CA1102609A - Total exhaust laminar flow biological fume hood safety cabinet and method - Google Patents
Total exhaust laminar flow biological fume hood safety cabinet and methodInfo
- Publication number
- CA1102609A CA1102609A CA299,395A CA299395A CA1102609A CA 1102609 A CA1102609 A CA 1102609A CA 299395 A CA299395 A CA 299395A CA 1102609 A CA1102609 A CA 1102609A
- Authority
- CA
- Canada
- Prior art keywords
- air
- worktray
- exhaust
- makeup
- blower
- 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.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B08—CLEANING
- B08B—CLEANING IN GENERAL; PREVENTION OF FOULING IN GENERAL
- B08B15/00—Preventing escape of dirt or fumes from the area where they are produced; Collecting or removing dirt or fumes from that area
- B08B15/02—Preventing escape of dirt or fumes from the area where they are produced; Collecting or removing dirt or fumes from that area using chambers or hoods covering the area
- B08B15/023—Fume cabinets or cupboards, e.g. for laboratories
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B08—CLEANING
- B08B—CLEANING IN GENERAL; PREVENTION OF FOULING IN GENERAL
- B08B2215/00—Preventing escape of dirt or fumes from the area where they are produced; Collecting or removing dirt or fumes from that area
- B08B2215/003—Preventing escape of dirt or fumes from the area where they are produced; Collecting or removing dirt or fumes from that area with the assistance of blowing nozzles
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S55/00—Gas separation
- Y10S55/18—Work bench
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S55/00—Gas separation
- Y10S55/29—Air curtains
Abstract
ABSTRACT OF THE DISCLOSURE
A total exhaust laminar flow biological fume hood safety cabinet is disclosed having a closed housing with a viewing panel and access port therebetween at its front portion.
Centrally a work tray is mounted with means permitting air passage thereabout. A plenum chamber connects the lower portion of the housing to the top, and an exhaust blower in closed pneumatic communication with the plenum delivers contaminated air to an exhaust filter for total exhaust. Makeup air means are provided at the upper portion of the housing to deliver filtered air downwardly over the work tray, and the blower capacities, flow rates, and filter capacitites are developed to the end that the air passing through the access port exceeds the quantity of filtered makeup air while providing for an access air velocity at least double that of the makeup air velocity.
A total exhaust laminar flow biological fume hood safety cabinet is disclosed having a closed housing with a viewing panel and access port therebetween at its front portion.
Centrally a work tray is mounted with means permitting air passage thereabout. A plenum chamber connects the lower portion of the housing to the top, and an exhaust blower in closed pneumatic communication with the plenum delivers contaminated air to an exhaust filter for total exhaust. Makeup air means are provided at the upper portion of the housing to deliver filtered air downwardly over the work tray, and the blower capacities, flow rates, and filter capacitites are developed to the end that the air passing through the access port exceeds the quantity of filtered makeup air while providing for an access air velocity at least double that of the makeup air velocity.
Description
2~g FIELD OF THE IN~ENTION
The subject invention is directe~ primarily to the handling of various biological specimens for examination in a laboratory. Particularly carcinogeous type material, or other toxic materials may be processed in the subject unit, by a trained patholo~ist or laboratory technician. In addition, the subject inven-tion is directed to a cabinet of this character in which total exhaust is achieved, thereby eliminating the possibility of explosive type material such as ether being recirculated over the work tray.
~` SUMMARY OF THE PRIOR ART
The prior ar-t is illustrated in J. J. Land~, United States Patent No. 3,926,597, and also in devices such as that manufactured by Contamination Control, Incorporated, of Rulpsville, Pennsylvania. While both devices are capable of providing a ~;~ degree of protection for the operator, they do not, because of the recirculating effect, virtually eliminate the possibility of an explosive environment existing interiorly of the cabinet.
Until the present time, the eq~ipment which is known has been limited to achieving one of the following objectives, but not all:
1. The protection of all personnel from exposure to potentially contagious particulate materials such as bacteria, viruses, parasites, fungi, etc., by the use of HEPA filters and an air curtain;
2. Establishment of a work area bathed with laminar flowing sterile area for the protection of materials being handled;
,
The subject invention is directe~ primarily to the handling of various biological specimens for examination in a laboratory. Particularly carcinogeous type material, or other toxic materials may be processed in the subject unit, by a trained patholo~ist or laboratory technician. In addition, the subject inven-tion is directed to a cabinet of this character in which total exhaust is achieved, thereby eliminating the possibility of explosive type material such as ether being recirculated over the work tray.
~` SUMMARY OF THE PRIOR ART
The prior ar-t is illustrated in J. J. Land~, United States Patent No. 3,926,597, and also in devices such as that manufactured by Contamination Control, Incorporated, of Rulpsville, Pennsylvania. While both devices are capable of providing a ~;~ degree of protection for the operator, they do not, because of the recirculating effect, virtually eliminate the possibility of an explosive environment existing interiorly of the cabinet.
