A TEST DEVICE FOR A POROUS LOADS STERILIZER

Abstract: A device for testing the presence of air in a steam sterilizer for porous loads, comprising four porous masses (10) each formed from a stack of single rectangular sheets of spun-bonded polypropylene, each mass being contained and enclosed by perforated shrink wrapping film to produce a block of typically some 4 cm in height and typically some 15 cm square. Interposed between the masses (10) are envelopes (13) of a similar material, each containing a thermocouple and conductor leads. The assembled stack is contained by upper and lower end plates (15) and resilient side panels (16) which serve as clamps to compress the stack. When placed in a steam sterilizer under operating conditions, the device serves to test the accuracy and efficiency of the sterilizer by taking accurate temperature readings from the thermocouples placed at the different heights, and by comparing these readings to the temperature in the condensate drain passage of the sterilizer.

Description: A TEST DEVICE FOR A POROUS LOADS STERILIZER THIS INVENTION concerns a device for testing the efficiency of sterilizers such as those used in hospitals for sterilizing porous loads, and for detecting the presence of air in such sterilizers. A test device of this kind is described in British patent specification GB 2143322 and includes a plurality of porous masses of substantially man-made material with an indicator sheet sandwiched between them, and the whole assembly is held in close superimposed relationship by means which are permeable to allow the free passage of air and steam to the external surfaces of the masses. Sterilizers for porous loads require periodic engineer's checks to be carried out with test devices using thermocouples to provide an accurate reading of temperatures within the porous masses, and the present invention is concerned with an adaptation of the test device described and claimed in GB 2143322 to enable it to be used in engineer's tests during commissioning and re- commissioning of sterilizers, and during quarterly and annual maintenance checks. Engineer's tests require the simultaneous use of up to five thermocouples to be located at different positions on the test device ithin the_ sterilizer, typically, one in the free space within the sterilizer " chamber, one or more within the mass of the test device and one in the condensate drain passage of the sterilizer , chamber. According to the present invention there is provided a device for detecting the presence of air in a steam sterilizer for porous loads, comprising at least two porous masses of substantially man-made material, at least one thermocouple and conductor leads, housed within a flat envelope open along one edge region to permit said leads to protrude therefrom and. of a material having sufficient thickness and compressibility to accommodate the protruding leads, said envelope being sandwiched between the masses thus to be in intimate contact therewith, and means for removably holding the masses and envelope in close superimposed relationship, said means being permeable to allow air and steam to pass freely in to and out of the porous masses. " An embodiment of the invention will be described, by way of example only, with reference to the accompanying drawings, in which:- Fig. 1 is an exploded perspective view of a test device made in accordance with the invention; Fig. 2 is a similar view showing the device assembled and closed; Fig. 3 is a similar view of the device upturned into an operative, position with a further optional device attached to carry a thermocouple in free space; and Fig. 4 is a view similar to Fig. 2 prior to closure of the device and showing a removable tool to serve as an aid to assembly. Referring now to the drawings, a test device made in accordance with one embodiment of the invention • comprises four porous masses 10 each formed from a stack of single rectangular sheets of a side dimension between 10cm and 20cm, of a man-made woven or non- woven material such as spun bonded polypropylene having a weight in the region of 50 to 150 grammes per square metre. The material is of a kind which will not undergo an exothermrc reaction with steam under the conditions within a sterilizer under test. Each stack contains an appropriate number (typically about 80) of such sheets arranged in close superimposed relationship and enclosed by perforated shrink wrapping film for convenience to produce a block of some 4cm in height. The overall height of the blocks making up the device is between 10cm and 20cm. The four blocks or masses 10 are superimposed but interposed by thermocouples generally indicated at 11. Each thermocouple consists of a pair of conductor leads 12 which join at the thermocouple itself (not visible), and the latter with its conductor leads is enclosed within a flat rectangular envelope 13 open at one side to permit the leads 12 to protrude therefrom and consisting of a material identical or similar to the man-made material from which the masses 10 are produced. For convenience, the envelopes 13 may be produced by folding a sheet of such material and then stitching along the two sides normal to the fold line. Alternatively, the thermocouple can be placed between two single sheets or a single larger sheet folded about its centre line to conform to the cross-sectional dimensions of the stack. Typically, the blocks 10 and envelopes 13 are between 10cm and 20cm square, and the material of the envelopes 13 is sufficiently thick and compressible to accommodate the leads 12 without any noticable increased thickness along the lines occupied by the leads. The housing of the leads in this way minimises the likelihood of steam tracking along the leads towards the thermocouple, owing to the effective seal created around the leads by the fabric of the envelope. An indicator 14 consisting of a sheet of paper bearing, for example, strips of so-called autoclave tape which is adapted to undergo a visual change under moist heat sterilizing conditions, and of the kind used for carrying out a normal test for such a device, can also be included in the engineer's test along with the thermocouples, and will be disposed, as illustrated in Fig. 1, at about the mid-point of the stack of blocks 10. The pack is assembled and held in close superimposed relationship by means of a stainless steel , clamp which consists of two square end plates 15 slotted to receive a pair of resilient side panels 16 which act as compression springs. As can be seen from Fig. 2, the side • panels 16 are shaped to present a pair of broad stabilising feet 17 when the pack is assembled as in Fig. 2 and overturned to rest upon them. Fig. 3 illustrates an optional resilient plastics bridging piece 18 which is located in appropriate slots of the upper end plate 15 and which is provided with a series of apertures 19 through which the conductor wires 20 of an additional thermocouple 21 may pass to position the latter at a height of approximately 5cm above the pack. The piece 18 may be omitted, however, since under certain circumstances it may act as a shield to the thermocouple thus providing a di sadvantageously false temperature recording. Referring now to Fig. 4 r as an aid to assembly of the test device, there is provided a stainless steel stand 22 having a right angled foot 23 which is located beneath the device. Three pairs of guide members such as resilient linings 24 are held captive in slotted edge regions of the stand 22 at heights thereon equivalent to those at which the thermocouples are placed within the test device pack. With this arrangement, the delicate thermocouple leads 12 can be pre-located, and supported with vertical and level alignment in the guides 24 leaving the user's hands free to assemble the blocks or masses 10 and to place over each thermocouple in turn, an envelope 13. Once the pack is assembled, the conductor wires 12 which are thus supported by the pack, are readily removed from the linings 24 which are slotted for this purpose, and the stand 22 can be removed. Preferably, the envelopes 13 are intended to be disposed of after each test so that any indentation or channel in their material created by the thermocouple wires t the elevated pressure and temperature experienced during the test, cannot permit steam to track inwardly along such indentation or channel during a subsequent test. In use, the device is placed in a steam sterilizer which then undergoes a normal operational cycle or special test cycle. An additional thermocouple is placed in the chamber drain passage and, if bridging piece 18 is omitted, also in the chamber free space about 5 cm above the stack. Readings of temperature are recorded in the usual way from the thermocouples at different positions throughout the sterilizer, so that an indication is provided of the presence or absence of air within the sterilizer and of the steam penetration pattern into the device, during the test. The invention is not limited to the above details. For example, the vertical thickness of the blocks may not be uniform, and the levels of the thermocouples within the stack can be selected according to the test requirements. In a further specific example, the blocks from top to bottom of the pack may contain respectively 20, 140", 140 and 20 sheets, and thus measure respectively, 2.5 cm, 5.5 cm, 5.5 cm and 2.5 cm. There will usually be a division at the mid-point, with each half measuring between 5cm and 10cm in height and consisting of one or more individual blocks. The materials from which the clamp and stand are constructed may be other than stainless steel. Anodised aluminium or alloys containing such may be used, or polymeric materials either alone or in combination with « metals.

