U.S. patent number RE40,276 [Application Number 10/800,357] was granted by the patent office on 2008-04-29 for biological safety cabinet with improved air flow.
This patent grant is currently assigned to Labconco Corporation. Invention is credited to Kevin Gilkison, Jim Hunter, Mary Ellen Kennedy, Gerhard W. Knutson, Greg Krueger, Larry Nelson, Jerry O'Dell, Burt Rhea, Gary Roepke.
United States Patent |
RE40,276 |
Hunter , et al. |
April 29, 2008 |
Biological safety cabinet with improved air flow
Abstract
A biological safety cabinet is provided that includes a frame.
The frame defines a protected work area and encloses the work area
on all but one side. A sash is coupled to the frame that at least
partially encloses the side that is not enclosed by the frame. A
blower is coupled to the frame generally above the work area. The
blower is adapted to circulate air through the work area to make
the work area a negative pressure area so that harmful materials
are confined. A sash grill is coupled to the frame generally below
the sash that has a curved top surface. The curved sash grill
provides a superior and less turbulent air-flow into the work area,
thereby better containing any harmful materials. The curved sash
grill is perforated, and the curvature and perforations of the sash
grill compensate for partial blockage by such things as the user's
arms and other objects. The curvature of the sash grill also avoids
a sharp angle at the same height as the work surface which reduces
the chance of contact and possible breakage of labware as it is
moved into the cabinet.
Inventors: |
Hunter; Jim (Overland Park,
KS), Gilkison; Kevin (Overland Park, KS), Nelson;
Larry (Kingsville, MO), Rhea; Burt (Overland Park,
KS), O'Dell; Jerry (Independence, MO), Krueger; Greg
(Trimble, MO), Roepke; Gary (Kansas City, MO), Knutson;
Gerhard W. (Edina, MN), Kennedy; Mary Ellen (Ashton,
CA) |
Assignee: |
Labconco Corporation (Kansas
City, MO)
|
Family
ID: |
24211328 |
Appl.
No.: |
10/800,357 |
Filed: |
March 15, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
09553923 |
Apr 20, 2000 |
06368206 |
Apr 9, 2002 |
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Current U.S.
Class: |
454/58; 312/209;
454/57 |
Current CPC
Class: |
B08B
15/023 (20130101); B08B 2215/003 (20130101) |
Current International
Class: |
B08B
15/02 (20060101) |
Field of
Search: |
;454/56,57,58
;312/209 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Wilson; Gregory A.
Attorney, Agent or Firm: Stinson Morrison Hecker LLP
Wharton; J. David
Claims
Having thus described the invention, what is claimed is:
1. A biological safety cabinet, comprising: a frame defining a
protected work area, said work area being enclosed on all but a
front face, said work area including a pair of spaced interior side
walls; a sash coupled to said frame, said sash at least partially
enclosing the open front face of said work area; a blower coupled
to said frame generally above said work area, said blower being
adapted to circulate air through said work area; and a sash grill
coupled to said frame generally below said sash, said sash grill
having a curved top surface, a plurality of first perforations
through said top surface, and a plurality of second perforations
through said top surface, said second perforations being
.Iadd.larger than said first perforations and being
.Iaddend.located generally adjacent each of said side walls, said
first and second perforations allowing air to flow through said
sash grill, wherein the curved sash grill promotes smooth air flow
into said work area, thereby better containing any harmful
materials.
2. The biological safety cabinet of claim 1, the safety cabinet
further comprising a pair of spaced side trim panels, one of said
trim panels being located adjacent each of said side walls of said
work area, said side trim panels forming an obtuse angle with
respect to said side walls thereby promoting smooth flow of room
air into said work area.
3. The biological safety cabinet of claim 1, wherein said sash has
a handle coupled thereto along the lower-most surface thereof, said
handle having a top surface adjacent said sash, a rear surface
facing said work area and a front surface extending between the top
and rear surfaces, said front surface of said handle being oriented
at an acute angle relative to said rear surface to allow air
entering said work area along said front surface to more smoothly
interface with the air traveling downwardly along said rear
surface.
4. The biological safety cabinet of claim 1, wherein said sash has
a handle coupled thereto along the lower-most surface thereof, said
handle having a top surface adjacent said sash, a rear surface
facing said work area and a front angled surface extending between
the top and rear surfaces, said angled front surface allowing air
entering said work area along said front surface to more smoothly
interface with the air traveling downwardly along said rear
surface.
5. A biological safety cabinet, comprising: a frame, said frame
having outer walls and inner walls, said inner walls being spaced
from said outer walls, said inner walls defining a protected work
area, said work area being enclosed on all but a front face; a sash
coupled to said frame, said sash at least partially enclosing the
front face of said work area; a blower coupled to said frame
generally above said work area, said blower being adapted to
circulate air through said work area; and a pressure gauge mounted
on one of said inner walls and located within said work area, said
pressure gauge adapted to measure a positive pressure environment
created by said blower above said work area, wherein any leaks in
said pressure gauge will be contained within said work area.
6. The biological safety cabinet of claim 5, further comprising a
supply filter forming a ceiling for said work area; said blower
directing air through said supply filter, said supply filter being
adapted to remove contaminants from the air flowing therethrough,
and a plenum box located between said supply filter and said
blower, said pressure gauge being adapted to measure the pressure
within said plenum box.
7. The biological safety cabinet of claim 6, wherein one of said
inner walls is a rear baffle plate defining the rear wall of said
work area and wherein said pressure gauge is mounted in said baffle
plate.
8. The biological safety cabinet of claim 7, wherein said sash is
transparent, and wherein said pressure gauge is mounted at a
location viewable through said sash.
9. A biological safety cabinet, comprising: a frame defining a
protected work area enclosed on all but a front face, said work
area including a rear baffle, opposing side walls, a ceiling and a
bottom surface, said baffle being spaced above said bottom surface;
a sash coupled to said frame, said sash at least partially
enclosing the front face of said work area; a blower coupled to
said frame above said ceiling of said work area, said blower being
adapted to circulate air through said work area; a rear panel
located behind said baffle of said work area, said rear panel
spaced from said baffle to create a void through which air can
flow; and a perforated towel catch extending between a lower-most
edge of said baffle and said rear panel, said towel catch being
closer to said bottom surface at said rear panel than at said
baffle, wherein said towel catch may be visually inspected for
blockage through said open front face of the safety cabinet.
10. The biological safety cabinet of claim 9, further comprising a
removable work surface spaced above said bottom surface, said work
surface concealing said towel catch from view when in place within
said work area.
