GB2323785A - Fumigation of microbiological safety cabinet - Google Patents

Abstract

A cabinet, which is to be fumigated, comprises a housing 10 defining a chamber 12 having an opening closable by a panel 20, an exhaust duct 22 leading from an outlet 15 of the chamber, a filter 26 across the outlet, an extractor fan 25 in the exhaust duct, a vaporiser (not shown), an additional aperture 29 with electrically actuable closure means 30 and electronic control means (not shown). The control means controls the sequence of fumigation operations including the length of time the vaporiser is switched on, the time interval before the extractor fan is activated and the time interval between opening and closing the additional aperture (to allow air into the housing). Preferably the housing also contains an upper chamber 14 having a recirculation fan 19 with a filter between the chamber 12,14 so that, in use, air can be recirculated from chamber 12 via a return duct 18 to chamber 14.

Description

FUMIGATION OF MICROBIOLOGICAL SAFETY CABINETS This invention concerns fumigation of microbiological safety cabinets.

A microbiological safety cabinet comprises a housing defining a working chamber having a front opening which is closeable by means of a panel or screen, an exhaust duct leading from an outlet of the working chamber, filter means disposed across the aforesaid outlet, and an exhaust fan disposed in the exhaust duct at a location remote from the working chamber and operative to draw air therefrom for exhaust to atmosphere.

Under current safety regulations, Class 1 safety cabinets are specifically designed for use when handling particularly hazardous or infectious materials. They do not incorporate a facility for recirculation of air to the working space. In some Class I cabinets the housing defines an upper chamber above the working chamber in which a further fan is arranged, which fan, in operation, draws air upwards from the working chamber and through an additional filter means which is located between the upper chamber and the working chamber.

Class II safety cabinets are designed for handling less hazardous materials. These invariably include an upper chamber above the working chamber, a recirculation fan disposed in the upper chamber and further filter means disposed between the working chamber and the upper chamber so that, in operation, the recirculation fan causes air to circulate downwards into the working space and upwards via, a return duct, to the upper chamber, with a certain volume of air being drawn in via the front opening, when it is open, and the exhaust fan causes a similar volume of air to pass out to atmosphere via the first filter means and the exhaust duct. In some cabinets a further filter is located in the return duct.

All microbiological safety cabinets have to be fumigated. The frequency of fumigation depends upon the type of research work undertaken. However, it usually varies between weekly and monthly.

Conventionally, fumigation is carried out by boiling off formalin in a vaporiser which is either built on to the side of a cabinet or free standing within the cabinet. Before this, the fan or fans is/are switched off and the cabinet is sealed off by placing a front panel over the front opening or actuating a mechanism to slide a screen down to seal off the front opening. The vaporiser takes about an hour to boil off all the formalin, after which the cabinet has to be left for at least six hours for the formaldehyde vapour to sterilise the interior. As formaldehyde is extremely hazardous, great care has to be taken when carrying out this procedure, particularly when discharging the vapour to atmosphere and subsequently removing the front panel or screen.

In this respect, discharge of the vapour to atmosphere is accomplished by switching on the extraction fan and then slowly removing the front panel or screen to allow ambient clean air to enter the cabinet.

In view of the necessary lengthy period of exposure of the cabinet interior to formaldehyde vapour, fumigation is usually carried out overnight, with the discharge of the hazardous vapour then being the first task of the following day. It usually takes, over an hour for full discharge of vapour, before normal operation of the cabinet can re-commence.

Clearly it would be advantageous if the fumigation procedure could be automated.

An object of the present invention is to provide a safety cabinet with facilities for automatic fumigation such that the hazards attendant on the conventional procedure are considerably reduced and working time is saved as manual intervention e.g for exhausting the vapour, is not necessary.

This is accomplished in accordance with the invention in that a vaporiser is provided within the housing, as is known, in that an additional aperture is provided in the housing and fitted with electrically closure means, and in that electronic means are provided which control a sequence of operations for fumigation of the working space, including, following switching on of the vaporiser, the time interval before it is switched off again, the time interval before the exhaust fan is activated, to commence discharge of the vapour, and the time intervals before the closure means to the additional aperture is opened to allow fresh air to enter the housing and is subsequently closed again.

