Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BLAST COMPRESSION WAVE ABSORBING DEVICE
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to blast effects suppression devices
used to limit
the damage associated with explosions. More specifically, the present
invention relates
to reduction of impulse and over-pressure of compression waves in order to
minimize
the damages in area being protected.
BACKGROUND OF THE INVENT10N AND PRIOR ART
Terrorist bombings have always been a problem. In many instances, the bomb or
explosive device is placed close to public buildings, embassies, sensitive
(nuclear)
installations, often in a parked vehicle. The damage associated with explosion
is
related to air compression waves (pressure waves, shock waves). The duration
of this
overpnasure may be milliseconds or more, and signficant impulse associated
with
compression wave results in damages to structures (buildings) having large
surface
areas.
Various means can be used to reduce compression wave effects: solid barriers
(including blast mats), foams (foam glass, aqueous foams), plastic bags filled
with
water, mechanical venting, and chemical agents. Solid barriers and blast mats
deflect
shock waves or absorb wave energy from shock waves through momentum transfer
to
supporting structure; therefore, they cannot be used to protect the internal
or external
surface of the buildings (petrochemical facilities, warships) from the impulse
associated
with the shock wave. In addition, they are not effective in confined spaces.
Foam glass, aqueous foams, and plastic bags filled with water are effective if
located
close to the source of shock wave and not effective in protection of large
areas and
protection from remote explosions.
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Mechanical venting is employed to reduce the overpressure and associated
stress in
containment structures below the level allowable by design. Being effective in
reducing
the impulse, it cannot reduce the peak overpressure due to response time
problem.
Chemical agents suppress shock waves by extinguishing the combustion process
which
generates them. Such agents are effective if used to suppress the explosion at
a
source.
The examples of explosion and shock wave suppression devices are shown in the
following patents granted in Canada:
2,284,694 John Donovan et al,
2,314,245 John Bureaux et a1,
2,335,788 Donald Butz et al.
The patent No. 2284694 discloses a method and apparatus for enclosing,
controlling
and suppressing the explosive destruction of munitions in an explosion
chamber.
Plastic bags of water are suspended within the chamber over the detonation
area and
Titled with water.
In patent No. 2314245, an apparatus for explosive blast suppression, and a
method
therefor, is disclosed. The apparatus comprises a hemispherical enclosure,
positioning
means associated with the enclosure, for positioning the explosive device
substantially
equidistant from any point on the wall. The enclosure is made of composite
textile
material, comprising one or several layers of a ballistic material.
In patent No. 2,335,788, a blast suppression system is disclosed. The system
includes
a plurality of command-actuated units located in the immediate vicinity of a
bomb. Each
of the units has nozzles configured to disperse the suppressant material into
the air
surrounding the bomb. Preferably, the transmission occurs prior to the
explosion of the
bomb.
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The prior art does not address the issue of absorption and dissipation of peak
overpressure and shock wave impulse from remote or internal explosions
provided the
position of explosive charge is unknown. There are no known devices, which can
protect from fuel-air explosives (FAE) and associated compression (shock)
waves. The
FAE shock waves are known as having lower peak pressure, longer duration and
higher
impulse. It is desirable to provide a device which absorbs the compression
wave and
reduce the structural and bodily injury caused by the blast over-pressure and
associated
impulse.
SUMMARY OF THE INVENTION
The present invention provides a blast compression wave absorbing device,
comprising
a container filled with a gaseous matter having a pressure below ambient
pressure and
a means for generation of a rarefaction wave (negative pressure wave) by
expansion of
a blast compn3ssion wave into a space occupied by said container. A
rarefaction wave
(negative pressure wave) can be defined as a pressure wave having a peak
pressure
below ambient pressure. The invention comprises at least one container having
an
interior filled with gaseous matter (nitrogen, carbon dioxide, air, etc.)
