GB2419415A

GB2419415A - Sterilisation sensor

Info

Publication number: GB2419415A
Application number: GB0420892A
Authority: GB
Inventors: David Watling
Original assignee: Bioquell UK Ltd
Current assignee: Bioquell UK Ltd
Priority date: 2004-09-20
Filing date: 2004-09-20
Publication date: 2006-04-26
Also published as: GB0420892D0; WO2006032867A1

Abstract

A condensation monitor suitable for use in sterilisation by condensation processes comprises an electrical circuit including a printed circuit board (10) having a surface with a pair of surface conductors (11,12) deposited thereon and separated by a predetermined gap. Means are provided responsive to variation in electrical resistance between the spaced conductors to indicate when condensation to a predetermined level has occurred on the surface of the board between the conductors. The resistance across the gap falls to about 20M L when the correct conditions for sterilisation have been achieved.

Description

STERILISATION SENSOR

This invention relates to methods and apparatus for decontaminating enclosed spaces and it is intended to supplement the disclosures in our UK Patent Application Nos. 0207452.4 and 0211851.1.

The present invention relates to equipment and a technique for establishing when a gaseous sterilization has been effective. The only technique previously available was with the use of Biological indicators (Bls) which had been inoculated with a known number of test organisms. Following exposure to the sterilising gas the B1 is removed from the space to be decontaminated and then placed wither in growth medium to see if any organisms have survived, or alternatively put in a buffer solution so that the organisms may be subsequently counted. This process is time consuming and means that live organisms have to be introduced into the space to be decontaminated. It also has the disadvantage that the results may not be available for several days.

By their nature Bls can only be used to test if the process has been successful and cannot be used to control the process. This lack of control and hence an understanding of the point at which the required level of decontamination has been achieved leads to the use of extended gassing periods to ensure a satisfactory result.

With the increasing need to decontaminate rooms in the Pharmaceutical industry, the Health Care Sector, and also to deal with big-terrorism a new technique is required to - 2 - establish the point at which decontamination has been achieved.

It has been known for a long time that water plays an important part in the gaseous decontamination processes, indeed Dorothy M Portor et al published a paper "Sporicidal Effect of Peracetic Acid Vapour" in Applied Microbiology Nov 1968 pl782 to 1785 showing that humidity was an essential component in the process. In recent years the preferred gaseous sterilizing gas in the pharmaceutical industry has changed from peracetic acid to hydrogen peroxide. Matthews Parks explored the relationship between the water and the active gas, in this case hydrogen peroxide, in a paper presented at the parenteral Society meeting in 2001. In this paper Parks showed that condensation was an essential phase of the decontamination process.

The relationship between deactivation of an organism and the dew point of the active gas was further examined in a paper by Watling at the ISPE meeting in Washington in June of 2002. The work of Parks and Watling shows that condensation is an essential part of the process, and hence a measuring device that indicates the level at which an adequate layer of condensation has been achieved would indicate that the deactivation process has started.

Deactivation processes are essentially in two parts, the first to subject the organism to a level of stress, and then maintain that level of stress for a sufficient period of time to achieve deactivation.

In a gaseous process the level of stress is a function of the amount of condensate that has formed on the organism - 3 and the concentration of the active component in the condensate. The concentration of the active component in the condensate will be a function of the gas concentrations used in the decontamination process. It has also been shown by experiment that, as the amount of condensation at a fixed level of concentration builds up so the speed of the deactivation process increases. This increase in speed of deactivation reaches a maximum after which any further increases in the amount of condensation has no further effect.

The objective therefore is to establish the point at which the optimum level of condensation has occurred and then hold that level for a sufficient period of time to achieve deactivation. The time required for deactivation of any particular organism by a specified process may be established by experiment. Generally with a gaseous process using hydrogen peroxide as the active gas the time required to achieve a one million fold reduction of the test organism used in the pharmaceutical industry would be no more than 12 minutes after the optimum level of condensation (stress) has been achieved. The micro-organism considered to be the most resistant to hydrogen peroxide gas by the pharmaceutical industry is B. stearothermophilus spores.

In our UK Patent Application No. 0207452.4, we describe a method of decontaminating an enclosed space comprising adjusting the relative humidity value within the space to a predetermined level, evaporating a liquid sterilant in the space until the due point of the sterilant gases reached and a requisite level of condensation has been deposited on surfaces within the enclosed space, maintaining the level of - 4 condensation for a predetermined period of time and then removing the gas and condensation from the enclosed space, wherein condensation is measured within the enclosed space at a number of locations to ensure that the requisite level of condensation takes place throughout the enclosed space.

In our UK Patent Application No. 0211858.1, we described and illustrate apparatus for decontaminating an enclosed space comprising a passageway having an air inlet at one end and an outlet at the other end, means to cause a flow of air through the passageway from the inlet to the outlet, means to heat the air flowing through the passageway to a predetermined temperature, evaporating means in communication with the passageway, means to deliver liquid contaminant from a supply of decontaminant to the evaporating means to be evaporated thereby and for the evaporant to be delivered to be delivered to the airflow in the passage to flow in the airflow from the outlet to a room to be decontaminated.