It will be appreciated that the provision of an additional aperture which, in practice, will be considerably smaller in area than the front opening, avoids the need for opening up the front panel or screen during the discharge process and therefore considerably reduces the hazards for the operatives, particularly since the additional aperture is opened and closed automatically, e.g. by a spring loaded electrically operated damper under control of an electronic timing circuit.

In practical embodiments of the cabinet of the invention the additional small aperture is generally provided in or near the top of the housing. In the case of Class II cabinets or Class I cabinet having an additional extraction fan in an upper chamber above working chamber, the additional aperture, which has an electrically controlled closure means, will generally be located above the recirculation or additional extraction fan. However, the said aperture could just as well be located in any part of the housing where there is negative air pressure (i.e. suction pressure), such as a side of the upper chamber, or the return duct in the case of Class II cabinets.

In the case of Class II cabinets, i.e. those which include a recirculation fan, the sequence of operations controlled by the electronic timing circuit, will also include the time interval before the recirculation fan is switched on to aid distribution of vapour, and the time interval until it is switched off again, also the time interval before the recirculation fan is switched on for a second time to aid removal of vapour, and the time interval before it is switched off again.

The invention will be described further, by way of example, with reference the accompanying drawing in which the single figure is a longitudinal cross section through a Class II microbiological safety cabinet in accordance with the invention.

The illustrated cabinet is a Class II cabinet. It comprises a housing (10) defining a lower chamber, which serves as a working space (12), and an upper chamber (14) with filter means (16) disposed therebetween. A passage (18) extends along the base and up the rear of the housing (10). Inlets (11) and (13) to the passage (18) are at the front and rear of the base of the working space (12). A further filter (26) is disposed across an outlet (15) from the upper chamber (14). A fan (19) is arranged in the upper chamber (14) so that, in operation, it causes air to circulate downwards through the first filter (16) and the working space (12) and upwards through the passage (18), with a proportion of air being drawn in via a front opening of the working space (12), and a proportion of air passing out through the second filter (26) to an exhaust duct (22) having an fan (25) located at or near its discharge end.

In the drawing, the front opening is shown sealed off by a closure panel (20). In normal operation of the cabinet, this would be open. The closure panel (20) may be manually locatable, or it may be slidable (e.g. downwards) and operated by a motor (not shown).

At the top of the housing (10), in the top wall of the upper chamber (14) and above the recirculation fan (19), an aperture (29) is provided which serves as an air intake during fumigation of the cabinet. This aperture (29) is provided with a spring loaded damper (30), which normally closes off the aperture (29), but can be actuated to open same, e.g during the fumigation procedure. In this respect, the spring is an effective fail safe device, which, in the event of a power failure, would close off the aperture (29) and ensure that no formaldehyde seeped out of the cabinet. For this reason it is considered safe to allow the automatic fumigation process to take place during periods when there are no operatives present i.e. overnight or at weekends.

An electronic timing circuit is also provided as part of the control unit (not shown) for the cabinet. This timing circuit controls a sequence of operations for automatic fumigation of the illustrated cabinet.

A vaporiser (not shown) is preferably built on to the side of the cabinet in a manner which is already known in the technical field.

Also shown are fluorescent tubes (17) for illumination of the working space (12).

The procedure for automatic fumigation of the illustrated Class II cabinet may be as follows: Firstly, the fans (19) and (25) are switched off. The panel (20) is then placed over the front opening and appropriately sealed.

The vaporiser is then filled with a pre-determined amount of formalin.

To commence fumigation, a switch on the control unit is depressed in order to activate the timing circuit. Yellow, green and red indicator lights are preferably provided on the control panel, the yellow light illuminating to indicate that the fumigation cycle has been initiated. A sequence of operations under the control of the timing circuit then proceeds as follows: a). The vaporiser is switched on to boil the formalin. The resulting formaldehyde vapour percolates into the working space (12) of the cabinet (10).

b). After 30 minutes the recirculation fan (19) is switched on for 10 seconds to disperse the formaldehyde throughout the cabinet.

c). After a further 30 minutes, the vaporiser is switched off and the recirculation fan (19) is switched on again for ten seconds to further distribute the formaldehyde throughout the cabinet interior.

