MX2008001781A - Space disinfection - Google Patents

Abstract

A method for disinfecting a volume or surfaces bounding a volume comprising nebulising a solution comprising a sterilizing agent in a solvent having a lower boiling point than the sterilizing agent, for example ultrasonic nebulization of aqueous hydrogen peroxide, to form a nebulant. The nebulant is subjected to energy of a kind and for a duration sufficient to vaporize solvent in preference to sterilizing agent, eg heating element means, infra red, laser, microwave, RF or other radiation generating means;induction heating means;heat exchanger means;conduction means;convection means;or mechanical energy transfer means to increase the concentration of the agent in the nebulant particles. Vaporized solvent is removed from the gas stream at or above atmospheric pressure and, if necessary, the nebulant is cooled to below 7O0C. The volume or surfaces are exposed to the nebulant for a time sufficient to sterilize said volume or surfaces. Also, apparatus for carrying out the method.

Description

DISINFECTION OF SPACE FIELD OF THE INVENTION The present invention relates to a method and apparatus for disinfecting or decontaminating large exposed surfaces or spaces that can be infected with fungal or bacterial bacteria, fungi, viruses or spores. A space to be disinfected can be a camera, for example, a shipping container, an operating theater, a hospital unit, the interior of an airplane, or it can be a shopping center, an underground train system, a warehouse, a silo, or a closed or semi-enclosed space. Exposed surfaces can be exemplified by wall surfaces or divisions that define space, work surfaces, machinery surfaces, air conditioning ducts, or other surfaces that are interior or can be enclosed or partially enclosed, at least temporarily, for the purpose of the present.

BACKGROUND OF THE INVENTION Any discussion of the prior art through the specification should in no way be construed as an admission that said prior art is widely known or forms part of the general knowledge common in the field. The most commonly used method for disinfecting such large spaces and surfaces involves the use of gases such as ozone and chlorine dioxide which are oxidative or corrosive and toxic, or may involve gases such as ethylene oxide or aldehydes, such as glutaraldehyde or formaldehyde, They are extremely toxic and leave potentially harmful residues on surfaces. Steam is sometimes used and is harmful to the operator due to the high temperatures involved and leaves a dense moisture on the surface that can cause rust. From a health and environmental perspective it may be preferable to use hydrogen peroxide or peracetic acid as a disinfectant. At present, as discussed in Ronian US 6,500,465, high-density fine aerosols (aerosol droplet diameter less than 50 microns) of peracetic acid or hydrogen peroxide suitable for disinfection are only considered stable at a relative humidity of 100 %. Also in the present, the aerosols have suffered from general problems in that they are not effective penetrating the covered surfaces. This means that locks, hinges and the like as well as occluded surfaces such as, for example, an area or floor below a chair, can house the organisms. Another problem is that the aerosol particles tend to set and impregnate on the surfaces where they fall, leaving an undesirable residue on the surface that must be cleaned. In co-pending applications, "Improved Aerosol" and "Membrane Sterilization" (copies appended hereto) whose contents are incorporated by reference, sterilizing agents or disinfectants are described which can be adapted to treat large surfaces or spaces.

BRIEF DESCRIPTION AND OBJECTIVE OF THE INVENTION It is an object of the invention to provide a method for disinfecting a large area or disinfecting a volume wherein at least some of the drawbacks of the prior art are avoided or mitigated. It is a further object of the invention to provide an improved apparatus and improved fumigators to carry out the method. By disinfecting a volume it is meant that the air in the volume and the organisms if they are suspended in the air are disinfected. It is an objective of the preferred embodiments to be able to disinfect surfaces in chambers such as operating theaters, hospital units, cold rooms, refrigerators, ventilators, marine containers, industrial areas where disinfection is a requirement and preferably to do this by means which are graduables Unless the context clearly requires otherwise, throughout the description and claims, the words "comprise", "comprising", and the like must be constructed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is, in the sense of "that includes, but is not limited to".

