A „deep stop“ table for recreational dives on air: Debunked!

Abstract

A „deep stop“ table for recreational dives on air: Debunked!

A "deep stop" table is challenged with 2 box-profiles:
the authors claims of reduced decompression stress and additional safety due to
deep stops are analyzed.

An in-depth analysis of the calculated inertgas partial pressures in theoretical tissue compartments reveals that the additional safety and micro-bubble control
can not be substantiated seriously. The manually inserted deep stops are following basically the DAN rule, thus the safety record of the original Bühlmann ZH-86
table is not substantially improved.

Full text

1
A „deep stop“ table
for recreational dives
on air: Debunked!
DOI: 10.13140/RG.2.2. ….: t.b.d.

2
excerpt from
the air-table
in question

3
However:
a graphical analysis of the air-table (pls. cf. slide #2)
reveals the following pattern
for this particular deep stops:
Bottom depths 18, 21 & 24 m:
deep stops @ half bottom depth of 24 (24/2 = 12 m) + 1 min stop at 9 m
Bottom depths: 27 & 30 m: deep stop @ 30/2 = 15 m + 1 min stop at 9 m
Bottom depths: 33 & 36 m: deep stop @ 36/2 = 18 m + stops at 12 & 9 m
Bottom depths: 39 & 42 m: deep stop @ 42/2 = 21 m + stops at 12 & 9 m
Bottom depths: 45 & 48 m: deep stop @ 48/2 = 24 m + stops at 15 & 9 m
This follows basically the empirical rule from DAN:
1 min @ bottom depth / 2
i.e.: not controlled via an algorithm

4
However:
the shallow stops (@ 6 & 9 m) are simply extracted from
an unmodified Bühlmann ZH-L 16 C with the
following boundary conditions:
ascent rate = 10 m / min
last stop depth = 6 m
Bühlmann correction / safety factor used, i.e.:
bottom depth * 1.03 + 1.00 m
As an example we take bottom depth 42 m, bottom time 20 min.
This yields (pls. cf. slide #2):
 42/2 = 21 m / 1 min, 12 m / 1 min, 9 m / 1 min, 6 m / 17 min
9 m / 1 min & 6 m / 17 min is the standard ZH-L16C with the above
boundary conditions:

5
Further claims from the authors:
and:

6
However;
an in-depth analysis of the calculated N2 compartment pressures
reveals the following from the above example:
@9 m, after the stops at 21 m & 12 m, i.e.: run time 25.3:

7
However;
an in-depth analysis of the calculated N2 compartment
pressures reveals the following from the above example:
@9 m, after the stops at 21 m & 12 m, i.e.: run time 25.3:

8
However;
an in-depth analysis of the calculated N2 compartment pressures
reveals the following from the above example:
@9 m, prior to first regular stop, i.e. run time 23.3:

9
However;
an in-depth analysis of the calculated N2 compartment
pressures reveals the following from the above example:
@9 m, prior to first regular stop, i.e. run time 23.3:

10
Final example:
As a final example we take
bottom depth 24 m, bottom time 40 min.
This yields (pls. cf. slide #2):
 24/2 = 12 m / 1 min, 9 m / 1 min, 6 m / 10 min
6 m / 10 min is the standard ZH-L16C with the above boundary
conditions (from slide # 4):
The next 2 slides feature the pN2 analysis and the heatmaps
with the deep stops @ 12 & 9 m (LHS)
and without these stops (RHS),
prior to the first regular stop @ 6 m,
i.e. after the run-times of 43.8 resp. 41.8 min:

11
Final example,
bottom depth 24 m, bottom time 40 min.
analysis of calculated pN2 per compartment
LHS: with deep stops, run time 43.8 min
RHS: ZH-L16 C, run time 41.8 min

12
Final example,
bottom depth 24 m, bottom time 40 min.
heat map pN2
LHS: with deep stops, run time 43.8 min
RHS: ZH-L16 C, run time 41.8 min

13
This demonstrates, that the claims
(pls. cf. slide #5 ) of:
pN2 reduction is not in „four to five“ compartments, instead
marginally, only in the first, the fastest compartment #1;
here from ca. 70 to 60 % (resp. ca. 55 to 50%)
And, negligible, in #2 & 3 from ca. 85 to 80 %
thus, the „micro-bubble control“ restricts to these two
(to three) 1 min stops
And, as well:
the leading compartment did not change at all
i.e.: the claims can not be verified seriously,
these deep stops are added not via a documented algorithm,
but just manually to an
unmodified version of a Bühlmann ZH-L 16
That is: the „reduction in decompression stress“ is, compared to
a Bühlmann ZH-86 table, if at all, negligible!
And so maybe the offered „extra safety“.

14
Bonus Material:
Source for
DIVE Version 3_09
Download free of charge:
DIVE V 3_09
(https://www.divetable.info/DIVE_V3/index.htm)
 and the german manual
https://www.divetable.info/DIVE_V3/DOXV3_0.pdf
The release train for
the english version (V3_04) is somewhat slower …
https://www.divetable.info/DIVE_V3/V3e/index.htm

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Fine tuning could be done via the commands:
 ascent rate („AR“)
ambient atmospheric pressure at start („L“)
the respiratory coefficient („R“)
the ambient (water)-temperature („te“)
the water density („di“)
Buehlmann Safety Factor („B“)
last stop depth („LS“)
And with: „a“ we recieve the complete decompression prognosis;
i.e.: the stop times in min per stage, modulo 3 m
and the responsible leading compartment & the rounded up TTS in
min. The latest DIVE Version for beta testing is always staged there:
https://www.divetable.info/beta/index.htm
along with information on production date, size in bytes, new features and
the checksums for verifying the download.
Fine tuning of DIVE:

16
The first paradigm from above via the commands,
the input of commands and parameters are in the quotes: „ “
(ZH-L 16 C is the default coeffcients matrix)
„b“ (setting of the Bühlmann correction/safety factor)
„ar“ „10.“ (setting the ascent rate to 10 m / min)
„ls“ „6.“ (setting the depth of the last stop to 6 m)
„d“ (simulation of a box profile with these parameters:)
„42.“ (bottom depth)
„20.“ (bottom time)
„a“ „“ (yields this decompression prognosis):
the heat maps (pls. cf. slides # 7, 9 & 12) are created via: „%p“
Handling of DIVE: