CLEAN AIR CABINETS

Abstract: A clean air cabinet has a pass through box with a top fitted HEPA filter for passage of external air into the box. The inflowing sterile air flows downwards through the box and via duct means under the cabinet worksurface into a recycling duct system under fan action. A turbulent air flow sterile isolation cabinet is provided, by means of a canopy, with a zoned downward unidirectional air flow region.

Description: CLEAN AIR CABINETS This invention relates to cabinets of the kind requiring a clean and/or sterile internal air environment. One example of such a cabinet is a containment dispensing cabinet used for the safe handling of hazardous pharmaceutical preparations, such, for example, as cytotoxic drugs. Another example of such a cabinet is a sterile " isolation cabinet, usually made from flexible film, and used for medical and pharmacological purposes and being adapted to isolate technicians from processes being carried out therein and substances being used therein, and vice versa. For convenience such cabinets will hereinafter and in the claims be called "clean air cabinets". In the art of clean air cabinets it is known to provide a clean air cabinet having an internal worksurface and, associated with the cabinet, a fan system adapted to deliver to the worksurface a uni-directional downward sterile airflow, whereby the whole worksurface is provided and covered with sterile air. The fan system recycles the air downwards through grilles from the worksurface through a recycling duct system to a fan chamber via decontamination filter means, usually a HEPA (high efficiency particulate air) filter. It is also known to provide clean air cabinets with glove systems and/or half-suits whereby a technician outside the cabinet can safely work with products internal of the cabinet on the aforesaid worksurface. It is further known to provide clean air cabinets with pass through boxes (usually one at each end of the cabinet) . Such a pass through box has an inner door between the box and the working region of the cabinet and an outer door between the cabinet exterior and the inside of the pass through box. In using such a clean air cabinet the inner and outer doors of a pass through box should not be open at the same time otherwise airborne cross-contamination of the working region of the cabinet or the surrounding atmosphere will occur. Consequently, some cabinets have door interlock systems to deal with this problem but often what is required is discipline by the technician using the clean air cabinet. It is an object of the present invention to provide a clean air cabinet with one or more pass through boxes in which airborne contamination of the working region of the cabinet or the surrounding atmosphere is obviated or mitigated if there is a failure of a door interlock system and/or failure of pass through box discipline by a technician. According to a first aspect of the present invention there is provided a clean air cabinet provided with a pass through box having inner and outer doors and fitted with top filter means through which external air can flow into and through the pass through box in downward sterile air flow and from thence under the cabinet worksurface via duct means, under the control of a fan means, into a recycling duct system. Preferably the clean air cabinet is provided with a working region through which is delivered a unidirectional downward sterile airflow controlled by a recycling fan system which incorporates the fan means for handling the airflow through the pass through box. Preferably the top fitted filter means comprises a prefilter and HEPA filter. Clean air cabinets are also known having filtered clean/sterile turbulent air flows and it is another object of the present invention to provide such a clean air_ cabinet with a unidirectional sterile air flow facility. This second aspect of the present invention is achieved by providing a turbulent air flow clean air cabinet, within its working region, with a canopy defining a predetermined zone of the working region for unidirectional downward sterile air flow, the canopy being open at its bottom and provided at its top with air filter means and a recycling fan means. Preferably the recycling fan means is housed in a chamber which communicates with the canopy interior and with the cabinet working region via HEPA filter means, and with external atmosphere via a prefliter. Embodiments of the present invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which:- Figs. 1 and 2 illustrate a clean air cabinet in accordance with the first aspect of the present invention in four different operational modes A to D; Figs. 3 and 4 illustrate in front view a clean air cabinet in accordance with the second aspect of the present invention in a first operational mode E and a second operational mode F respectively; Figs. 5 is a sectional view on the line X-X of either Fig. 3 or Fig. 4; Fig. 6 illustrates a modified clean air cabinet similar to that of Figs. 3 and 4; Fig. 7 is a sectional view of a further modified clean air cabinet in an operational mode El; Fig. 8 is a fragmentary sectional view corresponding to Fig. 7 in an operational mode Fl; and Fig. 9 is a fragmentary sectional view of yet another modified clean air room. Reference is made to Figs. 1 and 2 which illustrate a clean air cabinet in the form of a containment dispensing cabinet which is generally designated 10. The cabinet 10 comprises a horizontal work surface 11. The cabinet 10 is provided at the front with a door (not shown) horizontally hinged at the top, the door incorporating a glove system (not shown) known to those skilled in the art. At each end of the cabinet 10 is a pass through box generally indicated at 12, which box has a front outer door " (not shown) and an inner lateral door 13. At the top of the cabinet 10 is a fan chamber 14 which communicates with the internal working region 15 of the cabinet 10 via a HEPA filter 16. The work surface 11 of the cabinet 10 is provided at the rear, front and sides with grilles for downward passage of air into a duct 17 which communicates via a " HEPA filter 18 with a recycling duct system generally indicated at 19 which is in communication with the fan chamber 14. The grilles are such that the major portion of the air flow into the duct 17 is through the side grilles. The fan chamber 14 houses a pair of recycling fans 20 and an exhaust fan 21. In accordance with the present invention each pass through box 12 is provided at its top with a filter arrangement comprising a prefilter 22 and a lower HEPA filter 23. Each pass through box 12 has a perforated floor 24 under which is a duct 25 communicating with the duct 17 by a bridging or connecting duct 26. Air is delivered by the fans 20 through the HEPA_ filter 16 into the work region 15 of the cabinet 10 in a unidirectional downward sterile air flow as a result of which the whole of the worksurface 11 is provided and covered with sterile air. This air then passes into the duct 17 and through the HEPA filter 18 into the recycling duct system 19 back to the fan chamber 14. The arrangement of the fans 20 and associated recycling duct system 17, 19 and the fan chamber 14, ensures that the external carcase of the cabinet 10 is held under ' negative pressure to prevent cabinet leaks. The cabinet 10 is caused to operate at internal negative pressure by increasing the suction effect of the fan 21. To permit the cabinet 10 to operate internally at positive pressure the fan 21 is either rendered non- operational or is omitted. In the latter instance, a pre- filter (not shown) for incoming surrounding environmental air may be substituted for the fan 21. Finally it is to be noted that neutral internal operational pressure of the cabinet 10 is achieved by recycling of the air within the cabinet 10, the air being both pushed and pulled around the cabinet 10. It is to be noted that when the cabinet 10 is operating under positive internal pressure, the pass boxes 12 also operate under positive internal pressure. Similarly, a negative operational internal pressure, or a neutral operational internal pressure, within the cabinet 10 will involve a negative operational pressure within the pass boxes. Briefly, the pass through boxes 12 operate in a manner known to those skilled in the art and the essential discipline is that only one of the inner and outer doors is open at any one time. To introduce a product into the working region 15 the inner door 13 of a pass through box 12 is closed and the outer door is open. The product is introduced into the pass through box 12 and the outer door is closed. A sterilising medium can be introduced into the pass through box 12 with the inner door 13 either open or closed. With the outer door closed, the inner door 13 is then opened and the technician using the glove system transfers the product from the pass through box 12 onto the working surface 11 of the cabinet 10 and the inner door 13 ' is then closed. This sequence of actions is reversed to remove a product from the cabinet 10. Reference is now made to the various operational modes illustrated in Figs. 1 and 2. It is to be noted that in all modes there is present the recycling unidirectional downward sterile air flow through the working region 15 of the cabinet 10 as described above. In mode A both doors of each pass through box 12 are closed and external air is sucked into each pass through box through the filters 22 and 23 in a vertical downward sterile air flow, through the floor 24 of the pass through box 12 and via the ducts 25, 26 and 17 through the HEPA filter 18 into the recycling duct system 19. This air flow system through the pass through boxes 12 is controlled by the fan 21. In mode B the outer door of a pass through box 12 is open and this is indicated at 27. External unfiltered air therefore flows into the pass through box 12, but due to the fact that the inner door 13 is closed this air passes into the duct system 25, 26 and 17 through the HEPA filter 18 where it will be cleaned or decontaminated, through the recycling duct system 19 and back to the fan chamber 14 from which it is expelled by the fan 21. Mode C shows the condition where the inner door 13 of a pass through box 12 is open and in this instance the sterile vertical air flow passes downwards through the pass through box 12 and is constrained to pass into the duct and recycling systems mentioned above due to the action of the fan 21 and the presence of the main downward sterile air flow in the working region 15. Mode D illustrates the condition where pass through box discipline has been breached, i.e. both inner and outer doors open, and in this instance, unfil-tered incoming air through the outer door 27 again passes through the floor 24 of the pass through box 12 into the duct and recycling systems as in mode C. In modes B and D the interior of the pass through boxes 12 will begin to be purged of contamination when the outer doors 27 are closed and as the downward sterile air flow is re-established in the boxes 12. It is to be noted that any "stray" air pockets arising, in modes B and D would be catered for by the side grilles in the worksurface 11. The advantages of the above described pass through box system are as follows:- 1) An evacuated box ensures that there is no over pressure to contaminate the working region 15 of the cabinet 10. 2) There is a high air change rate which ensures fast cleaning of the pass through boxes 12. 3) There is sterile air flushing of the pass through boxes when the inner and outer doors are closed. 4) The perforated floors 24 of the pass through boxes 12 assist in the dissipation of sterilising media from the boxes 12 and it is to be noted that ' these floors are removable for periodic cleaning purposes. 5) The inner doors 13 (see Fig. 1) are sloped in order to minimize their intrusion into the work region 15 when open. 6) The pass through box exhaust air is, as described above, filtered through the main cabinet filtering and recycling system and this as a result of mixing with the main airflow from the work region assists in off-setting " heat gains in the recycling duct system 19. 7) As a result of the present invention failure of pass through box discipline does not lead to cross-over contamination in either direction. The clean air cabinet of Figs. 1 and 2 can be supplied either in a portable condition or as a fixture and is capable of adaptation for either laboratory recycling or direct exhaust to atmosphere. Reference is now made to Figs. 3 to 5 which illustrate a clean air cabinet in the form of a sterile isolation cabinet made from flexible film. The sterile isolation cabinet is generally indicated by the reference 30. This cabinet 30 has a glove system (three gloves) generally indicated at 31 and has, in general terms, a turbulent sterile air flow through the working region 32 as can be seen in the left hand side of Figs. 3 and 5. A pass through box having only one door (the outer door) is indicated at 33 and at its top it is provided with a HEPA filter 34. In mode E (Fig. 3) there is partial exhaustion of the air from the turbulent working region (clean zone) 32 via the HEPA filter 34 to the laboratory, the door of the pass through box 33 being closed. Mode F (Fig. 4) shows the condition prevailing when the door of the pass through box 33 is open and in this condition there is an increased loss of air to the laboratory as a result of an increased flow of air into the fan chamber 38 through the pre-filter 42 caused by depressurisation of the canopy 30. This ensures that surrounding environmental air does not enter the open pass box 33. The present invention is concerned with providing within the sterile isolation cabinet 30, .which normally has a turbulent sterile air flow, a work area generally indicated at 35 having a unidirectional downward vertical sterile air flow. This is achieved by providing a canopy 36 defining the work area 35. The canopy has a back and two side walls which extend almost to the worksurface 37 -of the cabinet 30. It also has a front wall which stops at a higher level to allow access to be gained to the work region 35 by a technician using the glove system 31 and_ this can be clearly seen in Figs. 4 and 5. The cabinet 30 above the canopy 36 is provided with a fan chamber 38 incorporating a fan 39 and a delivery duct 40. The chamber 38 communicates with the canopy 36 through the intermediary of a HEPA filter 41 in both the E and F modes. Air from the laboratory for example enters the fan chamber 38 through a prefilter 42. The working regions 32 and 35 of the cabinet 30 communicate with the fan chamber 38 via a minor section 41A of the HEPA filter 41. In mode E air is recycled from the cabinet 30 into the fan chamber 38 where it mixes with incoming external air and is passed back into the working regions 35 and 32 through the HEPA filter 41. In mode F, where pass through box discipline is breached, a major proportion of air within the cabinet working regions 32 and 35 passes out through the door of the through pass box 33, there is still being recycling of some of the air back to the fan cabinet 38. Inflow of air into the cabinet 30 is air from the laboratory for example passing through the pre-filter 42 into the fan chamber 38 and the recirculated air. The air from the fan chamber 38 passes through the HEPA filter 41 into the working regions 32 and 35. As long as the door of the pass through box 33 remains open then there will be loss of air to the laboratory as described above. This aspect of the present invention therefore provides the advantage in a conventional clean air cabinet having a turbulent sterile air flow of a dedicated area of unidirectional downward sterile air flow. Fig. 6 illustrates a sterile isolation cabinet 50 identical to cabinet 30 save that it has two pass boxes 51 and 52 and a four glove system 53. identical parts to those in Figs. 3 and 4 have the same references with the suffix "A". This sterile isolation cabinet 50 operates in the same way as cabinet 30. It is to be noted that the clean air cabinet of Figs. 1 and 2 can be made to operate in modes E and F. To achieve this the fan 21 is rendered non-operational or even omitted. In the latter case, it can be replaced by a ' prefilter. Also, to operate in these modes E and F, the front and rear grilles are increased in working area. If the inner doors 13 of the pass through boxes 12 are open, operational mode E is effective. Mode E operation, in this instance, is air flow from working region 15 via ducts 17 and 26 through the perforated floor 24 into the pass box 12 and out of the HEPA filter 18. If both inner and outer doors of the pass through boxes 12 are open, operational mode F is effective. Mode F operation, in this instance, is air flow from working region 15 via ducts 17 and 26 through the perforated flow 24 into the pass box 12 and out of the open outer door and possibly the HEPA filter 18. There is also direct air outflow via the open inner and outer