Rebreather Diving 101
By
Richie Kohler,
Wreck Diver, Rebreather and Technical Instructor
http://www.richiekohler.com
May 1,
2009 - Originally Posted to
AcademyOfScuba.com
rakohler@aol.com
Diving Silent, Diving
Deep - Rebreathers
Even
before we, as fledgling divers, ever strapped a tank on, SCUBA DIVING,
with its complex looking equipment and arcane terminology, seemed
pretty TECHNICAL to our untrained eyes and minds. Our instructors
tried to be gentle, but soon hit us with physics like
Archimedes principal and followed that up with the one-two punch of
Boyles then Daltons laws. Still reeling from that academic assault,
they went on to explain the difference between DIN and Yoke,and what a
BCD, SPG and VIP is. All in all it was pretty technical stuff to the
uninitiated. Through the classroom and pool, our instructors helped us
along and we began to grasp and make sense of it all. In the pool
lessons we conquered the challenge of mask clearing, putting our
regulators on the tank, and acquiring that Zen like state of neutral
buoyancy. Soon enough, we took that giant stride off the boat and
haven’t looked back since. I mention our humble beginnings and
reminisce to those awkward first steps because even as we see more
rebreathers in the dive shops, dive boats and local quarry, there are
some who think rebreathers may be too TECHNICAL for them, or worse,
beyond the ability or range of the sport diver. While its arguable
that rebreathers may not be for everyone, they’re most certainly for
the sport divers!
From our basic class through advanced open water, we mastered dive
computers and moved on to Nitrox, all to get longer bottom times and
allow us more of what we love to do, DIVE. Each step of the way we
learned a little more and embraced something new and in return, we got
to stay down longer! No where else is this payoff greater than when
diving with a rebreather. The advantages are many; they’re incredibly
more efficient, smaller, lighter and more manageable than open circuit
scuba tanks. The efficient use of gas relates to little or no bubble
noise, getting you a lot closer to marine life, (a huge bonus to
photographers or anyone who enjoys interacting with the locals). Add
to that a warm moist breathing gas that lasts for hours, regardless of
depth, with longer no deco times and its clear to see how rebreathers
are clearly the next level in sport diving! Needless to say for those
anyone with the desire to go into the more truly technical types of
diving, (cave, deep or wreck) and intend to stay long, the rebreather
is the only tool of choice.
It may seem to be a new trend in dive equipment but the idea of a
rebreather has been around for nearly 300 years. Original working
designs were intended for mine rescue and wasn’t long before someone
go the idea of diving with one. The first actual rebreather dive
occurred in 1879, almost sixty years before scuba was even invented.
Today there are quite a few commercially available rebreathers
available and all of them fall under one of the three basic designs;
oxygen closed circuit, semi closed circuit or fully closed circuit.
All three types operate similarly in that they clean (or scrub) out
the CO2 from our exhaled breath, re-circulate either part or all of
the unused gas, and then add oxygen to replace that which we have
metabolized. All have a flexible breathing bag with one-way
directional check valves, a
CO2 scrubber, and an oxygen supply. The fully closed units incorporate
a second gas supply known as a diluent (usually air), and sensors to
monitor the level of oxygen in the loop. There are manual, mechanical
and electronic variations of each rebreather.
Taking a brief look at each type; the oxygen closed circuit, (OCCR) is
the smallest and simplest of the three, mechanical in design. With
only oxygen in the loop it is limited to a very shallow depth (20
feet) and primarily used by military combat divers like Navy SEAL’s,
Special Forces etc. Semi-closed (SCR) rebreathers use nitrox (instead
of oxygen) and allow the diver to go deeper than a pure oxygen unit. A
small constant flow of fresh gas goes into the breathing bag and
bubbles will regularly burp out through an overpressure valve during
the dive. There are variations on how the gas is released into the
breathing bag but all are depth limited by the use of nitrox and
design. Fully
closed circuit rebreathers, (CCR) are the most efficient type of unit
which only vents gas, (make bubbles) on ascent. CCR’s operate with an
automatic electronic controller and sensors which monitor the oxygen
level in the loop and add more when it falls below the “set-point”.
Other features in CCR’s are redundant controllers, heads up display
(HUD) to augment the handset(s), audible and vibrating alarms,
scrubber monitors and integrated decompression computers that
calculate your deco and no stop time by knowing what your actually
breathing! Its design features like this that is making rebreathers
more and more user friendly.
Closed circuit rebreathers are in effect, on the fly Nitrox mixing
machine’s that provide the optimum blend of breathing gas during each
phase of the dive by maintaining a “set-point” or PPO2. This allows
you the “best” Nitrox mix with every breath at depth, extending your
bottom time. Like everything else in life there are limitations,
nuances and operational considerations that need to be learned, some
of which can vary from unit to unit. The basic rebreather class runs
approximately 5 days long and I feel is best taught in consecutive
days rather than over a few weekends. The class usually begins a with
a few hours of academics followed by a detailed introduction to the
assembly, part by part, O-ring by O-ring to the rebreather they are
training on. This explains what each component does, how it does it
and where it goes. Like a pilot does a pre-flight on their aircraft,
rebreather divers will follow a check-list through this process, EVERY
time they assemble and prepare their rebreather. Once the unit is
assembled, it goes through a negative and positive pressure test for
air and water integrity. Now your ready for that first confined water
dive.
After learning how to open and close the mouthpiece, also know as a
DSV or dive surface valve, (divers just love all these acronyms don’t
we), we trim our weight out, work on our breathing and buoyancy skills
as hour hands become familiar with the buttons, gauges and buckles.
Each subsequent dive introduces a new skill and the student learns not
only how to fly the unit manually but how troubleshoot any potential
problem that may arise. Like every class we took before, the student
develops confidence in their abilities and equipment simply by diving
the rebreather. Repetitive skill sets tune muscle memory and change
the response to a problem from an open circuit mentality to that of a
rebreather diver. The week flies by and most of every dive is spent
simply diving, racking up hours underwater.
Once certified the rebreather student you be pleased to find that more
and more charter boats, resort locations, and live aboard operations
are becoming rebreather friendly! Less equipment means more room on
deck and some operators are renting rebreathers so
you
can leave your unit at home!
Once you dive bubble free, into truly silent world, you will be amazed
at the difference it makes on the sea life around you, and your new
place as a denizen of the deep. If you are interested in going to the
next level of sport diving or have any questions at all about
rebreather diving, drop me an email, I LOVE this stuff!
Richie Kohler
www.RichieKohler.com
