US 3811250 A
The contamination control apparatus of this invention includes a hollow cabinet having a work area in one portion thereof and an opening therein permitting access to the work area from the exterior of the cabinet. Decontamination and air supply means are in the cabinet and positioned so that air discharge therefrom will be decontaminated and then passed into the work area. Diffusion means are mounted in the cabinet and positioned between the decontamination and supply means and the work area to facilitate the diffusion of the air as it enters the work area. Consequently, the air flows uniformly through the work area and assist in providing a clean air curtain over the access opening to the work area to facilitate the prevention of contaminated air from leaving or entering the work area through the access opening. A series of interconnected air plenum chambers are in the cabinet in communication with the work area, decontamination and air supply means, and the opening to the exterior of the cabinet to permit the air passing through the work area and a portion of air from outside of the cabinet to be directed to the decontamination and air supply means. Negative pressure reducing means are in the cabinet to direct a predetermined amount of decontaminated air out of the cabinet sufficient to maintain a lesser pressure within the cabinet and exteriorly thereof and, finally, air velocity indicator and control means are mounted on the cabinet to facilitate the control of air flow within the cabinet.
Claims available in
Description (OCR text may contain errors)
United States Patent 1191 Fowler, Jr.
[111 3,811,250 1451 May .21, 1974 CONTAMINATION CONTROL APPARATUS  Inventor: James McFarland Fowler, Jr.,
Albuquerque, N. Mex.
 Assignee: Bect'on, Dickinson and Company,
' East Rutherford, NJ.
1221 Filed: Apr. '25, 1973- 21 Appl. No.: 354,217
Related US. Application Data  Division of Ser. No. 208,454, Dec. 15, 1971, which is a continuation of Ser. No. 839,967, July 8, 1969,
 U.S. Cl 55/274, 55/473, 55/DlG. 29,
98/ 115 LH  Int. Cl.....; B01d 31/00  Field 61 Search 55/467; 470-472, 55/473, 274, DIG. 29; 98/115 LH; 62/256; 73/212; 417/43  I References Cited 3 Primary Examiner-Bernard Nozick Attorney, Agent, or Firm-Kane, Dalsimer, Kane,
Sullivan and Kurucz [571 9 ABSTRACT The contamination control apparatus of this invention includes a hollow cabinet having a work area in one portion thereof and an opening therein permitting access to the work area from the exterior of the cabinet. Decontamination and air supply means are in the cabinet and positioned so that air discharge therefrom will be decontaminated and then passed into the work area. Diffusion means are mounted in the cabinet and positioned between the decontamination and supply means and the work area to facilitate the diffusion of the air as it enters the work area. Consequently, the air flows uniformly-through the work area and assist in providing a clean air curtain over the access opening to the work area to facilitate the prevention of contaminated air from leaving orentering the work area through the access opening. A series of interconnected air plenum chambers are in the cabinet inacommunication with the work area, decontamination and air supply means, and the opening to the exterior of the cabinet to permit the air passing through the work area and av portion of air from outside of the cabinet to be directed to the decontamination and air supply means. Negative pressure reducing means. are in the cabinet to direct a predetermined amount of decontaminated air out of the cabinet sufficient to maintain a lesser pressure within the cabinet and exteriorly thereof and, finally, air velocity indicator and control means are mounted on the'cabinet to facilitate the control of air flow within the cabinet.
8' Claims, 6 Drawing'Fig ures minnow m4 3.811.250
SHEET 2 OF 4 F/G.Z
1 CONTAMINATION CONTROL APPARATUS BACKGROUND OF THE INVENTION When working in a biological environment it is extremely advantageous to provide means for controlling airborne contamination. In. addition to being able to control airborne contamination within the work area it is also particularly usefulto provide easy access to the work area so that normal and efficient operation withinthe area can be carried out. So, it is valuable to the art to be able to contain the work area within a protected atmosphere while simultaneously permitting easy access to the work area to carry out whatever functions are necessary within the area. Naturally, it is desirable to provide both protection against contamination from the exterior of the work area as well as protection against contaminating media from escaping from the confined work area into the surrounding atmosphere. In short, it is desirable to control the airborne contamination in a biological work environment by both preventing the ambient aerosols from contaminating a work sample and also preventing contaminating aerosols from escaping from the work sample into the surrounding environment.
A suggested method for accomplishing these objectives is to provide a cabinet to generally contain a work area and the work sample therein while providing an access means for a workman to handle the work sample. Simultaneously, a laminar flow environment is provided in the cabinet to provide an air curtain over the access means to prevent cross flow of aerosols between the work area and the exterior of the cabinet.
It is naturally advantageous to provide the most efficient means of insuring that no cross contamination occurs and by providing close control over the laminar flow air barrier provided by the cabinet arrangement. Therefore. control means which facilitates the control of the flow and the particular atmosphere and pressure within a contamination control cabinet would also be extremely advantageousto the art.
Naturally, the best possible protection and the most efficient and accurate working conditions should be provided when working in the presence of possible contamination produced by air flow. An apparatus which provides close control over the laminar flow of air in a biological contamination control cabinet so that the most uniform and positive protection is achieved during the greatest percentage of the work time is desirable. At the same time the ease of acce'ssand handling of the work sample should not be lessened thereby pro viding the greatest protection and most efficient working conditions while handling a sample subject to emanation or reception of ambient aerosols during handling thereof.
SUMMARY OF THE INVENTION With the above comments in mind, among the primary objectives of this invention is to provide a biological contamination control cabinet for controlling airborne contamination in a biological work environment. The cabinet and the apparatus associated therewith provide a filtered air barrier to prevent ambient aero' sols from'contaminating the work sample contained within the cabinet and also provides a filtered air curtain over the access opening of the cabinet to prevent ambient aerosols from leaving or entering the cabinet itself.
Furthermore, a negative pressure is provided in the cabinet to prevent contamination from the work samplefrom escaping into the surrounding environment through the access opening in the cabinet or through any other portion of the cabinet'where leakage might occur. All air recirculated through the cabinet and exhausted from the cabinet by the apparatus in general is filtered by absolute filters or, as commonly designated in the trade by HEPA filters, to remove contaminating aerosols. I
The apparatus provide a high velocity clean air curtain across the front opening which provides a kinetic air barrier between the inside and outside of the access opening in the cabinet front of the apparatus. Furthermore, all air-plenums containing contaminating aerosols are at a negative pressure with respect to the surrounding environment or completely contained within a surrounding negative pressure region. Thus preventi-ng leakage of contaminated air out into the laboratory.
Cooperating with the contamination control cabinet as part of the apparatus is a device which indicates the air velocity within the laminar flow cabinet by means of a pitot tube, or similar device, located the blower discharge within the cabinet and connected differentially across a sensitive flow meter. The air velocity through the cabinet is indicated by calibrating the flow meter to read the'velocity pressure in the blower'discharge against the air volume delivered by the blower. The air velocity is controlled by means of a solid state electronic speed controller of a'common commercial type, on the blower motor with the entire velocity indicator, speed control and switches being incorporated into an injection molded control panel which may be mounted on the laminar flow cabinet. The air velocity indicator and control indicates air velocity and is independent of static pressure while providing a combination velocity indicator and control which is incorporated as a one-piece. unit adapted to be mounted on the contamination control cabinetwith easy access and 0perability available to a person working with the contamination control apparatus in general.
In this manner, close control may be maintained at all times over the environment contained within the work area in which the work sample is located thereby providing an'effective and efficient contamination control apparatus which is a significant improvement over the known art. a a I Briefly, the contamination control apparatus of this invention includes a hollow cabinet having a work area in one portion thereof and an opening therein permittingaccess to the work area from the exterior .of the cabinet. Decontamination and air supply means are in the cabinet and positioned so that air discharge there.- from will be decontaminated and then passed into the work area. Diffusion means are mounted in the cabinet and positioned between the decontamination and supply means and the work'area to facilitate the diffusion of the air as it enters the work area. Consequently, the
air flows uniformly through the work area and assists in providing a clean air curtain over the access opening to through the access opening. A series of interconnected air plenum chambers are in the cabinet in communication with the work area, decontamination and air supply means, and the opening to the exterior of the cabinet to permit the air passing through the work area and a portion of air from outside of the cabinet to be directed to the decontamination and air supply means. Negative pressure reducing means are in the cabinet to direct a predetermined amount of decontaminated air out of the cabinet sufficient to maintain a lesser pressure within the cabinet and exteriorly thereof and, finally, air velocity indicator and control means are mounted on .the cabinet to facilitate the control of air flow within the cabinet.
'BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: FIG. 1 is a perspective view of a contamination control apparatus of this invention;
FIG. 2 is a side elevation view thereof with the frontpanels and base portions having beenremoved;
- FIG. 3 is a sectional end elevation view thereof taken along the plane of line 33-of FIG. 2 with arrows showing the direction of air flow within the apparatus;
FIG. 4 is a schematic wiring diagram of the electrical system incorporated in the apparatus of this invention;
DESCRIPTION OF THE PREFERRED EMBODIMENT Initially, referenceshould be made t e-FIGS. 1-3 I which depict the entire contamination control apparatus .20 in assembled and operational condition. As
shown in F lG. l, the apparatus consists of a cabinet 21 i and a removable floor stand 22. The removable floor stand is usable to facilitate bringing cabinet 21 to a more comfortable working level for the'operator. A glove port panel 23 is provided on the exterior of cabinet '21 with two glove ports 24 and 25 provided therein to facilitate reception of the hands of the operator when he is working on a work sample within cabinet 21. The glove port panel may be fastened by any common fastening means such as the thumb screws 26 shown in FIG. I. A portion of the front side of cabinet 21 is constructed of a transparent material such as glass. This portion 27 facilitates viewing of the interior of the cabinet 2] during operation. It might also be noted that the front portion of the cabinet which in cludes transparent portion 27 and glove port panel 23 is tapered outwardly from top to bottom with respect to the cabinet thereby providing a greater work area within the cabinet on which to rest the work element such as horizontal surface or work deck 28.
The velocity indicator and control panel 29 is located i i on the front side of cabinet 21 above transparent portion 27. The upper outer front portion ofv cabinet 21 contains a removable panel 30 which when removed permits access to the interior of the cabinet in the area where the blowers are located. This facilitates maintenance of the working components of the apparatus. Once again, removable panel 30 is fastened in position by any common means such as thumb screws 31.
Cabinet 21 itself takes a substantially rectangular configuration with the exception of the outwardly extending portion of the front side which was discussed above. The remainder of the cabinet is completely enclosed and includes a top panel 32, a rear panel 33, opposing sidepanels 34' and 35 and base panel 36. If the removable floor stand is employed, it is designed to mate with the bottom surface of bottom panel 36 so as to maintain cabinet 21 in an upright supported position.
Also to be noted in FIG. 1 in viewing the top panel 32, a protective screen 37 is present through which the exhaust air is expelled from the cabinet in a manner which will be explained in greater detail below. Also present on the top panel 32 is a make-up prefilter 38 and a slidablemake-up prefilter damper 39 to close make up prefilter 38 when it is not desirable to utilize this element. The make-up prefilter is utilized primarily only in facilitating initiation of operation of apparatus 20 and thereafter damper 39 is in the closed position. Theexhaust protective screen is necessary to provide the exhaust outlet for the exhaust blower as will be described in detail below.
Turning to FIG. 2 in particular, it will be noted that in this Figure the front panels of cabinet 21 have been removed and the interior of cabinet 21 as seen from the front view without the presence of removable panels is shown. On the lower portion of cabinet 21, a rear exhaust screen 40 is shown mounted to back panel 33 of the cabinet. The entire access opening 41 is exposed one glove port panel 23 has been removed. Gas air or water cocks 42 may be provided for the introduction of whatever fluid is desirable for a particular use to which the cabinet is to be put. Furthermore, adjacent thereto at the lower portion of the cabinet is a standard outlet 43 to which proper electrical connections for the system may be attached.
