U.S. patent application number 16/375925 was filed with the patent office on 2019-08-01 for device for hydrogen peroxide sterilization.
This patent application is currently assigned to STERIS EUROPE, INC. SUOMEN SIVULIIKE. The applicant listed for this patent is STERIS EUROPE, INC. SUOMEN SIVULIIKE. Invention is credited to Arja RULEY, Mauri SALMISUO.
Application Number | 20190231913 16/375925 |
Document ID | / |
Family ID | 52633196 |
Filed Date | 2019-08-01 |
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United States Patent
Application |
20190231913 |
Kind Code |
A1 |
RULEY; Arja ; et
al. |
August 1, 2019 |
DEVICE FOR HYDROGEN PEROXIDE STERILIZATION
Abstract
The invention relates to the sterilization of a load of goods
with hydrogen peroxide vapor in a closed space. The method involves
a sequence of creating a sub-atmospheric pressure in a
sterilization chamber, introduction of vaporized hydrogen peroxide
and the use of a gas circulation device within the sterilization
chamber, whereby the output of the gas circulation device is
controlled according to the pressure in the sterilization chamber.
A uniform and consistent distribution of hydrogen peroxide
throughout the load is achieved.
Inventors: |
RULEY; Arja; (Espoo, FI)
; SALMISUO; Mauri; (Tuusula, FI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
STERIS EUROPE, INC. SUOMEN SIVULIIKE |
Tuusula |
|
FI |
|
|
Assignee: |
STERIS EUROPE, INC. SUOMEN
SIVULIIKE
Tuusula
FI
|
Family ID: |
52633196 |
Appl. No.: |
16/375925 |
Filed: |
April 5, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
15014357 |
Feb 3, 2016 |
10293068 |
|
|
16375925 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61L 2202/122 20130101;
A61L 2202/15 20130101; A61L 2/208 20130101 |
International
Class: |
A61L 2/20 20060101
A61L002/20 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 13, 2015 |
EP |
15397506.5 |
Claims
1. An apparatus for sterilizing a load of goods, said apparatus
comprising a chamber for receiving a load of goods to be
sterilized, said chamber having a jacket for a heat transfer medium
as well as gas inlets and gas outlets; a device for delivering a
heat-controlled heat transfer medium to the jacket; within the
chamber, a gas circulation device capable of delivering a constant
volume flow at variable velocities; a device for producing
vaporized hydrogen peroxide: and a device for producing
sub-atmospheric pressures within the chamber.
2. An apparatus according to claim 1, wherein the gas circulation
device is a centrifugal fan.
3. An apparatus according to claim 1, further comprising a device
for introducing pressurized steam and/or air to the chamber.
4. An apparatus according to claim 2, further comprising a device
for introducing pressurized steam and/or air to the chamber.
Description
RELATED APPLICATIONS
[0001] The present application is a divisional of U.S. application
Ser. No. 15/014,357, filed Feb. 3, 2016, which claims the benefit
of European Patent Application No. 15397506.5, filed Feb. 13,
2015.
FIELD OF THE INVENTION
[0002] The invention relates to the sterilization of a load of
goods with hydrogen peroxide vapor in a closed space. In
particular, the invention relates to a rapid and effective process
for carrying out such a sterilization procedure, with consistent
and even distribution of sterilant throughout the load, and with
rapid and thorough outgassing of the sterilant after the
sterilization cycle has been finished, and to an apparatus for
carrying out the process.
BACKGROUND OF THE INVENTION
[0003] Gaseous sterilants are typically used for goods for which
simple heat sterilization is not appropriate. For example, products
containing heat-sensitive biological material in aqueous solution
or in dry form, require sterilization at relatively moderate
temperatures due to the thermal sensitivity of the materials
involved. Packages containing proteins, steroids and vaccine
components are examples. In such cases, the use of vacuum, steam
and a gaseous sterilant is often an adequate solution. Gaseous
sterilants in use include ethylene oxide, formaldehyde, peracetic
acid and hydrogen peroxide. Ethylene oxide and formaldehyde are
considered to be carcinogenic. Hydrogen peroxide is highly
effective and has the advantage that its decomposition products are
the relatively harmless substances oxygen and water.
[0004] Vaporized hydrogen peroxide (VHP) is used for
decontamination and sterilization of enclosed and sealed areas. It
is capable of destroying all forms of microbial life, including
bacteria, bacterial spores, fungi, fungal spores, and viruses. It
is commonly produced from a solution of liquid H.sub.2O.sub.2 and
water, by means of generators specifically designed for the
purpose. Aqueous hydrogen peroxide may be supplied as a 35%
stabilized solution, for example Vaprox.RTM. supplied by STERIS
Corporation.
[0005] VHP is used for loads that may be structurally fairly
complex, containing voids or spaces. The loads often have low
thermal conductivity, e.g. certain polymers. In these cases,
uniform distribution of sterilant and temperature is of great
importance.
