

Example
SI Special Rule-2 Rule
F 0:45 F L
10’ :07
60’ 60/30 60’ 60/80
30 ABT
30
76
36 RNT
+46 ABT
82 ESDT

Question #1: A diver wants to make the following three,
20 minute dives to the depths indicated. Can all three
dives be made using the no-decompression tables?
:30 :30
55’ 55’ 55’
SI Special Rule-3
Rule
20 ABT 20 ABT 20 ABT

Answer question #1: Yes, using the special rule!
D 0:30 D G :30 G J
55’ 60/20 55’ 60/40 55’ 60/60
20 ABT
20 24 RNT
+20 ABT
40 44 ESDT
SI Special Rule-4 Rule
40 44 RNT
60
+20 ABT
64 ESDT

40’
Question #2 : Solve using Special Rule
:17 ABT
1:00
47’
RNT
+ :30 ABT
ESDT
SI Special Rule-5 Rule
:31
47’
RNT
+:30 ABT
ESDT

40’
Answer question #2 : Using Special Rule
:17 ABT
C 1:00 C
47’
:17 :21 RNT
+ :30 ABT
:47 ESDT
SI Special Rule-6 Rule
G :31 G J
47’
:47 :56 RNT
+:30 ABT
:77 ESDT

Dive Sequencing-1
Sequencing
Always make the deepest dive first. Make repetitive dives
progressively shallower (Example: Deeper dives last)
50’ 70’ 90’
30 ABT
1:00 1:00
20 ABT
20 ABT

Dive Sequencing-2
Sequencing
Always make the deepest dive first. Make repetitive dives
progressively shallower (Example: Deeper dives last)
50’ 70’ 90’
30 ABT
E 1:00 D H 1:00 G
20 RNT
+20 ABT
40 ESDT
10’
29 RNT
+20 ABT
49 ESDT
L
18

Example: Deeper dives first
90’ 70’ 50’
20 ABT
F 1:00 E
Dive Sequencing-3
Sequencing
26 RNT
+20 ABT
46 ESDT
J 1:00 H
66 RNT
+30 ABT
96 ESDT
L

Learn when to use which dive table
Key Key Points
Avoid exceptional exposures and decompression diving
Ascend no faster than 30 fpm
Use Special Rule whenever appropriate
Always do deeper dive first whenever possible

US Navy Decompression
Tables and Procedures,
Part Three
Presented by the NOAA Diving Center
Seattle, Washington

Brief SIT
Safety stops
Cold or arduous dives
Ascent variations
Flying after diving
Omitted decompression
RNT table asterisk
Global View View

Brief SIT
If the SIT is less than 10 minutes, the RNT is the bottom time
from the previous dive.
Add the bottom times of the two dives, use the deepest depth
attained for the schedule, and ignore the SIT
Example: 80’/20, SIT = 0:08, 70/20 schedule is 80’/40
80’ 70’
20 ABT
20 ABT
+20 RNT
40 ESDT

Safety Stops
Definition: Precautionary decompression stops used to
compensate for ascent rate variation and individual variations
in nitrogen absorption and elimination
Recommendation: Use for all dives deeper than 60 fsw and/or
repetitive dives
Procedure: Stop between 15 and 20 fsw for 3 to 5 minutes
Dive table procedure: Safety stop
time does not count as either
bottom time or SIT
Safety stop depths are measured from
the level of the diver’s mouth
70’
15’ 3-5

Cold or Arduous Dives-1
Dives
Rule: For cold or arduous dives, use the next longer
duration for the dive schedule
– Example: Schedule for a 70’/30 dive that is cold or arduous is
70’/35
If you cannot use the next longer duration because it
places the diver into decompression, use the next less
available bottom time
– Example: Maximum no-deco bottom time allowed for a cold or
arduous dive to 70 feet is 45 minutes and the RNT would be
figured as if the dive was made for the next greater bottom time
(i.e. 50 mins)

Cold or Arduous Dives-2 Dives
When planning a cold or arduous repetitive dive, select
the RNT group that is less than the maximum allowable
RNT figured for the dive. This will automatically give you
a longer SIT
– Example: You figure the max allowable RNT for a repetitive
dive to 60’/30 is 30 minutes. Since you suspect the dive will
be cold or arduous you would use 24 minutes as your RNT
and follow 60’/55 schedule

