User Guide
The purpose of the program is to
analyse dive profiles. These dive profiles must first be generated by 3rd
party decompression software.
The analyser is based in Excel spreadsheet format. Inputting data is easy.
Simply enter figures into the data fields highlighted in yellow.
To enter a dive plan, Input your descent runtime, in one minute increments,
next, input the depth you expect to arrive at by this time.
Descent:
The
first input row is the dives “run time”, always start with zero time with
zero depth. The run time should move down the screen in one-minute intervals,
until the target depth is reached. You can input the depths you expect to be at
in the next column.
Bottom
Time:
Once
you have reached your target depth, input the time in 2 or 5-minute intervals at
the same depth. This staged input method will give smoother graphs later. As you
input the dive time at maximum depth you will notice in column C, your current
ascent ceiling. You could theoretically ascend directly to this depth, although
you should aim to ascend no faster than 10metres shallower every 1 minute on
dives shallower than 150m.
10
metres per minute is acceptable while ascending from 150m to 10m.
15
metres per minute is acceptable while ascending from 200m to 150m.
18
metres per minute is acceptable while ascending from 250m to 200m.
20
metres per minute is acceptable while ascending from 300m to 250m.
Ascent:
From
your bottom depth, add 1-minute time while ascending 10 metres depth, repeat
this until you reach the ascent ceiling (from column C). On deeper stops, remain
at the stop for as long as it takes to get a next stop depth at least 3m
shallower than your current depth.
Warnings:
If you ascend beyond a
decompression ceiling, you will see a
DCS warning appear in red. You should increase the time at the
previous stop until an ascent ceiling at least 3 metres shallower is shown.
A minus number is given as the ascent ceiling, when it is safe to go from the last decompression stop to the
surface.
Breathing
Gases:
Input
your chosen breathing gas selections into the columns 4 and 5. These values will
be oxygen values or helium values. The appropriate PO2 values will be shown in
column J. The appropriate EAD value for helium content will be shown in column
R. Adjust the oxygen values and helium to suit your personal preferences and the
logistics of the dive.
Warnings:
When selecting a new
ascent gas, if the gas you input puts you at risk of counter diffusion, a
warning will appear in red saying ICD, this is an abbreviation for Isobaric
Counter Diffusion. This condition
can occur when you breath a gas containing mixtures which effectively raise your
current EAD value above a pre determined limit. This limit is the result of the
current decompression ceiling relative to your current EAD.
You must avoid breathing
counter-diffusing gases when the ICD warning is given. To remove the ICD warning
you should increase the Helium value in your next mix or raise your ascent ceiling,
which is easiest to do by reducing time at depth.
In borderline cases, increasing the
pre gas switch stop by a minute or two can remove mild ICD risks.
Isobaric Counter Diffusion Predicting Algorithm
The DecoChek software is the first program to actively warn users
when conditions are present that have caused decompression complications due to
counter diffusing gases in the past. Technical divers are descending deeper and
longer than before. As the dive becomes more extreme, conditions will
occur that will become dangerous if counter diffusing gases are not considered
during pre dive planning.
Counter Diffusing Gases are seldom a problem during recreational
technical scuba dives, but as time spent in deep water increases, certain fast
tissues within the human body become very vulnerable to gas changes during
ascent. The gas mixes used in scuba diving often have very different solubility
and diffusing characteristics. A gas with high solubility for example Nitrogen
can have disastrous consequences if introduced to a tissue that is pre saturated
with Helium which has low solubility. The Helium will be rapidly displaced as a
gas, causing tissue damage. This tissue damage has typically impacted the faster
tissues during deep decompression stops during gas switches. The problem is
vastly exacerbated by inappropriate decompression schedules. A gas with low
solubility often has high diffusability and vice versa.
A
good analogy to picture the problem would be to consider the following.
A
bath tub is filled with small polystyrene balls (Helium) until it is completely
filled.
Water (Nitrogen) is added to the bath and quickly the Polystyrene Balls are
displaced, causing them to spill over the side.
This
spillage would be seen as damage, as the baths capacity (body tissue) has been
exceeded.
There
are other forms of Isobaric Counter Diffusion that have effected experimental
divers during descent,
another type affecting commercial divers inspiring mixtures that differ from
their surroundings.
Adjusting
Half Times
Warning
: Changing the pre set Half time values will make the sheet useless.
If
you change any of these values, save a copy of the original sheet first!
For
those wishing to change the Half time values and ascent limitation values
(purely for demonstration purposes), simply modify these values in the sheet. As
you modify these values, for instance, the fast times T1-T2, you will see the
changes to the first stop depths. If you change the slower tissue limits
T60-T120, you will see the shallower stop times change. The decompression stops
and times there at, are a function of tissue half time and ascent limit (crit-edge)
in bar (ata) for that tissue. You will see that the slower the tissue, the
smaller the ascent limit. The Ascent limit is sometimes called an M value.
Interestingly the ascent
limits for the fastest tissues T1-T2 have small ascent limits (crit-edge) also,
these are the helium stop values. Helium being a dynamic gas, needs a more
“controlled” ascent than nitrogen. If you are using Air or Nitrox gases, you
may want to want to make the fastest values the same as T3
The
DecoChek
incorporates many data fields, to get a less cluttered view of the dive plan,
choose one of the visual display options, by switching through the various graph
modes at bottom left.
To fix a dive plan full
of warnings, add time to the deco stops or, change your dive software!
Have
fun…dive safe…dive educated