183086d1241453026 u s navy decompression tables procedures usn decompression tables procedures by Watch Geeks

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

Global View • Table development • Definitions

• Residual nitrogen timetables

• Rules

• Diagramming dives

• No-decompression limits and Repetitive Group Designation table

Introduction-1 • What are decompression tables? – 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 • 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 • 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 • 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 • 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 • 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

USN No-Deco Tables-1 • The U. S. Navy NoDecompression Limits and Repetitive Group Designation Table • Summarizes all depth and bottom time combinations that do not require staged decompression

FSW

MAX

15 20

120

210

300

797

110

160

225

350

100

135

180

595

100

125

405

310

• Provides repetitive group designation (RGD) for each no-decompression dive

USN No-Deco Tables-2 No-Decompression Limits and Repetitive Group Designation Table For NoDecompression Air Dives - 1999 Depth

10 15 20 25 30 35 40 50 60 70 80 90 100 110 120 130

Max

595 405 310 200 100 60 50 40 30 25 20 15 10

A 60 35 25 20 15 5 5

B 120 70 50 35 30 15 15 10 10 5 5 5 5

C 210 110 75 55 45 25 25 15 15 10 10 10 7 5 5 5

D 300 160 100 75 60 40 30 25 20 15 15 12 10 10 10 8

E 797 225 135 100 75 50 40 30 25 20 20 15 15 13 12 10

F * 350 180 125 95 60 50 40 30 30 25 20 20 15 15

452 240 160 120 80 70 50 40 35 30 25 22 20

* 325 195 145 100 80 60 50 40 35 30 25

390 245 170 120 100 70 55 45 40

917 315 205 140 110 80 60 50

* 361 250 160 130 90

540 310 190 150 100

595 344 405 220 270 310 170 200

USN No-Deco Tables-3 • Description: – 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

USN No-Deco Tables-4 • Description, cont. FSW

MAX

120

210

300

797

110

160

225

350

452

100

135

180

240

325

390

917

595

100

125

160

195

245

315

361

540

595

405

120

145

170

205

250

310

344

405

310

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

USN No-Deco Tables-5 • 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

FSW

MAX

120

210

300

797

110

160

225

350

100

135

180

595

100

125

405

310

200

100

USN No-Deco Tables-6 • Questions 1 and 2: – What is the max. no-decompression limit for a dive to 60 feet? – What is the RGD for the 60’/:60 dive? FSW

MAX

120

210

300

797

110

160

225

350

452

100

135

180

240

325

390

917

595

100

125

160

195

245

315

361

405

120

145

170

205

250

310

100

120

140

160

200

100

110

130

100

USN No-Deco Tables-7 â&#x20AC;˘ Answers to questions 1 and 2: FSW

MAX

120

210

300

797

110

160

225

350

452

100

135

180

240

325

390

917

595

100

125

160

195

245

315

361

405

120

145

170

205

250

310

100

120

140

160

200

100

110

130

100

Question#1: #1:60 60minutes minutes Question

Question#2: #2:RGD RGD==JJ Question

USN No-Deco Tables-8 • Question #3: – What is the maximum no-decompression limit for a dive to 33 feet? FSW MAX

60 120 210 300 797 *

70 110 160 225 350 452 *

75 100 135 180 240 325 390 917 *

595

75 100 125 160 195 245 315 361 540 595

405

95 120 145 170 205 250 310 344 405

310

80 100 120 140 160 190 220 270 310

200

80 100 110 130 150 170 200

USN No-Deco Tables-9 • Answer to question #3: FSW

MAX

120

210

300

110

797

160

225

350

100

135

452

180

240

325

390

917

595

100

125

160

195

245

315

361

540

595

405

120

145

170

205

250

310

344

405

310

100

120

140

160

190

220

270

200

100

110

130

150

170

200

310

– The maximum no-decompression limit for a dive to 33 fsw is 310 minutes.

