Cited Passage
4-1
4.0 GENERAL
As explained in previous sections concerning the
physics and physiology of diving, body tissues absorb
additional nitrogen from the air breathed during dives
and release this excess nitrogen during ascent. After sur-
facing, body tissue continues to release excess nitrogen
until the level of nitrogen dissolved in the tissue returns to
normal. By keeping the amount of nitrogen being absorbed and
released within acceptable limits, the risk of a serious div-
ing malady known as decompression sickness, or DCS, is
reduced. Divers have many tools at their disposal to help
plan and make dives in which the risk of DCS remains
within acceptable levels. These tools include dive tables
and dive computers. Even when divers use computers as their primary dive
planning tool, it is important to have a working knowledge
of dive tables. Dive tables can provide an important back-
up in case of computer failure or operator error. They can
even help divers pre-plan a series of two or more dives—
which is something that is generally beyond the capabilities
of dive computers. There is a wide variety of dive tables available, includ-
ing versions by the U.S. Navy, other foreign governments,
and recreational training organizations. For military and
selected scientific and commercial divers in the United
States, the standard dive tables are those appearing in the
U.S. Navy Diving Manual . A complete set of the U.S. Navy
Dive Tables can be found in Appendix IV. This section of the NOAA Diving Manual is devoted to
the proper use of U.S. Navy Dive Tables for relatively
shallow, scientific and research diving. A working knowl-
edge of U.S. Navy dive table usage will also make it easi-
er to understand and use other dive tables as well. 4.1 DECOMPRESSION TABLE
DEVELOPMENT
4.1.1 Table Computation Prediction
The most common method used for predicting if a
profile (of pressure and gas as functions of time) will cause
DCS dates back to around the turn of the century, when
physiologist J.S. Haldane developed a hypothetical
method for tracking gas in the body and showed how to
develop decompression profiles or “tables.” At the outset,
it is important to realize that this “model” proposed by
Haldane, and later modified by others, is hypothetical. It
is not what really happens in the body, nor was it intended
to be; but, it does afford a method of moving from yester-
day’s dive experience to tomorrow’s new decompression
tables. This was the first such model; many others have
followed, and many are offshoots of the Haldane method. A well-developed computational method similar to Hal-
dane’s was published by the late Swiss cardiologist, Prof. A.A. Bühlmann, and it has been widely used by others. At today’s state of knowledge, the only sound criteri-
on for the preparation of useful decompression tables is
empirical experience. As models improve, prediction
capability will continue to improve, but the judgment as
to whether a model is right is how well it actually works,
not how sophisticated the math may be. 4.1.2 Computing Decompression Tables
Experience has shown that certain profiles, and pre-
sumably the hypothetical gas loadings produced by such
profiles, have or have not produced DCS. With enough
experience (data) it is possible to assign limits to various
ascents from depth. With these tools, table developers
calculate suitably slow ascent rates for a variety of expo-
sure profiles; the results of these calculations are decom-
pression tables.