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Scrubbers & Sensors
83
X-RAY MAG : 4 : 2005

EDITORIAL FEATURES TRAVEL NEWS EQUIPMENT BOOKS SCIENCE & ECOLOGY
EDUCATION
PROFILES PORTFOLIO CLASSIFIED
commercial,
generally
available dive-
system, and
this promoted
the later great
expansion of
sports diving
everywhere.
And it must
be said that
the regula-
tor is a fine
Contrary to popular belief rebreathers are actually a much older scuba diving technology than open circuit regulators
The Long (his)Story About
Scrubbers & Sensors
Ambient Pressure Divings Closed Circuit
Rebreather
Evolution is the latest step in CCR
...erh... evolution.
T
he greatest majority of the
readers of this magazine
will have learned to dive
with a regulator originating
from the Aqualung, which
the renowned Jacques
Cousteau and Emile
Gagnan invented in 1940.
The regulator was the first
From Fleuss to Evolution
piece of
equipment. It is reli-
able, more or less foolproof,
and its simple construction
is
very robust. These are good properties
to have when ones underwater breath-
ing depends on them. However, as we
will see, there are also a number of dis-
advantages. And it is these that make
re-breathers an interesting alternative
system.
When diving with a regulator, it is
said that one is diving with an
open
circuit, because the exhaled air
passes straight out into the surrounding
water, and is thereby lost. As only about
a quarter of the available oxygen has
been taken up by the body, and the rest
expelled, it is a rather ineffective utilisa-
tion of a scanty resource. (See table next
page.)
In addition, as the amount of air used
increases proportionally with depth, open
systems become more and more ineffi-
cient, and there are therefore major limi-
tations to how long a diver can remain
underwater. It seems obvious, then, to try
to re-use the air that has been exhaled,
by using a closed system.
Closed circuit systems
Closed circuit systems are a far from
new idea. It was Giovanni Borelli in the
1700s who first thought of re-using the
exhaled air. His idea was to recirculate
the air through a copper tube which was
cooled by the sea water, and thereby
cleaned the air before re-use. Luckily,
it was never made. The mining industry
and its problems with gas in the mine
shafts also stimulated the relevant tech-
nical developments during the 1700s.
Henry Fleuss, an English naval offic-
er from Germany, worked out the
principles for a re-breathing appa-
ratus, and produced a prototype at the
end of the 1870s. He stayed down in a
water tank for nearly an hour, and later
went down to 5 meters in a lake using
his system. Fleuss was the first diver in
history with a re-breathing apparatus. At
the beginning of the 1900s the military
were quick to take up this idea. Oxygen-
rebreathing equipment consisted of
an oxygen tank together with a bag of
potassium hydroxide and a breathing
loop, and was used to rescue submarine
crews and attack divers (there were no
revealing bubbles on the surface). The
German manufacturer Dräger released
several models for military use in connec-
tion with World Wars I and II.
There is more
and more talk of
rebreathers, stated
as being the future of
diving. However, not
many people have
tried them. So what is
all the fuss about?
WWW.AMBIENTPRESSUREDIVING.COM
focus 84
X-RAY MAG : 4 : 2005

EDITORIAL FEATURES TRAVEL NEWS EQUIPMENT BOOKS SCIENCE & ECOLOGY
EDUCATION
PROFILES PORTFOLIO CLASSIFIED
Scrubber, in this case
Sofnolime, comes in
small granules,
Respiration
In a modern medical textbook on physi-
ology, one of the several chapters on
aspects of respiration is entitled Physical
principles of gaseous exchange; diffusion
of oxygen and carbon dioxide through
the respiratory membrane. And it is these
very important principles that are of great
interest to divers. How we take in and
utilise oxygen, and how we get rid of the
carbon dioxide produced by metabolism.

Cellular metabolism is
independent of pressure
The amount of air which is needed to
take a normal breath at a depth of 20
meters is three times greater than at the
surface, and therefore the consumption
of air with open systems increases with
depth. However, more importantly, cel-
lular metabolism does not depend on the
pressure.
Oxygen is required to make adenosin
trifostat, ATP, the fuel of the human cell.
And a molecule of oxygen is a molecule
of oxygen, wherever it is to be found, at
the beach, or 100 meters deep, with the
corresponding increase in
pressure. Therefore, when
using a closed circuit there
is the same consumption of
air, whatever the depth. At
rest, 0.3 to 0.5 liters of oxy-
gen are used per minute
(l/min), and with maxmum
work up to 3.0 l/min are
used. Of course, there are
differences between indi-
viduals, depending on the
size of the diver and his or
her physical condition.