11. The biological safety cabinet of claim 10, wherein said towel
catch is oriented at an acute angle with respect to said bottom
surface.
12. The biological safety cabinet of claim 11, wherein said towel
catch is removably coupled to said baffle.
13. The biological safety cabinet of claim 12, further comprising a
pressure gauge coupled to said baffle, said pressure gauge adapted
to measure a positive pressure environment created by said blower
above said work area, wherein any leaks in said pressure gauge will
be contained within said work area.
14. The biological safety cabinet of claim 10, further comprising a
sash grill coupled to said frame generally below said sash, said
sash grill having a curved top surface, wherein the curved sash
grill promotes smooth air flow into said work area and containment
of harmful materials.
15. A biological safety cabinet, comprising: a frame defining a
protected work area, said work area being enclosed on all but a
front face; a sash coupled to said frame, said sash at least
partially enclosing the front face of said work area, said sash
being moveable to allow access to said work area; a blower coupled
to said frame above said work area, said blower being adapted to
circulate air through said work area; a sash pocket coupled to the
exterior of said frame generally above said work area and above
said sash, said sash pocket being enclosed on all but a lower end
thereof, said sash extending into said lower end of said sash
pocket; a front panel coupled to said frame above said work area
and in front of said blower, said sash pocket being coupled to said
front panel, said sash being spaced outwardly away from said front
panel, and wherein said front panel includes a plurality of holes
extending therethrough above said work area, said holes providing
fluid communication between the exterior of the safety cabinet and
the interior thereof, wherein said sash pocket provides a
protective housing for said sash when said sash is moved upwardly
away from said work area.
16. The biological safety cabinet of claim 15, wherein said sash is
spaced away from said work area, allowing fluid communication
between said work area and the exterior of the safety cabinet, the
cabinet further comprising a deflector plate coupled to said frame
at the upper end of said work area, said deflector plate extending
towards said sash and being spaced away therefrom, said deflector
plate operating to maintain a uniform negative pressure in the area
of said holes thereby insuring a uniform flow of air into said
holes.
17. The biological safety cabinet of claim 16, further comprising a
front cover coupled to said frame, said cover extending over said
sash pocket and said front panel to remove said sash pocket and
said front panel from view.
18. A biological safety cabinet, comprising: a frame defining a
protected work area enclosed on all but a front face, said work
area having a back wall, opposing side walls, a ceiling and a
bottom surface; a blower coupled to said frame above said ceiling
of said work area, said blower being adapted to circulate air
through said work area; a supply filter forming said ceiling of
said work area, said blower directing air through said supply
filter, said supply filter being adapted to remove contaminants
from the air flowing there through; a plenum box located between
said supply filter and said blower; and a distribution baffle
located within said plenum box and extending generally across said
plenum box, said distribution baffle being mounted with a first end
located adjacent an output region of said blower and being angled
upwardly as said baffle extends away from said blower, wherein said
distribution baffle operates to evenly distribute the air flowing
from said blower across said supply filter.
19. The biological safety cabinet of claim 18, further comprising a
pair of curved deflector plates mounted within said plenum box, one
of said deflector plates being mounted on each side of said box and
oriented to direct air flowing within said box downwardly.
20. The biological safety cabinet of claim 18, further comprising
an exhaust filter coupled to said frame above said plenum box, said
exhaust filter being in fluid communication with the exterior of
the cabinet and with the plenum box, said exhaust filter being
adapted to remove contaminants from the air passing there through
prior to being exhausted.
21. The biological safety cabinet of claim 20, further comprising
an exhaust filter frame coupled to said frame and adapted to hold
said exhaust filter, said exhaust filter frame having a sealing
mechanism coupled thereto and coupled to said plenum box, said
sealing mechanism including a threaded member mounted between said
filter frame and said plenum box, said member being adapted to turn
to move said frame upward and place an upward force on said exhaust
filter while placing a downward force on said plenum box and said
supply filter.
22. An exhaust control cap for a biological safety cabinet having
an exhaust port, said control cap comprising: an enclosure for said
exhaust port, said enclosure having sides projecting above the top
of said cabinet; at least one side panel presenting a plurality of
apertures therein; a top panel extending over said sides and
covering the top of said enclosure; and a plurality of plugs shaped
to extend over a selected aperture, wherein said plugs may be
placed over selected apertures to control the flow of air through
the control cap, wherein air exhausted from said cabinet is
directed outwardly through said apertures not covered with said
plugs.
23. The exhaust control cap of claim 22, wherein said enclosure is
generally rectangular and has four of said side panels, each having
apertures therein.
24. The exhaust control cap of claim 23, wherein the apertures
within the side panels are round and are varied in diameter.
25. An exhaust control cap for a biological safety cabinet having
an exhaust port and an associated exhaust control system, said
control cap comprising: an enclosure for said exhaust port, said
enclosure having sides projecting above the top of said cabinet,
said enclosure being coupled with said exhaust control system; an
apertured plate coupled with said enclosure and intersecting the
flow of air; and a plurality of plugs shaped to extend over a
selected aperture within said apertured plate, wherein said plugs
may be placed over selected apertures to control the flow of air
through the control cap, wherein said apertured plate controls the
flow of air exhausted from the cabinet and into said exhaust
control system.
26. The exhaust control cap of claim 25, wherein the apertures
within said apertured plate are round and are varied in diameter.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to biological safety
cabinets.
Biological safety cabinets are laboratory containment devices
equipped with High Energy Particulate Air (HEPA) filters. These
cabinets are used in microbiological laboratories and provide a
work area with safe environment in which a variety of experiments
and studies can be performed. Rather than providing only a hood
above a working surface, these cabinets provide a more protective
working environment. The safety cabinet has a frame that surrounds
the work area on all but one side. The remaining open side is
enclosed by a moveable sash. The sash may be moved upwardly to
provide access to the work area, so that work can be performed. The
sash may be moved downwardly to partially or completely close the
work area. A blower unit is provided in the cabinet above the work
area. The blower is used to circulate air downwardly through the
safety cabinet. A portion of this downward air flow forms an air
curtain at the front of the cabinet work area and passes beneath
the floor of the work area and a portion is directed to the back of
the cabinet where it is drawn upwardly through a plenum chamber.
This air may be contaminated by materials being used within the
working environment. Therefore, prior to being exhausted into the
room or a fume system, the air is first passed through a HEPA
exhaust filter.
