Patent Application
20110281514
The present invention relates generally to biological safety cabinets and, more particularly, to structural elements of biological safety cabinets by which the flow of air is directed within biological safety cabinets.
Biological safety cabinets provide a biohazard containment means which enable laboratory personnel in diverse industries, e.g., life science, medical, and pharmaceutical industries, to perform various laboratory, experimental and like procedures utilizing biologically hazardous substances while protecting the personnel, the work product and the ambient environment from exposure to and contamination by such substances. Biological safety cabinets are currently certified by the National Sanitation Foundation (NSF) International, of Ann Arbor, Mich., according to three levels of classification. The present invention is particularly applicable to the class of biological safety cabinets referred to as Class II, Type A2 cabinets.
Class II A2 biological safety cabinets basically have a work chamber that is mostly enclosed except for a front access opening sufficient for a user's hands to perform procedures within the work chamber. An air circulation system maintains a continuously circulating positive air flow within the work chamber which is controlled to move laminarly in parallel relation to the front access opening to prevent escape of the internal cabinet air outwardly through the forward access opening to protect the user and the ambient area from contamination. The air circulation system utilizes a fan to continuously withdraw air from the work chamber into an adjacent filtration chamber from which a portion of the air is recirculated into the work chamber through a first high efficiency particulate air filter, commonly referred to as a HEPA filter, while the balance of the withdrawn air is exhausted outside the cabinet through a second HEPA filter. Typically, a ratio of about 70% recirculated air to 30% exhausted air is maintained in Class II A2 cabinets. The exhausted air is replaced by ambient air from the surrounding room drawn first into the filtration chamber before entering the work chamber through the first filter, thereby to prevent room air contamination of the work chamber and also to maintain the integrity of the laminar air flow along the front access opening.
It is important that the laminar character of the internal air flow within the biological safety cabinet is maintained with minimal turbulence. This is especially important in the forward area of the work chamber in the region of the user access opening, as turbulence in the air currents in this region can result in undesirable escape of contaminated internal air outwardly through the access opening, posing a hazard to users and other laboratory personnel, and/or ingress of unfiltered ambient air into the work chamber, posing a risk of contaminating procedures conducted within the work chamber.
Thus, air flow directional control elements are particularly critical in biological safety cabinets for maintaining air flow within the work chamber to move decisively downward along the forward access opening in a laminar manner that does not migrate inward or outward nor leftward or rightward, and for equally constraining the intake of ambient air solely into the filtration system of the cabinet. While all biological safety cabinets seek to meet these operational parameters, it remains a continuing objective in the industry for enhanced reliability in the directional control of air flow into and within the cabinets.
The present invention seeks to meet the foregoing objectives in an improved manner over conventional biological safety cabinets. Basically, the present invention provides a biological safety cabinet comprising a housing defining a work chamber, a filtration chamber, and a forward opening into the work chamber for user access. An air recirculation system circulates internal air within and between the work chamber and the filtration chamber in a controlled manner for mitigating escape of circulating internal air from the work chamber and for mitigating ingress of ambient air into the work chamber through the forward opening. The air recirculation system includes a filter between the filtration chamber and the work chamber for removing contaminants from the air before re-entering the work chamber. More specifically, the air recirculation system includes an air exhaust sub-system for discharge of a portion of the internal air from the filtration chamber and an air intake sub-system for directing make-up ambient air into the filtration chamber for replacement of the exhausted internal air, and the air intake sub-system includes an intake opening disposed adjacent the forward opening.
In accordance with one aspect of the invention, the air intake opening of the air recirculation system is formed by a perforated air intake grille disposed within the work chamber inwardly spaced from the forward opening by a flat unperforated wall section, the grille having an asymmetrical angular configuration defining a make-up air intake surface and an internal air intake surface oriented angularly upwardly in converging relation to one another. The make-up air intake surface faces forwardly toward the forward opening for intake therethrough of ambient make-up air and the internal air intake surface faces rearwardly away from the forward opening for intake therethrough of circulating internal air moving downwardly through the work chamber, to promote a physical division between the intake of ambient air and the recirculation of internal air. Advantageously, the flat unperforated wall section may serve as an arm rest area for a technician while working within the work chamber.
