CA1126566A - Biological safety cabinet having jet air inflow barrier - Google Patents
Biological safety cabinet having jet air inflow barrierInfo
- Publication number
- CA1126566A CA1126566A CA317,396A CA317396A CA1126566A CA 1126566 A CA1126566 A CA 1126566A CA 317396 A CA317396 A CA 317396A CA 1126566 A CA1126566 A CA 1126566A
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- Canada
- Prior art keywords
- work chamber
- access opening
- air
- wall
- work
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Abstract
ABSTRACT OF THE DISCLOSURE
A biological safety cabinet that has front, rear, bottom, top and side walls joined to form an enclosure, a movable viewing window to selectively vary the effect size of the work access opening in the front wall, a high efficiency particulate air filter (HEPA Filter), rear wall and bottom wall that in conjunction with the housing side and front walls defines a work chamber accessible through the front wall opening, a plenum chamber between the top wall and high efficiency filter, a dampered outlet in the top wall opening to the plenum chamber, a blower compart-ment in the enclosure having a blower therein for drawing air from the work chamber and discharging the drawn air to the plenum chamber, and a pressurized air discharge nozzle.
In one embodiment the nozzle discharges air to flow along the viewing window and thence be drawn in into the work chamber, and in a second embodiment the nozzle is mounted adjacent the lower edge of the viewing window.
A biological safety cabinet that has front, rear, bottom, top and side walls joined to form an enclosure, a movable viewing window to selectively vary the effect size of the work access opening in the front wall, a high efficiency particulate air filter (HEPA Filter), rear wall and bottom wall that in conjunction with the housing side and front walls defines a work chamber accessible through the front wall opening, a plenum chamber between the top wall and high efficiency filter, a dampered outlet in the top wall opening to the plenum chamber, a blower compart-ment in the enclosure having a blower therein for drawing air from the work chamber and discharging the drawn air to the plenum chamber, and a pressurized air discharge nozzle.
In one embodiment the nozzle discharges air to flow along the viewing window and thence be drawn in into the work chamber, and in a second embodiment the nozzle is mounted adjacent the lower edge of the viewing window.
Description
6S~6 This invention relates to a biological safety cabinet having a work area therein. More particularly this invention relates to a biological safety cabinet having a source of air under pressure for discharging air downwardly outside of the cabinet to induce air flow from the room into the safety cabinet.
In the prior art it is known to provide an air hood apparatus having a work area, an access opening to the work area and a blower that draws filtered air through the access opening and discharges air to a suitable exhaust system, see for example U.S. Patent 3,273,323. However with such prior art apparatus when ambient air is drawn in through the work area access opening tne air barrier pro-tection is limited because the air inflow velocity is non-uniform, ranging from a relatively high velocity at the lower part of the access opening to a relatively low vel-ocity at the top of the access opening. For example in one embodiment of a prior art biological safety cabinet wherein there is provided a work chamber with a grill lo-cated in the bottom of the work chamber adjacent thebottom edge of the work access opening and an air foil be-tween the bottom edge and the grill, the air barrier pro-tection at the access opening is limited because the air inflow velocity at the access opening i5 non-uniform across the height of the access opening, ranging from as much as 600 FPM over the air foil to as little as 30 FPM at the lower edge of the viewing window extending across the upper part of the access opening. Reducing the vertical spacing between the lower edges of the access opening and the view-ing window improves the uniformity of air flow, but re-stricts access to the work area. Further, normal movement of people in ~he room can create stray airflow currents that result in pulses that would result in air being drawn out from the work area and into the room if the velocity of air inflow through at least part of the access opening is low or there is no inflow. This can result in toxic or other undesirable material escaping to the ambient atmosphere in the room, which is undesirable.
In another form of a prior art safety cabinet, the lower part of the work chamber extends further for-wardly than the top part of the work chamber and is of a substantially larger front to rear dimension. The HEPA
filtered air is passed into a plenum chamber above the work chamber and thence in part th rough a perforated panel into the work chamber and in part passes between parallel viewing windows to be discharged under pressure downwardly of the lower edges of the windows toward the lower edge of the access opening. A blower withdraws air from the work chamber through a front grill in the lower wall there-of, the withdrawn air including warm air drawn in through the work chamber access opening, the air discharged down-wardly from between the lower edges of the viewing windows, and air passing through the front part of the per~orated panel into the front part of the work chamber. However a problem encountered with this prior art arrangement is that when an operator has his arms extended into the work chamber, sometimes air will flow outwardly along his arms into the room is undesirable.
~lZ~i~;i66 The bioloyical safety cabinet of this invention includes a front wall having an access opening which opens to a work chamber that in part is defined by a bottom wall having an air outlet adjacent the access opening, a blower to draw air through the access opening into the work cham-ber and thence to the outlet, and a source of air under pressure for discharging air downwardly outside of cabinet from the top of the access opening toward the bottom there-of to result in induced air flow from the room moving to said air outlet.
One of the objects of this invention is to provide a biological safety cabinet having new and novel air barrier protection for an operator. Another object of this inven-tion is to provide a biological safety cabinet having new and novel means for preventing aerosols, fumes and other materials from escaping from the work zone interior into the ambient atmosphere where it c~ be ingested or inhaled by the operator. A further object of this invention is to provide a biological safety cabinet having new and novel means for improviny the internal sterility of the work zone by promoting a distinct downflow velocity vector of airflow adjacent the access opening to the work area of the cabinet.
The invention will now be described with reference to the accompanying drawings in which:
Figure 1 is a vertical cross sectional view of the first embodiment of the biological safety cabinet of this invention, said view being generally taken along the line and in the direction of the arrows 1-1 of Figure 2;
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Figure 2 is a fragmentary front view of the cab-inet of the first embodiment of this invention with a hor-izontally intermediate portion broken away;
Figure 3 is an enlarged fragmentary cross section-al view with vertically intermediate parts broken away to more clearly illustrate the structure at the front part of the cabinet of the first embodiment of the invention; and Figure 4 is a fragmentary cross sectional view of the second embodiment of the invention to show the struc-ture thereof adjacent the work chamber access opening.
Referring now in particular to Figures 1-3, the biological safety cabinet of the first embodiment of this invention, generally designated 10, provides a work sta-tion and includes a front wall 11, a rear wall 12, side walls 13 and 14, a top wall 15 and a bottom wall 16 that are joined together to form a generally rectangular box shaped encloseure that is provided with a work access opening 24 in the front wall and a discharge opening 42 in the top wall. Provided within the enclosure formed by the walls 11-16 is a work chamber 19 that the access open-ing 24 opens to. The work chamber in part is defined by a bottom wall 20 and a rear wall 21 which advantageously extend between the side walls 13 and 14. The bottom wall ~0 extends between front wall 11 and the rear chamber wall 21. Further, the work chamber is in part defined by the front wall 11. The top pressurized air inlet of the work chamber has extended thereacross a hi.gh efficiency parti-culate air filter (HEPA filter) 22 that has at least a 75 ~ ~Z65i~
efficiency for the removal of 0.3 micron particles as determined by the standard D.O.P. Test of the Army Chemi-cal Corps and preferably provides a 99.9% removal of all aerosol particulate contaminants, 0.3 microns or larger, as determined by the government specification TID-7023, ~igh Efficiency Particulate Air Filter Units. Thus, dur-ing operation, the air flowing into the work chamber through the work chamber top inlet is filtered by filter 22, the lower portion of which forms the top of the work chamber.
Located within the work chamber and extending the transverse width of the lower edge of opening ~ from said lower edge to the bottom wall 20 is an air foil 25 that is sloping downwardly in the direction toward the rear wall 21.
The bottom wall 20 is provided with an opening just rear-wardl~ of the air foil that has a grill 20a. The distance of the opening extends rearwardly of the foil is only a small fraction of the distance from the air foil to the rear wall 21. The grill provides for fluid communication between the work chamber 21 and the blower compartment 35 which is located between the work chamber bottom wall 20 and the cabinet bottom wall 16.
Located within the blower compartment 35 is a blower 36 that has an inlet 36A for withdrawing air from the chamber 19. The outlet 36B of the blower is fluidly connected by a duct 37 for discharging air through an open-ing 38A in a wall 38 that extends between the work chamber rear wall 21 and the cabinet rear wall 12, and transver-sely between the end walls 13 and 14. Thus, a plenum 5~ti chamber 39 is defined by the wall 38, and the portions of wall 12, 13, 14 and 21 that extend between the top wall 15 and wall 38 and filter 22; and the portion of the front wall extending between the top wall 15 and the filter 22.
Due to the provision of the plenum chamber, air discharged from duct 37 thereinto is of relatively uniform pressure across the top of the filter material of the filter 22 for movement of air through the filter into the work chamber.
To aid in controlling the volume of air discharged from the duct 37 that flows through the filter into the work chamber, the top wall mounts a perforated grill 43 that extends across the top wall opening 42. A second perforated grill 44 is located between grill 42 and the filter 4~ in the outlet duct 46. Grill 44 may be mounted in a suitable manner for movement relative to grill 43 for a selectively amount of air flow from the plenum chamber to the outlet duct 46. Grills 43, 44 may be of conventional contruction and of a type that grill 44 may be moved relative grill 43 to completely block the flow of air through opening 42. A
damper may be used in place of grills 43, 44. The filter 48 that may be provided in duct 46, may be of a high effi-ciency HEPA filter, depending on the work being performed and the type of air discharge system that duct 46 is con-nected to.
To permit selectively varying the effective height of the access opening to the work chamber, slide s-trips 26 are mounted on the front wall to mount a viewing window 27 6~
for vertical movement between a position closing the ac-cess opening and a position the lower edge of the window is adjacent the upper edge of the access opening, and re-tain the window in selected vertically adjusted positions on the front wall, the window extending transverse across the width of the access opening 24.
