Shearwater DCIEM User manual

DCIEM OPERATING INSTRUCTIONS

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Shearwater dive computers are capable of calculating decompression
stop requirements. These calculations are at best a guess of real
physiological decompression requirements. Even when following
computer directions exactly, there is a risk of decompression sickness
causing injury or death. Dives requiring staged decompression are
substantially riskier than dives that stay well within no-stop limits.
YOU REALLY ARE RISKING YOUR LIFE WITH THIS ACTIVITY.
DANGER
Shearwater computers have bugs. Although we haven’t found them all
yet, they are there. It is certain that there are things that our computers
do that either we didn’t think about, or planned for them to do something
different. Never risk your life on only one source of information. Use a
second computer or tables. If you choose to make riskier dives, obtain
the proper training and work up to them slowly to gain experience.
Your computer will fail. It is not whether it will fail but when it will fail.
Do not depend on it. Always have a plan on how to handle failures.
Automatic systems are no substitute for knowledge and training.
No technology will keep you alive. Knowledge, skill, and practiced
procedures are your best defense (Except for not doing the dive, of
course).
WARNING

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DCIEM Decompression Algorithm
P1 P2 P3 P4
Pa
Controlling Controlling
Compartment 1Ambient Compartment 2 Compartment 3 Compartment 4
What is DCIEM?
The DCIEM 1983 decompression model is a serial, 4 compartment decompression model
used by many naval, governmental, commercial, and scientific divers around the world.
In the DCIEM model, only the first tissue compartment is exposed to ambient pressure.
Tissue tension diffuses into each adjacent tissue compartment, and critical supersaturation
ratios in the first two compartments control decompression requirements.
Caution
This document is not a complete reference or a substitute for professional
training. Read your dive computer’s operating instructions prior to use and
never dive beyond your training. What you don’t know can hurt you.
The DCIEM model was developed by the Canadian Defense and Civil Institute of
Environmental Medicine, now renamed Defense and Research Development Canada
(DRDC Toronto). The model has been extensively tested with working divers in cold
water using Doppler ultrasonic bubble monitoring. While the model was not designed to
be bubble-free, it is comparatively well validated and considered by many experts to be
safer than other decompression models.
Shearwater has worked closely with DRDC Toronto to ensure our DCIEM algorithm
implementation is true to their model. We would like to give credit and thanks to DRDC
for their work on developing the DCIEM decompression model but note that they are not
responsible for our implementation of the algorithm.
For more information about the DCIEM model and its rigorous validation we recommend
the book “Deeper Into Diving, 2nd edition” by John Lippmann & Dr. Simon Mitchell.

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Computer Behavior
Shearwater computers using DCIEM operate in largely the same way as they do when
running any other decompression algorithm, though some info row displays will differ.
DCIEM is currently available for the Perdix, Petrel 2, Peregrine, and NERD 2. For basic
dive computer instructions, please see the primary operating instructions manual for
your model of computer.
DCIEM
MAX
52
ft
DCIEM is currently only available in single gas open circuit
Air and Nitrox modes with a maximum oxygen fraction of
40%. Multi-gas, accelerated decompression and closed-
circuit diving are not currently supported.
A DCIEM indicator is displayed above the current oxygen
fraction on the home screen when DCIEM is enabled.
Divers who are accustomed to other decompression algorithms may be surprised at the
conservatism of the DCIEM algorithm. The built in NDL and decompression planners
will run DCIEM when enabled. This is a good tool for understanding the effects of the
algorithm on NDL and decompression requirements.
DCIEM Setup
An additional unlock fee is required to use the DCIEM algorithm. Contact your
Authorized Shearwater Dealer for more information on obtaining an unlock code.
To unlock DCIEM on your dive computer, enter the
unlock code in System Setup > System Setup > Unlock.
Your computer will restart, and all tissue information
will be reset. Manage repetitive diving accordingly.
Enable DCIEM in the System Setup > Deco Setup menu.
Changing to DCIEM from another algorithm will reset
the computer into Air diving mode if the current mode
is unsupported and decompression tissues will be
cleared. Plan repetitive dives accordingly.
Date 8-Aug-2015
Clock 12:28PM
Unlock
Log Rate 10 Sec
Reset to Defaults
Next
Unlock
System Setup
Deco Model DCIEM
Safety Stop Adapt
Next
Edit
Deco Setup
Caution

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FAQ
Do I need any special training to use the DCIEM algorithm?
No, if you are a certified diver comfortable using a dive computer you should not notice
a practical difference in how the dive computer operates. The DCIEM algorithm is more
conservative than some other algorithms, so it’s important to plan your dives and prepare
accordingly. The built-in dive planners are useful tools for dive planning with DCIEM.
Will the computer tell me my repetitive group and repetitive factor?
No, Shearwater’s DCIEM implementation does not produce repetitive groups or repetitive
factors. These are components of the DCIEM table system. There is no currently validated
way to determine these values algorithmically.
How does a DCIEM computer manage repetitive diving?
Like all dive computers, tissue compartment tensions are continuously tracked and
updated, even when the computer is ‘off’. Due to this continuous tracking, there is no need
to calculate repetitive groups or factors. However, as is standard practice in computer
diving, each diver must use the same dive computer for every dive and dive computers
cannot be shared between dives.
What are the advantages to using a DCIEM computer over DCIEM tables?
There are many advantage to using a dive computer instead of dive tables. Some examples
include:
• Continuously calculated tissue tensions. This means that the diver gets credit for
multi-level diving which can dramatically increase the amount of available dive time
in a day when compared to running square profiles.
• More flexibility during decompression, crediting the diver for sub-optimal
decompression stops that occur at deeper depths due to environmental conditions.
• Automatic electronic logging of dives reducing the need to manage paper logs.
• Simplified dive planning. Built in NDL and decompression planners make planning
dives and required surface intervals easy.

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What does the Nitrogen Loading Bar graph represent when running
the DCIEM algorithm?
DCIEM
MAX
52
ft
The nitrogen loading bar graph is a representation of the
decompression stress a diver is under according to the DCIEM
algorithm. It is calculated based on the supersaturation ratios of
the model’s compartments.
No-decompression limit is not a good predictor of decompression sickness risk. The
nitrogen loading bar graph is a much better tool for managing this risk.
What does the tissue loading bar graph represent when running the
DCIEM algorithm?
TISSUES
TISSUES
TISSUES
TISSUES
TISSUES
The tissue loading bar graph shows loading of the 16
Bühlmann ZHL-16C tissue compartments, exactly like it does
when running the Bühlmann decompression algorithm.
We chose to leave this graph in place while the computer is running DCIEM for interest
and so tissue loading could be compared. The tissues represented in this graph have no
impact on decompression calculations when running the DCIEM algorithm.
Can I revert my computer to the Bühlmann ZHL-16C algorithm after
upgrading it to DCIEM.
Yes, once a computer is DCIEM unlocked it can be freely switched between algorithms.
Note that changing algorithms will clear decompression tissues. Plan repetitive dives
accordingly.
Why did we limit our DCIEM implementation to a single open-cricuit gas
of up to 40% oxygen? Will we introduce multi-gas and helium capable
DCIEM in the future?
This implementation is designed to cover the majority of use cases for the DCIEM
algorithm. We may introduce additional capabilities or features in the future depending
on market demand. We always appreciate getting feedback from fellow divers about
how we can make our products better.

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Shearwater Research Inc.
Headquarters
100-10200 Shellbridge Way,
Richmond, BC
V6X 2W7
Tel: [phone]
[e-mail]
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