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On the reliability of dive computer
generated run-times, Part XII:
Altitude Challenge for DCIEM
Abstract:
Here, in Part XII, we performed another altitude test: simulation of diving in a
mountain lake, i.e.: at a reduced ambient pressure of ca. 0.8 Bar, that is: a
mountain lake at a ca. altitude of 2000 m above sea-level (aSL).
This test / challenge is somewhat similar to those in refs. [1] & [2], but with the
latest firmware as per 2024 for the tested dive computers.
Introduction: slide # 3
Methods: slides # 4 → 7
Results: slides # 8 → 14
Discussion & Conclusion: slides # 15 → 18
References: slides # 19 & 20
Appendix: Comparison with U.S.N., NDTT, CIRIA & RN altitude procedures
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Introduction (1):
Same as per references [1], [2], [3], [4] & [5] and all the used
references therein.
Methods (0):
This yields also for the description of some of the methods.
One of the 4 computers is the Scubapro UWATEC Aladin TEC 2G:
it has no new firmware, no fancy display, no gimmicks etc.:
BUT is used instead as our
most reliable work-horse since 2007!
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Methods (1):
We simulated two of our notorious test-profiles on air:
➔30 m bottom depth (BD) / 30 min bottom time (BT) and
➔42 m BD, 25 min BT
at the reduced ambient pressure in the passengers cabin during various
intercontinental flights from Zürich to Tel Aviv with commercial, civilian air-
planes. The measured cabin-pressures were read by the dive computers after
ca. 1.5 h into the flight, that is ca. 60 min after reaching the final, cruising
height of ca. 32,000 feet:
ALADIN TEC 2G UWATEC G2 UWATEC G2 TEK SHEARWATER PERDIX
The readings for this topical test were ca. 780 +/- 6 mbar, equivalent to an
approximate altitude of ca. 2000 to 2300 m aSL.
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Results (1):
The displayed pressures / calculated altitudes
(pls. cf. slide # 4) are well within the limited precision of the dive
computers pressure (piezo-)sensors, the daily variations and the
cabin-pressures, announced from the cockpit; with these readings, the
following tables / procedures have to be used for comparison:
[65], Table 32 for 701 – 2500 m aSL on pp. 229 & 230, with an
adaption of minimum 60 min required.
This table yields the following stop times:
stop depth [m] / stop times [min] TTS [min] (*)
12 9 6 4 2
30 m / 30 min - - 1 4 11 19
42 m / 24 min -- 4 4 7 18 36
42 m / 27 min 1 5 5 9 21 44
(*) TTS as tabulated in Table 32
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Results (4):
The DCIEM procedures from [28], table 5, 1B-59 require
for the target altitude of 2100 → 2399 m aSL
a depth correction of + 9 m for the planned,
actual diving depth of 30 m @ aSL.
Thus the altitude corrected DCIEM stop times yield for
30 + 9 = 39 m on page 1B-14:
stop depth [m] / stop times [min] TTS [min] (*)
15 12 9 6 3
39 m / 30 min - - 7 8 22 37 + 3 =
ca. 40
For this target altitude group (2100 → 2399 m) the stop depths
have to be corrected accordingly, i.e:
15 → 12.0 ; 12 → 9.5 ; 9 → 7.0 ; 6 → 5.0 ; 3 → 2.5!
(*) total stop times as tabulated + ascent times
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Results (5):
The DCIEM procedures from [28], table 5, 1B-59 require
for the target altitude of 2100 → 2399 m aSL
a depth correction of + 12 m for the planned,
actual diving depth of 42 m @ aSL.
Thus the altitude corrected DCIEM stop times yield for
42 + 12 = 54 m on page 1B-16:
stop depth [m] / stop times [min] TTS [min] (*)
15 12 9 6 3
54 m / 25 min 5 5 7 9 39 65 + 4 =
ca. 69
For this target altitude group (2100 → 2399 m) the stop depths
have to be corrected accordingly, i.e:
15 → 12.0 ; 12 → 9.5 ; 9 → 7.0 ; 6 → 5.0 ; 3 → 2.5!
