GB2468518A - Sterilisation of a environment with ozone and increased humidity - Google Patents

Abstract

A method of sterilisation, sanitisation and/or decontamination comprises the steps of producing a humidified environment having a partial pressure of water vapour of at least 5.00 torr; discharging ozone into the humidified environment; and then introducing a cycloalkene into the humidified environment in such a manner as to cause atomisation thereof to react preferentially with the discharged ozone. Apparatus for carrying out the method is also claimed.

Description

Improvements in and relating to sterilisation and decontamination This invention relates to an improved method of sterilisation, sanitisation and/or decontamination.

It is a requirement to sterilise and sanitise enclosed spaces, such as kitchen areas and hospital rooms quickly and effectively, to destroy potentially harmful microorganisms, such as bacteria and viruses, contaminating the air and surfaces therewithin, in an acceptable timescale.

The biocidal activity of ozone is widely known and appreciated, and it is also known that the provision of ozone in a humid atmosphere increases the biocidal effectiveness.

However, problems associated with the use of ozone as a biocide have been the relatively lengthy post-treatment process to ensure that the environment is safe for returning occupants, the use of potentially environmentally damaging chemicals during the process, the general ineffectiveness of the process package in sanitising the environment, and the overall lack of simplicity in quickly setting up and using the apparatus.

The Applicant's previous application (EP 1500404, Steritrox Limited), demonstrated a method whereby the beneficial effect of ozone in a humid atmosphere could be utilised with the residual atmosphere being freed from harmful ozone within a useful timescale. The method involved the addition of an olefinic compound, in particular butene-2 to the atmosphere in sufficient quantity to react with and remove all of the residual ozone. Whilst this process is efficient at providing a sterile environment, it has now been recognised that the reaction between the residual ozone and the olefinic compound leads to the production of a range of volatile compounds, some of which have harmful properties when present in the atmosphere above a certain concentration, commonly referred to as the Occupational Exposure Level (OEL). The combination of products thus formed also contributes to a residual odour which may be unacceptable to many people.

Without prejudice to the invention, the range of compounds may include, for example, acetaldehyde, acetic acid, formaldehyde, formic acid, methanol, propionaldehyde, iso-valeraldehyde and the like. Additionally, it would be beneficial to provide for faster removal of the ozone from the environment.

The present invention seeks to provide a solution to these problems, in particular to provide a sterilisation, sanitisation and/or decontamination process and an apparatus that enables a treated area to be made safe from harmful products within an acceptable timescale and with a more acceptable residual odour.

According to the present invention, there is provided a method of sterilisation, decontamination and/or sanitation, the method comprising the steps of: a) producing a humidified environment wherein the water vapour has a partial pressure of at least 5.00 torr; b) discharging ozone into the humidified environment; and c) introducing a cycloalkene into the humidified environment to react preferentially with the discharged ozone.

It has surprisingly been found that use of a cycloalkene, particularly having a C5 or C6 ring, most preferably cyclohexene, provides for a cleaner reaction and faster removal of ozone, together with fewer toxic by-products.

Additional means may be provided for reducing the level of ozone subsequent to decontamination of the area, such as natural decomposition, catalytic decomposition and/or photochemical decomposition.

The water vapour preferably has a partial pressure of around 6 torr for cool applications, such as the sanitation of food store areas but has a partial pressure of around 13.00 torr for warmer environments, such as hospital and other healthcare environments.

Preferable and/or optional features of the first aspect of the invention are set forth in claims 2 to 11 inclusive.

According to a second aspect of the present invention, there is provided a sterilisation, decontamination and/or sanitation apparatus, optionally for use in accordance with the method of the first aspect of the present invention, the apparatus comprising a humidifier unit, an ozone discharge unit, a hydrocarbon discharge unit including atomisation means for dispersion of the hydrocarbon, and a controller by which the humidifier unit, ozone discharge unit and hydrocarbon discharge unit are controllable based on pre-determined conditions.

Preferably, the hydrocarbon is discharged by means of a high pressure pump, preferably via an injection nozzle. Any suitable high pressure pump may be used, including for example, a piezoelectric pump for controlled metering of the amount of hydrocarbon to be discharged.

Preferable and/or optional features of the second aspect of the invention are set forth in claims 13 to 16 inclusive.

