CA1108372A - Method of and apparatus for biocidal sterilization using cyclic subatmospheric pressure conditioning - Google Patents
Method of and apparatus for biocidal sterilization using cyclic subatmospheric pressure conditioningInfo
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- CA1108372A CA1108372A CA334,711A CA334711A CA1108372A CA 1108372 A CA1108372 A CA 1108372A CA 334711 A CA334711 A CA 334711A CA 1108372 A CA1108372 A CA 1108372A
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Abstract
METHOD OF AND APPARATUS FOR BIOCIDAL STERILIZATION
USING CYCLIC SUBATMOSPHERIC PRESSURE CONDITIONING
ABSTRACT OF THE DISCLOSURE
Conditioning of goods for subsequent sterilization with a biocidal agent in a sealable chamber includes removal of air, and moistening and heating the goods to the desired temperature levels. Controlled evacuation of the chamber and coordinated admission of conditioning vapor into the chamber provides cyclic variations in chamber pressure between pre-selected subatmospheric pressures to subject goods in the chamber to a plurality of cyclic subatmospheric pressure pulses. The time required for the cyclic pressure variations is responsive to load characteristics, including heat and moisture absorption characteristics of the goods being condi-tioned, and is independent of prescribed times or direct measurement of load temperature. The subatmospheric pressure levels are selected based on the temperature-pressure rela-tionship of the conditioning vapor so that chamber temperature during cyclic pulsing does not exceed the desired steriliza-tion temperature.
USING CYCLIC SUBATMOSPHERIC PRESSURE CONDITIONING
ABSTRACT OF THE DISCLOSURE
Conditioning of goods for subsequent sterilization with a biocidal agent in a sealable chamber includes removal of air, and moistening and heating the goods to the desired temperature levels. Controlled evacuation of the chamber and coordinated admission of conditioning vapor into the chamber provides cyclic variations in chamber pressure between pre-selected subatmospheric pressures to subject goods in the chamber to a plurality of cyclic subatmospheric pressure pulses. The time required for the cyclic pressure variations is responsive to load characteristics, including heat and moisture absorption characteristics of the goods being condi-tioned, and is independent of prescribed times or direct measurement of load temperature. The subatmospheric pressure levels are selected based on the temperature-pressure rela-tionship of the conditioning vapor so that chamber temperature during cyclic pulsing does not exceed the desired steriliza-tion temperature.
Description
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1`l~is invelltio~ col~cern~cl wlt~l s~rillzation of goocls Witll ~iocidal acJel-ts. In its more specific aspects, the invention is concernecl with methods and apparatus for more effective an~ more accurate preparation of gooc~s for biocidal gas sterilization and automated control of such con-ditioning of goods for biocidal yas sterilization.
Sterilization Wit}l a biocidal agent, e.q., with ethylene oxide yas, is utilized for sterilizing goods wllich could be damaged by the hiyh temperature requirements of steam sterilization. ~ackgrouncl on prior types of c~as sterilizing processes and apparatus, and advantages of utilizing ethylene oxide, are covered in "Principles and ~ethods of Sterilization"
~- by John J. Rerkins, E~irst Edition 1956, payes 325-334; Second Edition 1969, pages 501-530.
15The effects of time, temperature, gas concentration and humidity are integrated in accomplishiny the desired kill of microbial spores, veyetative bacteria and other micro-organisms. Humidifieation and heating of the goods to be sterilized, and penetration of the sterilizing or biocidal gas, can be more effectively carried out if air is first evacuated from the sterilizinc~ chamber and from any packaged goods, fabric-type goods, or goods with interstitial spaces to be s-terilized. Therefore, the conditioning of goods for gas sterilization involving evacuation of t}le chamber is generally carried out prior to injection of a biocidal gas in order to avoid loss of such gas through evacuation.
1`l~is invelltio~ col~cern~cl wlt~l s~rillzation of goocls Witll ~iocidal acJel-ts. In its more specific aspects, the invention is concernecl with methods and apparatus for more effective an~ more accurate preparation of gooc~s for biocidal gas sterilization and automated control of such con-ditioning of goods for biocidal yas sterilization.
Sterilization Wit}l a biocidal agent, e.q., with ethylene oxide yas, is utilized for sterilizing goods wllich could be damaged by the hiyh temperature requirements of steam sterilization. ~ackgrouncl on prior types of c~as sterilizing processes and apparatus, and advantages of utilizing ethylene oxide, are covered in "Principles and ~ethods of Sterilization"
~- by John J. Rerkins, E~irst Edition 1956, payes 325-334; Second Edition 1969, pages 501-530.
15The effects of time, temperature, gas concentration and humidity are integrated in accomplishiny the desired kill of microbial spores, veyetative bacteria and other micro-organisms. Humidifieation and heating of the goods to be sterilized, and penetration of the sterilizing or biocidal gas, can be more effectively carried out if air is first evacuated from the sterilizinc~ chamber and from any packaged goods, fabric-type goods, or goods with interstitial spaces to be s-terilized. Therefore, the conditioning of goods for gas sterilization involving evacuation of t}le chamber is generally carried out prior to injection of a biocidal gas in order to avoid loss of such gas through evacuation.
- 2 -~.' Suc~l con(litiollin(J can be carried out by first eva-cuatincJ the chan~er, t~len adding moisture to the chamber after evacuation is completed, and then addiny the sterilizing qas at a desired hiyller pressure. It has been generally recogllized t~lat more complete removal of air and more rapid heat up times are available witil a cycle in which steam flows into and tllrouyh tlle charllber while evacuatinc~ continues; see e~g., U.S. Patent No. 3,598,516, dated ~ugust 10, 1971.
Ill such. steam flow conditioning practice, a timer sets a prescribed period for steam flow while evacuating of tlle cilamber continues durillg conditioning of the goods. This prescribed time period is built into the control apparatus to provide for heating the most-difficult-to-heat load which might be encountered plus, usually, an added safety factor.
, This practice can extend the condit~ioning period much longer than necessary for most loads. ~ suygested alternative has been the packing of load sensors directly in the load to measure load temperature directly. But such a procedure places further burden Oll the operator and requires greater reliance on operator control.
The present invention requires neither prescri~ed times nor sensors placed in the load, but rather utilizes sub-atmospheric pressure cycIic pulsiny and load-responsive char-acteristics o t~e yoods to provi-le accurate an~ proficient conditioning for biocidal gas sterilization. The invention utilizes a control]ed pulsing action for a condensable condi-
Ill such. steam flow conditioning practice, a timer sets a prescribed period for steam flow while evacuating of tlle cilamber continues durillg conditioning of the goods. This prescribed time period is built into the control apparatus to provide for heating the most-difficult-to-heat load which might be encountered plus, usually, an added safety factor.
, This practice can extend the condit~ioning period much longer than necessary for most loads. ~ suygested alternative has been the packing of load sensors directly in the load to measure load temperature directly. But such a procedure places further burden Oll the operator and requires greater reliance on operator control.
The present invention requires neither prescri~ed times nor sensors placed in the load, but rather utilizes sub-atmospheric pressure cycIic pulsiny and load-responsive char-acteristics o t~e yoods to provi-le accurate an~ proficient conditioning for biocidal gas sterilization. The invention utilizes a control]ed pulsing action for a condensable condi-
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tioninc3 vapor, such as s-team. This pulsing ac-tion provides a drive power Eor -the conditioning vapor which Eurther reduces cycle t.ime.
Thus by one aspect oE this invention there is provi.ded a me-thod ~or conditioning goods for sterilizat.ion and steriliz-ing such goods wikh ethylene oxide in a sealable chamber capable of operating below atmospheric pressure within prescribed leak rate limits, such conditioning being carried ou-t prior to introduc-tion of the ethylene oxide and independent of load contact measurement requirements of temperature in the goods, the conditioning including heating the goods, mo.isteniny the goods and removal of air from the goods to facilitate heating and moistening of the goods to be sterilized, the method comprising the steps of loading the goods to be sterilized into tHe chamber and sealing the chamber, preselecting upper and lower subatmospheric pressure levels for controlled cyclic pulsing operation of such chamber during load conditioning, evacuating the chamber and injecting a condensable vapor having transferrable latent heat and moisture into the chamber to condition the goods to be sterilized by cyclically ; varying chamber pressure between such upper and lower sub-atmospheric pressure levels independent of prescribed evacuat-ing and vapor injecting times such that the time duration of a pressure rise from lower to higher preselected subatmospheric pressure levels during a cyclic variation is responsive to characteris-tics oE the goods being conditioned including moisture and heat absorption charac~eristics of such goods, such subatmospheric pressure levels being selected based on an interrelationship of pressure and temperature of pressuxe and temperature of the condensable vapor with such upper pressure level establishing an upper temperature for injecting the condensable vapor which approximates without exceeding the desired final sterilization temperature for the goods to be sterilized, the evacuating of such chamber and the injecting of the condensable vapor into such chamber being carried out alternately to bring about such cyclic variations in char[~er pressure, repeating such cyclic variation of chamber pressure be-tween the preselected subatmospheric pressure levels to provide a plurality oE cyclic pulses during such load condi-tioning before termination of evacuation of the sealable chamber in preparation for ethylene oxide gas sterilization, and aEter such termination of evacuation of the sealable chamber, introducing ethylene oxide gas into such chamber to accomplish the desired sterilization of goods in the chamber.
By another aspect of this invention there is provided an apparatus for conditioning goods in a sealed chamber for subsequent sterilization with a biocidal agent, the condition-ing including moistening and heating to a desired temperatureby subjecting the chamber and goods to a plurality of cyclic pressure pulses between predetermined subatmospheric pressure levels, comprising, in combination, a conditioning chamber capable of being evacuated to desired vacuum levels and operable within a maximum prescribed leakage rate, inlet conduit means connecting the conditioning chamber to a source of conditioning vapor, inlet valve means connected in the inlet conduit means and including power means for operating the valve to control the flow of conditioning vapor into the chamber, evacuation means for evacuating the conditioning chamber, : - 4A ~
exhaust condui-t means connecting the conditioning chamber to the evacuation means, exha~l~t valve means connected in the exhaust conduit means and including power means for operating the exhaust valve to control -the flow through the e~haust conduit to thereby control evacuation of the conditioning chamber by the e-~acua-tion means, - pressure sensing means including means for sensing lower and upper predetermined subatmospheric pressure levels in the conditioning chamber and for transmitting a signal in response -to the sensing of such pressure levels, and control means including means responsive to signals from the pressure sensing means including, means for generating operating signals for subjecting the conditioning chamber to a plurality of cyclic subatmsopheric pressure pulses independent of preselected time intervals, and means for operating the power means of the exhaust and inlet valve means in response to the generated operating sig-nals to alternately open the exhaust valve means and close theinlet valve means to exhaust the conditioning chamber to a lower prede-termined suhatmospheric pressure and to close the exhaust valve means and open the inlet valve means to increase the pressure within the conditioning chamber to an upper pre-determined subatmospheric pressure to control such cyclic subatmospheric pressure pulsing.
The advantages of rapid heating and short conditioning :
-times are made available while adding accuracy of conditioning and dependability of operation.
Other advantages and contributions of the invention will be more apparent from a more specific presentation of the methods and description of the apparatus shown in the accompanying drawings.
f L ~
Figure 1 is a schematic representa-tlon ~f apparatus in accordance with the invention;
Figure 2 is a process flow chart for carry.~ng out a conditioning cycle in accordance with an embodiment of the invention in which ma-terial to be sterilized is subjected to a fixed number of conditioning pressure pulses;
Figure 3 is a schema-tic representa-tion of control logic apparatus for carrying out conditioning in accordance with the process of Figure 2;
Figure 4 is a graphie representation of chamber pressure versus time -through the conditioning phase of Figure 2;
Figure 5 is a process flow ehart for carrying out a conditioning cycle in accordance with an embodiment of the invention in which conditioning i5 terminated when two succes-sive pressure pulses exhibit substantially the same character-istics;
-- ~C --., ',2 ~i(;ure 6 is a scll~matic representation of control '~ loyic aE)E)aLa~us for ca.rryi.llg out corlditioniily in accordance ~ith t~e process of Fi~ure 5;
r~icJure~ 7 is a c~ra~llic rel~resentation of chamber pres-sure versus time throucJh the conditionin~ phase of Figure S, of a minimal fabric loadcd cl~amber in accorclance ~ith the in-vention; and Yi.gure 8 is a graphical representation of chamber pressure versus time during conditioning of a full fabric load in accordance with the i.nvention.
During load conditioniny in accordallce with the in-vention, the chan~er is operated betweell preselected subat-mospheric pressure l.evels to provide cyclic pulsing utilizing a condensable vapor haviny transferrable latent heat and moisture for conditioniny the goods to be sterilized. Evacua-tion of the chamber and introduction oE such vapor are con- ::
trolled to provide cyclic variation in chal~er pressure be-tween such preselected subatmospheric pressure levels. The cyclic variation is independent of prescribed times in that the time duration of a pressure rise from lower to higher : preselected subatmospheric pressure level.s duriny a cyclic variation is responsive to characteristics of the goods being ,:
conditioned and can vary for differiny loads. Such load char-acteristics include moisture and heat absorption properties of materials forminy tl~e load; load characteristics can also V3ry clepel~di~g on the slze and manner of packlng the load.
~' ~
.
~ s is kno~n, cha~ r ternp~rature ls clirectly rela-ted to ch~rlber pressure or a particular vapor, e.g., steam.
~herefor~, pressure levels are selected so as not to cause the temperclture to excec!d a desired final sterilization tem perature for the goods to be sterilized. Cyclic v~riation of chamber pressure is carried out so as to provide a plurality of cyclic pulses. Since individual pulses are load responsive and independent of fixed time intervals, the total time dura-tion of the load conditionirlg phase is independent of any prescribed ti~e interval.
Load conditionin~ can be initiated by purging air from the sterilizing cllamber by evacuating the chamber while simultaneously introdueing the eonditioning vapor into the ~' ehamber at a controlled rate to prevent overheating the load prior to cyclic pulsing. Conditioning can be further auto-mated by establislling a time relation between corresponding ' phases of successive puIses. For example, the number of cyelie pulses can be automatieally selected based on the time duration of pressure rise from the lower to the higher of the preseleeted subatmospherie pre,ssure levels oE eonseeutive cyelic pulses. In one embodiment, eyelie pulsinc~ is termi-natecl when the time duration of the pressure rise of two sueh , eonsecutive pulses is approximately equal.
'~ Operatioll involvillc~ a fi~ed number of pulses is earried out in aeeordanee with the proeess outlined in the flow chart of ~igure 2. ~ e conditionincJ cyele includes the :
3~
steps of sul~jictii~g t!~e material to a fixed number of cycllc variations at subatl-nos~heric pressures by ~lternately evacua-ting the conditionin~3 challlber and increasing the pressure by admitting steam into ~he chan1ber a~ a controlled rate. ~n 5up-down counter, whicll counts the pulses, is pre-set, either manually or automatically, for the required number of pulses before comrnencing the cycle.
Operation can be initiated by a manual switch. The control logic provided by a înaster controller starts the 10chamber evacuation means and opens a power-operated exhaust valve to permit evacuation of the chamber. Steam is admitted into the chamber by actuation of a second power-operated ?
valve. The rate of flow of steam into and evacuation of the chamber can be coordinated so that the pressure in the cham-15ber is reduced by the pump while steam is being admitted.
The vacuum pump continues operation with steam flowing at a controlled rate into the chamber until the pressure within the chamber reaches a first predetermined subatmospheric level.
The pressure withill the chamber is continuously monitored by 20 a pressure-sellsin~ assembly mounte~ within the chamber.
When the pressure reaches an upper predetermined level, for example 90 ~n ~Ig. abs., a first set of contacts in the pressure sensor is actuated to signal the controller to stop the flow oE steam into tlle chamber. ~ith the steam supply valve closed, the vacuum pump continues to operate to further reduce the pressure in the chamber, with pressure 3t~J~
beiny mol~itol-e(l L~y the pressur2 sensillc~ assembly. ~hen the pressure reaches a lower predetermined level, Eor example, 60 ~n ~ig. a~s , a second set o~ colltacts in the pressure sensing assem~ly is actuated, siynallil-y the controller to simultancously close the exhaust valve and open the steam sup-ply valve to aclrnit a controlled flow of steam into the cham~er.
In the latter condition, steam entering tlle cham-ber at a controlled rate will yradually increase the pressure, and consequently the temperature, in the chatnber~ This in-crease in pressure is continuously monitored by the pressure sensiny assembly WhiC}I, acting throuyh the controller, main-tains the apyaratus in the stated mode until the pressure re-turns to or exceeds the upper predetermined pressure level.
- At this point, a third set of contacts in the pressure sen-siny assembly is actuated to simu1taneously open the exhaust valve and close the steam supply valve. ~gain, this mode of operation is maintained constant, under the monitoring oE the ;~ pressuxe sensing assembly, until the pressure within the cham-ber ayain reaches -the lower predetermined level ~t that time, the second set oE contacts are again actuated to again close the e~haust valve and open the steam supply valve to repeat the evacuation phase of -the cycle. Pressure pulses between Ei~ed pressure levels during a typical conditioning phase arc showll in l;'igurc 4. Cyclic yressure pulses can take place between differing pressure levels during the conditioning phase, but the upper pressure level is generally held at or 3 ~ ~
slightly below t~le pressu~-e corres~onding to the deslred sterilization temperature.
Sterili~lnc~ apparatus emboc]ying this invention is illustrat~l schernatically in Eiglire 1. Conventional sterili-zing chamber conEigurations can be utilized. ~s shown, theapparatus includes a double-walled cylindrical structure indi-cated generally at 10 and having an inner, open-ended pressure vessel 12 defining, with an end closure, door 19, a sterili-zing cham~er 16. Pressure vessel 12 is supported within an outer wall 18 which is spaced outwardly from and circurn-scribes a major portion of vessel 12. An open end of the wall 18 is joined to the adjacent end of the inner pressure - vessel 12 by an annular flange 20 to de~ine a sealable space 22 between the inner and outer walls, commonly referred to as a jacket. Other lleat insulating means for chan~er 16 can be used.
Tlle door 14 can be hinged or otherwise mounted at one side of the open end of the double wall structure to facilitate opelling and closing the chan~er 16. A conventional lock assem~ly can be used for door 14, e.g., a cam lock assembly, including an actuating lever or wheel 24 and locking cams 26, enabling the door to be firmly locked to tightly seal the chamber 16 during the sterilizing operation. A drain conduit 28 is fitted in a bottom portion of jacket wall 18, and a one-way check valve 30, connected in conduit 28, permits fluidto flow through COIl~Uit 28 to escape from tlle jacket 22. A
g æ3~z variablc-orifice flow-res~rLctor 32 is connected in the con-duit 28 to cnable tlle rate of flow thro~gh the conduit to be controlled so that the pressure, and thereby the temperature, witl~in t~le jacket 22 can be regulated.
The sterilizer includes a plumbing systern for sup-plying conditiollincj vapor and biocidal steriliziny gas to chamber 16, ancl steam to the jac~;et 22 The plumbing system is illustrated as includincJ a main steam supply line or con-duit 34 conllected to a source of low-pressure steam, such as boiler 36, for supplyincJ steam as a conditioning vapor, through ; one-way check valve 38, solenoid-actuated cut-off valve 40, and variable-orifice flow-restrictor 42, to an~inlet 43 in sterilizing chamber 16. A branch conduit 44, connected in ; the main steam line 3~ upstream of check valve 38, supplies steam to the jacket 22 to help insulate the inner pressure vessel 12 against heat loss. A temperature sensor, for exampLe a thermocouple 4S, is mounted on the wall of chamber 12 to continuously monitor the temperature of the wall which closely corresponds to the temperature of tlle steam in jacket 22.
This measured temperature is employed to control actuation of solenoid-actuated valve 48 whlch, together with one-way check valve 46, and a variable-orifice flow-restrictor 50 in line 40 and check valve 30 and flow-restrictor 32 in drain line 28, control stcaln Elow throuyll conduit ~4 to jacket 22.
The pressure within sterilizing chamber 16, and the flow of vapor or c~ases through that cl~ambcr during the condi-3 t `2 tionincJ p~lase Or ~lle cycle is controll~d hy a charn~er exhaust system includillc~ suital~le evacuating means such lS a vacuum pump or ejector 52 connectecl through exhaust line or conduit 5~ to an outlet 55 Wllicil is showrl in the bottom of sterili-zing chamber 1~ but whicll can be located at any convenientlocation. One-way check valve 56 and solenoicl-actuated sh;lt-off valve 58 are collllected in exhaust lirle 54 to regulate the flow through the exllaust line. The temperature and pressure within the sterllizing chamber 16 may be regulated in part lQ by this arranyement.
Sterilant supply means for supplying a controlled flow of biocidal gas such as ethylene oxide to the sterili-zing chamber 16 includes a supply line or conduit 60 connected between conduit 34 downstream of check valve 38 and a source of the biocidal gas indicated in Figure 1 as a pressurized container or bottle 64. Flow through the conduit 60 is regu-lated by one-way check valve 66 solenoid-actuated shut-off valve 68 and a variable-orifice flow-restrictor 70. A
baffle 72 mounted ~ithin tlle interior of chamber 16 adjacent the inlet 43 provides for a more uniform distribution of bio-cidal gas enteriny the chamber 16.
The temperature of the biocidal gas supplied to the ; chamber 16 can be regulated by a heat exchanger 74 connected in t~le line G0 in heat excllange relation with steam supplied through a conduit 76 connected in the main steam line 34. A
solenoid-actuatecl sh-lt-off valve 78 and a variable-orifice 3~
flow-restrictoL ~0, con~ectecl in line 76, re-~ulate the flow of steam tl~rouc~h the heat exchanc3er 74 and thereby the tem-perature of the biocidal yas flo~ing into chanlber 16. Steam is e~:hausted rom ~l~e heat exchanc3er 74 through a suitable conduit 82 to a sump or clrain 84.
