TREATMENT OF AIR CONDITIONING SYSTEM

Abstract: Air conditioning systems are treated by admitting a space spray of a biocidal composition which is effective against microorganisms in the system and which is substantially harmless to humans. A preferred biocidal composition is oil of Melaleuca and the spay preferably has a mean droplet size of from 2 to 20 microns.

Description: Title: "TREATMENT OF AIR CONDITIONING SYSTEM" Field of the Invention This invention relates to a novel method of treating an air conditioning system, and to novel compositions for use in the method. The term "air conditioning system" is here used to refer collectively to ducts, fans, filters, humidifiers, coolers and other.plant and equipment assembled for air conditioning and, where the context admits, to parts of such systems. Background Art In recent years, there has been considerable concern with Legionnaires Disease and with other infections and allergic reactions which can be spread by microorganisms consisting of bacteria, fungi and protozoans which breed in airconditioning systems under certain conditions. These include Leαionella pneumophila and Staphylococcus aureus. At the present time, the accepted practice for prevention of such diseases is to avoid the accumulation of stagnant water in cooling towers or humidifiers, regularly to clean filters and periodically to treat or scrub filters and airconditioner system surfaces with a chemical disinfectant solution. The accepted methods suffer from the disadvantages that they are labour intensive and costly to implement. Parts of the system need to be discarded. In many cases ducts cannot be physically reached. The air conditioning system is unusable during the treatment time which may be long. Moreover since the treatment is applicable on a periodic basis, often at intervals weeks or months apart, the risk of infection grows as the length of time since the previous scrubbing increases. It is an object of the present invention to provide a method of preventing the multiplication of pathogenic microorganisms in air conditioning systems which avoids or at least ameliorates some of the above discussed disadvantages of previous methods. Preferred embodiments of the invention inhibit or prevent the spread of microorganisms in an air conditioning system without requiring an air conditioning plant to be dismantled or closed down, except in so far as may be required for routine filter or mechanical maintenance. Disclosure of the Invention According to a first aspect, the invention consists in a method comprising the step of admitting into an air conditioning system as a space spray whereof the mean droplet size is less than 20 microns an amount of a biocidal composition which is effective against microorganisms in said system and which is substantially harmless for humans. According to a second aspect, the invention consists of a biocidal composition for use as a space spray in an air conditioning system comprising oil of Melaleuca. or a germicidal, bacteriacidal, or fungicidal constituent thereof, dissolved in liquid carbon dioxide under high pressure. Preferred Embodiments of the Invention In preferred embodiments the space spray is introduced repetitively at timed intervals into the air conditioning ducting downstream of the heat exchange system. It will be appreciated that the droplet size indicated is close to a bacterial size and the space spray may be a vapour, fog, aerosol or even a molecular solution of tea tree oil in a carbon dioxide based fluid. It has not hitherto been practiced to introduce a germicidal, bacteriacidal or fungicidal spray directly and continuously into an airconditioning system for circulation throughout a building. Hitherto, it was considered that such agents were most effective upon contact with bacteria or mould and therefore are best applied directly to contaminated surfaces. Also, it was believed that it would be unacceptable to building occupants to circulate a germicide in the air either because the substances involved might be toxic to humans at an effective concentration or because of the risk of odours or irritation associated therewith. Commonly used germicides such as formaldehyde or carbolic acid are toxic to humans and do not suggest themselves for circulation through a building via an airconditioning system. An embodiment of the invention will now be described by way of example only. A concentrate comprising Oil of Melaleuca dissolved in alcohol was dissolved in liquid carbon dioxide under pressure. The effective concentration of oil of Melaleuca in the product solution is from 0.1%-2% and preferably approx. 