Patent Publication Number: US-7713473-B2

Title: Sterilization system and vaporizer therefor

Description:
FIELD OF THE INVENTION 
     The invention relates to sterilization of articles, and more particularly to vaporization of a liquid sterilant solution to provide a sterilant vapor. 
     BACKGROUND OF THE INVENTION 
     It is known to sterilize articles with a vaporized chemical sterilant, such as hydrogen peroxide, peracetic acid and glutaraldehyde. Wu et al. U.S. Pat. No. 6,365,102, incorporated herein by reference, describes a hydrogen peroxide/gas plasma sterilization system comprising a vacuum chamber, source of hydrogen peroxide vapor and a source of RF energy to create a plasma. Such systems marketed under the name STERRAD® are available from Advanced Sterilization Products division of Ethicon, Inc. in Irvine, Calif. 
     Rapid and efficient vaporization of a liquid sterilant solution to produce the sterilant vapor speeds the overall sterilization process, ensures complete vaporization and ensures that the vaporization phase of a sterilization cycle completes in a timely and repeatable fashion. 
     SUMMARY OF THE INVENTION 
     The present invention improves the speed with which a sterilization cycle can be completed. 
     A method, according to the present invention, provides a vapor phase sterilant to a sterilizing chamber. The method comprises the steps of: heating a vaporizing surface, the vaporizing surface being inclined; flowing a liquid sterilant solution over the vaporizing surface causing the sterilant solution to vaporize into a sterilant vapor; and delivering the sterilant vapor to the sterilization chamber. 
     In one aspect of the invention, the vaporizing surface has a plurality of downwardly running channels and the sterilant solution, while flowing over the surface, runs down the channels. 
     In one aspect of the invention the liquid sterilant solution is sprayed onto the vaporizing surface, preferably onto an upper half of the vaporizing surface. 
     In one aspect of the invention, the vaporizing surface comprises a first face and a second face which join at upper extents thereof, with a portion of the liquid sterilant solution flowing over the first face and another portion of the liquid sterilant solution flowing over the second face. 
     Preferably, the liquid sterilant solution comprises hydrogen peroxide and water. 
     In one aspect of the invention, the vaporizing surface comprises a plurality of wells which capture portions of the liquid sterilant solution as it flows down the vaporizing surface and hold these portions until they are vaporized. Preferably, the individual volume of the portions captured within the wells is between 10 and 50 micro liters. 
     In one aspect of the invention, the vaporizing surface comprises a plurality of protuberances wherein to increase its surface area. 
     Preferably, the vaporizing surface is inclined at an angle of between 15 to 60 degrees with respect to horizontal, and more preferably at an angle of between 25 to 50 degrees with respect to horizontal. 
     A sterilization system, according to the present invention, comprises a sterilization chamber and a vaporizer for supplying a vapor phase chemical sterilant to the sterilization chamber. The vaporizer comprises a vaporizing surface which is inclined with respect to horizontal. A means is provided for heating the vaporizing surface and a further means is provided for flowing a liquid sterilant solution onto the vaporizing surface. A passage between the vaporizer and the sterilization chamber provides for pathway for supplying the vaporized sterilant to the sterilization chamber. 
     Preferably, the means for flowing a liquid sterilant solution onto the vaporizing surface comprises a nozzle whereby the liquid sterilant solution is sprayed onto the vaporizing surface. More preferably, the nozzle is directed so that a majority of the liquid sterilant solution is sprayed onto an upper half of the vaporizing surface. 
     A plurality of ports can be provided for directing liquid sterilant over the vaporizing surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a sterilization system according to the present invention; 
         FIG. 2  is a block diagram of a vaporizer and diffusion path of the sterilization system of  FIG. 1 ; 
         FIG. 3  is a block diagram of an alternate embodiment of a sterilization system according to the present invention; 
         FIG. 3A  is a block diagram of an alternative embodiment of a sterilization system according to the present invention. 
         FIG. 3B  is a sectional view taken along lines  3 B- 3 B of  FIG. 3A ; 
         FIG. 4  is a block diagram of an alternate embodiment of a sterilization system according to the present invention; 
         FIG. 5  is a block diagram of an alternate embodiment of a sterilization system according to the present invention; 
         FIG. 6  is a section view taken along lines  6 - 6  of  FIG. 5 ; 
         FIG. 7  is a block diagram of an alternate embodiment of a sterilization system according to the present invention; 
         FIG. 8  is a section view taken along lines  8 - 8  of  FIG. 7 ; 
         FIG. 9  is a block diagram of a sterilization system according to the present invention; 
         FIG. 10  is a cut-away view of an outlet condenser/vaporizer for use in the system of  FIG. 9 ; 
         FIG. 11  is a cut-away view of an inlet condenser/vaporizer for use in the system of  FIG. 9 ; 
         FIG. 12  is a perspective view of an alternative inlet condenser/vaporizer for use in the system of  FIG. 9 ; 
         FIG. 13  is an exploded perspective view of the condenser/vaporizer of  FIG. 12 ; 
         FIG. 14  is a section view taken along lines  14 - 14  of  FIG. 12 ; 
         FIG. 14A  is a close-up section view of the valve assembly shown in  FIG. 14 ; 
         FIG. 15  is an exploded perspective view of a thermoelectric heat pump and rod assembly employed in the condenser/vaporizer of  FIG. 12 ; 
         FIG. 16  is an alternative sterilization system according to the present invention; 
         FIG. 17  is an alternative sterilization system according to the present invention; 
         FIG. 18  is an alternative sterilization system according to the present invention; 
         FIG. 19  is an alternative sterilization system according to the present invention; 
         FIG. 20  is a perspective view of an alternative inlet condenser/vaporizer for use in the system of  FIG. 9 ; 
         FIG. 21  is a valve block employed in the inlet condenser/vaporizer of  FIG. 20 ; 
         FIG. 22  is a cut-away view of the valve block of  FIG. 21  as employed in the inlet condenser/vaporizer of  FIG. 20 ; and 