d). The cabinet is then left for a minimum of six hours so that the formaldehyde can sterilise the interior.

e). At the end of the exposure period, the exhaust fan (25) is switched on and, five seconds thereafter, so long as air flow is sensed in the exhaust duct (22) (by a pressure sensor linked to the electronic circuit), the damper (30) is opened to allow ambient air to enter the cabinet via the aperture (29). After a further 10 seconds the recirculation fan (19) is switched on. Both the exhaust fan (25) and the recirculation fan (19) then run for two hours to ensure that the formaldehyde is completely removed from the cabinet (10), particularly from the material of the HEPA filter (16) at the top of the working space (12).

f). At the end of the two hour period the damper (30) is closed and the exhaust and recirculation fans (25), (19) are switched off. At this point, the yellow indicator light on the control panel goes out and the green light is illuminated. This indicates that the fumigation cycle has been completed.

g). If a fault occurs during the sequence the components will immediately shut down, the red light will illuminate and an audible alarm will sound.

The foregoing description is, of course, not limitative of the scope of the invention. Numerous variations are possible.

As mentioned previously, in the case of cabinets where the front panel or screen is slidable and operated by a motor, the closure of this panel can be included as a first step in the fumigation procedure under the control of the electronic timing circuit.

In the case of Class I safety cabinets where there is no recirculation fan, the steps involving that fan will, of course, be omitted. However, in Class I cabinets which have an additional extraction fan in the upper chamber that fan could be switched on in place of the recirculation fan in the sequence described above, firstly to assist in distribution of the formaldehyde vapour and later to assist in the final stages when the formaldehyde is being removed.

All the time periods stated above are merely by way of illustration of the periods of time likely to be necessary for successful and thorough fumigation. Naturally, these may be varied by alteration of the timing circuit programme as desired or necessary, depending upon the circumstances.

Claims (10)

1. A microbiological safety cabinet comprising a housing defining a working chamber, having a front opening which is closable by means of a panel or screen, an exhaust duct leading from an outlet of the working chamber, filter means disposed across the aforesaid outlet, and an exhaust fan disposed in the exhaust duct at a location remote from the working chamber and operative to draw air therefrom for exhaust to atmosphere, characterised in that a vaporiser is provided within the housing, in that an additional aperture is provided in the housing and fitted with electrically actuable closure means, and in that electronic means are provided which control a sequence of operations for fumigation of the working space, including, following switching on of the vaporiser, the time interval before it is switched off again, the time interval before the exhaust fan is activated, and the time intervals before the closure means to the additional aperture is opened to allow fresh air to enter the housing and is subsequently closed again.

2. A safety cabinet as claimed in claim 1 wherein the housing also defines an upper chamber above the working chamber, a recirculation fan is disposed in the upper chamber and further filter means are disposed between the working chamber and the upper chamber so that in operation the recirculation fan causes air to circulate downwards into the working space and upwards, via a return duct, to the upper chamber, with a certain volume of air being drawn in via the front opening, when it is open, and the exhaust fan causes a similar volume of air to pass out to atmosphere via the first filter means and the exhaust duct.

3. A safety cabinet as claimed in claim 2 wherein the additional aperture is provided at a location above the recirculation fan.

4. A safety cabinet as claimed in claim 2 or 3 wherein the sequence of operations controlled by the electronic means include switching on the recirculation fan to aid distribution of vapour and subsequently switching it off.

5. A safety cabinet as claimed in claim 2, 3 or 4 wherein the sequence of operations controlled by the electronic means include switching on the recirculation fan to aid removal of vapour and subsequently switching it off.

6. A safety cabinet as claimed in any preceding claim wherein the closure means of the additional aperture is a spring loaded electrically operated damper.

7. A safety cabinet as claimed in any preceding claim wherein the additional aperture is provided in or near the top of the housing.

8. A safety cabinet as claimed in any preceding claim wherein the panel or screen for closing the front opening of the working chamber is slidable and motorised.

9. A safety cabinet as claimed in claim 7 wherein the sequence of operations controlled by the electronic means include, as an initial step, closure of the front opening.

10. A microbiological safety cabinet substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.