5
60 NAUI Nitrox Diver
In order to effectively and safely switch between
gas mixes or to use nitrox blends not encompassed by
the EAN32 and EAN36 tables, you should use EAD. By
applying the equivalent air depth formula to your diving,
you can use any navy-based or RGBM standard air table
as long as you also follow oxygen exposure limits.
EQUIVALENT AIR DEPTH AND
STANDARD AIR DIVE TABLES
As noted earlier, equivalent air depth (EAD) is
determined by the partial pressure of nitrogen that the
diver is actually breathing. Because nitrox has a lower
fraction of nitrogen than air, the nitrogen partial pressure
will also be less than with air for any given depth, and
the diver’s equivalent depth for nitrogen absorption will
also be less than with air. It is not the actual depth, but
the partial pressure of nitrogen in the breathing gas that
matters.
The theory behind equivalent air depth is that
an EAN diver’s exposure to nitrogen for any absolute
pressure (depth) will be proportionally less than with air
as the fraction of nitrogen in the mix is less than 0.79 (the
fraction of nitrogen in air). Moreover, the rate at which
nitrogen is absorbed by the various tissues is related
to the pressure gradient between the inspired nitrogen
partial pressure and the tension of nitrogen dissolved in
the tissues. If the inspired nitrogen partial pressure is less,
the pressure gradient is less, and nitrogen moves into the
tissues more slowly. And, according to Henry’s Law the
total amount of nitrogen that will dissolve in the tissues
over time is directly proportional to the nitrogen partial
pressure.
If you find this difficult to conceptualize or
understand, here is a concrete example. If you were
breathing a mixture that is 36% oxygen, then the nitrogen
percentage would be 64%, and the nitrogen fraction
would be 0.64. When you dive with this mixture, you
expose yourself to 64/79ths the nitrogen partial pressure
that you would encounter if breathing air. Therefore, you
can consider your depth to be 64/79ths (roughly 80%)
of the absolute pressure that you would encounter at
your actual depth if you were breathing air. If you were
breathing EAN40, your nitrogen partial pressure would
be 60/79ths (about three-quarters) of what it would be
if you were breathing air. You must relate your nitrogen
advantage to absolute pressure and then convert that
absolute pressure to a depth. If you were to try to relate
it immediately to a depth, you would be neglecting the
one atmosphere of air pressure at the surface. You should
remember this from your beginning class in which you
learned about pressure at depth and the volume of air in
a flexible container.
AIR DIVE TABLES
TABLE 1: END-OF-DIVE LETTER GROUP
DIVE TIME REQUIRING DECOMPRESSION
NUMBER MINUTES REQUIRED AT 15-FSW STOP (5-MSW) 00 00
26
17
12
9
7
6
5
4
4
3
3
2
260
5
140
6
167 193 223
121 130
80
2
330 461
108
75
48
2
55
2
145
95
71
35
1
30
5
25
5
256
125
84
63
50
40
20
5
205
107
73
56
45
37
30
25
15
5
165
91
63
48
39
32
28
24
20
10
5
START
DEPTH
MSW FSW
6
9
12
15
18
21
24
27
30
33
36
40
20
30
40
50
60
70
80
90
10 0
11 0
12 0
13 0
MAXIMUM DIVE
TIME (MDT)
43
27
20
15
12
10
9
7
6
61
38
27
21
17
14
12
11
9
8
7
6
82
50
36
28
22
19
16
14
12
11
10
00
106
62
44
34
28
23
20
17
15
14
133
76
53
41
33
28
24
21
18
6
5
4 8
12
15
A B C D E F G H I J K L M N
24 : 00
10:02
10:01
8:45
8:44
7:51
7:50
6:59
6:58
6:07
6:06
5:14
5:13
4:22
4:21
3:30
3:29
2:38
2:37
1:45
1:44
0:53
0:52
0:10
24:00
9:10
9:09
7:53
7:52
6:59
6:58
6:07
6:06
5:14
5:13
4:22
4:21
3:30
3:29
2:38
2:37
1:45
1:44
0:53
0:52
0:10
24 :00
8:17
8:16
7:01
7:00
6:07
6:06
5:14
5:13
4:22
4:21
3:30
3:29
2:38
2:37
1:45
1:44
0:53
0:52
0:10
24:00
7:25
7:24
6:09
6:08
5:14
5:13
4:22
4:21
3:30
3:29
2:38
2:37
1:45
1:44
0:53
0:52
0:10
24:00
6:33
6:32
5:17
5:16
4:22
4:21
3:30
3:29
2:38
2:37
1:45
1:44
0:53
0:52
0:10
24 : 00
5:41
5:40
4:24
4:23
3:30
3:29
2:38
2:37
1:45
1:44
0:53
0:52
0:10
24:00
4:49
4:48
3:32
3:31
2:38
2:37
1:45
1:44
0:53
0:52
0:10
24:00
3: 56
3: 55
2: 40
2: 39
1: 45
1: 44
0: 53
0: 52
0: 10
24 : 00
3:04
3:03
1:48
1:47
0:53
0:52
0:10
24:00
2:12
2:11
0:56
0:55
0:10
24 :00
1:17
1:16
0:10
NEW
GROUP
24 : 00
0:10 A
B
C
D
E
F
G
H
I
J
K
L
WARNING: EVEN STRICT COMPLIANCE WITH
THESE TABLES WILL NOT GUARANTEE AVOIDANCE
OF DECOMPRESSION SICKNESS. CONSERVATIVE
USAGE IS STRONGLY RECOMMENDED.