The invention will now be more specifically described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic side elevational view of a sterilisation and decontamination apparatus for performing a method in accordance with the invention; and Figure 2 is a diagrammatic front view of the apparatus shown in Figure 1; Referring now to the accompanying drawings, there is shown an example of a sterilisation and decontamination apparatus 10 for carrying out the process of the present invention. The apparatus comprises a portable enclosure 12 which optionally can be opened and which, in use, can generate a positive pressure within the interior to protect sensitive devices within the enclosure from the deleterious affects of ozone. However, it is to be appreciated that alternative means could be provided to protect any internal sensitive components from being damaged by the ozone. The enclosure 12 has wheels 14 and houses a humidifier unit 16 having a humidified air outlet 17, an ozone discharge unit 18 having an ozone discharge outlet 20, a cycloalkene discharge unit 22 having a cycloalkene discharge outlet 24, and a control unit 26.

The humidifier unit 16 in the illustrated example includes a humidifier 28, a humidistat sensor 30, a temperature sensor 31 and a water reservoir 34. If the humidifier comprises an ultrasonic humidifier, a compressed air supply 32 should be provided, for example, in the form of a compressed air tank or container housed within the enclosure 12. The compressed air tank is connected to the water reservoir 34 and the humidifier 28. Water droplets having a diameter of less than microns, preferably 2-3 microns, are introduced into the air to enhance the rate of evaporation into the atmosphere.

The ozone discharge unit 18 includes an ozone generator 36, an ozone detector sensor 38, and an oxygen supply 40 for supplying oxygen to the ozone generator 36. Oxygen is preferred to air for the generation of ozone because this avoids the formation of toxic oxides of nitrogen, increases the rate at which the required concentration of ozone is achieved and also increases the yield of ozone.

The cycloalkene discharge unit 22 includes a cycloalkene supply 42 in the form of a tank or container containing the cycloalkene, such as cyclohexene and/or cyclopentene, most preferably cyclohexene, with an injection nozzle 58 such as that supplied under the trade name Delavan. The cyclohexene is pumped from the discharge unit using a high pressure pump (not shown) and microbore tubing to connect it to the injection nozzle to introduce the cyclohexene in the form of fine droplets into the environment at high pressure. Once dispersed at high pressure the cyclohexene vapourises very quickly due to its highly volatile nature, the small droplet size and its low latent heat of evaporation.

The control unit 26 controls the apparatus 10 and is preset with at least one sterilisation and decontamination routine. The control unit 26 includes a controller 46 and a user interface 48 by which a user can input commands to the apparatus 10.

The apparatus 10 may include an on-board battery 50 and/or may be connectable to a mains power supply. In the case of the on-board battery 50, the battery is preferably rechargeable. If a mains-operated apparatus is provided, this may have a battery back-up system to enable the machine to failsafe in the event of a main power failure.

The apparatus 10 will also typically include other safety features, such as safety sensors, and software routines to prevent start-up or initiate shut-down in the event of a system failure.

In use, the apparatus 10 is first located in the area which is to be sterilised and/or decontaminated. The power to the apparatus 10 is switched on, and the control unit 26 undertakes an initial safety check including checking the level of the cycloalkene supply 42, and checking the relative humidity. If the safety check is not passed, the apparatus 10 does not operate and outputs a suitable indication using warning lights 52. During operation of the process, safety checks are made continuously, and in the event of a system failure, the system defaults to a safe mode.

The temperature of the humidified air is above the dew point of the environment, and thus condensation does not occur.

The controller 46 continues to monitor the ozone level, humidity through the humidistat sensor 30 and the ambient temperature through the thermocouple. If after a predetermined interval of time, for example 10 minutes, the calculated relative humidity level and/or the required ozone level has not been reached, the controller 46 aborts the sterilisation and/or decontamination routine and provides a

suitable indication.

Oxygen is supplied to the ozone generator 36, and ozone is generated. The generated ozone is then fed into the discharging humidified airstream. The controller 46 provides a suitable indication that the ozone generator 36 is operating, and monitors the ambient ozone levels through the ozone detector sensor 38.

Both the ozone and water vapour concentrations to be detected can be altered. However a typical setting is 25 ppm v/v of ozone and 13.6 torr. Once the preset ozone and water vapour levels have been detected within the allotted interval, the controller 46 enters a timing phase, known as the "dwell time".

The dwell time can also be altered, for example, to one hour, and will depend on the degree and type of decontamination / sanitisation to be provided.