The carbon dioxide
problem
As we have seen, cellular
metabolism depends on oxygen, which
is inhaled from the atmosphere. The fol-
lowing table gives the composition, in
volume percent, of inhaled atmospheric
air (on an average cool, clear day), and
also the corresponding composition of
exhaled air. (There is also a minor content
of the non-reactive noble gases such
as argon, helium, etc., but this has been
ignored here.) It will be seen that the
uptake of oxygen in the lungs has caused
the oxygen content of the inhaled air
to be reduced from its original 20.84%
to 15.7% in the exhaled air. It will also be
seen that the concentration of carbon
dioxide, a biproduct of metabolism, has
gone up by about ninety times, to 3.6%.
So, it is not so much the reduction in
amount of oxygen that is the problem, for
there is still some 16% available in each
expelled breath, which should be avail-
able for re-use. It is the increase in carbon
dioxide, CO2, that is the real problem. A
diver can tolerate a build up to a CO2
concentration of about 10%, increasing
respiratory volume to compensate for
the increased CO2. However, beyond
the 10% level the respiratory center in the
brain stem begins to be depressed rather
than stimulated, and the divers respira-
tion then actually begins to fall rather
than to compensate. As a result of this,
varying degrees of lethargy, narcosis,
and, finally, anesthesia will occur. The
CO2 in the exhaled air must therefore be
removed before the remaining oxygen
can be re-used. Luckily, this is quite easy
to do, using calcium hydroxide, Ca(OH)2,
which reacts with, and therefore fixes, the
carbon dioxide. It is called CO2-scrub-
bing and the filtering material, in this case
teh calcium hydroxide, which comes as

A REBREATHER TIMELINE
1500´s In England and France, full diving
suits made of leather with metal helmets. The
diving helmets were already some sort of
rebreather, but needed surface supply and
were without scrubber
1680
Giovanni Borelli designed a closed
breathing circuit. The idea was to recirculate
air through a copper tube which was cooled
by sea water. The assumption was that al the
impurities would then condense out of the air
inside the tube.
1726
Stephen Hale designed the first
scrubber: a flannel liner, soaked in salt and
tarter, used in a helmet for mine disasters.
1772-4 Oxygen independently discovered
by Swedish chemist, Carl Wilhelm Scheele, in
1772, and the English chemist Joseph Priestly,
in 1774. Soon followed the first known ideas
to use Oxygen for diving and first functional
ideas to build autonomous rebreathers.
1876
Henry Fleuss began to develop an
oxygen rebreather. He used a rubber face
mask and a breathing bag connected to
a copper oxygen tank. The carbon dioxide,
scrubber was a rope yarn soaked in a solu-
tion of caustic potash. Enabling Fleuss to walk
along a river, this was the first SCUBA Dive.
1879
Fleuss builds a Mining-Rescue
Rebreather for Siebe/Gorman
1881
A special rebreather scrubber using
a barium hydroxide is patented by Khotinsky
and Lake.
1904
Siebe and Gorman patent Oxylite, a
potassium- and sodium-peroxide mixture that
produces oxygen on contact with water.
1907
A Dräger rebreather is used as sub-
marine rescue equipment
1912
Dräger helmet-diving-rebreathers are
available
1913
Dräger performs a successful simu-
lated 40 minute dive to 80m in chamber.
1914
Dräger introduce a selfmixing Nitrox-
Rebreather for max. 40m.
1926
Dräger presents the first early recrea-
tional rebreather, the Bade-tauchretter.
1941 Dräger Kleintauchgerät 138
1953 Dräger Leutnant Lund II and
Barakuda Delphin I
1967
Russians experiments with predeces-
sor to AKA-60
No, rebreathers are not new. In this
1912-footage we see Drägers helmet
diving rebreather in use.
Pho