(*) total stop times as tabulated + ascent times
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Discussion / Conclusion (1):
Synopsis of TTS-results for:
BD 30 m / BT 30 min @ 2100 → 2399 m aSL:
ZH-86 table 30 m / 30‘ TTS = 19 min
Scubapro Galileo „G2 TEK“@ GF 1.00 TTS = 20 min
Scubapro ALADIN TEC 2G @ MB Level = 0: TTS = 25 min
Scubapro Galileo „G2“@ MB Level = 0: TTS = 26 min
(NDTT, pls. cf. Appendix TTS = 28 min)
PERDIX with DCIEM option TTS = 34 min
(USN, pls. cf. Appendix TTS = 38:40)
DCIEM table 39 m / 30‘ TTS = 40 min
MB Level (= Micro Bubble Level) and the gradient factors (GF) are
proprietary modifications of the tolerated compartment inertgaspressures,
here they are set = 0 resp GF 1.00. This implies that the original ZH-L16 C
values should be used.
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Discussion / Conclusion (2):
Synopsis of TTS-results for:
BD 42 m / BT 25 min @ 2100 → 2399 m aSL:
ZH-86 table 42 m / 24‘ TTS = 36 min
Scubapro Galileo „G2 TEK“@ GF 1.00 TTS = 41 min
ZH-86 table 42 m / 27‘ TTS = 44 min
Scubapro ALADIN TEC 2G @ MB Level = 0: TTS = 48 min
(NDTT, pls. cf. Appendix TTS = 49 min)
Scubapro Galileo „G2“@ MB Level = 0: TTS = 51 min
PERDIX with DCIEM option TTS = 62 min
DCIEM table 54 m / 25‘ TTS = 69 min
(USN, pls. cf. Appendix TTS = 79:40)
MB Level (= Micro Bubble Level) and the gradient factors (GF) are
proprietary modifications of the tolerated compartment inertgaspressures,
here they are set = 0 resp. GF 1.00. This implies that the original ZH-L16 C
values should be used.
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Discussion / Conclusion (3):
The deviation of the Scubapro / UWATEC computers
using the ZH-L16 C system from the ZH-86 tables with proprietary,
undocumented factors are omitting the deepest table-stops and yielding a
slower ascent rate and increased TTS than the original tables, for altitude and
as well for SL diving; [1] & [2]. So all three of the computers err, but on the
conservative, the safer side.
The Shearwater DCIEM option with the latest firmware is also close to the
original procedure, but with an error of a slightly decreased TTS due to the
omitted deepest table-stops. This is already reflected as well in refs. [1] & [2],
and, especially for the DCIEM implementation in ref. [3], and, as always: all
the references therein. So it seems that with the firmware upgrades from
v87 to v93 nothing substantial has changed.
Within the limited precision of the dive computers depth sensors, the
agreement between the original tables / procedures is quite sensible. The
deviations fall quickly within the error margins of civilian / recreational
diver behaviour.
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Discussion / Conclusion (4):
The TTS > 20 min between the ZH-L and DCIEM tables
for these two benchmarked box-profiles are clearly due to the fundamentally
different algorithms and the different scope of these frameworks:
DCIEM is tested and intended for dives in cold water with a substantial
physical workload (ref. [26]); whereas the ZH-L is not!
Also the tabulation as such of the Cross-corrections for altitude diving
(DCIEM, table 5 on page 1B-59 from [28]), are adding to the
TTS. The
TTS is as well mirrored @ SL:
TTS ZH-86 [min] TTS DCIEM [min]
30 m / 30 min 11 15 + 3
42 m / 25 min 28 32 + 4
Nevertheless there is a mapping of the two frameworks possible
with simple gradient factors (GF), pls. cf. ref. [4]. (For the general idea of the
gradient factors as such, pls. cf. ref. [5].)
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On the reliability of dive computer
generated run-times, Part XII
References (1):
[1] Salm, Albi & Rosenblat, Miri & Vered, Nurit & Eisenstein, Yael. (2022).
On the reliability of dive computer generated run-times, Part VII: Altitude Test.
10.13140/RG.2.2.14589.64487.
DOI: 10.13140/RG.2.2.14589.64487
[2] Salm, Albi & Eisenstein, Yael. (2022).
On the reliability of dive computer generated run-times, Part IX:
G2 TEK Altitude Adaption. 10.13140/RG.2.2.16961.84326.
DOI: 10.13140/RG.2.2.16961.84326
[3] Salm, Albi & Rosenblat, Miri & Vered, Nurit & Eisenstein, Yael. (2022).
