GB2127692A - Hydrogen peroxide liquid film sterilization method - Google Patents

Abstract

Hydrogen peroxide sterilization of medical articles whereby there are obtained the advantages of both vapour penetration, especially for such articles as surgical packs, and direct liquid-sterilant article contact, in which a vapour mixture comprising hydrogen peroxide is brought into contact with the article to be sterilized, the article being at a temperature below the dew point or condensation temperature of the vapour mixture, is caused thus to condense as a liquid film on the article, and is revapourized and hence removed from the so-sterilized article.

Description

SPECIFICATION Hydrogen peroxide liquid film sterilization method Background of the Invention Field of the Invention This invention relates to an improved method of sterilizing articles employed in surgery, treatment, and diagnosis.

Description of the PriorArt It is well known that the dipping of articles into concentrated solutions of hydrogen peroxide (10% to 40%) will sterilize such articles as disclosed and claimed in for example U.S. Patents Nos.

3,854,874 and 3,904,361. It is also known that hydrogen peroxide vapours will effect such sterilization as taught in U.S. Patents Nos.

4,169,123 and 4,169,124. Reference is particularly made to the latter two patents which compare the bactericidal or sporicidal action of both liquid and gaseous hydrogen peroxide and further note that the sporicidal activity as recommended by the Food and Drug Administration, of a sterilizing process must assure a probability of less than one organism out of one million surviving the sterilization cycle.

While the dipping of articles to be sterilized in solutions of liquid hydrogen peroxide is, it is well established, effective to reduce bacterial spore concentration to about 1 0-5 or better there are disadvantages to be encountered in this process: (1) dipping objects to be sterilized in a bulk liquid can lead to the contamination of the entire solution and prevent its future use, (2) dipping objects exposes workers and the surrounding environment to the usual hazards of working with fairly large quantities of the sterilant hydrogen peroxide and its attending vapours, and (3) dipped objects may have to be rinsed with sterile distilled water before drying to ensure that any non-volatile materials present in the sterilization solution will not remain on the objects following the required drying step.Inasmuch as hydrogen peroxide is unstable in solution it is necessary to employ stabilizers to control its rate of decomposition.

While such deposition of solid stabilizers on the products to be sterilized is avoided in the aforementioned Patents 4,169,123 and 4,169,124, the advantage of bringing the articles to be sterilized into positive contact with liquid hydrogen peroxide solutions is not thereby obtained. When, in addition, hydrogen peroxide aerosols are employed (Nasa Technical Translation TTF-1 5, 127, of Fedyayev et al., Virucidal Action of Hydrogen Peroxide Aerosols in Decontamination of Air in an Influenza Nidus, Zhurnal Mikrobiologii, Eipidemologii Immunobiologii, 9, 137--142 (1972)) there is no assurance that the aerosols will not carry with them dispersed particles of the sterilizer.

And while the dipping of articles to be sterilized into all quantities of hydrogen peroxide solutions does not introduce excessive hazards from decomposition of the hydrogen peroxide solutions since the decomposition products, water and oxygen, are obviously non-toxic it is clearly preferable to avoid exposure to hydrogen peroxide.

In addition dipping methods introduce the inherent unreliability of individual action in that for example articles may not be completely dipped in solution or they may be protected by air pockets and solution thereby does not contact every surface of the article; or the article may not be immersed for a sufficient period of time in the solution.

The foregoing U.S. Patents Nos. 4,169,123 and 4,169,124 also teach the notable sporicidal action of gaseous hydrogen peroxide even in low concentrations in the gas phase and at such low temperatures that such sterilization as might be expected from concomitant steam could not be present.

Summary of the Invention This invention is directed to improvements in methods for the sterilization of articles in which both the advantages of liquid sterilization and gas sterilization can be obtained. None of the aforementioned disadvantages of liquid dipping sterilization exist in the process of invention and yet the sterilizing impact of the relatively high concentrations of hydrogen peroxide that exist in liquid as compared to gaseous form are brought into liquid-surface contact with the articles to be sterilized. At the same time the substantial advantages of gas sterilization are also obtained especially in the high penetration of the particular articles which results in unusually high sporicidal action, for example as cited in U.S.Patent 4,169,124, whereby sporicidal activity in the order of magnitude of assuring the survival of less than one organism out of one million is obtained.