Velocity indicator and control panel 29 is mounted on thepermanent portion of the front side of cabinet 21 and noted thereon is thevariable air velocity control knob 44 as well as an off-on switch 45 to turn the blowers olf and on and a light switch 46 to turn the lights within the unit off and on as .will'be described in detail below. Also on control panel 29 is the velocity indicator 47 shown in connection with the air supply blower 58 exposed with the removal of upper front panel 30 from cabinet 21. The particular elements of control panel 29 will be described in detail at a later point in this disclosure; It may be noted that an input hose 49 forair is connected between the blower 48 and the lower end of velocity indicator or flow meter 47 and a corresponding output line 50 is also connected between air supply blower 48 and the upper end of flow meter 47 to return the air to the blower exhaust when it has passed through flow' meter 47.
within the cabinet. Suitable mounting shelves are shown in the drawings in particular in FIG. 2.
All of the filters employed with the apparatus of this invention are filters which are generally known in the art as absolute filters which prevents the transferring of contamination along with air flow into and out of the cabinet. A designation well known in the art for a filter which will work satisfactorily with a cabinet of this type is a filter known as an HEPA filter which will achieve the desired results during the operation of the apparatus 20.
Mounted adjacent to air supply blower 48 within the upper portion of cabinet 21 is exhaust blower 53 which is also suitably mounted within the cabinet by means of any convenient means such as the shelving and bracketing shown in FIG. 2. The exhaust end of exhaust blower 53 is connected to exhaust filter 54 which is also an absolute filter of the HEPA type as mentioned above. The upper end of exhaust filter 54 communicates with screen 37 and therethrough to the atmo- ,20 sphere out of cabinet 21. Exhaust filter 54 is mounted within cabinet 21, as shown, in an enclosed arrangement so that the only communication with screen 37 i and the exterior of the cabinet is by passage through filter 54. Consequently, all air exhausted through exhaust blower 53 passes through'filter54 and in this manner contaminating aerosols are filtered out and prevented from leaving the cabinet through the opening in which screen 37 is mounted.
The remaining elements of the interior apparatus of the cabinet which are subject to air flow within the cabinet are depicted most clearly in FIG. 3 of the drawings. A description of the flow patterns of the air within the cabinet would be an effective way to describe the cooperation between the various portions of the cabinet structure. To initiate operation of the laminar flow cabinet. switches 45 and 46'are initiated to turn on the lights within cabinet 21 and air supply blower 48 respectively. The lights are located in the upper forward portion of the work area and mounted to the cabinet walls. Two conventional white lights 55 and 56 are located adjacent an ultraviolet light 57. As will be described in connection with the wiring diagram of the electrical system of the apparatus 20, either the'conventional lighting or the' ultraviolet lighting may be utilized as desired.
Air supply blower 48 then discharges a volume of air into discharge chamber 58 where it passes through air supply filter 51. Air chamber 58 and air supply filter 51 are confined in bracketing within the cabinet 21. The clean filtered air from filter 51 then passes through openings in the bracketing at the lower side of the filter 51 into a plenum chamber 59 from where it'continues its downward flow through diffusion screen 60. Diffusion screen 60 is mounted to two opposing substantially vertical bracket platesmounted within the cabinet and horizontally bridges the two vertical plates at a point adjacent the upper ends thereof. Screen 60 forms a diffusion means for forming uniform laminar flow of the air as it passes therethrough and continues on down through work area 52. Screen 60 is constructed so that a laminar flow transfer of air is accomplished between plenum 59 and work area 52.
The uniform flow of air downward through work area 52 and over the work surface protects the work sample located within work area 52 from external airborne contamination. A horizontal deck 28 is located at the base of work area 52 and forms a working surface. Deck 28 may be formed of a formica material or any other common working surface for an apparatus of this type. The two previously mentioned vertical plates 61 and 62 along with deck 28 and screen form substantially the entire confining dimensions of the work area 52 particularly when taken in combination with side panels 34 and 35 of cabinet 21 itself.