~fter sterilization, air ~low through the chamber 16 is provicled by air supply line ~6 connected in the char~er supply line 34 downstream of the steam control valves 38, 40 and flow-restr~ctor 42. Air is supplied to the air line 86 through a suitable filter 88 having an inlet 90 open to the atmosphere. ~ solenoid-actuated shut-off valve 92 and one-way check valve 94 control flow throuyh line ~6. Since air flows tllrouyh or into chamber 16 only when the pressure with-in the cha~ber is below atmosphere, atmospheric air pressure is sufficient to provide the necessary air flow. Filter 88 is of a type to effectively remove bacteria from the air and can also include other air sterilizing means.
; In the embodlment of Figure 1, a pressure sensing assembly 96 is mounted within ehamber 16. Chamber pressure signals generated by the pressure sensinc3 assel~bly 96 are ; supplied, through suitable electrieal eonneetions inc~ieated by line 98, to a eentral eontrol 100. Pressure sensing assembly 96 ineludes a ~irst set of eontacts whieh are ae-tuatecl UpOIl the pre.sure withill the ehan~er 16 being ini-tially lowered to the upper predetermined pressure to thereby generate a signal for tlle eontrol 100 to actuate the solenoid of tlle illLet valvc ~10 t-o s~oL~ the 10w of steam. Valve 40 can be a conven~iollal normally-closed, energized-open valve so that the control de-etler~izes tl-e solenoid to close the valve. Power mealls ot~ler than a solcnoid rnay be employed to control operation of the inlet and exhaust valves.
~ secolld set of contacts in pressure sensing assembly 96 are actuated to c~ellerate a sicjnal each time the pressure in chamber 16 reaches the lo~er predetermined level. This siynal is utilized by the control 100 to operate the solenoids of both the :inlet valve ~0 and the exhaust valve 58 to open the inlet valve and close the exhaust valve. This results in an increase in pressure wit}lin the chamber to the upper pre- -~
determined level. ~hen approaching the upper pressure level in this manner a third set of contacts in the pressure sensing assembly 96 is actuated, signalling con-trol 100 to operate the solenoids to close inlet valve ~0 and open eY.haust valve 58 . . .
each time the upper predetermined pressure is reached from a lower pressure. The function of the first and thixd set of ~-contacts may be achieved by a sinc;le set of contacts, but the control is simplificd by using separate contacts wllic}l are actuated when the desired pressure is attained from higher and lo~er pressures. It is also possible to use separate contacts or other sensors to generate signals each time the lower pres-surc is rcacllccl al~d thcse separlte scnsors may havc difrcerent settinc;s if desired to change the lower pressure of the indi-vidual pressure pulses.
~ o~ oller I00 ill~Lu~l~s a courlt~r me~c-ilanism, pre-ferably in the Lorm o~ a solid state up-do~n counter illus-trate~ sc~lematically in ~icJure 3, wl~ich coun~s the number of actua~ions of tlle contacts in pressure sensiny assembly 96.
~Eter a predetermil)ed number of cyclic pulses, when the pres-sure within chamber 16 xeaches the upper predeter~ined subat-mosplleric levcl, actuation of tlle third set of Collt.lCts in p~essure sensinc3 assembly 96 results in the shut-off valve 40 being closecl and shut-off valve 58 remaininy closed. At the same time, shut-off valve 78 is opened to permit steam to flow through the heat exchanyer 7~ and shut-off valve 68 in biocidal gas supply line 60 is opened to permit biocidal gas to flow througll tlle heat exchangerO Biocidal yas then flows through flow-restrictor 70 into chamber 16 to pressurize the ; 15 chamber to tlle recluired level and the pressure is held for the required time to complete desired sterilization of the material in the cham~er.
After completion of the biocidal yas treatment phase ;~ of the sterilization process, the interior oE the chamber 16 can be flushed with filtere~ air by initially opening the valve 58 and operating the Vacuum pump 52 to withclraw the residual biocidal gas from the chamber. The shut-off valve 58 is then closed and shut-off valve 92 opened to permit fil-tered air to enter the chamber. Sllut-off valve 92 may then be ; 25 closed and the air withdrawn by openiny valve 58, and the pro-cess repeate~ as necessary to flusll the biocidal gas from the article~; I)eill(J sterili-~ecl. ~lterl~atively, t}-e challlber can be flushe~ by simultaneously operatincj the evacuatil-g pump and permitting air to flow into the chamber.
Tl~e final step in tl~e sterilization process ~ill S normally consist o permitting filtered air at atmosp}leric pressure to enter the chamber and to stabilize the pressure througllout the sterilized articles w}lereupon the door 14 may be opened and the sterilized articles removed.
I)uriny the conc1itiolling phase of the steriliæiny process, air is witlldrawn frorn porous articles to be processed and, in turn, the steam admitted to the chamber permeates the articles. The articles are heated from the latent heat of the steam which condenses on and within the articles, thereby simultaneously moistening and conditioning them for subsequent sterilization by the biocidal gas. ~s the outer layers of a load oE material become heated, the steam penetrates deeper before it is condensed until eventually the load is completely permeated Witil steam and is heated and moistened substantially uniformly throughout. The pressure pulsing has been found to greatly facilitate steam penetration and air removal so that a more thorough and uniform conditioning is achieved.
With a controlled rate of admission of steam into the cllamber during the repressurization phase of the cyclic i pulses, the rate of condensation, and consequently -the heating and humidification of the sterilizer load, will directly affect the lengtll of time required for the chamber to become repres-~ 3~ ~
suri -~,t~ Lrorn t~-~ se~o~ O~L pr~ssure level to the upper predeterlllinc~ p;essure level. It hcls been determined that, when the reE~ressurization phase o~ two successive pulses re-quires su~stalltially the sarlle time, the load has been thoroughly conditiolled, i.e., moistened and heated throughout. By measuriny the time o~ the repressurization phases of each pulse, and comparing these times for successive pulses, the condi-tioning phase of the sterilization cycle can he terminated automatically when two succeeding measured times are substan-tially eclual. Tilis fully autornated conclitioning method isdependent directly u~or) the pressure which is continuously monitored in the chamber 16.
; ~xperience has sho~n that conditiorling can also be carried out with a fixed number of pulses~ With normal steam flow it has boen cletermined that four such cyclic pulses will adequately condition standard types of hospital loads inclu-ding a devised pack considered to be the most difficult load to be encountered in the operation of a modern hospital. In operating a sterili7er accordiny to the fixed number of pulses method, wherl four pulses have been completed, a counter auto-matically terminates the pulse conditioning phase in prepara-tion for the sterilization phase. The total time duration for such four pulses will vary according to load characteris-tics.
~igure 3 illustrates schematically the electronic control system for controlllng the conditionillg of material to be sterilize~l tllrou~ a ~re~e~cr~ ne~ nu~ber oE condi-tioning pulses, followiny the steps outlioed in the flow diagram of Fi~3ure 2. The control system includes a conven-tional u~-down counter 102 whicll can be up~counted by feeding a signal in on the "count" line whell tlle "control" line is in a given state and whicll can be down-counted by eeding a signal in on the "count" line when the "control" line is in a differellt given state. ~efore the process is begun, up-down counter 102 is loadecl with a precletermined count which correspon~s to the number of cyclic pulses which are to be used for the conditioning phase. This may be done automa-`:
tically, that is with the number of pulses preset and fixed for a particular sterilizer; or, as shown in Figure 3, can be set by depressing the button 106 on selector 109 the appro- ~ ;~
priate number o times. The pulse selector 104 is a conven-tional pulse generator, arranged so that the number o times that the button 106 is depressed appears on a display window 108. ~;
The outputs of up-down counter 102 are connected to a decoder 10~, each output line of which is representative of .~ :
a given number. Thus, at the t1me that the initial number of pulses are loaded into counter 102, the correspondiny output line o decoder 110 has a signal thereon. ~hen this initial number of pulses is counted down to zero, then the zero out~
put line of decoder 110 has a signal thereon. This indicates the final evacuation and, upon repressurization of the chamber to the upper pressure, the end of the conditiolliny phase o ... .
3~;;Z
tl~e cycle. Il~c outl~ut o~ tllc zcro linc of the decoder is conllected to one side oE ~ gate 112. The lligh pressure level signal ~rorn pressure sellsor 96 is conllected to the other side o ~ c~ate 112 so that, when a hi~ll pre~sure level sig-nal is present and at t~le same time a signal is present rom decoder 110, ~ND gate 112 is effective to pass a signal stop-ping t~e conditioning cycling and sic;nalling the commencing of the sterilization pl~ase of the cycle.
Each time that button 106 is pressed, pulse selec-tor 104 gellerates a pulse on the count line input to counter 102 to up-count the counter. In the ernbodiment shown, but-ton 106 has been pressed four (4) times to effectively load the number "4" into the counter 102. This number can be preset.
~ith the up-down counter pre~loaded ~ith the number of pulses corresponding to the number of pressure pulses in the conditioning phase of the sterilization cycle, a start signal is generated by any convenient means such as manually closing a conventional on-off switch connected in the main ~ power circuit of the control. The start signal actuates - 20 vacuum pump 52 and opens control valve 58 to thereby imme~
diately commence evacuation of the chamber 16~ Either simul-taneous with the commencement of evacuation, or at a prede termined time thereafter, valve 40 is opened to admit steam to flow, at a rate controlled by tlle setting of flow-restrictor 42, into the chamber 16 while continuing to evacuate the cham-ber. Tllro~gllout tl~e remainder of the conditioning phase of ~ 18 -~8~
the c~cle, o~)cration is ul~c~er col~trol of the absolute pressure responsive pr~ssure-serlsinc3 assembly 9G which continuously monitors the ~bsolute pressure withirl the chamber 16, as pre-viously described. Tllis pressure is precerably continuously recorded by a convelltional pressure recorder, the output of which is plottecl against time and illustrated in ~igure 4, W}liCh shows the pressure within the chamber 16 at the start of the cycle to be 760 mm ~Ig., or one atmosphere.
The controller 100 includes a timing system which monitors the time required for the conditioning phase of the cycle ancl aborts the cycle when an excessive amount of time is rec~uired to reach the sterilizing phase. This timing sys-tem can abort the cycle after termination of the conditioning phase, as showli schematically in Figure 3, or alternatively can abort the cycle after a predeterrnined time, regardless of whet}ler or not the conditioning phase has been completed. In the systern shown in Fiyure 3, the start signal which commences the cycle also starts a pulse ~enerator 114 whieh supplies - the pulses to a pre-loaded down-counter 116. The down-counter11~ is a eonventional, commereial]y-available item whieh is down-eounted by the pulses from c;enerator 114.
The outputs of the down-counter 116 are connected to a deeoder 118, each output line of which is representative of a number of pulses counted by the down-counter. i~}len the preset number of pulses has been down-countcd to zero, then the zero output line of the decoder llB has a signal tilereon, ' . .
:
`. sicJnallil)(3 ~ t tllc ~lowll-coullter h~s ~imecl out, i.e., tllat a predeteLmined time has lapsecl since the start sicJnal started the ~ulse c~c~nerator ancl commencecl the conclitioning phase of the cycle 'i`he output sigllal froln decoder 118 sets a latch 120 which, in turn, latches a signal onto one input of ~ND
gate 122.
