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1. We've learned that every dive is a decompression dive.
You on-gas; you off-gas. Surface with too much of the former
and not enough of the latter: You're bent. Safety stops are
a decompression stop. Slow ascents are a decompression
technique. You're a decompression diver, like it or not.
2. We like it. There's no reason that with proper
training, skills and equipment recreational divers
can't employ this legitimate technique for maximizing
hard-earned diving dollars. Especially considering
the next reason:
3. We're wired. Virtually all of today's dive
computers provide the information you need to plan
and execute simple forms of decompression diving.
Some computers do it with graphic displays and
flashing icons. Some talk us through it.
4. We're stupid. Boiled down, decompression
is a relatively simple procedure. You ascend
to a given depth and hang out for a period of
time prescribed by your computer, then go up
another 3 meter/10 feet and zone out again.
Try not to fall asleep. But don't be fooled:
At some point, a few curve balls will get
tossed your way and the best laid plans
take a turn south. That's why the key to
responsible decompression dives is planning
and preparing for the things that can go wrong.
What's Wrong With This Picture?
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Most divers are never taught proper deco technique
in traditional diving courses. And that's fine since
PADI, SDI, SSI, NAUI and others do not consider
planned decompression as part of their charter.
Safety stops receive strong mention, but little
attention is paid to precision and accuracy.
Consequently, watching many sport divers do safety
stops is like trying to follow a yo-yo in action.
You can get away with that kind of sloppy technique
in safety stops because they aren't required for
the dive profile.
But with planned decompression, stops are
factored into the overall dive profile. If
you decide to take your 9 meter stop at 6
meter or 3 meter, the odds are you may get
to experience the reality of decompression
sickness firsthand.
Method 1: Use dive tables to predict a dive
profile that includes required decompression stops.
This allows advance planning for "bottom gas"
(what you will need to breathe during the working portion
of the dive) and "deco gas" (which you'll need to
complete the decompression). Given this scenario,
the diver can easily compute a schedule that will
allow him to carry enough gas supply for both portions dive.
Indeed, most tables published for sport diving assume that
any deco will be made on the same stuff that the diver was
breathing while he was swimming about on the reef or
around a wreck.
However, most divers planning decompression today
look for an additional safety edge by using pure oxygen
or a Nitrox mix to increase the efficiency of off-gassing.
These divers carry a smaller cylinder of "deco gas"
to switch to, usually around the 6 meter stop, or
they use one provided by the dive boat.
Method 2: Plan the dive and the decompression as it
occurs. This is done with dive computers and allows a
much greater window of flexibility to the dive plan
since no rigid profile is set in advance. The governing
factor in this type of plan is to allow enough gas to
complete whatever decompression may be required. There
are endless variations to gas volume management that
can be calculated by the diver under water, including
the classic cave diving "rule of thirds" (one-third
of your gas for the descent and dive, one-third for
the ascent and decompression, and one-third for reserve).
Method 3: Divers using secondary deco cylinders
have an extra edge on the folks who want to decompress
on the remaining air in their primary tanks. Not only
will they benefit from the higher oxygen mix, they
will also generally have from 3 liter to 8 liter
of additional gas to breathe during the hang.
Tips for Avoiding the Chamber.
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So you completed your dive and are ready to head up to
begin the decompression indicated. Here are some basic
do's and don'ts.
Know your computer. If you haven't thoroughly familiarized
yourself with your computer's decompression functions, don't
even think about trying a deco dive just to see what happens.
Some units will default if no-decompression profiles are
exceeded. Others will scramble if you venture beyond a
certain depth limit. Still others have deco models so
conservative that you will spend more time at 3 meters
than you spent in line at the DMV.
Monitor ascent rate. Your ascent is part of your
total decompression profile. If it's supposed to
take you two minutes to come up to your first stop,
don't do it in 30 seconds. Likewise, don't come up
unreasonably slow as this will only increase nitrogen
gas loading during the deeper part of the ascent.
Your computer should remind you if you ascend too
quickly for its deco model by either flashing a
warning on its display or beeping at you with an
audible signal.
Control your buoyancy. Stay in control by dumping
excess air during the ascent, and stop completely
at least 3 meters below the first stop to ensure
you can hover comfortably. Dive with extra weight
to counteract the positive buoyancy of tanks as
they are empty.
Stay static. Preferably, your first experiences
should include some type of static support like
an anchor line or deco bar. This also gives you
a firm handhold if current is present or if
the dive boat is swinging on its mooring.
Use the KISS system. Keep it simple stupid.
Initially, no decompression should be planned
with more than one stop until you are completely
comfortable with your ability to maintain depth,
predict breathing rate, and manage your gauges.
Do it all. Never cut a decompression stop short.
Spend all the time required at the depth prescribed.
It's OK to extend the last stop. You can consider
that part of your "safety stop".
Decompression Diving. The Real Risks.
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Over the years, the mainstream diving community has
shunned stage-decompression diving by sport divers,
resulting in a significant stigma surrounding the
practice. The fact is: Many, if not most, shop owners
and instructors do not have an adequate understanding
of stage-decompression diving and its risks. The
risk of DCS for a diver properly executing a
stage-decompression dive is probably about the same,
if not less, than it is for a diver making a no-stop
dive because of more efficient off-gassing, thus
minimizing "silent" bubbles formed during ascent.
Less risk of DCS, however, does not mean that the
stage-decompression diver does not face other
significant risks. Stage-decompression divers are
forced to stay below a virtual ceiling or face a
high risk of DCS. Therefore, they must carry
additional equipment that allows them to solve
problems at depth, because surfacing is not an
acceptable option.
| Risk - Dealing with this gear on a dive boat results in a higher risk of physical injury. |
| Risk - The extra gear results in a larger profile while diving, creating an increased risk of overexertion due to swimming resistance. |
| Risk - The additional equipment creates a greater number of potential failure points in the gas delivery system, increasing the potential of a failure. |
| Risk - Because stage-decompression divers cannot rise above the decompression ceiling, should they miss the ascent/descent line, their risk of being carried away from the boat in a current is greater. |
| Risk - Stage-decompression diving also tends to result in longer in-water exposure times, greatly increasing the chance of hypothermia. |
| Risk - The extended exposure time also equates to increasing the odds of experiencing a problem while under water. |
Bottom Line, Decompression diving.
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Stage-decompression diving requires training and
experience beyond the norm. The only way to truly
learn to properly execute stage-decompression dives
is to seek out a quality training program from an
experienced, knowledgeable instructor. While there
are increased risks involved, done properly the
risks of stage-decompression diving are manageable
within an acceptable level.
Technical Training Agencies.
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IANTD (International Association of Nitrox and Technical Divers)
reorganized in 1992 to expand from basic Nitrox training.
Offers full curriculum of tech courses, instructor programs
and insurance.
ANDI, American Nitrox Divers International. Ed Betts
and Dick Rutkowski joined together in 1988 to form
American Nitrox Divers, Inc. ("ANDI").
The purpose was to standardize Instructor Training,
Sport Diver Training, and refill station dispensing
procedures for Enriched Air Nitrox diving.
Contact Information.
Neptune Dive Center. 312/12 Pattaya 3rd Road,
Pattaya, 20150, Chonburi, Thailand.
Tel: 038-720603 Fax: 038-720608
Mobile: English, Nederlands, Deutsch.
086-1532636
Mobile: Thai 081-1509562
Email:
scuba@tttmaxnet.com
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