GB2112298A

GB2112298A - Air filter

Info

Publication number: GB2112298A
Application number: GB08236480A
Authority: GB
Inventors: Willy Smets
Original assignee: ENI Electrische Nijverheidsinstallaties
Current assignee: ENI Electrische Nijverheidsinstallaties
Priority date: 1979-05-18
Filing date: 1982-12-22
Publication date: 1983-07-20
Also published as: GB2112298B

Abstract

A stream of sterile air, to be blown over an operating area, is produced by passing the air through a filter 37 sufficiently fine to remove micro-organisms, which are killed by a microwave generator 35 which heats the filter. A piston 40 is adjustable to enable standing microwaves to be established in the zone around the filter. <IMAGE>

Description

SPECIFICATION The sterilization of gas This invention relates to the sterilization of gas which may, for example, be used for conditioning of a zone within a space and the protection of said zone against the entry of contaminating agents, for example, the protection of an operating field relative to the surrounding environment.

According to a first aspect of the invention there is provided a method of sterilizing a gas and comprising passing said gas through a filtering medium to retain micro-organisms, and subjecting said filtering medium to an in-depth sterilization treatment to destroy micro-organisms which have been retained by said filtering medium.

According to a second aspect of the invention, there is provided a sterilizing apparatus comprising at least one micro-filter and sterilizing means, mounted upstream from or at the location of the micro-filter, the micro-filter being for retaining micro-organisms in the gas and the sterilizing means being for sterilizing the gas, before the passage thereof to the outlet and the duct, the sterilizing means also sterilizing the micro-filter.The following is a more detailed description of an embodiment of the invention, given by way of example, reference being made to the accompanying drawings, in which: Figure 1 is a diagrammatic perspective view of a device for conditioning and protecting an operating field, Figure 2 is a section on the line Il-Il in Figure 1, Figure 3 is a section on the line II I-Ill in Figure 1, Figure 4 shows diagrammatically the air flow in the device of Figures 1 to 3 in a vertical plane extending lengthwise of the operating field, Figure 5 is a block diagram of a first form of sterilizing apparatus of the device of Figures 1 to 4.

Figure 6 is a section, to a larger scale, of a part of the apparatus of Figure 5, Figure 7 is a block diagram of a second form of sterilizing apparatus of the device of Figures 1 to4.

In the various Figures, the same reference numerals pertain to identical or similar elements.

The device is for protecting a zone within a space against the entry of contaminating agents which might originate from the outside, and for conditioning said zone as regards temperature and water vapour content.

The preferred use of the device is for conditioning and protecting a surgical operating field relative to the environment and the following description will be limited to such a specific use.

Referring first to Figures 1 to 3, the device comprises a blowing outlet 1 for sterile air and a sucking inlet 2, both outlet and inlet having the shape of an arc of circle lying in respective vertical planes which are spaced but substantially parallel to one another.

The blowing outlet 1 and the sucking inlet 2 are so directed towards one another as to produce between them a screen 3 having the shape of a sector of a cylinder and formed by a substantially laminar stream of sterile air. This sterile air screen forms a barrier against contaminating agents, which as they contact said screen, are carried by the stream into the sucking inlet 2. The blowing outlet 1 comprises an arcuate distributing chamber 4 extending over an angle from 1 10 to 1200 and having open that side which faces the sucking inlet 2. The open side is provided with an outlet mouth 5 forming an elongate outlet slot 6.

In the slot 6, a flexible adjusting needle 7 is provided for varying the air flow rate and for adjusting uniformly the air distribution of air along the length of the slot 6.

The sucking inlet 2 has substantially the same shape as said outlet 1 and comprises an arcuate distributing chamber 8 which is open on that side thereof which faces the blowing outlet. The inlet 2, along said open side, is provided with a mouth 9 having a slot 10 (see Fig. 3). The slot width is much larger than the width of the slot 6 in the blowing outlet 1 since the inlet slot 10 has to receive a diverging air jet from said blowing outlet and also has to receive some air from the zone to be protected.

A distributing strip 21 which a honeycomb structure is arranged over a porous support 57 and located inside a slot 10 to form side-by-side channels 21' extending generally parallel to the gas stream passing through said slot 10. The channels 21' form within the slot 10 a substantially laminar flow with uniform distribution.