doors. Referring to Figs. 7 and 8, the clean air room 50 is a flexible film isolator similar to that illustrated in Figs. 3 to 6 which has a generally turbulent sterile air flow with an internal canopy 51 provided a unidirectional downward sterile air flow. The canopy is an open-bottom square or rectangular transparent plastics box with the front wall 52 shorter than the back wall 53 and side walls 54 to facilitate access. A top HEPA filter 55 covers the air inflow area of both the turbulent air working region and the zoned unidirectional downward air working region defined by the canopy 51. Environmental air is sucked into the isolator via a pre-filter 56, a system closure valve 57 and a duct 58 by a fan 59 housed in a fan chamber 60, the air being pushed through the HEPA filter 55 into the aforesaid working regions. Air is pulled out or exhausted from the working regions via a HEPA filter 61 by an exhaust fan 62 housed in a fan chamber 63, the latter being connected to an exhaust duct 64 incorporating a system closure valve 65. Work is done within the isolator 50 by the operator working within a half-suit 66 with gloved assistance as indicated at 67 if necessary. The isolator 50 is provided with one or more pass boxes 68 (only one shown) having an outer door 69 (no inner door) and a top HEPA filter 70. Operational mode El corresponds to operational mode E of Fig. 3, and in Fig. 7 it can be seen that there is partial air exhaustion through the HEPA filter 70, the door 69 being closed. Operational mode Fl corresponds to operational mode F of Fig. 4, and in Fig. 8 it can be seen that the door 69 is open with increased loss of air to the laboratory, air also being exhausted by the fan 62 and supplied by the fan 59. The isolator 50 operates at positive pressure only. A fumigation facility may be provided for the isolator 50. The system closure valves 57 and 65 serve, inter alia, to close if fan failure occurs. Referring now to Fig. 9, the isolator 80 is as described with reference to Fig. 7 and like parts are given. the same references with the suffix A. In this case, however, one or more pass boxes 81 are provided (only one shown) with inner and outer doors 82, 83 and no top HEPA filter. The isolator 80 can operate at either positive or negative pressure. All air loss is through the fan 62A, the pass box 81 being operated with pass box discipline, i.e. only one door 82 or 83 open at a time.

Claims: CLAIMS 1. A clean air cabinet provided with a pass through box having inner or outer doors and fitted with top filter means through which external air can flow into and through the pass through box in downward sterile air flow and from thence under the cabinet worksurface via duct means, under the control of a fan means, into a recycling duct system. 2. A clean air cabinet as claimed in claim 1 provided with working region through which is delivered a unidirectional downward sterile airflow controlled by a recycling fan system which incorporates the fan means for handling the airflow through the pass through box. 3. A clean air cabinet as claimed in claim 1 or 2, in which the top fitted filter means comprises a prefilter and HEPA filter. 4. A clean air cabinet as claimed in any one of claims 1 to 3 comprising a top fan chamber in communication with the top of an internal working region of the cabinet via a HEPA filter. 5. A clean air cabinet as claimed in claim 4 in which the cabinet working region, at its bottom, communicates via a HEPA filter with the recycling duct systems which communicates, in turn, with the fan chamber. 6. A clean air cabinet as claimed in claim 4 or 5 in which the fan chamber houses recycling fan means. 7. A clean air cabinet as claimed in claim 6 in which the fan chamber houses exhaust fan means. 8. A clean air cabinet as claimed in claim 6 in which the fan chamber is fitted with a prefilter for incoming surrounding environmental air. 9. A clean air cabinet comprising a working region and means for providing a turbulent air flow therein, the cabinet being characterised in that, within the working region, there is provided a canopy defining a predetermined zone of the working region for unidirectional downward sterile air flow, the canopy being open at its bottom and provided at its top with air filter means and a recycling fan means. 10. A clean air cabinet as claimed in claim 9 in which the recycling fan means is housed in a chamber which communicates with the canopy interior and with the cabinet working region via HEPA filter means, and with external atmosphere via a prefilter. 11. A clean air cabinet as claimed in claim 9 or 10 in which air from the working region including the unidirectional air zone is adapted to recycle back to the fan chamber via the HEPA filter means. 12. A clean air cabinet as claimed in any one of claims 9 to 11 comprising a pass box with an outer door only and a top HEPA filter for partial air exhaustion from the working region. 13. A clean air cabinet as claimed in claim 9 comprising a pass box with an inner and an outer door. 14. A clean air cabinet as claimed in claim 12 or 13 • when dependent on claim 9 comprising an air inlet fan and an air exhaust fan. 15. A clean air cabinet as claimed in claim 14 in which the air inlet fan delivers air into the working region via a HEPA filter while the exhaust fan pulls air from the working region via a HEPA filter. 16. A clean air cabinet as claimed in any one of claims 9 to 15 comprising an operating facility constituted by glove means and/or half-suit means.

Inventors: BROMLEY GRAHAM, BROMLEY, GRAHAM
Applicants: ENVAIR UK LTD, ENVAIR (UK) LIMITED
Application year: 1989
Main classification: F24F3
IPC codes: B01L1, F24F3