In the method of invention uniformly vaporized mixed hydrogen peroxide -- water vapours are delivered at uniform intervals into a closed sterilizer zone, which has been evacuated prior to the vapour introduction; articles to be sterilized resting in a container in the said zone will if necessary be cooled prior to the introduction of the vapour (or be cooled by the evacuation of air from the sterilizing zone) to a temperature below the dew point of the entering vapours, whereby the vapours penetrate all the interstices of the said articles, contact all surfaces thereof, and by condensing deposit a film of moisture on all such cool surfaces; and the liquid film is subsequently evaporated and swept out of the chamber by the introduction of filtered air which will act to strip the liquid film from the sterilized articles, the said articles being preferably warmed to aid in driving off the said liquid film.

Aparatus for carrying out the method of the invention while specially adapted to the method can be of widely varying sophistication and it is contemplated that commercial apparatus will be actuated by set timer switches or the like. After the sterilizer is loaded, a single actuator button can be pressed and conventional sequentially timed apparatus will carry out the entire sterilization cycle.

Brief Description of the Drawing The single figure is a side elevational view of means for carrying out the method of the invention, in which figure the means are shown to be manually operated in order to permit simplification of description of the novel method.

Detailed Description of the Preferred Embodiments A sterilizer 10 is shown with its front section containing a door (not shown) removed.

Contained within the sterilizer section is an instrument table 11 having means for heating or cooling its base 1 2 such means being symbolized by the electrical cord 13. Resting on the instrument table 11 is a container 14 in which are placed materials emanating from surgical or medical procedures and which require sterilization in high degree before reuse. The sterilization chamber is provided with a pressure gauge 1 6 and a fan 17. A supply of filtered air is provided to the chamber 10 by valved line 18 and vacuum may be imposed upon the sterilization chamber 10 by withdrawal of air or vapours through valved line 1 9. Equipment for vaporization of hydrogen peroxide solutions 20 consists of a supply flask 21, a valved supply line 22, and an evaporator 23 having a source of heat symbolized by electrical line 24.Means are provided for releasing the generated hydrogen peroxide vapour through connecting valved line 26.

In operation of the foregoing apparatus according to the method of the invention an aqueous concentrated solution, (having for example from about 10% to 40% of hydrogen peroxide) is permitted to flow from the storage or supply vessel 21 in small volume increments through the valved supply line 22 into the vaporization chamber 23.

At the same time the sterilization chamber 10 is evacuated by pump means not shown through vacuum line 1 9 the valved lines 1 8 and 26 being closed during this operation. The increment of hydrogen peroxide solution in the vaporizer 23 is heated by means 24 and vapours so produced are allowed to flow through valved line 26, by opening the valve therein, into the sterilization chamber 10.

Importantly the articles (not shown) in the container 14 in the sterilization chamber are maintained at a temperature below the dew point of the hydrogen peroxide vapours entering the said chamber. This is basically accomplished by maintaining the evacuated ambient low pressure air in the chamber at a temperature only slightly above, if at all, of the articles to be sterilized and/or by circulating cooling medium in the base 1 2 of instrument table 11. Accordingly hydrogen perixide vapours will condense on the entire surfaces of the articles within the container 14.

The valved line 26 will thereupon be closed and the sterilization chamber will be maintained under stable conditions for a selected period of sterilization time. Thereafter valved line 1 8 and valved line 1 9 are opened and filtered aseptic air is caused to flow through the chamber 10 to evaporate from the surface of articles being sterilized the liquid film that had been maintained thereon. These vapours are caused to escape through the open valved line 19. Evaporation of the film of liquid on the articles that have been sterilized is augmented by heat delivered by device 13 and associated heating elements (not shown) in the said base 12.The fan 17, the blades of which are mounted in the upper area of the sterilization chamber free of contact with the sterilization articles can be used either to ensure uniform distribution of inflowing hydrogen peroxide vapours (in which case the operation of the fan blades will be at a low velocity) or it may be used at high velocity to aid in the vaporization of the film of liquid on the articles that have been sterilized.

