Abstract:
A cassette handling system for sterilant filled cassettes employs RFID or other electromagnetic signal technology to track the cassettes. A method for tracking the sterilant cassettes includes the steps of reading for the presence of a cassette within a cassette processing area of the sterilizer by transmitting a non-optical electromagnetic signal between the cassette and a receiver on the sterilizer, via the electromagnetic signal transmitting identifying information between the cassette and the receiver, and verifying that a proper cassette is loaded into the sterilizer based upon the identifying information.

Description:
BACKGROUND OF THE INVENTION 
     This application relates to the delivery of sterilant from a cassette to an instrument sterilizer, and more particularly to the extraction of sterilant from the cassette. 
     One popular method for sterilizing instruments, such as medical devices, is to contact the devices with a vapor phase chemical sterilant, such as hydrogen peroxide. In many such sterilizers, it is preferred to deliver the sterilant in liquid form and vaporize it in the sterilizer. One particularly convenient and accurate method for delivering the liquid sterilant is to put a predetermined quantity of sterilant into a cassette and deliver the cassette to the sterilizer. The sterilizer then automatically extracts the sterilant from the cassette and uses it for sterilization procedure. Typically, such a cassette would entail multiple cells containing equal amounts of liquid sterilant with a sterilization procedure employing the sterilant from one or more cells. Such a system is currently available in the STERRAD® sterilization system available from Advanced Sterilization Products in Irvine, Calif. 
     U.S. Pat. Nos. 4,817,800; 4,869,286; 4,899,519; 4,909,287; 4,913,196; 4,938,262; 4,941,518; 5,882,611; 5,887,716; and 6,412,340, each incorporated herein by reference, disclose such cassettes and a method for draining liquid sterilant from a cell within a cassette. 
     If an operator employs a cassette which has already been used, time can be wasted before the operator realizes that no sterilant has reached the articles during the failed sterilization cycle. A convenient disposal method for spent cassettes would also be desirable. 
     The present invention overcomes these and other limitations of the prior art. 
     SUMMARY OF THE INVENTION 
     A method according to the present invention for tracking sterilant cassettes within a sterilizer includes the steps of: reading for the presence of a cassette within a cassette processing area of the sterilizer by transmitting a non-optical electromagnetic signal between the cassette and a receiver on the sterilizer; via the electromagnetic signal transmitting identifying information between the cassette and the receiver; and verifying that a proper cassette is loaded into the sterilizer based upon the identifying information. 
     The electromagnetic signal can comprise, for instance, a magnetic coupling between the receiver and the cassette, or an inductive coupling between the receiver and the cassette, or a conductive coupling between the receiver and the cassette, or a radio frequency transmission. 
     Preferably, the receiver comprises one or more antennas, preferably sequenced in use to identify the location of the cassette. 
     Preferably, the cassette contains an RFID tag. 
     The method preferably further includes the step of altering a portion of data stored in the RFID tag, such as filling status of sterilant in the cassette and the filling status data is updated when sterilant is removed from the cassette. Where the cassette contains multiple cells containing the sterilant preferably, the RFID tag includes a filling status of sterilant in each of the cells and the filling status data for a cell is updated when sterilant is removed from that cell. If less than the entire contents of one of the cells is removed, preferably this data is stored on the tag. 
     In one aspect of the invention, the RFID tag contains temperature sensing instrumentation and the data includes temperature information regarding the shipping and storage temperatures to which the cassette has been subjected. 
     In another aspect of the invention, the data is updated with one or more cycle parameters, such as a concentration of sterilant achieved during a cycle. 
     Updateable data can also include the amount of time the cassette has spent within the sterilizer. Identifying data can include the type of cycle for which a particular cell or group of cells is intended (such as cycle times, amount of sterilant to be used etc.). It could also include an expiration date for the cassette and the method further include the step of rejecting the cassette if the expiration date has passed. 
     Preferably, the method further includes the step of reading the presence and filling status of a spent cassette collection box via a non-optical electromagnetic signal. 