Until the present time, the eq~ipment which is known has been limited to achieving one of the following objectives, but not all:
1. The protection of all personnel from exposure to potentially contagious particulate materials such as bacteria, viruses, parasites, fungi, etc., by the use of HEPA filters and an air curtain;
2. Establishment of a work area bathed with laminar flowing sterile area for the protection of materials being handled;
,
3. Protection of personnel from noxious fumes, poten-tial carcinogens, and ptential explosive liquids and~
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gases, as well as radioactive materials, by totally exhausting air from the chamber;
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gases, as well as radioactive materials, by totally exhausting air from the chamber;
4. Providing for free ingress and egress of the hands of the operator at all times through a partially open front.
The methoa and apparatus of the present invention seeks to satisfy all these results.
SUMMARY OF THE INVENTION
:.
The present invention is directed to a unidirectional, mass-displaced, laminar flow air bathed work area, which joins with ambient air entering the cabinet through an access port, at a sufficient linear velocity to provide for containment of airborne hazards within the unit. The ambient air is directed downwardly so that it does not pass over the workarea and cannot contaminate the work in progress. Provision is made for an exhaust blower at the lower portion of the unit, and an inlet air blower at the top, and an interconnection and intercontrol of the same to vary their speeds empirically to the end that the ratio between air moved by the lower or exhaust blower to the makeup air blower is greater than two to one.
A total exhaust laminar flow biological fume hood safety cabinet, according to the present invention comprises in combination:
- a closed housing having a viewing panel and access port therebeneath at its front poxtion;
- an interiorly mounted work tray;
- means for supporting the work tray and permitting air passage thereabout;
4~ :
- a plenum chamber from the lower portion of the housing to the top;
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- an exhaust blower Eor deli.vering positive pressure air to the plenum;
- an exhaust port at ~he upper yortion o:E the housing and plenum;
- makeup air means at the top of the housing dellvering air downwardly over the work tray; and - differentially powered motors and blowers for the makeup air and exhaust air wherein the air passiny through the access port exceeds the quantity of makeup air and where the access air~velocity is at least double -th~e makeup air - velocity, whereby contaminated air over the work tray~is inhibited from passage outwardly through the-access port and all air is discharged to exhaust.
method of purging a worktray for use in handling bio-hazardous and e~plosive materlals, accordiny -to the present invention comprises the steps of:
- positioning the worktray in a confined vertical space;
.- dellverying alr passing vertically downward and filtered of particulate matter over the worktray;
- providing a work opening alony one edye of the tray;
- beneath the worktray providiny a neyative pressure to draw -the ~iltered air over the work-tray and the makeup air over the worktray at one edge thereof adjacent the openiny;
- confining the air at the terminus of the negative pressure area ben~eath the worktray in a ver-tical path substantially parallel to the path of .the filtered air passing downwardly over the worktray;
- and applying positive pressure to the ai~ at the position beneath the worktray to deliver the same in lts confined path Vertlcally and opposed to the particulate filtered ai.r passiny _q_ :
downwardly over the worktray; and - filtering or otherwise purging the thus defined exhaustair passing vertically and thereafter passing the same to a remote environmen-t separate from the worktray.
DESCRIPTION OF ILLUSTRATIVE DRAWINGS
Further objects and advantages of the present invention will become apparent as the following description of an illustra-tive embodiment of the apparatus and method proceeds, taken in conjunction with the accompanying illustrative drawings in which:
FIGURE 1 is a perspective front view of an illustrative total exhaust laminar flow biological fume hood safety cabinet.
FIGURE 2 is a transverse sectional view taken through a mid-portion of the subject cabinet as shown in Figure 1, and looking towards the left-hand portion thereof, and also showing the viewing panel in phantom lines in its open posiion.
FIGURE 3 is a lateral section view from the interior of the subject cabinet taken generally along section line 3-3 of Figure 2, and in reduced scale therefrom.
DESCRIPTION OF PREFERRED ~ETHOD
Both the method and the apparatus of the invention will be better understood by first directing the description to the method. Essentially the method involves the purging of a worktray used for handling biohazardous as well as explosive materials. The worktray is first positioned in a confined vertical space, but with means for passing air around the periphery for the worktray. Thereafter air is delivered ~
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vertically downwardly and over the work tray, with particulate matter filtered from that air. The subjec-t air is "make~up"
type air.
In addition, a work opening is provide along one edge of the tray and over a pathway, the work opening being generally ; lateral to accommodate the lateral movement of the hands of the operator or technician. Beneath the work tray provision is made to achieve a negative pressure to draw the filtered air over the work tray, and yet to induce the make-up air over the work tray at one portion thereof to pass by -the work opening.
Because the negative pressure area beneath the work tray is confined in a vertical path, substantially parallel to the path of the filtered air, and since the ratio provided is at least two to one the flow rate of the make-up air, the ambient air passing through the work tray opening is constantly under a ; negative pressure, and therefore passes inwardly, shielding the make-up filtered air from passing outwardly after the same has been in contact with the material on the work tray. Thereafter the combination of work tray opening air as well as make-up air is the subject of positive pressure and delivered in a con-fined pathway vertically to an exhaust area, which subsequently is subjected to -the further step of filtering the same. The net result/ of course, is to thus, provide for filtered air to pass over the work tray, and yet have access for the hands of the operator, through an area accessible to ambient, and yet dictate the result of all of the air passing outwardly to a total exhuast from the area above the work tray. Since the work tray may include biohazardous materials, such as carcino-geous materials as well as emit noxious or explosive fumes, the provision for 100% total exhaust eliminates the possibility of such materials re-entering the area above the work tray.