DETAILED DESCRIPTION OF THE INVENTION According to a first aspect, the present invention provides a method for disinfecting an area or a volume comprising the steps of: 1) nebulizing a solution comprising a sterilizing agent in a solvent to form a nebulizer of finely divided particles of the solution in a gas stream, said solution includes a solvent having a boiling point lower than the sterilizing agent; 2) subjecting the nebulizer to energy of a type and for a time sufficient to vaporize the solvent, preferably the sterilizing agent, increasing the concentration of the agent in the nebulizer particles; 3) remove the vaporized solvent in step 2 from the gas stream at or above atmospheric pressure and, if necessary, cool the nebulizer to below 70 ° C; and 4) exposing the surface to the nebulizer of step 3 for a sufficient time to disinfect said area or volume.

In preferred embodiments, the nebulizer is a solution of hydrogen peroxide in water, desirably at an initial concentration of 35% or less. If desired, the method can sterilize said surface, or the surfaces containing the volume. According to a second aspect, the invention provides a method for disinfecting a large area or volume comprising the steps: 1) exposing the surface to, or introducing into said volume, a nebulizer comprising a solution of hydrogen peroxide in water; and 2) control the relative humidity in the volume or the vicinity of the surface from 20% to 70% RH. The invention will now be described more particularly by way of example only with reference to the accompanying drawings. With reference to Figure 1, a first embodiment of the invention is shown schematically. In figure 1 a chamber 1 to be disinfected is shown in a vertical cross section. Chamber 1 is defined by walls 2, 3, floor 4, and ceiling 5 (the remaining walls and the entrance are not illustrated). Inside the chamber is an ultrasonic nebulizer 6 for example of the type described in our co-pending application "Improved Aerosol" in Figures 3 and 4, which are shown here as Figures 2 and 3. The nebulizer 6 is fed in this example as a 35% solution of hydrogen peroxide in water contained in a reservoir 7 by means of a feeding line 8. The nebulizer 6 extracts air in the air inlet 9, in this example from inside the chamber 1. The nebulizer generated by the nebulizer 6 leaves the outlet of the nebulizer 10 and is withdrawn by means of a conduit 11 on the suction side of the fan 12 and is pumped from the pressure side of the fan 12 to a heater 13. The nebulizer of the nebulizer 6 passes over a heating element in the heater 13 and directed from the outlet of the heater 14 by means of a conduit 15 to a spout 16 where the volume of the chamber penetrates. The humidity removal unit 20 draws air from inside chamber 1 to 21, cools it and dehumed it and returns it to the room at a predetermined temperature and relative humidity. In the example hereof, the humidity removal unit 20 is an air conditioning system. In operation, the nebulizer 6 nebulizes a solution comprising hydrogen peroxide in water from the reservoir 7 to form a nebulizer of finely divided particles of the solution in the air stream. The water has a lower boiling point than hydrogen peroxide. In this example the nebulizer is heated in a heater 13 sufficient to vaporize water in preference to peroxide, whereby the concentration of peroxide in the nebulizer particles is increased to about 60-70% and reduces the particle size as discussed in FIG. the copendientes requests. The dispenser 16 can have one or more deflectors, which can be stationary or driven or can be other means such as a fan to supply the nebulizer. In this embodiment of the invention, the water vapor removed from the nebulizer during the passage through the heater 13 is removed from the chamber 1 with an air conditioning system 20 at or above the atmospheric pressure which the nebulizer and the vapor of the vaporizer extract. Water from the room removes the water vapor and returns the nebulizer frozen in space. The treated nebulizer consists of particles that have a smaller size (nano particles) than the untreated particles produced by the nebulizer (micro particles) and therefore have a much lower tenacity to be fixed in the gas stream. The smaller particles also have a much higher velocity of diffusion and ability to penetrate the covered spaces. The treated nebulizer has a much higher concentration than the untreated nebulizer or feeding solution. In the co-pending application "Improved Aerosol", the nebulizer of the nebulizer is heated in a heat exchanger and subsequently cooled in a condenser to remove the water (with reference to figure 2 of the application, the vapor of the nebulizer 5 is heated in 17 and then cooled in 20 to remove water). In figure 1 of the present, when controlling the relative humidity within the space 1 by an air conditioner 20, an effect similar to that obtained by the examples of the co-pending specification is obtained. As described in more detail in the co-pending applications: • Other sterilizing agents can be used and the sterilizing agent can be dissolved in other solvents, • Other types of nebulizer can be used • Other gases can be fed to the nebulizer • Solutions of the air hydrogen peroxide solution are greatly preferred. • The solvent can be removed in preference to the biocide by supplying energy in other ways. • Water can be removed from the chamber by other means. • It is desirable to control the relative humidity, and the temperature within the predetermined limits as detailed herein. In the present application the air conditioner can take the form of a piped room system or can be a portable unit placed in the room. The unit does not need to employ a condenser but may for example be a desiccant system such as a system of double cycles that absorbs moisture during a cycle, and is subsequently dried by venting the moisture externally during a second cycle while a double unit absorbs moisture, or a device such as that described in the co-pending application "Membrane Concentrator", for example, a device shown in Figure 4 wherein a nebulizer stream enters duct 171 to 173 and exits at 174 and an air countercurrent u another dry gas 176 passes on either side of the semipermeable membrane 172. The mist droplets that exit at 174 are more concentrated than those that enter 173. A catalytic destroyer can be used to remove excess peroxide from the chamber. The reservoir, nebulizer, fan and heater can be combined into a portable unit that can be moved from camera to camera, and if desired a separate air conditioning or air drying system can be made portable for use in the same chamber as the nebulizer or can be combined with the nebulizer unit. A preferred embodiment will now be described by way of example. In this mode, 35% hydrogen peroxide in water was used as the biocide. The components of the device include a nebulizer arrangement, (6 x 2 cm diameter transducers in a circular arrangement), a heater element, a first and second fan, and a dehumidifier system. The dehumidifier used is a small air conditioning unit that is properly positioned within the space. The purpose of the first fan is to drive nanoparticles from the heater into the space and the purpose of the second fan is to ensure an equal distribution of the aerosol to all surfaces within the space. It has been found highly desirable that the transducers be synchronized within the arrangement, otherwise the waveforms produced will potentially cancel each other within the liquid resulting in an inefficient production of the peroxide nebulizer towards the heater.