The output signal of ~NV yate 11.2 is fed into the other side oE ~N~ gate 122 so that, when a signal is present on the input line from latch 120 and from AND yate 112, AND
gate 122 procluees an output siynal which aborts the eyele and can energize a sui.table signal sueh as a buzzer, warni.ng light, or the like.
The output from ~ND gate 112 also applies a stop signal to pulse generator 114 and resets down-eounter 116.
Thus, if a signal is present from ~ND gate 112 indieating that the eonditioning phase has been eompleted prior to the timing ~ -out of pre~loaded down-eounter 116, no signal will be reeeived from deeoder 118 to ~ND gate 122. Under these eonditions, the signal from up-down counter 102, through ~ND gate 112, will be effeetive to eontinue the sterilization eyele by the ad-mission of sterili.zing gas into ehamber 16.
The start signal, whieh starts the pulse generator 114 and eommenees the eomplete eyele, is also eonneeted to the re-set of latell 12n so tllat any previously set signal. is erased at the beginnilltJ of eaeh eyele.
~leasurinc3 tlle time lapse durlncJ the eonditioning -3~2 pll~sc oL tllc cyclc or por~iol~s tl~ereoe, and aborting the cycle ; in the evellt of excessive time, cJ~arcls agains~ the application of biocidal sterilants SUC~l as ethylene oxide gas to a possibly clefective stcrilizer. ~hus, a leak in tl~e sterilizer seal can result in an excessive amount of ~ime required to reach vacuum, thereby causincJ tlle timing mechanism to time out prior to completion of the condi~ioning phase. By sensiny t~lis exces-sive time an~l aborting the cycle prior to admitting the steri-liæing gas, any potential hazard rom such a leak is minimized.
The upper predetermine~ subatmosplleric pressure is inclicated in Figure 4 as being 90 mm llg abs. As is known from standard steam tables, this pressure will produce a tem-perature within the chamber of about 122F. When steriliza-tion is to be completed in chamber 16 immediately follo~ing completion of the conditiol-ing cycle, this upper pressure is selected so as to produce a maximum temperature within the chamber which is slightly, preferably about 5 - 8 F., ~elow sterilization temperature of about 130 F. This permits a slight increase in cnamber temperature without exceeding the desired 130 ~. temperature when the biociclal sterilization gas is admitted into the cha~ber at a pressure above the upper predetermined pressure.
Referring to Figure 5, a flow chart illustrating tlle succcssive steps of the conditionillg phase utilizing the repressurization timing and comparing system is illustrated~
From this flow chart, it is seen that the sequence of steps 7~
is iclentical to thclt ~escr:i}~ccl above with the exception that, after eac~ low~r prc-clet~rrnin~c~ pressure is reached, the time required for the pressure to returll to the upper predetermined pressure level is rneasured ancl comparecl with the correspo~ding time of the precedincJ pulse. Wl-len two such successive times are substantially equal, that load is conditioned and the conditioniny phase can be termlnated regarclless of the number of pulses.
Figures 5 - 7 illustrate the operation of the em-bodiment of the i.nvention wherein the control system termi-nates the conclitioniny phase when two successive pulse repres~ ~:
surizations require su~stantially the same time. In this embodiment, the pressure responsive control signals are also - directed to a conventional timing pulse counter 124 whi.ch, ~.
in turn, is connected to a conventi.onal timing pulse gellera-tor 126. The initial low pressure signal starts the timing pulse counter whicil continues to operate and feed timing pulses . to a shift register until a high pressu.re level signal is re-ceived which stops the timing pulsé counter ancl conditions the shift register 128 of the timing pulse counter to accept the data in the first register positi.on. The time between the low and high pressure signals is thus stored in the first register position. When a second low pressure signal is re-ceived, the timillcj pulse counter i.s agai-l startecl and runs continuously until a second high pressure control signal is received. lhe seconcl higll pressure control si~nal also condi-^~i$~3 ~'~
tions the s~lift recJistel to ~ccept the new timing data from the timiny pulse counter and to shift the data from the pre~
ceding pressurization pulse p~lase to the second position. ~t ~;
this point, a cligital comparator 130 compares the duration of the two timed pulses and, i~ the times are the same, within predetermined limits, a sic;nal is emitted stopping the cycling.
If, however, tlle tin~es are not within acceptable limits, the cycling is repeated until the comparator, comparing the times of the last two successive repressurization cycle phases, is within acceptable limits, or, alternatively, the up-down coun-ter mechanisrn described above can override the comparator control ancl stop the cycling after four complete pulses regard-less of the times for the third and fourth repressurizatlon pulse phases. ~s with the embodiment shown in Figure 3, this ernbodiment can include timing means for aborting the cycle in the event that excesslve time is required for the condi- `
tioning phase.
Figure 8 shows a cycle wherein the conditioning was terminated after three repressurization pulse phases. As illustrated, the time of repressurization of the second and third phases are substantially equaI. Termination of the cycle, as well as the lenyth of time required for the indivi-dual pulses, was determined by the characteristics of the load rather ~hall ~y any predeter~ led time or temperature con-sideration.
The conditionlng and sterilizing apparatus of the 8;~
invention C(~ e controlle(l ~y a micro-processor progranuned to accom~lish tl~ various ~unctions and sequence of steps des-cribed above. ~ccordinc~ly, it is conternplated that such a processor may be employed in place of the control system des-cribed with reference to Fic~ures 3 and 6 to control operationof the apparatus to perforrn the process described.
A number oE tests llave been conducted in order to prove the effectiveness and efficiency of tile method and apparatus of this invention. Microbiological data was col-lected using a 24" x 36" x 48" steriliziny chamber, with the cont~ols functioning to subject the ch~mber to the condi-tioniny and sterilization cycle described above. Ethylene oxide gas was used as the biocidal agent during the sterili-~ing phase of the cycle.
The testiny employed standard biological indicators (BI's) containing 106 spores of Bacillus subtilis (globigii) on filter paper strips. Standard culture procedures were used to evaluate the BI's following the exposure in the test ~$
process. The BI's were placed inside two different types of test packs to determine steriliziny eEficacy. The test packs were assembled as described in the proposed Canadian Standard Association document, "CS~ Standard Z314.2 Guide for Effective Sterilization in llospitals by the Ethylene Oxide Process".
The test packs employed inclu(led cl~allenye test packs as de-fined by Sec. 7.2.2 and routine test packs as defined by Sec. 7.3 of tllat document.
- 24 ~
. -~l~e~t:~ were con~uc-e~l usin~J proc3ress~vely lon~er steriliza~ioll exposure times until ar~ exposure tirne was es-tablished after whlch no BI in the test: pack tested positive.
When this result was ol~tainecl, a series o~ at least five (5) tests ~ere conductecl at that exposure time to establish re-peatability o the test xesults.
The average ethylene oxide gas concentration for the tests was 713 mg/l. ~11 gas samples were less than ~ 10~ from the average. ~11 tests were conducted with the chamber temperature equilibrated at 130 F.
Co-nparative tests were also conducted on routine test packs and challenge packs employing a commercially available ethylene oxide sterilizer operated according to the recommended procedure for that sterilizer. These tests were conducted using a steam-flow throug}l conditioning cycle in order to provide a basis of comparing the present inven-tion with what has been generally recognized as the shortest :.
- and most rapid gas sterilizing cycle presently available commercially.
The average ethylene oxide gas concentration for the comparative tests was 719 my/l. All yas samples were less than ~ 10~ from the averaye. ~11 tests were conductecl with the chamber temperature equilibrated at 130 F.
comparison of the tcst clata obtaillecl from use of the present invention with that obtained by usiny the commer-cially availablc and accepted sterilizer of the same size 3~
reve~ls tlla~ ~le effective con~litiolling o~ained by the pre-sent inventio~l results in t~le complete and rellable sterili-~ation of tlle tes~ pac~s witll less exposuLe tlme than re-quired using the avai1able sterili~er.
~ ile specific embodiments of the invention have been disclosecl and described, it is to be understood that adaptation o~ structure, steps, and materials will be avail-a~le to those skilled in the art in the light of the present disclosure. For example, while steam is generally consi-dered the most practical conditioning vapor, solvents such as alcohols, ketones, and ethers can be used in conjunction with steam ~y taking into account the effect on the tempera-ture-pressure interrelationship. Also, the temperature of operation can be selected based on the biocidal gas; in general, ethylene oxi.de c~cles would be carried out at a tem-perature of about 100~ F. t.o about 150 F. Therefoxe, it is to be understood that various changes and modiEications may be made to the details of the foregoing without departing from the spirit and scope of the invention.
The claims:
tioninc3 vapor, such as s-team. This pulsing ac-tion provides a drive power Eor -the conditioning vapor which Eurther reduces cycle t.ime.
Thus by one aspect oE this invention there is provi.ded a me-thod ~or conditioning goods for sterilizat.ion and steriliz-ing such goods wikh ethylene oxide in a sealable chamber capable of operating below atmospheric pressure within prescribed leak rate limits, such conditioning being carried ou-t prior to introduc-tion of the ethylene oxide and independent of load contact measurement requirements of temperature in the goods, the conditioning including heating the goods, mo.isteniny the goods and removal of air from the goods to facilitate heating and moistening of the goods to be sterilized, the method comprising the steps of loading the goods to be sterilized into tHe chamber and sealing the chamber, preselecting upper and lower subatmospheric pressure levels for controlled cyclic pulsing operation of such chamber during load conditioning, evacuating the chamber and injecting a condensable vapor having transferrable latent heat and moisture into the chamber to condition the goods to be sterilized by cyclically ; varying chamber pressure between such upper and lower sub-atmospheric pressure levels independent of prescribed evacuat-ing and vapor injecting times such that the time duration of a pressure rise from lower to higher preselected subatmospheric pressure levels during a cyclic variation is responsive to characteris-tics oE the goods being conditioned including moisture and heat absorption charac~eristics of such goods, such subatmospheric pressure levels being selected based on an interrelationship of pressure and temperature of pressuxe and temperature of the condensable vapor with such upper pressure level establishing an upper temperature for injecting the condensable vapor which approximates without exceeding the desired final sterilization temperature for the goods to be sterilized, the evacuating of such chamber and the injecting of the condensable vapor into such chamber being carried out alternately to bring about such cyclic variations in char[~er pressure, repeating such cyclic variation of chamber pressure be-tween the preselected subatmospheric pressure levels to provide a plurality oE cyclic pulses during such load condi-tioning before termination of evacuation of the sealable chamber in preparation for ethylene oxide gas sterilization, and aEter such termination of evacuation of the sealable chamber, introducing ethylene oxide gas into such chamber to accomplish the desired sterilization of goods in the chamber.
