Sterilant challenge device

Abstract

Sterilant challenge device for use in steam sterilizers are described, including devices suitable for determining the efficacy of the non-condensable gas removal stage of a sterilization cycle and/or the quality of steam sterilant in relation to its content of non-condensable gas(es) are disclosed. Sterilant challenge devices having a metal tube having a defining a free space which is open at one end for the entry of sterilant and closed at the other end and at least one thermal load located around the tube are also described.

Claims

1. Sterilant challenge device for use in a steam sterilizer for determining the efficacy of the non-condensable gas removal stage of a sterilization cycle and/or the quality of steam sterilant in relation to its content of non-condensable gas(es), the device comprising: a metal tube (1) having a bore (2) defining a free space which is open at one end for the entry of sterilant and closed at the other end, wherein the metal tube is open to an outside environment; and at least one solid thermal load (3) located around the tube (1).

2. The device of claim 1, wherein the metal tube (1) has a thermal conductivity of 30 Wm.sup.1K.sup.1 or less.

3. The device of claim 2, wherein the metal tube (1) has a thermal conductivity of 2 Wm.sup.1K.sup.1 or more.

4. The device of claim 1, wherein the metal tube (1) has a length of 15 cm or less.

5. The device of claim 1, wherein the metal tube is a hollow cylinder having a wall thickness of 2 mm or less.

6. The device of claim 1, wherein the bore of the metal tube has a bore diameter of between 2 mm and 12 mm.

7. The device of claim 1, wherein the cross section of the metal tube has an area of 210 mm.sup.2 or less.

8. The device of claim 1, wherein the material properties of the metal tube, in particular its thermal conductivity, are essentially isotropic.

9. The device of claim 1, wherein the metal tube comprises one or more selected from: stainless steel; non-rusting steel; CrNi-containing steel; titanium; and titanium alloys.

10. The device of claim 1, wherein the at least one load (3) has a bore (4).

11. The device of claim 10, wherein the size and shape of the bore (4) of the load generally corresponds to the outer size and shape of the metal tube (1).

12. The device of claim 10, wherein the bore (4) of the at least one load (3) and/or the surface of the bore of the at least one load is shaped such as to intermittently contact the metal tube (1).

13. The device of claim 10, wherein the surface of the bore (4) of the at least one load (3) comprises at least one laterally or longitudinally extending groove (5).

14. The device of claim 10, wherein the at least one load (3) has a shape substantially corresponding to a cylinder.

15. The device of claim 14, wherein the at least one load (3) comprises at least one radial slit (6) extending from the outer surface of the cylinder towards the bore (4) of the cylinder.

16. The device of claim 15, wherein the at least one load (3) comprises two or more radial slits (6) and said slits (6) are spaced equidistantly from each other.

17. The device of claim 1, wherein a foil or sheet (15) of thermally insulating material is provided between the tube and the at least one load.

18. The device of claim 17, wherein the foil or sheet (15) comprises a material comprising one or a combination of: polyester, polypropylene, polyacrylonitrile, Kapton, polyurethane, polyamide, polyimide, polyether imide, PTFE, polyvinylchloride, polycarbonate, epoxy resin, polymethyl-methacrylate, polyethylene, and polystyrene.

19. The device of claim 17, wherein the foil or sheet (15) comprises a material having a thermal conductivity which is lower than that of the tube.

20. The device of clam 17, wherein the foil or sheet (15) comprises several holes and/or cut-outs to adjust the thermal coupling between the tube and the at least one load.

21. The device of claim 1, wherein the at least one load comprises or consists of aluminium.

22. The device of claim 1, wherein the open end (8) of the metal tube is tapered.

23. The device of claim 1, wherein the metal tube (1) is positioned such that, when exposed to steam sterilant, condensed steam sterilant flows down at an inner surface (2) of the metal tube and forms water droplets at the open end (8) of the metal tube (1).

24. The device of claim 1, further comprising: a base (12), wherein the open end (8) of the metal tube (1) is adjacent to the base.

25. The device of claim 24, further comprising: at least one housing (10) mounted to the base (12).

26. The device of claim 1, wherein each load from the at least one load comprises a temperature sensor (9).

27. The device of claim 26, wherein the temperature sensor (9) measures an increase of temperature of the at least one load (3).

