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rodfarb@CE*.NE* (Rod Farb) wrote on Wed 16 Nov 1994 15:48:12 -0800 (Subject:
article):-
> Here is an article I wrote for the tek conference issue of Aquacorps.
Posted with permission. Tek is January 21-24, 1995, Moscone Center, San
Francisco, CA. If it's too long to read, trash it and get the Aquacorp later.
Aquacorp e-mail address: 73204,542@co*.co*. ... (This file must be
converted with BinHex 4.0) ...
(a) What is BinHex 4.0? Where to get a copy of it?
(b) For those like me who haven't got Microsoft Word (I use Word Perfect 5.1
for DOS), here is a copy of Rod Farb's article which I have edited into plain
ASCII text, <=78 chars/line, using Emacs directly on the partly-binary
Microsoft Word file. (I wrote the Emacs myself: it can cope with the
ascii-zero char etc and so can handle binary matter.) This version of Rod
Farb's article is 171 lines long:-
--------------------------------------------
[REBREATHER COURSE] by Rod Farb
CCR 155 Closed Circuit Rebreather by Rod Farb
A rebreather design with tens of thousands of hours of testing behind it and
years of use under a variety of conditions may become available for under
$10,000 if diver demand is there. Bio Marine - restructured, but none-the-less
containing the heart of the original company that manufactured Mark 15 and 16
rebreathers for the U.S. government before Carleton Technologies took over the
contract - has expressed interest in producing a commercial version of the CCR
155 closed-circuit rebreather - the BMR 155 - for the sport diving market.
Here is what might become available. Bio-Marine's back-mounted, twin hose,
BMR 155 rebreather weighs 64 pounds fully charged in air; it is neutrally
buoyant in seawater. Like all rebreathers, it recirculates the diver's
respiratory gases, removing exhaled carbon dioxide via a large capacity
scrubber that occupies nearly one-half of the unit's size. The scrubber
carries eight pounds of absorbent capable of removing all carbon dioxide
during a full eight hours of use. Cold water temperatures reduce the effective
life of scrubber absorbent material, but even at temperatures as low as 29O F
the BMR 155 is operational for five hours. Because it is a closed-circuit
system, breathing gases are completely contained within the unit except during
ascent when excess pressure escapes to the surrounding water. Oxygen is mixed
with a diluent gas such as air or helium in precise quantities to maintain a
constant preset absolute oxygen level. Oxygen and diluent gases are delivered
from 21 cu.ft capacity (@ 3000 psi) spherical tanks. Sophisticated electronics
control the partial pressure of oxygen delivered to the diver at a set point
that may be varied from 0.4 to 1.4 atmospheres. A triple redundant system of
galvanic oxygen sensors constantly measure oxygen levels, averaging the
results and comparing it to the set point; an alarm is given if one sensor's
measurement deviates from the set point. Based upon information supplied by
the sensors, pulses of oxygen are added to the diluent to maintain the oxygen
set point. There are two displays worn by the diver that relay information
about oxygen levels - the primary display, worn on the left wrist, signals
high and low oxygen trends alerting the diver to significant deviations from
the set point. The secondary display, clipped to a D-ring on a chest strap,
allows precise determination of oxygen measurements from each sensor plus a
battery check. An expendable battery, whose life is 12 hours under load,
provides power to operate the automatic oxygen control and primary display.
The unit has an override that may be used to manually add oxygen or diluent to
the system, if necessary. The secondary display requires no battery or
electronics for its operation and can be used to manually control oxygen
levels in the system.
The CCR 155 is an impressive system and the price is right. I had the
opportunity to purchase one of the units this summer. John McKenney, president
of Jack McKenney Productions, an L.A.-based documentary film company,
contacted me about joining him in buying two CCR 155 units that had recently
become available. McKenney Productions, whose credits include four underwater
film series produced for Discovery Channel, is starting work on a fifth series
that will incorporate stealth in filming the behavior of marine species.
