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The original Amphibian triple
purpose apparatus, i.e. for use in poison gas or under water, consist of
a steel cylinder, charged with pure oxygen for depths not exceeding 30
feet; CO2 absorbent chamber, mouthpiece, noseclip, goggles, a
streamlined bag, with excess air escape valve; and- for the use under
water only- a lead balance-weight at back, jock strap, etc. For use at
greater depths, a mixture of oxygen and air, or of oxygen and helium is
used in certain proportions according to the depth at which the diver
has to work. (note: first trimix dives?) In some cases the gases are in
separate cylinders, each with its own reducing valve set to deliver the
gases in correct proportion. In the modified Amphibian apparatus the
excess air of exhaust valve is fitted in front of the wearer, over his
shoulder, so as to be more readily accessible. While still of the
automatic type, like the more remotely placed valve, the new arrangement
also enables the valve to be controlled by hand.
In de the model III the excess
air or exhaust valve is fitted in front of the wearer, over his
shoulder, as it was modified in the II series, so as to be more readily
accessible. While still of the automatic type,like the more remotely
placed valve to be controlled by hand.
Because this set was used by
frogman there were requirements of easy breathing. All these
requirements mean that special care must be given to the design of the
breathing set. It must be designed so that the essentially heavy items
such as cylinders and reducers do not upset the delicate balance of the
frogman, and must give comfortable, effortless breathing in any and
every position that the diver may assume. Siebe’s Amphibian MK III and
MK IV, Dunlop’s Underwater Swimming Breathing Apparatus (U.W.S.B.A.) and
the Admiralty “Universal” are all designed with this end of view. The
design of the breathing system is based upon confirmatory work done at
the national Institute of Medical Research for the Admiralty by Docters
Sands and Paton. (U.P.S. Report No. 61).
These workers determined the maximum resistance, expressed in terms of
millimetres head of water, wich could be tolerated by divers in all
positions under water without interference with normal repiration. The
ideal for the breathing bag relative to a diver’s ear was named
“Eupnoeic depth”, and it was shown how this depth varied with the depth
of respiration. By designing the breathing set so that the eupnoic depth
is never exceeded under any conditions, the best breathing conditions
are obtained.
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