Patent Publication Number: US-2007098592-A1

Title: Parallel flow VHP decontamination system

Description:
FIELD OF THE INVENTION  
      The present invention relates generally to the art of sterilization and decontamination, and more particularly to a system for controlling the humidity level in a sterilization or decontamination system that uses a sterilant in its gaseous or vapor phase.  
     BACKGROUND OF THE INVENTION  
      Gaseous and vapor sterilization/decontamination systems rely on maintaining certain process parameters in order to achieve a target sterility or decontamination assurance level. For Vaporized Hydrogen Peroxide (VHP) sterilization/decontamination systems, one such critical process parameter is the humidity level within the space where sterilization is to occur. By controlling the humidity level, it is possible to reduce the condensation of the hydrogen peroxide due to vapor saturation and thereby provide a more efficient sterilization/decontamination cycle. Conventional Vaporized Hydrogen Peroxide (VHP) sterilization systems for decontaminating large rooms or isolators are generally closed loop systems that include both a vaporizer and a dryer in the same flow path. When the dryer and the vaporizer are in the same flow path, the amount of air flow through the system is determined by balancing the needs of the dryer versus the vaporizer. A problem with such systems is that the humidity level in a large room or isolator space to be sterilized cannot be easily controlled during a sterilization/decontamination cycle.  
      The present invention overcomes this and other problems, and provides a decontamination system that allows for varying humidity levels during a sterilization/decontamination cycle, independent of the flow through the vaporizer.  
     SUMMARY OF THE INVENTION  
      In accordance with the present invention, there is provided a closed loop vapor decontamination system for decontaminating a defined region. The system has a chamber that defines a region. A first fluid flow path is connected at both ends to the chamber to define a first closed loop path through the chamber. A second fluid flow path is connected at both ends to the chamber to define a second closed loop path through the chamber. Means for conveying a carrier gas simultaneously along the first and second fluid flow paths. A generator for generating vaporized hydrogen peroxide is disposed along the first fluid flow path for introducing vaporized hydrogen peroxide into the carrier gas as it circulates through the first fluid flow path. A destroyer for converting the vaporized hydrogen peroxide into water and oxygen, is disposed along the second fluid flow path for breaking down the vaporized hydrogen peroxide in the carrier gas as it circulates through the second fluid flow path. A controller controls the amount of the carrier gas flowing along the first and second fluid flow paths.  
      In accordance with another aspect of the present invention, there is provided a method for controlling the humidity level in an isolator or room, comprising the steps of: providing a sealable region, a first fluid flow path and a second fluid flow path, said first fluid flow path and said second fluid flow path both include said sealable region; conveying a flow of a carrier gas simultaneously along said first fluid flow path and said second fluid flow path; introducing vaporized hydrogen peroxide into said carrier gas flowing along said first fluid flow path; and destroying said vaporized hydrogen peroxide in said carrier gas flowing along said second fluid flow path.  
      In accordance with another aspect of the present invention, there is provided another method for controlling the humidity level in an isolator or room, comprising the steps of: providing a decontamination system having a sealable region, a first fluid flow path and a second fluid flow path that both include said sealable region and a sensor disposed within said sealable region operable to monitor the conditions within said sealable region to provide signals indicative of said conditions; conveying a flow of a carrier gas simultaneously along said first fluid flow path and said second fluid flow path; introducing vaporized hydrogen peroxide into said carrier gas flowing along said first fluid flow path; destroying said vaporized hydrogen peroxide in said carrier gas flowing along said second fluid flow path; and varying the relative flow of carrier gas along said first fluid flow path and said second fluid flow path based on signals from said sensor.  
      An advantage of the present invention is a system for the sterilization or decontamination of a large room or isolated space.  
      Another advantage of the present invention is a system, as described above, that allows for varying the humidity level in the room or isolator during the operating cycle.  
      Another advantage of the present invention is a system, as described above, that reduces the pressure drop throughout the entire system to provide for more efficient flow of the carrier gas.  
      Another advantage of the present invention is a system, as described above, that provides independent flow through a vaporizer and a dryer to allow for smaller blowers to be utilized.  
      This and other advantages will become apparent from the following description of a preferred embodiment taken together with the accompanying drawings and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention may take physical form in certain parts and arrangement of parts, a preferred embodiment of which will be described in detail in the specification and illustrated in the accompanying drawings which form a part hereof, and wherein:  
       FIG. 1  is a schematic view of a vaporized hydrogen peroxide deactivation system illustrating a preferred embodiment of the present invention;  
       FIG. 2  is a schematic drawing of a control system for the vaporized hydrogen peroxide decontamination system shown in  FIG. 1 ;  
       FIG. 3  is a schematic view of a vaporized hydrogen peroxide deactivation system illustrating an alternative embodiment of the present invention with independent first and second fluid flow paths;  
       FIG. 4  is a schematic drawing of a control system for the vaporized hydrogen peroxide decontamination system shown in  FIG. 3 ;  
       FIG. 5 . is a schematic view of a vaporized hydrogen peroxide deactivation system illustrating another alternative embodiment of the present invention with first, second and third fluid flow paths;  
       FIG. 6  is a schematic drawing of a control system for the vaporized hydrogen peroxide decontamination system shown in  FIG. 5 ;  
       FIG. 7  is a schematic view of a vapor hydrogen peroxide deactivation system illustrating another alternative embodiment of the present invention with independent first and second fluid flow paths and a bypass conduit around the dryer in the second fluid flow path; and  
       FIG. 8  is a schematic drawing of a control system for the vaporized hydrogen peroxide decontamination system shown in  FIG. 7 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT  
      Referring now to the drawings wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only, and not for the purpose of limiting same,  FIG. 1  shows a vaporized hydrogen peroxide sterilization system  10 , illustrating a preferred embodiment of the present invention. System  10  includes an isolator or room  12  that defines an inner sterilization/decontamination chamber or region  24 . Articles to be sterilized or decontaminated may be disposed within isolator or room  12 . A first humidity sensor  16  is disposed within isolator or room  12 . First humidity sensor  16  is operable to provide a variable electrical signal that is proportional to the humidity of the carrier gas within isolator or room  12 . A VHP sensor  26  is disposed within isolator or room  12 . VHP sensor  26  can be an electrochemical cell that gives a signal proportional to the gas concentration or it can be a near infrared spectrophotometer that provides a similar signal or some other commercially available sensor for detecting the concentration of VHP in an isolator or room.  
      System  10  is comprised of a first fluid flow path “A” and a second fluid flow path “B.” First fluid flow path “A” is defined by isolator or room  12  and a first conduit  14 . One end of first conduit  14  connects to isolator or room  12 . The other end of first conduit  14  also connects to isolator or room  12 . In this respect, isolator or room  12  and first conduit  14  define a closed loop path. Second fluid flow path “B” is defined by isolator or room  12 , a portion of first conduit  14  and a second conduit  22 . One end of second conduit  22  connects to first conduit  14  at a junction  18 . The other end of second conduit  22  connects to isolator or room  12 . In this respect, isolator or room  12 , a portion of first conduit  14  and second conduit  22  defined a closed loop path.  
      A vaporizer  28  (also referred to herein as generator) is disposed along first fluid flow path “A” to introduce vaporized hydrogen peroxide into first fluid flow path “A.” Vaporizer  28  is connected to a liquid sterilant supply  32  by a feed line  34 . A conventionally known balance device  36  is associated with sterilant supply  32 , to measure the actual mass of sterilant being supplied to vaporizer  28 . A pump  38  driven by a motor  42  is provided to convey metered amounts of the liquid sterilant to vaporizer  28  where the sterilant is vaporized by conventionally known means. In an alternate embodiment, pump  38  is provided with an encoder (not shown) that allows monitoring of the amount of sterilant being metered to vaporizer  28 . If an encoder is provided with pump  38 , balance device  36  is not required. A pressure switch  44  is provided in the feed line. Pressure switch  44  is operable to provide an electrical signal in the event that a certain static head pressure does not exist in feed line  34 .  
      A VHP temperature sensor  52  is disposed on vaporizer  28  to measure the temperature of the VHP exiting vaporizer  28 . VHP temperature sensor  52  is operable to provide a variable electrical signal that is proportional to the temperature of the VHP exiting vaporizer  28 . A vaporizer inlet temperature sensor  54  is provided to measure the temperature of the carrier gas entering vaporizer  28 . Vaporizer inlet temperature sensor  54  is operable to provide a variable electrical signal that is proportional to the temperature of the carrier gas entering vaporizer  28 . A heater  56  is provided prior to vaporizer  28 . Heater  56  is operable to heat the carrier gas circulating through first fluid flow path “A.” In this respect, the carrier gas is heated prior to the carrier gas entering vaporizer  28 . A first flow element  59  provides a variable electrical signal that is proportional to the air flow entering vaporizer  28 . A second flow element  59  provides a variable electrical signal that is proportional to the air flow entering destroyer  62 .  
      A destroyer  62  is disposed along second fluid flow path “B” to destroy hydrogen peroxide (H 2 O 2 ) flowing therethrough, as is conventionally known. Catalytic destroyer  62  converts the hydrogen peroxide (H 2 O 2 ) into water and oxygen. A dryer  64  is disposed along second fluid flow path “B.” Dryer  64  is located downstream of destroyer  62 . In this respect, dryer  64  is disposed between destroyer  62  and chamber or region  24 . Dryer  64  is operable to remove moisture from the carrier gas flowing through second fluid flow path “B.” A catalytic destroyer temperature sensor  66  and a second humidity sensor  68  are disposed along second fluid flow path “B.” Catalytic destroyer temperature sensor  66  and second humidity sensor  68  are located upstream of dryer  64 , as seen in  FIG. 1 . Catalytic destroyer temperature sensor  66  is operable to provide a variable electrical signal that is proportional to the temperature of the carrier gas exiting catalytic destroyer  62 . Second humidity sensor  68  is operable to provide a variable electrical signal that is proportional to the humidity of the carrier gas exiting catalytic destroyer  62 .  
      A blower  82 , driven by a motor  84 , is provided to circulate a carrier gas simultaneously along first fluid flow path “A” and second fluid flow path “B.” A filter  86  is provided upstream of blower  82 . Filter  86  is operable to filter dirt and/or debris from the carrier gas circulated along first fluid flow path “A” and second fluid flow path “B.” A first valve  88  is provided to regulate flow along first conduit  14 . First valve  88  is a variable flow valve. A second valve  92  is provided to regulate flow along second conduit  22 . Second valve  92  is a variable flow valve.  
      Referring now to  FIG. 2 , a control system  100  for controlling the operation of system  10  is schematically illustrated. Control system  100  includes a controller  110  that controls the operations of motors  42 ,  84  and valves  88  and  92 . Controller  110  also monitors VHP sensor  26 , pressure switch  44 , VHP temperature sensor  52 , vaporizer inlet temperature sensor  54 , catalytic destroyer temperature sensor  66 , balance device  36  that feeds a sterilant to vaporizer  28 , flow elements  59 , and first and second humidity sensors  16  and  68 . Controller  110  also controls the operation of heater  56  and vaporizer  28 . Controller  110  is a system microprocessor or a micro-controller that is programmed to control the operation of system  10 . Controller  110  controls the flow position of first valve  88  and second valve  92  by providing an electronic signal to first valve  88  and second valve  92 . Based on the selected flow position, first valve  88  and second valve  92  control the carrier gas flow rate along first fluid flow path “A” and second fluid flow path “B.” First valve  88  and second valve  92  can increase the flow of the carrier gas along first fluid flow path “A” while decreasing the flow of the carrier gas along second fluid flow path “B” or vice versa. In the preferred embodiment, first valve  88  and second valve  92  are capable of causing more carrier gas to flow along first fluid flow path “A” than second fluid flow path “B” or vice versa. Controller  110  may also control the speed of motor  84  to provide a reduced flow to either flow path.  
      An input unit  112  is provided and attached to controller  110  to allow a user of system  10  to input operation parameters. Input unit  112  may be any device that would facilitate the input of data and information to controller  110  by a user of system  10 , such as by way of example and not limitation, a keypad, a keyboard, a touch screen or switches. An output unit  114  is also connected to controller  110 . Output unit  114  is provided to enable controller  110  to provide information to the user on the operation of system  10 . Output unit  114  may be, by way of example and not limitation, a printer, display screen or LED display. Controller  110  is programmed such that system  10  operates in certain operating phases while maintaining certain preferable operating conditions.  
      The present invention shall now be further described with reference to the operation of system  10 . A typical sterilization/decontamination cycle includes a drying phase, a conditioning phase, a decontamination phase and an aeration phase. Prior to the initiation of a sterilization/decontamination cycle, input unit  112  is used to provide the operational parameters to controller  110 . The operational parameters include a target humidity level for a drying phase, a target VHP concentration for a conditioning phase, a target humidity level and a target VHP concentration for a decontamination phase, and a target VHP concentration for an aeration phase.  
      When a sterilization/decontamination cycle is first initiated, controller  110  starts with a drying phase. Controller  110  causes motor  84  to drive blower  82 , thereby causing a carrier gas to circulate simultaneously along first and second fluid flow paths “A” and “B.” During this phase, controller  110  positions valves  88  and  92  such that the majority of the carrier gas will flow along second fluid flow path “B.” The carrier gas will be directed between the flow paths by controller  110  as required for correct system operation. During the drying phase, vaporizer  28  is not operating, but is being heated to operating temperature. Dryer  64  removes moisture from the air circulating through second fluid flow path “B.” Throughout the drying phase, first humidity sensor  16  provides a signal to controller  110  that is proportional to the actual humidity level of the carrier gas in isolator or room  12 . Throughout the drying phase, controller  110  periodically compares the actual humidity level, as measured by first humidity sensor  16 , to the target humidity level for the drying phase. If the actual humidity level is higher than the target humidity level, controller  110  continues to operate in the drying phase. Once the actual humidity level is lower than the target humidity level controller  110  ends the drying phase.  
      Following the drying phase, the conditioning phase is then initiated. Controller  110  causes first valve  88  and second valve  92  to move to a flow position to cause a majority of the carrier gas to flow along first fluid flow path “A.” The speed of motor  84  may be adjusted to provide the required flow along fluid flow path “A”. The carrier gas will be directed between the flow paths by controller  110  as required for correct system operation. Controller  110  activates vaporizer  28  and sterilant supply motor  42  to provide sterilant to vaporizer  28 . Within vaporizer  28 , the liquid sterilant is vaporized to produce vaporized hydrogen peroxide (VHP) and water vapor, in a conventionally known manner. The vaporized sterilant is introduced into first fluid flow path “A” and is carried by the carrier gas into sterilization/decontamination chamber or region  24  within isolator or room  12 . Carrier gas is circulated simultaneously through first fluid flow path “A” and second fluid flow path “B.” Because more carrier gas is circulated along first fluid flow path “A” than second fluid flow path “B,” more VHP will be injected into chamber or region  24  and less will be destroyed by destroyer  62 . Throughout the sterilization/decontamination cycle, VHP sensor  26  provides a signal to controller  110  that is proportional to the concentration of the VHP in isolator or room  12 . Throughout the conditioning phase, controller  110  periodically compares the actual VHP concentration, as measured by VHP sensor  26 , to the target VHP concentration of the conditioning phase. If the actual VHP concentration is lower than the target VHP concentration level, controller  110  continues to operate in the conditioning phase. Once the actual VHP concentration is above the target VHP concentration, controller  110  ends the conditioning phase.  
      After the conditioning phase is completed, the decontamination phase is initiated. During the decontamination phase, controller  110  receives electrical signals from VHP sensor  26  and first humidity sensor  16  that are proportional to the concentration of VHP and the humidity level in isolator or room  12 . Throughout the decontamination phase, controller  110  periodically compares the actual VHP concentration and humidity level to the target VHP concentration and the target humidity level for the conditioning phase. If the actual humidity is above the target humidity or the actual VHP concentration is above the target VHP concentration, controller  110  sends an electronic signal to second valve  92 . Second valve  92  then opens to a position to cause more carrier gas to flow along fluid flow path “B.” Controller  110  also sends an electronic signal to motor  84  to increase speed to provide increased air flow. Controller  110  sends an additional signal to motor  42 . Motor  42  then turns pump  38  at a slower rate to reduce the amount of liquid sterilant being supplied to vaporizer  28 . If the actual VHP concentration or the actual humidity level drops below the target VHP concentration or the target humidity level, controller  110  sends an electronic signal to second valve  92 , and motor  84 . Second valve  92  moves to a position to reduce the carrier gas flow along second fluid flow path “B,” while motor  84  speed is adjusted to reduce air flow. Controller  110  also sends an electrical signal to motor  42 . Motor  42  then turns pump  38  at a faster rate to increase the output of liquid sterilant to vaporizer  28 . For the remainder of the decontamination phase, controller  110  continues to control valves  88  and  92 , motor  84 , and motor  42  based on the actual VHP concentration and humidity levels in isolator or room  12 . The decontamination phase ends once the target conditions have been achieved in isolator or room  12  for a predetermined period of time that is sufficient to effect the desired sterilization or decontamination of sterilization/decontamination chamber or region  24 , and/or items therein.  
      After the decontamination phase is completed, the aeration phase is initiated. Controller  110  causes first valve  88  and second valve  92  to move to positions wherein the majority of the carrier gas flowing in system  10  flows along second fluid flow path “B.” The carrier gas will be directed between the flow paths by controller  110  as required for correct system operation. Controller  110  also causes vaporizer  28  and motor  42  to turn off thereby stopping the introduction of VHP into first fluid flow path “A.” The aeration phase is run until the vaporized hydrogen peroxide (VHP) level in isolator or room  12  is below an allowable threshold (about 1 ppm). In this respect, as will be appreciated, blower  82  continues to simultaneously circulate the carrier gas and sterilant through the first fluid flow path “A” and second fluid flow path “B,” thereby causing the last of the vaporized hydrogen peroxide (VHP) to be broken down by catalytic destroyer  62 .  
      Referring now to  FIGS. 3 and 4 , an alternative embodiment of a vapor decontamination system  210  is shown. System  210  includes an isolator or room  212  that defines an inner sterilization/decontamination chamber or region  224 . Articles to be sterilized or decontaminated, a first humidity sensor  216  and a VHP sensor  226  are disposed within isolator or room  212 . Sterilization/decontamination system  210  is comprised of a first fluid flow path “A” and a second fluid flow path “B.” First fluid flow path “A” is defined by isolator or room  212  and a first conduit  214 . One end of first conduit  214  connects to isolator or room  212 . The other end of a first conduit  214  also connects to isolator or room  212 . In this respect, isolator or room  212  and first conduit  214  define a closed loop path. Second fluid flow path “B” is defined by isolator or room  212  and a second conduit  222 . One end of second conduit  222  connects to isolator or room  212 . The other end of second conduit  222  also connects to isolator or room  212 . In this respect, isolator or room  212  and second conduit  222  define a closed loop path.  
      A vaporizer  228  (also referred to herein as generator) is disposed along first fluid flow path “A” to introduce vaporized hydrogen peroxide into first fluid flow path “A” as described above. A VHP temperature sensor  252 , a vaporizer inlet temperature sensor  254  and a heater  256  are also connected to first fluid flow path “A” as described above in the preferred embodiment. As described in the preferred embodiment, a catalytic destroyer  262 , a dryer  264 , a catalytic destroyer temperature sensor  266 , and a second humidity sensor  268  are also provided along second fluid flow path “B.” Other elements such as a pump  238 , driven by a motor  242 , a balance device  236 , a sterilant supply  232 , a pressure switch  244  and a feed line  234  are involved in advancing hydrogen peroxide to vaporizer  228 . The operation of these elements is described in the preferred embodiment.  
      A first blower  282 , driven by a first motor  284 , is provided to circulate a carrier gas along first fluid flow path “A.” A first filter  286  is provided upstream of first blower  282 . First filter  286  is operable to filter dirt and/or debris from the carrier gas circulated along first fluid flow path “A.” A flow element  259  is provided in conduit  214  to provide a variable electrical signal that is proportional to the air flow.  
      A second blower  302 , driven by a second motor  304 , is provided to circulate a carrier gas along second fluid flow path “B.” A second filter  306  is provided upstream of second blower  302 . Second filter  306  is operable to filter dirt and/or debris from the carrier gas circulated along second fluid flow path “B.” A flow element  259  is provided in conduit  222  to provide a variable electrical signal that is proportional to the air flow.  
      Referring now to  FIG. 4 , a control system  400  for controlling the operation of system  210  is schematically illustrated. Control system  400  includes a controller  410  that is provided to control the operation of motors  242 ,  284  and  304 . Controller  410  also monitors VHP sensor  226 , pressure switch  244 , VHP temperature sensor  252 , vaporizer inlet air temperature sensor  254 , catalytic destroyer air temperature sensor  266 , balance device  236  that feeds a sterilant to vaporizer  228 , flow elements  259 , and first and second humidity sensors  216  and  268 . Controller  410  also controls the operation of heater  256  and vaporizer  228 . Controller  410  is a system microprocessor or a micro-controller that is programmed to control the operation of system  210 . Controller  410  controls the rotational speed of second motor  304  by providing an electrical signal to second motor  304 . Second motor  304  then controls the speed of second blower  302 . Second blower  302  in turn controls the flow rate of the carrier gas through fluid flow path “B.” Controller  410  operates second motor  304  in response to electrical signals received from VHP sensor  226  and first humidity sensor  216 . Controller  410  monitors the actual VHP concentration and humidity level and calculates the appropriate speed of motors  304  and  242  to achieve the target operational conditions. Motor  284  is preferably a single speed motor sized for the desired flow through fluid flow path “A,” but may be speed controlled as illustrated above. It can be appreciated that input unit  412  and output unit  414  are the same as described above in the preferred embodiment.  
      The alternative embodiment shall now be further described with reference to the operation of system  210 . A typical sterilization/decontamination cycle includes a drying phase, a conditioning phase, a decontamination phase and an aeration phase. Prior to the initiation of a sterilization/decontamination cycle, input unit  412  is used to provide the operational parameters to controller  410 . The operational parameters include a target humidity level for a drying phase, a target VHP concentration for a conditioning phase, a target humidity level and a target VHP concentration for a decontamination phase, and a target VHP concentration for an aeration phase.  
      When a sterilization/decontamination cycle is first initiated, controller  410  starts with a drying phase. Controller  410  causes first and second motors  284  and  304  to drive first and second blowers  282  and  302 , thereby causing a carrier gas to circulate through system  210  simultaneously along first fluid flow path “A” and second fluid flow path “B.” Preferably, both blowers will be operated at their maximum speed. Dryer  264  removes moisture from the carrier gas circulating through second fluid flow path “B.” Controller  410  ends the drying phase when the actual humidity level, as measured by first humidity sensor  216 , is less than the target humidity level.  
      The conditioning phase is then initiated. Controller  410  continues to cause first and second motors  284  and  304  to drive first and second blowers  282  and  302 , thereby causing the carrier gas to simultaneously circulate along first and second fluid flow paths “A” and “B.” It can be appreciated that the remainder of this conditioning phase is operated in the same manner as described in the preferred embodiment in regards to vaporizer  228 .  
      After the conditioning phase is completed, the decontamination phase is initiated. Throughout the sterilization/decontamination cycle, VHP sensor  226  and first humidity sensor  216  send an electric signal to controller  410  that is proportional to the actual VHP concentration and humidity level in isolator or room  212 . If the actual VHP concentration or humidity level increases above the target VHP concentration or humidity level, controller  410  causes second motor  304  to drive second blower  302  faster to increase the flow of the carrier gas along fluid flow path “B.” Controller  410  also sends an additional signal to motor  242  to reduce the amount of liquid sterilant being supplied to vaporizer  228 . If the actual VHP concentration or humidity level drops below the target VHP concentration or humidity level, controller  410  sends an electronic signal to motors  304  and  242 . Motor  304  reduces the flow of the carrier gas along fluid flow path “B,” and motor  242  increases the output of liquid sterilant to vaporizer  228 . For the remainder of the decontamination phase, controller  410  continues to control motors  304  and  242  based on the actual VHP concentration and humidity levels in isolator or room  212 . The decontamination phase ends once the target conditions have been achieved in isolator or room  212  for a predetermined period of time that is sufficient to effect the desired sterilization or decontamination of sterilization/decontamination chamber or region  224 , and/or items therein.  
      After the decontamination phase is completed, the aeration phase is run to bring the vaporized hydrogen peroxide (VHP) level down to an allowable threshold (about 1 ppm). In this respect, first and second blowers  282  and  302  continue to circulate the carrier gas through the first and second fluid flow paths “A” and “B,” thereby causing the last of the vaporized hydrogen peroxide (VHP) to be broken down by catalytic destroyer  262 . During the aeration phase, the flow along second fluid flow path “B” is greater than the flow along first fluid flow path “A.” Controller  410  also causes vaporizer  228  and motor  242  to turn off thereby stopping the introduction of VHP into first fluid flow path “A.” 
      Referring now to  FIGS. 5 and 6 , another alternative embodiment of a vapor decontamination system  510  is shown. System  510  includes an isolator or room  512  that defines an inner sterilization/decontamination chamber or region  524 . A first humidity sensor  516  and a VHP sensor  526  are disposed within isolator or room  512 . Sterilization/decontamination system  510  is comprised of a first fluid flow path “A,” a second fluid flow path “B” and a third fluid flow path “C.” First fluid flow path “A” in system  510  is identical to first fluid flow path “A” as defined in system  210 . Second fluid flow path “B” in system  510  is identical to second fluid flow path “B” in system  210 , except regarding a dryer  564 . Third fluid flow path “C” is defined by isolator or room  512  and a third conduit  602 . One end of third conduit  602  connects to isolator or room  512 . The other end of third conduit  602  also connects to isolator or room  512 . In this respect, isolator or room  512  and third conduit  602  define a closed loop path.  
      First fluid flow path “A” in system  510  includes the same components, a vaporizer  528 , a VHP temperature sensor  552 , a vaporizer inlet temperature sensor  554  and a heater  556  as described in the preferred embodiment. Other elements such as a pump  538  driven by a motor  542 , a balance device  536 , a sterilant supply  532 , a pressure switch  544  and a feed line  534  are involved in advancing hydrogen peroxide to vaporizer  528 . The operation of these elements is described in the preferred embodiment. Second fluid flow path “B” includes a catalytic destroyer  562 , a catalytic destroyer temperature sensor  566 , and a second humidity sensor  568  as described in the preferred embodiment. Second flow path “B,” however, does not include a dryer  564  as in system  210  above.  
      Dryer  564  is disposed within third fluid flow path “C.” Dryer  564  is operable to remove moisture from the carrier gas flowing through third fluid flow path  
      A first blower  582 , driven by a first motor  584 , is provided to circulate a carrier gas along first fluid flow path “A.” A first filter  586  is provided upstream of first blower  582 . First filter  586  is operable to filter dirt and/or debris from the carrier gas circulated along first fluid flow path “A.” 
      A second blower  606 , driven by a second motor  608 , is provided to circulate a carrier gas along second fluid flow path “B.” A second filter  612  is provided upstream of second blower  606 . Second filter  612  is operable to filter dirt and/or debris from the carrier gas circulated along second fluid flow path “B.” 
      A third blower  614 , driven by a third motor  616 , is provided to circulate a carrier gas along third fluid flow path “C.” A third filter  618  is provided upstream of third blower  614 . Third filter  616  is operable to filter dirt and/or debris from the carrier gas circulated along third fluid flow path “C.” 
      A control system  700  for controlling the operation of system  510  is schematically illustrated in  FIG. 6 . Control system  700  is identical to control system  400  described above, except for the additional control by a controller  710  of third motor  616 . Controller  710  sends electronic signals to second and third motors  608  and  616  to operate at various speeds. Second and third motors  608  and  616  then cause second and third blowers  606  and  614  to circulate the carrier gas at various flow rates. It can be appreciated that input unit  712  and output unit  714  are the same as described above in the preferred embodiment.  
      Alternative embodiment shall now be further described with reference to the operation of system  510 . A typical sterilization/decontamination cycle includes a drying phase, a conditioning phase, a decontamination phase and an aeration phase. Depending on the operating phase, the flow along first fluid flow path “A,” or second fluid flow path “B,” or third fluid flow path “C” may be greater than the flow along the other two fluid flow paths. Prior to the initiation of a sterilization/decontamination cycle, input unit  712  is used to provide the operational parameters to controller  710 . The operational parameters include a target humidity level for a drying phase, a target VHP concentration for a conditioning phase, a target humidity level and a target VHP concentration for a decontamination phase, and a target VHP concentration for an aeration phase.  
      When a sterilization/decontamination cycle is first initiated, controller  710  starts with the drying phase. Controller  710  causes first and third motors  584  and  616  to drive first and third blowers  582  and  614 , thereby causing a carrier gas to circulate through system  510  along first and third fluid flow paths “A” and “C.” The majority of the carrier gas will flow along third fluid flow path “C.” The carrier gas will be directed between the flow paths by controller  710  as required for correct system operation. Dryer  564  removes moisture from the carrier gas circulating through third fluid flow path “C.” Controller  710  ends the drying phase when the actual humidity level, as measured by first humidity sensor  516 , is less than the target humidity level.  
      During the conditioning phase, controller  710  continues to cause first and third motors  584  and  616  to drive first and third blowers  582  and  614  thereby causing carrier gas to circulate along first and third fluid flow paths “A” and “C.” The remainder of this conditioning phase is operated in the same manner as described in the preferred embodiment in regards to vaporizer  528 .  
      Throughout the sterilization/decontamination cycle, VHP sensor  526  and first humidity sensor  516  send an electronic signal to controller  710  that is proportional to the actual VHP concentration and humidity level in isolator or room  512 . Controller  710  periodically compares the actual VHP concentration and humidity levels to the target VHP concentration and humidity levels. If the actual VHP concentration or actual humidity level is higher than the target VHP concentration or humidity level, controller  710  cause third motor  616  to drive third blower  614  faster to provide more flow along fluid flow path “C.” Controller  710  sends an additional signal to motor  542  to reduce the amount of liquid sterilant being supplied to vaporizer  528 . If the actual VHP concentration or humidity level drops below the target VHP concentration or humidity level, controller  710  causes third motor  616  to drive third blower  614  slower to provide less flow along third fluid flow path “C.” Controller  710  sends an additional signal to motor  542  to increase the amount of liquid sterilant being supplied to vaporizer  528 . For the remainder of the decontamination phase, controller  710  continues to control motors  542 ,  584  and  616  based on the actual VHP concentration and humidity levels in isolator or room  512 . The decontamination phase ends once the target conditions have been achieved in isolator or room  512  for a predetermined period of time that is sufficient to effect the desired sterilization or decontamination of sterilization/decontamination chamber or region  524 , and/or items therein.  
      After the decontamination phase is completed, the aeration phase is run to bring the vaporized hydrogen peroxide (VHP) level down to an allowable threshold (about 1 ppm). In this respect, controller  710  sends a signal to first, second and third motors  584 ,  608  and  616  causing first, second and third blowers  582 ,  606  and  614  to simultaneously circulate the carrier gas through the first, second and third fluid flow paths “A,” “B” and “C.” The majority of the carrier gas will flow along second fluid flow path “B” and third fluid flow path “C.” The carrier gas will be directed between the flow paths by controller  710  as required for correct system operation. The vaporized hydrogen peroxide (VHP) flowing along second fluid flow path “B” is broken down by catalytic destroyer  562 . Dryer  564  removes moisture of the carrier gas flowing through third fluid flow path “C.” 
      Referring to  FIGS. 7 and 8 , still another alternative embodiment of a vapor decontamination system  810  is shown. System  810  includes an isolator or room  812  that defines an inner sterilization/decontamination chamber or region  824 . A first humidity sensor  816  and a VHP sensor  826  are disposed within isolator or room  812 . Sterilization/decontamination system  810  is comprised of a first fluid flow path “A,” a second fluid flow path “B,” and a third fluid flow path “C.” First fluid flow path “A” in system  810  and second fluid flow path “B” are identical to the first and second fluid flow paths “A” and “B” as defined in system  510 . Third fluid flow path “C” is defined by isolator or room  812 , a portion of a second conduit  846  and a bypass conduit  904 . One end of bypass conduit  904  connects to second conduit  846  at a first intersection  902 . The other end of bypass conduit  904  connects to second conduit  846  at a second intersection  906 . First intersection  902  is located upstream of second location  906 . In this respect, isolator or room  812 , a portion of second conduit  846  and bypass conduit  904  define a closed loop path.  
      A dryer  864  is disposed within bypass conduit  904 . Dryer  864  is operable to remove moisture from the carrier gas flowing through third fluid flow path “C.” A dryer valve  908  is disposed between dryer  864  and second intersection  906 . Dryer valve  908  is downstream of dryer  864 . Dryer valve  908  is operable to control the flow of the carrier gas through third fluid flow path “C.” A bypass valve  912  is located in second fluid flow path “B” downstream of first intersection  902 . Bypass valve  912  is located between first intersection  902  and second intersection  906 . Bypass valve  912  is a control valve operable to control the flow of the carrier gas along second fluid flow path “B.” 
      Control system  1000  for controlling the operation of system  810  is schematically illustrated in  FIG. 8 . Control system  1000  includes a controller  1010  that is provided to control operations of motors  842 ,  884  and  914 . Controller  1010  also monitors VHP sensor  826 , pressure switch  844 , VHP temperature sensor  852 , vaporizer inlet air temperature sensor  854 , catalytic destroyer air temperature sensor  866 , balance device  836  that feeds a sterilant to vaporizer  828 , and first and second humidity sensors  816  and  868 . Controller  1010  also controls the operation of heater  856  and vaporizer  828 . Controller  1010  is a system microprocessor or a micro-controller that is programmed to control the operation of system  810 . Controller  1010  controls motors  884  and  914 . Motors  884  and  914  in turn control the speed of blowers  882  and  916 . Blowers  882  and  916  control the rate of flow of the carrier gas along fluid flow paths “A,” “B” and “C.” Controller  1010  provides an electronic signal to valves  908  and  912  to control the position of valves  908  and  912 . Valves  908  and  912  control the flow of the carrier gas along fluid flow paths “B” and “C.” It can be appreciated that input unit  1012  and output unit  1014  are the same as described above in the preferred embodiment.  
      Operation of this embodiment shall now be further described with reference to the operation of system  810 . A typical sterilization/decontamination cycle includes a drying phase, a conditioning phase, a decontamination phase and an aeration phase. Depending on the operating phase, the flow along first fluid flow path “A,” or second fluid flow path “B,” or third fluid flow path “C” may be greater than the flow along the other two fluid flow paths. Prior to the initiation of a sterilization/decontamination cycle, input unit  1012  is used to provide the operational parameters to controller  1010 . The operational parameters include a target humidity level for a drying phase, a target VHP concentration for a conditioning phase, a target humidity level and a target VHP concentration for a decontamination phase, and a target VHP concentration for an aeration phase.  
      When a sterilization/decontamination cycle is first initiated, controller  1010  starts with the drying phase. Controller  1010  causes first motor  884  and second motor  914  to drive first blower  882  and second blower  916 , thereby circulating the carrier gas along first, second and third fluid flow paths “A,” “B” and “C.” Controller  1010  sends an electrical signal to bypass valve  912  and dryer valve  908 . Bypass valve  912  and dryer valve  908  in turn cause an increase in the flow of the carrier gas along third fluid flow path “C” and a decrease in the flow of the carrier gas along second fluid flow path “B.” The majority of the carrier gas will flow along third fluid flow path “C.” The carrier gas will be directed between the flow paths by controller  1010  as required for correct system operation. During the drying phase, first motor  884  and first blower  882  are both operating to circulate the carrier gas along first fluid flow path “A.” Dryer  864  removes moisture from the carrier gas circulating through third fluid flow path “C.” Controller  1010  ends the drying phase when the actual humidity level, as measured by first humidity sensor  816 , is less than the target humidity level.  
      The conditioning phase is then initiated. Controller  1010  causes motor  842  to drive pump  838  to supply hydrogen peroxide to vaporizer  828 . It can be appreciated that the remainder of this conditioning phase is operated in the same manner as described in the preferred embodiment with regards to vaporizer  828 .  
      After the conditioning phase is completed, the decontamination phase is initiated. During the decontamination phase, the sterilant injection rate to vaporizer  828  and to sterilization/decontamination chamber or region  824  is decreased to maintain the concentration of vaporized hydrogen peroxide (VHP) constant and at a desired level. Controller  1010  uses VHP sensor  826  and first humidity sensor  816  to continuous monitor the VHP concentration and the humidity level in isolator or room  812 . As the humidity level or the VHP concentration exceeds the target VHP concentration or humidity level, controller  1010  sends a signal to bypass valve  912  and dryer valve  908 . Bypass valve  912  moves to a position to reduce the flow of the carrier gas along second fluid flow path “B” while dryer valve  908  moves to a position to increase the flow of the carrier gas along third fluid flow path “C.” Controller  1010  also sends an electrical signal to motor  842 . Motor  842  reduces the amount of liquid sterilant being supplied to vaporizer  828 . As the concentration of VHP and water in the isolator or room  812  drops below the target levels, controller  1010  sends an electronic signal to valves  908  and  912 . Bypass valve  912  and dryer valve  908  reduce the carrier gas flow along fluid flow path “C.” Controller  1010  also sends a third signal to motor  842 . Motor  842  in turn increases the output of liquid sterilant to vaporizer  828 . For the remainder of the decontamination phase, controller  1010  continues to control motors  914 , and  842  and valves  908  and  912  based on the actual VHP concentration and humidity levels in isolator or room  812 . The decontamination phase ends once the target conditions have been achieved in isolator or room  812  for a predetermined period of time that is sufficient to effect the desired sterilization or decontamination of sterilization/decontamination chamber or region  824 , and/or items therein.  
      After the decontamination phase is completed, controller  1010  causes vaporizer  828  and motor  842  to stop, thereby stopping the supply of vaporized hydrogen peroxide to the carrier gas flowing along first fluid flow path “A.” 
      Thereafter, the aeration phase is run to bring the vaporized hydrogen peroxide (VHP) level down to an allowable threshold (about 1 ppm). In this respect, as will be appreciated, first blower  882  and second blower  916  continue to circulate the carrier gas and sterilant through the second fluid flow path “B,” thereby causing the last of the vaporized hydrogen peroxide (VHP) to be broken down by catalytic destroyer  862 . It can be appreciated that the majority of the carrier gas will flow along second fluid flow path “B” and third fluid flow path “C.” The carrier gas will be directed between the flow paths by controller  1010  as required for correct system operation.  
      The foregoing descriptions are a specific embodiment of the present invention. It should be appreciated that this embodiment is described for purposes of illustration only, and that numerous alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the invention. It is intended that all such modifications and alterations be included insofar as they come within the scope of the invention as claimed or the equivalents thereof.