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Abstract:
The DCIEM air diving tables [1] are wide-spread in professional
use [2] and considered conservative due to a low rate of DCS
([3], [4] & [5] and all the references therein).
We selected several air diving schedules incl. repetitive dives from the
recreational / TEC diving community and tried to recover these schedules
from the printed DCIEM tables with a simple decompression shareware [6] &
[7].
Despite the diverging underlying algorithms and methods they used, the
mapping of a printed DCIEM schedule to an on-line calculated ZH-L16 run-
time was possible with only minimalistic adaptions in the shareware and
only one (relative) constant conservatism factor of ca. 0.95 0.9 & resp.
ca. 0.7 0.6 for repetitive dives, depending on the length of the surface
intervalls between these dives.
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Introduction:
The DCIEM air diving tables [1] and the underlying
deterministic algorithm, the Kidd-Stubbs model from 1971
(KS-1971) with 4 serial compartments ([3 5]) was extensively tested
and the resulting diving manuals and procedures [1] & [2] achieved a low
DCS rate and are widespread in use in military-, C&R- & scientific-diving.
As the KS-1971 is very different in nature to the perfusion models from the
Haldane/Workman/Schreiner methods (pls. cf. the discussion and slides # 17
& 18) and the resulting schedules are considered the most conservative in the
field and usually are blessed with substantial longer TTS than the others, the
question of safety & security arises from the recreational diving community;
and, if both model-types could be benchmarked against each other.
As a simple & straight-forward benchmark method we used the transparent
1:1 comparison of printed DCIEM schedules with the ZH-86 air tables
resp. an on-line calculated version via a desktop decompression
shareware [6], [7], when bottom depths / bottom times / surface intervalls
did not match the printed entries.
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Methods (1):
We selected (15 * 4 = 60) single & repetitive air-diving
schedules (20) from 9 to 50 m bottom-depth and from 5 to 30 min
bottom times and SI with 75, 100 & 130 min, which are common in the
recreational / TEC diving community and could be carried out with standard
SCUBA equipment / dry-suits and single air-tanks with 10 to 12 l WC.
These schedules from the printed DCIEM tables [1] were compared with the
ZH-86 tables and with the calculated run-times from DIVE Version 3_11 [6] &
[7]. The software was basically used „as is“, that is: with the defaults. These
are:
coefficient set ZH-L16C
water temperature 20.0° C
respiratory coefficient Rq = 1.00
oxygen consumption 0.2500 L / min
dry, compressed air (fO2 = 0.2095/ fN2 = 0.7902)
ambient pressure at start of dive: 1,013.00 mbar
ascent speed 9.00 m / min.
gravity acceleration for central europe
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Methods (2):
Only 2 adaptions were required to obtain a maximal similarity
between the printed DCIEM entires and an on-line ZH-L16 C version:
the water density was changed and set to the (ca.) EN 13319 value of
1020.
a certain, required conservatism was achieved via the „Gradient Factor“
settings dialogue in the software.
The afore mentioned „conservativism“ is just a multiplicative factor < 1.0,
applied to the calculated values for the tolerated inertgas partial pressures per
compartment. A factor of 1.0, or 100 % means, that the original values, being
M-values, MPTT, or other, are used; a factor of 0.8, or 80 % means a
reduction of 20 percent.
This method of gaining additional safety, i.e. the scaling-down of the
compartmental tolerated inertgas supersaturations is here since long:
Haldane et al. used it for the first air decompression table with staged
decompression [9], Workman / Schreiner / Bühlmann & Hahn used these
methods as well [10], sometimes clearly documented, and sometimes not.
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Methods (3):
In the TEC-lingo of recreational divers these factors are
called „gradient factors“ (GF). Standard, off-the-shelf, desktop decompression
software and mix gas dive computers allow for the input of 2 of them:
a GF low & a GF high.
In the DATA section (slides # 9 14) we compared the DCIEM data with
screenshots from DIVE, the „GF“s are free input parameters, displayed in the
middle of the screenshot along with the # of the responsible leading
compartment from the used perfusion model. The sliding mechanism from
GF Low to an increased GF High is a simple linear interpolation without any
physiological basis: it is just to avoid excessively long stops near the surface.
The top part of these screenshots are showing the original ZH-L16C
„undisturbed“, i.e.: without any conservatism settings.
The duration of the surface intervalls (SI) were picked so as to get as well a
straight-forward comparison with an original printed ZH-86 table [8].
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Methods (4):
The procedure within the DCIEM framework to plan repetitive
dives is from [1], p. 1-17 1-25; the table 4, p. 1B-55 is used
to get the „repetitive factors“ (RF) for the 2nd. or next repetitive dive.
The procedure to calculate the residal nitrogen time according to the
reduction of the repetitive groups with increased SI for the ZH-86 system is
described in [8] on p. 235 along with table 32.
