This invention relates to a method of sterilisation and/or decontamination, including sanitation, and to apparatus for use with said method.

It is a requirement to sterilise and sanitise enclosed spaces, such as kitchen areas and hospital rooms quickly and effectively, in order 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 olefϊnic compound, such as 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 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). Without prejudice to the invention, the range of compounds may include, for example, acetaldehyde, acetic acid, formaldehyde, formic acid, methanol, _j propionaldehyde and the like.

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

According to a first aspect of 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 having a partial pressure of water vapour which is higher than 5.0 torr; b) discharging ozone into the humidified environment; c) maintaining the ozone level at a concentration that will achieve the required degree of decontamination, sterilisation and/or sanitation of the humid environment; d) reducing the concentration of ozone to a predetermined level; and e) introducing a hydrocarbon containing a carbon-carbon double bond into the environment to react preferentially with the discharged ozone.

The reduction of the concentration of ozone to a predetermined amount in step (d) prior to introduction of the hydrocarbon may be achieved by any suitable means, such as spontaneous decomposition (natural decay), catalytic decomposition and/or photochemical decomposition. Preferably, the reduction is provided by means of catalytic or. photochemical decomposition. More preferably, a further step f) is included wherein the air is recycled through a catalyst until the concentration of harmful products falls to a safe level.

Preferable and/or optional features of the first aspect of the invention are set forth in claims 2 to 10 inclusive.

According to a second aspect of the present invention, there is provided a sterilisation, sanitisation and/or decontamination apparatus for use with a method in accordance with the first aspect of the present invention, the apparatus comprising a humidifier unit, an ozone discharge unit, an ozone depletion unit, a hydrocarbon discharge unit and a controller by which the humidifier unit, ozone discharge unit and hydrocarbon discharge unit are controllable based on pre-determined conditions. Preferably, the ozone depletion unit comprises an ozone depletion catalyst or a photochemical system.

Preferable and/or optional features of the second aspect of the invention are set forth in claims 12 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 one embodiment of sterilisation and decontamination apparatus for carrying out the process of the invention; and

Figure 2 is a diagrammatic front view of the apparatus shown in Figure 1 ;

The process and apparatus of the present invention use ozone for the sterilisation and decontamination of an environment and include means for reducing levels of the ozone and any unwanted by-products to a safe level in minimal time, thereby reducing the time during which a room has to be kept unoccupied. The invention introduces ozone to decontaminate the environment and then reduces the level of ozone in the environment before the addition of a hydrocarbon having a carbon-carbon bond for reaction with the residual ozone. This allows a reduced amount of hydrocarbon to be introduced into the environment ensuring that any byproducts produced as a result of the reaction between the ozone and hydrocarbon are kept below their Occupational Exposure Limit (OEL). This is the upper safe limit for human exposure to a given chemical and is found by reference to the safety literature. It is the level above which the concentration of a given compound must not be allowed to rise, and may be quoted in the units mg.m ^"3 in the humid atmosphere. The level is generally different for different compounds, and may be changed from time to time as further information becomes available.

The main product of the reaction of ozone with a substance containing a carbon-carbon double bond is an ozonide, which in turn decomposes by hydrolysis in the humid atmosphere into aldehydes and hydrogen peroxide. This reaction is exemplified by, but not limited to, the reaction of ozone and butene:

CH ₃ CH=CHCH ₃ + O ₃ + H ₂ O ►

CH ₃ CH ₂ CH=CH ₂ + O ₃ + H2O— ^►

CH ₃ CH ₂ CHO + HCHO + H ₂ O ₂

As can be seen from this, the formation of the main organic by-products is a stoichiometric reaction and the quantity of compound thus formed is easily calculated by those skilled in the art. For example, in the above equation, the molar proportions of ozone to butene are 1:1 but will produce 2 moles of aldehyde. It is therefore possible to calculate the maximum volume/mass of aldehyde that will be produced from a given quantity of ozone and olefin. Thus, the invention requires that the ozone level is reduced, preferably by means of a catalyst or photochemistry (although any other selected decomposition procedure may be used) to a value at least approximating, or somewhat below, the level at which the maximum concentration of by-product that could be formed through stoichiometric reaction with the hydrocarbon that is introduced into the airstream after the ozone-containing air has been drawn through the catalyst is below the OEL of the by-product. Without prejudice to the invention, it is also recognised that an ozonide can also decompose by a radical mechanism, in which case a rather different spectrum of products may be obtained, including oxides of carbon etc. The calculated amount of aldehyde that could be formed by hydrolytic decomposition of the ozonide is therefore considered to be a maximum, thus enabling the process to operate safely.