         FIG. 23  is a perspective view of a vaporizer according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows in block diagram form a sterilization system  10  comprising a sterilization chamber  12 , a vaporizer  14 , and a vacuum pump  16 . The vacuum pump is capable of drawing a vacuum on the chamber, preferably as low as 0.5 torr. Between the vacuum pump  16  and the chamber  12 , is preferably located at throttle valve  18  and optionally an orifice plate  20 . The throttle valve  18  preferably also has good shut-off capability. A pressure gauge  22 , preferably located adjacent to the throttle valve  18 , shows the vacuum in the chamber  12 . A vent valve  23  employing a HEPA antimicrobial filter allows clean sterile air to enter the chamber  12 . The vaporizer  14  connects to the chamber  12  by means of an elongated diffusion path  24 . Turning also to  FIG. 2 , the diffusion path  24  incorporates temperature control elements  26  to control the temperature along the diffusion path  24 . 
     Vaporizers suitable for vaporizing a liquid sterilant such as hydrogen peroxide solution are known in the art. Kohler et al. U.S. Pat. No. 6,106,772 and Nguyen et al. U.S. patent application Ser. No. 09/728,973 filed Dec. 10, 2000, both incorporated herein by reference, illustrate vaporizers suitable for the present application. In its simplest for the vaporizer can comprise a small chamber into which the liquid hydrogen peroxide solution is injected. The low pressure in the vaporizer caused by the vacuum in the chamber causes the hydrogen peroxide solution to vaporize. 
     Preferably, the vaporizer  14  itself incorporates heating elements  28  which control the temperature in the vaporizer to optimize the vaporization process. Preferably, where the vaporizer  14  connects to the diffusion path  24  some form of thermal insulation  30  provided at the interface so that the high temperatures of the vaporizer  14  will not unduly affect the temperature in the diffusion path  24 . The vaporizer  14  and diffusion path  24  are preferably formed of aluminum; the thermal insulation  30  can take the form of a polyvinyl chloride (PVC) joint connecting the two together. 
     The heating elements  28  preferably comprise electric resistance heaters although other types of heating can be employed such as induction heaters, Peltier effect heaters, chemical heaters, fuel based heaters such as natural gas burners, etc. 
     Further, it is preferable to include a heater  32  inside the chamber  12 , preferably near a lower portion of the chamber  12  for revaporizing condensed hydrogen peroxide inside the chamber  12 . 
     The chamber  12  preferably includes a mechanism (not shown) to create a plasma therein. Such mechanism can include a source of radio or low frequency energy as described by Jacobs et al. U.S. Pat. No. 4,643,867, or by Platt, Jr. et al. in published U.S. Application Document No. 20020068012, both of which are incorporated herein by reference. 
     The present invention achieves its beneficial effect by allowing some of the hydrogen peroxide which is vaporized out of solution in the vaporizer  14  to condense onto the diffusion path  24 . After most of the hydrogen peroxide solution has vaporized, the temperature control elements  26  raise the temperature of the diffusion path to allow the condensed hydrogen peroxide to re-vaporize. Water has a higher vapor pressure than hydrogen peroxide, thus hydrogen peroxide in the vapor condenses more easily than water. Thus, the material which condenses in the diffusion path will have a higher concentration of hydrogen peroxide than the starting concentration of the hydrogen peroxide solution in the vaporizer  14 . 
     The temperature control elements  26  in simple form can comprise mere electric resistance heaters. In such case, the low ambient temperature of the diffusion path  24  provides the low temperature for condensing hydrogen peroxide thereon, and the control elements  26  later heat the diffusion path  24  to re-vaporize the now more highly concentrated hydrogen peroxide from the diffusion path  24 . Because the vapor pressure of hydrogen peroxide drops with lower temperatures, lower initial temperatures in the diffusion path  24  allows a lower pressure in the chamber  24  without subsequently preventing the condensation of hydrogen peroxide in the diffusion path. Lower chamber pressures promote system efficiency and thus, the temperature control elements  26  can further comprise a chilling component to lower the temperature of the diffusion path below ambient. Suitable chilling components include thermoelectric coolers or a typical mechanical refrigeration system. In such case, the diffusion path  24  would be first chilled, preferably to about 10° C., and then some time after vaporization has begun or even after it has completed, the diffusion path  24  is then heated, preferably up to 50° C. or 110° C. 
     When vertically oriented as in  FIG. 2 , the diffusion path  24  can potentially cause the vaporizing sterilant to condense in cooler regions between the temperature control elements  26  and then re-vaporize as it passes the temperature control element  26 . 
     The following example illustrates the benefits of controlling the heat in the diffusion path. 
     EXAMPLE 1 
     The efficacy tests were conducted by placing a CSR-wrapped tray (3.5″×12″×20″) consisting of representative medical devices and test lumens in a 20-liter aluminum chamber (4.4″×12″×22″) A one-inch stainless steel wire inoculated with at least 1×10 6    Bacillus stearothermophilus  spores was placed in the center of each of the test lumens. The effects with and without temperature control of the diffusion path were investigated with both a TEFLON, poly(tetrafluoroethylene)lumen having an internal diameter of 1 mm and a length of 700 mm, and a stainless steel lumen having an internal diameter of 1 mm, and a length of 500 mm. All lumens were open at both ends. Each of the samples was subjected to a sterilization cycle in a 20 liter vacuum chamber, which was held at 40° C. and 3 torr for 5 minutes. 1.44 ml of a 59% solution of hydrogen peroxide in water was injected at atmospheric pressure into the vaporizer which was held at 60° C. The 5 minute clock then started and the chamber was pumped down to 3 torr, which took less than one minute. In one case the diffusion path  24  had an initial temperature of 30° C. for the first minute while the chamber was evacuated to 3 torr and was then heated to 50° C. to release the condensed peroxide from the diffusion path into the chamber for the remainder of the cycle while pressure was maintained at 3 torr. In the other case, the diffusion path was held at 50° C. throughout the cycle. By maintaining the diffusion path at 50° C., no or little peroxide was retained in the diffusion path. Sterilization effectiveness was measured by incubating the test samples in growth media at 55° C. and checking for growth of the test organism. Table 1 shows the results of these tests. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                   
                   
                 30° C. 
               
