Cited Passage
4-2 NOAA Diving Manual
hypothetical gas loadings have “decayed” to below the
limits for that depth; the diver then ascends to the next
stop and the process is repeated. The J.S. Haldane decompression model goes back
nearly a century, but by using it with continuously updat-
ed experience, it can be used to produce reliable decom-
pression tables. It is not quite correct to consider this a
‘theory” of how the human body works. Rather, it is a
computational tool that allows prediction of tomorrow’s
dive from yesterday’s experience. The A.A. Bühlmann
model uses the same equations for on-gassing, but calcu-
lates the ascent limits in a different way; it, too, is firmly
based on experience. 4.1.3 Reliability of Tables
Virtually any exposure to pressure imposes an obliga-
tion for decompression, and even when it is done correct-
ly it will create some probability of symptoms of a decom-
pression disorder. For this reason, it is preferable not to
use the word “safe” to describe a decompression proce-
dure. In the sense that “safe” means “an acceptable level
of risk” the word may be applicable, but too many people
perceive that as meaning no risk at all, which is not the
case. Satisfactory decompression tables can be referred to
as being “reliable.” The NOAA and U.S. Navy Dive
Tables in this manual are considered reliable. The limits of a decompression procedure do not rep-
resent a hard line between developing or not developing
decompression sickness symptoms, but rather a fuzzy
boundary of “acceptable risk.” Accordingly, one should
always consider DCS as a possibility. Be prepared for it
psychologically and have a plan for dealing with it. There is a wide variation in the physical makeup of
divers, and part of this variation is in susceptibility to
decompression disorders. There are differences among
individuals, and in one person at different times. There
are also environmental effects. Immersion, exercise, and
warmth increase gas uptake and elimination; cold and
dehydration reduce them. Depending on where in the
dive these conditions occur, they may be either beneficial
or detrimental to the decompression. Because of the variations, a given schedule is not
“safe” or “unsafe;” rather, DCS has a certain probability
of occurring, therefore, decompression data is analyzed
statistically. The U.S. Navy and other decompression
researchers have developed means of analyzing past dives
using statistics, one form of which is called “maximum
likelihood.” With it, the probability of DCS can be pre-
dicted from a given profile by comparing it with a collec-
tion of past dives of the same general type. 4.1.4 Dive Planning Software
In recent years there has been a remarkable develop-
ment in the field of decompression technology; the
development and marketing of commercially available
computer programs for generating decompression tables. For decades it has been felt that only decompression
specialists were qualified to produce decompression
tables, and that all tables needed extensive testing before
operational use. Several entrepreneurs have prepared and distributed
computer programs that can be used to generate decom-
pression tables. This has been possible because of publica-
tions by Prof. Bühlmann that outline tested and accepted
algorithms for computing tables. Most programs available
are based, at least fundamentally, on Prof. Bühlmann’s
algorithms. The different programs manage the algorithm in dif-
ferent ways, especially with regard to introducing extra
conservatism into the computations.