0.3% by weight of solution. Oil of Melaleuca is an essence produced by the distillation of leaves from the genus Melaleuca in particular the species Melaleuca alternifolia also known as "tea tree" or "ti-tree" . It is known to contain mono- and sesquiterpenes including pinenes, terpineols and cineole. The oil of Melaleuca concentrate possessed the following characteristics: Cineole content 7.0% av. Terpinen-4-ol content 63.0% min. Specific Gravity @ 20°C 0.9302 Refractive Index @ 20°C 1.4763 A small quantity of a deodorizer, for example Lauryl Methacrylate, was added to counter the "swampy" smell of oil of Melaleuca and a solvent added to enhance the mutual solubility of the solution components. The concentrate was admitted to the duct of an operating building air conditioning system downstream of the heat exchange system, as a space spray in which the particles were of from 2 to 20 microns in mean diameter. The building was situated in a tropical climate and had a problem with tendency for mould growth on interior walls. It was found that rooms in the building through which the treated air circulated remained mould-free, while a mould was found to grow on walls in rooms used as a control in which the circulating air was not treated with the spray. The air in the treated rooms was not noticably different in smell from the untreated air and did not cause irritation or discomfort to the occupants of the building. A bacterial count conducted on surfaces exposed to the treated and untreated control circulating air showed a significant reduction in the number of microorganisms in rooms through which treated air circulated. A series of tests were performed in which the oil of Melaleuca concentrate was tested according to the procedures of the Therapeutic Goods Act Disinfectant Test, Option A - Hospital Grade Clean. This test is applicable to a surface spray. The solution was used undiluted. The following results were obtained and show that the solution was effective as a surface spray against a range of microorganisms. TABLE 1 Dilution used: used undiluted Recovery Broth Initial Inoculum Status +/- Growth orgs/ml. Challenge 1 Challenge 2 Day 1 S. aureus - - 5.3 X 10 8 Pass --J E. coli - - 6.1 X 10 8 Pass P. aeruqinosa - - 6.9 X 10 8 Pass P. vulgaris - - 8.4 X 10 8 Pass Controls: all valid Day 2 S. aureus - - 2.1 x 10 8 Pass E. coli - - 1.1 x 10 8 Pass P. aeruqinosa - - 8.0 x 10 8 Pass P. vulgaris - - 9.5. x 10 8 Pass Controls: all valid TABLE 1 (Cont'd.) Dilution used: used undiluted Recovery Broth Initial Inoculum Stat +/- Growth orgs/ml. Day 3 S. aureus 3.9 x 10 8 Pass E. coli 4.0 x 10 8 Pass P. aeruqinosa 3.8 x 10 8 Pass P. vulgaris 1.1 x 10 9 Pass Controls: all valid A further series of tests was performed wherein surface plated cultures of various microorganisms were exposed to a known concentration of the concentrate injected into a space as a spray having average particle diameter of 2-20 microns over a set period of time and then examined for viability. More particularly, fresh cultures of test organisms identified as 1 to 4 in Table 2 were prepared from stock culture slopes and sub-cultured into Association of Official Analytical Chemists (AOAC) broth daily for 5 days prior to testing, the fifth day culture was the initial inoculum. The exception to this procedure was Leqionella pneumophila SGI (identified as 5 in Table 2) which was subcultured onto a BCYE media and then the slope washed with 0.9% Saline solution to give the initial inoculum. The organisms were diluted to an approximate concentration of 10 1 and 102 and surface spread onto either Tryptone Soya agar (Organisms 1-4) or a BCYE agar and allowed to air dry for 20 mins. The inoculated plates were positioned, uncovered, within the test chamber and the sample was introduced into the chamber via a 0.004" diameter crevice nozzle over a 5 second time period. This equates to a final concentration of sample of 0.43 g/1 within the test chamber. The sample was reintroduced into the cabinet each 24 hrs., as detailed above, and the plates were examined for viability at the exposure times detailed in the results section. Viability was confirmed by subculturing onto appropriate media. TABLE 2 Organisms (Same for a3 .1 test procedures ) 1 Staphylococcus aureus NCTC 4163 2 Escherischia coli NCTC 8196 3 Pseudomonas aeruginosa NCTC 6749 4 Proteus vulgaris NCTC 4635 5 Legionella Pneumophi .la SGI EML 80 Series 1 Organisms concentration 10 cfu/plate Organism Time 0 6hrs 1 day 2 days 7 days 1 + + + + - 2 + + + + - 3 + + + + + 4 + + + + - 5 + + + + - Series 2 Organism concentration 100 cfu/plate Organism Time 0 6hrs 1 day 2 days 7 days 1 + + + + - 2 + + + + - 3 + + + + + 4 + + + + - 5 + + + + - Controls Both organism concentrations Method As test method but with C02 instead of test sample Organism Time 0 6hrs 1 day 2 days 7 days 1 + + + + + 2 + + + + + 3 + + + + + 4 + + + + + 5 + + + + + The results shown in table 2 indicate that the Oil of Melaleuca was effective over 7 days against Staphylococcus aureus and Legionella pneumophila as well as E. coli and Proteus vulgaris when admitted as a space spray. In further tests concentrates according to the invention were introduced as a fog of particle size less than 20 microns into an air conditioning system for short periods repetitively. Plates were deposited in the ductwork and microorganism counts at