Cold or Arduous Dives-3 Dives
Answer:
– Step 1: Find the max RNT for repetitive dive 60/30 = 30 min
– Step 2: Since cold or arduous go to next lesser RNT = 24 min
– Step 3: Move vertically to locate RGD for repetitive dive
15 18 22 25 28 31 34 37 40 GROUP
50 60 70 80 90 100 110 120 130 Letter
6 5 4 4 3 3 3 3 3
94 55 46 36 27 22 17 12 7
13 11 9 8 7 7 6 6 6
87 49 41 32 23 18 14 9 4
21 17 15 13 11 10 10 9 8
79 43 35 27 19 15 10 6 2
29 24 20 18 16 14 13 12
71 36 30 22 14 11 7 3
38 30 26 23 20 18 16
62 30 24 17 10 7 4
A
B
C
D
E

Ascent Variations
The normal rate of ascent is 30 fpm (2 secs/ft)
If the rate is less than 30 fpm and the delay exceeds one
minute, add total delay time to bottom time and revise
dive schedule
If the rate is greater than 30 fpm, stop ascent for the
time that it should have taken to reach the present depth

Diving At Altitude-1
Altitude
Ambient pressure decreases with altitude and flying after
diving or driving over mountains is risky
Because of the reduced ambient pressure, dives conducted at
altitude require more decompression than identical dives
conducted at sea level
Two different approaches used for altitude diving:
– Calculate specific decompression tables for use at each altitude
– Calculate the equivalent sea level depth and use standard
decompression tables (i.e. Cross Correction Technique)
Refer to the section 10.12 NDM for more information on the
Cross Correction Technique and altitude diving

Diving At Altitude-2
Altitude
The US Navy air decompression tables may be used without
correction for dives conducted at altitudes between sea level
and 300 feet
At altitudes between 300 – 1,000 feet, correction is required
for dives deeper than 145 fsw (actual depth)
At altitudes above 1,000 feet, correction is required for all
dives
Diving at altitude requires special training

Flying After Diving-1 Diving
The cabin pressure of a modern, pressurized airplane is normally
maintained at an altitude of 8,000 feet
This reduction in ambient pressure may be sufficient to cause the
formation of bubbles following a dive at sea level
Termination of the flight, which increases the ambient pressure to 1
atmosphere, may not necessarily reduce the size of the bubble
enough to relieve the signs and symptoms of DCS, and
recompression therapy may be required
NOAA dive regulations state that the minimum surface interval
required before flying after diving shall be in accordance with Table
9-5, Required Surface Interval Before Ascent to Altitude After
Flying, USN Dive Manual, Revision 4, Jan. 20, 1999

Flying After Diving-2 Diving
R equired Surface Interval Before Ascent to Altitude After D iving.
R epetitive Increase in Altitude
Group 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
Designator
A 0:00 0:00 0:00 0:00 0:00 0:00 0:00 0:00 0:00 0:00
B 0:00 0:00 0:00 0:00 0:00 0:00 0:00 0:00 0:00 2:11
C 0:00 0:00 0:00 0:00 0:00 0:00 0:00 0:00 3:06 8:26
D 0:00 0:00 0:00 0:00 0:00 0:00 0:09 3:28 7:33 12:52
E 0:00 0:00 0:00 0:00 0:00 0:51 3:35 6:54 10:59 16:18
F 0:00 0:00 0:00 0:00 1:12 3:40 6:23 9:43 13:47 19:07
G 0:00 0:00 0:00 1:23 3:34 6:02 8:46 12:05 16:10 21:29
H 0:00 0:00 1:31 3:26 5:37 8:05 10:49 14:09 18:13 23:33
I 0:00 1:32 3:20 5:15 7:26 9:54 12:38 15:58 20:02 24:00
J 1:32 3:09 4:57 6:52 9:04 11:32 14:16 17:35 21:39 24:00
K 3:00 4:37 6:25 8:20 10:32 13:00 15:44 19:03 23:07 24:00
L 4:21 5:57 7:46 9:41 11:52 14:20 17:04 20:23 24:00 24:00
M 5:35 7:11 9:00 10:55 13:06 15:34 18:18 21:37 24:00 24:00
N 6:43 8:20 10:08 12:03 14:14 16:42 19:26 22:46 24:00 24:00
O 7:47 9:24 11:12 13:07 15:18 17:46 20:30 23:49 24:00 24:00
Z 8:17 9:54 11:42 13:37 15:49 18:17 21:01 24:00 24:00 24:00