RNT
+ ADT
TNT
(USE THIS FIGURE TO DETERMINE
END-OF-DIVE LETTER GROUP.)
RESIDUAL NITROGEN TIME
ACTUAL DIVE TIME
TOTAL NITROGEN TIME
12
40
13
117
21
109
29
101
37
93
45
85
55
75
64
66
74
56
85
45
97
33
109
15
50
18
60
21
70
24
80
27
90
30
100
33
110
36
120
40
130
11
64
17
58
23
52
29
46
35
40
42
33
49
26
57
18
65
9
41
14
36
19
31
24
26
29
21
35
15
40
10
46
8
32
12
28
16
24
20
20
25
15
29
11
34
6
39
7
23
10
20
14
16
18
12
22
8
25
5
29
6
19
9
16
12
13
16
9
19
6
22
3
25
5
15
8
12
11
9
14
6
17
3
20
5
10
8
7
10
5
13
2
15
5
7
7
5
9
3
12
4
4
6
2
8
24:00
11:46
11:45
10:30
10:29
9:35
9:34
8:43
8:42
7:51
7:50
6:59
6:58
6:07
6:06
5:14
5:13
4:22
4:21
3:30
3:29
2:38
2:37
1:45
24:00
10: 54
10: 53
9: 38
9: 37
8: 43
8: 42
7: 51
7: 50
6: 59
6: 58
6: 07
6: 06
5: 14
5: 13
4: 22
4: 21
3: 30
3: 29
2: 38
2: 37
1: 45
1:44
0:53
0:52
0:10
1:44
0:53 M
N 0:52
0:10
TABLE 2: SURFACE INTERVAL TIME (SIT) TABLE
0
0
0
0
10
AVOID
REPETITIVE
DIVES OVER
30 MSW
(100 FSW)
6
20
27
434
44
417
62
399
83
378
106
355
134
327
166
295
206
255
257
204
331
130
461
9
30
18
205
28
195
39
184
51
172
63
160
77
146
92
131
108
115
126
97
146
77
168
194
0
55
29
30
0
41
50 40
00
10
21
122
8
223
0
130
0
73
2
75
0
TABLE 3: REPETITIVE DIVE TIMETABLE
TIME RANGES IN HOURS : MINUTES 00
00
LIGHT FACE / BLUE NUMBERS ARE RESIDUAL NITROGEN TIMES (RNT)
BOLD FACE / RED NUMBERS ARE ADJUSTED MAXIMUM DIVE TIMES (AMDT).
ACTUAL DIVE TIME SHOULD NOT EXCEED THIS NUMBER
© 2019 NAUI WORLDWIDE
#30033 (Rev.07/19)
Figure 5-4 NAUI Air Dive Tables
Equivalent air depth is especially useful if you want
MSW
FSW
to change blends from one dive to the next, if you are
requesting a custom blend based on “best mix,” or if for
some reason you find yourself diving with a mix that is
not standard EAN32 or EAN36. If you know equivalent
air depth for your mix, you can use that EAD with the
NAUI standard Air Dive Tables (or any air dive
tables) to plan your dive or to plan repetitive dives. By
determining the EAD prior to each dive, you can easily
change mixes to either richer or leaner oxygen content
from one dive to the next. You can find equivalent air
depth by using a table, by calculating EAD, or with the
NAUI MobileTM App. Let’s begin with using a table.
EQUIVALENT AIR DEPTH BY TABLE
The Equivalent Air Depth (EAD) table relates the
percentage of oxygen in your nitrox mix to an actual dive
depth to show an equivalent air depth. The actual dive
depth is not usually a round number because it is relating
to a round-number equivalent air depth that will be used
on the dive tables.
To use the Equivalent Air Depth (EAD) table
(Figure 5-5), enter the table at the upper left and move
to the right to the oxygen percentage that corresponds
to the nitrox mix that you will be using. Move down that
column to the maximum planned depth of your dive. If