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Emulation of selected DCIEM Heliox schedules via a decompression shareware

Authors:

Abstract

The DCIEM Heliox diving tables [2] are widespread in professional use [1] and considered conservative due to a low rate of DCS ([3], [4] & [5] and all the references therein). We selected two Heliox diving schedules as primary, 1st. dives on the day, and tried to emulate these schedules from the printed DCIEM tables with a simple, publicly available decompression shareware [6] & [7]. Despite the diverging underlying algorithms and methods used ([9] & [10] and all the references therein), the emulation of a printed DCIEM schedule with an on-line calculated ZH-L16 run-time was possible with only minimalistic adaptions in the shareware and only two (relatively) constant conservatism factors (GF) of ca. 0.90 +/-0.05 for the bottom-phase with Heliox and, respectively, ca. 0.80 +/-0.05 for the decompression-phase with oxygen.
1
Emulation of selected DCIEM
Heliox schedules via a
decompression shareware
01.01.2024
Miri Rosenblat, TAU
Nurit Vered, Technion Haifa
Albi Salm, SubMarineConsulting
DOI:
2
Abstract:
The DCIEM Heliox diving tables [2] are wide-spread in professional
use [1] and considered conservative due to a low rate of DCS
([3], [4] & [5] and all the references therein).
We selected two Heliox diving schedules as primary, 1st. dives on the day,
and tried to emulate these schedules from the printed DCIEM tables with a
simple, publicly available decompression shareware [6] & [7].
Despite the diverging underlying algorithms and methods used ([9] & [10] and
all the references therein), the emulation of a printed DCIEM schedule with an
on-line calculated ZH-L16 run-time was possible with only minimalistic
adaptions in the shareware and only two (relatively) constant conservatism
factors (GF) of ca. 0.90 +/- 0.05 for the bottom-phase with Heliox and,
respectively, ca. 0.80 +/- 0.05 for the decompression-phase with oxygen.
3
Contents:
Abstract: slide # 2
Introduction: slide # 4
Methods: slides # 5 9
DATA: slides # 10 12
Discussion & Conclusion: slide # 13
Discussion & Conclusion; Caveat: slides # 14 & 15
References: slides # 16 18
4
Introduction:
The DCIEM air- & Heliox-diving tables [1], [2] 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 achieved a low DCS
rate and are widespread in use in military-, C&R- & scientific-diving.
The KS-1971 is very different in nature to the perfusion models from the
Haldane/Workman/Schreiner methods (pls. cf. the discussions in [9] and
[10]), and the resulting schedules are considered the most conservative in the
field and usually are blessed with substantial longer TTS than the others.
Presently there are discussions in professional diving circles, if and how diver
carried computers should be used for Heliox diving and how to achieve a
certain safety & security standard, complying with regulatory provisions,
despite the dive computer manufacturers usual black box“ approach
concerning the implementation of their algorithms [11]. However, the black
box“ situation could be mitigated by running benchmarks from documented
standard algorithms against the results from the planning- /simulation tools of
the dive computers [12].
5
Methods (1):
We selected only two profiles as our show cases:
case A: 42 m / 30 min
case B: 36 m / 100 min.
Case A is very similar to our ubiquitous test diveof 42 m / 25 min on air;
whereas case B is very similar to a historical Heliox-jump dive of 1982, tested
by Albert Alois Bühlmann [13].
The schedules A & B from the printed DCIEM tables [2] were compared with
the calculated run-times from DIVE Version 3_11 [6] & [7]. The software was
basically used as iswith only marginal adaptions. These adaptions have to
reflect the specialties of the DCIEM system on one side, and on the other side
the mitigation of the usual lacking conservativism of the original ZH-L16 C
system [8].