USN No-Deco Tables-10 • Question #4: – What would be the RGD for a dive to 115 fsw for 14 minutes? FSW

MAX

100

110

120

130

USN No-Deco Tables-11 • Answer to question #4: FSW MAX

7 10

20 22

100

110

5 10

15 20

120

5 10

130

8 10

– The RGD for a dive to 115 fsw for 14 minutes is F

USN Repetitive Dive Tables-1 • 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

USN Repetitive Dive Tables-2 • Surface Interval Credit Table – Credits time that a diver at the surface off-gasses nitrogen – Minimum SIT must be 10 minutes

– Dives 12 hours or more after a previous dive are not repetitive dives and do not require RNT A calculation 0:10 B

– A dive started less than 10 minutes after a previous dive is considered part of the same dive

0:10 12:00

3:20

3:21 12:00

0:10 1:39

1:40 4:49

4:50 12:00

0:10 1:09

1:10 2:38

2:39 5:48

5:49 12:00

0:10 0:54

0:55 1:57

1:58 3:24

3:25 6:34

6:35 12:00

0:10 0:45

0:46 1:29

1:30 2:28

2:29 3:57

3:58 7:05

7:06 12:00

USN Repetitive Dive Tables-3 • Description--Surface Interval Credit Table: – Diagonal = Beginning RGD – 16 columns in hours : minutes – Bottom horizontal = Ending RGD th at

su e h F ft o g n ni G 0:10 n 0:40 i g e b 0:10 0:37 H

0:10 12:00

0:10 3:20

3:21 12:00

0:10 1:39

1:40 4:49

4:50 12:00

0:10 1:09

1:10 2:38

2:39 5:48

5:49 12:00

0:10 0:54

0:55 1:57

1:58 3:24

3:25 6:34

6:35 12:00

0:10 0:45

0:46 1:29

1:30 2:28

2:29 3:57

3:58 7:05

7:06 12:00

0:41 1:15

1:16 1:59

2:00 2:58

2:59 4:25

4:26 7:35

7:36 12.00

0:36

1:06

1:07 1:41

1:42 2:23

2:24 3:20

3:21 4:49

4:50 7:59

8:00 12:00

0:10 0:33

0:34 0:59

1:00 1:29

1:30 2:02

2:03 2:44

2:45 3:43

3:44 5:12

5:13 8:21

8:22 12:00

0:10 0:31

0:32 0:54

0:55 1:19

1:20 1:47

1:48 2:20

2:21 3:04

3:05 4:02

4:03 5:40

5:41 8:50

8:51 12:00

0:10 0:28

0:29 0:49

0:50 1:11

1:12 1:35

1:36 2:03

2:04 2:38

2:39 3:21

3:22 4:19

4:20 5:48

5:49 8:58

8:59 12:00

0:10 0:26

0:27 0:45

0:46 1:04

1:05 1:25

1:26 1:49

1:50 2:19

2:20 2:53

2:54 3:36

3:37 4:35

4:36 6:02

6:03 9:12

9:13 12:00

0:10 0:25

0:26 0:42

0:43 0:59

1:00 1:18

1:19 1:35

1:40 2:05

2:06 2:34

2:35 3:08

3:09 3:52

3:53 4:49

4:50 6:18

6:19 9:28

9:29 12:00

0:10 0:24

0:25 0:39

0:40 0:54

0:55 1:11

1:12 1:30

1:31 1:53

1:54 2:18

2:19 2:47

2:48 3:22

3:23 4:04

4:05 5:03

5:04 6:32

6:33 9:43

9:44 12:00

0:10 0:23

0:24 0:36

0:37 0:51

0:52 1:07

1:08 1:24

1:25 1:43

1:44 2:04

2:05 2:29

2:30 2:59

3:00 3:33

3:34 4:17

4:18 5:16

5:17 6:44

6:45 9:54

9:55 12:00

0:10 0:22

0:23 0:34

0:35 0:48

0:49 1:02

1:03 1:18

1:19 1:36

1:37 1.55

1:56 2:17

2:18 2:42

2:43 3:10

3:11 3:45

3:46 4:29

4:30 5:27

5:28 6:56

6:57 10:05

10:06 12:00

pe e R

ce a f r

l va r te in D

ve iti

p ou r g

USN Repetitive Dive Tables-4 • 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 F bottom of the column

0:10 12:00

0:10 3:20

3:21 12:00

0:10 1:39

1:40 4:49

4:50 12:00

0:10 1:09

1:10 2:38

2:39 5:48

5:49 12:00

0:10 0:54

0:55 1:57

1:58 3:24

3:25 6:34

6:35 12:00

0:10 0:45

0:46 1:29

1:30 2:28

2:29 3:57

3:58 7:05

7:06 12:00

OUT

USN Repetitive Dive Tables-5 • 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