The blowing outlet 1 and the sucking inlet 2 are mounted, independently of one another, by respective fasteners 11, 12 on guide rails 13 which extend along the side edges of an operating table 14 on which the protecting device is mounted. The fasteners 1 1, 12 can be clamped to and unclamped from the rails 13 to allow adjustment of the positions of the outlet and the inlet 1, 2 to accommodate differing lengths of operating table 14.

Each end of the blowing inlet 1 is connected to a pipe 15, 16, respectively, for feeding sterile air thereto.

In the same way, sucked air discharge pipes 17 and 18 are connected to respective ends of sucking inlet 2.

The screen 3 formed by the sterile air stream bounds the top of the zone 19 to be protected and conditioned. The end of said zone at the blowing outlet is closed by a baffle 20 which is concave on the zone side. The blowing outlet 1 is provided with a curved wall 22 which faces the zone 19 and extends downwardly from the slot 6. The wall 22 extends the baffle 20 which has substantially the same curvature as said wall, to form therewith a substantially continuous concave surface. To ensure optimum sealing the baffle 20 is made from a relatively tight fabric and includes stiffening elements 23 which allow the lower edge of the baffle to adapt to the shape of a patient lying on an operating table 14.

A similar baffle 24 is provided on the sucking inlet to close the opposite end of the zone.

Flexible side barriers 25 and 26 are also provided and are adjustable to the shape of a patient to prevent, as far as possible, side entry of outside air to the operating zone. The side barriers 25, 26 hang from telescoping rods 55 and 56 extending between the outlet 1 and the inlet 2.

In this way, a closed enclosure is formed with a top wall provided by the screen 3, end walls provided by baffles 20 and 24 and side walls provided by flexible barriers 25 and 26.

A sterile conditioned gas is fed into the zone at such a speed and in such a direction that the screen 3 is not broken. The gas is preferably fed into the zone 19 in a direction opposed to the direction of the screen-forming gas stream 3, towards the sucking inlet end of the zone 1 9 and substantially level with the operating table 14.

The location and speed of the gas feed are selected in accordance with the speed of the gas in the section 3, in such a way as to neutralize, in a part of the said zone (e.g. in the part of the zone where surgery is to be performed), disturbances in the gas flow within the zone caused by the screenforming gas stream. Thus, in this part of the zone, a gas layer is generated with a very slow speed of flow so that said layer can be considered substantially unmoving or stationary.

Figure 4 shows diagrammatically the dynamic action of the air inside the zone 19. As shown in Figure 4, the screen-forming gas stream 3 produced secondary gas streams due to friction between the stream and adjacent air layers. Above the screen 3 uncontrolled vortices are formed in the air layer contacting the screen (shown by arrows 27) as predicted by the theory of free jets in the presence of a boundary layer.

Below the screen in the zone 19 to be protected, the flow is different due to the presence of the baffle 20, as predicted by the theory of recirculated restrained jets. Due to the friction between the screen-forming air stream the adjacent air layers in the zone to be protected, a secondary air stream is generated adjacent the baffle 20 which produces a low pressure family area in an underpressure which then in turn causes a local re-circulation in the direction shown by arrows 28. This re-circulating stream 28 then causes, together with the gas stream forming the screen 3, a gas stream through the zone, substantially parallel to the screen 3, as shown by reference numeral 29.

As mentioned above, a substantially unmoving air layer 31 can be created in a part of said zone by feeding gas into the zone in a direction opposed to the direction of the gas flow in the screen 3.

This gas feed is indicated at 30 in Figure 4. The selection of the location and speed for said gas feed is dependent on the required location in the zone of the part where said substantially unmoving gas layer is to be generated, as well as on the speed of the gas in the curtain-3.

The air in said part of the zone 19 is only substantially unmoving so that it is continuously renewed by the gas feed 30 and the low-speed substantially laminar gas streams 29 which bound the zone part 31 to carry air from said part 30 to the sucking inlet 2. There is thus actually generated a quasi-stationary gas layer at the location where surgery is to be performed.

Due to the dynamics of the gas in zone 19, it is possible to generate, in some pre-determined part thereof, a micro-climate by conditioning the gas fed into the zone 19. This gas may be moist, preferably saturated, with water-vapour or steam and may have a controlled temperature.

A stable micro-climate in the operating field can be achieved when the curtain 3 lies at a distance from 10 to 30 cm, and preferably from 10 to 15 cm. from the operating table 14.