According to a further aspect of the present invention, the housing is supported on a stand at an elevation suitable for user access into the work chamber through the forward opening, and a user arm rest is affixed to the support stand extending alongside the forward opening at a spacing outwardly from the housing to avoid the potential for cross-contamination between the arm rest and the work chamber. The arm rest is disposed adjacent the air intake grille at an outward spacing therefrom and has an aerodynamic configuration for assisting in direction of ambient make-up air to the make-up air intake surface. Preferably, the arm rest is of a generally elliptical shape to enhance the aerodynamics of intake air flow thereover.
The housing also includes a transverse air transmission grille between the work chamber and the filtration chamber, and a sash forwardly and downwardly of the grille for defining a forward boundary to the work chamber. According to another aspect of the present invention, the grille has a generally flat main extent terminating at a spacing from the sash and an upwardly angled extent adjacent the sash. Both the main extent and the angled extent of the grille are perforated for passage of internal air circulating through the filter from the filtration chamber into the work chamber, the angled extent of the grille being effective to direct an increased flow of circulating internal air downwardly along the sash to promote laminar flow of the circulating air therealong.
Referring now to the accompanying drawings, and initially to
The partial front wall 24 predominately encloses only the air recirculation chamber 32, leaving open front access by users into the work chamber 30. A transparent sash 34 is supported by and extends downwardly from the front wall 24 to partially enclose the work chamber 30 except for a narrow front access opening 36 into the work chamber 30 between the bottom wall 20 and the lower edge of the sash 34 through which users may have manual access into the work chamber 30. The transparency of the sash 34 permits visual access into the work chamber 30 by users. The sash 34 may also be retractable as necessary to permit greater access into the work chamber 30 by users.
In
The intake side of the fan 38 draws air from within the work chamber 30 and also from the ambient air surrounding the safety cabinet 10 through hollow interior channels defined within the bottom and rear walls 20, 22 of the housing 12. More specifically, as best seen in
The housing 12 of the safety cabinet 10 will thus be understood to provide a controlled air recirculation system which operates as follows. The fan 38 continuously creates a negative pressure condition within its end of the air recirculation chamber 32 which acts through the airflow channel 48 to draw air from within the work chamber 30 through the perforations 52 and into the airflow channel 48. To a somewhat lesser extent, surrounding ambient air is drawn into the airflow channel 48 through the perforations 50. The fan 38 pressurizes the in-drawn air and discharges it under positive pressure into the filtration chamber 42 from which a portion of the air passes downwardly through the filter 44 into the work chamber and a portion of the air passes upwardly through the filter 46 into an exhaust 55. The filter 44 is of a substantially larger size than the filter 46 such that the majority of the airflow, preferably approximately 70%, returns into the work chamber 30 through the filter 44, with only a smaller proportion, preferably approximately 30%, of the airflow being exhausted. Within the work chamber 30, the air passing downwardly through the filter 44 moves predominantly vertically downwardly in a laminar manner which, together with the constraint of the sash 34, the constraint of incoming ambient air into the perforations 50, and the negative pressure exerted from the fan through the rearward perforations 52, substantially prevents the escape of any of the airflow outwardly through the access opening 36. Thus, users may perform laboratory procedures within the work chamber 30 utilizing hazardous substances, e.g., microorganisms, particulate toxic chemicals, etc., without risking escape of such substances into the ambient area outside the cabinet. Moreover, as such procedures are ongoing, the continuous recirculation of the air internally within the housing 12 progressively filters airborne contaminants so as to maintain sufficient cleanliness within the internal air to prevent contamination of the procedure.
To the extent thus far described, the basic structure and operation of the biological safety cabinet 10 is essentially conventional. In accordance with the present invention, the biological safety cabinet 10 is equipped with several air flow directional control enhancements effective to mitigate turbulent air currents and, in turn, to provide improved laminar air flow within the cabinet 10, thereby to mitigate ambient air ingress into and internal air escape from the work chamber 30.
More specifically, as best seen in
In this manner, the grille 54 provides several aerodynamic and other distinct advantages over ambient air intake designs of conventional biological safety cabinets. Specifically, conventional biological safety cabinets are known to have ambient air intakes wherein the openings or perforations are formed in the horizontally flat surface of the bottom surface of the work chamber. This design suffers the disadvantage that its flat configuration is less effective in insuring that incoming ambient air is drawn into the air recirculation system. In one known design of biological safety cabinet manufactured by ESCO Technologies (ASIA) PTE Ltd., of Singapore, the ambient air intake grille is of a symmetrical angularly raised configuration, but is located immediately at the forward access opening into the work chamber. This design suffer the disadvantage that its location necessarily tends to promote its use as an arm rest for technicians working within the cabinet, which typically causes a not insignificant number of the air intake openings to be covered and thereby to inhibit the intended air flow within the work chamber.