Mounted by the slide strips 26 (or the front wall~
to extend across the access opening 24 adjacent the upper edge thereof is a light fixture 29 for directing light through the window into the work chamber. The light fix-ture mounts a nozzle 30 for directing air downwardly under pressure along the outer surface of the window across the width of the access opening, the air under pressure being applied to the nozzle by a conduit 31. The source of air under pressure for the conduit 31 may be an air blower 32 mounted on the cabinet, or a conduit may be connected di-rectly to a pressurized air system in the building in which the cabinet is used.
Provided in the work chamber rear wall 21 adjacent the bottom wall 20 at an elevation below wall 38 to open to the blower compartment 35 is a grilled opening 21a to per-mit the passage of air from the work chamber to the blower.
The grilled opening extends across substantially the trans-verse width of the work chamber and only a small fraction of the height of wall 21. The blower compartment is de-fined by wall 38, the portion of wall 21 that is below wall 38, wall 20, the portions of wall 11-14 below walls 20 and 38, and bottom wall 16. A door (not shown) is provided in one of the walls 11-14 to permit access to the blower.
Referring to Figure 4, the second embodiment of the invention, generally designated 50 is the same as the first embodiment except that instead of the nozzle being mounted on the light fixture, the nozzle 51 thereof is mounted on a channel 52 affixed to the lower edge of the window pane 53 of the viewing window to move therewith.
The window pane extends across the access opening and is slideway movable between a position closing the access opening -to a position that the channel is adjacent the upper edge of the access opening in a manner described with reference to the first embodiment. The conduit (not shown) for applying air under pressure to the nozzle 51 is flexible and of sufficient length that the nozzle may be - moved with the window in the aforementioned manner.
In each of the embodiments the light fixture and viewing window may be hingedly mounted on the first wall adjacent the upper edge of the access opening whereby the viewing window may be moved upwardly and outwardly of the cabinet, instead of being vertically slidably mounted ~conduit 31 being flexible). Further the side walls of the work chamber are parallel to one another, and wall 21 i5 parallel to window 27 (when window 27 is in its verti-cal access opening partial closing position, if hingedly mounted) and in a horizontal plane wall 21 perpendicular to the work chamber side walls.
To be mentioned is that the nozzle of each of the embodiments may be of a type that it discharges one jet stream of air the continuous width of the access opening, or may be a series of small jets of air across the width of the access opening. In either event, the air discharged by the nozzle provides an air flow in a downward direction across the width of the access opening to flow in a "bound-ary sheet" that comprises the efflux from the air jet plus room air induced to flow downwardly therewith.
In using the apparatus of this invention, the work material is placed in the access chamber rearwardly of opening 20A. At this time, the blower 36 is operating for drawing air downwardly from the work chamber through the grill 21A and grill 20A and discharging air under pressure to the plenum chamber. The air under pressure in the plenum chamber in part is discharged through the duct 46 and in part flows through the filter 22 downwardly to the work cham-ber. The volume of air withdrawn from the work chamber by the blower and the volume of air exhausted through duct 45 is controlled such that air from the room and air flowing downwardly along the viewing window (or below channel 52) from the nozzle is drawn into the access opening. That is air drawn into the work chamber through the access opening flow~ downwardly through the grill 20A into the blower com-partment as does some of the air that passes through the filter 22. The remainder of the air that passes through the filter 22 is drawn through the work chamber and open-ing 21A. As a result no non~filtered room air moves into l~Z656,~
the work chamber rearwardly of the grill 20A. At the same time, the boundary flow air that flows downwardly of the lower edge of the viewing window resulting from discharg-ing of air by the nozzles provides a boundary layer at the access opening that has a strong uniform inward and down-ward vector which is compatible with the internal downward flow of air that has passed through the filter 22. This provides an air barrier that is less dependent on the height of the work access opening so that the viewing win-dow can be raised vertically and a strong air barrier curtain may be maintained by increasing the jet air velocity from the blower 32 with increasing height of the access opening. In this connection, it is to be mentioned that the volume of air drawn through the accesS opening is at least somewhat greater than the volume of air discharged through the nozzle 30. It might be mentioned that blowers 32 and 36 are preferably of variable volume type blowers.
Due to the provision of the nozzle discharge and the resulting air barrier curtain formed, it is less likely that movement of personnel within the room adjacent the cabinet will cause air current which would result in air being drawn from the wo~k chamber and through the access opening and out into the room interior. Likewise, such stray air currents resulting from the movement of personnel in the room is less likely to result in room air being moved into the work chamber rearwardly of the grill 20A whereby it may result in contamination of the work being performed in the work chamber that is rearwardly of the grill.
1~6~i~6 Even th~ugh the invention has been described withreference to the side walls of the work chamber being coex-tensive with the side walls of the cabinet, it is to be understood that the walls separate from the side walls of the cabinet may be provided for forming the side walls of the work chamber. Additionally, the plenum chamber may be located entirely above the filter 22 to have air therefrom pass through the filter 22, and the conduit 37 extended for dischargin~ into a plenum chamber at such a higher elevation, and opening 42 opening to the plenum chamber through any one of walls 11-14.