By another aspect of this invention there is provided an apparatus for conditioning goods in a sealed chamber for subsequent sterilization with a biocidal agent, the condition-ing including moistening and heating to a desired temperatureby subjecting the chamber and goods to a plurality of cyclic pressure pulses between predetermined subatmospheric pressure levels, comprising, in combination, a conditioning chamber capable of being evacuated to desired vacuum levels and operable within a maximum prescribed leakage rate, inlet conduit means connecting the conditioning chamber to a source of conditioning vapor, inlet valve means connected in the inlet conduit means and including power means for operating the valve to control the flow of conditioning vapor into the chamber, evacuation means for evacuating the conditioning chamber, : - 4A ~
exhaust condui-t means connecting the conditioning chamber to the evacuation means, exha~l~t valve means connected in the exhaust conduit means and including power means for operating the exhaust valve to control -the flow through the e~haust conduit to thereby control evacuation of the conditioning chamber by the e-~acua-tion means, - pressure sensing means including means for sensing lower and upper predetermined subatmospheric pressure levels in the conditioning chamber and for transmitting a signal in response -to the sensing of such pressure levels, and control means including means responsive to signals from the pressure sensing means including, means for generating operating signals for subjecting the conditioning chamber to a plurality of cyclic subatmsopheric pressure pulses independent of preselected time intervals, and means for operating the power means of the exhaust and inlet valve means in response to the generated operating sig-nals to alternately open the exhaust valve means and close theinlet valve means to exhaust the conditioning chamber to a lower prede-termined suhatmospheric pressure and to close the exhaust valve means and open the inlet valve means to increase the pressure within the conditioning chamber to an upper pre-determined subatmospheric pressure to control such cyclic subatmospheric pressure pulsing.
The advantages of rapid heating and short conditioning :
-times are made available while adding accuracy of conditioning and dependability of operation.
Other advantages and contributions of the invention will be more apparent from a more specific presentation of the methods and description of the apparatus shown in the accompanying drawings.
f L ~
Figure 1 is a schematic representa-tlon ~f apparatus in accordance with the invention;
Figure 2 is a process flow chart for carry.~ng out a conditioning cycle in accordance with an embodiment of the invention in which ma-terial to be sterilized is subjected to a fixed number of conditioning pressure pulses;
Figure 3 is a schema-tic representa-tion of control logic apparatus for carrying out conditioning in accordance with the process of Figure 2;
Figure 4 is a graphie representation of chamber pressure versus time -through the conditioning phase of Figure 2;
Figure 5 is a process flow ehart for carrying out a conditioning cycle in accordance with an embodiment of the invention in which conditioning i5 terminated when two succes-sive pressure pulses exhibit substantially the same character-istics;
-- ~C --., ',2 ~i(;ure 6 is a scll~matic representation of control '~ loyic aE)E)aLa~us for ca.rryi.llg out corlditioniily in accordance ~ith t~e process of Fi~ure 5;
r~icJure~ 7 is a c~ra~llic rel~resentation of chamber pres-sure versus time throucJh the conditionin~ phase of Figure S, of a minimal fabric loadcd cl~amber in accorclance ~ith the in-vention; and Yi.gure 8 is a graphical representation of chamber pressure versus time during conditioning of a full fabric load in accordance with the i.nvention.
During load conditioniny in accordallce with the in-vention, the chan~er is operated betweell preselected subat-mospheric pressure l.evels to provide cyclic pulsing utilizing a condensable vapor haviny transferrable latent heat and moisture for conditioniny the goods to be sterilized. Evacua-tion of the chamber and introduction oE such vapor are con- ::
trolled to provide cyclic variation in chal~er pressure be-tween such preselected subatmospheric pressure levels. The cyclic variation is independent of prescribed times in that the time duration of a pressure rise from lower to higher : preselected subatmospheric pressure level.s duriny a cyclic variation is responsive to characteristics of the goods being ,:
conditioned and can vary for differiny loads. Such load char-acteristics include moisture and heat absorption properties of materials forminy tl~e load; load characteristics can also V3ry clepel~di~g on the slze and manner of packlng the load.
~' ~
.
~ s is kno~n, cha~ r ternp~rature ls clirectly rela-ted to ch~rlber pressure or a particular vapor, e.g., steam.
~herefor~, pressure levels are selected so as not to cause the temperclture to excec!d a desired final sterilization tem perature for the goods to be sterilized. Cyclic v~riation of chamber pressure is carried out so as to provide a plurality of cyclic pulses. Since individual pulses are load responsive and independent of fixed time intervals, the total time dura-tion of the load conditionirlg phase is independent of any prescribed ti~e interval.
Load conditionin~ can be initiated by purging air from the sterilizing cllamber by evacuating the chamber while simultaneously introdueing the eonditioning vapor into the ~' ehamber at a controlled rate to prevent overheating the load prior to cyclic pulsing. Conditioning can be further auto-mated by establislling a time relation between corresponding ' phases of successive puIses. For example, the number of cyelie pulses can be automatieally selected based on the time duration of pressure rise from the lower to the higher of the preseleeted subatmospherie pre,ssure levels oE eonseeutive cyelic pulses. In one embodiment, eyelie pulsinc~ is termi-natecl when the time duration of the pressure rise of two sueh , eonsecutive pulses is approximately equal.
'~ Operatioll involvillc~ a fi~ed number of pulses is earried out in aeeordanee with the proeess outlined in the flow chart of ~igure 2. ~ e conditionincJ cyele includes the :
3~
steps of sul~jictii~g t!~e material to a fixed number of cycllc variations at subatl-nos~heric pressures by ~lternately evacua-ting the conditionin~3 challlber and increasing the pressure by admitting steam into ~he chan1ber a~ a controlled rate. ~n 5up-down counter, whicll counts the pulses, is pre-set, either manually or automatically, for the required number of pulses before comrnencing the cycle.
Operation can be initiated by a manual switch. The control logic provided by a înaster controller starts the 10chamber evacuation means and opens a power-operated exhaust valve to permit evacuation of the chamber. Steam is admitted into the chamber by actuation of a second power-operated ?
valve. The rate of flow of steam into and evacuation of the chamber can be coordinated so that the pressure in the cham-15ber is reduced by the pump while steam is being admitted.
The vacuum pump continues operation with steam flowing at a controlled rate into the chamber until the pressure within the chamber reaches a first predetermined subatmospheric level.
The pressure withill the chamber is continuously monitored by 20 a pressure-sellsin~ assembly mounte~ within the chamber.
When the pressure reaches an upper predetermined level, for example 90 ~n ~Ig. abs., a first set of contacts in the pressure sensor is actuated to signal the controller to stop the flow oE steam into tlle chamber. ~ith the steam supply valve closed, the vacuum pump continues to operate to further reduce the pressure in the chamber, with pressure 3t~J~
beiny mol~itol-e(l L~y the pressur2 sensillc~ assembly. ~hen the pressure reaches a lower predetermined level, Eor example, 60 ~n ~ig. a~s , a second set o~ colltacts in the pressure sensing assem~ly is actuated, siynallil-y the controller to simultancously close the exhaust valve and open the steam sup-ply valve to aclrnit a controlled flow of steam into the cham~er.
In the latter condition, steam entering tlle cham-ber at a controlled rate will yradually increase the pressure, and consequently the temperature, in the chatnber~ This in-crease in pressure is continuously monitored by the pressure sensiny assembly WhiC}I, acting throuyh the controller, main-tains the apyaratus in the stated mode until the pressure re-turns to or exceeds the upper predetermined pressure level.
- At this point, a third set of contacts in the pressure sen-siny assembly is actuated to simu1taneously open the exhaust valve and close the steam supply valve. ~gain, this mode of operation is maintained constant, under the monitoring oE the ;~ pressuxe sensing assembly, until the pressure within the cham-ber ayain reaches -the lower predetermined level ~t that time, the second set oE contacts are again actuated to again close the e~haust valve and open the steam supply valve to repeat the evacuation phase of -the cycle. Pressure pulses between Ei~ed pressure levels during a typical conditioning phase arc showll in l;'igurc 4. Cyclic yressure pulses can take place between differing pressure levels during the conditioning phase, but the upper pressure level is generally held at or 3 ~ ~
slightly below t~le pressu~-e corres~onding to the deslred sterilization temperature.
Sterili~lnc~ apparatus emboc]ying this invention is illustrat~l schernatically in Eiglire 1. Conventional sterili-zing chamber conEigurations can be utilized. ~s shown, theapparatus includes a double-walled cylindrical structure indi-cated generally at 10 and having an inner, open-ended pressure vessel 12 defining, with an end closure, door 19, a sterili-zing cham~er 16. Pressure vessel 12 is supported within an outer wall 18 which is spaced outwardly from and circurn-scribes a major portion of vessel 12. An open end of the wall 18 is joined to the adjacent end of the inner pressure - vessel 12 by an annular flange 20 to de~ine a sealable space 22 between the inner and outer walls, commonly referred to as a jacket. Other lleat insulating means for chan~er 16 can be used.
Tlle door 14 can be hinged or otherwise mounted at one side of the open end of the double wall structure to facilitate opelling and closing the chan~er 16. A conventional lock assem~ly can be used for door 14, e.g., a cam lock assembly, including an actuating lever or wheel 24 and locking cams 26, enabling the door to be firmly locked to tightly seal the chamber 16 during the sterilizing operation. A drain conduit 28 is fitted in a bottom portion of jacket wall 18, and a one-way check valve 30, connected in conduit 28, permits fluidto flow through COIl~Uit 28 to escape from tlle jacket 22. A
g æ3~z variablc-orifice flow-res~rLctor 32 is connected in the con-duit 28 to cnable tlle rate of flow thro~gh the conduit to be controlled so that the pressure, and thereby the temperature, witl~in t~le jacket 22 can be regulated.
The sterilizer includes a plumbing systern for sup-plying conditiollincj vapor and biocidal steriliziny gas to chamber 16, ancl steam to the jac~;et 22 The plumbing system is illustrated as includincJ a main steam supply line or con-duit 34 conllected to a source of low-pressure steam, such as boiler 36, for supplyincJ steam as a conditioning vapor, through ; one-way check valve 38, solenoid-actuated cut-off valve 40, and variable-orifice flow-restrictor 42, to an~inlet 43 in sterilizing chamber 16. A branch conduit 44, connected in ; the main steam line 3~ upstream of check valve 38, supplies steam to the jacket 22 to help insulate the inner pressure vessel 12 against heat loss. A temperature sensor, for exampLe a thermocouple 4S, is mounted on the wall of chamber 12 to continuously monitor the temperature of the wall which closely corresponds to the temperature of tlle steam in jacket 22.
This measured temperature is employed to control actuation of solenoid-actuated valve 48 whlch, together with one-way check valve 46, and a variable-orifice flow-restrictor 50 in line 40 and check valve 30 and flow-restrictor 32 in drain line 28, control stcaln Elow throuyll conduit ~4 to jacket 22.
The pressure within sterilizing chamber 16, and the flow of vapor or c~ases through that cl~ambcr during the condi-3 t `2 tionincJ p~lase Or ~lle cycle is controll~d hy a charn~er exhaust system includillc~ suital~le evacuating means such lS a vacuum pump or ejector 52 connectecl through exhaust line or conduit 5~ to an outlet 55 Wllicil is showrl in the bottom of sterili-zing chamber 1~ but whicll can be located at any convenientlocation. One-way check valve 56 and solenoicl-actuated sh;lt-off valve 58 are collllected in exhaust lirle 54 to regulate the flow through the exllaust line. The temperature and pressure within the sterllizing chamber 16 may be regulated in part lQ by this arranyement.