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 can be openable 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 appreciated that alternative means could be provided to protect the 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 vessel containing an ozone catalyst 70, an ozone catalyst fan (not visible), a hydrocarbon discharge unit 22 having a hydrocarbon discharge outlet 24, and a control unit 26.

The illustrated example has an ozone depletion catalyst but alternative suitable ozone depletion means may be used in the present invention, such as photochemical means.

The humidifier unit 16 in the illustrated example includes a humidifier 28, a humidistat sensor 30, a compressed air supply 32, and a water reservoir 34. If an ultrasonic humidifier is used, a source of compressed air 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 5 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 ozone catalyst 70 is a catalyst that is able to operate at low temperature and high humidity. The catalyst may be selected from a range of proprietary substances that are known to be active in the catalytic decomposition of ozone. Such catalysts may optionally include platinum group metals, oxides of manganese, and other substances that have a promoting effect. The hydrocarbon discharge unit 22 includes a hydrocarbon supply 42 in the form of a tank or container containing a volatile unsaturated hydrocarbon, such as butene. Preferably, the butene is butene-2. However, the hydrocarbon can be any suitable hydrocarbon having a carbon-carbon double bond, for reasons which will become apparent hereinafter. The selection of hydrocarbon is based on its speed of reaction with ozone and the toxicology of its decay products.

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 mains 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 decontaminated. The power to the apparatus 10 is switched on, and the control unit 26 undertakes an initial safety check. If the safety check is not passed, the apparatus 10 does not operate and outputs a suitable indication using warning lights 52. During 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, relative humidity through the humidistat sensor 30 and ambient temperature through the thermocouple 31. 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 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 oztone 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 (MRSA).

During the dwell time, the ozone concentration and relative humidity are continuously monitored. If the ozone level falls below a predetermined threshold, for example 9 ppm, 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, if either the ozone concentration or the relative humidity fails 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. A fan (not shown) then blows the atmosphere through the catalyst 70 to reduce the levels of ozone, the level of ozone being monitored continuously. When the concentration of the ozone has fallen to the required level, such as 8mg.m ^'3 , slightly in excess of the stoichiometric mass of butene-2 on ozone is introduced by means of a hydrocarbon discharge valve 58 of the hydrocarbon discharge unit 22. This quantity of butene-2 is sufficiently low so that the maximum amount of acetaldehyde that could theoretically be formed would be insufficient to raise the concentration of acetaldehyde in the atmosphere of the enclosure to the OEL value. The concentration of ozone is continuously monitored and seen to fall to an undetectable level. The catalyst 70 may be continuously deployed until the concentration of ozone falls below its OEL.

When the ozone detector sensor 38 detedts that the ozone concentration levels are less than a predetermined value, for example 0.2 ppm or less, the controller 46 closes the hydrocarbon 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 within 3 to 4 minutes. The apparatus may include a feedback ozone measurement system (not shown) to determine the quantity of hydrocarbon added to the environment thereby reducing the chance of overdosing the hydrocarbon input and minimising associated potential toxicology issues.

If the ozone detector sensor 38 fails to indicate that the predetermined safe level of ozone has been reached within a predetermined time interval, 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 pass 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 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.

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

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 for sterilisation, sanitisation and/or decontamination of an enclosed area which is fast, effective and does not provide harmful by-products above their OEL. Furthermore, the apparatus may be discrete and portable. The method can provide better than 99.99% effective sterilisation and decontamination of an area without an impact on the environment from harmful byproducts. Rapid re-use of a contaminated area can thus be realised.

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.