28. The device of claim 26, wherein the device comprises a plurality of thermal loads located around the tube.

Description

(1) Preferred embodiments of the present disclosure are further elucidated with respect to the following Figures.

(2) FIG. 1 shows a perspective, partial cross-sectional view of an exemplary embodiment of a sterilant challenge device according to the present disclosure;

(3) FIG. 2 shows a partial cross-sectional side view of the embodiment shown in FIG. 1; and

(4) FIGS. 3a-3d shows various exemplary embodiments of a thermal load according to the present disclosure.

(5) FIG. 1 shows a perspective cross-sectional view of a preferred embodiment of a sterilant challenge device for use in a steam sterilizer according to the present disclosure, while FIG. 2 shows a partial cross-sectional side view of the same. The sterilant challenge device is adapted for determining the efficacy of the non-condensable gas removal stage of the sterilization cycle andor the quality of steam sterilant in relation to its content of non-condensable gasgases. The device comprises a metal tube 1 having an inner bore 2 (see FIG. 2). The inner bore 2 of the metal tube 1 defines a free space which is open at an open end 8 (see FIG. 2) for the entry of sterilant and closed at the other closed end 11 (see FIG. 2). The device further comprises one or more thermal loads 3 located around the tube 1.

(6) In the specific embodiment of FIG. 1 two thermal loads 3 are depicted. In the exemplary embodiment shown in FIG. 1 each thermal load 3 is provided with its respective temperature sensor 9. However, it may be sufficient to provide a single temperature sensor at only one thermal load; in this case desirably at a thermal load near the closed end of the metal tube. If more than two thermal loads are provided, one or more of the thermal loads may comprise a temperature sensor or each of the thermal loads may comprise a temperature sensor.

(7) The metal tube 1, the thermal loads 3 and the temperature sensors 9 are provided within a housing 10 which is mounted on a base 12. The housing generally provides steam protection and typically the end of the housing opposite to the open end of the tube is closed (see FIG. 2). In FIG. 1, this closed end of the housing 10 was not been drawn to allow for ease in viewing of the interior of the housing. The housing 10 may include one or more inner housings 13 and 14 between the (outer) housing 10 and the metal tube, loads and temperature sensors. These inner housings may serve to thermally insulate the metal tube from the outside environment and to aid in limiting thermally influence to just over the open end of the tube. Typically the end of the inner housing opposite to the open end of the tube is closed (see FIG. 2), and once again for purposes of viewing, the closed ends of the inner housings 13 and 14 have been not been drawn in FIG. 1.

(8) In the exemplary embodiment shown in FIGS. 1 and 2 the metal tube 1 is a hollow cylinder and the two thermal loads 3 have a shape substantially corresponding to a cylinder with a bore 4 (see FIG. 3a). The size and shape of the bore 4 of the thermal loads 3 essentially corresponds to the outer size and shape of the metal tube 1. Thus, a tight connection between the inner surface of the bore 4 of the thermal loads 3 on the one hand and the outer surface of the metal tube 1 on the other hand may be achieved which allows for a well-defined heat transfer between the tube and the thermal loads.

(9) During use in a sterilization cycle, steam sterilant enters through the open end 8 of the metal tube 1 into the free space defined by the bore 2 of the metal tube 1. A portion of the steam sterilant condenses at the inner surface of the bore 2 of the metal tube 1 which leads to an increase of temperature of the thermal loads 3 due to condensation heat. This temperature increase is measured by means of the temperature sensors 9. The amount of temperature increase measured allows for calculation of the amount of steam condensed within the bore 2 of the metal tube 1 and consequently the volume of non-condensable gases formed at the top end of the bore 2 of the metal tube 1. The condensed steam sterilant flows down at the inner surface of the metal tube 1 forming water droplets at the open end 8 of the metal tube 1. In order to encourage the water droplets to drip off the edge of the open end 8 of the metal tube 1, a tapered open end 8 as shown in FIG. 2 is preferred. Due to the tapered end, condensed water will be drained down to and collected at the bottommost end of the tapered open end 8 of the metal tube 1, thus forming larger water droplets much quicker, which will then drip off the edge of the open end 8.