Closed circuit rebreathers mean no bubble sounds like those of open circuit
systems. Since I am involved with the new series it made sense for both of us
to have a unit. Howard Hall, who has used the CCR 155 rebreather for several
underwater film projects, extolls the stealth virtues of the unit for his very
successful work. After discussing the rebreather with Howard, I was totally
sold on owning the CCR 155. John and I bought the units and arranged to travel
to Downingtown, Pennsylvania - home of Bio-Marine Instruments - for a
rebreather training course. Louis Riccio, a former Bio-Marine engineer who
worked on the design of Mark 15, 155 and 16 rebreathers - military versions of
their CCR counterparts - taught the four-day course in three days for us.
Completion of the course is mandatory for purchase of the units. And rightly
so, because learning to dive closed-circuit rebreathers is more akin to
learning to fly an airplane than to learning to dive open-circuit scuba. Over
the years Riccio has trained hundreds of divers, including Hall, in rebreather
use. His course includes pool and classroom work covering topics which include
diving the unit, unit disassembly/assembly, charging the scrubber, calibrating
oxygen sensors, changing the battery and disinfecting the unit.
In early October, I flew to Philadelphia where I met John McKenney and Marty
Snyderman who also wanted to take the course because of an anticipated
rebreather purchase. Ironically, a rebreather would have been very useful for
the drive through Philly to Downingtown, about 45 minutes west; pollution hung
like a pall of chemical atmosphere choking every breath.
Lou Riccio met us at Bio-Marine where classroom work would be conducted;
diving was scheduled in a pool at a nearby YMCA facility. Our rebreathers were
waiting for us when we arrived. They were small, lightweight and beautiful -
the CCR 155 weighs less than a set of twin-50's. We began to work immediately;
there is quite a lot to understand about rebreathers. Lou told us the
fascinating history of the Mark 15, 155, and 16 units; it is a subject about
which he has first-hand information. An engineer with General Electric where
the first electronic rebreather units were developed, he was intimately
involved with their design; his knowledge of the theory and engineering of
rebreathers is extensive. Riccio covered topics like introductory O2 and CO2
physiology; scrubber theory; components of the CCR-155 and how they operate as
an integrated unit; electronics and battery; oxygen sensors; scrubber
technology and soda lime- how it works, temperature effects and charging the
scrubber; diaphragm (counterlung) operation and assembly; using the unit's
special mouthpiece; calibration of pO2; diluent and oxygen bottles;
decompression; automatic and manual operation of the unit; monitoring pO2
levels; messages and alarm signals of primary and secondary displays; complete
set up and break down of the unit; disinfecting the rebreather after diving,
and storage of the unit. We also received gratis a manual for the CCR 155. It
was a lot of material to digest; reading the rebreather manual was the order
of business after supper.
Disassembling and reassembling components of the unit under Riccio's
watchful eye to see how they worked, we not only learned how everything worked
and how to fix it when it didn't, but we also got a good feel for which spare
parts to keep on hand for the inevitable repair in the field.
We also discussed problems relating to traveling with a rebreather. Filling
the rebreather's high pressure gas spheres is obviously an important
consideration. The diluent bottle, if it is to be filled with air, should be
no problem. Use your compressor or have the 3000 psi sphere filled at any
scuba store fill station. The oxygen sphere poses the greatest logistical
problem - one that becomes a nightmare if travel is to a remote location.