               
                   
                   
                   
                 50° C. 
                 Diffusion 
               
               
                   
                   
                   
                 Diffusion 
                 Path For One 
               
               
                   
                   
                   
                 Path 
                 Minute Then 
               
               
                   
                   
                   
                 Throughout 
                 increased to 
               
               
                   
                 Lumen Type 
                 ID &amp; Length 
                 Process 
                 50° C. 
               
               
                   
                   
               
             
            
               
                   
                 Teflon 
                 1 × 700 
                 2/2 
                 0/3 
               
               
                   
                 Stainless 
                 1 × 500 
                 1/2 
                 0/3 
               
               
                   
                 Steel 
               
               
                   
                   
               
            
           
         
       
     
     When the diffusion path temperature was maintained at high temperature throughout the process, all of the samples in the TEFLON lumen tested positive for bacteria growth, indicating failure of sterilization, and one of two samples in the stainless steel lumen tested positive. Under the same conditions, but with an initially lower temperature diffusion path which was heated starting one minute after the diffusion began, none of the samples tested positive. Condensing the peroxide in the diffusion path during the initial vaporization stage and then re-vaporizing the condensed peroxide from the diffusion path into the chamber greatly enhance the efficacy. 
     Additional efficiencies can be achieved by alternating cool and warm regions in the diffusion path  24  as primarily illustrated in  FIG. 2 . The temperature control elements  26 , in simple form heating elements, are spaced apart from one another. Also, preferably, the diffusion path  24  is vertical in this respect. As the hydrogen peroxide solution vaporizes and passes through the diffusion path  24 , it is thought that it may alternately condense and re-vaporize as it passes over the heated and unheated sections of the diffusion path  24 . The diffusion path could alternatively comprise alternating heating and cooling elements. 
     The heater  32  within the chamber  12  acts similarly to the heating of the diffusion path  24 . By controlling the heater  32  temperature, the peroxide can be first condensed on the heater  32  and then re-vaporized into the chamber  12  to concentrate the peroxide. 
     A preferred cycle would be a modification of a cycle described in the Wu et al. U.S. Pat. No. 6,365,102, incorporated herein by reference. A series of pre-plasma energy additions with venting in-between dries moisture from the chamber  12 . A vacuum is then drawn upon the chamber  12  and the hydrogen peroxide solution injected into the vaporizer  14 . Alternatively, the peroxide solution can also be injected at atmospheric pressure. Some of the vaporizing solution condenses upon the cool diffusion path  24 . After a time sufficient for most or all of the hydrogen peroxide solution to vaporize from the vaporizer  14 , the diffusion path  24  is warmed by the temperature control elements  26  and the condensed hydrogen peroxide solution re-vaporizes. At about this time, the throttle valve  18  is closed and the pump  16  turned off to seal the chamber  12 . Much of the water fraction of the hydrogen peroxide solution has thus been drawn out of the chamber  12  by the vacuum pump  16  and the remaining hydrogen peroxide solution which re-vaporizes from the diffusion path  24 , or from the heater  32  in the chamber  12  if present, is of a higher hydrogen peroxide concentration than the starting solution. Preferably, a computer based control system (not shown) controls the functions of the process for ease and repeatability. 
     The hydrogen peroxide vapor thus produced contacts an article  34  or articles  34  in the chamber  12  and effects sterilization thereof. If those articles  34  have diffusion restricted areas, such as long, narrow lumens, it may be preferable to then vent the chamber  12  and allow clean sterile air therein to drive the hydrogen peroxide vapor deeper into the diffusion restricted areas. Then the chamber  12  is again subjected to vacuum and an additional injection of hydrogen peroxide, preferably with the heating sequence on the diffusion path, is repeated. After a time period sufficient to effect sterilization of the article  34 , preferably with a six-log reduction in challenge organisms such as  Bacillus stearothermophilus , a plasma is lit within the chamber  12 , thereby enhancing the sterilization and breaking down the hydrogen peroxide into water and oxygen. 
     The orifice plate  20  can enhance the effect of concentrating the hydrogen peroxide during its vaporization. As described in the Lin et al. U.S. Pat. No. 5,851,485, incorporated herein by reference, a controlled or slow pump-down of the chamber  12  initially draws off more water than hydrogen peroxide from solution as the water has a higher vapor pressure, thereby leaving a higher concentration hydrogen peroxide behind. Controlling the pump-down can be difficult as vacuum pumps generally do not throttle back well and throttle valves in such service are difficult to control and expensive. By placing the orifice plate  20  in the flow path to the pump  16 , the amount of atmosphere from the chamber  12  exhausted by the pump  16  is limited, and by selecting a proper size orifice  36  in the plate  20  can be controlled to a rate which effectively concentrates hydrogen peroxide in the chamber  12 . 
     Turning also to  FIG. 3 , a system  10   a , similar in most respects to the system  10  of  FIGS. 1 and 2 , with like part numbers denoted with an “a” appended thereto, also incorporates an orifice plate  20   a . However, to allow a quick pump-down of the chamber  12   a , yet retain the controlled pump-down benefits of the orifice plate  20   a , it incorporates two path ways from the pump  16   a  to the chamber  12   a . A first pathway  40  contains a throttle valve  42  and a second pathway  44  contains a throttle valve  46  and the orifice plate  20   a . Thus, during initial pump-down the first throttle valve  42  is open leaving the pump  16   a  freely connected to the chamber  12   a . As the chamber  12   a  approaches the vapor pressure of water, the first throttle valve  42  is closed thereby forcing the pump  16   a  to evacuate through the orifice plate  20   a  and thus draw out of the chamber  12   a  at a slower, controlled rate more conducive to preferentially drawing water out of the hydrogen peroxide solution and out of the chamber  12   a.    