This invention provides a condensation monitor for use in a method and apparatus as set out above comprising an electrical circuit including a printed circuit board having a surface with a pair of surface conductors deposited thereon and separated by a predetermined gap, and means responsive to variation in electrical resistance between the spaced conductors to indicate when condensation to a predetermined level has occurred on the surface of the board between the conductor.

As indicated in our Application No. 0207452.4, a plurality of monitors are located at different positions in - 5 - the enclosed space to be sterilized and the supply of sterilant to the enclosed space is terminated when the monitors have reached a predetermined level indicating that condensation has occurred to a sufficient level for the enclosure to be sterilized.

The monitors are placed strategically throughout the enclosure to respond to condensation of sterilant in different areas of the enclosure and in particular to indicate condensation in areas which the flow of sterilant is likely to have difficulty in penetrating to ensure that the flow of sterilant is not terminated until all such areas have received sterilant and the necessary level of condensation has occurred.

The following is a description of a specific embodiment of the invention reference being made to the accompanying drawings in which: Figure 1 is a diagrammatic view of a printed circuit board having a resistance extending in zig zag thrashing over the second board; Figure 2 is a plan view of a practical embodiment of a printed circuit board embodying a copper conductor extending in zig zag manner over the board; Figure 3 is a perspective view of a socket having a slot in which the printed circuit board is engaged showing the printed socket board being offered up to the slot; Figure 4 is a plan view of the socket; 6 - Figure 5 is a front elevation view of the socket; Figure 6 is a side view of the socket; and Figure 7 illustrates the components of a socket, that is base, top and inner socket board in an exploded fashion.

The drawings show an electronic device that responds to condensation and gives a signal when the condensation has reached a pre-set level. The optimum level of condensation that provides the maximum stress level for the organism is very small, generally invisible to the naked eye, and hence the electronic device has to be very sensitive. Referring to the diagram of Figure 1, the device consists of a printed circuit board 10 having two electrical conductors 11, 12 mounted on an insulating surface of the board. As condensation forms an electrical contact is made between the two conductors and the resistance measured between the conductors is reduced from an open circuit to a measurable value. The separation of the conductors is generally about O.lmm, and may be constructed by etching a narrow gap in the copper surface of printed circuit board material. By careful design of the etched pattern it is possible to create a long gap between the two conductors on a small circuit board, thus increasing the sensitivity of the device. A typical pattern for such a device is shown in Figure 1. It has been found by experiment that with a gap of O.lmm and a gap length of about 100 mm, that when the resistance across the gap falls to about 20MQ that the correct conditions have been achieved to cause the maximum - 7 - stress level, and hence the optimum decontamination conditions when the test organisms is B. stearothermophilus.

Figure 2 of the drawings illustrates a practical embodiment of the circuit board 10 comprising a plug section and tongue section 16 on which a pair of copper conductors are printed and to be exposed to condensation in an enclosure to be sterilised.

Figure 3 of the drawings show the printed circuit board allowing for insertion in a socket 17 providing electrical connections for the board. The socket has a front wall 18 formed with an elongate slot 19 to receive the plug section of the board.

Figure 7 shows the components of the socket in exploded form and comprising a base 20 having upstanding side walls 21, a mounting plate 22 having electrical components indicated at 23 supported thereon located in the base and a cap 24 having a top wall 25 and downturned front and rear walls 26 and 27 respectively. The elongate slot 18 referred to above is formed in the front wall as indicated.

The technique is to place a number of the sensors around the space to be decontaminated and measure the electrical resistance across each one. When the resistance of all of the sensors has fallen to 20MQ it indicates that the correct level of stress has been applied to the microorganisms and that the decontamination has started.

As with any gaseous process it is essential to ensure that there is a good gas distribution and that the sensors have been placed in the parts of the chamber where it is most 8 - difficult to achieve the correct conditions for decontamination. - 9 -

Claims

CLAIMS: 1. A condensation monitor for use in the method of sterilising of

UK Patent Application No. 0207452.4 or the apparatus of Application No. 0211851.1 comprising an electrical circuit including a printed circuit board having a surface with a pair of surface conductors deposited thereon and separated by a predetermined gap, and means responsive to variation in electrical resistance between the spaced conductors to indicate when condensation to a predetermined level has occurred on the surface of the board between the conductors.
2. A condensation monitor as claimed in claim 1, wherein the conductors comprise a copper layer deposited on the printed circuit board with a gap etched in the copper layer.
3. A condensation monitor as claimed in claim 2, wherein an elongate gap is etched in the copper layer.
4. A condensation monitor as claimed in claim 3, wherein the gap is of uniform width between 0.05 and 0.2 mm.
5. A condensation monitor as claimed in claim 4, wherein the gap is 0.1 mm.

575134: GCB; LMB