Ideally, oxygen should always be available locally or nearby where diving is
going to take place or transportable to the dock to be placed aboard a boat
for use at sea. If it is not, then you have a problem. I have been using T
bottles of aviator's oxygen (330 ft3 @ 2250 psi) - the same gas used on board
airliners - for decompression; it can be used to fill the oxygen sphere. A
diver can transport these bottles in a truck or order it trucked to a
location. Flying them to a location is expensive and requires air freight;
commercial airlines will not let you check the large high pressure bottles as
excess baggage. Once oxygen bottles are at the dive location, they should be
cascaded to efficiently fill the rebreather oxygen sphere maximally;
obviously, cascading requires multiple bottles - the more you have, the
greater the number of times high fill pressures can be achieved. However, if
you want to make the most efficient use of all the gas in a T bottle and
achieve 3000 psi oxygen fills, it is necessary to use a Haskel pump where upon
one T bottle of oxygen would suffice for several fills. A Haskel pump requires
a source of air pressure to pump the oxygen, so a compressor must be available
with the Haskel. Cumbersome equipment makes filling the oxygen spheres the
biggest obstacle to overcome while diving rebreathers anywhere, but especially
at remote locations.
Basic equipment required to support rebreather diving using air as the
diluent includes a large supply of oxygen, Haskel pump, scrubber material at
eight pounds per fill - figure 40 pounds per week - biocide and spare parts.
For deep diving, add nitrox and oxygen analyzer. For mixed gas diving, add
helium, nitrox and oxygen analyzer. You will also need a suitable computer
program that generates decompression tables for the type of diving intended -
so you also need a computer. Add a printer if you want a hard copy of the
tables. Printing tables before the trip will work if you are certain that you
have covered all depth and time combinations for all partial pressures and
percentages of oxygen, helium and nitrogen that will be used. The U.S. Navy
and others have published decompression schedules for commonly used pO2 levels
for dives at shallow depths (70 fsw or less) and long times (up to 4 hours).
Another very important component of the zen of rebreathers is disinfecting
the unit after a day's dive. A rebreather is in reality an electro-mechanical
extension of your lungs connected and sealed to your body via your lips and
the unit's mouthpiece. The mouthpiece should never be removed from the diver's
mouth unless the mouthpiece valve is closed, thereby always keeping the system
impervious to entry of water and ambient air. Because the inner respiratory
workings of the unit are always moist, they must be disinfected to prevent
growth of nasty microorganisms that can be transmitted to the diver when the
unit is next breathed. Several biocides are available for the job and must be
part of the basic equipment carried by the rebreather diver. Given all that
must be done before and after diving the unit, a rebreather diver will
probably spent two or more hours a day preparing the unit.
By this time in the course we knew the CCR 155 inside and out; we were ready
to dive it. In pool sessions, we learned to prepare the unit for diving by
completing the predive checklist that is a mandatory part of every rebreather
dive. The CCR 155 is positively buoyant; floating makes it easy to leak-check
the myriad of gas lines, swage locks and fittings in the system. During dives
the primary and secondary displays were made to simulate a variety of
conditions that may be encountered in the deep, like too little or too much
oxygen; we learned what to do to correct the problem. We operated the unit in
an open circuit mode, breathed the unit upside down (on back, face up) to
experience increased gas pressure on the mouthpiece, operated the unit
manually and learned how to buddy breath. Using the CCR 155 rebreather is a
piece of cake; breathing is easy and the silence is golden. Remembering
everything to check while breathing the unit is harder. The lack of bubbles
blasting past my mask was reminiscent of the early days of my diving career
when I used a U.S. Divers Aqua Master double hose regulator. Today, thirty-one
years later, I am back to wearing a double hose system; I loved it then and I
love it now.
After the course was over, we disinfected the units by flushing the
mouthpiece, hoses, and scrubber assembly with the biocide, QuatrylR, and
rinsing the components thoroughly with water. John packed his rebreather for
the flight home; I left mine for some modifications. Before leaving we
arranged for the necessary spare parts, batteries, oxygen sensors and soda
lime for upcoming practice dives in the ocean. Saying our good-byes, we left
town with the certainty that stealth diving and long bottom times were the
beginnings of a new adventure. For more information about the commercial
version of the CCR 155 rebreather - the BMR 155 - contact Dick King at
Bio-Marine Instruments, 131 Wallace Ave., Suite 3, Downingtown, PA 19335, USA.
Telephone 610.873.7200 (voice), 610.873.1712 (fax).
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