     A cassette, according to the present invention, comprises one or more cells having therein a liquid sterilant, and further comprises indicia readable electromagnetically and containing identifying data about the cassette including data identifying the liquid sterilant contents thereof. 
     The data can include such things as a filling status of the cells, an expiration date of the liquid sterilant, a manufacturing date of the cassette, a serial number of the cassette, a lot number of the cassette, and a maximum amount of time the cassette may reside within a sterilizer. 
     Preferably, the indicia comprises an RFID tag, more preferably an RFID tag with updateable memory. The updateable memory can contains such data as the filling status of the one or more cells within the cassette data regarding the cell being partially filled, temperature information regarding the shipping and storage temperatures to which the cassette has been subjected, one or more cycle parameters (such as a concentration of sterilant achieved during a cycle), and the amount of time the cassette has spent within a sterilizer. 
     A spent cassette collection box for receiving spent cassettes from a sterilizer, according to the present invention, comprises a bottom wall, upstanding walls attached to the bottom wall which extend upwards to terminate in an upper edge, and indicia readable electromagnetically and containing identifying data about the spent cassette collection box including data identifying its capacity to receive cassettes. 
     Preferably, the indicia is an RFID tag and more preferably, is an RFID tag having updateable data including a quantity of cassettes currently in the box. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a sterilizer employing a cassette handling system according to the present invention; 
         FIG. 2  is a rear perspective view of a cassette handling system according to the present invention; 
         FIG. 3  is a front perspective view of the cassette handling system of  FIG. 2 ; 
         FIG. 4  is a front perspective view of the cassette handling system of  FIG. 2  showing a spent cassette collection box; 
         FIG. 5  is a rear perspective view of the cassette handling system of  FIG. 2  showing its carriage in the insert position; 
         FIG. 6  is a rear perspective view of the cassette handling system of  FIG. 2  showing its carriage as it moves toward the home position; 
         FIG. 7  is a rear perspective view of the cassette handling system of  FIG. 2  showing its carriage in position to read a bar code on the cassette; 
         FIG. 8  is a rear perspective view of the cassette handling system of  FIG. 2  showing its carriage in the home position; 
         FIG. 9  is a front perspective view of the cassette handling system of  FIG. 2  showing its carriage in position to tap the cassette&#39;s first cell; 
         FIG. 10  is a cross sectional view of the cassette showing a cell therein; 
         FIG. 11  is a front perspective view of the cassette handling system of  FIG. 2  showing upper and lower needles on an extractor subsystem penetrating the first cell of the cassette; 
         FIG. 12  is a front perspective view of the cassette handling system of  FIG. 2  showing upper and lower needles on the extractor subsystem in position to penetrate the last cell of the cassette; 
         FIG. 13  is a front perspective view of the cassette handling system of  FIG. 2  showing the cassette being ejected therefrom; 
         FIG. 14  is a flow chart of the cassette handling process; 
         FIG. 15  is a rear perspective view of an alternative embodiment of a cassette handling system of the present invention employing RFID technology; 
         FIG. 16  is a memory map of an RFID tag of the cassette shown in  FIG. 15 ; 
         FIG. 17  is a top plan view of an unfolded blank for forming the spent cassette collection box of  FIG. 4 ; and 
         FIG. 18  is a perspective view of the blank of  FIG. 17  folded to form the spent cassette collection box. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows in block diagram form a vapor phase sterilizer  10  employing a cassette handling system  12  according to the present invention. The sterilizer  10  comprises a vacuum chamber  14  and a vacuum pump  16  for exhausting atmosphere therefrom. A vaporizer  18  receives liquid sterilant from the cassette handling system  12  and supplies it in vapor form to the vacuum chamber  14 . A screen grid electrode  20  is provided within the vacuum chamber  14  for exciting the contents into the plasma phase during a portion of the sterilization cycle. A micro filtered vent  22  and valve  24  allow sterile air to enter the vacuum chamber  14  and break the vacuum therein. A control system  28  ties in to all of the major components, sensors and the like within the sterilizer  10  to control the sterilization cycle. 