There are three potential exits points from work area 52 for the downwardly flowing air through the work area. These are through the front access opening 41 previously discussed and through bottom return screen 63,0r rear return screen 40. In actual operation as will be discussed in greater detail at a later point in the disclosure, the air passing through work area 52 is prevented from exiting through access opening 41 by means of an air curtain formed across this opening. Therefore all of the air passing through screen 60 and downward through work area 52 must exit the work area through bottom return screen 63 and rear return screen 40. Therefore, contamination generated by the work sample itself is picked up by the clean airflow passingvdownwardly through work area 52 and swept out of the work area through return screens 63 and 40.
The nature of the confining internal support structure within the cabinet to form work area 52, plenum 59, filter 51 and air chamber 58 is all support structure which is mounted in a conventional manner to the interior framework of the cabinet and also serves to form a series of interconnected plenum chambers between this confining structure and the interior surface of the outer confining walls of cabinet 21. This interconnected plenum system consists of plenum 65 adjacent the bottom of cabinet 21 which communicates with vertical rear plenum 66 which in turn communicates with upper plenum 67. Therefore, contaminated air passing through screen 63 and 40 is picked up in plenums 65 and 66 and returned to air supply blower 48 where it recirculates back through the work area after being filtered by HEPA filter 51.
Additionally, a portion of the contaminated air passing through plenum 65 and 66 enters upper plenum 67 at a position where it is picked up by exhaust blower 53 and this portion of contaminated air is exhausted from the cabinet through filter 54 and screen 37 at the top of cabinet 21. This portion of air is clean since the contaminated aerosols contained therein are removed by filter 54. In turn, this clean exhausted air which passes through screen 37 causes a negative pressure within cabinet 21, particularly in the areas defined by plenums 65, 66 and 67. This prevents contaminated air contained within these plenums from escaping through any construction I joint leaks which might exist in the outer cabinet wall construction into the laboratory. The slightnegative pressure is sufficient to assure that the outside atmospheric pressure presents any air from the inside of the cabinet 21 which is contained in areas such as plenum 65, 66 and 67 from escaping the interior of the cabinet. This is a particular advantageous feature because these plenums generally contain contami nating aerosols which should not be allowed to escape.
from the interior of the cabinet. All air which is permitted to escape from-the cabinet passes through an HEPA filter before it is allowed to pass therefrom.
As shown by the arrows, in order to maintain equilibrium within the cabinet 21 during operation of the apparatus, an equal quantity of air to that exhausted through screen 37 is made upor drawn into the cabinet through access opening 41 and mixes with internally contaminated air passing out of work area 52 through screen 63 and into plenum chamber 65. Additionally, screen 60-creates a slight pressure in plenum area 59 and causes a higher air flow velocity through slot 68 provided between plate 62 and transparent Outer surface 27 on the front of the cabinet. This slightly increased higher air flow velocity passing slot 68 provides a curtain across access opening 41 as it extends out of the bottom of slot 68 and continues downwardly through screen 63 into return plenum chamber 65 at the bottom of cabinet 21.