Furthermore, in order to "fail safe" the unit, the means for providing the exhaust and the maximum negative pressure beneath ;:
the-worktray are coordinated witll the means for deliv~rillg in-; let air, to the end that if the exhaust means Eail, the balance of the unit ceases operation and decontamination may begin.
While the ratio of air flow of two to one between the exhaus-t and the makeup air has been set forth above, a ratio of three to one optimiæes results. Ratios of less than two to one can cause the risk, particularly depending upon the motion of the arms and the hands of the operator, of some of the contaminated air over the worktray hitting the arms or hands and being deflected outwardly through the work access port. By providing for variable ratios between the pressures and flow-rates, the same can be adjusted empirically by the use of smoke or other detectors, for each particular operation -to insure ayainst contamination to the ambient environment, and the operator utilizlng the method.
DESCRIPTION OF PREFERRED E~BODIMENT
Turning now to the accompanying drawings, it will be observed in FIGURE 1 that the total exhaust laminar flow biological fume hood safety cabinet 10 is provided with a transparent viewing panel 11 in its front portion. Beneath the transparent viewing panel ll is an access por-t 14, shown as ; a transverse narrow open rectangular portion. Beneath the access port 14j provision is made for a knee space 12, so that the operator sltting before the cabinet 10 can move close to the viewlng panel ll and the legs are not impeded by the ~; lower structure~
An exhaust filter assembly 15 appears a-t the upper portion of the cabinet 10. The cabinet I-tselE has a pair of opposed parallel end walls 16, a top 18, on which a frame l9 ~- for the exhaust filter 17 (shown in FIGURES 2 and 3) is mounted.
. .
' ', .
The make-up air is taken from ambient by means of -the make~up air blower 20, the same being powered by the make-up air blower motor 30. The entire unit is llluminated by means of the light housing 24, and its contained lights.
As noted in FIGURE 3, an exhaust plenum 21 is provided at the rear portion of the unit, delivering the air from the portion rearwardly of the knee wall 22 into the exhaust blower 25 which is provided by the exhaust blower motor 27. The thus exhausted air is passed through the exhaust HEPA filter 17, and thereafter either to an air incinerator, a further scrubbing unit, or to an exterior portion shielded from the operator of the subject cabinet 10.
Turning now to FIGURE 2, it will be seen that the work tray 28 is provided above a work tray support 29, the latter being perforated at its front rear portions, but imper-forate at its end portions. In addition to the work tray support 29, a spill pan 31 is provided beneath the work tray 28, and its attendant support 29, so that fluids spilling off of the work tray 28 are directed into the spill pan 31. ~t the front portion of the unit, immediately beneath the access port 14, provision is made for a spill pan support 32, which also connects the entire unit to the front of the cabinet, to the same degree that the spill pan 31 is connected to the rear portion or inter-mediate front of the plenum 21 at the rear portion of the work area.
The make-up air is passed into a make-up air HEPA
filter 35, immediately beneath the make-up air blower 20.
The same is secured in place by means of the frame 36 in which the make-up air filter 35 is mounted. In all instances, the filters 17, 35, are sealed in place, so that all of the air passing through the cabinet 10 is directed through the subject filters. In addition, to further isolate the air, a rear double wall 38 at the rear of the cabinet, as well as an inner double wall 39 are provided so that if there are any leaks from the positive pressure on the interior portion o the exhaust plen~un 21, the same will be recirculated and directed again to exhaust, and not passed interiorly into the work chamber 45.
To be noted in particular is the divider 40 which passes transversely across the upper portion of the cabinet 10, and divides the plenum chamber for the exhaust 21 from the make-up chamber 48 which is immediately above the makeup~HEPA filter 35. Completing the enclosure of the cabinet, as observed in FIGURE 2~ is the kneewall 22 provided at the rear portion of the knee space 12, and the base 42. In reviewing the basic elements, therefore, it will be seen that the makeup air passes through the makeup chamber 48 and then into the makeup air HEPA filter 35, thence into the work chamber 45, and thereafter into the exhaust chamber beneath the worktray 2 8. Once the exhaust chamber 46 is entered by the contaminated air, it is immediately picked up by the exhaust blower 25, and directed through the plenum changer 21, the exhaust filter 17, and thence to further processing dictated by the particular installation. Furthermore, both the rear 26 and the rear portion of the work chamber 45 are provided with double walls for additional safety.
In a typical successful commercial embodiment, the flow rate through the makeup chamber is approximately 300 cubic feet per minute. The flow rate through the access port 14, is bet-ween 450 and 500 cubic feet per minute. This provides a total exhaust of 750 to 800 cubic feet per minute passing through the exhaust filter 17. ~t the access panel 14, the area of the entire access panel being approximately 2.1 square feet, there is a 222 linear velocity per minute.