Also, it is to be understood the same air barrier protection provided bv nozzles 30, 51 discharging exterior of the cabinet adjacent the viewing window ccnbe used with a cabinet having the top of the work chamber formed by dif-fuser panel in place of filter 22, plenum chamber 39 open-ing to the diffuser panel but not to ~ening 42, a duct that places outlet 21A in fluid communication with opening 42 in-stead of the blower chamber and duct 37 being connected to an exhaust blower external of the cabinet, and a plenum cham-ber located below wall 20 to have outlet 20A open thereto and having a HEPA filter outlet so that the blower 36 would withdraw air from the last mentioned plenum chamber through said HEPA filter and discharge air under pressure to the plenum chamber that opens to the diffuser panel to pass therethrough into the work chamber.
As another alternative type cabinet that the same air barrier protection provided by nozzles 30, 51 discharg-~12~5~
ing exterior of the cabinet adjacent the viewing window can be used with is a cabinet wherein wall 38 is left out, the blower 36 mounted above the filter 22 to wi-thdraw air through openings 20A, 21A and discharge air under pressure to an inlet of a separate plenum chamber, which opens direct-ly to filter 22 and has a top wall between filter 22 and wall 15, and a duct for fluidly connecting an outlet in the ~p-arate plenum chamber top wall to an outlet in the cabinet top wall that corresponds to 42 but is offset from that shown in the drawing.
The two type cabinets referred to in the two preced-ing paragraphs are prior art cabinets other than for the provision of nozzle system (30-32, 51) for discharging air downwardly exterior of the cabinet toward the access open-ing lower edge and having air discharged by such nozzles drawn into the access opening to flow through a grilled outlet in the front bottom part of the work chamber bot-tom wall.
In the prior art it is known to provide an air hood apparatus having a work area, an access opening to the work area and a blower that draws filtered air through the access opening and discharges air to a suitable exhaust system, see for example U.S. Patent 3,273,323. However with such prior art apparatus when ambient air is drawn in through the work area access opening tne air barrier pro-tection is limited because the air inflow velocity is non-uniform, ranging from a relatively high velocity at the lower part of the access opening to a relatively low vel-ocity at the top of the access opening. For example in one embodiment of a prior art biological safety cabinet wherein there is provided a work chamber with a grill lo-cated in the bottom of the work chamber adjacent thebottom edge of the work access opening and an air foil be-tween the bottom edge and the grill, the air barrier pro-tection at the access opening is limited because the air inflow velocity at the access opening i5 non-uniform across the height of the access opening, ranging from as much as 600 FPM over the air foil to as little as 30 FPM at the lower edge of the viewing window extending across the upper part of the access opening. Reducing the vertical spacing between the lower edges of the access opening and the view-ing window improves the uniformity of air flow, but re-stricts access to the work area. Further, normal movement of people in ~he room can create stray airflow currents that result in pulses that would result in air being drawn out from the work area and into the room if the velocity of air inflow through at least part of the access opening is low or there is no inflow. This can result in toxic or other undesirable material escaping to the ambient atmosphere in the room, which is undesirable.
In another form of a prior art safety cabinet, the lower part of the work chamber extends further for-wardly than the top part of the work chamber and is of a substantially larger front to rear dimension. The HEPA
filtered air is passed into a plenum chamber above the work chamber and thence in part th rough a perforated panel into the work chamber and in part passes between parallel viewing windows to be discharged under pressure downwardly of the lower edges of the windows toward the lower edge of the access opening. A blower withdraws air from the work chamber through a front grill in the lower wall there-of, the withdrawn air including warm air drawn in through the work chamber access opening, the air discharged down-wardly from between the lower edges of the viewing windows, and air passing through the front part of the per~orated panel into the front part of the work chamber. However a problem encountered with this prior art arrangement is that when an operator has his arms extended into the work chamber, sometimes air will flow outwardly along his arms into the room is undesirable.
~lZ~i~;i66 The bioloyical safety cabinet of this invention includes a front wall having an access opening which opens to a work chamber that in part is defined by a bottom wall having an air outlet adjacent the access opening, a blower to draw air through the access opening into the work cham-ber and thence to the outlet, and a source of air under pressure for discharging air downwardly outside of cabinet from the top of the access opening toward the bottom there-of to result in induced air flow from the room moving to said air outlet.
One of the objects of this invention is to provide a biological safety cabinet having new and novel air barrier protection for an operator. Another object of this inven-tion is to provide a biological safety cabinet having new and novel means for preventing aerosols, fumes and other materials from escaping from the work zone interior into the ambient atmosphere where it c~ be ingested or inhaled by the operator. A further object of this invention is to provide a biological safety cabinet having new and novel means for improviny the internal sterility of the work zone by promoting a distinct downflow velocity vector of airflow adjacent the access opening to the work area of the cabinet.