     Turning also to  FIGS. 3A and 3B , a system  110  similar to that of  FIG. 1  is shown. Here, rather than use two paths as in the system  10   a  of  FIG. 3 , a valve  112  comprises a valve body  114 , a valve seat  116  and a valve element  118 , such as a butterfly disc, plug or the like. An orifice  120  is provided through the valve element. Thus, when the valve  112  is open evacuation can occur quickly, and when the valve  112  is closed it can occur more slowly. Such a valve could also be employed between the vaporizer  14  and the chamber  12  to further control the preferential vaporization and removal of the water from the germicide solution. 
     Turning now to  FIG. 4 , while highly concentration of the sterilizing vapor is helpful in achieving sterilization efficiency and efficacy, getting the vapor into contact with the items to be sterilized is also a concern. Typically, the low pressures (0.5 torr to 10.0 torr) inside of a chamber  12  promotes quick diffusion of the sterilant vapor to all areas therein. 
       FIG. 4  illustrates a sterilization system  60  comprising a chamber  62  having a vaporizer  64 , vacuum pump  66  and vent  68  connected thereto. Preferably, an elongated, temperature controlled diffusion path  70  as previously described connects the vaporizer  64  to the chamber  62 . A throttle valve  72  and pressure gauge  74  are provided at the pump  66 . 
     Articles  76  to be sterilized are placed into trays or containers  78 . Two types of packaging are commonly used in preparing articles  76  for sterilization. In one, the articles  76  are placed into a tray having a plurality of openings therein, and the tray is then wrapped with a material such as CSR wrap which passes sterilizing gases and blocks contaminating microorganisms. Such a tray is described in the Wu, U.S. Pat. No. 6,379,631, incorporated herein by reference. An alternative package comprises a sealable container with several ports, preferably on top and bottom surfaces thereof, with each of the ports covered by a semi-permeable membrane which passes sterilizing gases and blocks admission of contaminating microorganisms. Such a container is described in Nichols U.S. Pat. No. 4,704,254, incorporated herein by reference. The first type of packaging is typically called a “tray” and the second a “container.” However, the term “container” as used herein is meant to refer to any container, packaging or enclosure suitable for containing articles to be sterilized in a chemical vapor environment. 
     The pump  66  connects to the chamber  62  via an exhaust manifold  80 . The manifold  80  comprises one or more shelves  82  for supporting and receiving one or more containers  78  and which connect fluidly through the throttle valve  72  to the pump  66 . An opening, or preferably a plurality of openings  84  on the upper surfaces of the shelves  82  allow the pump  66  to draw atmosphere within the chamber  62  through the openings  84 , through the manifold  80  and out through the pump  66 . 
     The containers  78  preferably have openings  86  on a lower surface  88  thereon and additional openings  90  on at least one other surface. When the containers  78  are placed on the shelves  82  atmosphere being exhausted by the pump  66  is drawn in part through the openings  90  into the container  78 , through the container into contact with the article or articles  76  therein and then out through the openings  86  into the manifold  80  through the openings  84  therein. When the atmosphere being so exhausted contains a sterilizing gas it enhances its penetration into the containers  78  and into contact with the articles  76  therein. 
     Sterilizing gases are so exhausted during the previously described cycle as the sterilant solution is vaporizing and immediately before the second admission of hydrogen peroxide. Such a cycle can also further provide a pump-down after some period of diffusion. After admitting the sterilant vapor the chamber  62  pressure rises slightly due to the presence of additional gas therein, typically from about 0.5 torr to about 10 torr. Higher pressures are as efficient with higher load and chamber temperatures. 
     Turning also to  FIGS. 5 and 6 , an alternative design (in which like part numbers to those of the design of  FIG. 4  are designated with a “b” appended thereto) replaces the manifold  80  of the design of  FIG. 4  with a simple port  92 . The port  92  is covered by a support  94  for the container  78 , the support  94  having a plurality of openings  96  therethrough so that the chamber  62   b  is in fluid communication with the pump  66   b  through the container  78 , the support  94  and the port  92 . The support  94  can be removable. 
     Turning also to  FIGS. 7 and 8  (in which like part numbers to those of the designs of  FIGS. 4 to 6  are designated with a “c” appended thereto) shows a support  100  resting on a surface  102  in the chamber  62   c  through which penetrates the port  92   c . The support  100  surrounds the port  92   c . Thus, most or all of the atmosphere being exhausted by the pump  66   c  passes through the container  78  into a space  104  formed between the container  78 , the support  100  and the surface  102  and then onto the pump  66   c  through the port  92   c.    
       FIG. 9  discloses an alternative system in which, similar to the system of  FIG. 1 , a portion of the vaporized germicide solution can be condensed and the solvent, typically water, which has not condensed as quickly is removed from the atmosphere to further concentrate the germicide. The germicide is then revaporized to produce a more concentrated germicidal vapor for more efficient sterilization. The system comprises a sterilization chamber  200  containing a load  202  of items to be sterilized. A source  204  of liquid germicide solution provides the solution through a valve  206  to a first vaporizer/condenser  208  where it is vaporized and then supplied to the chamber  200 . A valve  210  can be provided to isolate the vaporizer/condenser  208  from the chamber  200 . The chamber  200  is also provided with a valved vent  212 . 
     A vacuum pump  214  provides for lowering the chamber pressure as described in reference to the previous embodiments. Between the pump  214  and the chamber  200  a second vaporizer/condenser  216  is provided for condensing the vaporized solution. Preferably valves  218  and  220  isolate the second vaporizer/condenser  216  from the pump  214  and chamber  200  respectively. 
     Turning also to  FIG. 10  a simple version of the second vaporizer/condenser  216  preferably comprises walls  222  defining an enclosure  224  having an inlet  226  connected to the chamber  200  and an outlet  228  connected to the pump  214 . A plurality of baffles  230  provides a torturous flow path  232  through the vaporizer/condenser  216 . The walls  222 , and potentially the baffles  230 , are temperature controllable to enhance condensation of and re-vaporazation of the solution. 
     A similar structure with an inlet can be employed on the first vaporizer/condenser  208  as well. Turning also to  FIG. 11 , a simple version of the first condenser/vaporizer  208  is illustrated. It comprises an enclosure  240  having an inlet  242  connected to the source of solution  204  (not shown in  FIG. 11 ) and an outlet  244  connected to the chamber  200  (not shown in  FIG. 11 ). A plurality of baffles  246  provides a tortuous flow path through the first vaporizer/condenser  208 . The enclosure  240  and potentially the baffles  246  are temperature controllable to enhance condensation and revaporization of the solution. 