On the reliability of dive computer generated run-times (22.02.2022) Part IV.
10.13140/RG.2.2.11469.72169.
DOI: 10.13140/RG.2.2.11469.72169
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On the reliability of dive computer
generated run-times, Part XII
References (2):
[4] Salm, Albi & Rosenblat, Miri & Vered, Nurit & Eisenstein, Yael. (2022).
Recovery of selected DCIEM air-diving schedules via a decompression
shareware 14.03.2022. 10.13140/RG.2.2.15208.55046.
DOI: 10.13140/RG.2.2.15208.55046
[5] Salm, Albi & Vered, Nurit & Rosenblat, Miri. (2023).
Gradient Factors: on the rise? 10.13140/RG.2.2.20301.20963.
https://dx.doi.org/ 10.13140/RG.2.2.20301.20963
[28] DCIEM Diving Manual, DCIEM No. 86-R-35 (1992):
Part 1 Air Diving Tables and Procedures;
https://www.divetable.eu/p125936.pdf
[65] Albert A. Bühlmann, Ernst B. Völlm (Mitarbeiter), P. Nussberger
(2002) Tauchmedizin, Springer, ISBN 3-540-42979-4
https://www.divetable.eu/BOOKS/65.pdf
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Appendix (1): Comparison with USN altitude procedure (*)
@SL: (metric version from page D-7 & D-11 (**))
TTS ZH-86 [min] TTS DCIEM [min] TTS USN [min]
30 m / 30 min 11 15 + 3 2‘ @ 3m: 5:20
42 m / 25 min 28 32 + 4 2‘/8‘/16‘: 30:00
@ altitude 7000 feet, the following depth corrections from Table 9-4 (p. 474)
100 fsw → 130 fsw / 39.6(8) m; 140 fsw → 190 fsw / 57.9 (58.2) m
equivalent stop depths in fsw: 50 → 39; 40 → 31; 30 → 23; 20 → 15; 10 → 8
30 m / 30‘ ➔ from p. D-10:
39 m / 30‘: 1‘ / 8‘ / 26‘ ➔ TTS 38:40
42 m / 25‘ ➔ from p. D-15:
57 m / 25‘: 2‘ / 6‘ / 6‘ / 7‘ / 19‘ / 35‘ ➔ TTS 79:40
(*) U.S. Navy Diving Manual Revision 7, Change A 30 April 2018
resp.: (**) NEDU TR 16-05: VVAL-79 Thalmann Algorithm Metric and imperial
Air Decompression Tables, TA 16-25
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Appendix (2): Comparison with NDTT altitude procedure (*)
@SL from pages 48 / 52:
TTS ZH-86 [min] TTS DCIEM [min] TTS NDTT [min]
30 m / 30 min 11 15 + 3 5‘ / 5‘: 10 + 3
42 m / 25 min 28 32 + 4 5‘ / 15‘: 20 + 4
@ altitude 1750 – 2000 m, the following depth corrections from p. 60:
30 m → 39 m; 42 m → 54 m
equivalent stop depths in m: 15 → 13; 12 → 10; 9 → 8; 6 → 5
30 m / 30‘ ➔ from p. 51:
39 m / 30‘: 5‘ / 20‘ ➔ TTS 25 + 3
42 m / 25‘ ➔ from p. 56:
54 m / 25‘: 5‘ / 5‘ / 10‘ / 25‘ ➔ TTS 45 + 4
(*) NDTT Norwegian Diving- and Treatment Tables, 6th. ed. Rev 0;
with the total decompression times as indicated in the tables +
the ascent times
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Appendix (3): Comparison with CIRIA (1972) and RN
altitude procedures (*)
@aSL 2000 – 3000 m; depth correction factor = 1.5
30 m / 30‘ ➔ 45 m / 30‘
42 m / 25‘ ➔ 63 m / 25‘
This would yield by far the longest TTS.
(*) the CIRIA (1972) and RN procedures could be found @
Charles B. Shillings et al.:
➔The Underwater Handbook, p. 633
➔The Physician‘s Guide to Diving Medicine, p. 589
and nearly all handbooks / manuals for commercial diving.
[CIRIA is the „Construction Industry Research and Information Association” with their (then):
Underwater Engineering Group Report UR7;
RN is the “Royal Navy” of the United Kingdom with their RNPL, the Royal Naval Physiological Laboratory.]