The blower is operated so there is sufficient air flow through the
work area to insure that any harmful materials are contained and
eventually passed to a filter area rather than escaping into the
room or exhausted into the atmosphere. To this end some air is
drawn into the safety cabinet about the open perimeter formed when
the sash is in an open or partially open position.
The prior art safety cabinets are typically provided with a sash
grill located below the bottom of the sash. This sash grill forms
the lower-most surface of the opening into the work area.
Typically, the sash grill is provided with a number of
perforations, through which air can flow. Air flows downwardly from
the blower along the back of the sash and into these perforations.
Air is also drawn inwardly from the exterior of the cabinet along
the surface of the sash grill and into the perforations. The air
flowing through the sash grill flows under the work surface and
upwardly through the plenum at the back of the cabinet to be
recirculated or exhausted.
Safety cabinets have heretofore utilized a sash grill having a
generally flat surface which gives rise to a number of
disadvantages. The flat surface may be used by those operating the
safety cabinet as a surface on which to place a variety of labware.
This is undesirable because objects located on the sash grill
present a source of possible contamination of the room, and may be
inadvertently broken if bumped or knocked onto the floor. Moreover,
by placing an object on the sash grill, a portion of the
perforations therein may be blocked, which can adversely affect the
air flow of the safety cabinet. The flat surface of the sash grill
also results in a large portion of the perforations therein
becoming blocked by a user's arm as the user performs work within
the safety cabinet. As the user's arm blocks the perforations in
this fashion, it is difficult to properly maintain the negative
pressure environment about the user's arm, thereby risking possible
contamination. The flat sash grills of the prior art also present a
right angle with the work surface which projects far enough above
the work surface that labware is sometimes broken when it bumps
against the projecting vertical face. It is thus desirable to
provide a sash grill which does not provide a flat surface and does
not present a right angle corner at the entrance to the work area
opening.
Another drawback of prior art sash grills is attributable to the
fact that the grills are formed with a front face that is at a
right angle to the flat top of the grill. This orthogonal
relationship results in an air flow that is less than desirable.
When air is drawn inwardly and through the perforations in the sash
foil, it may cause a turbulence in the air flowing downwardly along
the back of the sash and through the working environment. This
turbulence is increased by the right angle relationship, as the air
encountering the front face of the grill will be partially directed
upwardly over the front face before being drawn through the
perforations in the flat top of the grill. Therefore, a biological
safety cabinet is needed with a sash grill that improves the air
flow and safety of the cabinet.
Similarly, air may be drawn into the opening of the safety cabinet
along the sides of the cabinet adjacent the opening when the sash
is in an open or partially open position. In prior art safety
cabinets, the front sides of the cabinet are oriented at right
angles relative to the interior side walls. When air is drawn into
the cabinet along these sides, it will initially be directed away
from the interior surface of the interior walls. However, it is
much more desirable to cleanly "sweep" the interior walls of the
cabinet, to ensure the best possible containment of any harmful
materials. A biological safety cabinet having a construction that
draws air inwardly to cleanly sweep the interior side walls is
needed.
After the safety cabinets have been used for a certain period of
time, they must be decontaminated. One method for performing this
decontamination involves sealing the front of the safety cabinet
with a plastic sheet. When the prior art safety cabinets are being
decontaminated, it is often necessary to first remove the sash to
insure proper decontamination. This is attributable to the location
of the sash within a U-shaped channel where contaminants may
accumulate. This procedure is time consuming and risks damage to
the sash. If the sash is dropped it may shatter, and contaminate an
entire room. Thus, a biological safety cabinet which can be
decontaminated without removal of the sash is needed.
Another drawback of prior art safety cabinets involves the lower
edge or handle of the moveable sash. When the sash is in an open or
partially open position, two bodies of air are coming together
adjacent the handle of the sash. One body of air is flowing from
the exterior of the cabinet into the interior thereof. The second
body of air is flowing downwardly from the blower unit of the
safety cabinet along the back of the sash. In prior art cabinets,
the sash handle has transitioned from the front face to the bottom
face at a right angle. This results in the inwardly flowing air
meeting the downwardly flowing air at a right angle, causing
turbulence. As noted above, turbulent air flow adjacent the opening
of the cabinet is undesirable. A sash handle that reduces
turbulence would represent an improvement over the prior art.
As stated above, the biological safety cabinet is operated with the
benefit of a blower which provides an air flow so that harmful
materials are contained within the cabinet. The cabinets are
constructed with the blower above the working environment, and the
working environment is subject to a continual flow of air to
contain contaminants and then move them to a filter area. Above the
working environment and beneath the blower, is a supply filter and
a positive pressure plenum. The pressure plenum receives air from
the blower and directs it through the supply filter.
To monitor the pressure within the cabinet, prior art safety units
have used a pressure gauge mounted on the exterior of the cabinet,
with the pressure being monitored in the positive pressure
environment of the pressure plenum immediately below the blower.
Monitoring the positive pressure allows a more meaningful pressure
reading to be obtained and used by the laboratory personnel.
However, the air within the pressure plenum immediately below the
blower has not yet been filtered. As such, the air may contain
harmful materials from the working environment below. If the gauge
on the exterior of the cabinet were to leak, contaminated air would
be allowed into the room. In some instances this concern has been
addressed by placing a HEPA filter in the pressure line to the
readout gauge. This of course results in additional expense both
initially and for ongoing maintenance. Another method of addressing
the potential problem of contamination through the pressure gauge
has been to monitor the air pressure in a negative pressure
environment (relative to the atmosphere surrounding the cabinet)
thus eliminating the possibility of contamination as a result of
leakage through the gauge into the room. Monitoring and displaying
a negative pressure, however, is more difficult to translate into
meaningful and usable numbers by laboratory personnel. A monitoring
apparatus is therefore needed which does not require any additional
filters and allows the monitoring and display of a positive
pressure, while eliminating the risk of possible contamination of
the room environment.
It has been found that it is desirable to equip the safety cabinet
with a "towel catch" to catch or filter out large objects from the
returning air flow prior to being recirculated through the blower.
This towel catch removes such things as paper towels and small
laboratory items from the returning air stream. Prior art safety
cabinets have located this towel catch in the plenum formed by the
rear wall of the work area and the rear wall of the safety cabinet.
While this location is effective in removal of the desired items,
it is impossible to visually inspect without taking the cabinet
apart. One method typically utilized for inspecting these prior art
towel catchers is to reach up within the plenum and feel the towel
catch to determine if any paper towels or other objects are lodged
within or against the towel catcher. This method can be
uncomfortable and dangerous to the extent that pieces of broken
laboratory glass and other sharp objects may be lodged within the
towel catch. The towel catch itself is normally formed from metal
with sharp edges which presents a safety hazard in and of itself if
it is placed in a traditional location where it is not visible to a
worker cleaning it. Therefore, a towel catch that is readily
accessible and can be visually inspected is needed.