The isolation between the air inside and outside of cabinet 21 across front access opening 41 is accomplished by three adjacent sheets of downwardly flowing air. .These sheets of air are substantiallyp'arallel and provide a triple thickness curtain to assure that no contamination can pass between work area 52 and the exterior ofcabinet 21. This triple curtain is formed by the I air being drawn into the cabinet by reason of the nega tive pressure condition within-the cabinet, the high ve locity air passing downward through slot 68 which is sandwiched between the outside air being'drawn in'and the laminar flow clean air passing downwardly through work area 52 from air supply blower 48. Contaminated air from inside of the cabinet 21 is drawn into the inner edge of bottom screen 63 and therefore all of the contaminated air from inside the cabinet passes into plenum 65 and contaminated air from outside the cabinet is drawn into the outer edge of bottom return screen 63 as shown by the arrows in FIG. 3. Thus, all of the contaminat'ed air from outside of the cabinet passes into plenum chamber 65 and does not reach work area 52 in contaminated condition. The high velocity air curtain extending downwardly from slot 68 positively 'sep-' arates these two contaminated flows and creates an additional positive kinetic barrier. Thus, for air to move from inside of the cabinet out or from outside in,-it must in effect cross three air streams. The resultant cabinet 21 in operation .provides a filtered air barrier opening 70, and light off-on switch 46 is mounted in opening 71. An external knob 72 is provided to rotate variable speed control 44 to vary the blower speed and knob 72 and control 44 are mounted by any convenient means such as lock nut 73 as shownin F IG. 5. Suitable electrical terminals are shown on variable controller 44 as well as on switches 45 and 46. A mounting bracket 74 is also provided to assure that blower variable control 44 is mounted in the most desirable fashion.
Turning to consideration of the flow meter 47, FIGS. 5 and 6 should be considered together. The internal chamber of flow meter 47 is formed in panel 29 and has a tapered frusto conical configuration which is of a wider diameter at the upper end thereof than at the lower end thereof. This chamber 55 is initially open at the upper and lower ends thereof, howeverplug 76 and 77 are fitted to suitable recesses in the upper and lower end of chamber 75 so that the ends thereof are sealed prior to operation of the apparatus.
Extending from the rear of panel 29 are tubular extensions 78 and 79 in vertical arrangement so that tubular extension 78 extends horizontally. from a position adjacent the upper portion of'pan el 29 and tubular extension 79 extends horizontally in substantially the same vertical plane from a position adjacent the lower portion of panel 29. A bore 80 extends through tubular extension 78 and through panel 29 into communication with chamber 75 in a substantially perpendicular relationship therewith. Similarly, a bore 81 extends through tubular section 79 and throughpanel 29 into communication with the lower portion of chamber 75 also at substantially a perpendicular relationship with respect thereto. Tube 49 has one end mounted-in any convenient manner within tubularext'ension 79 so that the passage therethrough communicates withbore 81 and the lower end of chamber 75. Similarly, one end of tube 50 is conveniently mounted within tubular extenacross access opening 41 which prevents ambient aerosols from contaminating the work sample in work area 52 and also provides afiltered air curtain andfa negative pressure within the cabinet to prevent contamination from the work sample from escaping into the surrounding environment. All air recirculated through the cabinet and exhausted from the cabinet is'filtered by HEPA filters to remove contaminating aerosols. Naturally, theair curtain across access opening 41 in no way interferes with an operator working on 'a work sample contained within working area 52. Only a kinetic air barrier seals access 41 and prevents cross flow of air between the inside and outside of the cabinet.
Turning to consideration of the controls employed in operating the apparatus 20 of this invention, FIGS. 5 and 6 best depict these features. The support panel 29 itself which is mounted on the front wall of cabinet 21 is of one-piece integral construction and contains a flow meter 47 therein and openings therethrough in. which to mount the variable velocity control 44, the
off-on switch for the air blowers, and the off-on switch for the lights contained within the cabinet. These openings are designated by the numeral 69, 70 and7l respectively in FIG. 5. Variable control 44 is mounted in opening 69, air blower off-on switch 45 is mounted in sion 78 and the passage therethrough communicates with bore 80 and the upper portion of chamber 75. As
previously discussed, the opposite endsof tubes 49 and a 50 are mounted to the blower discharge portion of air supply blower 48 so that a portion of tubes 49 and 50 extend within blower 48 in the air discharge portion thereof. Convenient sealing gaskets 82 and 83 may be employed to insure that no air escapes at the point where tubes 49 and 50 enter the air exhaust portion of air supply blower'48.-Ga'sket 82 assists in sealing the entrance of tube 49 and gasket 83 assist in sealing the entrance of tube 50 into air supply blower 48.