797

279

159

917

399

279

208

159

120

†

349

279

229

190

159

132

109

257

241

213

187

161

138

116

101

169

160

142

124

111

USN Repetitive Dive Tables-6 • 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

797

279

159

917

399

279

208

159

120

†

349

279

229

190

159

132

109

257

241

213

187

161

138

116

101

169

160

142

124

111

122

117

107

100

USN Repetitive Dive Tables-7 • Application--RNT: – 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

797

279

159

917

399

279

208

159

120

†

349

279

229

190

159

132

109

257

241

213

187

161

138

116

101

169

160

142

124

111

122

117

107

100

USN Repetitive Dive Tables-8 • Question #1: – 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 • Answer to question #1:

0:10 0:54

0:55 1:57

1:58 3:24

3:25 6:34

0:10 0:45

0:46 1:29

1:30 2:28

2:29 3:57

3:58 7:05

0:10 0:40

0:41 1:15

1:16 1:59

2:00 2:58

2:59 4:25

4:26 7:35

0:10 0:36

0:37 1:06

1:07 1:41

1:42 2:23

2:24 3:20

3:21 4:49

4:50 7:59

0:10 0:33

0:34 0:59

1:00 1:29

1:30 2:02

2:03 2:44

2:45 3:43

3:44 5:12

5:13 8:21

– RNT = 18 mins.

USN Repetitive Dive Tables-10 • Question #2: – 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 A

0:10 12:00

0:10 3:20

3:21 12:00

0:10 1:39

1:40 4:49

4:50 12:00

0:10 1:09

1:10 2:38

2:39 5:48

5:49 12:00

0:10 0:54

0:55 1:57

1:58 3:24

3:25 6:34

6:35 12:00

• Answer to question #2: – RNT = 15 mins.

USN Repetitive Dive Tables-12 • Question #3: – 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?

Diagramming Dives • Depth = Vertical axis Time = Horizontal axis RGD SIT RGD

RGD SIT RGD

RGD

D e p t h

Time ____ ABT

____ RNT +____ ABT ____ ESDT

USN Repetitive Dive Tables-13 • Answer to question #3:

Maximum of 19 minutes

F 2:30 C 95’ 100’/:20

90’ 90’/:30

20 ABT 11 RNT 19 ABT 30 ESDT

Key Points • 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

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

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

USN Decompression Tables-1 • Purpose: Provides decompression schedule information for dives that require staged decompression U. S. Navy Air Decompression Table - 1999

Bottom Time 60 Mins. 70 Mins. 80 Mins. 100 Mins. 120 Mins. 140 Mins. 160 Mins. 180 Mins. 200 Mins. 240 Mins. 360 Mins. 480 Mins. 720 Mins.

Time 1 Stop

20’ Stop

(1:40) (1:40) (1:40) (1:40) (1:40) (1:40) (1:40) (1:20) (1:20) (1:20) (1:20) (1:20)

1 2 20 44 78

10’ Stop 0 2 7 14 26 39 48 56 69 79 119 148 187

Total Time 2:00 4:00 9:00 16:00 28:00 41:00 50:00 58:00 72:00 83:00 141:00 194:00 267:00

Repet. Group * K L M N O Z Z Z ** ** ** **

USN Decompression Tables-2 • Description: – Dives <40 feet and/or bottom times less than the first bottom time listed for the depth are considered nodecompression dives – Dives listed as exceptional exposure are potentially dangerous and should only be conducted in a life and death emergency. – No repetitive dives following exceptional exposures – Use of exceptional exposure schedules must be fully justified and thoroughly documented and immediately reported to the DNDP

USN Decompression Tables-3 • 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 60

Bottom Time 60 Mins. 70 Mins. 80 Mins.

Time 1 Stop (1:40) (1:40)

20’ Stop

10’ Stop 0 2 7

Total Time 2:00 4:00 9:00

Repet. Group * K L

USN Decompression Tables-4 • 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. 60

Bottom Time 60 Mins. 70 Mins. 80 Mins.

Time 1 Stop (1:40) (1:40)

20’ Stop

10’ Stop 0 2 7

Total Time 2:00 4:00 9:00

Repet. Group * K L

USN Decompression Tables-5 • Description, cont. – 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 60 Mins. 70 Mins. 80 Mins.