Another drawback of prior art safety cabinets involves the
construction of the sash. The sash of the safety cabinet is
moveable upwardly and downwardly, to allow better access to the
working environment when needed and to more fully enclose the
working environment when access is no longer needed. In prior art
safety cabinets, the rear of the sash is provided with a seal to
prevent any contaminated air from escaping the working environment.
The seal wipes the back of the sash as the sash is raised. This
arrangement is disadvantageous in that the wiping action may create
an aerosol containing contaminants from the rear of the sash. While
in other prior art constructions holes communicating with the
exhaust system have been utilized in place of seals, such
constructions have not been particularly effective, largely because
there has been no means for insuring a uniform negative pressure
across the exhaust holes. Thus, an arrangement is needed for a
biological safety cabinet that eliminates the need for a wiping
seal at the rear of the sash and instead provides for a uniform
negative pressure which will insure removal of any contaminated air
from the back side of the sash.
Yet another drawback of existing prior art safety cabinets involves
the design of the positive pressure plenum box. This box is located
in the area below the blower and above the work area. More
specifically, in prior art cabinets, air leaving the blower is
directed to a perforated plate and then through a supply filter
prior to be recirculated downwardly through the work area. The
perforated plate is used to more evenly distribute the air flow
over and through the supply filter. The perforated plate creates an
undesirable increased load on the blower and can interfere with the
function of the supply filter. Moreover, this prior art
construction does not distribute air across the supply filter as
evenly as desired. Therefore, a structure is needed that both
evenly distributes the flow over and across the supply filter while
not overly increasing the load on the blower or interfering with
the function of the supply filter.
Prior art safety cabinets are typically equipped with exhaust
control systems. As contaminated air passes through the blower of
the safety cabinet, some of the air is recirculated through the
supply filter as described above and some of the air is routed
through an exhaust filter. This exhaust air is either discharged
into the room, or it passed to an exhaust system associated with
the safety cabinet which moves the air out of the building. In
cabinets routing the exhaust air directly back into the room, the
prior art cabinets have merely routed the air directly upwardly.
Prior art units routing the air into a building exhaust system
direct typically employ duct work coupling the safety cabinet
exhaust to the building exhaust system. Both prior art embodiments
require a certain amount of additional space above the ceiling of
the safety cabinet to allow for the exhaust control systems. This
need for space can place limitations on the rooms in which the
safety cabinets can be used.
In addition to routing the exhaust air, the exhaust control systems
of the safety cabinets are used to balance the air flow through the
safety cabinet. Prior art exhaust control systems use a guillotine
damper to allow more or less air to be exhausted, as needed to
balance the air flow through the safety cabinet and achieve the
proper pressure within the cabinet. This damper places some
additional load on the blower by restricting air flow to the
filter. Furthermore, a damper is not aerodynamically efficient and
interferes with the uniform flow of air. Such dampers are normally
not readily accessible for making adjustments. The use of such a
damper also tends to cause air to flow unevenly through the filter
thus not effectively using the entire filter surface area.
Therefore, a more efficient exhaust control system is needed for a
biological safety cabinet that reduces undesired blower loading,
makes better utilization of available filter surface area and is
readily accessible.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide a biological
safety cabinet having a novel sash grill that more effectively
prevents contaminated air from leaving the cabinet, and more
effectively draws air into the cabinet.
It is another object of this invention to provide a sash grill for
a biological safety cabinet that prevents objects from being placed
thereon.
It is a further object of the invention to provide a biological
safety cabinet having exterior front side panels that allow
incoming air to more effectively sweep the sides of the cabinet and
that allow the cabinet to more easily be decontaminated.
It is yet another object of the invention to provide a handle for
the sash of a biological safety cabinet that allows air to more
effectively flow thereover.
It is still another object of the present invention to provide a
biological safety cabinet in which the pressure gauge measures a
positive pressure environment while being contained within the
safety cabinet so that any risk of contamination through the gauge
is reduced while also eliminating the need for a separate HEPA
filter for the gauge.
Another object of the present invention is to provide a towel catch
for a biological safety cabinet that is visible to the user thereof
and that can be easily removed without disassembling the safety
cabinet.
Yet another object of the present invention is to provide a
biological safety cabinet that eliminates the need to wipe the back
of the sash with a seal so that still another risk of contamination
is reduced.
It is another object of the present invention to provide a
biological safety cabinet with a plenum box that evenly distributes
the air flow across a supply filter without increasing the load on
the blower of the cabinet.
A still further object of the present invention is to provide a
biological safety cabinet with a low profile, externally adjustable
exhaust control that does not require decontamination before
adjusting and provides for more uniform distribution of air across
the exhaust filter.
It is yet another object of the present invention to provide a
plenum chamber seal and tensioning device for the exhaust filter of
a biological safety cabinet that allows the supply filter and
exhaust filter to be simultaneously sealed.
According to the present invention, the foregoing and other objects
are attained by a biological safety cabinet that includes a frame
that defines a protected working environment and encloses the
working environment on all but one side. A sash is coupled to the
frame that at least partially encloses the side that is not
enclosed by the frame. A blower is coupled to the frame generally
above the working environment. The blower is adapted to circulate
air through the working area so that harmful materials are
confined. A sash grill is coupled to the frame generally below the
sash and has a curved top surface. The curved sash grill provides a
superior and less turbulent air-flow into the working environment,
thereby better containing any harmful materials. The curved sash
grill is perforated, and the curvature and perforations of the sash
grill compensate for partial blockage by the user's arms and other
objects. The curvature of the sash grill also presents a surface on
which objects cannot be easily placed, thereby avoiding a safety
hazard. The curved grill also eliminates a protruding right angle
corner at the cabinet opening which has been known to cause
breakage of labware being placed inside the cabinet.
Additional objects, advantages, and novel features of the invention
will be set forth in part in the description which follows, and in
part will be apparent to those skilled in the art upon examination
of the following, or may be learned from practice of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings which form a part of this
specification and which are to be read in conjunction therewith and
in which like reference numerals are used to indicate like parts in
the various views:
FIG. 1 is a perspective view of the biological safety cabinet of
the present invention, with parts being broken away to show
particular details of construction;
FIG. 2 is a front elevation view of the safety cabinet of FIG. 1,
with parts being broken away to show particular details of
construction;
FIG. 3 is a side cross sectional view taken along line 3-3 of FIG.