Positioned within chamber 75 of flow meter 47 is a movable indicator 84 which is free to move vertically within chamber 75. Movable member 84 may take any convenientform such as a ball shaped as shown in FIG. 6 and may be formed of any convenient material such as nylon. If it is desirable for any reason to remove or replace indicator 84 for calibration purposes or other reasons, a transverse passage 85 is located adjacent the The ends of tubes 49 and 50 contained within blower 48 are sealed by plugs 86 and 87 respectively. A plurality of spaced openings 88 are located in tube 49 along the portion thereof contained within blower 48 and face the direction from which air is being discharged from the blower. Therefore, air will enter openings 88 and pass through tube 49. Correspondingly, tube 50 has a plurality of spaced openings 89 located on its surface on the portion thereof which is inside of blower 48 and these openings face the direction in which air is being discharged from air supply blower 48. This is depicted by the arrows in FIG. 6. Therefore, air passing through tube 50 will exit through openings 89 into the discharge portion of air supply blower 48.
The above arrangement of openings facilitates operation of flow meter 47. As air is discharged from air supply blower 48, it will enter openings 88 in tube 49 and pass therethrough into the lower end of chamber 75. The air will pass upward through chamber 75 and exit through passage 80 into tube 50. It will pass through tube 50 and exit through openings 89 back into the discharge portion of air supply blower 58 and subsequently exit therefrom. The arrangement of openings within the discharge portion of air supply blower 48 may take the arrangement as is used in a common air velocity indicating device known in the art as a pitot tube. The force with which the air passes through chamber 75 will determine the height to which indica tor 84 is driven upward within chamber 75. The height at which indicator 84 is located is read in accordance with a calibration marking on the transparent outer surface of flow meter 47. Therefore, if a marked change in the height of indicator 84 is-noted, a subsequent change in the speed at which the blower discharges air may be made by adjusting variable speed controller 44. This is accomplished as discussed above by merely turning knob 72 on control panel 29.
Thus, a device is provided which indicates the velocity within the cabinet 21 by means of a pitot tube or similar device located in the blower discharge and connected differentially across a sensitive flow meter. Air velocity through the cabinet is indicated by calibrating the flow meter to read the velocity pressure in the blower discharge versus the air volume delivered by the blower. Air velocity is controlled by means of a speed controller. which may be of the solid state electronic type commonly known in the art,'located on the blower motor. The entire velocity indicator, speed control variation mechanism and switches for operation of apparatus 20 are incorporated into a single control panel. Control panel 29 may be conveniently injection molded of a common plastic material if desired. The control panel indicates air velocity and is independent of static pressure and the entire velocity indicator and control system is incorporated into a one-piece construction. Naturally if it is desirable to change the calibration, it may be accomplished in many ways one of which would be to change the diameter, weight or configuration of indicator 84.
Finally, consideration should be given to a suggested wiring arrangement which may be utilized with the apparatus of this invention such as the schematic arrangement shown in FIG. 4 of the drawings. A normal 120 volt system may be employed as indicated by leads 90 and 91 with a separate ground utilized as indicated by ground 92. The blower switch 45 is connected to the blower portionof the circuit and the light switch 46 is of the type which may be in an off position or which may be connected in one of two on positions. In one on position it would provide a close circuit to light two common types of white light devices such as common commercial neon lights as indicated by the reference numerals 55 and 56. Alternatively in the other on position it may be connected to form a close circuit with a common type of ultraviolet light as indicated by the reference numberal 57 in the drawings. A circuit containing switch 46 and lights 55 and 56 will generally also contain a ballast means 93 for use with the conventional neon or fluorescent lights 55 and 56. Similarly, when switch 46 is connected so as to close the circuit with ultraviolet light 57 to permit current to flow along that particular path, a transformer means 94 is included in the circuit as is conventionally done in accordance with the use of a commonly used ultraviolet light such as designated by the reference numeral 57. As shown in the drawings, the light circuit is such that the fluorescent lights are lit as current flows through the circuit formed by lead 90,-switch 46, lights 55 and 56, ballast 93 and lead 91 and the ultraviolet light is lit when current flows through the circuit formed by lead 90, switch 46, light 57, transformer 94 and lead 91.
As shown in FIG. 4, switch 45 for initiating operation of air supply blower motor 48 and exhaust motor 53 is in the open position so that the apparatus of the invention is not in operable position. Upon the closing of switch 45, current will flow through lead 90, switch 45 and the respective motors of air supply blower 48 and exhaust blower 53, and lead 91. lt should be noted that each of the blower motors are individually grounded and a capacitor is connected to the motor of the air supply blower 48 to prevent any premature surge of power to that motor which could cause an undesirable static discharge in the'electrical system. Variable speed controller 44 is shown connected to both the motor of the air supply blower and the exhaust blower. This is to assure that a uniform amount of air is constantly being circulated through cabinet 21. A variation in speed of the motor of air supply blower 48 should be accompanied by a proportional variation and speed in the motor of exhaust blower 53. This assures that a constant volume of air is being circulated through cabinet 21 and that the slight negative pressure is maintained at all times within the cabinet to prevent the cross contamination as discussed in detail above.
Thus, the above objectives of the invention, among others, are effectively attained.
I claim: v
1. A contamination-control apparatus comprising:
a hollow cabinet having a work surface mounted in one portion thereof and an opening in the front wall of the cabinet permitting access and being adjacent to a portion of the work surface;
air supply means mounted in said cabinet;
high efficiency filter means mounted in said cabinet and connected to the air supply means by a plenum and positioned so that air discharge from said air supply means passes therethrough for decontamination and diffusion of the air;
diffusion means mounted in the cabinet between the high efficiency filter means and the work surface for diffusion as air enters the work area so that laminar flow is provided on the work surface and projacent the access opening and adjacent the difiusion means for communication with flow from the filter for directing a predetermined portion of the filter air discharge from the air supply means across the access opening at a higher velocity than the air passing through the diffusion means and to thereby form an air curtain across the access opening within the cabinet and prevent interchangeability of air between the work area and the exterior of the cabinet; exhaust means from said cabinet communicating with said work surface to direct a predetermined amount of air from said cabinet; said exhaust means including negative pressure producing means sufficient to maintain a lesser pressure within a portion of said cabinet than exteriorly thereof; said exhaust means including air direction means within said cabinet to direct the flow of air there'- throughwith only a negative pressure condition present in that portion of the cabinet adjacent to the exterior walls thereof to-minimize the danger of leakage of air from the interior of the cabinet: and
tate the direction of air flow with respect to the interior of said cabinet.
3. The invention in accordance with claim 1 wherein said air supply means includes an air supply blower mounted in said cabinet and positioned so that air discharge therefrom will be directed into said work area, and said exhaust means including an exhaust blower mounted in said cabinet and in communication with the exterior of said cabinet to direct a predetermined amount of air out of said cabinet, and an exhaust filter mounted in said cabinet between the exhaust blower and the exterior of said cabinet to assure that only clean air is removed from the exterior of said cabinet.
4. The invention in accordance with claim 1 wherein said work surface includes the zone defined by a horizontal table and at least two substantially vertical plates spaced from oneanother and spaced above said table to permit removal of air from said work surface.
5. The invention in accordance with claim 1 wherein said diffusion means is a screen forming a substantial portion of the upper boundary of the work area and is positioned with respect to said filter means and air supply means so that a substantial portion of the air supply therefrom passes through said screen.
6. The invention in accordance with claim 1 wherein said channelmeans includes two substantially vertical plates in said cabinet adjacent to saidwork area and terminating above said access opening with the channel formed between said plates communicating at one end with the exhaust side of said filter and at the other end with the access opening so that a portion of the air exhausted from said filter passes at a relatively high velocity through said channel and across said access opening to provide an air curtain.
7. The invention in accordance with claim 1 wherein air velocity indicator means are mounted on said cabinet to monitor the air velocity in said cabinet.
8. The invention in accordance with claim 7 wherein control means are on said cabinet in connection with said air supply means to facilitate the adjustment of air flow within said cabinet in response to an indication of said air velocity indicator.