Content uploaded by Albi Salm
Author content
All content in this area was uploaded by Albi Salm on Jan 03, 2024
Content may be subject to copyright.
3
Abstract & Introduction:
We present some reflections on repetitive diving,
along the following paradigm from recreational scuba dives on air:
1st. dive on the day: 30 m bottom depth, 30 min bottom time
surface interval (SI): 90 min
2nd. dive: 30 m bottom depth, 30 min bottom time
We compare seasoned dive tables with dive computer simulations, have
a look back at repetitive dive trials from A. A. Bühlmann and check the
original sources to get an understanding, why dive computers on-line
displays are much different from the tabulated entries of a printed dive table.
As well we want to outline, how topical off-the-shelf dive computers could
mimick the safety- & security considerations from the „old masters“ (*) with a
simple pair of gradient Factors (GF).
(*) The Old Master, rubric in „FACEPLATE“, the official newsletter for the
Divers and Sailors of the United States Navy
5
Methods:
With this paradigm of one repetitive dive on air in the
domain of recreational diving we planned according to the
frameworks of Zürich and the widespread tables from United States Navy
Diving Manual (USN) and the canadian forces (DCIEM).
For the fun of it, we used as well seasoned air-diving tables, usually unknown
by the regular sports-diver:
the DRÄGER tables from 1960, still used today in some military- and
public-service-diving groups, a french MT92 table and a topical revision 0 of
the 6th. edition of the NDTT (Norwegian Diving- and Treatment Tables) from
2024.
The results are listed in table I in the order of gradually increasing time-to-
surface (TTS) for this particular 2nd dive.
As well we used desktop decompression software [4] for a Windows11® PC
to simulate the same paradigm, with and without gradient factors [5].
6
Data (1):
Table /
Method
Stop
time @
6 m
[min]
Stop
time @
3 m
[min]
Rept
.
Group
before
/
after SI
Residual
nitrogen
time
[min]
Stop time
@ 9 m / 6
m [min]
Stop
time @
3 m
[min]
TTS
[min]
1) DP 3.1.4
1
8
-
-
-
/ 1
14
16
2a) Deco2000
2b)
Deco-
Brain®
3
2
12
10
-
-
-
-
-
/ 3
-
/ 2
13
15
19
20
3) DIVE
3_11
2
10
-
-
-
/ 2
18
23
4) ZH
-83
2
6
F / A
7
-
/ 5
16
23
5) ZH
-86
2
7
F / A
9
-
/ 5
17
24
6) USN
Rev. 3
-
3
I / F
22
-
/ 9
28
39
7) DCIEM
5
10
G
RF = 1.6
4 / 8
29
41 + 2
8) Dräger
5
5
-
30
5 / 10
30
45 + 2
9) MT 92
-
10
-
25
3 / 15
35
55
10) USN
Rev. 7
3
-
J / I
30
-
/ 81
-
85
1st. dive:
30 m / 30 min 2nd. dive:
30 m / 30 min
SI: 90 min
Table I: TTS of various dive tables / methods
12
Data (7): Only 1st. dive: 30 m / 30 min;
The dive computers planning tools do not allow
for a repetitive dive.
Display of TTS / TAT / run times for 1st. dive
with Gradient Factors; used dive computer:
UWATEC / Scubapro G2 TEK, HW / SW-Ver.: 1.0
GF High = GF Low = 0.90 GF High = GF Low = 0.85
GF High = GF Low = 0.80 ➔
13
Table /
Method
Calculation
details for the repetitive dive
1) DP 3.1.4
Deco
Planner 3.1.4 from GUE with:
ZH
-L16 B, GF Hi = GF Lo = 1.0, Bühlmann safety factor = on,
instantaneous
descent
3) DIVE 3_11
ZH
-L16 C, GF Hi = GF Lo = 1.0, Bühlmann safety factor = on,
instantaneous
descent,
R
q= 1.0, water density EN13319, ascent speed = 9 / min
4) ZH
-86
p. 226 & 235, RNT= 9: 30 + 9 = 39
➔30 m / 40 min
5) ZH
-83
p. 68, p.66, RNT = 30
➔30 + 30 = 60 ➔30 m / 60 min
Discussion (1):
1) The DP 3.1.4 tries to mimick a Zürich table: it is missing
the original by ca. 8 min.
2a) Deco-Brain profile is simulated with the special bolt [3], the firmware being
the then (1984) firmware version P2-2
2b) As the repetitive dive is outside the Deco2000 table, it has to be simulated
with a computer program.
4) & 5) are from the series of books from 1983 –2002, [2a] &[2].
Legend for table I, part 1
14
Discussion (2):
Legend for table I, part 2
Used
Table &
Source:
Calculation
details for the repetitive dive
6) USN Rev. 3
0994-LP-001-9010
15.12.1988
Table 7
-5, p.7-38, p. 7-36: 30 + 22 = 52 ➔
30 m / 60 min
7) DCIEM 1992
Part 2
No.92-50
p. 1B
-11, repetitive factor (RF) @p. 1B-55: 1.6,
30 * 1.6 = 48
➔30 m / 50 min, + ascent time
8) Dräger 1960
Drägerwerk AG Lübeck
10 / 1984, Table 210
RNT =
dive time from 1st.dive
8a) NDTT 2024
Norwegian Diving- and
Treatment Tables 6th.
ed. Rev. 0
Not listed in table I.
Based on the modified Royal Navy Table 11; p. 48 & p. 59: RNT: 30 min; ascent speed 10 m / min.