various points in the system were recorded. These further tests confirmed the effectiveness of the treatment. Oil of Melaleuca contains sesquiterpenes and is a "swampy" smelling oil. It has been used as a mild antiseptic, germicide, bacteriacide and fungicide for which purpose it has been applied as a solution to infected surfaces. It has not previously been known to be effective as a space spray and has not been known to be effective against Legionella Sp. It is not clear whether the effectiveness of the system is due to a synergism between various oil of Melaleuca components, or to a particular component of oil of Melaleuca. or to synergism between one or more oil of Melaleuca components with the carbon dioxide or the deodorizer or the alcohol or the combination thereof. Any and all such combinations are deemed to be within the scope hereof. For what ever reason it appears that the treatment is effective in reducing or preventing the growth of Legionella bacteria and that the treatment will also reduce or prevent the growth of staphaloccocus and/or other microorganisms and moulds. The composition may be admitted to the ducts of an operating air conditioning system under automatic control to maintain a predetermined concentration in the atmosphere or may be injected repetitively at predetermined intervals, for example half hourly, to produce a desired peak concentration. In a typical system injections of duration 10-30 seconds at 30 minute intervals may be applied throughout the day while the building is occupied and treatment of different duration might be applied before start up or overnight in timer controlled systems. The treatment need not be applied to a system while in operation. The liquid carbon dioxide based product typically has a vapour pressure of around 5000 kPa at 15°C. When injected into an airconditioning system through a nozzle orifice of from 10 - 30 thousandths of an inch diameter, the particles have a high velocity and surprisingly reach into parts of the duct which are occluded from the nozzle. Accordingly, the space spray may be effective in an airconditioning system which is closed down. Although the invention has been described with particular reference to Oil of Melaleuca it would be expected from these results that a similar effect could be obtained from essential oils of other species of Myrtenceae such as Leptospermum and from Eucalvnts. The use of such other biocidal compositions which are effective against microorganisms but substantially harmless for humans are within the scope of the invention. Likewise carriers harmless to humans other than carbon dioxide may be employed. As will be apparent to those skilled in the art from the teaching hereof, the optimum concentrations of the active ingredient in solution and in the air of an airconditioned building may be determined by routine test based on the teaching herein.

Claims: THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:- 1. A method comprising the step of admitting to an air conditioning system as a space spray whereof the mean droplet size is less than 20 microns an amount of a biocidal composition which is effective against microorganisms in said system, and which is substantially harmless for humans. 2. A method according to claim 1 wherein the mean droplet size is from 2 to 20 microns. 3. A method according to claim 1 or claim 2 wherein the biocide comprises monoterpenes and sesquiterpenes. 4. A method according to claim 1 or claim 2 wherein the biocide comprises an essential oil from a tree of the Myrtenceae class or an active constituent thereof. 5. A method according to claim 4 wherein the biocide is an oil of Melaleuca or active constituent thereof. 6. A method according to any one of the preceding claims wherein the space spray is formed from a solution of the biocide in liquid carbon dioxide. 7. A method according to any one of the preceding claims wherein the space spray is admitted to the air conditioning system discontinuously and repetitively. 8. A method according to claim 1 substantially as herein described. 9. A composition for use in a space spray comprising a solution of an essential oil of the Myrtenceae class, or any active constituent thereof, in liquid carbon dioxide. 10. A composition according to claim 9 wherein the oil is Melaleuca oil or an active constituent thereof. 11. A composition according to claim 9 further including a solvent. 12. A composition according to claim 9 wherein the concentration of oil of Melaleuca is from 0.1-2%. 13. A composition according to any one of claims 9-12 when in the form of a space spray having a mean droplet size of from 2-20 microns. 14. A composition according to claim 6 substantially as herein described.

Inventors: RYAN ROBERT FRANCIS, VALE NICHOLAS FRANK, RYAN, ROBERT, FRANCIS, VALE, NICHOLAS, FRANK
Applicants: COMMW IND GASES, THE COMMONWEALTH INDUSTRIAL GASES LIMITED
Application year: 1988
Main classification: A61L9
IPC codes: A01N25, A01N31, A01N43, A01N65, A61L9, F24F3