Sterilant supply means for supplying a controlled flow of biocidal gas such as ethylene oxide to the sterili-zing chamber 16 includes a supply line or conduit 60 connected between conduit 34 downstream of check valve 38 and a source of the biocidal gas indicated in Figure 1 as a pressurized container or bottle 64. Flow through the conduit 60 is regu-lated by one-way check valve 66 solenoid-actuated shut-off valve 68 and a variable-orifice flow-restrictor 70. A
baffle 72 mounted ~ithin tlle interior of chamber 16 adjacent the inlet 43 provides for a more uniform distribution of bio-cidal gas enteriny the chamber 16.
The temperature of the biocidal gas supplied to the ; chamber 16 can be regulated by a heat exchanger 74 connected in t~le line G0 in heat excllange relation with steam supplied through a conduit 76 connected in the main steam line 34. A
solenoid-actuatecl sh-lt-off valve 78 and a variable-orifice 3~
flow-restrictoL ~0, con~ectecl in line 76, re-~ulate the flow of steam tl~rouc~h the heat exchanc3er 74 and thereby the tem-perature of the biocidal yas flo~ing into chanlber 16. Steam is e~:hausted rom ~l~e heat exchanc3er 74 through a suitable conduit 82 to a sump or clrain 84.
~fter sterilization, air ~low through the chamber 16 is provicled by air supply line ~6 connected in the char~er supply line 34 downstream of the steam control valves 38, 40 and flow-restr~ctor 42. Air is supplied to the air line 86 through a suitable filter 88 having an inlet 90 open to the atmosphere. ~ solenoid-actuated shut-off valve 92 and one-way check valve 94 control flow throuyh line ~6. Since air flows tllrouyh or into chamber 16 only when the pressure with-in the cha~ber is below atmosphere, atmospheric air pressure is sufficient to provide the necessary air flow. Filter 88 is of a type to effectively remove bacteria from the air and can also include other air sterilizing means.
; In the embodlment of Figure 1, a pressure sensing assembly 96 is mounted within ehamber 16. Chamber pressure signals generated by the pressure sensinc3 assel~bly 96 are ; supplied, through suitable electrieal eonneetions inc~ieated by line 98, to a eentral eontrol 100. Pressure sensing assembly 96 ineludes a ~irst set of eontacts whieh are ae-tuatecl UpOIl the pre.sure withill the ehan~er 16 being ini-tially lowered to the upper predetermined pressure to thereby generate a signal for tlle eontrol 100 to actuate the solenoid of tlle illLet valvc ~10 t-o s~oL~ the 10w of steam. Valve 40 can be a conven~iollal normally-closed, energized-open valve so that the control de-etler~izes tl-e solenoid to close the valve. Power mealls ot~ler than a solcnoid rnay be employed to control operation of the inlet and exhaust valves.
~ secolld set of contacts in pressure sensing assembly 96 are actuated to c~ellerate a sicjnal each time the pressure in chamber 16 reaches the lo~er predetermined level. This siynal is utilized by the control 100 to operate the solenoids of both the :inlet valve ~0 and the exhaust valve 58 to open the inlet valve and close the exhaust valve. This results in an increase in pressure wit}lin the chamber to the upper pre- -~
determined level. ~hen approaching the upper pressure level in this manner a third set of contacts in the pressure sensing assembly 96 is actuated, signalling con-trol 100 to operate the solenoids to close inlet valve ~0 and open eY.haust valve 58 . . .
each time the upper predetermined pressure is reached from a lower pressure. The function of the first and thixd set of ~-contacts may be achieved by a sinc;le set of contacts, but the control is simplificd by using separate contacts wllic}l are actuated when the desired pressure is attained from higher and lo~er pressures. It is also possible to use separate contacts or other sensors to generate signals each time the lower pres-surc is rcacllccl al~d thcse separlte scnsors may havc difrcerent settinc;s if desired to change the lower pressure of the indi-vidual pressure pulses.
~ o~ oller I00 ill~Lu~l~s a courlt~r me~c-ilanism, pre-ferably in the Lorm o~ a solid state up-do~n counter illus-trate~ sc~lematically in ~icJure 3, wl~ich coun~s the number of actua~ions of tlle contacts in pressure sensiny assembly 96.
~Eter a predetermil)ed number of cyclic pulses, when the pres-sure within chamber 16 xeaches the upper predeter~ined subat-mosplleric levcl, actuation of tlle third set of Collt.lCts in p~essure sensinc3 assembly 96 results in the shut-off valve 40 being closecl and shut-off valve 58 remaininy closed. At the same time, shut-off valve 78 is opened to permit steam to flow through the heat exchanyer 7~ and shut-off valve 68 in biocidal gas supply line 60 is opened to permit biocidal gas to flow througll tlle heat exchangerO Biocidal yas then flows through flow-restrictor 70 into chamber 16 to pressurize the ; 15 chamber to tlle recluired level and the pressure is held for the required time to complete desired sterilization of the material in the cham~er.
After completion of the biocidal yas treatment phase ;~ of the sterilization process, the interior oE the chamber 16 can be flushed with filtere~ air by initially opening the valve 58 and operating the Vacuum pump 52 to withclraw the residual biocidal gas from the chamber. The shut-off valve 58 is then closed and shut-off valve 92 opened to permit fil-tered air to enter the chamber. Sllut-off valve 92 may then be ; 25 closed and the air withdrawn by openiny valve 58, and the pro-cess repeate~ as necessary to flusll the biocidal gas from the article~; I)eill(J sterili-~ecl. ~lterl~atively, t}-e challlber can be flushe~ by simultaneously operatincj the evacuatil-g pump and permitting air to flow into the chamber.
Tl~e final step in tl~e sterilization process ~ill S normally consist o permitting filtered air at atmosp}leric pressure to enter the chamber and to stabilize the pressure througllout the sterilized articles w}lereupon the door 14 may be opened and the sterilized articles removed.
I)uriny the conc1itiolling phase of the steriliæiny process, air is witlldrawn frorn porous articles to be processed and, in turn, the steam admitted to the chamber permeates the articles. The articles are heated from the latent heat of the steam which condenses on and within the articles, thereby simultaneously moistening and conditioning them for subsequent sterilization by the biocidal gas. ~s the outer layers of a load oE material become heated, the steam penetrates deeper before it is condensed until eventually the load is completely permeated Witil steam and is heated and moistened substantially uniformly throughout. The pressure pulsing has been found to greatly facilitate steam penetration and air removal so that a more thorough and uniform conditioning is achieved.
With a controlled rate of admission of steam into the cllamber during the repressurization phase of the cyclic i pulses, the rate of condensation, and consequently -the heating and humidification of the sterilizer load, will directly affect the lengtll of time required for the chamber to become repres-~ 3~ ~
suri -~,t~ Lrorn t~-~ se~o~ O~L pr~ssure level to the upper predeterlllinc~ p;essure level. It hcls been determined that, when the reE~ressurization phase o~ two successive pulses re-quires su~stalltially the sarlle time, the load has been thoroughly conditiolled, i.e., moistened and heated throughout. By measuriny the time o~ the repressurization phases of each pulse, and comparing these times for successive pulses, the condi-tioning phase of the sterilization cycle can he terminated automatically when two succeeding measured times are substan-tially eclual. Tilis fully autornated conclitioning method isdependent directly u~or) the pressure which is continuously monitored in the chamber 16.
; ~xperience has sho~n that conditiorling can also be carried out with a fixed number of pulses~ With normal steam flow it has boen cletermined that four such cyclic pulses will adequately condition standard types of hospital loads inclu-ding a devised pack considered to be the most difficult load to be encountered in the operation of a modern hospital. In operating a sterili7er accordiny to the fixed number of pulses method, wherl four pulses have been completed, a counter auto-matically terminates the pulse conditioning phase in prepara-tion for the sterilization phase. The total time duration for such four pulses will vary according to load characteris-tics.
~igure 3 illustrates schematically the electronic control system for controlllng the conditionillg of material to be sterilize~l tllrou~ a ~re~e~cr~ ne~ nu~ber oE condi-tioning pulses, followiny the steps outlioed in the flow diagram of Fi~3ure 2. The control system includes a conven-tional u~-down counter 102 whicll can be up~counted by feeding a signal in on the "count" line whell tlle "control" line is in a given state and whicll can be down-counted by eeding a signal in on the "count" line when the "control" line is in a differellt given state. ~efore the process is begun, up-down counter 102 is loadecl with a precletermined count which correspon~s to the number of cyclic pulses which are to be used for the conditioning phase. This may be done automa-`:
tically, that is with the number of pulses preset and fixed for a particular sterilizer; or, as shown in Figure 3, can be set by depressing the button 106 on selector 109 the appro- ~ ;~
priate number o times. The pulse selector 104 is a conven-tional pulse generator, arranged so that the number o times that the button 106 is depressed appears on a display window 108. ~;
The outputs of up-down counter 102 are connected to a decoder 10~, each output line of which is representative of .~ :
a given number. Thus, at the t1me that the initial number of pulses are loaded into counter 102, the correspondiny output line o decoder 110 has a signal thereon. ~hen this initial number of pulses is counted down to zero, then the zero out~
put line of decoder 110 has a signal thereon. This indicates the final evacuation and, upon repressurization of the chamber to the upper pressure, the end of the conditiolliny phase o ... .
3~;;Z
tl~e cycle. Il~c outl~ut o~ tllc zcro linc of the decoder is conllected to one side oE ~ gate 112. The lligh pressure level signal ~rorn pressure sellsor 96 is conllected to the other side o ~ c~ate 112 so that, when a hi~ll pre~sure level sig-nal is present and at t~le same time a signal is present rom decoder 110, ~ND gate 112 is effective to pass a signal stop-ping t~e conditioning cycling and sic;nalling the commencing of the sterilization pl~ase of the cycle.
Each time that button 106 is pressed, pulse selec-tor 104 gellerates a pulse on the count line input to counter 102 to up-count the counter. In the ernbodiment shown, but-ton 106 has been pressed four (4) times to effectively load the number "4" into the counter 102. This number can be preset.
~ith the up-down counter pre~loaded ~ith the number of pulses corresponding to the number of pressure pulses in the conditioning phase of the sterilization cycle, a start signal is generated by any convenient means such as manually closing a conventional on-off switch connected in the main ~ power circuit of the control. The start signal actuates - 20 vacuum pump 52 and opens control valve 58 to thereby imme~
diately commence evacuation of the chamber 16~ Either simul-taneous with the commencement of evacuation, or at a prede termined time thereafter, valve 40 is opened to admit steam to flow, at a rate controlled by tlle setting of flow-restrictor 42, into the chamber 16 while continuing to evacuate the cham-ber. Tllro~gllout tl~e remainder of the conditioning phase of ~ 18 -~8~
the c~cle, o~)cration is ul~c~er col~trol of the absolute pressure responsive pr~ssure-serlsinc3 assembly 9G which continuously monitors the ~bsolute pressure withirl the chamber 16, as pre-viously described. Tllis pressure is precerably continuously recorded by a convelltional pressure recorder, the output of which is plottecl against time and illustrated in ~igure 4, W}liCh shows the pressure within the chamber 16 at the start of the cycle to be 760 mm ~Ig., or one atmosphere.