Exactly same results as per DRÄGER table: 1st. dive: 5 / 5; J ➔I, RNT: + 30 min;
2nd. dive: 5/10/30 = 45 min + 3
9) MT 92
(24 mai 2019)
RÈGLES RELATIVES AUX TRAVAUX HYPERBARES EFFECTUÉS EN MILIEU
SUBAQUATIQUE:
p
. 13, Tableau 11, p. 54 + 25 min: 30 m / 55 ➔30 m / 60 min
10) USN Rev. 7
SS521-AG-PRO-010
30.04.2018
30 m
➔95.97 fsw (p. 153), Table 9-9, p. 9-74 100 fsw (p. 500),
Table 9
-8, p. 9-64 (p. 490): RNT 30 ➔30 + 30 = 60 ➔
100
fsw / 60 min
15
Discussion (3):
The TTS entries # 1 ➔5 from table I with TTS < 30 min
are clearly for recreational diving, whereas entries # 6 ➔10
with TTS 40 ➔85 min are obviously for working dives (for e.g.: C&R),
so that the resulting TTS differ due to a substantial higher inert gas load due
to higher oxygen consumption required by a certain physical workload!
As well there is discrepancy between a tabulated entry and the on-line display
from a dive computer. This is basically due to three reasons:
1) the dive computer measures the pressure (depth) every ca. 3 to 10 sec,
thus following the dive profile accurately on-line and thus the calculated
inertgas-loadings;
2) a dive table calculates the inertgas-loading with only one pressure step,
valid for the complete dive (box-profile);
3) this pressure step is usually called “instantaneous” or “immediate descent”,
something what in real-world diving, being it in the water or also in a pressure
chamber test, will not happen.
16
Discussion (4):
Thus the discrepancy is, in the first place, due to reduced
calculated inertgas pressures in the diver-carried computers
in comparison to the box-profiles of the tables.
As well for calculating the so-called “RNT” (residual nitrogen time), i.e.: the
inertgas load from the previous dive, the procedures from a table
require usually 3 to 4 rounding-up steps,
whereas a dive computer doesn’t.
17
Discussion (5):
Finally, there is this principal divergent philosophy in
calculating the compartmental inert gas loads during
an SI, i.e.: how exactly this RNT is derived.
➔A dive computer uses all of the compartments, i.e.: half-times;
➔a table uses only one for the SI-credits tables;
for eg.: the opld USN used 120 min (and so all the old PADI-, NAUI & SSI-
tables), the RDP® uses 60 min half-time for the calculation of the
desaturation during SI.
One recipe for the RNT, originally from Haldane for repetitive dives, was just
to add the bottom-times from the previous dives; this is the method also used
in the Dräger 1960 tables (and, b.t.w., still used in some japanese and russian
tables, not displayed in table I):
here the RNT is the bottom-time from the 1st. dive.
All of the above has been pointed out from Ernie Völlm (the designer of the
famous ALADIN computers) in the Bühlmann books since 1993:
19
[2] … translation:
Dives at altitude, repetitive and jo-jo dives will display
differences between a dive computer and a table ...
...
The calculation of a repetitive dive with the aid of a
repetitive system, which is common in tables, is a very
idealistic simplification, which is unavoidable for practical use,
as the repetitive groups always consist of combinations
of various compartments super-saturations.
... the sur-charges are always too big ...
... as well the tables entries consist of at least two times a
rounding up …
... resulting in decompressions times for rept. dives which
are too long. … By using a table the tolerated inertgas pressures are
normally not reached, but with a computer you could.
… :eot]
21
Discussion (9):
In a study with 83 divers on repetitive dives [1], AAB pointed
out, that the calculation of up to 3 repetitive dives with the then
(1987) ZH-L12 matrix of coefficients would offer enough safety margin, as
there have been only 6 cases of mild DCS type I and no DCS type II out of
201 exposures. For all experimental air dives in Zürich from 1972 to 1986
(362) an approx. DCS rate of only 1.93 % was attributed.
As well from another study with 166 repetitive dives in [2], p. 147 - 149,
a ca. 3 % to 7 % increase in calculated inertgaspressures for the
6 N2-compartments with the halftimes of 27 →146 min would suffice to take
the effects of an intrapulmonary R-/L shunt into account which would
eventually take place during the SI between dives. These calculations were
done with one ZH-L16A matrix which appeared for the first time 1990 in the
2nd. edition [2a] of AABs books on “Tauchmedizin”, p. 107 ([2], p. 158).
22
Discussion (10):
All of the considerations above could be easily mimicked in topical dive
computers with gradient factors (GF): a GF High = GF Low = 0.90,
already for the 1st. dive of a series of repetitive dives, would do!
(pls. cf. DATA(6)).
With the GF Hi = GF Lo = 0.85 ➔0.8 the insinuated safety- & security of a
ZH-table would be outperformed easily. And, as by convention, the GF work
on all compartments of a model, the herewith achieved conservatism should
be definitively more than contemplated above (only for the 6 compartments
#5
→
#10).
23
References (1):
[1] Bühlmann A. A. Decompression after repeated dives.
Undersea Biomed. Res. 1978; 14(1): 59 – 66
[2] Bühlmann, Albert Alois et al. (2002) Tauchmedizin, 5th. edition, Springer,
ISBN 3-540-42979-4 (cover & TOC)
[2a] Bühlmann, Albert Alois (1990) Tauchmedizin, 2nd. edition, Springer,
ISBN 3-540-52533-5
[3] the Deco-Brain®:
https://www.divetable.info/kap2_e.htm
And, as well:
https://www.divetable.eu/242.pdf
[4] Rosenblat, Miri & Vered, Nurit. (2021).
Synopsis & Fact Sheet: update per 11/2021 for DIVE Version 3_11.
10.13140/RG.2.2.17024.56326.
https://dx.doi.org/10.13140/RG.2.2.17024.56326