     In a simple cycle, a liquid germicide solution, such as hydrogen peroxide and water is admitted into the first vaporizer/condenser  208  where it is vaporized and then flows into the chamber  200  which is at a low pressure, all as described in reference to previous embodiments herein. During vaporization and for sometime thereafter pump  214  continues to exhaust atmosphere from the chamber  200 . By controlling temperature and pressure this preferentially vaporizes water from the solution over the hydrogen peroxide and the water vapor is extracted from the system via the pump  214  to concentrate the hydrogen peroxide solution during the vaporization phase. Additionally, hydrogen peroxide, having the lower vapor pressure, will tend to condense more quickly than the water vapor in the first vaporizer/condenser  208 . As the pump  214  continues to exhaust atmosphere from the chamber  200  the vaporized hydrogen peroxide solution flows out of the chamber and into the second vaporizer/condenser  216  where a portion thereof will condense. Due to the preferential condensation of hydrogen peroxide over the water more of the water vapor will pass through the condenser  216  uncondensed and be exhausted via the pump  214  thus allowing further concentration of the hydrogen peroxide solution. At some point, the pump is turned off and the valve  218  closed. The condensed hydrogen peroxide within the vaporizer/condenser  216  is then re-vaporized preferably by heating the condenser  216 . This hydrogen peroxide will have a higher concentration for more efficient sterilization of the load  202 . 
     Turning also to  FIGS. 12 through 15 , a more elaborate condenser/vaporizer  250  is illustrated. In gross, it comprises an inlet manifold  252  which connects to the source of sterilant solution  204  and which acts as a vaporizer to provide initial vaporization, a condensing/revaporization section  254 , an outlet manifold  256  and a control valve  258  via which the vaporizer/condenser  250  connects to the chamber  200 . A resistance heater  260  affixes to the inlet manifold  252  and to the outlet manifold  256  to provide heat to assist in the initial vaporization within the inlet manifold  252  and to prevent condensation in the outlet manifold  256 . Other types of heating can be employed such as induction heaters, Peltier effect heaters, chemical heaters, fuel based heaters such as natural gas burners, etc. 
     Preferably, the inlet manifold  252  and outlet manifold  256  are formed of aluminum. Further, an insulator  262  is provided between the inlet manifold  252  and the vaporizer/revaporizer section  254 . 
     The condensing/revaporization section  254  comprises a housing  264 , preferably formed of aluminum, open on a first side  266  and second side  268 . A first thermo-electric device  270  and second thermo-electric device  272  affix to the first side  266  and second side  268 , respectively. The thermoelectric devices  270  and  272  preferably operate under the Peltier effect, although other classes of thermoelectric devices could be substituted therefor. More conventional heat pumps, such as freon or ammonia based systems can also be employed with somewhat greater complexity. 
     A first rod assembly  274 , comprising a plate  276  and a plurality of rods  278  extending normally therefrom affixes to the first thermo-electric device  270  with the rods  278  extending laterally into the housing  264 . A second rod assembly  280  similarly attaches to the second thermo-electric device  272  with its rods  278  extending laterally into the housing  264  in facing relationship to the first rod assembly  274 . The rod assemblies  274  and  280  are preferably formed of aluminum. 
     Preferably, the rods  278  extend almost to, without touching, the opposing plate  276 . Also, the rods  278  from the two rod assemblies  274  and  280  lie in a generally parallel relationship with each other with a spacing therebetween designed to, along with the volume within the vaporizer/revaporizer section  254 , provide a preferred flow rate of the vaporized sterliant therethrough to provide efficient condensation on to the rods  278 . Preferably, a flow rate is in the range of 0.1 ft/sec to 5 ft/sec, and more preferably a flow rate of 0.24 ft/sec is provided. 
     In a small condenser with a vapor path length of 3 inches, the residence time would be 1 second at a preferred velocity of 0.24 ft/sec. This residence time would be sufficient for the vaporized sterilant to interact with the cooler condenser surfaces and to condense. For a typical injection volume of 2 ml of sterilant solution, the surface area of the condensing/revaporization section  254  would be about 90 square inches to permit mass transfer for condensation. High temperature at low pressure in the initial vaporizer (inlet manifold  252 ) maintains the water and hydrogen peroxide in the vapor phase for delivery to the condensing/revaporization section  254 . For example, a vaporizer temperature of 70 degrees C. or greater at a pressure of 125 torr or lower ensures that a 59 wt % solution of hydrogen peroxide and water will be in the vapor phase. 
     As vapor enters the condensing/revaporization section  254 , which has a lower temperature, the hydrogen peroxide condenses on the cooler surface forming a concentrated solution. The temperature and pressure therein determine the concentration of the condensed solution. For example, at 50 degrees C. and 13 torr in the condensing/revaporization section  254 , the condensed hydrogen peroxide concentration would be 94 wt %. At 30 degrees C. and 3.8 torr, the condensed hydrogen peroxide concentration also would be 94 wt %. As the pressure in the condensing/revaporization section  254  is lowered, the temperature must also be lowered to maintain the same concentration of solution. 
     The orifice  308  offers the advantage of a more concentrated solution by restricting the flow from the condensing/revaporization section  254  to provide a more controlled vaporization. Variations in pressure in the condensing/revaporization section  254  and in the vaporizer due to vacuum pump pressure fluctuations are dampened out by the orifice  308  to prevent surges of water vapor from carrying hydrogen peroxide droplets from the condensing/revaporization section  254 . Another advantage of flow restriction by the orifice  308  is achieving a low pressure (less than 1 torr) in the sterilization chamber  200  to improve the diffusion coefficient in lumens while maintaining a greater pressure in the vaporizer/condenser  250  to operate at a greater temperature in the condensing/revaporization section  254 . Without an orifice  308 , sterilization chamber  200  and vaporizer/condenser  250  pressures must both be reduced to the same low pressure together, and the condenser must be operated at a very low temperature to maintain equilibrium of the solution. A lower condenser temperature is more difficult to control and may produce ice or condensate, which requires a more expensive design to protect electrical equipment. 