6
Methods (2):
This lack of conservativism, i.e.: too short a TTS in comparison to other
procedures, and/or too less a pO2 during decompression phase, was already
discussed in the ‘80s and one of the reasons why commercial diving
contractors rejected the Bühlmann procedures ([14] and all the references
therein, especially the discussion on p.4 and the further involved
reference to the Bühlmann Symposion in Zürich form 2019:
https://www.divetable.info/BS_ZH/Sat_Diving.pdf )
7
Methods (3):
The used parameters for DIVE Version 3_11 [7] were:
Helium coefficients set to ZH-L16A; pls. cf. [8], p. 158, table 26
Nitrogen coefficients set to ZH-L16C; pls. cf. [8] p. 158, table 25
water temperature 20.00° C
water density ca. EN 13 319
respiratory coefficient Rq = 1.000
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 14.00 m / min
last stop depth 9 m
used GFs (Gradient Factors), pls. cf. slides # 9 & 13
gravity acceleration for central europe
breathing mixes used:
bottom phase Heliox 16/84
intermediate stages: Air
decompression stage 9 m: 100 % O2
8
Methods (4):
The main adaptions to obtain a maximal similarity between the
printed DCIEM values and an on-line ZH-L16 version were twofold:
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 conservativismis just a multiplicative factor, per
convention < 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 ca. 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; Workman / Schreiner / Bühlmann & Hahn used these
methods as well, sometimes clearly documented, and sometimes not ([9] &
[10]).
9
Methods (5):
The so-called gradient factors(GF) are offered in standard,
off-the-shelf, desktop decompression software and mix gas dive computers.
These GF come in pairs: a GF low (GF Lo) & a GF high (GF Hi).
Per convention: 1.0 > GF High > GF Low
In the DATA section (slides # 10 12) we compared the DCIEM data with
screenshots from DIVE, with the used „GF“s 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.
For the DCIEM Heliox-working dives we used two pairs of GFs:
one pair of GFs for the bottom-phases, usually ca. 0.90 +/- 0.05,
and a 2nd. pair of GFs for the last decompression stage on pure oxygen,
usually ca. 0.80 +/- 0.05 .
The change of breathing mix from Heliox to Air was simulated during the
deepest stops at 18 resp. 21 m, and at the end of the 12 m stop to 100 %O2.
10
DATA (1) DCIEM p. 2B-9:
Case A) dive bottom depth: 42 m, bottom time 30 min, Heliox16/84
stop times [min] @ 21 / 18 / 15 / 12 m (Air) 9 m (O2) TTS [min] (*)
DCIEM: - / 2 / 4 / 4 37 + 5 min air break 55
DIVE 3_11: - / 2 / 3 / 5 38 + 5 min air break 53
Case B) dive bottom depth: 36 m, bottom time 100 min, Heliox16/84
stop times [min] @ 21 / 18 / 15 / 12 m (Air) 9 m (O2) TTS [min] (*)
DCIEM: 2 / 7 / 13 / 23 90 + 3 * 5 min air break 152
DIVE 3_11: 4 / 8 / 12 / 18 93 + 15 min air break 150
(*) the TTS = time-to-surface, defined as:
sum of all stop times (as printed in the DCIEM table) +
(bottom depth / ascent speed )
11
DATA (2):
case A, bottom depth: 42 m, bottom time 30 min
bottom phase & intermediate stages:
decompression stage w. 100 % O2 @ 9 m:
12
DATA (3):
case B, bottom depth: 36 m, bottom time 100 min
bottom phase & intermediate stages:
decompression stage w. 100 % O2 @ 9 m:
13
Discussion & Conclusion (1):
The two selected Heliox-DCIEM schedules could be emulated
with only two additional parameters, i.e.:
GF Hi = GF Lo = ca. 0.9 +/- 0.05
for the bottom-phase with Heliox and intermediate stages with air; and a
GF Hi = GF Lo = ca. 0.8 +/- 0.05
for the decompression stages on pure oxygen.