For instance, contamination by spores or moulds, such as clostridium difficile, generally require a longer dwell time than contamination by bacteria, such as listeria and methicillin resistant staphylococcus aureus (MRS A).

During the dwell time, the ozone concentration and relative humidity are continuously monitored. If the ozone level falls below a predetermined threshold, the ozone discharge unit 18 is reactivated to replenish the ozone levels. If the humidity falls below the calculated value, the humidifier unit 16 is reactivated to restore the water vapour level.

Again, during the reactivation period, should either the ozone concentration or the relative humidity fail to reach the above-mentioned predetermined minima within a set time interval, for example 10 minutes, the controller 46 aborts the sterilisation and decontamination routine and outputs a

suitable indication.

After the dwell time has elapsed, the controller 46 closes the compressed air valve 54 and the oxygen supply valve 56, and the humidifier unit 16 and the ozone discharge unit 18 are switched off. The controller 46 then operates a cyclohexene discharge valve 58 of the cyclohexene discharge unit 22 to discharge the cyclohexene into the ambient environment. The cyclohexene is preferably provided at a level slightly in excess of the level of ozone to be destroyed. The cyclohexene preferentially reacts with the residual ozone to accelerate the breakdown of the ozone. The cyclohexene is provided in excess to ensure complete removal of the ozone, thereby offering faster user re-entry to the treated area.

When the ozone detector sensor 38 detects that the ozone concentration levels are less than a predetermined value, for example 0.2 ppm or less, the controller 46 closes the cyclohexene discharge valve 58 and outputs an indication that the sterilisation and decontamination routine is complete. The ozone level of 0.2 ppm, depending on the size of the area being sterilised and decontaminated, is usually achieved in less than 3 to 4 minutes.

Tn very simplistic terms, the reactions that are followed are 03 + H20 = H202 +02 H0 + OH H0 + 02 (ozone) and preferential reaction: 03 + C6HI0 C6HI0O3 C6H1003 + H20 CoHioO + H20 An intermediary cyclohexene ozonide is formed from the reaction of ozone with cyclohexene which is hydrolysed by water to form the linear dialdehyde C6H1002.

The stereochemistry of the double bond of the cyclohexene is determined by the cyclic structure, causing the bond to be somewhat strained and therefore more reactive. In particular, the presence of different carbon geometries in the cyclohexene molecule causes an increase in strain which leads to greater reactivity. In this respect, the geometry about a carbon to carbon double bond is planar, with bond angles of 120°. In marked contrast, the geometry about a carbon to carbon single bond is three-dimensional with a tetrahedral arrangement about each carbon atom and bond angles of about 109°. Cyclohexene, and other cycloalkenes, contain both tetrahedral and planar carbon geometries leading to strain on at least some of the bonds. Without prejudice to the invention, it is this degree of strain that is believed to give an enhancement in the rate of ozone depletion.

The ozone reacts with the cyclohexene to produce a bicyclic ozonide. The geometry of all the bonds in the ozonide is tetrahedral, since the double bond has undergone an addition reaction. The ozonide itself is very reactive and decomposes via both a hydrolytic and a free radical mechanism. However, unlike linear olefins, a single compound will result from the hydrolytic decomposition, namely the linear C6 dialdehyde. This is commonly known as adipaldehyde (technical name 1, 6 hexanedial). This is believed to have low toxicity.

Further oxidation proceeds to the dibasic acid (adipic acid) which has been produced for commercial applications (for example, the manufacture of nylon 6,6) for many years and its toxicity is well understood.

Thus, the use of a cyclohexene for the removal of ozone has significant advantages over the prior art quenching techniques, in particular the speed of the reaction and the low toxicity of the by-products formed.

If the ozone detector sensor 38 fails to indicate that the predetermined safe level of ozone has been reached within a predetermined time interval following introduction of the cycloalkene, for example within 10 minutes, the controller 46 outputs an indication warning of potentially hazardous ozone levels in the room.

The controller may be programmed to allow a time interval to elapse in excess of the standard half-life of ozone before announcing that the room may be re-occupied.

It is envisaged that the sterilisation and decontamination apparatus may be integrally formed as part of an area, or may be only partly portable. For example, the compressed air supply and/or oxygen supply could be integrally formed as part of the area to be regularly sterilised and decontaminated. Alternatively, components could be housed within the enclosure of the apparatus. In this case, the required supply could be linked to the apparatus via a detachable umbilical pipe. The machine may also consist of a main unit and a wirelessly connected remote controller wherein the required preset routine may be remotely initiated by a user from outside the area to be sterilised and/or decontaminated.