The invention will now be described with reference to the accompanying drawings in which:
Figure 1 is a vertical cross sectional view of the first embodiment of the biological safety cabinet of this invention, said view being generally taken along the line and in the direction of the arrows 1-1 of Figure 2;
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Figure 2 is a fragmentary front view of the cab-inet of the first embodiment of this invention with a hor-izontally intermediate portion broken away;
Figure 3 is an enlarged fragmentary cross section-al view with vertically intermediate parts broken away to more clearly illustrate the structure at the front part of the cabinet of the first embodiment of the invention; and Figure 4 is a fragmentary cross sectional view of the second embodiment of the invention to show the struc-ture thereof adjacent the work chamber access opening.
Referring now in particular to Figures 1-3, the biological safety cabinet of the first embodiment of this invention, generally designated 10, provides a work sta-tion and includes a front wall 11, a rear wall 12, side walls 13 and 14, a top wall 15 and a bottom wall 16 that are joined together to form a generally rectangular box shaped encloseure that is provided with a work access opening 24 in the front wall and a discharge opening 42 in the top wall. Provided within the enclosure formed by the walls 11-16 is a work chamber 19 that the access open-ing 24 opens to. The work chamber in part is defined by a bottom wall 20 and a rear wall 21 which advantageously extend between the side walls 13 and 14. The bottom wall ~0 extends between front wall 11 and the rear chamber wall 21. Further, the work chamber is in part defined by the front wall 11. The top pressurized air inlet of the work chamber has extended thereacross a hi.gh efficiency parti-culate air filter (HEPA filter) 22 that has at least a 75 ~ ~Z65i~
efficiency for the removal of 0.3 micron particles as determined by the standard D.O.P. Test of the Army Chemi-cal Corps and preferably provides a 99.9% removal of all aerosol particulate contaminants, 0.3 microns or larger, as determined by the government specification TID-7023, ~igh Efficiency Particulate Air Filter Units. Thus, dur-ing operation, the air flowing into the work chamber through the work chamber top inlet is filtered by filter 22, the lower portion of which forms the top of the work chamber.
Located within the work chamber and extending the transverse width of the lower edge of opening ~ from said lower edge to the bottom wall 20 is an air foil 25 that is sloping downwardly in the direction toward the rear wall 21.
The bottom wall 20 is provided with an opening just rear-wardl~ of the air foil that has a grill 20a. The distance of the opening extends rearwardly of the foil is only a small fraction of the distance from the air foil to the rear wall 21. The grill provides for fluid communication between the work chamber 21 and the blower compartment 35 which is located between the work chamber bottom wall 20 and the cabinet bottom wall 16.
Located within the blower compartment 35 is a blower 36 that has an inlet 36A for withdrawing air from the chamber 19. The outlet 36B of the blower is fluidly connected by a duct 37 for discharging air through an open-ing 38A in a wall 38 that extends between the work chamber rear wall 21 and the cabinet rear wall 12, and transver-sely between the end walls 13 and 14. Thus, a plenum 5~ti chamber 39 is defined by the wall 38, and the portions of wall 12, 13, 14 and 21 that extend between the top wall 15 and wall 38 and filter 22; and the portion of the front wall extending between the top wall 15 and the filter 22.
Due to the provision of the plenum chamber, air discharged from duct 37 thereinto is of relatively uniform pressure across the top of the filter material of the filter 22 for movement of air through the filter into the work chamber.
To aid in controlling the volume of air discharged from the duct 37 that flows through the filter into the work chamber, the top wall mounts a perforated grill 43 that extends across the top wall opening 42. A second perforated grill 44 is located between grill 42 and the filter 4~ in the outlet duct 46. Grill 44 may be mounted in a suitable manner for movement relative to grill 43 for a selectively amount of air flow from the plenum chamber to the outlet duct 46. Grills 43, 44 may be of conventional contruction and of a type that grill 44 may be moved relative grill 43 to completely block the flow of air through opening 42. A
damper may be used in place of grills 43, 44. The filter 48 that may be provided in duct 46, may be of a high effi-ciency HEPA filter, depending on the work being performed and the type of air discharge system that duct 46 is con-nected to.
To permit selectively varying the effective height of the access opening to the work chamber, slide s-trips 26 are mounted on the front wall to mount a viewing window 27 6~
for vertical movement between a position closing the ac-cess opening and a position the lower edge of the window is adjacent the upper edge of the access opening, and re-tain the window in selected vertically adjusted positions on the front wall, the window extending transverse across the width of the access opening 24.
Mounted by the slide strips 26 (or the front wall~
to extend across the access opening 24 adjacent the upper edge thereof is a light fixture 29 for directing light through the window into the work chamber. The light fix-ture mounts a nozzle 30 for directing air downwardly under pressure along the outer surface of the window across the width of the access opening, the air under pressure being applied to the nozzle by a conduit 31. The source of air under pressure for the conduit 31 may be an air blower 32 mounted on the cabinet, or a conduit may be connected di-rectly to a pressurized air system in the building in which the cabinet is used.
Provided in the work chamber rear wall 21 adjacent the bottom wall 20 at an elevation below wall 38 to open to the blower compartment 35 is a grilled opening 21a to per-mit the passage of air from the work chamber to the blower.