having a pressure
below ambient (atmospheric) pressure. If the container is ruptured, collapsed,
or its
interior is connected to environment (to atmosphere or, for submerged
installations, to
water), the ambient air (or water) starts to fill the container (or a space
previously
occupied by container) generating a rarefaction wave and expanding the
compression
wave, thereby reducing a peak pressure of compression wave and associated
impulse
in predetermined area. The amplitude and the duration of rarefaction wave
depends on
container internal volume, the pressure of gaseous matter inside the
container, and the
contact area between container internals and environment (the area of the
ruptureable
diaphragm, of valve, etc). A plurality of ruptureable or collapsible at a
predetermined
external pressure containers can be placed on the external surface of the wall
of the
building being protected (embassy, hangar, nuclear installation, or any other
high-risk
facility), on the ground level around the building, or on the external surface
of
submerged structures. The collapsible or ruptureable containers can be placed
on the
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ceiling of a tunnel or in a bunker to protect from fuel-air explosives and
associated
compression (shock) waves. The larger container can be provided with the means
(such as ruptureable diaphragms or valves) to connect its internal part with
atmosphere
when the shock wave is detected. The rarefaction wave interferes with
compression
wave (shock wave) and reduces its pressure, a pressure of reflected wave and
associated impulse to acceptable limit. The device is located so that the
rarefaction
wave reaches the part of the object being protected at the same moment as a
blast
compression wave. To maintain required vacuum inside said container, vacuum
pumps
or gas ejectors can be employed. An internal pressure detector (pressure
switch) or a
timer can be used to start a vacuum pump.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view of a blast compression wave absorbing device
according to one embodiment of the present invention in a form of collapsible
container;
FIG. 2 is a cross-sectional view of a collapsible container shown on FIG. 1,
in collapsed
form;
FIG. 3 is a cross-sectional view of a blast compression wave absorbing device
according to one embodiment of the present invention in a form of container
having
ruptureable diaphragm;
FIG. 4 is a cross-sectional view of a collapsible container consisting of a
plurality half
cylinders having ruptureable diaphragm and welded to a flat metal sheet.
FIG. 5 is a cross-sectional view of a collapsible containers attached to a
wall and held in
place by mounting means;
FIG. 6 is a cross-sectional view of a frame structure with collapsible
containers to be
placed on a ground level;
FIG. 7 is a cross-sectional view of a tunnel with collapsible containers
attached to a
ceiling and held in place by mounting means;
FIG. 8 is a cross-sectional view of a hangar with collapsible containers
attached to
external surtaces of the roof and the walls;
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FIG. 9 is a plan view of a building with collapsible containers attached to
internal
surfaces of the walls (mounting means are not shown);
FIG. 10 is a top-plan view of a high-risk facility (embassy, nuclear
installation, etc)
having a plurality of frame structures with collapsible or ruptureable
containers placed
on the ground level around the building;
FIG. 11 is a semi-diagrammatic view of a blast compression wave absorbing
device
having a container located under ground level, a ruptureable diaphragm, a
diffuser to
direct the rarefaction wave to the wall of an object being protected, and a
vacuum
pump;
FIG. 12 is a semi-diagrammatic view of a blast compression wave absorbing
device
having a container located under ground level, a ruptureable diaphragm with
small
explosive charges and activation circuit, a diffuser to direct a rarefacfron
wave to the
wall of the object being protected, and a vacuum pump;
FIG. 13 is a semi-diagrammatic view of a blast compression wave absorbing
device
having a container located under ground level, a valve with actuator and
activation
circuit, a diffuser to direct a rarefaction wave to the wall of the object
being protected,
and a vacuum pump;
FIG. 14 is a semi-diagrammatic view of a blast compression wave absorbing
device
having a container located under ground level, a valve with actuator and
activation
circuit, a diffuser to direct a rarefaction wave to the wall of the object
being protected,
and a plurality of gas ejectors;
FIG. 15 is a cross-sectional view of a gas ejector having a solid fuel gas
generator as a
source of compressed gas;
FIG. 18 discloses a graph demonstrating the reduction in incident and
reflected
pressure of blast compression wave vs. capacity of blast compression wave
absorbing
device;
FIG. 17 discloses a graph demonstrating the reduction in incident and
reflected impulse
of blast compression wave vs. capacity of blast compression wave absorbing
device;
FIG. 18 illustrates the reduction of incident pressure around protected
facility when the
device of this invention is in use.
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DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 1 of the drawings, a blast compression wave absorbing device
is
shown consisting of hollow thin-walled cylindrical container 1 having an
interior 2 filled
with gas (for example, with air). The gas has a pressure below ambient
pressure
(below atmospheric pressure or, for submerged objects, below hydrostatic
pressure at
the depth of installation), for example, 1 psia (7 kPa abs). The container has
sufficiently
thin walls designed to collapse or rupture at a predetermined external
pressure, for
example, at 4 psig (27.2 kPa gauge). The collapsed cylindrical container can
be seen in
FIG. 2.
As can be seen from FIG. 3 and FIG 4, the container 1 can have a ruptureable
diaphragm 3 with a groove 4. Similarly, the diaphn~gm 3 is designed to rupture
at
predetermined external pressure, for example, at 4 psig (27.2 kPa gauge). The
container (FIG. 4) consists of a group of interconnected half cylinders having
ruptureabfe diaphragms and welded to the base plate. The container can be
provided
with pressure indicator and nipple to connect the container intemais with a
vacuum
pump in order to restore deteriorating internal pressure if required. The long
containers
(for example, longer than 2 m) can be provided with several diaphragms.
As can be seen in FIG. 5, a plurality of collapsible or ruptureable containers
can be
attached by mounting means 5 to the external surface of the wall 6 of t~
building being
protected (embassy, hangar, nuclear installation, or any other high-risk
facility). The
containers can be placed in the post-supported or freestanding frame 7 (see
FIG. 6) on
the ground level around the building, or be attached to the external surface
of
submerged structures. After explosion, the compression (shock) wave propagates
radially from the burst point. When the compression wave reaches the
container, it
collapses (in case of collapsible container) or its diaphragm ruptures, the
ambient air
starts to fill the container or a space previously occupied by container,
generating a
rarefaction wave (expanding the compression wave), thereby reducing a peak
pressure
of compression wave and associated impulse in predetermined area around the
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container. The collapsed cylindrical container can be seen in FIG. 2. As a
result, an
object (structure) being protected is subjected to a resulting pressure wave
with
substantially reduced peak pressure and impulse. The required rarefaction wave
parameters depend on blast effects of a design-basis bomb, available and
required
safe-standoff distances, and the size of vital areas and maximum allowable
peak
overpressure and impulse of the structure (object) being protected. The
containers can
also be placed on the ceiling of a tunnel (see FIG. 7) or in a bunker to
protect from fuel-
air explosives (FAE) and associated compression (shock) waves.
As can be seen in FIG. 8, a plurality of collapsible containers 1 can be
attached to the
external surface of the wall 6 of the hangar. The containers can be attached
to the
internal walls of the building in the areas with insufficient venting
capabilities and
subjected to a highest impulse in case of internal explosion (see FIG. 9). To
protect the
high-risk facility such as embassy or nuclear installation from large vehicle
bombs, a
plurality of freestanding or post-supported frames 7 with containers should be
placed
around the building within the fence 8 (see FIG. 10).
In case of building demolition involving shaped charges of explosives of known
weights
and pov~r, the aforementioned embodiment of blast compression wave absorbing
device can be used to prevent propagation of overpressures that cause glass
breakage.
Another embodiment of the invention is shown in FIG. 11. The blast compression
wave
absorbing device is provided with large volume container 1 having internals 2
filled with
a gas at a pressure below atmospheric pressure, for example, with the air at a
pn,.ssure
in the range of 0.1 psia to 1.0 psia. In this embodiment, the container is
located below
the ground level. The ruptureable diaphragm 3 covers the opening in the duct
11
(extended part of the container 1 ) connecting the container 1 to the
atmosphere. The
vacuum pump 9 maintains the pnrdetermined negative pressure of air (vacuum) in
the
container 1. The check valve 10 is installed upstream the vacuum pump 9 to
prevent
the air in-leakage when the vacuum pump 9 is not operating. The diaphragm 3 is
positioned between a source of compression wave and the building being
protected.
When the compression wave 21 having a peak pressure, exceeding a predetermined
pressure (for example, 4 psi (27.2 kPa)), reaches the diaphragm 3, it ruptures
allowing
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the air between the diffuser 20 and the wall 6 of the building being protected
to enter the
container 1. The generated rarefaction wave propagates outside and interferes
with
moving compression wave 21 (compression wave expands into the container 1 )
and
reduces the peak pressure and impulse a~'ecting the wall 6 of the building.
The diffuser
20 directs the rarefaction wave to the wall 8. After explosion, the diaphragm
3 should
be replaced, and the vacuum pump 9 should be restarted to restore the vacuum
in the
container 1. Because the air in-leakage is always present in vacuum systems,
the
internal pressure detector (pressure switch) is provided to start the vacuum
pump when
internal pressure in container 1 deteriorates. The internal pressure detectors
(pressure
switches) are not shown on drawings.
In addkion to the elements shown in FIG 11, the blast compression wave
absorbing
device as seen in FIG 12 is provided with external pressure detector 12
positioned
between a potential source of compression wave and the building being
protected,
controller 13, actuator 14, and at least one small explosive charge 15. The
external
pressure detector 12 is located outside the container and measun3s ambient
pressure.
If the peak pressure or the impulse of the compression wave exceeds
predetermined
level as detected by external pressure detector 12, the controller 13
generates the
signal, and the actuator 14 initiates the explosion of the small charge 15.
The
diaphragm 3 ruptures, connecting the internals 2 of the container 1 with
atmosphere
and generating the rarefaction wave. When the diaphragm 3 with small explosive
charges is replaced, the vacuum pump 9 should be restarted to restore the
vacuum in
the container 1.
The blast compression wave absorbing device as seen in FIG 11 and FIG 12 can
be
used if the second explosion immediately after the first one is improbable.
Another embodiment of the invention is shown in FIG. 13. It differs from the
blast
compression wave absorbing device shown in FIG 11 by having a valve 16. The
valve
18 is actuated by pneumatic actuator 17, which is actuated by controller 13.
The
controller 13 generates the signal to open the valve 18 if the peak pressure
or impulse
of the compression wave exceeds a predetermined level as detected by external
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pressure detector 12. The opening time of the valve 16 should be in the range
of 30 to
100 msec for most applications. The valve 16 opens, allowing the ambient air
to move
into container 1 and generating a rarefaction wave, which interferes with
blast
compression wave and reduces the peak pressure and impulse affecting the wall
6 of
the building. The valve 16 closes automatically after predetermined period of
time,
depending mostly on the volume of the container, for example, after 1 sec.
When the
vacuum in the container 1 deteriorates due to air in-leakage or due to
operation of the
valve 16 in order to suppress the compression wave generated by explosion, the
internal pressure detector (pressure switch), which is not shown in FIG. 13,
detects the
higher pressure in the container than a set pressure (for example, 0.1 psia}
and, if the
valve 16 is closed, starts the vacuum pump 9 in order to restore the set
pressure
(vacuum) in container 1. When the vacuum is restored, the blast compression
wave
absorbing device is ready to suppress the compression wave generated by next
explosion. Similarly, the vacuum pump will be restarted if the internal
pressure
deteriorates due to slow air in-leakage.
In the embodiment of the invention disclosed in FIG. 14, the blast compression
wave
absorbing device is also provided with external pressure detection and valve
actuation
equipment. It differs from the blast compression wave absorbing device shown
in FIG
13 by having an ejector 18 to maintain a predetermined pressure (vacuum) in ~e
container. The ejector can use the high-pressure water, compressed gas, or
compressed air as a motive fluid. The FIG. 14 discloses the embodiment with a
solid
fuel gas generator as a source of high-energy gas being used as a motive
fluid. When
the vacuum in the container 1 deteriorates, for example, due to opening of the
valve 16
in order to suppress the compression wave generated by previous explosion, the
pressure switch detects in the container the pressure higher than the set
pressure and,
if the valve 16 is closed, starts one of ejectors in order to restore the set
pressure
(vacuum). The signal from the pressure switch (not shown in FIG. 14) ignites
the solid
fuel gas generator 19, which develops a high velocity flow of hot gas in the
nozzle 22 of
the ejector. The vacuum generated by ejector evacuates the air from the
internals of
container 1 and restores the set pressure (vacuum}. When the vacuum is
restored, the
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blast compn3ssion wave absorbing device is ready to suppress a blast
compression
wave generated by next explosion.
The FIG. 15 discloses a cross-sectional view of the ejector with solid fuel
gas generator.
It consists of vacuum chamber 18, solid fuel gas generator 19 connected to the
nozzle
22, and ejector diffuser 23. The solid fuel gas generators are wail kn~nm and
widely
used as solid fuel rocket engines, gas generation charges for various
purposes, etc.
FIG. 18 discloses a graph demonstrating the reduction in incident and
reflected
pressure of blast compression wave vs. capacity of blast compression wave
absorbing
device.
FIG. 17 discloses a graph demonstrating the reduction in incident and
reflected impulse
of blast compression wave vs. capacity of blast compression wave absorbing
device.
The latter is measured by the ability of the blast compression wave absorbing
device to
generate the negative incident impulse (measured in psi-msec) at the standard
distance
from the device. In this example, if the incident impulse should be reduced
from 22 psi-
msec to 10 psi-msec, the blast compression wave absorbing device should have
capacity of 12 psi-msec. The calculated incident pressure of 6 psi at the
surface of the
facility being protected will be reduced to 2.7 psi (in this example). To do
that, the blast
compression wave absorbing device should be placed at appropriate distance
from the
wall of the facility.
FIG. 18 illustrates the reduction of incident pressure around protected
facility when the
device of this invention is in use.