2;
FIG. 4 is a partial cross sectional view taken along line 4-4 of
FIG. 3;
FIG. 5 is an enlarged view of the encircling line 5 of FIG. 2,
showing the sealing arrangement between the supply filter and the
exhaust filter;
FIG. 6 is an enlarged view of the encircling line 6 of FIG. 1;
FIG. 7 is a partial sectional view taken along line 7-7 of FIG. 3
showing a partial top plan view of the sash grill used in the
safety cabinet of FIG. 1;
FIG. 8 is a partial sectional view taken along line 8-8 of FIG. 3,
showing an elevation view of the towel catch used in the safety
cabinet of FIG. 1;
FIG. 9 is perspective view of an alternate embodiment of the
exhaust body used in the safety cabinet of FIG. 1; and
FIG. 10 is an enlarged view of the encircling line 10 of FIG.
3.
DETAILED DESCRIPTION OF THE INVENTION
Referring initially to FIG. 1, a biological safety cabinet
according to the present invention is broadly designated in the
drawings by the reference numeral 10. A broad overview of the
construction of cabinet 10 is set forth below, followed by a more
detailed description of certain features of the cabinet. Broadly,
cabinet 10 has a bottom panel 14 and a pair of upwardly extending
opposing side panels 16 which are rigidly coupled to bottom panel
14, such as by welding. Extending upwardly from the bottom panel 14
and rigidly coupled between side panels 16 is a rear panel 18, as
best seen in FIG. 3. Rear panel 18 extends upwardly from bottom
panel 14 as do side panels 16. Bottom panel 14, side panels 16 and
rear panel 18 form apartial frame in which the other components of
cabinet 10 are held. A baffle 20 is coupled between side panels 16
and is spaced outwardly away from real panel 18. The bottom of
baffle 20 is spaced upwardly away from bottom panel 14. Panels 14,
16 and 18, as well as baffle 20 are preferably made from metal,
such as stainless steel.
As best seen in FIG. 3, a work surface 22 is suspended above bottom
panel 14. Work surface 22 is used to hold the objects necessary to
perform experiments within cabinet 10, such as beakers, flasks and
other conventional labware. Extending generally along the front of
cabinet 10 between side panels 16, and extending from work surface
22 to bottom panel 14, is a sash grill 24, the importance of which
is further described below.
As best seen in FIGS. 2-4, a blower assembly 26 is located in the
upper part of cabinet 10. Assembly 26 includes a blower 28, an
exhaust filter 30, a supply filter 32 and a plenum box 33 which is
in communication with the blower outlet. A top panel 34 presents
the enclosed top of the cabinet. Panel 34 extends from rear panel
18 to the front of the cabinet and between side panels 16. An
exhaust control cap 36 is coupled to top panel 34 directly above
exhaust filter 30. Top panel 34 also has coupled thereto an
electronics housing 38. Housing 38 houses and protects the
electronics necessary to operate cabinet 10. As best seen in FIGS.
1 and 3, a cover panel 40 that is coupled to top panel 34 and
extends between side panels 16. Panel 40 extends only partially
down cabinet 10 from top panel 34. A movable sash 42 is mounted
between side panels 16 in a manner allowing it to be moved upwardly
and downwardly. Work surface 22, baffle 20, side panels 16 and an
air diffuser plate 43 below supply filter 32 form a protective work
area 44 within which work can be performed.
In use, blower 28 of cabinet 10 is operated to provide an air-flow
through the cabinet, and particularly through work area 44. Prior
to the air entering the work area 44, it is first passed through
supply filter 32 to remove any contaminants. Cabinet 10 may be
operated with sash 42 located a specified distance away from sash
grill 24, as is shown in FIG. 3. To ensure that contaminants do not
escape through the opening between sash 42 and grill 24, blower 28
will direct air downwardly along the rear of sash 42 and into the
perforations of grill 24 from above the work area to provide a
protective curtain of air that facilitates containment within work
area 44. A portion of the air from blower 28 also moves toward the
rear of the surface 22 as will be explained hereinafter. The action
of blower 28 provides a certain amount of suction, causing an air
flow inwardly along the opening defined by the bottom of sash 42,
side panels 16 and sash grill 24. Air which is drawn through this
opening also passes through the perforations in sash grill 24. The
air, once drawn through sash grill 24, will travel beneath work
surface 22 and through the plenum defined by baffle 20 and real
panel 18 as it is drawn upwardly by blower 28. The air moving from
the blower to the rear of surface 22 will also be drawn into this
same plenum.
Air that has passed through working environment 44 is likely to
contain contaminants and thus, before being recirculated or
exhausted to the room, is first passed through a HEPA filter. Prior
to being recirculated into working environment 44 the air passes
through supply filter 32. Similarly, prior to being exhausted to
the room, the air is passed through exhaust filter 30. Filters 30
and 32 are both High Efficiency Particulate Air (HEPA) filters of a
type well known to those skilled in the art. Thus, cabinet 10 is
used to perform experiments within work area 44 and to contain any
contaminated air within the cabinet. Particular and novel details
of construction are more fully set out below.
As best seen in FIG. 3, work surface 22 is positioned above bottom
panel 14 by a number of supports 46 that are preferably screwed
directly into bottom panel 14 (additional support is provided by a
rear lip to be described hereinafter). Supports 46 are thus easily
removable and can be decontaminated and cleaned after removal from
bottom panel 14 as needed. Work surface 22 rests directly upon
supports 46 and is thus spaced from bottom panel 14. The spacing
between bottom panel 14 and work surface 22 allows air to circulate
beneath work surface 22. Surface 22 can be made from a material
such as stainless steel and is placed on supports 46 so that the
rear edge thereof rests on a lip at the bottom of baffle 20. Work
surface 22 may be held in place through the use of removable
fasteners which require no tools. Work surface 22 is thus mounted
within safety cabinet 10 in a manner allowing the easy removal
thereof, such as may be needed for decontamination and cleaning of
the safety cabinet.