Moreover to ensure the required dynamics of the gas inside the zone 19 and to prevent the leakage of contaminating agents through the screen 3, the speed of the gas stream forming the screen 3 should not fall below 2 m/sec as is enters sucking inlet 2. For this reason a speed of between 2 and 20 m/sec is advantageously maintained in the gas stream between the outlet 1 and the inlet 2.

The stream thickness preferably has a mean value between .2 and 5 cm, while the length and width thereof, which vary according to the nature of the surgical operation, may be, respectively, from 40 to 70 cm and from 20 to 60 cm.

Due to the dynamics of the gases inside the zone 1 9 substantially all of the gas originating from blowing outlet 1, is received by the suction inlet 2 as well as some gas from the zone 19, this amount corresponding substantially to the gas amount fed into the zone 19. The gas sucked into the inlet 2 is returned to a sterilizing apparatus, which will be further described below. This apparatus has an outlet which is connected to the blowing outlet 1 and to a gas-feeding pipe 32 opening inside the zone 19 to be protected. Thus the majority of the gas used is re-circulated.

The gas-feeding pipe 32 comprises at least one flexible section to allow adjustment within the zone 1 9 of the position of the pipe 32 and the direction of gas flow therefrom. The pipe 32 is advantageously provided with an outlet opening 33 in the shape of a flattened cone so that gas emerges therefrom into the zone 19 in the form of a sheet and at a relatively low speed.

To allow adjustment of the moistness of the gas fed through pipe 32, a moistening and, possibly, a cooling and heating device are built into the sterilizing apparatus.

In order to sterilize the gas used, it is passed through a filtering medium for retaining microorganisms, the filtering medium being subjected to an in-depth sterilizing treatment to destroy retained micro-organisms. This will be described in more detail with reference to Figures 5 to 7.

Referring first to Figures 5 and 6, a sterilizing apparatus comprises a micro-filter 34 which will retain particles of at least .2 microns in size and preferably particles of .01 microns. Sterilizing means are arranged upstream of, or at the location of, the micro-filter and are so designed as to cause an in-depth sterilization of the filtered medium from said micro-filter.

In the embodiment shown in Figures 5 and 6, the sterilizing means comprises a microwave transmitter 35 which is mounted inside the microfilter 34.

The micro-filter is shown in more detail in Figure 6 and is provided with a cylindrical casing 36 containing a cylindrical filtering wall 37 which forms the actual filtering medium. The filtering wall divides the enclosure into two compartments 38 and 39.

The transmitter 35 is mounted on the casing 36 inside the compartment 38.

Said filtering wall 37 is advantageously formed by at least two filter layers with differing porosities; the first layer forming a prefilter and being located adjacent the compartment 38 and the second layer having a finer structure, such as a micro-fibre fabric. The length of the compartment 38 is adjustable, in accordance with the wave length of the microwaves, by means of a ring-like piston 40 which is slidable over a core 41. The position of said piston is selected to cause resonance of the microwaves inside said micro-filter 34.

This causes a dielectric heating of the filtering wall 37 to a temperature between 100 and 2000 C, according to the flow rate, the moisture content of the gas and the power of the magnetron, not shown, which generates the microwaves. The temperature of the gas passing through the wall 37 only increases by a few degrees (4 to 10 C).

The apparatus also comprises a prefilter 42 for catching particles with a size larger than 10 microns, which might clog subsequent parts of the apparatus. The micro-filter 34 is followed by a cooler 43 injected with water supplied through a metering pump 44 connected to a water tank 45, which recovers water from the cooler. The sterilized gas is thus cooled to room temperature and is fed through a pipe 46 to, for instance, a device for conditioning and protecting a zone 19 as described above.

The pipe 46 is connected to a pipe 47 directly connected to the blowing outlet 1 and also to a pipe 32 feeding part of the sterilized gas to a conditioning unit formed by a heater 48, a cooler 49 and a moistener 50, into which is injected steam, as shown by arrow 51, to produce a steam-saturated gas stream which is then fed directly to the zone 19 through the outlet opening 33. The amount of gas fed through the pipe 32 into the zone 19 may be, for example, 10% of the total of gas flow. Thus, when the gas flow rate to the blowing outlet 1 is from 40 to 50 m3/hour, the gas subjected to conditioning and passage to the outlet opening 33 is about 5 m3/hour.

It is possible to provide an additional microfilter 34' connected in parallel with micro-filter 34.

