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Inflatable Dwelling (SPID)After reading the article, you will write an article review that includes a short summary of the article and your general thoughts about the article. You should address how the physical concepts that we have learned in this unit are used or applied. In your discussion of how this article applies to the unit concepts, you should:describe various fluid dynamics terminologies within the article,distinguish between atmospheric pressure and liquid pressure, anddescribe ideal gas law for various practical applications.Your article review should be at least three pages long, and it should be formatted in APA style. You are not required to useany references other than the article, but any information from outside sources, including the article, should be cited in APAstyle.

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By Kevin H ardy and Ian Koblick
Following the theme of manned undersea habitats, outposts to explore, work and live in the sea, we continue the series with an
excerpt from Dr. Joseph Maclnnis’s informative March 1966 Scientific American article “Living under the Sea”.
Ed Link’s Submerged Portable
Inflatable Dwelling (SPID)
By Dr. Joseph B. Maclnnis
Adapted from
March 1966
n 1956 Edwin A. Link, the inventor of the Link
Trainer for simulated flight training, was engaged in
undersea archaeological investigations. He recognized
that a diver could work more effectively at substantial
depths if he could live there for prolonged periods instead
of having to be decompressed to the surface after each
day’s work. Link set out to build a vehicle that could
operate as an underwater elevator, a diving bell and a
decompression chamber. The “submersible decompression
chamber” (SDC) he designed is an aluminum cylinder
11 feet long and 3 feet in diameter [see Figure 2], With
its outer hatches closed it is a sealed capsule in which a
diver can be lowered to the bottom. On the bottom, with
the internal gas pressure equal to ambient water pressure
and the hatches open, the SDC serves as a dry refuge from
which the occupant can operate as a free diver. Then, with
the hatches again closed, it becomes a sealed chamber in
which the diver can be decompressed safely and efficiently
on shipboard or during his ascent to the surface. An inner
hatch provides an air lock through which someone else
can enter the chamber (or pass food and other supplies
into it) during the decompression phase.
Early in September 1962, the SDC underwent its
critical test in the Mediterranean Sea off Villefranche on
the French Riviera. A young Belgian diver, Robert Stenuit,
descended in it to 200 feet and lived there for 24 hours,
swimming out into the water to work and returning to rest
in the warm safety of the pressurized chamber. When the
time came to return to the surface, Stenuit did not have
to face hours of dangling on a lifeline or perching on a
platform, decompressing slowly in the cold water. Instead
he sealed himself into the chamber, was hoisted to the
deck of Link’s research vessel, the Sea Diver, and there was
Figure 1: An underwater dwelling called the SPID (for “subm erged, portable,
inflatable dwelling”) was designed by Edwin A. Link as a base of operations
fo r long dives to the continental shelf, here undergoing a pressure test at
70 feet. In the sum m er of 1964 two divers occupied the SPID fo r two days
at 432 feet below the surface.
The Journal of Diving History
First Quarter 2016, Volume 24, Number 86
Figure 2: Two chambers used in the Man in Sea 432-foot, tw o-day dive are diagrammed. The “submersible decompression
chamber,” or SDC (le ft), is an aluminum cylinder II-fe e t long and 3-feet in Diameter. With the hatches open and the inside gas
pressure equal to the external w ater pressure, the SDC serves as a diving bell. The SPID (right) is an eigh t-b y-fo u r-fo o t inflatable
rubber dwelling w ith a steel fram e and ballast tray. Access to it is through an open entry port at the bottom
First Quarter 2016, Volume 24, Number 86
The Journal of Diving History
decompressed in safety and relative (although somewhat
cramped) comfort.
Link had decided that the second phase of his “Man in Sea” project
would attempt to demonstrate that men could work effectively at 400 feet
for several days. He established a “life-support” team under the direction
of Christian J. Lambertsen of the University of Pennsylvania School of
Medicine to undertake preliminary research and supervise the medical
aspects of the dive. Under Lambertsen’s direction James G. Dickson and
1 first evaluated the accuracy and reliability of gas analyzers that would
monitor the divers’ breathing atmosphere. In addition to proving out the
system, our experiments showed that mice could tolerate saturation at
(and decompression from) pressures equivalent to 4,000 feet of seawater.
The 400-foot dive required the design of a larger and more
comfortable “dwelling” on the ocean floor. Such a dwelling presents
unusual engineering problems. It must provide shelter and warmth and
be easy to enter and leave underwater, simple to operate and resistant to
the corrosive effects of seawater. The dwelling must be heavy enough to
settle on the bottom but not so heavy that it is hard to handle from the
deck of a support ship.