EXAMPLE 1 The tests were performed in a volume of 8 cubic meters of a cubic shape. The samples were coated with an inoculum at levels of approximately log 6 and air-dried for 2 hours in a plastic Petri dish (Techno-Plas, Australia) in a laminar flow cabinet. The samples were placed in various positions in the room including on the walls, floor and ceiling. In the example below, the samples were placed in the center of the wall adjacent to the corner and on the floor approximately in the center of the room and exposed to a hydrogen peroxide nebulizer treated as described with reference to the Figure 1. Unless stated otherwise, the operating conditions were: Solution: 35% peroxide Temperature: 25 degrees RH: ranging from 45% to -65%. Sometimes 75% Nebulizer arrangement: 2.4 MHz Peroxide vapor: 300-500 ppm Post heater. of air flow: 400-600 cubic meters per hour Heater temperature: 80-90 degrees Peroxide supply: Optimally approximately 0.75 grams per cubic meter per minute, that is, 12.6 grams for the room of 8 cubic meters. The results obtained for several bacteria are the following: (In the tables "TNTC" = too numerous to count, "ND" = was not performed) Table 1 shows the results for an experiment where open carriers were used. Table 2 shows the result for the same conditions except that the carriers were in closed Petri dishes, ie plates with lids. The closed petri dishes allowed penetration through very narrow spaces. The plates and covers are specifically designed to allow gas exchange with an incubator environment while keeping the plate free of external microbial contamination. Tables 3 and 4 show the results of Aspergillus niger.

EXAMPLE 2 The test of example 1 was repeated in 69 cu m, the chamber under substantially the same conditions except as shown in table 5. Table 5 shows the scalability of the procedure in a room of 69 cubic meters. In general, the results with Bacillus stearothermophillus showed that reductions of more than 6 log can be obtained in 550 ppm in the walls and floors.

EXAMPLE 3 The air was recirculated through a catalytic destructive system (using in this example a mixture of metal oxides including aluminum oxide) to "decontaminate" the room by removing excess peroxide. Otherwise, the peroxide can be broken more slowly by recirculating the conditioned dry air into the space or possibly by increasing the temperature to help facilitate the process. This takes approximately 1 hour to reduce the peroxide vapor levels to approximately 10 ppm from a maximum of approximately 400-700 ppm in a room of 16 cubic meters. The final 10 ppm take much longer to reduce to a significant degree.

To a degree which is obvious from the description herein, the features described in this specification may be combined with characteristics or combinations of features described in the copending applications and such combinations are within the scope of the invention as described.

TABLE 1 TABLE 2 TABLE 3 TABLE 4 TABLE 5

Claims (15)

NOVELTY OF THE INVENTION CLAIMS

1. - A method for disinfecting a volume or surfaces by joining a volume comprising the steps of: (1) nebulizing a solution comprising a biocidal agent in a solvent to form a nebulizer of finely divided particles of the solution in a gas stream, said solution includes a solvent having a lower boiling point than the sterilizing agent; (2) subjecting the nebulizer to energy of a type and for a time sufficient to vaporize the solvent in preference to a sterilizing agent, whereby the concentration of the agent in the nebulizer particles is increased; (3) remove the vaporized solvent in step 2 from the gas stream at or above atmospheric pressure and, if desired, cool the nebulizer to below 70 ° C; and (4) exposing the volume or surfaces to the nebulizer of step 3 for a sufficient time to sterilize the volume or surfaces.

2. The method according to claim 1, further characterized in that the nebulizer is a solution of hydrogen peroxide in water.

3. The method according to claim 2, further characterized in that the hydrogen peroxide nebulized in step 1 is in an initial concentration of 35% or less.

4. - A method for disinfecting a volume or surfaces by joining a volume comprising the steps of: (1) exposing the surfaces or introducing to the volume a nebulizer comprising a solution of hydrogen peroxide in water; and (2) control the relative humidity in the volume or in the vicinity of the surface from 20% to 70% relative humidity.

5. The method according to claim 4, further characterized in that the relative humidity in step 2 is controlled from 45% to 65%.

6. The method according to any of the preceding claims, further characterized in that the nebulizer particles have an average diameter of less than 1 miera.

7. The method according to any of the preceding claims, further characterized in that the temperature in the volume is maintained at 20-30 degrees centigrade.

8. The method according to any of the preceding claims, further characterized in that the peroxide nebulizer is supplied to the volume at a rate of 0.5 to 1.0 gram / cubic meter of the volume to be disinfected.

9. An apparatus for carrying out a method according to any of claims 1 to 8, comprising in combination: (1) means adapted to produce a nebulizer comprising finely divided particles of a solution suspended in a gas, the solution comprises a solute and a solvent; (2) means for supplying sufficient energy to the nebulizer to air selectively select at least some of the solvent as a vapor, whereby the concentration of the solute in the nebulizer particles increases; and (3) means for separating vapor from the nebulizer solvent after step 3 at atmospheric pressure, and if necessary, cooling the nebulizer below 70 ° C; (4) means for contacting the surface to be sterilized with the nebulizer from step 3.

10. The apparatus according to claim 9, further characterized in that it additionally comprises means for controlling the energy supplied in step (2) to ensure that the solvent vaporizes in preference to the solute and that relatively little vaporizes from the solute.

11. The apparatus according to claim 10, further characterized in that the means for nebulization used in step 1 are selected from the group comprising ultrasonic nebulizers, sprinklers, jet nebulizers and piezoelectric nebulizers, operated continuously or cyclically.

12. The apparatus according to claim 11, further characterized in that the nebulizers are switched on and off cyclically (or at irregular intervals).

13. The apparatus according to claim 12, further characterized in that the nebulizer operates for about 15-25 seconds per minute.

14. - The apparatus according to any of claims 9 - 13, further characterized in that the step 2 is carried out by means selected from the means of the heating element, infrared, laser, microwave, RF or other means of generation of radiation; induction heating means; means of heat exchange; driving means, convection means, or mechanical energy transfer means.

15. The apparatus according to any of claims 9-14, further characterized in that the step of vapor removal is carried out by the means selected from the means for passing the gas through a drying agent, desiccant , or through suitable molecular sieves, membranes, means for passage through centrifugation, means of a suitable cyclonic separator, or the like.