     An O-ring  282  seals the plates  276  on the thermo-electric devices  270  and  272  against the housing  264 . An aperture  284  through the housing  264  aligns with an aperture  286  through the insulator  262  to place a chamber  288  defined by the housing  264  into fluid communication with the inlet manifold  252 . An outlet passage  290  in the housing  264  connects to an upper portion of the chamber  288  and to a second aperture  292  through the insulator  262  which in turn aligns with the outlet manifold  256  to place the chamber  288  in fluid communication with the outlet manifold  256 . A safety thermostat  294  atop the housing  264  is wired outside of the control system to shut down heating of the vaporizer/condenser  250  above a predetermined temperature. Temperature sensors  295  and  297  measure temperature in the inlet manifold  252  and condensing/revaporization section  254  respectively. A pressure sensor  296  interfaces with the outlet manifold  256 . Heat sinks  298  having fan housings attach to each of the thermo-electric devices  270  and  272 . 
     The outlet manifold connects to a valve manifold  300  which provides three possible flow paths between the vaporizer/condenser  250  outlet manifold  256  and a valve manifold outlet  302  from the valve manifold  300 . The valve manifold outlet  302  communicates with the main chamber  200 . A main flow passage  304  is controlled by a valve  306  which can open to allow flow through the main passage  304  to the valve manifold outlet  302  or close to block such flow. The second passage is through an orifice  308  in an orifice plate  310  which provides a flow restriction to enhance the ability to preferentially draw water vapor from the vaporizer/condenser  250 . A third potential passage is through a rupture disk  312  which is designed to rupture in case of a catastrophic overpressure within the housing chamber  288 , such as in the unlikely event that an oxidizable sterilant such as hydrogen peroxide combusts therein. The orifice  308  could be moved to a position within the shut-off valve  306 , similar to that described in reference to the valve element  118  in  FIGS. 3A and 3B . 
     In operation, the main chamber is first evacuated to a low pressure sufficient to induce vaporization, such as 0.4 torr and the valve  306  is closed placing the vaporizer/condenser  250  into fluid communication with the chamber  200  solely through the orifice  308 . The inlet manifold  252  is heated with the heater  260  and a quantity of sterilant solution such as a 59% hydrogen peroxide/water solution is injected into the inlet manifold  252  where it vaporizes and diffuses into the housing  264  through the apertures  286  and  284 . The thermo-electric devices  270  and  272  at this time are drawing energy out of the rods  278  and dissipating it through the heat sinks  298  thus allowing the vaporized sterilant to recondense on the rods  278 . 
     The temperature of the inlet manifold  252  can be controlled to slowly vaporize the sterilant thus allowing the water to more quickly vaporize and flow through the vaporizer  250  and out through the orifice  308  to concentrate the remaining sterilant. The condenser/revaporization section  254  quite effectively concentrates the sterilant such that to speed up the process a fast vaporization in the inlet manifold can be employed while still achieving a high degree of concentration. 
     The condensate on the rods  278  tends to be more highly concentrated in the sterilant. After a time, when the initial charge of sterilant solution has been vaporized and a portion thereof condensed on to the rods  278 , the thermo-electric devices  270  and  272  are reversed to apply heat to the rods  278  and revaporize the sterilant. At this time, the heat sink  298  will still contain heat which had been extracted during the prior step and that heat can be used by the thermo-electric devices  270  and  272  to very efficiently heat the rods  278  and revaporize the sterilant. This added efficiency improves the energy efficiently of the device and allows a smaller and more compact vaporize condenser  250  to provide adequate heating and cooling. After the sterilant has been revaporized, the valve  306  is opened to allow efficient diffusion of the sterilant vapor into the main chamber  200 . 
     If a second vaporizer/condenser  216  is employed, its structure preferably mimics that of the vaporizer/condenser  250  without the inlet manifold  252 . In such a system, after initial diffusion into the main chamber  200 , rods within the second condenser  216  would be chilled and the pump  214  turned on to preferably extract water vapor from the condensing sterilant. After a period of time when sterilant has condensed, the rods would be heated to revaporize the sterilant and the pump  214  turned off. This revaporized sterilant would have somewhat higher concentration and would then re-diffuse into the chamber  200  to further enhance the sterilization process. 
     Other system arrangements are possible.  FIG. 16  illustrates an alternative embodiment which can enhance efficiency in conserving and concentrating the germicide solution. In this system, a chamber  314  containing a load  316  has a first condenser/vaporizer  318  connected to a source  320  of germicide solution and a second condenser/vaporizer  322 . The first condenser vaporizer  318  is isolated from the source  320  by a valve  323  and from the chamber  314  by a valve  324 . It also connects to an exhaust pump  325  and is isolated therefrom via a valve  326 . The second condenser vaporizer  322  is isolated from the chamber  314  by a valve  327  and connects to the pump  325  and is isolated therefrom via a valve  328 . A vent  329  is also provided. 
       FIG. 17  illustrates a similar system  330  employing a single condenser/vaporizer  332  (of structure similar to the condenser/vaporizer  250  with an additional outlet) connected to a sterilization chamber  334  adapted to receive a load  336  of instruments to be sterilized. A vacuum pump  338  connects to the chamber  334  via a valve  340  and to the condenser/vaporizer  332  via a valve  342 . A three-way valve may substitute for valves  340  and  342 . A source of germicidal solution  344  connects to the condenser/vaporizer  332  and the chamber  334  has a vent  346 . During initial vaporization and concentration of germicide from the source  344 , valve  342  is closed. After the vapor is diffused into the chamber  334 , valve  340  can be closed and the pump  338  used to draw vapor out of the chamber through the condenser/vaporizer  332  in its condensing mode to further concentrate the germicide. The concentrated germicide is then revaporized and diffused back into the chamber  334 . 
     The second condenser/vaporizer  216  of  FIG. 9  can be used to maximize germicide utilization when running a sterilization process with two full cycles of vacuum, inject, diffuse and vent. Prior to venting during the first cycle, the pump  214  is run with the condenser/vaporizer  216  being chilled to condense the germicide therein. The valves  220  and  218  are closed during the venting process. During the subsequent pump down, the condenser/vaporizer is kept chilled to keep the germicide from unduly vaporizing and being carried out of the system. 