Links unique solution was in effect an underwater tent: a fat rubber
sausage eight feet long and four feet in diameter, mounted on a rigid
steel frame. Deflated at the surface, the “submerged, portable, inflatable
dwelling” (SPID) is remarkably easy to handle: an important advantage
when undersea habitations are established in remote locations. As it is
submerged, the tent is inflated so that its internal gas pressure is equal to
the ambient water pressure. There are no hatches; an open, cuff like entry
port in the floor of the SPID allows easy access and provides the necessary
vertical latitude for variations in the pressure differential. Inside the SPID
1# 1
Jr *
F ig u re 3: The d eflated SPID is hoisted o ve r th e side o f Link’s vessel Sea Diver. One end o f th e SDC is visib le in th e le ft fo re g ro u n d ,
w ith p a rt o f th e deck decom pression ch a m b e r beyond it.
The Journal of Diving History
First Quarter 2016, Volume 24, Number 86
and in watertight containers on the frame and on the ballast tray below it
are stored supplies and equipment: gas cylinders and the gas-circulating
system, a closed-circuit television camera, communications equipment,
food, water, tools and underwater breathing gear.
In the 400-foot dive the SPID was to be one of three major pressure
chambers. The second was the proved SDC and the third was a new
deck decompression chamber (DDC). This time the SDC was to serve
as an elevator and also as a backup refuge on the bottom but not as the
main decompression chamber. After a long, deep dive, decompression
takes several days, and it is important that the divers be as comfortable
as possible. An eight-by-five-foot decompression chamber with a fourfoot air lock was therefore secured to the deck of the Sea Diver. The SDC
could be mated to it so that the divers could be transferred to it under
deep-sea pressure. Decompression could then proceed under the direct
supervision of life support personnel.
Early in June 1964, Link and his research group sailed to the Bahamas
to test the three-chamber diving concept. We checked the chambers with
dives to 40 and 70 feet, spending several weeks refining techniques for
handling the SDC and the SPID and coping with potential emergencies.
The exact site for the dive, chosen with the cooperation of Navy personnel
using sonar and underwater television, was a gentle coral sand slope 432
feet deep, about three miles northwest of Great Stirrup Cay.
On June 28 the underwater dwelling, with its vital gear carefully
stowed aboard, was lowered slowly to the ocean floor. When it had settled
on the shelf, the oxygen level inside was adjusted to 3.8 percent, the
equivalent of a sea-level partial pressure of 400 millimeters of mercury.
The inert gas was helium with a trace of nitrogen because there had been
air in the tent to start with. Then the SPID was left, a habitable outpost
autonomous except for communications, power and gas lines, ready for
its occupants.
The next step was to transport Stenuit and Jon Lindbergh, another
experienced diver, to the shelf. As usual, the SDC was placed in the water
at the surface so that the divers could enter it from below. At 10:15 A.M.
on June 30 Stenuit and Lindbergh went over the side and swam up into
the chamber, closed the outer hatches and checked their instruments. At
10:45, still at the surface, the SDC was pressurized to the equivalent of
150 feet with oxygen and helium to check for leaks; one minor leak was
discovered and repaired. At noon the chamber started down, slipping
through the clear purple water toward the deep shelf. When it reached
300 feet, Lindbergh reported the bottom in sight. At 1:00 P.M. the
anchor weights touched bottom and the chamber came to a stop five feet
above the sand. It was just 15 feet from the waiting SPID. During the
descent the SDC’s internal pressure had been brought to 200 feet; now
pressurization was completed. At 1:15 the bottom hatches were opened
and Stenuit swam over and entered the dwelling. Lindbergh joined him
and they began to arrange the SPID for their stay.
At that point Lindbergh reported that the carbon dioxide scrubber
had been flooded and was not functioning. The divers found the backup
scrubber in its watertight container and prepared to set it up as the
carbon dioxide level rose to almost 20 millimeters of mercury. Then they
found they could not get at the reserve scrubber: the pressure-equalizing
valve that would make it possible to open the container was missing.
With the carbon dioxide level rising rapidly as a result of their muscular
exertion, they had to leave the dwelling and return to the SDC. We had
hoped to maintain the diving team on the shelf with a minimum of
First Q uarter 2016, Volume 24, Num ber 86
support from the surface, but it now became necessary to send a spare
scrubber down on a line from the Sea Diver. The divers installed it in the
SPID and the dwelling was soon habitable.
Later that evening the divers took over control of the dwellings
atmosphere, monitoring it with their own high-pressure gas analyzer and
adding makeup oxygen as required. We kept watch from the surface by
closed-circuit television as Stenuit and Lindbergh settled down for the
night. While one slept the other kept watch, checking instruments and
communications (a procedure that, as confidence in the system increases,
should not be necessary in the future). The water temperature that night
was 72 degrees and the dwelling was at 76 degrees, yet both divers later
reported that the helium atmosphere was too cold for comfortable sleeping.
