9-38 Change A
U.S. Navy Diving Manual—Volume 2
at sea level to atmospheric pressure at altitude. Using millibars (mb) as a unit for
expressing atmospheric pressure at altitude equivalent depth is then:
Example: A diver makes a dive to 60 fsw at an altitude of 5000 ft. The atmo-
spheric pressure measured at 5000 ft is 843 millibars (0.832 ATA). Atmospheric
pressure at sea level is assumed to be 1013 millibars (1.000 ATA). Sea level
equivalent depth is then:
9-12.1.2
Correction for Decompression Stop Depths. Depth of the corrected stop at alti-
tude is calculated by multiplying depth of a sea level equivalent stop by a ratio of
atmospheric pressure at altitude to atmospheric pressure at sea level. [Note: this
ratio is inverse to the ratio in the formula above.
Example: A diver makes a dive at an altitude of 5000 ft. An equivalent sea level
dive requires a decompression stop at 20 fsw. Stop depth used at altitude is then:
To simplify calculations, Table 9-3 gives corrected sea level equivalent depths
and equivalent stops depths for dives from 10-190 ft and for altitudes from 1,000
to 10,000 ft in 1000 ft increments.
WARNING
Table 9-3 cannot be used with constant ppO2 diving equipment, such as
the MK 16.
9-12.2
Need for Correction. No correction is required for dives conducted at altitudes
between sea level and 300 ft. The additional risk associated with these dives is
minimal. At altitudes between 300 and 1000 feet, correction is required for dives
Equivalent Depth (fsw)
Altitude Depth (fsw)
Pressure at Sea Level (mb)
Pressure at Altitude (mb)
----------------------------------------------------------------
=
Equivalent Depth (fsw)
60 fsw
1013 mb
843 mb
---------------------
72.1 fsw
=
=
Altitude Stop Depth (fsw)
Sea Level Stop Depth (fsw)
Pressure at Altitude (mb)
Pressure at Sea Level (mb)
----------------------------------------------------------------
=
Altitude Stop Depth (fsw)
20 fsw
843 mb
1013 mb
---------------------
16.6 fsw
=
=