The angularly raised form of the grille 54 of the present invention orients the make-up air intake surface 56 into a forwardly facing relation to the access opening 36, to more reliably capture and direct the incoming ambient air into the channel 48 with lesser risk of any portion of the ambient air flow passing over the grille 54 into the work chamber 30. The angular configuration also defines a distinct physical separation of the make-up air intake surface 56 from the recirculating internal air intake surface 58 to better induce the recirculating internal air to flow only, or at least mainly, into the perforations of the surface 58 and the incoming ambient air to flow only, or at least mainly, into the intake surface 56, which assists in promoting and maintaining laminar internal air flow downwardly through the work chamber in the region of the access opening 36. The slight rearward spacing of the grille 54 from the forward access opening 36 provides a flat surface suitable for resting of a technician's wrists or forearms without obstructing, or at least with substantially lesser obstruction, of the perforations of the grille 54 so as not to inhibit its intended operation. The angular form of the grille 54 also deters users from placing any work materials, such as laboratory equipment or devices or biological materials, on the bottom wall of the work chamber adjacent the access opening, a not uncommon occurrence in conventional safety cabinets which risks accidental spillage or other cross-contamination through the access opening. Additionally, the forward end of the flat unperforated bottom wall section forwardly of the grille 54 forms a bullnose-like edge 60 against which the sash 34 may abut in a secure sealing manner when the sash is fully extended to fully close the work chamber, such as during disinfecting operations as may be performed by applying ultra-violet light within the work chamber.
As also seen in
As best seen in
In this manner, the baffles 70, 72 mitigate any tendency of the air to stagnate or become turbulent within the filtration chamber 42, thereby assisting in maintaining flow of the incoming air to the filters 44, 46. The two baffles 70, 72 thus cooperate in promoting a uniform movement and presentation of the airflow to each filter 44, 46 essentially across the full lengthwise and widthwise extent of each filter which promotes the desired laminar flow of air downwardly within the work chamber 30 substantially over its full lengthwise and widthwise extent to assist in optimizing the intended operative flow of air within the work chamber 30. The baffles 70, 72 also tend to reduce the noise generated by turbulence in the airflow within the filtration chamber 42.
According to a further aspect of the invention best seen in
As will be recognized by those persons skilled in the relevant field, the flow of air within the forward region of the work chamber 20 inwardly adjacent the sash 34 and downwardly therefrom inwardly adjacent the access opening 36 is critical, particularly in view of the differing air flow vectors that can prevail in this area. In a conventional biological safety cabinet, air passes only downwardly through and from the lower filter, resulting in a relatively weak flow of air in the forward region of the work chamber adjacent the sash. In turn, the continuing flow of air downwardly along the access opening can be less than optimal to prevent undesired inflow of ambient air. By contrast, the design of the grille 28 is effective to positively direct filtered air flow at and then along the sash 34. In particular, the angled orientation of the angled extent 28B of the grille 28 provides a substantial increase in the number of perforations per linear horizontal inch as compared to the main extent 28A of the grille to insure a greater quantity of air in the region along the sash 34. This more concentrated air flow insures not only a stronger and more positive movement of air downwardly along the sash but also, as a result, maintains the air flow moving in a laminar flow without migration of the air leftward or rightward.
It will therefore be readily understood by those persons skilled in the art that the present invention is susceptible of a broad utility and application. Many embodiments and adaptations of the present invention other than those herein described, as well as many variations, modifications and equivalent arrangements will be apparent from or reasonably suggested by the present invention and the foregoing description thereof, without departing from the substance or scope of the present invention. Accordingly, while the present invention has been described herein in detail in relation to its preferred embodiment, it is to be understood that this disclosure is only illustrative and exemplary of the present invention and is made merely for purposes of providing a full and enabling disclosure of the invention. The foregoing disclosure is not intended or to be construed to limit the present invention or otherwise to exclude any such other embodiments, adaptations, variations, modifications and equivalent arrangements, the present invention being limited only by the claims appended hereto and the equivalents thereof.