BACKGROUND ART
[0006] In the International patent application published as WO
2010/000022 is disclosed a method of sterilizing objects using a
sterilizing mist, e.g. hydrogen peroxide. The mist is delivered to
a sterilization chamber and allowed to contact the objects for a
given duration; subsequently the sterilizing mist is displaced by a
gas flow which during a given period removes possibly condensed
mist from the object. The reduction in microorganisms for this
cycle is less than log 6, and the cycle is repeated until a
predetermined sterilization parameter is achieved. The process is
preferably carried out at atmospheric pressure or above.
[0007] In the International patent application published as WO
2008/134290, a decontamination system utilizing vaporized hydrogen
peroxide is disclosed. The system is provided with a controller for
modifying the concentration of the vaporized decontaminant in the
relevant space in response to operating conditions, thereby
preventing condensation of the vaporized decontaminant during a
cycle; i.e. the decontamination system can operate at an optimal
concentration level while maintaining a dew point margin.
[0008] In European patent application No. 01930156.3 is disclosed a
process using gaseous hydrogen peroxide for sterilizing sealing
members like elastomer stoppers. The cycle involves a vacuum stage,
introduction of gaseous hydrogen peroxide and a hold period, a
period of clean gas pressure to cause penetration of hydrogen
peroxide into the material; and a number of aeration pulses.
[0009] In the International patent application published as WO
97/25075 is disclosed a method for sterilization of articles using
hydrogen peroxide, in which method the treatment with sterilant at
sub-atmospheric pressure is followed by a sequence of warm steam
pulses at a higher pressure, causing rapid outgassing of the
hydrogen peroxide absorbed on the articles. Thus, the process is
shortened since outgassing to an acceptable level may take a
significant amount of time without steam pulsing.
SUMMARY OF THE INVENTION
[0010] In particular when the load is prone to absorb sterilant,
the concentration of hydrogen peroxide tends to rise at the edges
of the load. The concentration of hydrogen peroxide can be
monitored using standardized indicator devices which are placed at
selected locations in the load. It has been shown, that with prior
art methods where e.g. VHP is introduced into an evacuated
sterilizer chamber and a hold period follows, a gradient of
hydrogen peroxide concentration is formed, the concentration being
excessively high at the periphery of the load while the
concentration at the center may still be insufficient for proper
sterilization. Excessive concentration of sterilant may lead to
excessive absorption of sterilant into the material, leading in
turn to problems with residual, slowly desorbing toxic substances
and prolonged processing periods.
[0011] According to the present invention, an improved method is
provided for the reliable and repeatable sterilization of loads
having a complicated structure and absorbing characteristics, using
vaporized hydrogen peroxide and steam and enhanced gas circulation
within the sterilization chamber. Excessive use of sterilant may
thus be avoided.
[0012] The method involves a sequence of creating a sub-atmospheric
pressure in a sterilization chamber, introduction of VHP and the
use of a gas circulation device within the sterilization chamber
whereby the output of the gas circulation device is controlled
according to the pressure prevailing in the sterilization
chamber.
[0013] According to a first aspect of the present invention, a
method for sterilizing a load of goods is provided comprising the
following steps: a sterilization chamber is charged with a load of
goods to be sterilized; the chamber is evacuated to a minimum
pressure determined by the characteristics of the load; an
atmosphere of vaporized hydrogen peroxide is introduced in an
amount determined by the desired final concentration throughout the
load; the resulting sterilizing atmosphere is circulated within the
chamber at a flow rate determined by the prevailing pressure using
a gas circulation device internal to the chamber; and the
sterilizing atmosphere is removed.
[0014] According to a further aspect of the invention, an apparatus
is provided for carrying out the method according to the invention,
the apparatus comprising: A chamber for receiving a load of goods
to be sterilized, said chamber having a jacket for a heat transfer
medium as well as gas inlets and gas outlets; a device for
delivering a heat-controlled heat transfer medium to the jacket;
within the chamber, a gas circulation device capable of delivering
a constant volume flow at variable velocities; a device for
producing vaporized hydrogen peroxide: and a device for producing
sub-atmospheric pressures within the chamber.
[0015] The apparatus further comprises at least one sensor for
measuring temperature and at least one sensor for measuring
humidity within the chamber, and optionally one or more sensors for
measuring hydrogen peroxide concentration at selected points.
[0016] The apparatus may also comprise a device or devices for
introducing pressurized steam and/or air to the chamber.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The invention is described in further detail with reference
to FIG. 1, showing a schematic drawing of the main components of an
apparatus according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] With reference to FIG. 1, chamber 3, built according to
standards for vacuum use is arranged for receiving a load. The load
may be arranged on a rack or racks 4 designed for easy handling of
various types of goods, which are typically packed in plastic
covers, e.g. Tyvek.RTM.. The load on the uppermost shelf of the
rack is indicated by reference number 1, the lower shelves are
loaded similarly but reference numbers are omitted.
[0019] The temperature in the chamber is preferably controlled by
means of a heat transfer medium generated in heater 6 and
circulated through a jacket 2 provided on the chamber walls.
Preferably, the heat transfer medium is steam. At the beginning of
a sterilization cycle, the sterilization chamber is charged with a
load of goods to be sterilized. Indicators of hydrogen peroxide
exposure, e.g. as provided by the STERIS corporation, are placed at
representative locations throughout the load, as shown in an
exemplary manner by reference number 5, in particular when a new
type of load is being treated. Loads for which hydrogen peroxide
sterilization are suited are usually heat sensitive, and the
temperatures used in the process may range from room temperature to
about 40.degree. C. Preferably, the load is heated to the
predetermined operating temperature by circulating dry air within
the chamber while the chamber walls are heated by providing steam
to the jacket.
[0020] Following a possible preheating as explained, the chamber is
evacuated using pump 7 to a minimum pressure determined by the
characteristics of the load. This minimum pressure may be as low as
1 mbar, typically about 4 mbar. An atmosphere of vaporized hydrogen
peroxide (VHP) produced in generator 8 in a manner known as such is
then introduced to the chamber 3. A typical pressure after charging
VHP in this case is in the range 20-35 mbar.
[0021] According to the present invention, the VHP is preferably
charged to the chamber based on a measurement of humidity. The
initial evacuation of the chamber is carried out according to the
minimum pressure that is acceptable for the current load.
[0022] The charged amount of VHP may be monitored using humidity
sensors. When measuring the humidity of a VHP atmosphere generated
in an evacuated space, the impact of the hydrogen peroxide must be
taken into account. The ratio of hydrogen peroxide and water
determines the saturation vapor pressure of the gas mixture.
Sensors capable of measuring the humidity of such a mixed
atmosphere are available, e.g. from the Vaisala corporation. A
percentage reading indicating the VHP saturation rate is obtained.
The practical operational pressure when VHP saturation humidity is
used as a parameter is no higher than 100 mbar, and percentage
readings in the range of 60 to 85 are typical.
[0023] The humidity readings may thus be correlated to the VHP
concentration while dew point conditions are avoided. At suitable
humidity levels, a pressure of 10 to 65, preferably 15 to 40, most
preferably 20 to 35 mbar above the initial minimum pressure is
typically reached.
[0024] Hydrogen peroxide concentration sensors can be provided as
desired for reference. The final proof of sufficient and consistent
hydrogen peroxide concentration is obtained via the mentioned
indicators 5 within the load.
[0025] In the chamber, preferably in the roof of the chamber, a gas
circulation device 9 is provided having a variable speed drive 11
and being capable of providing a constant volume flow regardless of
gas density. Preferably this is a mechanical fan, e.g. a
centrifugal fan. When the selected humidity is reached, a
sterilization phase is initiated. During this phase, the output of
the gas circulation device is preferably controlled to be inversely
proportional to the pressure in the chamber. Thus, at a low
pressure, a high rate of gas circulation is provided. For example,
at a hydrogen peroxide/water vapor pressure of 20 to 35 mbar, the
output should correspond to at least 1/2 times the chamber volume
per second to ensure uniform distribution of hydrogen peroxide
throughout the load. As another example, at a pressure of 500 mbar,
the output of the gas circulation device should correspond to 1/3
of the chamber volume per second. "Chamber volume" refers to the
volume of the empty sterilization chamber, without load.
[0026] Drain connections (not shown) are provided in the chamber 3
and jacket 2 as required.
[0027] Appropriate control equipment and instrumentation, such as
controllers, temperature and pressure sensors and required valves
for automating the processes carried out in the apparatus are
provided as contemplated by the skilled person, but not shown in
FIG. 1.
[0028] The period necessary for obtaining a desired concentration
of hydrogen peroxide throughout the load may be determined and
validated empirically using hydrogen peroxide indicators as
explained above. The time used for the sterilization phase may be
in the range of 0.5 to 1 h for a chamber with a volume of 2
m.sup.3.
[0029] When the sterilization phase is finished, the hydrogen
peroxide-containing atmosphere is preferably displaced using steam
at a temperature not exceeding the maximum allowed temperature for
the specific load.
[0030] The effective use of a gas circulation device internal to
the chamber during the VHP treatment period ensures the uniform
distribution of sterilant throughout the load, compared to prior
art methods using sub-atmospheric pressure and a static sterilant
atmosphere; or processes using atmospheric or near atmospheric
pressure and the sterilant feed is arranged in an external loop
including a blower, whereby VHP enters the chamber from the
external loop through an inlet and leaves the chamber through an
outlet into the loop.
[0031] Preferably, an outgassing cycle as disclosed in WO97/25075,
hereby incorporated by reference, is applied to remove hydrogen
peroxide absorbed into the material of the load. This procedure
involves admitting steam to the chamber raising the pressure
significantly, and possibly raising the pressure further using air.
The temperature may also be raised according to the specifications
of the load. Subsequently, the chamber is evacuated, again
according to the tolerances of the load, and the cycle is repeated
until an acceptable level of residual hydrogen peroxide is
achieved. The process is enhanced using the gas circulation device
9 internal to the chamber. Typically, a sequence of five steam
pressure--vacuum cycles may be used for sufficient outgassing. The
apparatus is equipped with a catalytic destroyer 10 of leaving
hydrogen peroxide, for decomposing the hydrogen peroxide to water
and oxygen as known in the art.
* * * * *