Sash grill 24 extends between the front of work surface 22 and
bottom panel 14 from one side panel 16 to the other. As best seen
in FIGS. 6 and 7, grill 24 has a plurality of main perforations in
48 therein. Perforations 48 allow air to flow through sash grill 24
as air passes downwardly along the rear of sash 42 and inwardly as
air enters the safety cabinet adjacent the surface of sash grill
24. Preferably, perforations 48 extend generally from one side of
sash grill 24 to the other. However, as best seen in FIGS. 6 and 7,
a series of enlarged side holes 50 are provided along each side of
grill 24. Enlarged holes 50 provide additional air flow adjacent
side panels 16 and operate to better contain the air within working
environment 44. Further, grill 24 is provided with a front row of
scavenger holes 52. Scavenger holes 52 operate to provide an
additional source of protection should the main perforations 48
become blocked along the length of sash grill 24.
As best seen in FIGS. 3 and 6, sash grill 24 has a curved surface.
This curved surface provides a number of advantages. First, it
prevents objects from being placed on the sash grill and blocking
any of the perforations within sash grill 24. This not only
prevents blockage of the perforations, but also eliminates any
possibility of objects being placed on the grill and then knocked
off and broken. The curved shape of the grill also eliminates a
sharp edge at the same level as that of the work surface which
greatly reduces the possibility of accidental contact when labware
is being moved in and out of the work area. Contact at this point
has been a source of breakage of glass labware in the past.
Further, the curvature provided also prevents all of the main
perforations 48 in a particular area from being blocked by a
relatively linear object, such as a person's arm. Safety standards
require a certain minimal opening for the sash while a user is
performing a task in the work area with the sash raised. This means
that there must be a certain minimal distance between the bottom of
the sash and the top of the sash grill. With the curved grill of
the present invention, since the height of the grill relative to
the floor is lower than it would be if the grill was flat, the
minimal distance between the bottom of the sash and the grill can
be met with the sash lower relative to the floor than with prior
flat grills. This results in the sash handle, which interferes with
the view of the worker, being in a lower position and improves the
worker's available viewing area. It also improves work safety by
increasing the distance between the opening and the worker's face.
The curved surface of grill 24 also operates to allow the air
flowing downwardly along the back of sash 42, and the air flowing
inwardly from the opening in cabinet 10, to more effectively sweep
across the grill surface and enter the work area. In prior art
systems, the air flowing inwardly is confronted with a front face
that is located at a right angle to the flat horizontal surface of
the sash foil. This air is then forced in an upward arc away from
the surface of the sash grill prior to entering any perforations
therein. With the novel curved sash grill of the present invention,
the downwardly moving air is not confronted with a surface at a
sharp (right) angle to the direction of air flow, which allows it
to more effectively enter through the perforations within the sash
grill with less turbulence. The curved surface of grill 24 also
promotes smooth flow of air across the grill into the work area
from outside the cabinet. Less turbulence is experienced then with
prior art designs where the grill presents a right angle relative
to the work surface.
Turning to the rear of cabinet 10, baffle 20 is mounted between
side panels 16 and can be secured in place such as by bolting or
welding. The lower-most edge of baffle 20 may be provided with a
support lip 58 as best seen in FIG. 3. Lip 58 is used to support
work surface 22 and may be provided with a number of threaded holes
to secure work surface 22 to baffle 20. Located above the lower
most surface of baffle 20 and extending from one side of baffle 20
to the other, are a number of slots 60, as best seen in FIG. 8.
Slots 60 are provided to allow air flowing downwardly from blower
28 to pass there through and into the plenum formed by baffle 20
and rear panel 18.
As best seen in FIG. 3, a pressure gauge 62 is mounted within
baffle 20 above slots 60. Gauge 62 can be viewed by the user of
safety cabinet 10 through sash 42, which is made from a clear
material such as tempered glass. Gauge 62 is used to measure a
positive pressure within a plenum box 64 that is located
immediately below blower 28. Measuring the positive pressure within
plenum box 64 allows the user of cabinet 10 to obtain a more
accurate indication of the load on filters 30 and 32. To measure
the pressure within plenum box 64, a hose barb 66 is placed through
the rear plate of plenum box 64. A piece of tubing 68 is mounted to
hose barb 66 and extends downwardly through the rear plenum and is
connected to a plastic Y-hose barb 70. Another piece of tubing 72
extends from the lower end of barb 70 downwardly and into the space
between bottom panel 14 and work surface 22. Finally, the remaining
end of hose barb 70 is connected to a third piece of tubing 74
which is coupled to the high pressure port of gauge 62. Gauge 62
thus is mounted entirely within safety cabinet 10 and is adapted to
measure the positive pressure within plenum box 64. Should any
leakage occur within gauge 62, any contaminants within tubing 68,
72 or 74 would be contained within cabinet 10 and would be filtered
prior to being exhausted into the room.
As best seen in FIGS. 3 and 8, cabinet, 10 is also provided with a
perforated towel catch 78. More specifically, a towel catch 78
extends from lip 58 at the bottom of baffle 20 downwardly to bottom
panel 14. Preferably, catch 78 is angled rearwardly as shown in
FIG. 3, and is mounted to baffle 20 with the same screws that are
used to attach work surface 22 to baffle 20. This mounting allows
towel catch 78 to easily be removed, such as may be necessary to
clean towel catch 78 or bottom panel 14 in the event of a spill. As
best seen in FIG. 8, catch 78 has a number of rectangular slots 80
which allow air to pass through catch 78 and upwardly behind baffle
20. Moreover, the lower tubing 72 associated with pressure gauge 62
may be passed through one of the slots 80. Catch 78 is used to
prevent objects such as broken pieces of glass and paper towels
from traveling upwardly through the rear plenum and into blower 28.
In use, work surface 22 may be pulled away from baffle 20 which
allows towel catch 78 to be visually inspected for any blockage. If
an object is lodged against towel catch 78, it may be easily
removed by the user of safety cabinet 10. Moreover, the visual
inspection allows the user of safety cabinet 10 to avoid contact
with the catch which might result in injury and to be forewarned if
a sharp of dangerous object is lodged against the catch. Prior art
safety cabinets have located the towel catch associated therewith
upwardly from the bottom of the safety cabinet. Generally, such a
prior art towel catch would be located somewhere above the rear
intake of the exhaust plenum 20. In such a location the towel catch
becomes a safety hazard in and of itself and can also result in
injury if sharp objects are restrained by it. Location of towel
catch 78 as described for the present invention allows the towel
catch 78 to be visually inspected and cleaned. Further, the towel
catch may be much more easily removed from safety cabinet 10 if
needed, such as when surface 22 is to be removed for cleaning
beneath it.