The controller 100 includes a timing system which monitors the time required for the conditioning phase of the cycle ancl aborts the cycle when an excessive amount of time is rec~uired to reach the sterilizing phase. This timing sys-tem can abort the cycle after termination of the conditioning phase, as showli schematically in Figure 3, or alternatively can abort the cycle after a predeterrnined time, regardless of whet}ler or not the conditioning phase has been completed. In the systern shown in Fiyure 3, the start signal which commences the cycle also starts a pulse ~enerator 114 whieh supplies - the pulses to a pre-loaded down-counter 116. The down-counter11~ is a eonventional, commereial]y-available item whieh is down-eounted by the pulses from c;enerator 114.
The outputs of the down-counter 116 are connected to a deeoder 118, each output line of which is representative of a number of pulses counted by the down-counter. i~}len the preset number of pulses has been down-countcd to zero, then the zero output line of the decoder llB has a signal tilereon, ' . .
:
`. sicJnallil)(3 ~ t tllc ~lowll-coullter h~s ~imecl out, i.e., tllat a predeteLmined time has lapsecl since the start sicJnal started the ~ulse c~c~nerator ancl commencecl the conclitioning phase of the cycle 'i`he output sigllal froln decoder 118 sets a latch 120 which, in turn, latches a signal onto one input of ~ND
gate 122.
The output signal of ~NV yate 11.2 is fed into the other side oE ~N~ gate 122 so that, when a signal is present on the input line from latch 120 and from AND yate 112, AND
gate 122 procluees an output siynal which aborts the eyele and can energize a sui.table signal sueh as a buzzer, warni.ng light, or the like.
The output from ~ND gate 112 also applies a stop signal to pulse generator 114 and resets down-eounter 116.
Thus, if a signal is present from ~ND gate 112 indieating that the eonditioning phase has been eompleted prior to the timing ~ -out of pre~loaded down-eounter 116, no signal will be reeeived from deeoder 118 to ~ND gate 122. Under these eonditions, the signal from up-down counter 102, through ~ND gate 112, will be effeetive to eontinue the sterilization eyele by the ad-mission of sterili.zing gas into ehamber 16.
The start signal, whieh starts the pulse generator 114 and eommenees the eomplete eyele, is also eonneeted to the re-set of latell 12n so tllat any previously set signal. is erased at the beginnilltJ of eaeh eyele.
~leasurinc3 tlle time lapse durlncJ the eonditioning -3~2 pll~sc oL tllc cyclc or por~iol~s tl~ereoe, and aborting the cycle ; in the evellt of excessive time, cJ~arcls agains~ the application of biocidal sterilants SUC~l as ethylene oxide gas to a possibly clefective stcrilizer. ~hus, a leak in tl~e sterilizer seal can result in an excessive amount of ~ime required to reach vacuum, thereby causincJ tlle timing mechanism to time out prior to completion of the condi~ioning phase. By sensiny t~lis exces-sive time an~l aborting the cycle prior to admitting the steri-liæing gas, any potential hazard rom such a leak is minimized.
The upper predetermine~ subatmosplleric pressure is inclicated in Figure 4 as being 90 mm llg abs. As is known from standard steam tables, this pressure will produce a tem-perature within the chamber of about 122F. When steriliza-tion is to be completed in chamber 16 immediately follo~ing completion of the conditiol-ing cycle, this upper pressure is selected so as to produce a maximum temperature within the chamber which is slightly, preferably about 5 - 8 F., ~elow sterilization temperature of about 130 F. This permits a slight increase in cnamber temperature without exceeding the desired 130 ~. temperature when the biociclal sterilization gas is admitted into the cha~ber at a pressure above the upper predetermined pressure.
Referring to Figure 5, a flow chart illustrating tlle succcssive steps of the conditionillg phase utilizing the repressurization timing and comparing system is illustrated~
From this flow chart, it is seen that the sequence of steps 7~
is iclentical to thclt ~escr:i}~ccl above with the exception that, after eac~ low~r prc-clet~rrnin~c~ pressure is reached, the time required for the pressure to returll to the upper predetermined pressure level is rneasured ancl comparecl with the correspo~ding time of the precedincJ pulse. Wl-len two such successive times are substantially equal, that load is conditioned and the conditioniny phase can be termlnated regarclless of the number of pulses.
Figures 5 - 7 illustrate the operation of the em-bodiment of the i.nvention wherein the control system termi-nates the conclitioniny phase when two successive pulse repres~ ~:
surizations require su~stantially the same time. In this embodiment, the pressure responsive control signals are also - directed to a conventional timing pulse counter 124 whi.ch, ~.
in turn, is connected to a conventi.onal timing pulse gellera-tor 126. The initial low pressure signal starts the timing pulse counter whicil continues to operate and feed timing pulses . to a shift register until a high pressu.re level signal is re-ceived which stops the timing pulsé counter ancl conditions the shift register 128 of the timing pulse counter to accept the data in the first register positi.on. The time between the low and high pressure signals is thus stored in the first register position. When a second low pressure signal is re-ceived, the timillcj pulse counter i.s agai-l startecl and runs continuously until a second high pressure control signal is received. lhe seconcl higll pressure control si~nal also condi-^~i$~3 ~'~
tions the s~lift recJistel to ~ccept the new timing data from the timiny pulse counter and to shift the data from the pre~
ceding pressurization pulse p~lase to the second position. ~t ~;
this point, a cligital comparator 130 compares the duration of the two timed pulses and, i~ the times are the same, within predetermined limits, a sic;nal is emitted stopping the cycling.
If, however, tlle tin~es are not within acceptable limits, the cycling is repeated until the comparator, comparing the times of the last two successive repressurization cycle phases, is within acceptable limits, or, alternatively, the up-down coun-ter mechanisrn described above can override the comparator control ancl stop the cycling after four complete pulses regard-less of the times for the third and fourth repressurizatlon pulse phases. ~s with the embodiment shown in Figure 3, this ernbodiment can include timing means for aborting the cycle in the event that excesslve time is required for the condi- `
tioning phase.
Figure 8 shows a cycle wherein the conditioning was terminated after three repressurization pulse phases. As illustrated, the time of repressurization of the second and third phases are substantially equaI. Termination of the cycle, as well as the lenyth of time required for the indivi-dual pulses, was determined by the characteristics of the load rather ~hall ~y any predeter~ led time or temperature con-sideration.
The conditionlng and sterilizing apparatus of the 8;~
invention C(~ e controlle(l ~y a micro-processor progranuned to accom~lish tl~ various ~unctions and sequence of steps des-cribed above. ~ccordinc~ly, it is conternplated that such a processor may be employed in place of the control system des-cribed with reference to Fic~ures 3 and 6 to control operationof the apparatus to perforrn the process described.
A number oE tests llave been conducted in order to prove the effectiveness and efficiency of tile method and apparatus of this invention. Microbiological data was col-lected using a 24" x 36" x 48" steriliziny chamber, with the cont~ols functioning to subject the ch~mber to the condi-tioniny and sterilization cycle described above. Ethylene oxide gas was used as the biocidal agent during the sterili-~ing phase of the cycle.
The testiny employed standard biological indicators (BI's) containing 106 spores of Bacillus subtilis (globigii) on filter paper strips. Standard culture procedures were used to evaluate the BI's following the exposure in the test ~$
process. The BI's were placed inside two different types of test packs to determine steriliziny eEficacy. The test packs were assembled as described in the proposed Canadian Standard Association document, "CS~ Standard Z314.2 Guide for Effective Sterilization in llospitals by the Ethylene Oxide Process".
The test packs employed inclu(led cl~allenye test packs as de-fined by Sec. 7.2.2 and routine test packs as defined by Sec. 7.3 of tllat document.
- 24 ~
. -~l~e~t:~ were con~uc-e~l usin~J proc3ress~vely lon~er steriliza~ioll exposure times until ar~ exposure tirne was es-tablished after whlch no BI in the test: pack tested positive.
When this result was ol~tainecl, a series o~ at least five (5) tests ~ere conductecl at that exposure time to establish re-peatability o the test xesults.
The average ethylene oxide gas concentration for the tests was 713 mg/l. ~11 gas samples were less than ~ 10~ from the average. ~11 tests were conducted with the chamber temperature equilibrated at 130 F.
Co-nparative tests were also conducted on routine test packs and challenge packs employing a commercially available ethylene oxide sterilizer operated according to the recommended procedure for that sterilizer. These tests were conducted using a steam-flow throug}l conditioning cycle in order to provide a basis of comparing the present inven-tion with what has been generally recognized as the shortest :.
- and most rapid gas sterilizing cycle presently available commercially.
The average ethylene oxide gas concentration for the comparative tests was 719 my/l. All yas samples were less than ~ 10~ from the averaye. ~11 tests were conductecl with the chamber temperature equilibrated at 130 F.
comparison of the tcst clata obtaillecl from use of the present invention with that obtained by usiny the commer-cially availablc and accepted sterilizer of the same size 3~
reve~ls tlla~ ~le effective con~litiolling o~ained by the pre-sent inventio~l results in t~le complete and rellable sterili-~ation of tlle tes~ pac~s witll less exposuLe tlme than re-quired using the avai1able sterili~er.
~ ile specific embodiments of the invention have been disclosecl and described, it is to be understood that adaptation o~ structure, steps, and materials will be avail-a~le to those skilled in the art in the light of the present disclosure. For example, while steam is generally consi-dered the most practical conditioning vapor, solvents such as alcohols, ketones, and ethers can be used in conjunction with steam ~y taking into account the effect on the tempera-ture-pressure interrelationship. Also, the temperature of operation can be selected based on the biocidal gas; in general, ethylene oxi.de c~cles would be carried out at a tem-perature of about 100~ F. t.o about 150 F. Therefoxe, it is to be understood that various changes and modiEications may be made to the details of the foregoing without departing from the spirit and scope of the invention.
The claims:
Claims (18)
1. Method for conditioning goods for sterilization and sterilizing such goods with ethylene oxide in a sealable chamber capable of operating below atmospheric pressure within prescribed leak rate limits, such conditioning being carried out prior to introduction of the ethylene oxide and independent of load contact measurement requirements of temperature in the goods, the conditioning including heating the goods, moistening the goods, and removal of air from the goods to facilitate heating and moistening of the goods to be sterilized, the method comprising the steps of loading the goods to be sterilized into the chamber and sealing the chamber, preselecting upper and lower subatmospheric pressure levels for controlled cyclic pulsing operation of such chamber during load conditioning, evacuating the chamber and injecting a condensable vapor having transferrable latent heat and moisture into the chamber to condition the goods to be sterilized by cyclically varying chamber pressure between such upper and lower subatmospheric pressure levels independent of prescribed evacuating and vapor injecting times such that the time duration of a pressure rise from lower to higher preselected subatmospheric pressure levels during a cyclic variation is responsive to characteristics of the goods being conditioned including moisture and heat absorption characteristics of such goods, such subatmospheric pressure levels being selected based on an interrelationship of pressure and temperature of the condensable vapor with such upper pressure level establishing an upper temperature for injecting the condensable vapor which approximates without exceeding the desired -final sterilization temperature for the goods to be sterilized, the evacuating of such chamber and the injecting of the condensable vapor into such chamber being carried out alternately to bring about such cyclic variations in chamber pressure, repeating such cyclic variation of chamber pressure between the preselected subatmospheric pressure levels to provide a plurality of cyclic pulses during such load conditioning before termination of evacuation of the sealable chamber in preparation for ethylene oxide gas sterilization, and after such termination of evacuation of the sealable chamber, introducing ethylene oxide gas into such chamber to accomplish the desired sterilization of goods in the chamber.