(10) Preferably, the metal tube has a low thermal conductivity of 30 Wm.sup.1K.sup.1 or less, more preferably of 25 Wm.sup.-1K.sup.1 or less, and most preferably of 20 Wm.sup.1K.sup.1 or less. The metal tube preferably has a thermal conductivity greater than 2 Wm.sup.1K.sup.1, more preferably greater than 4 Wm.sup.1K.sup.1. Suitable materials for the metal tube include stainless steel; non-rusting steel; CrNi-containing steel; titanium; and titanium alloys.

(11) The thermal loads, on the other hand, preferably have a large heat capacity of preferably equal to or greater than 0.5 Jg.sup.1K.sup.1 at 25 C., more preferably of equal to or greater than 0.7 Jg.sup.1K.sup.1, even more preferably of equal to or greater than 0.85 Jg.sup.1K.sup.1. An exemplary suitable material for the thermal loads is aluminium.

(12) During the non-condensable gas removal stage of a sterilization cycle the metal tube 1 and the thermal loads 3 may exhibit different rates of expansioncontraction. In order to accommodate the stress involved the cylinder of the thermal load 3 preferably comprises a radial slit 6 (see FIG. 1 and in particular FIG. 3a) extending from the outer surface of the cylinder to the bore 4 of the cylinder. Such a slit is referred to in the following as an end-to-end slit. It is to be recognized that the end-to-end slit 6 in the illustrated embodiment is as such not visible in FIG. 2, because the cross-sectional slice runs through the gap formed by the slit. By expansion and compression of said slit 6 the thermal load 3 slightly flexes. While a single slit extending from the outer surface of the cylinder to the bore of the cylinder as shown in FIG. 3a may be sufficient, it may be desirable to provide one or more additional radial slits 7 which extend from the outer surface of the cylinder towards (but not extending to) the bore 4 of the cylinder as shown in FIG. 3d. In the event there are two or more radial slits, preferably they are spaced equidistantly from each other.

(13) It is furthermore preferred that the bore 4 of the load 3 andor the surface of the bore 4 of the load 3 is shaped such as to only intermittently contact the metal tube 1. Thus, the amount of heat transfer between the tube and the load may be controlled and optimized. For example, the surface of the bore 4 of the load 3 may comprise at least one laterally or longitudinally extending groove 5, preferably two or more laterally andor longitudinally extending grooves 5 as shown in FIG. 3b. In essence, heat transfer only takes place at the intermittent contact between the load 3 and the tube 1 where no grooves 5 are present. Alternatively or in addition, a foil or sheet 15 of thermally insulating material may be provided between the metal tube 1 and the thermal load 3 as shown in FIG. 3c.

(14) The different aspects shown in FIGS. 3a-3d may be combined with each other. For example, a plurality of grooves 5 as shown in FIG. 3b and a plurality of slits 6 as shown in FIG. 3d may be combined. Similarly, a plurality of slits 6 as shown in FIG. 3d may be combined with a foil or sheet 15 of thermally insulating material as shown in FIG. 3c. It will also be evident to the skilled person that the number and shape of the grooves and slits may be varied without departing from the scope of the present invention. Moreover, while a cylindrical thermal load 3 is preferred, the thermal load 3 does not necessarily have to be cylindrical, but its cross-section may also be elliptical, hexagonal, quadratic or the like.

(15) It is, however, preferred that each thermal load, which substantially entirely surrounds the metal tube is provided as a single integral piece (apart from the end-to-end slit, if applicable),. Thermal loads may be mounted onto the tube by first cooling the tube and warming the load and then subsequently sliding and positioning the load onto the tube. Alternatively and more conveniently, the thermal load may comprise an end-to-end slit as described above. By means of a simple wedge the end-to-end slit (e.g. the slit 6 shown in FIG. 3a) may be slightly expanded thus increasing the diameter of the inner bore of the thermal load. The thermal load may then be easily slipped over the metal tube. Once the load is positioned at the right height of the metal tube, the wedge may be removed, thus decreasing the inner diameter of the bore of the thermal load which may thus tightly enclose the outer surface of the metal tube. Such thermal loads consisting of a single integral piece may be more easily mounted than the thermal loads known in the prior art. Ease in mounting, in particular expansion with a wedge during mounting, may be further facilitated by providing one or more radial slits from the outside towards the bore of the thermal load as described above.