Claims: CLAIMS 1. A device for testing the presence of ai r in a steam sterilizer for porous loads, comprising at least two porous masses of substantially man-made material, at least one thermocouple and conductor leads, housed within a flat envelope open along one edge region to permit said leads to protrude there from and of a material having suf f ic ient thickness and compressibility to accommodate the protruding leads , said envelope being sandwiched between the masses thus to be in intimate contact therew ith, and means for removably holding the mas s es and envelop e in clos e s uperimposed relationsh ip, . said means being permeable to allow air and steam to pass freely into and out of the- ' porous masses. 2. A test device according to Claim 1, in which said porous masses are formed from a stack of single rectangular sheet s o f a man-made mat erial s uch as sp un-bonded polypropylene, having a weight in the region of 50 to 150 grammes per square metre. 3. A test device according to Claim 1 , wherein the material of said masses is s elected as one which will not undergo an exothermic reacti on w ith steam under the conditions within a sterilizer under test. 4.- A test device according to any preceding claim, wherein each said mass is enclosed by perforated shrink wrapping film. 5. A test device according to any preceding claim, wherein said envelope is formed from a sheet of substantially man-made material folded, to conform to the cross-sectional dimensions of the stack and joined along two sides normal to the fold line. 6. A test device according to any one of Claims 1 to 4, wherein said envelope is formed from two superimposed single sheets of said material. 7. A test device according to any preceding claim, wherein said envelope is formed from spun-bonded polypropylene having a weight in the region of 50 to 150 grammes per square metre. 8. A test device according to any preceding claim, comprising four of said porous masses, interposed by thermocouples housed within flat envelopes, there being an indicator sheet interposed between one pair of adjacent masses . g. A test device according to any preceding claim, wherein said holding means comprises upper and lower end plates between which the masses and thermocouples are enclosed and compressed by a pair of resilient side panels . 10. A test device according to any preceding claim, including a bridging p iece located at an upper end of the device and adapted to re tain a further thermocouple at a predetermined distance in free space above the device. 11. A test device accordi ng to any preceding claim, including a removable tool to serve as an aid to assembly of the device and compri sing a stand having a foot to be located beneath the device and guide means adapted removably to retain the conductor leads of a thermocouple such that, after assembly, the wires may be readily removed therefrom and the tool removed , from the device. 12. A test device according to Claim 10, wherein said ' stand is slotted to receive resil ient linings serving as said guide means. 13. A test device according to any preceding claim, wherein the holding means is of stainless steel. 14. A test dev ice according to any preceding claim, wherein said holding means is constructed , at least in part, of anodised aluminium. 15. A test device according to any preceding clai m, wherein said holding means is constructed, at least in part, of a polymeric material. 16. A test device according to any preceding claim, wherein said porous masses making up the device are between 10cm and 20cm in height, each having a side dimension of between 10cm and 20cm, and the or each envelope has a side dimension of between 10cm and 20cm, the material of the or each envelope being sufficiently thick and compressible to accommodate the conductor leads without any noticable increased thickness along the lines occupied by the leads. 17. A test device according to any preceding claim, wherein the masses are divided at or about a mid-point in the overall height of the device, such that each part is between 5cm and 10cm in height and consists of one or more individual blocks.

Inventors: HAMBLETON ROGER, THORNBER MICHAEL NEIL, HAMBLETON, ROGER, THORNBER, MICHAEL, NEIL
Applicants: UNIV MANCHESTER, THE VICTORIA UNIVERSITY OF MANCHESTER
Application year: 1987
Main classification: G01M3
IPC codes: A61L2, G01M3