2. The method of Claim 1 including purging air from the sealable chamber by evacuating such chamber while simultaneously introducing the condensable vapor into such chamber prior to commencing the cyclic pulsing.
3. The method of Claim 1 in which such subatmospheric pressure levels are selected to provide an upper selected subatmospheric pressure level in the chamber corresponding to a temperature level which is about 5 degrees below the desired final sterilization temperature.
4. Method for conditioning goods to be sterilized and sterilizing such goods with ethylene oxide gas in a sealable chamber capable of operating below atmospheric pressure within prescribed leak rate limits, such conditioning being carried out prior to the introduction of the ethylene oxide gas into the chamber and independent of load-contact measurement requirements of temperature in the goods, the conditioning including heating the goods to a selected temperature related to the desired sterilization temperature, moistening the goods for such ethylene oxide gas sterilization, and removal of air from the goods to facilitate such heating and moisturizing conditioning of the goods, the method comprising the steps of loading the goods to be sterilized into the chamber and sealing the chamber, preselecting subatmospheric pressure levels for controlled cyclic pulsing operation of such chamber during load conditioning, evacuating the chamber and injecting a condensable vapor having transferrable latent heat and moisture into the chamber for conditioning the goods to be sterilized by cyclically varying chamber pressure between such preselected subatmospheric pressure levels independent of prescribed evacuating and vapor injecting times such that the time duration of a pressure rise from lower to higher preselected subatmospheric pressure levels during a cyclic variation is responsive to characteristics of the goods being conditioned including moisture and heat absorption characteristics of such goods, such subatmospheric pressure levels being selected based on interrelationship of pressure and temperature of the condensable vapor with such selection of pressure levels for cyclic pulsing establishing temperature levels within the chamber which do not exceed a desired final sterilization temperature for the goods to be sterilized, repeating such cyclic variation of chamber pressure between the preselected subatmospheric pressure levels to provide a plurality of cyclic pressure pulses during such load conditioning before termination of evacuation of the sealable chamber in preparation for biocidal gas sterilization, with total time duration of such load conditioning being independent of a prescribed time interval, the number of cyclic pulses between the preselected subatmospheric pressure levels being determined by characteristics of the goods being conditioned, such number of cyclic pulses being responsive to the time duration of the pressure rise from the lower to the higher preselected subatmospheric pressure level of consecutive cyclic variations, terminating such chamber pressure cycling in preparation for ethylene oxide gas sterilization when the time duration of the pressure rise of two such consecutive cyclic variations is approximately equal, and then introducing ethylene oxide into the chamber to complete the desired sterilization of goods in the chamber.
5. Method for conditioning goods for sterilization and sterilizing such goods with ethylene oxide gas in a sealable chamber capable of operating below atmospheric pressure within prescribed leak rate limits, such conditioning being carried out prior to the introduction of the ethylene oxide gas into the chamber and independent of load-contact measurement requirements of temperature in the goods, the conditioning including heating the goods to a selected temperature related to the desired sterilization temperature, moistening the goods for such ethylene oxide gas sterilization, and removal of air to facilitate heating and moisturizing conditioning of the goods, the method comprising the steps of loading the goods to be sterilized into the chamber and sealing the chamber, preselecting subatmospheric pressure levels for controlled cyclic pulsing operation of such chamber during load conditioning, evacuating the chamber and injecting a condensable vapor having transferrable latent heat and moisture into the chamber for conditioning the goods to be sterilized by cyclically varying chamber pressure between such preselected subatmospheric pressure levels independent of prescribed evacuating and vapor injecting times such that the time duration of a pressure rise from lower to higher preselected subatmospheric pressure levels during a cyclic variation is responsive to characteristics of the goods being conditioned including moisture and heat absorption characteristics of such goods, such subatmospheric pressure levels being selected based on interrelationship of pressure and temperature of the condensable vapor with such selection of pressure levels for cyclic pulsing establishing temperature levels within the chamber which do not exceed a desired final sterilization temperature for the goods to be sterilized, repeating such cyclic variation of chamber pressure between the preselected subatmospheric pressure levels to provide a plurality of cyclic pressure pulses during such load conditioning before termination of evacuation of the sealable chamber in preparation for ethylene oxide gas sterilization, with total time duration of such load conditioning being independent of a prescribed time interval, measuring and comparing the time duration of the pressure rise phase of consecutive cyclic pulses, establishing a maximum number of such cyclic pressure pulses and terminating such cyclic pressure pulses upon completion of the established maximum number of pulses, terminating such chamber pressure cycling in preparation for ethylene oxide gas sterilization when the time duration of the pressure rise of two such consecutive cyclic variations is approximately equal regardless of whether or not the established maximum number of cyclic pressure pulses has been accomplished, and, then introducing ethylene oxide gas into the chamber to complete the desired sterilization of goods in the chamber.
6. The method of Claim 4 in which such plurality of cyclic pulses in chamber pressure is preselected prior to start of such conditioning.
7. The method of Claim 1, 4, or 5 in which such vapor comprises steam and the cyclic variations in pressure are carried out at preselected subatmospheric pressure levels between about 50 millimeters and about 100 millimeters of mercury.
8. The method of Claim 7 in which the pressure differential between two preselected subatmospheric pressure levels is about 25 millimeters of mercury.
9. The method of Claim 8 in which such vapor consists essentially of steam and in which the cyclic variation of subatmospheric pressure within such chamber is carried out between about 60 and about 90 millimeters of mercury.
10. Apparatus for conditioning goods in a sealed chamber for subsequent sterilization with a biocidal agent, the conditioning including moistening and heating to a desired temperature by subjecting the chamber and goods to a plurality of cyclic pressure pulses between predetermined subatmospheric pressure levels, comprising, in combination, a conditioning chamber capable of being evacuated to desired vacuum levels and operable within a maximum prescribed leakage rate, inlet conduit means connecting the conditioning chamber to a source of conditioning vapor, inlet valve means connected in the inlet conduit means and including power means for operating the valve to control the flow of conditioning vapor into the chamber, evacuation means for evacuating the conditioning chamber, exhaust conduit means connecting the conditioning chamber to the evacuation means, exhaust valve means connected in the exhaust conduit means and including power means for operating the exhaust valve to control the flow through the exhaust conduit to thereby control evacuation of the conditioning chamber by the evacuation means, pressure sensing means including means for sensing lower and upper predetermined subatmospheric pressure levels in the conditioning chamber and for transmitting a signal in response to the sensing of such pressure levels, and control means including means responsive to signals from the pressure sensing means including, means for generating operating signals for subjecting the conditioning chamber to a plurality of cyclic subatmospheric pressure pulses independent of preselected time intervals, and means for operating the power means of the exhaust and inlet valve means in response to the generated operating signals to alternately open the exhaust valve means and close the inlet valve means to exhaust the conditioning chamber to a lower predetermined subatmospheric pressure and to close the exhaust valve means and open the inlet valve means to increase the pressure within the conditioning chamber to an upper predetermined subatmospheric pressure to control such cyclic subatmospheric pressure pulsing.
11. Apparatus as defined in Claim 10 wherein the means for generating operating signals generates signals for operating the power means of the inlet and the exhaust valve means to initially open both the exhaust valve means and the inlet valve means to simultaneously evacuate the conditioning chamber and admit conditioning vapor into the conditioning chamber to purge air from the chamber to initiate a conditioning cycle.
12. Apparatus as defined in Claim 10 wherein the means for operating the power means of the exhaust and inlet valve means includes means to open both the inlet and exhaust valve means at the beginning of a conditioning cycle, means operating the power means of the inlet valve means to close the inlet valve means in response to a signal from the pressure sensing means upon sensing of an upper predetermined subatmospheric pressure to prevent further flow of conditioning vapor into the conditioning chamber while permitting continued evacuation of the conditioning chamber, and means operating the power means of the inlet and the exhaust valve means to open the inlet valve means and close the exhaust valve means in response to a signal from the pressure sensing means upon sensing a lower predetermined subatmospheric pressure to thereby permit conditioning vapor to flow into the conditioning chamber while stopping the evacuation thereof to thereby increase the pressure within the chamber to the upper predetermined subatmospheric pressure to complete one subatmospheric pressure pulse cycle, the means operating the power means of the inlet and exhaust valve means being operable thereafter to reverse the open-closed condition of both the inlet and the exhaust valve means upon sensing of each successive predetermined subatmospheric pressure level to thereby subject the chamber to a plurality of such cyclic subatmospheric pressure pulses.
13. Apparatus as defined in Claim 10 wherein the means for generating operating signals is operable to generate such operating signals for maintaining the pressure within the conditioning chamber between the same fixed upper and fixed lower preselected subatmospheric pressure levels during each of the plurality of cyclic subatmospheric pressure pulses.
14. Apparatus as defined in Claim 13 wherein the control means includes timing means for measuring the time interval between such lower and such upper preselected subatmospheric pressure levels during consecutive cyclic pressure pulses, means for comparing such consecutive pulse measured times, and means for terminating the conditioning cycle when measured times of such two consecutive pulses are substantially equal.
15. Apparatus as defined in Claim 14 wherein the control means includes counter means operable to count the number of subatmospheric pressure pulses within the chamber, and override means for terminating the pressure pulsing after a predetermined number of pulses, regardless of measured times of consecutive pulses.
16. Apparatus as defined in Claim 15 wherein the counter means includes means enabling the preselecting of the number of pressure pulses prior to initiation of a conditioning cycle.
17. Apparatus as defined in Claim 16 wherein the means for sensing the predetermined subatmospheric pressures senses pressures and generates signals at preselected atmospheric pressure levels between about 50 mm Hg. abs. and 100 mm Hg. abs.
18. Apparatus as defined in Claim 10 wherein the control means includes counter means operable to count the number of subatmospheric pressure pulses within the chamber, and means for terminating the pressure pulsing after a predetermined number of pulses.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA334,711A CA1108372A (en) | 1979-08-29 | 1979-08-29 | Method of and apparatus for biocidal sterilization using cyclic subatmospheric pressure conditioning |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA334,711A CA1108372A (en) | 1979-08-29 | 1979-08-29 | Method of and apparatus for biocidal sterilization using cyclic subatmospheric pressure conditioning |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1108372A true CA1108372A (en) | 1981-09-08 |
Family
ID=4115040
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA334,711A Expired CA1108372A (en) | 1979-08-29 | 1979-08-29 | Method of and apparatus for biocidal sterilization using cyclic subatmospheric pressure conditioning |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1108372A (en) |
-
1979
- 1979-08-29 CA CA334,711A patent/CA1108372A/en not_active Expired
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