The grilled opening extends across substantially the trans-verse width of the work chamber and only a small fraction of the height of wall 21. The blower compartment is de-fined by wall 38, the portion of wall 21 that is below wall 38, wall 20, the portions of wall 11-14 below walls 20 and 38, and bottom wall 16. A door (not shown) is provided in one of the walls 11-14 to permit access to the blower.
Referring to Figure 4, the second embodiment of the invention, generally designated 50 is the same as the first embodiment except that instead of the nozzle being mounted on the light fixture, the nozzle 51 thereof is mounted on a channel 52 affixed to the lower edge of the window pane 53 of the viewing window to move therewith.
The window pane extends across the access opening and is slideway movable between a position closing the access opening -to a position that the channel is adjacent the upper edge of the access opening in a manner described with reference to the first embodiment. The conduit (not shown) for applying air under pressure to the nozzle 51 is flexible and of sufficient length that the nozzle may be - moved with the window in the aforementioned manner.
In each of the embodiments the light fixture and viewing window may be hingedly mounted on the first wall adjacent the upper edge of the access opening whereby the viewing window may be moved upwardly and outwardly of the cabinet, instead of being vertically slidably mounted ~conduit 31 being flexible). Further the side walls of the work chamber are parallel to one another, and wall 21 i5 parallel to window 27 (when window 27 is in its verti-cal access opening partial closing position, if hingedly mounted) and in a horizontal plane wall 21 perpendicular to the work chamber side walls.
To be mentioned is that the nozzle of each of the embodiments may be of a type that it discharges one jet stream of air the continuous width of the access opening, or may be a series of small jets of air across the width of the access opening. In either event, the air discharged by the nozzle provides an air flow in a downward direction across the width of the access opening to flow in a "bound-ary sheet" that comprises the efflux from the air jet plus room air induced to flow downwardly therewith.
In using the apparatus of this invention, the work material is placed in the access chamber rearwardly of opening 20A. At this time, the blower 36 is operating for drawing air downwardly from the work chamber through the grill 21A and grill 20A and discharging air under pressure to the plenum chamber. The air under pressure in the plenum chamber in part is discharged through the duct 46 and in part flows through the filter 22 downwardly to the work cham-ber. The volume of air withdrawn from the work chamber by the blower and the volume of air exhausted through duct 45 is controlled such that air from the room and air flowing downwardly along the viewing window (or below channel 52) from the nozzle is drawn into the access opening. That is air drawn into the work chamber through the access opening flow~ downwardly through the grill 20A into the blower com-partment as does some of the air that passes through the filter 22. The remainder of the air that passes through the filter 22 is drawn through the work chamber and open-ing 21A. As a result no non~filtered room air moves into l~Z656,~
the work chamber rearwardly of the grill 20A. At the same time, the boundary flow air that flows downwardly of the lower edge of the viewing window resulting from discharg-ing of air by the nozzles provides a boundary layer at the access opening that has a strong uniform inward and down-ward vector which is compatible with the internal downward flow of air that has passed through the filter 22. This provides an air barrier that is less dependent on the height of the work access opening so that the viewing win-dow can be raised vertically and a strong air barrier curtain may be maintained by increasing the jet air velocity from the blower 32 with increasing height of the access opening. In this connection, it is to be mentioned that the volume of air drawn through the accesS opening is at least somewhat greater than the volume of air discharged through the nozzle 30. It might be mentioned that blowers 32 and 36 are preferably of variable volume type blowers.
Due to the provision of the nozzle discharge and the resulting air barrier curtain formed, it is less likely that movement of personnel within the room adjacent the cabinet will cause air current which would result in air being drawn from the wo~k chamber and through the access opening and out into the room interior. Likewise, such stray air currents resulting from the movement of personnel in the room is less likely to result in room air being moved into the work chamber rearwardly of the grill 20A whereby it may result in contamination of the work being performed in the work chamber that is rearwardly of the grill.
1~6~i~6 Even th~ugh the invention has been described withreference to the side walls of the work chamber being coex-tensive with the side walls of the cabinet, it is to be understood that the walls separate from the side walls of the cabinet may be provided for forming the side walls of the work chamber. Additionally, the plenum chamber may be located entirely above the filter 22 to have air therefrom pass through the filter 22, and the conduit 37 extended for dischargin~ into a plenum chamber at such a higher elevation, and opening 42 opening to the plenum chamber through any one of walls 11-14.
Also, it is to be understood the same air barrier protection provided bv nozzles 30, 51 discharging exterior of the cabinet adjacent the viewing window ccnbe used with a cabinet having the top of the work chamber formed by dif-fuser panel in place of filter 22, plenum chamber 39 open-ing to the diffuser panel but not to ~ening 42, a duct that places outlet 21A in fluid communication with opening 42 in-stead of the blower chamber and duct 37 being connected to an exhaust blower external of the cabinet, and a plenum cham-ber located below wall 20 to have outlet 20A open thereto and having a HEPA filter outlet so that the blower 36 would withdraw air from the last mentioned plenum chamber through said HEPA filter and discharge air under pressure to the plenum chamber that opens to the diffuser panel to pass therethrough into the work chamber.