     The systems of  FIGS. 16 and 17  allow even more of the germicide to be retained between cycles in a two cycle process. Prior to venting in the first cycle germicide is condensed into the condenser/vaporizer  332 . However, during the subsequent pump down it can be isolated from the pump via the valve  342  thus minimizing the tendency of the pump  338  to pump the saved germicide out of the system during pump down. 
     In each of this type of system the steps of condensing and concentrating the vaporized germicide and then revaporizing it can be repeated as needed to further concentrate the germicide. 
       FIG. 18  illustrates a system  350  plumbed in an alternative fashion. In this system  350  a condenser/vaporizer  352  connects through a valve  354  to a sterilization chamber  356  adapted to receive a load  358  and having a vent  360 . A vacuum pump  362  connects to the condenser/vaporizer  352  through a valve  364 , but has no separate connection to the chamber  356 . A source  366  of germicide connects to the condenser/vaporizer  352 . 
       FIG. 19  illustrates a system  370  plumbed as in  FIG. 17 , having a condenser/vaporizer  372  which connects through a valve  374  to a sterilization chamber  376  adapted to receive a load  378  and having a vent  380 . A vacuum pump  382  connects to the condenser/vaporizer  372  through a valve  384 , but has no separate connection to the chamber  356 . Rather than an inlet for germicide through the condenser/vaporizer  382 , a source  386  of germicide solution is provided within the chamber  376 . The source can be simple such as a well containing a quantity of liquid germicide solution. Preferably, it is covered with a semi-permeable membrane or filter so that liquid germicide can not be accidentally spilled therefrom yet as the germicide vaporizes under low chamber pressures the vapors thus generated can pass through the membrane into the chamber. In both systems the condenser/vaporizer  352  or  372  concentrates the germicide via condensation and revaporization of germicide vapor as described above. 
       FIG. 20  illustrates a further embodiment of an inlet condenser/vaporizer  400 . It is similar in most respects to that illustrated in  FIG. 12 . However, as shown primarily in  FIGS. 21 and 22 , it features an orifice control valve  402 . A valve block  404  receives an outlet control valve  406 , a rupture disk  408  and the orifice control valve  404 . 
       FIG. 21  shows the valve block  404  in isolation and illustrates three manifold passages which connect the valve block  404  to the rest of the condenser/vaporizer  400 : a large pressure relief manifold passage  410  which leads to the rupture disk  408 , a smaller upper manifold passage  412  which leads to the outlet control valve  406  and a smaller lateral manifold passage  414  which leads to an orifice  416  and the orifice control valve  402 . 
       FIG. 22  best illustrates the orifice control valve  402 . A valve seat  418  on the valve block  404  surrounds the orifice  416 . A valve member  420  on the orifice control valve  402  can extend toward to valve seat  418  to seal against it and block fluid communication through the orifice  416 . A cleaning pin  422  penetrates the orifice  416  when the orifice control valve  402  is closed to clean the orifice  416  and keep it clear of foreign matter. An annular guide  424  connected to the valve member  420  slides within a bore  426  within the valve block  404  to properly align the cleaning pin  422  with the orifice  416 . This view also illustrates a valve seat  428  for the outlet control valve  406  and a valve block outlet passage  430  which leads to the sterilization chamber (not shown in  FIGS. 20 to 22 ). 
     Operation of a sterilization cycle proceeds nearly the same as afore-described regarding the system shown in  FIGS. 12 to 15 . However, after the initial vaporization of the sterilant in the inlet manifold  252  (see  FIG. 14 ) the orifice control valve  402  is closed thereby isolating the condenser/vaporizer  400  from the sterilization chamber (not shown in  FIGS. 20 to 22 ). This condition can be monitored most easily be monitoring the pressure within the vaporizer/condenser  400  and assuming that when a particular pressure has been reached that essentially all of the sterilant has been vaporized. Pressure in the sterilization chamber is then reduced, preferably to approximately 0.5 Torr. The outlet control valve  406  is then opened and the rods  278  (see  FIG. 14 ) are heated to vaporize condensed sterilant and pass it through the outlet control valve  406  and outlet passage  430  to the sterilization chamber. 
     By lowering the pressure in the sterilization chamber prior to admitting the bulk of the sterilant it has been found that overall cycle times may be reduced. Closing the orifice control valve  402  and reducing pressure in the sterilization chamber takes additional time. However, the lower pressure provides a more favorable condition for diffusion of the sterilant into diffusion restricted areas, such as lumens, of instruments to be sterilized. It has been found that the time saved through the increased diffusion efficiency can more than offset the time lost in lowering the pressure in the sterilization chamber. Sterilization cycle speed is an important factor for sterilizer users. 
     Water vapor in the sterilization chamber can affect time required to lower the pressure therein. Such water vapor typically arises from a load of instruments that have not been properly dried. If undue time is required to remove the water vapor it can be indicated to the user so that they can be reminded to be more vigilant in drying the load for future cycles. There may exist loads of water vapor for which it may take too long to withdraw or to withdraw effectively. In such case the cycle should be cancelled and the user informed as to why. 
     Table 2 shows control points for three different cycles—a flash or very quick cycle having no lumens, a short cycle having only lumens which present a mild challenge and a long cycle for sterilizing devices with more challenging long and narrow lumens. During an initial pump-down to remove air from the sterilization chamber and vaporizer/condenser  400  the outlet control valve  406  is left open. As the pressure reaches P1 the outlet control valve  406  is closed but the orifice control valve  402  is left open; this starts the vaporization and concentration of the sterilant. Upon reaching pressure P2 within the vaporizer/condenser  400  the pressure Pc within the chamber is checked. If it is above the value listed in Table 2 then the orifice control valve  402  is closed and pump-down continues until Pc is reached and then the outlet control valve  406  is opened to transfer the sterilant into the sterilization chamber. Otherwise, the outlet control valve  406  is opened right away. If the chamber pressure exceeds Pc-cancel at the time that the vaporizer/condenser pressure reaches P2 it is assumed that the sterilization chamber contains too much water and the cycle is cancelled. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Examples of temperature and pressure set points 
               