The unit is preferably constructed of a 304 stainless ~2~9 steel, althou~h an op-tional 316 or 316L s-tainless may be employed. The cabinet 10 is 53 inches wide, ~8 inches high, ancl 33 inches ~eep. The exhaus-t filter ]7 and frame 19 may be removed for installation purposes, as well as the makeup air blower 20. The exhaust filter is centered on the t~p wi-th its long axis parallel to the long ax~s of the unit. The exhaust filter itself is approximately 36 inches long, 12 inches wide and 11 1/2 inches deep. The filter conforms to Federal speci-; fications 20~B HEPA filters. To be notecl is the posi-tioning of both of the filters parallel to each other. The makeup air filter 35 is approximately 46 inches wide, 20 inches deep and ? nominal 3 lnches across the area through which the air flows.
The ~IEPA filters are substantially g9.99% efficient and, as pointed out above, attached with a positive seal.
The connection be-tween the exhaust motor 27, and the makeup air motor 30 is such that in the event of the failure or reduction in speed of the exhaust motor 27 in comparison to the makeup air motor 30, an alarm is sounded, and the en-tire unit shut-down for decontamination. Preferably, the shut-down is sequential with the makeup air motor 30 being disengaged first, and thereafter the exhaust motor 27.
In review it will be seen that the principle of the operation of the method, as well as the apparatus, is to define a unidirectional, mass-displaced laminar flow of air which bathes the work area with ultra clean air passing through the makeup air HEPA filter 35 first. Thereafter, the makeup air joins the amblent air passing through the access port 14, and entering at sufficlent linear velocity to provide for con-tainment of airborne ha2ards within the ~ork chamber 45. The 30 ~ ambient air is then directed downwardly so that lt does not pass .
, over tlle work area and cannot contamillate wor~ in ~)rog:ress.
A 100~ exhaust of all air flowing -throucJIl the cabinet without any recircula-tion is directed by means of the exhaust plenum 21 to the exhaust filter assembly 15. Further provision can be made to purify the exhausted air by pclssing it throuyh charcoal or other absorbents, chemical. scrubbers, air incinera-tors, and the like. Otherwise, duc-ting proceduresmay he directed by the particular ma-terials being handled in -the hood.
. The differential between -the blower motor capacity, and filter capacities is controlled to the end that the air flow cubic rate through the access port 14 is optimally 15~% of the air flow -through the makeup ai.r filter. Cn the other hand, the velocity of the makeup air is approxima-tely 50 feet per minu-te, whereas at leas-t 150 feet per minute velocity is provicled through the access port 14. The air thereafter passes through the perforated portion of the tray support 29, the same being per-forated to substan-tially 50% of its surface. The speed rates of the two blowers 20, 25 are controlled empirically, but normally to achieve the ratios set for-th hereinabove. In additionl smoke or other control procedures can be employed to adjust the flow ra-tes wi-th precision to -the particular opera-tor and the work being processed. In addition, an anemometer or pitot tube may be placed within the uni-t -to constantly monitor the flow rates, irrespective of the speeds of the inlet air motor 30 and the exhaust air motor 27.
Materials such as high grade stainless steel have : been referenced for cons-truc-tion, it will be appreciated that other materials such as fiberglass, polypropylene, and other imperforate substitutes may be employed. ~xplosion proof motors are preferable, where an explsoive invironment is con-- templated. In the event duct work is used coupled to the exhaust fil-ter assembly lS, a furtiler blower downstream oE the same is required, to constantly accelerate the removal of any exploslve or other hazardous materials.
~lthough particular embodiments of the invention have been shown and déscribed in fu]l here, -there is no in-ten-tion to thereby limit the invention -to the details of such embodiments. On -the contrary, the intention is to cover all modifications, alternatives, embodiments, usa~es and equivalents of a total exhaus-t laminar ;Elow biological fume hood safety .
cabinet and me-thod as fall within the scope of the invention, specification and appended claims.
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The methoa and apparatus of the present invention seeks to satisfy all these results.
SUMMARY OF THE INVENTION
:.
The present invention is directed to a unidirectional, mass-displaced, laminar flow air bathed work area, which joins with ambient air entering the cabinet through an access port, at a sufficient linear velocity to provide for containment of airborne hazards within the unit. The ambient air is directed downwardly so that it does not pass over the workarea and cannot contaminate the work in progress. Provision is made for an exhaust blower at the lower portion of the unit, and an inlet air blower at the top, and an interconnection and intercontrol of the same to vary their speeds empirically to the end that the ratio between air moved by the lower or exhaust blower to the makeup air blower is greater than two to one.
A total exhaust laminar flow biological fume hood safety cabinet, according to the present invention comprises in combination:
- a closed housing having a viewing panel and access port therebeneath at its front poxtion;
- an interiorly mounted work tray;
- means for supporting the work tray and permitting air passage thereabout;
4~ :
- a plenum chamber from the lower portion of the housing to the top;
~, .