In DATA (3) we have as a paradigm one repetitive dive for 30 m / 30 min after
3 different SI according to the ZH-86 system. The schedules & TTS
are to be contrasted with the DCIEM results (DATA (1)) and the on-line
calculated ZH-L16C version (DATA (2)) with the conservativism setting.
As further paradigms, clearly outside from a recreational / TEC scope, there
are the comparisons of a 60 m / 20 min (DATA (4)) and 72 m / 40 min (DATA
(5a & 5b)). The DCIEM and the calculated ZH-L16C schedules / TTS are
substantially more conservative than the original ZH-86 / ZH-L16B schedules.
However, the displayed conservativism factors give a clear match between
the DCIEM data and the thus modified ZH-L16C system.
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DATA (1):
1st. dive bottom depth: 42 m, bottom time 25 min
stop times [min] @ 9 / 6 / 3 m TTS [min] (*)
DCIEM 1st. dive: 7 / 8 / 17 32 + 4
DCIEM 2nd. dive: 30 m / 30 min,
(as a 1st. dive: 5 / 10 15 + 3)
SI 75 min RF 2.0; 30 * 2 = 60 min 6 / 9 / 40 55 + 3
SI 100 min RF 1.8; 30 * 1.8 = 54 55: 5 / 9 / 34 48 + 3
SI 130 min RF 1.7; 30 * 1.7 = 51 55: 5 / 9 / 34 48 + 3
(*) the TTS = time-to-surface, defined as:
sum of all stop times (as printed in the DCIEM table) +
(bottom depth / ascent speed )
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DATA (3):
Only for comparison with ZH-86 [8], p. 227, air at sea-level:
1st. dive bottom depth: 42 m, bottom time 27 min
stop times [min] @ 9 / 6 / 3 m TTS [min] (*)
ZH-86 1st. dive: 4 / 7 / 19 33
ZH-86 2nd. dive: 30 m / 30 min,
(as a 1st. dive: 2 / 7 11)
SI 75 min, residual nitrogen time: 16 min: 30 + 16 = 46 50
SI 100 min, residual nitrogen time: 11 min: 30 + 11 = 41 45
SI 130 min, residual nitrogen time: 9 min: 30 + 9 = 39 40
SI 75 min, 30 m / 50 min: 1 / 10 / 28 41
SI 100 min, 30 m / 45 min: 9 / 23 34
SI 130 min, 30 m / 40 min: 3 / 17 24
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DATA (4):
Only for comparison with ZH-86 [8], p. 228, air at sea-level:
bottom depth: 60 m, bottom time 21 min
stop times [min] @ 15 / 12 / 9 / 6 / 3 m TTS [min] (*)
ZH-86: 3 / 4 / 6 / 11 / 28 56
DCIEM, p. 1B-17:
60 m / 20 min: 5 / 5 / 6 / 10 / 33 59 + 6
DIVE Version 3_11:
ZH-L16C w.o.
and with
conservatism
setting = 0.9
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DATA (5a):
Only for comparison with an on-line calculated ZH-86 [6]:
bottom depth: 72 m, bottom time 40 min
stop times [min] @ 30 / 27 / 24 / 21 / 18 /15 / 12 / 9 / 6 / 3 m TTS [min] (*)
DCIEM, p. 1B-18:
72 m / 40 min: 3 / 3 / 3 / 4 / 6 / 6 / 13 / 28 / 67 / 153 286 + 8
DIVE Version 3_11:
ZH-L16C w.o.
and with
conservatism
setting = 0.9
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DATA (5b):
Only for comparison with an on-line calculated ZH-86 [6]:
bottom depth: 72 m, bottom time 40 min
stop times [min] @ 30 / 27 / 24 / 21 / 18 /15 / 12 / 9 / 6 / 3 m TTS [min] (*)
DCIEM, p. 1B-18:
72 m / 40 min: 3 / 3 / 3 / 4 / 6 / 6 / 13 / 28 / 67 / 153 286 + 8
DIVE V 3_11
ZH-L 16 B
and the
Bühlmann-
safety factor
for table-
calculations
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Discussion & Conclusion (1):
The selected DCIEM schedules from the TEC / rec. domain
could be recovered over a broad range of depths / bottom times:
for the 1st. dive with a conservatism (= Gradient Factor) of ca. 0.9 +/- 0.05;
for the 2nd. dive, depending on the duration of SI, with a conservatism
setting of ca. 0.75 0.60 +/- 0.05.
No further adaptions where required for the software, except setting the water
density to the value of the EN 13 319, which is intermediate between fresh- &
sea water.
The discrepancies between a printed DCIEM table schedule and the ones,
calculated on-line via DIVE or any other desktop deco-software with the fitting
conservativism factors, which invariably do appear for some schedules & SI,
are regularly in an order of magnitude that are irrelevant for practical,
recreational diving. Especially when the limited precision of dive computers /
depth gauges is taken into account and the limited skills of recreational
SCUBA divers concerning constant depth & precise timing.
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Discussion & Conclusion (2):
This conservatism factor could be applied even for schedules,
outside the ZH-86 framework, clearly in the professional scope.