Time 1 Stop (1:40) (1:40)

20’ Stop

10’ Stop 0 2 7

Total Time 2:00 4:00 9:00

Repet. Group * K L

USN Decompression Tables- 6 • Application: (60 foot table) 60

Bottom Time 60 Mins. 70 Mins. 80 Mins. 100 Mins. 120 Mins.

Time 1 Stop (1:40) (1:40) (1:40) (1:40)

20’ Stop

10’ Stop 0 2 7 14 26

Total Time 2:00 4:00 9:00 16:00 28:00

Repet. Group * K L M 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

USN Decompression Tables-7 • Question #1 : – What is the schedule, decompression requirement, and RGD for a dive to 60 fsw for 80 minutes?

Bottom Time 60 Mins. 70 Mins. 80 Mins. 100 Mins.

Time 1 Stop (1:40) (1:40) (1:40)

20’ Stop

10’ Stop 0 2 7 14

Total Time 2:00 4:00 9:00 16:00

Repet. Group * K L M

USN Decompression Tables-8 • Answer to question #1: 60

Bottom Time 60 Mins. 70 Mins. 80 Mins. 100 Mins.

Time 1 Stop

20’ Stop

(1:40) (1:40) (1:40)

– 60’/80, 10’/7, Group L

10’ Stop 0 2 7 14

Total Time 2:00 4:00 9:00 16:00

Repet. Group * K L M

USN Decompression Tables-9 • Question #2: – 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 • Answer question #2: I 10’

115’

3 hrs. :06 108’

120’/:25 24 ABT

N 10’ 10 20’

110’/:60 :13 RNT :42 ABT :55 ESDT

:36 :18

Calculating Minimum SIT-1 • 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 # m aximum 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 â&#x20AC;˘ 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 • 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

22 25 28 31 34 37 40

80 90 100 110 120 130 Letter

6 94

5 55

4 46

4 36

3 27

3 22

3 17

3 12

3 7

13 87 21

11 49 17

9 41 15

8 32 13

7 23 11

7 18 10

6 14 10

6 9 9

6 4 8

79 29 71 38 62

43 24 36 30 30

35 20 30 26 24

27 18 22 23 17

19 16 14 20 10

15 14 11 18 7

10 13 7 16 4

6 12 3

G RO UP

D E

Minimum SIT-4 – Step 6: Use SIT Table to determine minimum time to change from RGD “E” to RGD “D” = 55 minutes

G RO UP

Letter 1 2 :0 0 1 2 :0 0 1 2 :0 0 1 2 :0 0 1 2 :0 0 1 2 :0 0

A B C D E

0 :1 0

3 :2 1 3 :2 0

4 :5 0 4 :4 9

5 :4 9 5 :4 8

6 :3 5 6 :3 4

7 :0 6 7 :0 5

0 :1 0

1 :4 0

2 :3 9

3 :2 5

3 :5 8

1 :3 9 0 :1 0

2 :3 8 1 :1 0

3 :2 4 1 :5 8

3 :5 7 2 :2 9

1 :0 9

1 :5 7

2 :2 8

0 :1 0

0 :5 5

1 :3 0

0 :5 4 0 :1 0

1 :2 9 0 :4 6

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

55’

30 ABT

55’

30 ABT

Minimum SIT-6 • Answer to question #1: F 0:46 55’

55’

2:21

55’

30 ABT 30 RNT +30 ABT 60 ESDT

30 RNT +30 ABT 60 ESDT

SI Special Rule-1 • Special table 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

SI Special Rule-2 • Example F 0:45 60’ 60/30

30 ABT

10’ 60’ 60/80

30 36 RNT +46 ABT 76 82 ESDT

L :07

SI Special Rule-3 • 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

55’

:30

55’

20 ABT

55’

20 ABT

SI Special Rule-4 • Answer question #1: Yes, using the special rule! D 0:30 D 55’

60/20

20 ABT

55’

60/40

20 24 RNT +20 ABT 40 44 ESDT

:30

55’ 60/60

40 44 RNT +20 ABT 60 64 ESDT

SI Special Rule-5 • Question #2 : Solve using Special Rule 1:00 40’

:31 47’

47’