            
           
           
               
               
               
               
            
               
                   
                   
                 Short 
                 Long 
               
               
                   
                   
                 1 mm × 150 mm SS 
                 1 mm × 500 mm SS 
               
               
                   
                 Flash 
                 1 mm × 350 mm 
                 1 mm × 1000 mm 
               
               
                 Load condition 
                 Surface 
                 Plastic 
                 Plastic 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Vaporizer 
                 70° 
                 C. 
                 70° 
                 C. 
                 70° 
                 C. 
               
               
                 temperature 
               
               
                 Condenser 
                 58° 
                 C. 
                 52° 
                 C. 
                 43° 
                 C. 
               
               
                 temperature 
               
               
                 P1 
                 140 
                 torr 
                 140 
                 torr 
                 140 
                 torr 
               
               
                 Vaporizer/ 
               
               
                 condenser 
               
               
                 pressure to 
               
               
                 remove air 
               
               
                 P2 
                 22 
                 torr 
                 16 
                 torr 
                 10 
                 torr 
               
               
                 Vaporizer/ 
               
               
                 condenser 
               
               
                 pressure to 
               
               
                 concentrate 
               
               
                 sterilant 
               
               
                 Pc 
                 1.5 
                 torr 
                 0.6 
                 torr 
                 0.3 
                 torr 
               
               
                 Chamber 
               
               
                 pressure to 
               
               
                 select transfer, 
               
               
                 additional 
               
               
                 vacuum or 
               
               
                 cancellation 
               
               
                 Pc-cancel 
                 8 
                 torr 
                 6 
                 torr 
                 4 
                 torr 
               
               
                 Chamber 
               
               
                 pressure to 
               
               
                 cancel cycle 
               
               
                 Condenser 
                 68° 
                 C. 
                 68° 
                 C. 
                 68° 
                 C. 
               
               
                 temperature to 
               
               
                 transfer 
               
               
                 concentrated 
               
               
                 sterilant 
               
               
                   
               
            
           
         
       
     
       FIG. 23  illustrates an alternative vaporizer  500  according to the present invention. It comprises a cavity  502  open at an upper extent  504  for connection to the condensing/revaporization section  254  (see also  FIG. 14 ) and having a lower vaporizing surface  506 . The vaporizing surface  506  comprises a first face  508  and second face  510  inclined toward each other to join at a ridge  512 . The vaporizing surface can be formed integrally with the cavity  502  or be a separate part which fits therein. An inlet  514  provides liquid sterilant solution, such as a solution of hydrogen peroxide and water, to the vaporizing surface  506 . 
     The inlet  514  can take several forms. Preferably it showers droplets of liquid sterilant solution evenly over the ridge  512 , allowing the droplets to flow down the first and second faces  508  and  510  thereby evenly distributing vaporization over the vaporizing surface  506 . It can comprise multiple nozzles or openings distributed above the ridge  512 . Each nozzle could comprise multiple openings. Even distribution promotes more rapid vaporization which can lower the time to complete a sterilization cycle. It also promotes uniformity in vaporization to maintain synchronicity with the condensing and revaporization. 
     The sloping faces  508  and  510  also economize space and enhance vaporization by enhancing the surface area to volume ratio for a given footprint, simultaneously promoting even distribution of liquid sterilant solution over the vaporizing surface  506 . Preferably, the first face and second face  508  and  510  are inclined between 15 to 60 degrees with respect to horizontal, and more preferably 25 to 50 degrees. 
     The vaporizing surface  506  can be configured to promote an even distribution of flow over it. For instance it can be textured, or provided with flow enhancing grooves, preferably vertically oriented. It can also be provided with a plurality of small pockets which catch a small amount of the liquid sterilant as it flows over the vaporizing surface  506  thereby evenly distributing the vaporization. Preferably, each pocket traps about ten to fifty micro liters of sterilant solution. In one aspect of the invention the total amount of sterilant would be 1.8 ml of 59% hydrogen peroxide solution. 
     The vaporizing surface  506  can also be covered with protrusions to increase its surface area. A surface of densely packed half-spheres would increase the surface area by about 78%. The additional surface area promotes more rapid vaporization of the liquid sterilant solution. 
     In addition to the triangular prism shape of the vaporizing surface  506  shown, other shapes would achieve a similar goal. For instance, the vaporizing surface could comprise an outer surface of a vertical cone, a pyramid or a half-sphere. 
     While described in connection with the condensing/revaporization section  254  and other equipment to concentrate sterilization vapors, the vaporizer  500  would similarly enhance a more typical vapor phase sterilization system in which the liquid sterilant solution is vaporized and fed directly into a sterilization chamber without attempts at concentration thereof. 
     The invention has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.