,: , . . .
r~
- an exhaust blower Eor deli.vering positive pressure air to the plenum;
- an exhaust port at ~he upper yortion o:E the housing and plenum;
- makeup air means at the top of the housing dellvering air downwardly over the work tray; and - differentially powered motors and blowers for the makeup air and exhaust air wherein the air passiny through the access port exceeds the quantity of makeup air and where the access air~velocity is at least double -th~e makeup air - velocity, whereby contaminated air over the work tray~is inhibited from passage outwardly through the-access port and all air is discharged to exhaust.
method of purging a worktray for use in handling bio-hazardous and e~plosive materlals, accordiny -to the present invention comprises the steps of:
- positioning the worktray in a confined vertical space;
.- dellverying alr passing vertically downward and filtered of particulate matter over the worktray;
- providing a work opening alony one edye of the tray;
- beneath the worktray providiny a neyative pressure to draw -the ~iltered air over the work-tray and the makeup air over the worktray at one edge thereof adjacent the openiny;
- confining the air at the terminus of the negative pressure area ben~eath the worktray in a ver-tical path substantially parallel to the path of .the filtered air passing downwardly over the worktray;
- and applying positive pressure to the ai~ at the position beneath the worktray to deliver the same in lts confined path Vertlcally and opposed to the particulate filtered ai.r passiny _q_ :
downwardly over the worktray; and - filtering or otherwise purging the thus defined exhaustair passing vertically and thereafter passing the same to a remote environmen-t separate from the worktray.
DESCRIPTION OF ILLUSTRATIVE DRAWINGS
Further objects and advantages of the present invention will become apparent as the following description of an illustra-tive embodiment of the apparatus and method proceeds, taken in conjunction with the accompanying illustrative drawings in which:
FIGURE 1 is a perspective front view of an illustrative total exhaust laminar flow biological fume hood safety cabinet.
FIGURE 2 is a transverse sectional view taken through a mid-portion of the subject cabinet as shown in Figure 1, and looking towards the left-hand portion thereof, and also showing the viewing panel in phantom lines in its open posiion.
FIGURE 3 is a lateral section view from the interior of the subject cabinet taken generally along section line 3-3 of Figure 2, and in reduced scale therefrom.
DESCRIPTION OF PREFERRED ~ETHOD
Both the method and the apparatus of the invention will be better understood by first directing the description to the method. Essentially the method involves the purging of a worktray used for handling biohazardous as well as explosive materials. The worktray is first positioned in a confined vertical space, but with means for passing air around the periphery for the worktray. Thereafter air is delivered ~
;' S
. ~ :
6~i~
vertically downwardly and over the work tray, with particulate matter filtered from that air. The subjec-t air is "make~up"
type air.
In addition, a work opening is provide along one edge of the tray and over a pathway, the work opening being generally ; lateral to accommodate the lateral movement of the hands of the operator or technician. Beneath the work tray provision is made to achieve a negative pressure to draw the filtered air over the work tray, and yet to induce the make-up air over the work tray at one portion thereof to pass by -the work opening.
Because the negative pressure area beneath the work tray is confined in a vertical path, substantially parallel to the path of the filtered air, and since the ratio provided is at least two to one the flow rate of the make-up air, the ambient air passing through the work tray opening is constantly under a ; negative pressure, and therefore passes inwardly, shielding the make-up filtered air from passing outwardly after the same has been in contact with the material on the work tray. Thereafter the combination of work tray opening air as well as make-up air is the subject of positive pressure and delivered in a con-fined pathway vertically to an exhaust area, which subsequently is subjected to -the further step of filtering the same. The net result/ of course, is to thus, provide for filtered air to pass over the work tray, and yet have access for the hands of the operator, through an area accessible to ambient, and yet dictate the result of all of the air passing outwardly to a total exhuast from the area above the work tray. Since the work tray may include biohazardous materials, such as carcino-geous materials as well as emit noxious or explosive fumes, the provision for 100% total exhaust eliminates the possibility of such materials re-entering the area above the work tray.
Furthermore, in order to "fail safe" the unit, the means for providing the exhaust and the maximum negative pressure beneath ;:
the-worktray are coordinated witll the means for deliv~rillg in-; let air, to the end that if the exhaust means Eail, the balance of the unit ceases operation and decontamination may begin.
While the ratio of air flow of two to one between the exhaus-t and the makeup air has been set forth above, a ratio of three to one optimiæes results. Ratios of less than two to one can cause the risk, particularly depending upon the motion of the arms and the hands of the operator, of some of the contaminated air over the worktray hitting the arms or hands and being deflected outwardly through the work access port. By providing for variable ratios between the pressures and flow-rates, the same can be adjusted empirically by the use of smoke or other detectors, for each particular operation -to insure ayainst contamination to the ambient environment, and the operator utilizlng the method.
