Method for varying the ambient pressure in a vessel

The ambient pressure of the environment of an individual within a vessel is varied between an upper and lower pressure value by providing the vessel with a mass of gas sufficient to fill at least a substantial part of the vessel, and varying the quantity of liquid, primarily water, in the vessel in order to cause the pressure therein to vary correspondingly between the upper and lower values.

BACKGROUND OF THE INVENTION 
The present invention relates to varying the ambient pressure to which 
individuals are exposed, and particularly to compression and decompression 
of divers for passage to and from undersea work locations. 
Because of the reaction of the human body to substantial changes in ambient 
pressure and particularly its inability to tolerate rapid pressure 
reductions, it has always been necessary for divers to undergo carefully 
controlled decompression procedures following deep dives, and a wide 
variety of devices and systems has been employed for carrying out these 
procedures. 
In recent years, various factors have created a need to perform undersea 
tasks at increasingly great depths, and submersible pressure vessels have 
been developed to transport divers between worksites at those depths and 
the surface. 
Such pressure vessels may be arranged to be lowered to the worksite from a 
surface support vessel, the pressure vessel then functioning as a diving 
bell, or it may be part of an independently movable, i.e. untethered, 
submarine, the pressure vessel then constituting part of a diver lockout 
submersible, or the pressure vessel may form part of a quasi-permanent 
undersea structure, or habitat. 
The interior of the pressure vessel can be brought to the worksite ambient 
pressure either before or after reaching the worksite. 
In known arrangements, pressure within the vessel is increased by 
introducing gas from a high pressure supply. The containers constituting 
this supply are extremely bulky and heavy and in some cases may constitute 
a major portion of the system or vehicle. 
In order to return the interior of the pressure vessel to a reduced, i.e. 
surface atmosphere, pressure, gas therein is simply vented to the outside 
either during or after return of the vessel to the surface. 
Depressurization is not performed while the pressure vessel is at the 
worksite depth because a compressor capable of expelling gas at an 
appropriate rate against the ambient pressure of the surrounding sea water 
would present unacceptably high weight, power and volume requirements. 
According to another approach to permitting the performance of work by 
divers at the sea floor, which is applicable to a limited range of 
situations where the work is to be performed on equipment installed at the 
sea floor within a pressure-tight, water-filled chamber, it has been 
proposed to bring the pressure in that chamber to one atmosphere before 
diver entry. One system, which has been proposed by Vickers-Intertek, for 
this purpose is known as the neutrabaric system. In this system, which is 
particularly applicable to the servicing of wellheads, the wellhead 
components which are to be available for servicing are housed in a chamber 
which is connected to a second water-filled transfer chamber, the interior 
of the two chambers being in communication via a passage which is 
sufficiently large to accomodate a diver. Divers are brought to the 
worksite in a third chamber constituting a dry, one-atmosphere unit which 
is mated to a passage presented by the second chamber. The interior of the 
third chamber is then placed in communication with the interiors of the 
first and second chambers, so that the water in the latter chambers can be 
expanded into the bottom of the third chamber to bring the interiors of 
all three chambers to a pressure of one atmosphere. This result can easily 
be achieved because a very small change in the volume of a given mass of 
water corresponds to a substantial pressure change. For example, at a 
depth of 700 feet, where the ambient pressure is of the order of 20 
atmospheres, the volume of a given mass of water must increase by only 0.1 
percent in order to bring the pressure in that mass of water to a value of 
one-atmosphere. 
Thus, the concept underlying this system is to always maintain divers in a 
one-atmosphere enviroment, thereby eliminating any need for decompression, 
which is possible only when work is to be performed on equipment already 
housed in a water-tight, pressure resistant chamber. This system is 
incapable of producing a meaningful or controlled variation in the ambient 
pressure to which the divers are exposed. 
It is also known to effect escape from a submerged, disabled submarine via 
an excape trunk connected to the submarine, by a procedure in which a 
submarine enters the trunk from the submarine, the trunk is then sealed 
and its interior pressure is raised as rapidly as possible from the 
submarine interior pressure to the ambient pressure of the surrounding sea 
water, and the trunk is then opened to the sea and the submariner exits 
from the trunk and ascends to the surface. Sea water is introduced into 
the trunk either to raise the pressure therein to ambient or to displace 
the gases therein, and in the latter case subsequent rapid compression is 
effected by introduction of a high pressure gas. No control is exerted 
over the rate of pressurization--in fact pressurization proceeds as 
rapidly as possible for the purpose of eliminating the need to 
subsequently perform a controlled depressurization--and a submariner is 
never subjected to depressurization within the trunk. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide an improved procedure for 
adapting individuals to substantial pressure changes. 
A more specific object of the invention is to effect diver compression and 
decompresssion in a simple and cost saving manner. 
A further specific object of the invention is to substantially reduce, or 
eliminate the need for any compressed gas supplies to effect compression 
and decompression. 
Another object of the invention is to provide the capability for performing 
decompression at any depth, including the working depth. 
These and other objects are achieved, according to the invention, by a 
method for varying the ambient pressure of the environment of an 
individual within a vessel between an upper and lower pressure value, 
which is carried out by providing the vessel with a mass of gas, normally 
air or another breathable composition, sufficient to fill at least a 
substantial part of the vessel when the pressure is at the lower value; 
providing the vessel with a mass of liquid sufficient to fill at least a 
substantial part of the vessel when the pressure is at the upper value; 
and varying the quantity of water in the vessel in order to cause the 
pressure therein to vary correspondingly between the upper and lower 
values. 
The invention is conceived primarily for subjecting divers to compression 
for performance of tasks at a selected depth and for subsequently 
decompressing divers to surface atmospheric pressure. For these purposes 
the liquid employed is preferably water taken from the body of water in 
which the vessel is immersed. 
The present invention offers the advantages, inter alia, of significantly 
reducing, or eliminating, gas consumption to effect compression and 
decompression, and permitting decompression to surface pressure even while 
submerged without requiring large, heavy compressors which have high power 
requirements. 
A significant advantage of the invention is that it permits the use of a 
side-mounted diver lockout hatch, since compression is intended to result 
in a water level inside the vessel which is above the uppermost point of 
the hatch. Such a side-mounted hatch facilitates diver egress and ingress 
and offers the particular benefit of facilitating recovery of an 
unconscious diver via a neutral buoyancy recovery. In addition, the 
side-mounted hatch eliminates bottom clearance problems, associated with 
the bottom hatch required in conventional gas pressurization methods. 
Moreover, the method according to the invention permits of an improved 
decompression technique in that a major portion of decompression is 
effected in a "head out immersion" condition, which enhances inert gas 
elimination from the body. In addition, decompression according to the 
invention can readily be performed by withdrawing water at a constant 
rate, thereby easily permitting an exponential pressure reduction, which 
for some pressure/time exposures may be physiologically superior to the 
linear pressure reduction produced by removing gas at a constant mass rate 
.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 illustrates a basic preferred embodiment of the invention which 
offers the advantage that it requires no auxiliary vessel or container. 
According to this embodiment, the diver's vessel is initially filled with 
air at atmospheric pressure, for example at the surface. It can then be 
lowered to the diving depth, either with the divers on board or with the 
divers having descended in a different vehicle or in a free dive. 
An intake valve 2 in vessel 1, is opened, either while the vessel is being 
lowered or after the vessel has reached the diving depth, to admit water 
to the vessel. If the vessel is to be used in such a manner that flow of 
water between the surrounding sea and the vessel interior is to be 
controlled from the outside, valve 2 can be mounted outside the vessel or 
can be equipped with a control extending outside the vessel. As water 
enters, the gas within the vessel becomes increasingly compressed in the 
upper part of the vessel interior until its pressure comes into 
equilibrium with the ambient pressure at the diving vessel depth. The 
vessel may also be equipped with an auxiliary source 5 of gas under high 
pressure from which gas can be supplied to the vessel interior if 
necessary, for example to maintain a minimum volume of trapped gas or to 
maintain physiologically acceptable partial pressures of the gaseous 
components. 
If divers are present in the vessel during its descent, pressurization is 
controlled at a rate which assures safe and comfortable diver compression, 
and the divers can than leave the vessel via either a side-mounted exit 
hatch 3 or a bottom hatch to perform their tasks. 
At the end of a dive, divers can swim easily through the side hatch 3 into 
the water-filled vessel and can then assume a standing or seated position 
with their heads extending into the gaseous region at the top of the 
vessel. 
Then decompression proceeds by withdrawing water from the vessel at a rate 
determined by the decompression requirement of the divers. This can be 
effected by a discharge pump 4 at the bottom of the pressure vessel, it 
having been found that water can be discharged in this manner by a low 
capacity pump at a rate which can be accurately controlled to effect safe 
decompression. 
The pump 4 can be operated to discharge the water while the vessel remains 
at the diving depth, or the water can be permitted to flow out of the 
vessel at a controlled rate while the vessel is being raised to the 
surface or after it reaches the surface. Any residual excess gas which may 
remain due to having been added as part of the compression sequence, may 
then be simply vented. If the entire decompression to 1 atm pressure is to 
occur in the submerged condition, this relatively small volume of gas may 
be removed using a relatively small compressor. 
In accordance with a further embodiment of the invention, control of the 
pressure in the diver's vessel is effected by exchange of water between 
that vessel and an associated water tank. The combined weight of this 
system remains constant as the diver's vessel pressure is varied, so that 
the entire system can remain neutrally buoyant to facilitate, inter alia, 
midwater diver lockout. 