Turning to details of the plenum box 33 and associated filters, and
as best seen in FIGS. 3 and 4, the supply filter 32 is located
above work area 44 at the upper end of the baffle 20. Air diffuser
43 is located immediately below supply filter 32. Diffuser 43
operates to properly direct the air as it exits supply filter 32 to
obtain the desired air flow through work area 44. Immediately above
supply filter 32 is the plenum box 33. Box 33 directly abuts supply
filter 32 and is held against it as described below. As best seen
in FIG. 4, plenum box 33 extends from the exit of blower 28 and
provides a structure for evenly distributing the air flow to both
the supply and exhaust filters. More specifically, box 64 includes
a distribution baffle 88 that tapers upwardly from the exit of
blower 28 as it extends across the side of safety cabinet 10.
Preferably, baffle 88 extends from the front of plenum box 64 to
the back thereof. A portion of the output from blower 28 will pass
upwardly to exhaust filter 30 while a portion will be directed into
a narrow channel 90. The air leaving channel 90 is directed to a
first curved deflector 92, as shown on the left-hand side of FIG.
4. Deflector 92 operates to redirect the air downwardly and to the
right as viewed in FIG. 4. Deflector 92 is preferably made from a
rigid material such as steel and is rigidly mounted within plenum
box 33, such as by welding. As the air travels back to the right as
viewed in FIG. 4, distribution baffle 88 forces the air downwardly
and into a second narrow channel 94. The angle of baffle 88 is
selected to insure that the volume of air passing across supply
filter 32 is relatively constant across the entire width of the
filter. The angle will vary depending upon the output of the blower
and the size of filter 32. The air at the far right hand portion of
plenum box 64, as viewed in FIG. 4, is directed downwardly by a
second deflector 96. Thus, construction of plenum box 64, with
baffle 88 and deflectors 92 and 96, operates to evenly distribute
the air flow across and through supply filter 32. This is done
without restricting the air flow, such as with the use of a prior
art perforated plate. Therefore, the above construction of plenum
box 64 achieves a more uniform distribution of air across supply
filter 32 without placing an increased load on blower 28.
As best seen in FIG. 4, the upper end of plenum box 64 has an
exhaust channel 98 therein that communicates directly with exhaust
filter 30. Baffle 88 directs some of the air leaving blower 28
upwardly through exhaust channel 98 and exhaust filter 30
ultimately exiting cabinet 10 through exhaust control cap 36. As
best seen in FIG. 5, exhaust filter 30 is held in position with an
exhaust frame 100. Frame 100 includes a recessed portion 102 which
is shaped to conform to the outer perimeter of exhaust filter 30.
Portion 102 thus operates as a placement guide when filter 30 is to
be replaced. Frame 100 also includes an upper bracket 104 and a
lower leg 106, which extends downwardly into a labyrinth seal 108.
As shown in FIG. 5, seal 108 includes a pair of upwardly extending
plates 110 which are bolted to the top of plenum box 64. Leg 106
extends between the plates 110 and is movable there between.
To adjust the position of filter 30, the upper bracket 104 includes
a pair of threaded holes 112, through which are placed a plurality
of bolts 114. A retaining nut 116 is rigid with bracket 104 and in
alignment with each bolt 114. Each bolt 114 has a head 114a, a
threaded portion 114b and a length such that it extends to the
upper surface of plenum box 64, and as shown in FIG. 5, may extend
to the upper surface of a horizontal portion of plates 110 of the
labyrinth seal 108. Exhaust frame 100 cooperates with bolts 114,
the top of plenum box 64 and labyrinth seal 108 to simultaneously
position and seal exhaust filter 30 upwardly and supply filter 32
downwardly. More specifically, in use, both head 114a is turned
with a wrench to move portion 102 upwardly or downwardly along
threaded portion 114b. When portion 102 is lowered, lower leg 106
will move lower within labyrinth seal 108. Thereafter, the exhaust
filter 30 may be replaced by placing a new or clean exhaust filter
30 within recessed portion 102. Exhaust filter 30 is then raised
into place by turning bolt 114 in the opposite direction. Bolt 114
may be rotated sufficiently to place a downward force on plenum box
64. This downward force on plenum box 64 forces exhaust filter 30
into a sealing engagement with top panel 34. Thus, bolt 114 in
cooperation with portion 102 and nut 116 serves as a jack screw to
raise and lower the filter housing and apply pressure in opposite
vertical directions to hold the filter firmly in place.
Any air that is not recirculated through supply filter 32 and work
area 44 must be filtered and exhausted from the cabinets. If air is
to be exhausted into the room, exhaust control cap 36 is used. As
best seen in FIGS. 1 through 3, exhaust control cap 36 is mounted
on top of top panel 34 and directly above exhaust filter 30.
Control cap 36 is generally rectangularly shaped and has a pair of
mounting flanges 122 extending from each side thereof. Flanges 122
are used to mount control cap 36 to top panel 34. Control cap 36
has a solid top 124 and sides 126 which have a plurality of exhaust
apertures 128 extending there through. Apertures 128 are preferably
varied in diameter and operate to accommodate outward flow of
exhaust air in a lateral as opposed to a vertical direction. As can
be seen, control cap 36 thus provides a low profile mechanism for
directing the exhaust air from safety cabinet 10 in a horizontal
direction. As seen in FIG. 2, removable plugs 130 may be used to
block the apertures 128. The number and size of the blocked
apertures, in combination with the blower output, determines the
volume of air that is exhausted through the control cap. The
control cap 36 can therefore be used to regulate the flow of air
being exhausted from safety cabinet 10. This regulation is done
while evenly distributing the flow of exhaust air over the entire
surface exhaust filter 30 and without placing an increased load on
blower 28 by significantly restricting the passage of air.
The above described embodiment of control cap 36 is utilized when
the exhaust air from safety cabinet 10 is exhausted directly into
the room. In an alternative embodiment, the air is not exhausted
directly into the room, but rather is directed into an exhaust
system that removes the air from the building. In this embodiment,
a different exhaust control cap 131 used, and is shown in FIG. 9.
As shown, control cap 131 has mounting flanges 132 that secured to
top panel 34. In this embodiment, rather than the side surfaces 133
being provided with apertures 128, the side surfaces 133 are solid.