Flying After Diving-3 Diving
NOTE 1: When using Table 9-5, use the highest repetitive group designator
obtained in the previous 24-hour period
NOTE 2: Table 9-5 may only be used when the maximum altitude achieved is
10,000 feet or less
NOTE 3: The cabin pressure in commercial aircraft is maintained at a
constant value regardless of the actual altitude of the flight. Though cabin
pressure varies somewhat with aircraft type the nominal value is 8,000 feet.
For commercial flights, use a final altitude of 8000 feet to compute the
required surface interval before flying
NOTE 4: No surface interval is required before taking a commercial flight if
the dive site is at 8000 feet or higher. In this case, flying results in an increase
in atmospheric pressure rather than a decrease

Flying After Diving-4
Diving
Example: A diver surfaces from a 60 fsw for 60 minutes
no-decompression dive at sea level with a Repetitive
Group J. After a surface interval of 6 hours and 10
minutes, the diver makes a second dive to 30 fsw for 20
minutes placing him/her in Repetitive Group C. The
diver plans to fly in a commercial aircraft in which the
cabin pressure is controlled at 8,000 feet. What is the
required surface interval before flying?

Flying After Diving-5
Diving
Answer: The planned increase in altitude is 8,000 feet.
Because the diver has made two dives in a previous
24-hour period, he/she must use the highest Repetitive
Group Designator of the two dives. Enter the table at
8,000 feet and read down to Repetitive Group J. The
diver must wait 17 hours and 35 minutes after
completion of the second dive before flying

Omitted Decompression-1
Decompression
Should a diver realize that they have exceeded the nodecompression
limits prior to reaching the surface, and
they do not have access to USN decompression tables to
determine required in-water deco time, they should:
– Stop at 10 – 15 fsw for a minimum of 15 minutes or until they
reach 300 psi in their cylinder, which ever comes first
– Once on the surface they should be placed on oxygen for a
minimum of 30 minutes, observed, and restricted from diving
for 12 hours
– If symptoms occur during or after breathing oxygen for 30
minutes, they should be transported (on oxygen) to the nearest
medical facility for treatment

Omitted Decompression-2
Decompression
Should a diver not realize that they have exceeded the nodecompression
limits prior to reaching the surface, or they have
insufficient gas to perform in-water decompression, they should:
– Proceed to the surface at a normal rate of ascent
– Once on the surface they should notify the divemaster of their omitted
decompression
– If asymptomatic, and the diver can be returned safely to the water
within 5 minutes after surfacing, they should dive to the depth of the
missed decompression stops and remain for 1½ times the required
decompression stop time
– If the diver cannot be returned to the water within 5 minutes, they
should be placed on oxygen for a minimum of 60 minutes

Cont:
Omitted Decompression-3
Decompression
– If asymptomatic after breathing oxygen for 60 minutes, they
should be observed for a minimum of 12 hours for signs and
symptoms of DCS and restricted from diving during this
observational period
– If symptoms occur during or after breathing oxygen for 60
minutes, they should be transported (on oxygen) to the
nearest medical facility for treatment
Note: Note: If If a diver diver is is asymptomatic and and unable to to return to to the the water water to to
complete omitted decompression, and and a recompression chamber is is
available within 1 hour hour travel, the the diver diver should be be transported to to the the
chamber for for possible treatment using using USN USN TT5 TT5 or or 6

RNT Table Asterisks - 1
The repetitive groups represent the amount of nitrogen in
the 120 min half-time tissue
If at the end of a surface interval you have a repetitive
group that leads you to a double asterisk in the RNT
tables (**), it means that the tissue N2 tension in the 120
min tissue is still higher than the inspired N2 tension at
this depth
Therefore, during the dive the 120 min tissue will actually
off-gas rather than on-gas resulting in a lower group letter

RNT Table Asterisks - 2
To avoid publishing separate off-gassing tables for 10
and 20 fsw dives, the USN decided to have their divers
assume that the repetitive group does not change
during the dive (i.e. it is the same after surfacing as it
was when the diver began the descent)
This is in contrast to normal repetitive dives in which the
repetitive group is always greater after surfacing than it
was at the beginning of the dive

RNT Table Asterisks - 3
Example: A diver surfaces as a “G” diver. After 1
hour on the surface the diver becomes a “F” diver.
The repetitive dive is to 10 fsw and ( ** ) represents
the RNT value from the RNT Table. The dive is for
:40. At the completion of the dive and planning for
another, RGD “F” would be used to enter into the
Surface Interval Table

Key Key Points
If the SIT is less than 10 minutes, the RNT is the bottom
time from the previous dive
Safety Stops are recommended for dives >60’ and all
repetitive dives
For cold or arduous dives, use the next longer duration
for the dive schedule
The normal rate of ascent is 30 fpm (2 secs/ft)
USN Deco Tables can be used without correction to
300 feet elevation