One embodiment of a system constructed to operate in this manner is shown 
in FIG. 2 and includes, in addition to the diver's vessel, a water tank 6 
having a capacity at least equal to the quantity of water which must be 
removed from the diver's vessel during an operating cycle and dimensioned 
and possibly filled with a charge of gas to assure that the pressure in 
the water tank is always above the minimum inlet pressure of an intake 
pump 7 disposed in vessel 1, and is approximately equal to one atmosphere 
when all water in the system is in the water tank. To pressurize the 
diver's vessel, water is pumped thereinto by the pump 7 from the water 
tank 6 until the vessel interior is at the diving depth pressure. 
Decompression is attained by opening an outlet valve 8 disposed in the 
diver's vessel to permit water to flow through a conduit connected to the 
water tank at a controlled rate. 
One advantage of this procedure is that decompression is an essentially 
passive operation which can proceed even if a power failure should occur. 
Each of the above-described systems may also include an attached manned 
normo baric pressure vessel in which case the pump, and water and gas 
supply valves may be located in the manned normo baric pressure vessel and 
in the embodiment of FIG. 2. The water tank may have the capability of 
being brought into pressure equilibrium with the normo baric chamber. 
Likewise, the method according to the invention could also advantageously 
be employed in conjunction with a submarine to permit passage out of and 
back into the submarine while it is submerged, thereby providing a 
convenient and efficient means for making underwater exterior repairs, 
conducting sea floor exploration and effecting escapes from crippled 
vessels. 
For such purposes, the diver's vessel would be provided with a bottom hatch 
for mating with a hatch on the deck of the submarine as well as with a 
side hatch. The vessel would further be provided with a coupling arranged 
for connection to a tank analogous to tank 6, disposed in the submarine, 
for holding a mass of water at the ambient pressure within the submarine, 
and possibly with a valve via which the interior of the vessel can be 
placed in communication with the surrounding sea. In addition, a pump 
could be provided in the pressure vessel, either for pumping water from 
the vessel back into the sea, or for pumping water from the submarine tank 
into the vessel. 
To use the vessel for passage out of and into a submerged submarine, the 
bottom hatch of the vessel is mated to the submarine deck hatch and both 
hatches are opened, placing the vessel and submarine interiors in 
communication. The interior of the vessel is then dry and at the submarine 
interior pressure, and can be entered from the submarine. 
The vessel hatch is then closed and the vessel is filled with water to 
bring its interior to the ambient sea pressure. This can be achieved 
either by opening the valve which communicates between the vessel interior 
and the sea or by pumping water into the vessel from the tank disposed in 
the submarine. 
The side hatch is then opened for passage of the diver into the sea to 
perform any necessary inspection and repairs. 
To return to the submarine, the diver reenters the vessel via the side 
hatch, which is then closed, and the water is removed from the vessel, 
either by pumping it into the sea or venting it to the tank disposed in 
the submarine, at the rate dictated by diver decompression requirement, 
until the pressure within the vessel returns to the submarine interior 
pressure. The communicating hatches are then opened and the diver reenters 
the submarine. 
The provision of the above-described water holding tank in the submarine 
offers the advantage of permitting completely passive cycling of vessel 
interior pressure, at least for one or a small number of uses. Thus, the 
vessel interior pressure can be varied from the submarine interior 
pressure to the ambient sea pressure by opening the valve connected in a 
line extending therebetween, the extent to which the valve is opened 
determining the rate of pressure rise. Return to the submarine interior 
pressure can then be effected by opening the valve connected in a line 
between the vessel interior and the tank in the submarine, again the rate 
of pressure drop being controlled by adjusting the valve opening. 
The invention is preferably practiced using vessels having a size and shape 
sufficient to assure that at the highest pressure to be encountered the 
portion of the top of the vessel which is filled with gas will be of 
sufficient size to enable the divers to comfortably maintain their heads 
out of water, taking into account that the proportion of the vessel volume 
occupied by a given mass of gas will be substantially linearly inversely 
proportional to the absolute pressure in the vessel, assuming no change in 
temperature. 
Of course, the pressure vessel must be connected to a source of a 
breathable atmosphere which can be pumped in according to known techniques 
during decompression or compression, without substantially influencing 
pressure conditions in the vessel. 
Pressure vessels for carrying out the invention will normally be provided 
with a source of a breathable gas supply, an atmosphere conditioning unit, 
and use of a separate mask breathing supply system of an open, closed, or 
semi-closed nature, are all expected features of any embodiments, that are 
incidental to the ambient pressure variation methods described herein. The 
pressure vessel of the invention may be part of a larger underwater 
system, such as a diver lockout system or an underwater habitat, or can be 
used in conjunction with a separate underwater system, such as a 
submarine, as described above, or an underwater habitat. 
It will be understood that the above description of the present invention 
is susceptible to various modifications, changes and adaptations, and the 
same are intended to be comprehended within the meaning and range of 
equivalents of the appended claims.