     A typical sterilization cycle might include drawing a vacuum upon the vacuum chamber  14  and turning on power to the electrode  20  to evaporate and extract water from the vacuum chamber  14 . The electrode  20  is then powered off and a low vacuum of less than 1 torr drawn on the vacuum chamber  14 . Sterilant, such as hydrogen peroxide solution, is vaporized by the vaporizer  18  and introduced into the vacuum chamber  14  where it diffuses into contact with the items to be sterilized and kills microorganisms thereon. Near the end of the cycle, power is again applied to the electrode  20  and the sterilant is driven into the plasma phase. The electrodes  20  are powered down and filtered air is drawn in through the valve  24 . This process can be repeated. 
     Turning also to  FIGS. 2 to 4 , the cassette handling system  12  according to the present invention is shown. It comprises in gross, a carriage  32  for holding a cassette  34 , a lead screw  36  and motor  38 , an extractor subsystem  40  and a scanner  42 . 
     The carriage  32  comprises a bottom panel  44 , a side panel  46  and top panel  48  along with small vertical flanges  50  and  52  on the top and bottom and top panels  48  and  44 , respectively, to capture the cassette  34 . The bottom, side and top panels  44 ,  46  and  48  flare outwardly at an entrance  54  of the carriage to aid in insertion of the cassette  34 . Two spring catches  56  on the flanges  50  and  52  engage irregular surfaces of the cassette  34  to firmly position the cassette  34  within the carriage  32 . 
     The carriage  32  travels along the lead screw  36  and is supported on an upper rail  58 . A lead screw nut  60  attached to the bottom panel  44  and having a threaded opening  62  and an unthreaded opening  63  receives the lead screw  36  and effects horizontal movement of the carriage  32  in response to rotations of the lead screw  36 . Flanges  64  extend outwardly from the top panel  48  and flanges  66  extend outwardly from the side panel  46  each having openings  69  for receiving the upper rail  58 . The motor  38  is preferable a stepping motor and connects to the lead screw  36  to precisely control the horizontal position of the cassette  34  relative to a frame  68 . 
     The extraction assembly  40  comprises an upper needle  70  and a lower needle  72 , each being of a lumened configuration. The upper needle connects to an air pump  74  which can force air out through the upper needle  70 . The lower needle  72  connects to a valve  76  and from there is plumbed to the vaporizer  18 . 
     The scanner  42  is oriented so as to be able to read a barcode  80  on the cassette  34  as well as a barcode  82  on a spent cassette collection box  84 . Upon insertion of the cassette  34  into the carriage  32  the scanner  42  reads the cassette barcode  80 . The barcode  80  is preferably encoded with information regarding the contents of the cassette  34 , including lot numbers and expiration dates. This information can be used to determine whether the cassette  34  is fresh and of the correct type and whether the cassette  34  has been used in the system before and thus is at least partially empty. The code is communicated to the control system  28  which makes these determinations. 
     The scanner  42  can also see the spent cassette collection box barcode  82  when the carriage  32  moves inwardly and away from the scanner  42 . Each spent cassette collection box  84  preferably has two barcodes  82 , one in each opposing corner so that the scanner  42  can see one of them regardless of which end of the spent cassette collection box  84  is inserted first. With the spent cassette collection box  84  filled, the spent cassettes  34  block the barcode  82  which alerts the control system  28  that there is no capacity for receiving additional spent cassettes  34 . Preferably this message will be output to a user, such as on a display screen (not shown). If the cassette  34  is empty it will not be ejected and no new cycles will be run until a spent cassette collection box  84  having capacity to receive a spent cassette  34  is placed into the sterilizer  10 . 
     A forward flag  86  and rearward flag  88  project outwardly and downwardly from the carriage side panel  46 . They slide through a slot  90  in a slot sensor  92  which detects their presence within the slot  90 , such as by blocking a beam of light. Travel of the front flag  86  and rear flag  88  through the slot sensor  92  provides a reference location of the carriage  32  to the control system  28 . 
     The top panel  48  of the carriage  32  can rotate about the upper rail  58 . A spring  94  between the top panel  48  and side panel  46  biases the top panel  48  downwardly to hold the cassette  34  within the carriage  32 . A disposing cam  96  sits behind the side panel  46  and aligns with an ejecting tab  98  which extends outwardly and downwardly from the top panel  48  and which can project through an opening  100  in the side panel  46  when the top panel  48  rotates upwardly. Such rotation of the top panel  48  releases its hold upon the cassette  34  and due to the ejecting tab  98  projecting through the opening  100  pushes the cassette  34  out of the carriage  32  and into the spent cassette collection box. 
     The disposing cam  96  controls rotation of the top panel  48 . It comprises a generally triangular shape, having an outwardly facing side  102 , forwardly facing side  104  and rearwardly facing side  106 . Turning also now to  FIG. 5 , it mounts for rotation upon an upwardly extending spindle  108 . A spring  110  biases the disposing cam  96  counterclockwise, urging the outwardly facing side  102  into contact with an abutment  112 . Inward movements of the carriage  32  allow the ejecting tab  98  to cam over the rearwardly facing side  106  of the disposing cam  96 , thus allowing the disposing cam  96  to rotate clockwise and allow the ejecting tab  98  to pass thereby without effecting rotation of the top panel  48 . However, outward movement of the carriage  32  causes the ejecting tab  98  to cam over the forwardly facing side  104  of the disposing cam  96 . During such motion contact between the outwardly facings side  102  of the disposing cam  96  and the abutment  112  prevents rotation of the disposing cam  96 . The camming of the ejecting tab  98  thus causes it to move laterally toward the side panel  46  thereby rotating the top panel  48  upwardly and releasing the cassette  34  from the carriage  32 . 
     Prior to inserting the cassette  34  the carriage  32  is fully retracted to its outward position (to the left as shown in  FIG. 5 ). In this position also, a forward end  114  on the lead screw nut  60  engages a stop  116  thus positively locating the position of the carriage  32 . Turning also now to  FIG. 6 , manual insertion of the cassette  34  causes the carriage  32  to move inwardly (to the right as shown in  FIG. 6 ) and moves the front flag  86  into the slot sensor  92 . This movement is preferably caused by the physical force from inserting the cassette  34 , however, a torque or other sensor could be applied to allow the stepping motor  38  to take over this movement upon feeling the force of the cassette  34  being inserted into the carriage  32 . Allowing this movement to come from the force of the insertion of the cassette  34  ensures that the cassette  34  is fully seated within the carriage  32  before the movement begins. 
     Once the front flag  86  is read by the slot sensor  92  the stepper motor  38  takes over and starts to move the carriage  32  inwardly. Turning also now to  FIG. 7 , during this stage, the scanner  42  scans the barcode  80  on the cassette  34 . The control system  28  interprets the information coming from the barcode  80  and determines whether the cassette  34  has been used in the sterilizer  10  before, whether the cassette contains fresh sterilant, and other data as appropriate. Preferably, the information on the barcode  80  is encrypted to prevent unauthorized parties from creating cassettes which may not meet the quality standards necessary for proper sterilization. 
     If the control system  28  rejects the cassette  34  a carriage  32  is moved sufficiently inwardly so as to pass the ejecting tab  98  past the disposing cam  96  and is then moved back to the insertion position shown in  FIG. 5  to eject the rejected cassette  34 . If the cassette  34  is accepted, the carriage  32  continues inward movement to the home position as shown in  FIG. 8  in which the rear flag  88  has just passed out of the slot sensor  92 . 
     Turning also now to  FIGS. 9 and 10 , the cassette  34  comprises a plurality of cells  118  containing liquid sterilant  120 . Various structures of a cassette may be employed. The cassette  34  shown comprises a hard outer shell  122 , preferably formed of an injection molded polymer, such as high impact polystyrene, high density polyethylene or high density polypropylene, which encloses the individual cells  118 , the cells  118  being formed of a blow molded polymer such as low density polyethylene. However, a more rigid material can be used to form the cassette cells  118  in which case the outer shell  122  could be omitted. In the cassette  34  shown, an upper aperture  124  and lower aperture  126  through the shell  122  allows the upper and lower needles  70  and  72  to penetrate the shell. The cell  118  is formed of a material easily penetrated by the needles. If the cell  118  is formed of a more substantial material, a thinning of the material could be provided at the locations to be penetrated by the needles  70  and  72 . 
     The control system  28  uses the home position of  FIG. 8  as a reference position for positioning the various cells  118  in front of the extractor subsystem  40 . By moving the carriage  32  a predetermined amount from the home position a given cell  118  can be brought to face the extractor system  40 . In  FIG. 9 , cell one has been placed in front of the extractor system  40 . Turning also now to  FIG. 11 , an actuator  128  drives the extractor subsystem  40  toward the cassette  34  causing the upper and lower needles  70  and  72  to penetrate the upper and lower apertures  124  and  126  and enter the cell  118 . After the needles have fully extended, the air pump  74  drives air into the cell  118  through the upper needle  70 . The system waits a couple of seconds before starting the air pump  74  and opening the valve  76  to ensure proper placement and settling of the needles within the cell  118 . The sterilant  120  flows out through the lower needle  72  and is piped off to the vaporizer  18 . After a sufficient time to extract the sterilant  120 , the air pump  74  switches off and the actuator retracts the extractor subsystem  40  from the cassette  34 . 
     The vaporizer  18  connects to the vacuum chamber  14  which allows the lower needle  72  to easily be placed at a pressure below atmospheric. Thus, the pump  74  can optionally be replaced by a valve (not shown) open to atmosphere, in which case the incoming atmospheric pressure air will provide the driving force to empty the cell  118 . 
     Rather than employ upper and lower needles  70  and  72 , one needle having two lumens therethrough would suffice. One of the lumens would provide pressurizing gas and one would extract liquid sterilant. A further alternative arrangement would be to pierce the cell  118  vertically, or substantially so, from an upper part of the cell  118 , preferably with such a double lumen needle. This would minimize leakage around the hole created by the needle entering the cell  118 . Such entry would also allow the tip of the needle to come closer to the lowest point of the cell  118  for maximum extraction efficiency. If one desired to extract less than all of the contents of the cell  118 , one method would be to position the needle extracting the sterilant, such as the lower needle  72  or the just mentioned double lumen needle, at the level in the cell  118  down to which extraction is desired. Liquid sterilant above the position would be extracted and sterilant below would remain. This would be particularly convenient with the just mentioned vertically traveling needle. 
     Turning also to  FIG. 12 , each time the control system  28  determines that a new dose of sterilant  120  is required, the stepper motor  38  moves the cassette to position the next cell  118  in front of the extractor subsystem  40  and a new extraction takes place. Multiple extractions may be employed for a given sterilization cycle. When the cassette  34  has been depleted, the carriage  32  moves towards the insert position thus causing the ejecting tab  98  to cam over the disposing cam  96  to rotate the top panel  48  upwardly and project the ejecting tab  98  through the opening  100  to drive the cassette  34  out of the carriage  32  as described above and as shown in  FIG. 13 . The cassette  34  falls into the spent cassette collection box  84  and the carriage  32  returns to the insertion position as shown in  FIG. 5 . 
     The foregoing discussion described the operation of the cassette handling system in some detail.  FIG. 14  shows, in block diagram form, the basic operation of the cassette handling system  12 . 
     The system of reading barcodes on the cassette  34  and spent cassette box  84  can be replaced with radio frequency identification tags, commonly known as RFID tags. An RFID system  130  is shown in  FIG. 15 . It comprises a controller  132  connected via an SPDT reed relay  134  to a cassette insertion antenna  136  located on the carriage  32  and a cassette disposal antenna  138  located beneath the spend cassette box  84 . Each cassette  34  carries a cassette RFID tag  140 . Similarly, each spent cassette collection box  84  carries a collection box RFID tag  142 . Preferably, the controller  132  comprises a Texas Instruments multifunction reader module S4100 and the RFID tags  140  and  42  comprise Texas Instruments RFID tag RI-101-112A each of which are available from Texas Instruments, Dallas, Tex. 
     The control system  28  ( FIG. 1 ) selects one of the antennas, as for instance the cassette insertion antenna  136  and sends a signal to the relay  134  to engage this antenna with the RFID controller  132 . The antenna reads the information stored on the cassette insertion RFID tag  140  which identifies the cassette  34  and its contents. The information read is similar to the information read using the barcode, however preferably, the RFID tag  140  has the ability to update the information stored thereon. Accordingly, additional data such as the filling status of individual cells  118  within the cassette  34  can be stored on the RFID tag. Thus, if the cassette  34  is removed and then reinserted into the sterilizer  10 , or even into different sterilizer  10 , the control system  28  can be apprised of the status of each of the individual cells  118  within the cassette  34 . This allows the reuse of a partially used cassette  34 . Also, since the RFID tag  140  can hold more data than the barcode  80 , more data about the cassette  34 , its contents and manufacturing can be included thereon. 
     The spent collection box antenna  138  reads the spent collection box RFID tag  142  to determine the presence or absence of the spent cassette collection box  84 . Other data such as a unique identifier for the box  84 , the capacity of the box  84 , how many cassettes  34  are currently in the box  84  and how many of the cells  118  therein are not empty can be included on the RFID tag  142 . The control system  28  can track how many cassettes  34  have been ejected into the box to determine whether it has room for more spent cassettes  34 . The antenna  138  can also read the cassette RFID tags  140  and count the number of cassettes  34  within the box  84 . When the box  84  is full the control system  28  alerts the operator, as by a message on a screen. This message can also include information regarding the cassettes  34  within the box  84 . For instance if not all of the cassettes  34  have been completely drained the operator can be informed of this to decide if more careful disposal may be indicated. 
     RFID technology is disclosed in the following U.S. Patents, each of which is incorporated herein by reference: U.S. Pat. Nos. 6,600,420; 6,600,418; 5,378,880; 5,565,846; 5,347,280; 5,541,604; 4,442,507; 4,796,074; 5,095,362; 5,296,722; 5,407,851; 5,528,222; 5,550,547; 5,521,601; 5,682,143 and 5,625,341. 
     RFID tags typically comprise an antenna and an integrated circuit produced in a thin form factor so they can be inconspicuously placed upon an object such as the cassette  34 . Radio frequency energy sent by the antennas  136  and  138  induce sufficient current within the antenna inside the RFID tags  140  and  142  to power the integrated circuit therein. Some types of RFID tags carry their own power source and have longer detection ranges, but that adds additional expense and is probably not justified for the present use. 
       FIG. 16  shows the memory map for the memory within the RFID tags  140  and  142 . A 64-bit unique ID (UID) is set at the factory and cannot be changed. Each RFID tag has its own unique number here. Sixty-four 32-bit blocks can be programmed by the user. These can be populated with information such as the manufacture date, expiration date, product ID, serial number, lot numbers, manufacturing location, filling status of the cells, strength and type of sterilant, time spent within the sterilizer  10  and the like. 
     Some sterilants are affected by heat. The RFID tag  140  can optionally include temperature collection instrumentation and update that information on the tag. If design temperature profiles are exceeded, such as a maximum temperature or excessive temperature over a time period, then the cassette  34  can be rejected by the control system  28 . Temperature measuring RFID tags are available from KSW-Microtec, Dreseden, Germany and from Identec Solutions, Inc., Kelowna, British Columbia, Canada. The interior of the sterilizer  10  where the cassette  34  sits may be higher than ambient temperature. Thus, it may be beneficial to put a maximum residence time (on board shelf life) on the tag  140  or even to update on the tag  140  this time the cassette has already spent inside of the sterilizer. 
     To test sterilant measuring equipment in the sterilizer  10 , it may be beneficial to provide cassettes  34  having water or other fluids within one or more cells  118 . Information regarding the special nature of the cassette  34  and its contents could be written onto the RFID tag. 
     During a cycle the sterilizer may only require part of the contents of a cell  118 . For instance, a particular cycle may call for the contents of one and a half cells. The half filled nature of the cell  118  can be stored and then for the next cycle that cell  118  can be drained. 
     Preferably, communications between the tag  140  and  142  and the controller  132  are encrypted. For instance, the UID can be XORed with an eight-bit master key to form a diversified key for encrypting the data. Encryption algorithms such as the data encryption standard (DES) triple DES, asymmetrical encryption standard (AES) or RSA security can be used for the encryption. The RFID controller  132  reads the data and the algorithm in the control system  28  decrypts the data to reveal the stored information. 
     Other methods could be used to communicate between the cassette  34  and the sterilizer  10 . For instance information could be stored magnetically on the cassette  34 , such as with a magnetic encoded strip, and be read by a magnetic reader on the sterilizer. Wireless technology is becoming cheaper every day and it is envisioned that the cassette  34  could include an active transmitter and a power source (i.e. a battery) such as powered RFID tags or Bluetooth, 802.11b or other communication standard. 
     Further, the sterilizer  10  can be set up to communicate back to a central source, such as the manufacturer or distributor thereof, and provide information regarding its performance and the performance of the cassettes  34 . Poorly performing cassettes  34  could be identified, as for instance sterilant monitors in the sterilizer not detecting sterilant during a cycle thus indicating some failure such as an empty cassette or bad sterilant therein. An improperly manufactured batch of cassettes  34  could then be quickly identified and recalled. Such communication could occur over telephone, pager or wireless telephone networks or over the Internet. 
     Turning now also to  FIGS. 17 and 18 , the spent cassette collection box  84  is preferably folded from a single sheet of printed cardboard or other stock.  FIG. 17  shows an unfolded blank  150  and  FIG. 18  shows the blank  150  folded to form the spent cassette collection box  84 . 
     The blank  150  is divided by a series of fold lines (shown dashed) and cut lines into a bottom panel  152 , side panels  154 , end panels  156  and top flaps  158 . Folding tabs  160  extend laterally from the side panels  154 . Additional folding tabs  162  extend laterally from the end panels  156 . Barcodes  82  are printed on the side panels  154  in a position to be visible in an upper interior corner of the spent cassette collection box  84  when it is folded into the configuration shown in  FIG. 18 . A pair of top flap locking tabs  164  extend from the top flaps  158  and fit into slots  166  in the opposing top flap  158  when the box  84  is closed and into slots  168  at the intersection of the bottom panel  152  and side panel  154  when the box  84  is opened. 
     To fold the box, the folding tabs  160  on the side panels  154  are folded upwardly and then the side panels  154  are folded upwardly, thereby aligning the folding tabs  160  with the intersection between the bottom panel  152  and the end panels  156 . The end panels  156  are then folded upwardly and the end panel folding tabs  162  are folded downwardly over the folding tabs  160 . Locking tabs  170  on the end panel folding tabs  162  fit into slots  172  at the intersection between the bottom panel  152  and end panels  156 . 
     To place the box  84  into the open position as shown in  FIG. 18 , the top flaps  158  are folded downwardly to the outside and the locking tabs  164  fitted into the slots  168 . Once the box  84  is filled with spent cassettes, the top flaps  158  are folded upwardly over the top and the locking tabs  164  can then be fitted into the slots  166  on the opposing top flaps  158 . This unique folding arrangement allows spent cassettes  34  to fall into the open box  84  easily without the top flaps  158  getting in the way and also allows easy closure of the box  84  once it has become filled. 
     While the invention has been particularly described in connection with specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and that the scope of the appended claims should be construed as broadly as the prior art will permit.