This would allow the gas to be sterilized to be passed through the micro-filters alternately, with the non-operative micro-filter being treated with microwaves for a sufficient time to ensure destruction of the micro-organisms retained therein.

The gas flow in the sterilizing apparatus is generated by one or a plurality of pumps or blowers 52, of blowing or high-pressure type.

The embodiment shown in Figure 7 differs from the embodiment shown in Figures 5 and 6 in the sterilizing means used to destroy the microorganisms in the filtering medium 37.

In this embodiment, sterilizing is performed in infra-red radiation. The micro-filter is preceded by a heating chamber 53 for heating the gas to a temperature from 180 to 2200 C. Thus the filtering medium 34 is indirectly brought to the sterilizing temperature by the gas stream. The chamber 53 is preceded by a heat exchanger 54 for pre-heating the gas stream to, for example, a temperature of about 1000 before its entry into the chamber 53.

After the stream has passed through the microfilter 34, it is cooled in the cooling unit 43, which should have a much larger capacity than the cooler 43 shown in Figure 5.

Indeed, in the embodiment of Figures 5 and 6, the filtering medium 37 is heated by the frictional action, on a molecular and atomic scale, within the filtering medium under the action of the electro-magnetic field generated by said microwaves. As the air molecules are not subjected to this action, the gas will not be so heated but will undergo only a slight temperature increase, as already mentioned above, as they pass through the filtering medium.

For this reason, there is a preference for the use of microwaves for sterilizing the gas. The wave frequency lies between 2,000 and 30,000 MHz and is preferably 2,450 MHz at which very efficient bactericidal results have been noticed.

In some cases, however, a sterilization by microwaves might be combined with sterilization by infra-red radiation.

The sterilizing apparatus can be controlled by means of a microprocessor.

It is possible to condition some or all of the gas forming the screen 3 as well as the gas fed through the pipe 32 into the zone 19.

The gas may be air.

Claims

1. A method of sterilizing a gas and comprising passing said gas through a filtering medium to retain micro-organisms, and subjecting said filtering medium to an in-depth sterilization treatment to destroy micro-organisms which have been retained by said filtering medium.

2. A method as defined in claim 1, in which said filtering medium is continuously subjected to a sterilizing treatment during the passage of the gas through said medium.

3. A method as defined in claim 1, in which the gas to be sterilized is passed alternately through a first filtering medium and a second filtering medium, in parallel with the first medium, and the inoperative filtering medium, loaded with microorganisms, being subjected to the sterilization treatment while the gas passes through the other filtering medium.

4. A method as defined in any one of claims 1 to 3, in which the filtering medium is sterilized by means of electro-magnetic microwaves.

5. A method as defined in claim 4, in which the electro-magnetic microwaves have a frequency of 2,000 to 30,000 MHz, and preferably 2,450 MHz.

6. A method as defined in any one of claims 1 to 5, in which the speed of the gas through the filtering medium is from .05 to .25 m/sec.

7. A method of sterilizing a gas substantially as hereinbefore described with reference to Figures 5 and 6 or to Figures 5 and 6 as modified by Figure 7 of the accompanying drawings.

8. A sterilizing apparatus comprising at least one micro-filter and sterilizing means, mounted upstream from or at the location of the microfilter, the micro-filter being for retaining microorganisms in the gas and the sterilizing means being for sterilizing the gas, before the passage thereof to the outlet and the duct, the sterilizing means also sterilizing the micro-filter.

9. An apparatus as defined in claim 8, in which said sterilizing means comprise a transmitter for sending electro-magnetic microwaves inside a cavity containing said at least one micro-filter.

10. An apparatus as defined in claim 9, in which the micro-filter comprises a casing defining an enclosure within which is a cylindrical filtering wall dividing said enclosure into two compartments, one compartment communicating with an inlet for the gas to be filtered and forming said cavity, the other compartment having an outlet for the filtered gas, the transmitter being so mounted inside the cavity as to generate therein an electro-magnetic microwave field which propagates substantially along the cylindrical wall thereof.

11. An apparatus as defined in claim 10, in which the axial length of the cavity is adjustable to allow the generation therein of standing microwaves.

12. An apparatus for sterilizing a gas substantially as hereinbefore described with reference to Figures 5 and 6 orto Figures 5 and 6 as modified by Figure 7 of the accompanying drawings.