Equivalent Air Depth (in msw)
Percent O2 26% 27% 28% 29% 30% 31% 32% 33% 34% 35% 36% 37% 38% 39% 40%
EAD msw
12 13 13 14 14 14 15 15 16 16 16 17 17 18 18 19
15 16 17 17 17 18 18 19 19 20 20 20 21 21 22 22
18 19 20 20 21 21 22 22 23 23 24 24 25 25 26 26
21 23 23 24 24 25 25 26 26 27 27 28 28 29 30 30
24 26 26 27 27 28 28 29 30 30 31 32 32
27 29 30 30 31 31 32 33 33 34 35
30 32 33 33 34 35 35 36 37 37
33 36 36 37 37 38 39 39
36 39 39 40 41 41
40 43 44 44 45
MOD/1.4 ata 43 41 40 38 36 35 33 36 31 30 28 27 26 25 25
MOD/1.6 ata 51 49 47 45 43 41 40 38 37 35 34 33 32 31 30
To use the Equivalent Air Depth Table, 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 your exact maximum
depth is not on the table, use the next greater
depth. Move to the left along that row to the column at
the far left. The equivalent air depth that you should use
with air dive tables is shown in the left column. For
example, for 32% oxygen, any dive between 26 meters
and 29 meters would use 24 meters on an air table, and
any dive between 86 feet and 98 feet would use 80 feet
on an air table for dive planning. Contingency depths
for which the PO2 is between 1.4 and 1.6 atmospheres
have been shaded darker.
Example 1: On the first dive of the day, your
planned depth is 24 meters (80 feet), and your cylinder
is filled with EAN38. What is your maximum dive time
for the dive?
Enter the equivalent air depth table at the 38%
column and move down. Twenty-four meters (80 feet)
does not appear on the table, so continue down to the
next depth–25 meters (85 feet). Moving to the left, the
equivalent air depth for this dive is 18 meters (60 feet).
Using standard NAUI Dive Tables for air, you will find
Chapter 5 - Dive Tables and Dive Computers
that your maximum dive time for a 18 meter (60-foot)
dive is 55 minutes.
Example 2: Your actual dive time for the dive in
Example 1 is 35 minutes. Two hours later, you re-enter
the water to return to the same location. You are diving
with EAN32. What is your adjusted maximum dive time
for this repetitive dive?
Determine your exiting letter group for the first dive.
With an EAD of 18 meters (60 feet) for the first dive and a
35-minute dive time, you emerge from the water as a “G”
diver on the NAUI (air) Dive Tables. Two hours later you
are a “D” diver. Since you are now diving to a depth of
24 meters (80 feet) with EAN32, your equivalent air depth
from the EAD table is 21 meters (70 feet). A “D diver”
diving to 21 meters (70 feet) has an adjusted maximum
dive time of 25 minutes on the NAUI Dive Tables.
CALCULATING EQUIVALENT AIR DEPTH
As with MOD and best mix, equivalent air depth can
be calculated in discrete steps, or the procedure can be
combined into a single formula. As a step-wise process,
you would first determine the absolute pressure at the
depth to which you will be diving. Second, apply the
nitrogen “credit” that your nitrox blend gives you.
Dive Tables and Dive Computers
59
FIGURE 5-5b: EQUIVALENT AIR DEPTH FOR VARIOUS NITROX MIXES. A DIVER DIVING UP TO THE DEPTH SHOWN IN THE CORRECT EANx COLUMN
WOULD USE THE DEPTH IN THE LEFT-HAND COLUMN OF THE SAME ROW WITH AN AIR DIVE TABLE. SHADED AREAS HAVE A PO2
BETWEEN 1.4 ATA AND 1.6 ATA