The temperature of operation within the sterilization chamber and especially of the articles to be sterilized will be basically governed by the dew point of the particular concentration of hydrogen peroxide in the vapours introduced into the chamber. Temperatures generally within the range of about 1 50C to 550C effect sterilization of most articles in a period of hours, the temperature primarily being selected so that a film of liquid forms on the articles while nevertheless the inflowing vapours are not so rapidly condensed but what in the gaseous form they can and do penetrate all the interstices of the said articles.

A 30 per cent by weight solution of hydrogen peroxide is heated in the vessel 23 to a temperature of about 1 300F thereby producing a vapour containing about 2 to 2.5 per cent by weight of hydrogen peroxide. Air in sterilization chamber 10 is evacuated therefrom to an absolute pressure between 2 and 4 inches of Hg. The aforesaid hydrogen peroxide vapour is then permitted to flow into the chamber the walls of which are maintained at or near 1000F and into contact with articles to be sterilized at normally about 700F, these articles having just been placed in the chamber at the usual ambient room temperature or at slightly cooler temperatures.

That portion of the 2 to 2.5 per cent hydrogen peroxide vapour which comes in contact with the said articles will be cooled to about 700 F, a temperature below the dew point of the vapour, and a condensation of a liquid film will result, the condensate liquid containing about 37 per cent by weight of hydrogen peroxide. Vapour is allowed to flow into the sterilization chamber until equilibrium pressure is established, the condensation of liquid on the articles to be sterilized in the meantime raising the surface temperature of the said articles, it may be until they reach an equilibrium temperature with the vapour in the chamber. The sterilization zone is then closed and stable conditions are maintained therein for a period which may vary widely from several minutes to several hours with different materials to be sterilized and different microorganism to be killed, until conventional laboratory monitoring means shows complete kill to be obtained. Microorganisms commonly employed in such test procedures are Bacillus Subtilis spores, being highly resistant to sterilization.

Actual temperatures and liquid and vapour concentrations can be varied within the limits of about 100 to 300"F in the vapourisation chamber, 6% to 70% concentration of hydrogen peroxide in the aqueous solution in the vapourizing zone (preferably 30 to 70 per cent) and from 50 to 2000F original temperature in the sterilization zone.

Claims (6)

1. A method of liquid-contact sterilization which comprises: vapourizing from an aqueous solution of hydrogen peroxide a gaseous vapour consisting of hydrogen peroxide and water vapour; passing the said vapour in admixture with air into a partially evacuated sterilisation zone and into contact therein with an article to be sterilized; maintaining the article at a temperature below the dew point of the entering vapour so that aqueous hydrogen peroxide solution is condensed out of that said vapour in contact with the said article in and as a layer of liquid thereon; and maintaining the said film of liquid on the article for a predetermined period to effect sterilization of the article.

2. The method of claim 1 in which there is employed an aqueous solution of hydrogen peroxide in concentration between 6% and 70% by weight of solution.

3. The method of claim 1 in which the hydrogen peroxide is vapourized at a temperature between 100 and3000F.

4. The method of claim 3 in which the temperature in the sterilization zone is upon introduction of the said hydrogen peroxide vapour mixture at a temperature between 500 and 2000F that is lower than the vapourisation temperature.

5. The method of claim 1 in which so-formed vapour of hydrogen peroxide and water is introduced into the sterilization zone, articles to be sterilized are placed in the sterilization zone, thereafter closed to ambient air, at a temperature substantially below the temperature of the introduced said vapour, and the sterilization zone is warmed to a temperature above the temperature of the said article but below the temperature of the introduced vapour.

6. Means for carrying out the method claimed in claim 1 and substantially as hereinbefore described and as shown in the single figure of the accompanying drawing.