In this embodiment however, a top surface 134 is provided with an
exhaust duct 135. Preferably, duct 135 is cylindrical. Duct 135 may
be provided with a damper 136 as is known to those of skill in the
art. An apertured plate 138 mounted below duct 135 and above the
exhaust filter 30 provides a mechanism for controlling the flow of
air through the exhaust filter in much the same manner as control
cap 36 described above. As shown in FIG. 9, the apertures 140
within plate 138 can be varied in size. Further, selected apertures
140 may be plugged to regulate the volume of air passing through
plate 138. Plate 138 is preferably attached to control cap 131 with
screws 142. Control cap 131 preferably includes an access port 144
along one side thereof, which is covered with a plate 146 in normal
use. Plate 146 may be bolted or screwed to control cap 131. Port
144 is used to visually inspect plate 138 and obtain access thereto
without removing plate 138. In use, the desired number of apertures
140 are plugged within plate 138 to regulate the amount of air
flowing through cap 131. Plate 138 is then secured within control
cap 131. Thereafter, the exhaust system associated with safety
cabinet 10 is coupled to duct 135 so that air passing through
exhaust filter 30 would be directed through control cap 131 and
into the exhaust system. In the case of both cap 36 and plate 138
the fact that the mechanical device for controlling air flow is
located on the "clean" side (i.e the downstream side) of the
exhaust filter means that it can be accessed for adjustment or
service without danger of contamination to either the worker or the
room environment.
The front of cabinet 10 also has a novel construction. As best seen
in FIG. 3, front panel 40 is coupled to top panel 34 and extends
between side panels 16 to enclose the area above supply filter 32.
Front panel may be held in place with any suitable attachment
mechanism, such as by bolting. Sash 42 is held within cabinet 10
and travels along a pair of sash tracks 150, as best seen in FIG.
7. Tracks 150 are defined by a pair of front trim panels 152. As
best seen in FIGS. 2 and 7, trim panels 152 have a wide and angled
front face 154. Face 154 thus forms an acute angle with its
associated side panel 16. The angle of face 154 directs air
downwardly toward the sash opening and then inwardly to the
interior side surfaces of work area 44. The angle of face 154 thus
allows the air entering work area 44 to sweep the interior side
surfaces of the work area as it passes over grill 24.
As best seen in FIG. 3, the lower-most edge of sash 42 is provided
with a handle 156. Handle 156 is used to raise and lower sash 42 as
may be needed to gain access to work area 44. As seen in FIG. 3,
handle 156 is equipped with a curved or angled lower surface 158.
While surface 158 is shown as being flat, but angled, it should
also be understood that surface 158 could be curved in a concave
shape. In use, surface 158 provides for a smooth interface of two
bodies of air. The first body of air is that which is entering the
cabinet from the outside through the sash opening. This air will
travel along surface 158 as it approaches the sash opening. The
second body of air is that which is moving downwardly along the
back side of the sash inside the cabinet as a result of blower 28.
By providing an angled or curved surface 158, the two bodies of air
will not be meeting at a right angle, resulting in less turbulence
and better containment of the air within work area 44. A third body
of air is that which flows from the blower toward the rear of the
work area.
Referring to FIGS. 1, 3 and 10, as sash 42 is moved upwardly within
tracks 150, it will slide behind an upper sash pocket 160. As best
seen in FIGS. 1 and 3, sash pocket 160 is preferably bolted to
front panel 40 and trim panels 152. Pocket 160 is shaped to extend
from one side of sash 42 to the other, and is enclosed along the
top thereof. Pocket 160 thus cooperates with front panel 40 to
enclose the top and sides of sash 42 as it is moved upwardly along
tracks 150. Pocket 160 acts to prevent the operator of cabinet 10
from accessing the upper portion of sash 42 as it slides away from
work area 44. As best seen in FIG. 10, there is no physical contact
between the rear of sash 42 and any type of seal. In the prior art,
a wiping seal would exist in the area of a screw 133 shown in FIG.
10. This wiping seal resulted in certain disadvantages as explained
above. Such a seal is not needed with the present invention. A
front cover 165 is secured over the front of cabinet 10. More
specifically, cover 165 is placed over sash pocket 160 and front
panel 40 to present a more appealing front face for cabinet 10. The
design of face 154 also facilitates decontamination of the cabinet
as is required from time to time by safety regulations.
Decontamination may occur by leaving pocket 160 in place and
lowering the sash. The entire front of the cabinet is then sealed
with plastic which is secured by tape to the angled surfaces 154.
Alternatively, sash pocket 160 may be removed and the sash
completely lowered followed by sealing off the front of the cabinet
with plastic. Another alternative is to remove pocket 160 and place
the sash in the fully raised position before the front face is
sealed with plastic. In the latter two cases the pocket 160 may be
placed inside the cabinet so that it will be decontaminated. In all
three cases effective decontamination is accomplished without the
need to actually remove the sash.
As can be seen in FIG. 10, there is no physical contact with the
back of sash 42 and the prior art wiping seal has been eliminated.
In order to insure that contaminated air from the work area 44 does
not escape into the room a plurality of upper scavenger holes 168
are provided immediately above work area 44 along the front of
cabinet 10. Any air leaving environment 44 will be drawn back
through holes 168 and will not be leaked into the room. While the
use of scavenger holes in this location has been taught by prior
art constructions, it has been discovered that the effectiveness of
these holes 168 is greatly enhanced if structure is provided to
insure that the area in front of these holes will be a uniform
negative pressure area relative to the work area 44. To this end a
restrictor plate 172 is coupled between air diffuser plate 43 and a
filter shelf 170 used to hold supply filter 32 in place. Restrictor
plate 172 is preferably held in place with a series of screws 174.
The location of plate 172 may be altered by loosening screws 174
and sliding the plate inwardly or outwardly. By adjusting the
location of plate 172 the balance between air flow down into the
work area and air flow passing through the exhaust is maintained in
favor of exhaust air. Plate 172 serves to even out any pressure
differences in the area of holes 168 resulting from the competing
air flows and the fact that the holes are interrupted with solid
areas. This insures that air will flow into the holes and out the
exhaust rather than out into the room in the area behind the sash.
It is to be understood that holes 168 extend across the entire
front of the cabinet to insure that the entire back side of the
sash is effectively "sealed" against contaminate air entering the
room.
As can be seen from the above, the invention provides a biological
safety cabinet with a number of improved features and achieves a
better air-flow into and through the cabinet. From the foregoing,
it will be seen that this invention is one well adapted to attain
all of the ends and objects herein above set forth, together with
other advantages which are inherent to the structure. It will be
understood that certain features and subcombinations are of utility
and may be employed without reference to other features and
subcombinations. This is contemplated by and is within the scope of
the claims.
Since many possible embodiments may be made of the invention
without departing from the scope thereof, it is to be understood
that all matter herein set forth or shown in the accompanying
drawings is to be interpreted as illustrative and not in a limiting
sense.
* * * * *