:17 ABT

RNT + :30 ABT ESDT

RNT +:30 ABT ESDT

SI Special Rule-6 • Answer question #2 : Using Special Rule C 1:00 C 40’

G :31 G

47’

:17 ABT

47’

:17 :21 RNT + :30 ABT :47 ESDT

:47 :56 RNT +:30 ABT :77 ESDT

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

1:00

70’ 30 ABT

90’ 20 ABT

20 ABT

Dive Sequencing-2 • Always make the deepest dive first. Make repetitive dives progressively shallower (Example: Deeper dives last) E 1:00 D 50’

H 1:00 G

70’ 30 ABT

20 RNT +20 ABT 40 ESDT

90’

L 10’

29 RNT +20 ABT 49 ESDT

Dive Sequencing-3 • Example: Deeper dives first F 1:00 E 90’

J 1:00 H

70’

20 ABT

50’

26 RNT +20 ABT 46 ESDT

66 RNT +30 ABT 96 ESDT

Key Points • Learn when to use which dive table • 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

Global View • • • • • • •

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

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 15’ 3-5 bottom time or SIT 70’ • Safety stop depths are measured from the level of the diver’s mouth

Cold or Arduous Dives-1 • 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 • 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 • 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

22 25 28

90 100 110 120 130 L etter

6 94 13

5 55 11

4 46 9

4 36 8

3 27 7

3 22 7

3 17 6

3 12 6

3 7 6

21 79 29

17 43 24

15 35 20

13 27 18

11 19 16

10 15 14

10 10 13

9 6 12

8 2

71 38 62

36 30 30

30 26 24

22 23 17

14 20 10

11 18 7

7 16 4

G R O UP

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 • 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 • 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 • 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 R e q u ir e d S u r f a c e I n t e r v a l B e f o r e A s c e n t t o A lt it u d e A f t e r D iv i n g . R e p e t it iv e G roup D e s ig n a t o r

1000

2000

3000

I n c r e a s e in A lt i t u d e 4000 5000

6000

7000

8000

9000

10000

0 :0 0

2 :1 1

0 :0 0

3 :0 6

8 :2 6

0 :0 0

0 :0 9

3 :2 8

7 :3 3

12:52

0 :0 0

0 :5 1

3 :3 5

6 :5 4

10:59

16:18

0 :0 0

1 :1 2

3 :4 0

6 :2 3

9 :4 3

13:47

19:07

0 :0 0

1 :2 3

3 :3 4

6 :0 2

8 :4 6

12:05

16:10

21:29

0 :0 0

1 :3 1

3 :2 6

5 :3 7

8 :0 5

10:49

14:09

18:13

23:33

0 :0 0

1 :3 2

3 :2 0

5 :1 5

7 :2 6

9 :5 4

12:38

15:58

20:02

24:00

1 :3 2

3 :0 9

4 :5 7

6 :5 2

9 :0 4

11:32

14:16

17:35

21:39

24:00

3 :0 0

4 :3 7

6 :2 5

8 :2 0

10:32

13:00

15:44

19:03

23:07

24:00

4 :2 1

5 :5 7

7 :4 6

9 :4 1

11:52

14:20

17:04

20:23

24:00

5 :3 5

7 :1 1

9 :0 0

10:55

13:06

15:34

18:18

21:37

24:00

6 :4 3

8 :2 0

10:08

12:03

14:14

16:42

19:26

22:46

24:00

7 :4 7

9 :2 4

11:12

13:07

15:18

17:46

20:30

23:49

24:00

8 :1 7

9 :5 4

11:42

13:37

15:49

18:17

21:01

24:00

Flying After Diving-3 • 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 â&#x20AC;˘ 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 â&#x20AC;˘ 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 • 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 • 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

Omitted Decompression-3 • Cont: – 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:IfIfaadiver diverisisasymptomatic asymptomaticand andunable unabletotoreturn returntotothe thewater watertoto Note: completeomitted omitteddecompression, decompression,and andaarecompression recompressionchamber chamberisis complete availablewithin within11hour hourtravel, travel,the thediver divershould shouldbe betransported transportedtotothe the available chamberfor forpossible possibletreatment treatmentusing usingUSN USNTT5 TT5oror66 chamber

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 â&#x20AC;˘ 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) â&#x20AC;˘ 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 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