In the morning the divers swam over to check the SDC, making
sure that it was available as a refuge in case of trouble in the SPID. For
the rest of the day both men worked out of the dwelling, observing,
photographing and collecting samples of the local marine life. While they
were in the water the divers breathed from a “closed” rebreathing system
connected to the SPID rather than from an “open” SCUBA system. An
open apparatus spills exhaled gas into the sea. At 432 feet, under 14
atmospheres of pressure, each exhalation expends gas equal to a sea-level
volume of some seven liters, which would be prohibitively wasteful. Link
had designed a system that pumped the dwelling atmosphere through
a long hose to a breathing bag worn by the diver. Exhaled gases were
drawn back to the dwelling through a second hose to be purified and re­
circulated. The apparatus worked well except that the breathing mixture
was so dense under 14 atmospheres that the pumps could not move quite
enough of it to meet the divers’ maximum respiratory demand.
During the second evening we carried out and recorded voicecommunication tests with the divers breathing either pure air or a
mixture of 75 percent air and 25 percent helium. Voice quality was
considerably better than in a helium atmosphere, but even 30 seconds
of breathing air caused a noticeable degree of nitrogen narcosis. At
11:00 P.M. the two men bedded down for the second night. They were
disturbed from time to time by heavy thumps against the outside of the
dwelling. It was found that large groupers, attracted by the small fishes
that swarmed into the shaft of light spilling from the open port of the
SPID, were charging the swarm and hitting the dark bulk of the dwelling.
The next day the divers measured the visibility in the remarkably
clear water; they could see almost 150 feet in the horizontal plane and
200 feet vertically. Then they took more photographs and collected
animal and plant specimens. At 1:30 P.M. on July 2 both men were back
in the SDC with the hatches secured. At 2:20, after 49 hours on the deep
shelf, the SDC began its ascent. The internal pressure was maintained
at 432 feet; although the divers were being lifted toward the surface,
they were not yet being decompressed. At 3:15 the dripping SDC was
hoisted onto its cradle aboard the Sea Diver. Now the internal pressure
was decreased to 400 feet to establish a one-atmosphere differential
between the divers’ tissues and the chamber environment and make it
possible for helium to begin escaping effectively from their tissues. Then,
at 4:00, the SDC was mated to the deck decompression chamber, which
was also at a pressure of 400 feet. Stenuit and Lindbergh, transferred to
the deck chamber and we began to advance them to surface pressure at
the rate of five feet, or about 0.15 atmosphere, per hour. With the divers
safe in their chamber another advantage of deck decompression became
evident: mobility. While decompression proceeded the Sea Diver weighed
The Journal o f Diving History
anchor and steamed for Florida. By the time it moored in Miami on the
afternoon of July 5 the pressure had been reduced to 35 feet.
During the shallow stages of decompression, breathing pure oxygen
establishes a larger outward pressure gradient in the lung for the inert
gas to be pulled out of the diver’s tissues, thus helping prevent the bends.
Since breathing pure oxygen under pressure for a sustained period can
cause lung damage, Lambertsen had in the past suggested alternating
between pure oxygen and compressed air. We instituted this interrupted
oxygen-breathing schedule when the divers reached 30 feet. Still, we had
one period of concern about decompression sickness. At about 20 feet
Stenuit reported a vague “sawdust feeling” in his fingers that seemed to
progress to the wrists. I examined him under pressure in the chamber.
There were no abnormal neurological findings, but decompression
sickness is so diverse in its manifestations that almost any symptom has
to be taken seriously. Dickson and I therefore recompressed the chamber
one atmosphere and then resumed decompression at the slower rate
of four feet per hour. Finally, at noon on July 6, Stenuit and Lindbergh
emerged from the chamber in excellent condition after 92 hours of
decompression. The important point about saturation diving is that their
decompression time would have been the same if they had stayed down
49 days instead of 49 hours.
Their dive had shown that men could live and work effectively more
than 400 feet below the surface for a substantial period, protected by an
almost autonomous undersea dwelling, and be successfully recovered from
such depths and decompressed on the surface at sea. More specifically, it
demonstrated the flexibility and mobility of the three-chamber concept. It
also emphasized some problems, including the voice distortion caused by
helium and the need for a larger breathing-gas supply to support muscular
exertion. It showed that the control of humidity in an atmosphere in direct
contact with the sea is extraordinarily difficult. The relative humidity in the
chamber was close to 100 percent and both divers complained of softened
skin and rashes. Temperature was a problem, too. Both men preferred
having the chamber temperature between 82 and 85 degrees. In the water,
we realized, heated suits are required to keep divers comfortable even in
the Caribbean Sea. £
Author: Dr. Joesph Maclnnis currently studies leadership in lethal
environments. He worked on James Camerons last three deep-sea science
expeditions, including the DEEPSEA CHALLENGE Expedition. His latest
book, “Deep Leadership: Essential Insights From High-Risk Environments,”
was published by Random House.
The full text o f Maclnnis’ original Scientific American article is
available for a small fee at:
( oceaneering)
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The Journal o f Diving History
First Q uarter 2016, Volume 24, Num ber 86
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