As another alternative type cabinet that the same air barrier protection provided by nozzles 30, 51 discharg-~12~5~
ing exterior of the cabinet adjacent the viewing window can be used with is a cabinet wherein wall 38 is left out, the blower 36 mounted above the filter 22 to wi-thdraw air through openings 20A, 21A and discharge air under pressure to an inlet of a separate plenum chamber, which opens direct-ly to filter 22 and has a top wall between filter 22 and wall 15, and a duct for fluidly connecting an outlet in the ~p-arate plenum chamber top wall to an outlet in the cabinet top wall that corresponds to 42 but is offset from that shown in the drawing.
The two type cabinets referred to in the two preced-ing paragraphs are prior art cabinets other than for the provision of nozzle system (30-32, 51) for discharging air downwardly exterior of the cabinet toward the access open-ing lower edge and having air discharged by such nozzles drawn into the access opening to flow through a grilled outlet in the front bottom part of the work chamber bot-tom wall.
Claims (16)
1. In a work station, a wall portion having means defining an effective access opening, the above means in-cluding means defining an upper access opening edge and a lower access opening edge, means joined to the wall portion to in conjunction therewith define a work chamber having the access opening opening thereinto, the work chamber means including a bottom wall having an outlet adjacent the access opening lower edge, blower means for drawing air through the access opening into the work chamber and thence from the work chamber through said outlet, a source of air under pressure, and means fluidly connected to the source of air under pressure for discharging air under pressure ex-terior of the work chamber and adjacent the upper edge down-wardly toward the lower edge to be drawn through the access opening into the work chamber by the blower means.
2. The apparatus of claim 1 further characterized in that there is provided means that in conjunction with the work chamber means defines a plenum chamber exterior of the work chamber, said blower means having an outlet, means for conducting fluid under pressure from the blower outlet to the plenum chamber, said work chamber means including HEPA
filter means for placing the plenum chamber in air flow com-munication with the work chamber and filtering the air flow-ing from the plenum chamber to the work chamber.
filter means for placing the plenum chamber in air flow com-munication with the work chamber and filtering the air flow-ing from the plenum chamber to the work chamber.
3. The apparatus of claim 2 further characterized in that the plenum chamber means includes a dampered opening remote from the access opening for discharging air from the plenum chamber and controlling the pressure of air in the plenum chamber.
4. A biological safety cabinet comprising front, rear, side, top and bottom walls joined together to form a generally rectangular enclosure, said front wall having a work access opening including edges that define an access opening upper edge and an access opening lower edge, means that in conjunction with at least one of the above mentioned walls defines a substantially enclosed work chamber that has said access opening opening thereinto, the work chamber means including a bottom wall extending from adjacent the access opening to a location remote from the access opening, said work chamber bottom wall having an outlet opening ad-jacent the lower edge, and a high efficiency filter remote from the work chamber bottom wall, means that in conjunction with at least one of the enclosure walls and the work cham-ber means defines a plenum chamber that opens to said filter and a dampered outlet for exhausting air from the plenum cham-ber, a blower located within said enclosure and having an outlet in fluid communication with the plenum chamber to discharge air thereinto and an inlet in fluid communication with work chamber for withdrawing a greater volume of air therefrom than that passed from the plenum chamber through the filter to the work chamber, and means for discharging air under pressure exterior of the enclosure across the access open-ing downwardly toward the lower edge to be drawn in through the access opening by operation of the blower withdrawing air from the work chamber.
5. The apparatus of claim 4 further characterized in that the last mentioned means includes a nozzle extend-ing substantially across the access opening for discharg-ing air under pressure toward lower edge and means for supply-ing air under pressure to said nozzle.
6. The apparatus of claim 4 further characterized in that the work chamber bottom wall is located a substan-tial distance vertically above the enclosure bottom wall, that the means for defining the plenum chamber includes wall means extending between at least one of the enclosure walls and the work chamber means to in conjunction therewith pro-vide a blower compartment within the enclosure, exterior of the work and plenum chambers and that opens through the work chamber bottom wall opening to the work chamber for passage of air from the work chamber to the blower compartment, the blower being located in blower compartment and having the blower inlet opening thereto for withdrawing air therefrom.
7. The apparatus of claim 4 further characterized in that there is provided a viewing window movably mounted on the front wall adjacent said upper edge for varying the effective size of the access opening by movement toward and away from said lower edge and that the means for dis-charging air under pressure includes a nozzle for dis-charging an air jet downwardly along the window exterior of the enclosure, said nozzle being mounted adjacent the upper edge.
8. The apparatus of claim 4 further characterized in that there is provided a viewing window movably mounted on the front wall adjacent said upper edge for varying the effective size of the access opening by movement toward and away from the access opening lower edge, said window having a lower portion, and that the means for discharging air under pressure includes a nozzle mounted on the window lower edge portion for discharging an air jet downwardly toward the access opening lower edge.