Here with a conservatism factor set = 0.9 a mapping could be achieved
(DATA (4) & (5a & 5b)) for single, box-profiles.
As the underlying decompression models and the algorithms between the
DCIEM / KS-1971 model and a ZH-L16C model are at maximal variance,
(pls. cf. slide # 17 & 18 with the lineup) this mutual mapping with only one
additional parameter, a conservatism factor, is a rare case of real serendipity.
And it gives true peace of mind for all involved parties, being a
decompression-researcher, a top-side LST or a diver at the other end of the
umbilical: the relative similarity conveys a feeling of safety & reliability of the
schedules; none being superior to the other resp. both of them are solid
ground.
As most of the ZH-86 schedules are not tested, but the DCIEM are,
and as the ZH-86 specialties were saturation & altitude diving and the DCIEM
were not, but for working dives in cold water (as the ZH-86 were not!) the
data from the test dives could be used for a mutual confirmation.
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Discussion (4):
DCIEM: ZH-L 16 C:
1 half-time: 20.8 min for air,
pressure dependant 16 half-times, fix, from
ca. 4 635 min for air
4 free parameters 16 * 3 free parameters
4 (2) coupled ODE, non-linear (*) 1 linear ODE (Haldane equation)
solved numerically via:
modified Euler or Runge-Kutta analytic solution:
simple exponential function
saturation / de-saturation:
asymmetric saturation / de-saturation:
symmetric
safe ascent depth:
linear equation tolerated inertgas overpressure:
linear equation
# test dives [3 5]: >> 7.500;
Air + Heliox16, also:
long bottom times, deep air,
workload & cold water
# test dives [8], p.134:
1.311 air, 426 Heliox (p. 138); also:
hypobaric & repetitive and
saturation regime
ODE: ordinary differential equation
(*): only the first 2 compartments used for real table calculations
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References:
[1] DCIEM Diving Manual, DCIEM No. 86-R-35: Part 1 AIR Diving Tables and
Procedures, Defence and Civil Institute of Environmental Medicine, Canada,
March 1992
[2] DCIEM Diving Manual, DCIEM No. 92-50: Part 2 Helium-Oxygen Surface-
Suppplied Decompression Procedures and Tables; Defence and Civil Institute
of Environmental Medicine, Canada, October 1992
[3] Nishi R. Y., Lauckner G. R. (September 1984) Development of the DCIEM
1983 Decompression Model for compressed Air diving, DCIEM No. 84-R-44
[4] Nishi R. Y. (Oct. 1980) A user guide to the DCIEM XDC-1 digital
decompression calculator, DCIEM-TC-80-C-58
[5] AD-765 704 DIGITAL COMPUTATION OF DECOMPRESSION
PROFILES Ronald Y. Nishi, et al. Defence and Civil Institute of Environmental
Medicine Downsview, Ontario January 1973
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References:
[6] Rosenblat M., Vered N., Eisenstein Y.,
Salm A. (17.01.2022) Recovery of selected ZH-86
air-diving schedules via a decompression shareware
DOI: 10.13140/RG.2.2.34235.13609
[7] Vered N., Rosenblat M., Salm A. (2021):
Synopsis & Fact Sheet DIVE Version 3_11,
DOI: 10.13140/RG.2.2.17024.56326
[8] Bühlmann, Albert Alois et al. (2002) Tauchmedizin, 5th. edition, Springer,
ISBN 3-540-42979-4 (cover & TOC)
[9] Salm, A. (2016) Did Haldane really use his "2:1"?
DOI: 10.13140/RG.2.2.21318.91209
[10] Rosenblat M., Vered N., Eisenstein Y., Salm A. (24.01.2022)
„Executive Editing“ in printed diving tables,
DOI: 10.13140/RG.2.2.10471.93605
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Procedure required for DIVE V 3_11 to
reflect the compartment saturation for the various
surface intervals prior to a repetitive dive:
(source: https://www.divetable.info/beta/D3_11.exe)
after surfacing, i.e.: „a“ „0.0“
ascend to depth = 0.0
„d“ „0.0“ „100.“
dive to a depth of 0.0 m for the time of the required
SI, here: 100 min
then start of dive planning for the next repetitive
dive with:
„d“ „bottom depth.0“ „bottom time.0“
Bonus Material (1):
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Procedure, for DIVE afficionados,
to save the calculated compartment saturations,
along with the values of other parameters at a certain state or a
certain stage of the schedule in planning, to re-use them later on:
(source: https://www.divetable.info/beta/D3_11.exe)
„f“ , then enter filename <fname>, then „W“
for writing the compartment saturations to disk
A file of <fname>.TXT is written to C:\DIVE\Prot\
provided this directory exists prior to start of DIVE.
It could be edited with any Ascii-editor or re-used later on via:
„f“ , then enter filename <fname>, then „R“
for reading this particular file to the DIVE memory. With:
„z“ , you could control the contents of the topical DIVE
memory
Bonus Material (2):