Although the oxygen supply is typically in the form of one or more oxygen tanks or cylinders, a commercially available oxygen concentrator can be used.

Whilst the example shown uses a high pressure injection nozzle to disperse the cyclohexene into the environment, this may also be achieved by alternative means, such as an aerosol propellant. The cycloalkene may be combined with a suitable inert propellant, such as liquid carbon dioxide, for dispersion into the environment.

The apparatus uses an electric fan 72 as a gas movement device to circulate the humidified air, ozone and cycloalkene. However, dependent on the particular application, an air mover may be used instead of an electric fan.

hi the example described above, the method allows for natural decay of the by-products of the reaction of ozone with the cycloalkene. However, additional means may be included to assist in removal of the ozone and any by-products, such as a catalyst or UV radiation.

The above-described apparatus utilises a method of producing an artificially high level of non-condensing humidity, and generating in-situ a high concentration of ozone.

The materials of the apparatus are resistant to the corrosive effects of ozone and high humidity, and the solvent effects of the hydrocarbon.

The condition of all the valves are monitored using integrally incorporated sensors connected to the controller. The valves failsafe to an appropriate position, such as the closed position, so that user safety is maintained at all times. The controller may also incorporate a tamper proof recording system to monitor use, time, date, operational success/failure and other parameters required to measure performance of the machine.

It is thus possible to provide a method which is fast and effective, and an apparatus which is discrete and portable. The method may provide better than 99.99% effective sterilisation and/or decontamination of an area without an impact on the environment from harmful by-products. Rapid re-use of a contaminated area can thus be realised. The above-described method has proven to be lethal to a wide variety of pathogens, including bacteria such as Methicillin Resistant Staphylococcus Aureus (MRSA).

The embodiments described above are given by way of examples only, and other modifications will be apparent to persons skilled in the art without departing from the scope of the invention as defined by the appended claims.

Claims (16)

1. Claims 1. A method of sterilisation and decontamination, the method comprising the steps of: a) producing a humidified environment having a partial pressure of water vapour of at least 5.00 torr; b) discharging ozone into the humidified environment; and c) introducing a cycloalkene into the humidified environment to react preferentially with the discharged ozone.
2. 2. A method as claimed in claim 1, wherein the humidity produced in step (a) is non-condensing humidity.
3. 3. A method as claimed in claim 1 or 2, wherein the cycloalkene contains an
4. 4. A method as claimed in any one of claims 1 to 3, wherein the cycloalkene is selected from cycohexene or cyclopentene.
5. 5. A method as claimed in claim 4 wherein the cycloalkene is cyclohexene.
6. 6. A method as claimed in any one of the preceding claims, wherein the cycloalkene is provided in a quantity not greater that a level in excess of 15% v/v above the stoichiometric ozone level.
7. 7. A method as claimed in claim 6 wherein the cycloalkene is provided in a quantity not greater than 5% v/v above the stoichiometric ozone level.
8. 8. A method as claimed in claim 7 wherein the cycloalkene is provided in a quantity slightly in excess of the stoichiometric ozone level.
9. 9. A method as claimed in any one of the preceding claims wherein, in step c) the cycloalkene is pumped under pressure into the environment.
10. 10. A method as claimed in claim 9 wherein the cycloalkene is injected into the environment at high pressure through a nozzle designed for effective atomisation.
11. 11. A method as claimed in any one of claims 1 to 8 wherein the cycloalkene is dispersed with an aerosol propellant into the environment.
12. 12. A sterilisation, decontamination and/or santitation apparatus comprising a humidifier unit, an ozone discharge unit, a hydrocarbon discharge unit including atomisation means for dispersion of the hydrocarbon, and a controller by which the humidifier unit, ozone discharge unit and hydrocarbon discharge unit are controllable based on pre-determined conditions.
13. 13. An apparatus as claimed in claim 12 wherein the atomisation means comprises a high pressure pump for discharge of the hydrocarbon via an injection nozzle.
14. 14. An apparatus as claimed in claim 12 wherein the atomisation means comprises a piezoelectric pump for controlled metering of the hydrocarbon.
15. 15. An apparatus as claimed in claim 12, 13 or 14 for use with a method as claimed in any one of claims 1 to 11.
16. 16. An apparatus substantially as hereinbefore described and with reference to the accompanying drawings.