9. A biological safety cabinet comprising front, rear, side, top and bottom walls joined together to form an enclosure, said front wall having a work access opening including edges that define a work access opening upper edge and a work access opening lower edge, means to in con-junction with said side walls and front wall define a work chamber within the enclosure that has the access opening opening directly thereinto, the work chamber defining means including a rear wall, a bottom wall extending from the last mentioned rear wall to the front wall at an elevation below the access opening lower edge, the last mentioned bottom wall being vertically spaced from the enclosure bottom wall and having a grilled opening adjacent the front wall and re-mote from the work chamber rear wall that extends substan-tially the length of the access opening lower edge and a HEPA filter substantially below the enclosure top wall and substantially spaced therefrom for defining the top wall of the work chamber, wall means extending between the work cham-ber means and the enclosure front and side walls within the enclosure and exterior of the work chamber to separate the enclosure into a plenum chamber that opens to the filter for passage of air from the plenum chamber to the work chamber and a blower compartment that extends between said bottom walls with the bottom wall grilled opening opening thereto, the wall means having a duct opening, the enclosure having a discharge outlet, blower means in the blower compartment and having an inlet for drawing air through the filter and access opening and thence through the grilled opening, and an outlet for discharging air under pressure through the wall means opening to the plenum chamber, and nozzle means for discharging air under pressure downwardly exterior of the enclosure toward the said lower edge.
10. The apparatus of claim 9 further characterized in that the work chamber rear wall has a lower portion hav-ing a grilled opening for placing the work chamber in air flow communication with the blower compartment, the height of the rear wall grilled opening being less than 25% of the height of the work chamber rear wall and the dimension of the bottom wall grilled opening in a direction between the work chamber rear wall and the front wall being less than 25% of the minimum horizontal distance between the work chamber rear wall and the front wall.
11. A biological safety cabinet comprising wall means defining a work chamber having an access opening, the above mentioned means comprising front wall edge por-tions defining an access opening upper edge and an access opening lower edge, a work chamber rear wall rearwardly remote from the said front wall edge portions, said work chamber rear wall having an outlet opening to the work chamber, a work chamber bottom wall extending from adja-cent said access opening lower edge to the work chamber rear wall, said work chamber bottom wall having an outlet adjacent the access opening lower edge and remote from the work chamber rear wall opening to the work chamber, means defining a cabinet discharge outlet, a viewing window mounted for closing at least an upper part of the access opening and having a surface exterior of the work chamber and the cabinet and a lower edge portion, means mounted exterior of the work chamber and adjacent the viewing win-dow for discharging air under pressure across the access opening downwardly toward the access opening lower edge, a blower having an inlet and an outlet, and means joined to the cabinet discharge outlet means, the work chamber de-fining means and the blower outlet to in conjunction there-with place at least the rear wall outlet in fluid communi-cation with cabinet discharge outlet to discharge air there-through, and the blower in fluid communication with the work chamber to draw air that is discharged by the means for dis-charging air under pressure downwardly toward the access opening lower edge through the access opening into the work chamber and through the work chamber bottom wall outlet and discharge HEPA filtered air into the work chamber remote from the work chamber outlets to flow at least initially downwardly to the work chamber outlets.
12. The apparatus of claim 11 further characterized in that the means for discharging air under pressure toward the access opening lower edge includes an air nozzle and means connected to the air nozzle for supplying air under pressure to the air nozzle.
13. The apparatus of claim 12 further characterized in that air nozzle is mounted on the window lower edge por-tion.
14. The apparatus of claim 12 further characterized in that the air nozzle is mounted adjacent the access open-ing upper edge to discharge air to flow along the window ex-terior surface downwardly toward the access opening lower edge.
15. The apparatus of claim 11 further characterized in that the means acting in conjunction includes a cabinet front wall that in part constitutes part of the wall means and has the access opening therein, a cabinet top wall that includes the cabinet discharge outlet means, a cabinet bot-tom wall and cabinet side walls, the cabinet walls being joined together to form an enclosure in which the blower is located.
16. The apparatus of claim 15 further characterized in that the wall means includes wall portions defining a work chamber top pressurized air inlet and that the means acting in conjunction includes a HEPA filter extended across the top inlet.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US86058777A | 1977-12-14 | 1977-12-14 | |
| US860,587 | 1977-12-14 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1126566A true CA1126566A (en) | 1982-06-29 |
Family
ID=25333549
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA317,396A Expired CA1126566A (en) | 1977-12-14 | 1978-12-05 | Biological safety cabinet having jet air inflow barrier |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1126566A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6089970A (en) * | 1997-11-24 | 2000-07-18 | The Regents Of The University Of California | Energy efficient laboratory fume hood |
| US6428408B1 (en) | 2000-05-18 | 2002-08-06 | The Regents Of The University Of California | Low flow fume hood |
-
1978
- 1978-12-05 CA CA317,396A patent/CA1126566A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6089970A (en) * | 1997-11-24 | 2000-07-18 | The Regents Of The University Of California | Energy efficient laboratory fume hood |
| US6428408B1 (en) | 2000-05-18 | 2002-08-06 | The Regents Of The University Of California | Low flow fume hood |
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| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |