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Soon after the rescue of the crew was completed plans were formulated to recover the submarine. This was important in order to determine the cause of the accident. If a fatal flaw existed in this new class of submarine it was vital to ascertain it as quickly as possible.
On May 25th orders were issued to salvage the Squalus. Commander Charles "Swede" Momsen was in command of the recovery mission. He had at his disposal the USS Falcon ASR-2, a vessel equipped to conduct rescue, diving, and salvage operations.
LCDR Momsen
Early on it was determined that diving on surface air to the depth of Squalus would not be safe or practical.
Below is a excerpt from a lecture given by Swede Momsen to the Harvard Engineering Society on October 6, 1939. To see the full text go to http://www.history.navy.mil/faqs/faq99-6.htm
"After
one or two exploratory dives it was clearly indicated that we had little chance
of success unless we used helium.
At the Experimental Diving Unit we had found that the ill effects of nitrogen
under high pressure were almost entirely eliminated when using helium oxygen
mixture as a substitute. We had spent nearly two years developing the proper
decompression procedure following exposures with helium. Unfortunately some
writers had created the impression that very little, if any, decompression is
required when using helium. I have found in experimental work that most failures
are caused by disregarding the simple laws of physics. Here was an example.
Helium, nitrogen, argon or any other non-reacting gas that might be used as a
dilutent or carrier in respiration, goes into the blood in simple solution by
way of the lungs. As pressure is applied this gas is distributed throughout the
body and enters the various tissues, water, fat etc. The quantity of gas that
enters depends on the rate of blood supply. The tissues with great blood supply
such as the brain, kidney, liver, stomach are fast tissues while those with a
meager supply such as fat, joints, bones, etc. are called slow tissues.
Naturally given time enough all tissues approach a condition of full saturation
for the given pressure. It follows that when the pressure is released the
non-reacting gas must be given an opportunity to come off and if insufficient
time is taken, those parts known as slow tissues will be the first to give
trouble by the gas forming as bubbles. While gas does move from one part of the
body to another by direct diffusion as well as by the blood stream, and the rate
of diffusion varies with various gasses, it can be clearly seen that all gasses
must require decompression.
The theory of handling helium had been worked out, but the equipment for
handling it was not quite ready when we were called to this job. That is the
reason that helium was not used immediately. However, we started in, within a
few days, to use the helium and thence forth used it exclusively when working at
great depths. Knowing that 2.5 atmospheres of oxygen is safe to breath, the
percentage of oxygen in the helium mixtures was calculated to give slightly less
than this amount, and was roughly 28%. Since the gas that goes into solution in
the blood varies directly as the percentage present in the lungs, it is
advantageous to use as low a percentage of helium and as high a percentage of
oxygen as is possible, but keeping the oxygen tension below 2.5 atmospheres.
In order to conserve helium which costs the government about one cent per cubic
foot we devised a means of recirculating the gas in the helmet, through a CO2
absorbent, using a small gas supply as the driving agent, by admitting it
through a venturi tube. By this means the oxygen supply was adequate in the
driving gas and CO2 was kept at its proper level. This apparatus was not quite
satisfactory at first but by making daily corrections and with the assistance of
Mr. Philip Drinker and his friends we finally obtained satisfactory performance,
and used the helium.
The minds of the divers were clear and they were so much more efficient when
breathing helium that all divers were quickly converted to helium users by
choice. As regards to this mental effect I feel sure that there is a definite
relation between the molecular weight of the carrier gas to the mental effect.
For instance the ratio of molecular weights of helium to nitrogen is as 4 is to
28, and the consensus of opinion of the divers as to feeling of depth seems to
verify this. As a further study of the effect we used argon, molecular weight 40
as a carrier gas and found the effects on the minds to be similar to nitrogen,
but proportionally worse. At ten atmospheres, I myself, was able to endure
breathing a mixture of argon and oxygen, but a few moments. At atmospheric
pressure the argon was not unlike air. If hydrogen were not so dangerous as an
explosive it might make the ideal carrier gas. It may be used in the future for
very great depths where the percentage of oxygen required would be very low.
The greatest single development produced on this job was the decompression
system. Divers were brought by stages, calculated to be safe, to 50 feet. From
this depth they were brought quickly to the surface, undressed and placed in a
pressure tank within five minutes after surfacing. There he was fitted with a
mask and given pure oxygen for a time sufficient to remove all of the excess gas
from his body. 50 feet of salt water is equivalent to 1-1/2 atmospheres of
pressure which added to the atmospheric pressure gives us 2-1/2 absolute. At
this pressure the blood stream can handle in physical solution just about the
amount of oxygen that is required by the body. Thus the blood stream as
transportation is free to carry the greatest amount of the helium away to the
lungs. Since the solubility of a gas in a liquid varies as the pressure, at a
pressure of less than 2-1/2 atmospheres, the carrying capacity of the blood
would be reduced, hence it would take longer to remove the gas.
Since at pressures substantially greater than 2-1/2 atmospheres man develops
serious symptoms, commonly and I believe erroneously, called oxygen poisoning,
we do not desire to use higher pressures. It is my own opinion that when the
oxygen tension is increased beyond 2-1/2 atmospheres, the carbon dioxide removal
is interfered with, for the reason that the oxygen in the hemoglobin is not
reduced and the hemoglobin is unable to function as a chemical carrier of carbon
dioxide. The removal of carbon dioxide by physical solution alone is
insufficient. If this theory were correct we would expect to find the venous
blood stream so crowded with CO2 in physical solution that the removal of helium
or other carrier gases would be interfered with. This is, in fact, exactly what
we did find. The amount of helium or nitrogen given off when breathing oxygen,
following a measured exposure, reached a maximum at 2.5 atmospheres and then
fell off rapidly as the oxygen tension was increased. The symptoms developed by
breathing excess oxygen were found by Dr. R.A. Behnke to disappear very rapidly
when the pressure was released and to leave no after effects. This gives further
evidence that the symptoms are caused by excess carbon dioxide and not a
"poison." We were little concerned over the possibility of our divers developing
symptoms from breathing excess oxygen.
An interesting problem arose when using helium which was easily explained once
we saw the light. Divers suffered much more from cold water, than from breathing
air. The answer was that the specific heat of helium is greater than nitrogen
and body heat was lost through radiation from the body. The development of
electrically heated clothing solved this one. Resistance wire, wrapped in glass
thread woven into glass cloth to reduce the fire hazard, was made up into
panels. These were inserted between layers of wool. Electricity supplied by
storage batteries furnished as much heat as was necessary."
The plan was to attach salvage pontoons along the sides of the submarine with chains slung under the hull. The boat would then be lifted off the bottom and moved to shallower water where the pontoons would be reset. The process would be repeated until Squalus was shallow enough to enter the river at Portsmouth.
This was the first practical use of Helium gas in deep diving. Max Gene Nohl made a dive to 420 feet two years earlier but it was a experimental dive. The Navy divers would have to be able to work effectively at more than two hundred feet.