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 and adjusting the ascent rate to values, which match the DCIEM
tabulated Heliox entries and setting the last-stop-depth (from 3 or 6 m) to 9 m.
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, are
regularly in an order of magnitude that are irrelevant for practical diving.
Especially when the limited precision of dive computers / depth gauges and
oxygen-analyzers is taken into account and the time gaps in proper execution
of a run-time through divers communication with top-side.
14
Discussion & Conclusion (2); Caveat:
The sheer size of the GFs is not written in stone!
This yields as well for the relation of a GF Hi to a GF Lo:
they depend on an entanglement of many parameters:
1) nearly on all of the parameters discussed on the slide “Methods (3)”,
as these influence directly the calculated inertgas-saturations
2) on the rigor of the implementation of the Schreiner equation
3) on the internal, over-all precision of the used frame-work, i.e.:
the digital word length of the variables
type of used mathematical libraries
floating-point treatment
rounding
quickly converging numerical methods (not needed for Heliox,
but for Trimix)
AND, as well there is presently no accepted “Gold Standard” on the
implementation details of a GF calculation: there is leeway in programming
them into a high-level language (like Fortran or C) in a decompression
frame-work or in a dive computer.
15
Discussion & Conclusion (3); Caveat:
There is also a word of caution needed concerning the
complete matrix of compartment halftimes with their corresponding
parameters for the linear supersaturation equations (a- & b-coefficients, i.e.:
axis intersections and slopes): these are basically tools to make a best-fit to
experimental data. The # of compartments and the GF are increasing the
degree of freedom of the model / the framework: so they just make this
best-fit easier:
Their physiological relevance, right from the start
ca. 100 years ago already open to conjecture,
dwindles away the more compartments
and GF you throw into the game!
For our short communication here, the DCIEM Heliox-table is considered as
the experimental data and the fit with the GF from a perfusion model is only to
show that an off-the-shelf mix-gas dive computer could be used to guide
divers and top-side along a proven DCIEM-framework for working-dives with
Helium in cold waters and by the same token, exploiting the advantages of a
real-time display for the diver and an electronically stored dive-log.
16
References (1):
[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
17
References (2):
[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, Albi & Rosenblat, Miri & Vered, Nurit & Eisenstein, Yael. (2022).
Recovery of selected DCIEM air-diving schedules via a decompression
shareware, DOI: 10.13140/RG.2.2.15208.55046.
[10] Salm, Albi & Eisenstein, Yael & Vered, Nurit & Rosenblat, Miri. (2022).
The mapping of the DCIEM Air-diving table to a standard Haldane-/Workman-
/Schreiner-algorithm. DOI: 10.13140/RG.2.2.27420.36480.
18
References (3):
[11] Salm, Albi & Rosenblat, Miri & Vered, Nurit &
Eisenstein, Yael. (2022). On the reliability of dive computer generated run-
times (22.02.2022) Part IV.
DOI 10.13140/RG.2.2.11469.72169.
[12] Rosenblat, Miri & Vered, Nurit & Salm, Albi. (2023). On the reliability of
dive computer generated run-times (01.01.2023) Part X: a conciliatory
proposal of a benchmark.
DOI 10.13140/RG.2.2.31895.04006.
[13] Salm, Albi. (2020). ZH-L 12 : Validation of an old (1982) experimental
Heliox jump dive (30 m, 120 min).
DOI: 10.13140/RG.2.2.24608.20482/1.
[14] Salm, Albi & Eisenstein, Yael & Vered, Nurit & Rosenblat, Miri. (2022).
On the arbitrariness of the ZH-L Helium coefficients (16.08.2022).
DOI: 10.13140/RG.2.2.19048.55040.
ResearchGate has not been able to resolve any citations for this publication.
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) A user guide to the DCIEM XDC-1 digital decompression calculator
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Nishi R. Y. (Oct. 1980) A user guide to the DCIEM XDC-1 digital decompression calculator, DCIEM-TC-80-C-58
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