DESCRIPTION OF PREFERRED E~BODIMENT
Turning now to the accompanying drawings, it will be observed in FIGURE 1 that the total exhaust laminar flow biological fume hood safety cabinet 10 is provided with a transparent viewing panel 11 in its front portion. Beneath the transparent viewing panel ll is an access por-t 14, shown as ; a transverse narrow open rectangular portion. Beneath the access port 14j provision is made for a knee space 12, so that the operator sltting before the cabinet 10 can move close to the viewlng panel ll and the legs are not impeded by the ~; lower structure~
An exhaust filter assembly 15 appears a-t the upper portion of the cabinet 10. The cabinet I-tselE has a pair of opposed parallel end walls 16, a top 18, on which a frame l9 ~- for the exhaust filter 17 (shown in FIGURES 2 and 3) is mounted.
. .
' ', .
The make-up air is taken from ambient by means of -the make~up air blower 20, the same being powered by the make-up air blower motor 30. The entire unit is llluminated by means of the light housing 24, and its contained lights.
As noted in FIGURE 3, an exhaust plenum 21 is provided at the rear portion of the unit, delivering the air from the portion rearwardly of the knee wall 22 into the exhaust blower 25 which is provided by the exhaust blower motor 27. The thus exhausted air is passed through the exhaust HEPA filter 17, and thereafter either to an air incinerator, a further scrubbing unit, or to an exterior portion shielded from the operator of the subject cabinet 10.
Turning now to FIGURE 2, it will be seen that the work tray 28 is provided above a work tray support 29, the latter being perforated at its front rear portions, but imper-forate at its end portions. In addition to the work tray support 29, a spill pan 31 is provided beneath the work tray 28, and its attendant support 29, so that fluids spilling off of the work tray 28 are directed into the spill pan 31. ~t the front portion of the unit, immediately beneath the access port 14, provision is made for a spill pan support 32, which also connects the entire unit to the front of the cabinet, to the same degree that the spill pan 31 is connected to the rear portion or inter-mediate front of the plenum 21 at the rear portion of the work area.
The make-up air is passed into a make-up air HEPA
filter 35, immediately beneath the make-up air blower 20.
The same is secured in place by means of the frame 36 in which the make-up air filter 35 is mounted. In all instances, the filters 17, 35, are sealed in place, so that all of the air passing through the cabinet 10 is directed through the subject filters. In addition, to further isolate the air, a rear double wall 38 at the rear of the cabinet, as well as an inner double wall 39 are provided so that if there are any leaks from the positive pressure on the interior portion o the exhaust plen~un 21, the same will be recirculated and directed again to exhaust, and not passed interiorly into the work chamber 45.
To be noted in particular is the divider 40 which passes transversely across the upper portion of the cabinet 10, and divides the plenum chamber for the exhaust 21 from the make-up chamber 48 which is immediately above the makeup~HEPA filter 35. Completing the enclosure of the cabinet, as observed in FIGURE 2~ is the kneewall 22 provided at the rear portion of the knee space 12, and the base 42. In reviewing the basic elements, therefore, it will be seen that the makeup air passes through the makeup chamber 48 and then into the makeup air HEPA filter 35, thence into the work chamber 45, and thereafter into the exhaust chamber beneath the worktray 2 8. Once the exhaust chamber 46 is entered by the contaminated air, it is immediately picked up by the exhaust blower 25, and directed through the plenum changer 21, the exhaust filter 17, and thence to further processing dictated by the particular installation. Furthermore, both the rear 26 and the rear portion of the work chamber 45 are provided with double walls for additional safety.
In a typical successful commercial embodiment, the flow rate through the makeup chamber is approximately 300 cubic feet per minute. The flow rate through the access port 14, is bet-ween 450 and 500 cubic feet per minute. This provides a total exhaust of 750 to 800 cubic feet per minute passing through the exhaust filter 17. ~t the access panel 14, the area of the entire access panel being approximately 2.1 square feet, there is a 222 linear velocity per minute.
The unit is preferably constructed of a 304 stainless ~2~9 steel, althou~h an op-tional 316 or 316L s-tainless may be employed. The cabinet 10 is 53 inches wide, ~8 inches high, ancl 33 inches ~eep. The exhaus-t filter ]7 and frame 19 may be removed for installation purposes, as well as the makeup air blower 20. The exhaust filter is centered on the t~p wi-th its long axis parallel to the long ax~s of the unit. The exhaust filter itself is approximately 36 inches long, 12 inches wide and 11 1/2 inches deep. The filter conforms to Federal speci-; fications 20~B HEPA filters. To be notecl is the posi-tioning of both of the filters parallel to each other. The makeup air filter 35 is approximately 46 inches wide, 20 inches deep and ? nominal 3 lnches across the area through which the air flows.
The ~IEPA filters are substantially g9.99% efficient and, as pointed out above, attached with a positive seal.
The connection be-tween the exhaust motor 27, and the makeup air motor 30 is such that in the event of the failure or reduction in speed of the exhaust motor 27 in comparison to the makeup air motor 30, an alarm is sounded, and the en-tire unit shut-down for decontamination. Preferably, the shut-down is sequential with the makeup air motor 30 being disengaged first, and thereafter the exhaust motor 27.
