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FALL 2014
when using standard tables that
are based on sea-level diving) is
computed by multiplying the actual
dive depth by the atmospheric
pressure at the exposure altitude,
then dividing by the normal sea-level
pressure assumed for the tables.
The equivalent depth is thus 10
feet x 12.05 psi/ 14.7 psi = 8.3 feet.
The equivalent depth for a 15-foot
actual dive depth is 12.3 feet and for
a 20-foot actual dive depth is 16.4
feet. Given the rules of rounding up
with dive tables, there is effectively
no change in the depths used for the
computation of repetitive groups.
(Note: This would not hold true for
deeper dives.)
The U.S. Navy Revision 6 Table
9-7 places a diver completing a
dive to 10 feet for between 102 and
158 minutes in repetitive group C.
Diving to 15 feet (5 m) for between
121 and 163 minutes would put the
diver in repetitive group E. Diving
to 20 feet (6 m) for between 106
and 133 minutes would put the
diver in repetitive group F. The
altitude change from the lowest to
highest point of travel you reported
is just less than 6,200 feet (1,890 m).
Table 9-6 does not restrict a 7,000-
foot (2,134 m) climb in altitude
for repetitive groups A-D. The
minimum surface interval to precede
travel is one hour and 37 minutes for
repetitive group E, four hours and
four minutes for F and six hours and
10 minutes for G.
Assuming the dives are conducted
as planned and the travel takes place
the next day (likely more than six
hours later), there should be minimal
risk of decompression sickness
resulting from the diving. There are
two points worth noting for those
being exposed to altitude after diving.
First, the 10-foot depth involved in
your case is highly unusual. More
typical diving exposures would
warrant longer surface intervals
before travel. The second point is
that while the U.S. Navy tables give
seemingly precise schedules, they do
not consider the myriad factors that
can alter the risk of decompression
sickness. It is important to maintain
the mindset of prevention by building
in additional safety factors wherever
feasible.
AD
— Neal Pollock, Ph.D.
ASK US!
The DAN Medical Information Line is
here to answer all your dive-related
medical questions. You can reach
the medical staff during regular
business hours (Monday through
Friday, 9 a.m. to 5 p.m. ET) by call-
ing
+1-919-684-2948, ext. 222.
You can also submit an email at
.
REFERENCES
1. Sheffield PJ, Vann RD, eds. Flying
After Recreational Diving Workshop
Proceedings. Durham, N.C.: Divers
Alert Network, 2004.
2. U.S. Navy Diving Manual, Vol. 2,
Rev. 6. NAVSEA 0910-LP-106-0957.
U.S. Naval Sea Systems Command:
Washington, D.C., 2008: Chapter 9.
3. U.S. Standard Atmosphere, 1976.
National Oceanic and Atmospheric
Administration, National Aeronautics
and Space Administration, and United
States Air Force. NOAA-S/T 76-1562.
U.S. Government Printing Office:
Washington, D.C., 1976; 227 pp.
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