In review it will be seen that the principle of the operation of the method, as well as the apparatus, is to define a unidirectional, mass-displaced laminar flow of air which bathes the work area with ultra clean air passing through the makeup air HEPA filter 35 first. Thereafter, the makeup air joins the amblent air passing through the access port 14, and entering at sufficlent linear velocity to provide for con-tainment of airborne ha2ards within the ~ork chamber 45. The 30 ~ ambient air is then directed downwardly so that lt does not pass .
, over tlle work area and cannot contamillate wor~ in ~)rog:ress.
A 100~ exhaust of all air flowing -throucJIl the cabinet without any recircula-tion is directed by means of the exhaust plenum 21 to the exhaust filter assembly 15. Further provision can be made to purify the exhausted air by pclssing it throuyh charcoal or other absorbents, chemical. scrubbers, air incinera-tors, and the like. Otherwise, duc-ting proceduresmay he directed by the particular ma-terials being handled in -the hood.
. The differential between -the blower motor capacity, and filter capacities is controlled to the end that the air flow cubic rate through the access port 14 is optimally 15~% of the air flow -through the makeup ai.r filter. Cn the other hand, the velocity of the makeup air is approxima-tely 50 feet per minu-te, whereas at leas-t 150 feet per minute velocity is provicled through the access port 14. The air thereafter passes through the perforated portion of the tray support 29, the same being per-forated to substan-tially 50% of its surface. The speed rates of the two blowers 20, 25 are controlled empirically, but normally to achieve the ratios set for-th hereinabove. In additionl smoke or other control procedures can be employed to adjust the flow ra-tes wi-th precision to -the particular opera-tor and the work being processed. In addition, an anemometer or pitot tube may be placed within the uni-t -to constantly monitor the flow rates, irrespective of the speeds of the inlet air motor 30 and the exhaust air motor 27.
Materials such as high grade stainless steel have : been referenced for cons-truc-tion, it will be appreciated that other materials such as fiberglass, polypropylene, and other imperforate substitutes may be employed. ~xplosion proof motors are preferable, where an explsoive invironment is con-- templated. In the event duct work is used coupled to the exhaust fil-ter assembly lS, a furtiler blower downstream oE the same is required, to constantly accelerate the removal of any exploslve or other hazardous materials.
~lthough particular embodiments of the invention have been shown and déscribed in fu]l here, -there is no in-ten-tion to thereby limit the invention -to the details of such embodiments. On -the contrary, the intention is to cover all modifications, alternatives, embodiments, usa~es and equivalents of a total exhaus-t laminar ;Elow biological fume hood safety .
cabinet and me-thod as fall within the scope of the invention, specification and appended claims.
~ ' '^
;~. $ ~' ' ' '' ~, .
i30
Claims (11)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A total exhaust laminar flow biological fume hood safety cabinet comprising, in combination, a closed housing having a viewing panel and access port therebeneath at its front portion;
an interiorly mounted worktray; means for supporting the worktray and permitting air passage thereabout; a plenum chamber from the lower portion of the housing to the top; an exhaust blower for delivering positive pressure air to the plenum; an exhaust port at the upper portion of the housing and plenum; makeup air means at the top of the housing delivering air downwardly over the worktray; and differentially powered motors and blowers for the makeup air and exhaust air wherein the air passing through the access port exceeds the quantity of makeup air and where the access air velocity is at least double the makeup air velocity, whereby contaminated air over the worktray is inhibited from passage outwardly through the access port and all air is discharged to exhaust.
an interiorly mounted worktray; means for supporting the worktray and permitting air passage thereabout; a plenum chamber from the lower portion of the housing to the top; an exhaust blower for delivering positive pressure air to the plenum; an exhaust port at the upper portion of the housing and plenum; makeup air means at the top of the housing delivering air downwardly over the worktray; and differentially powered motors and blowers for the makeup air and exhaust air wherein the air passing through the access port exceeds the quantity of makeup air and where the access air velocity is at least double the makeup air velocity, whereby contaminated air over the worktray is inhibited from passage outwardly through the access port and all air is discharged to exhaust.
2. In the cabinet of Claim 1, a diagonal divider between the plenum and the area beneath the makeup air means, whereby makeup air and exhaust filters may be positioned above the worktray.
3. In the cabinet of Claim 1, perforations in the worktray support approximating one-half the area of the front and rear thereof, the ends being inperforate.
4. In the cabinet of Claim 1, switching means between the exhaust blower and makeup air blower to close down both blowers when the exhaust blower velocity decreases below a predetermined ratio with the makeup air blower.
5. In the cabinet of Claim 2, perforations in the worktray support approximating one-half the area of the front and rear thereof, the ends being imperforate.
6. In the cabinet of Claim 2, switching means between the exhaust blower and makeup air blower to close down both blowers when the exhaust blower velocity decreases below a predetermined ratio with the makeup air blower.
7. In the cabinet of Claim 3, switching means between the exhaust blower and makeup air blower to close down both blowers when the exhaust blower velocity decreases below a predetermined ratio with the makeup blower.
8. A method of purging a worktray for use in handling bio-hazardous and explosive materials, comprising the steps of:
positioning the worktray in a confined vertical space; delivering makeup air passing vertically downward and filtered of particulate matter over the worktray; providing a work opening along one edge of the tray to admit access port air; beneath the worktray providing a negative pressure to draw the makeup air over the worktray and the access port air over the worktray at one edge thereof adjacent the opening; confining the air at the terminus of the negative pressure area beneath the worktray in a vertical exhaust air path substantially parallel to the path of the filtered air passing downwardly over the worktray; and applying positive pressure to the exhaust air at the position beneath the worktray to deliver the same in its confined path vertically and opposed to the particulate filtered air passing downwardly over the worktray; and filtering or otherwise purging the thus defined exhaust air passing vertically and thereafter passing the same to a remote environment separate from the worktray.
positioning the worktray in a confined vertical space; delivering makeup air passing vertically downward and filtered of particulate matter over the worktray; providing a work opening along one edge of the tray to admit access port air; beneath the worktray providing a negative pressure to draw the makeup air over the worktray and the access port air over the worktray at one edge thereof adjacent the opening; confining the air at the terminus of the negative pressure area beneath the worktray in a vertical exhaust air path substantially parallel to the path of the filtered air passing downwardly over the worktray; and applying positive pressure to the exhaust air at the position beneath the worktray to deliver the same in its confined path vertically and opposed to the particulate filtered air passing downwardly over the worktray; and filtering or otherwise purging the thus defined exhaust air passing vertically and thereafter passing the same to a remote environment separate from the worktray.
9. In the method of Claim 8, proportioning the air velocity to at least two to one between the access port air and the makeup air.
10. In the method of Claim 8, proportioning the air volume so that the access port air is at least 50% of the volume of the makeup air.
11. In the method of Claim 9, proportioning the air velocity so that the access port air velocity is at least 150% of the makeup air velocity.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US675,257 | 1976-04-08 | ||
| US05/675,257 US4098174A (en) | 1976-04-08 | 1976-04-08 | Total exhaust laminar flow biological fume hood safety cabinet and method |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1102609A true CA1102609A (en) | 1981-06-09 |
Family
ID=24709700
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA299,395A Expired CA1102609A (en) | 1976-04-08 | 1978-03-21 | Total exhaust laminar flow biological fume hood safety cabinet and method |
Country Status (6)
| Country | Link |
|---|---|
| US (1) | US4098174A (en) |
| JP (2) | JPS52126281A (en) |
| CA (1) | CA1102609A (en) |
| DE (1) | DE2716317A1 (en) |
| FR (1) | FR2347115A1 (en) |
| GB (1) | GB1530867A (en) |
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| US10376936B2 (en) * | 2016-06-21 | 2019-08-13 | Gurmeet Singh | Method and apparatus of optimizing performance of fume hoods |
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| KR102012962B1 (en) * | 2017-11-24 | 2019-08-21 | 최진선 | Fume hood |
| KR102139249B1 (en) * | 2018-04-03 | 2020-07-29 | 우범제 | EFEM, Equipment Front End Module |
| JP6875320B2 (en) * | 2018-04-24 | 2021-05-19 | 株式会社日立産機システム | Safety cabinet |
| JP7116953B2 (en) * | 2018-06-12 | 2022-08-12 | 株式会社ゲンダイプラント | push-pull unit |
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| US3000292A (en) * | 1958-01-23 | 1961-09-19 | Norbute Corp | Fume hood |
| US3273323A (en) * | 1963-12-24 | 1966-09-20 | Willis J Whitfield | Laminar flow air hood apparatus |
| US3340788A (en) * | 1966-02-28 | 1967-09-12 | Lab Construction Company | Fume hood including air deflecting baffle |
| US3811250A (en) * | 1971-12-15 | 1974-05-21 | Becton Dickinson Co | Contamination control apparatus |
| NL7215945A (en) * | 1972-11-24 | 1974-05-28 | ||
| US3926597A (en) * | 1973-01-26 | 1975-12-16 | Jerome J Landy | Cabinet for biohazardous materials |
-
1976
- 1976-04-08 US US05/675,257 patent/US4098174A/en not_active Expired - Lifetime
-
1977
- 1977-03-30 GB GB13403/77A patent/GB1530867A/en not_active Expired
- 1977-04-07 FR FR7710671A patent/FR2347115A1/en active Granted
- 1977-04-07 DE DE19772716317 patent/DE2716317A1/en active Granted
- 1977-04-08 JP JP4023177A patent/JPS52126281A/en active Pending
-
1978
- 1978-03-21 CA CA299,395A patent/CA1102609A/en not_active Expired
-
1985
- 1985-03-13 JP JP1985034750U patent/JPS60168545U/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| FR2347115B1 (en) | 1984-04-27 |
| FR2347115A1 (en) | 1977-11-04 |
| JPS60168545U (en) | 1985-11-08 |
| JPS52126281A (en) | 1977-10-22 |
| GB1530867A (en) | 1978-11-01 |
| DE2716317A1 (en) | 1977-10-27 |
| US4098174A (en) | 1978-07-04 |
| DE2716317C2 (en) | 1987-08-06 |
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