GB2501283A

GB2501283A - Microbiological safety cabinet with an external air regulator

Info

Publication number: GB2501283A
Application number: GB201206808A
Authority: GB
Inventors: Christopher Popple; Mark Gallagher; Roger David Lownds
Original assignee: CONTAINED AIR SOLUTIONS Ltd
Current assignee: CONTAINED AIR SOLUTIONS Ltd
Priority date: 2012-04-18
Filing date: 2012-04-18
Publication date: 2013-10-23
Anticipated expiration: 2032-04-18
Also published as: GB201206808D0; GB2501283B

Abstract

A microbiological safety cabinet comprising a housing 10 with: a lower chamber 11 providing a working space 12 with an access aperture 14 and work surface 16; an upper chamber 13 comprising an air grille 26 on its exterior front panel; and a duct 24 appended to the upper chamber for connection to an exhaust system; the upper chamber comprising: a damper 21 defining upper and lower sub-chambers 23, 22 respectively; a double filter 17 disposed in said lower sub-chamber; a second filter 19 disposed in said upper sub-chamber; a fan 20 disposed between the double filter and the damper; and an opening located in said upper sub-chamber between the damper and the second filter; wherein the fan is arranged to draw air from the working space through said double filter and in through said access aperture, a remote fan of the exhaust system being operative to draw air through the second filter and the upper sub-chamber opening, characterised in that the upper sub-chamber opening comprises an airflow regulator 25 there across.

Description

MICROBIOLOGICAL SAFETY CABINETS

BACKGROUND

Technical Field

The present invention relates generally to the field of microbiological safety cabinets.

Microbiological safety cabinets are an enclosed, ventilated laboratory workspace for safely working with materials contaminated with (or potentially contaminated with) pathogens requiring a defined biosafety level. Several different types of microbiological safety cabinet exist, differentiated by the degree of bio-containment that is required. All exhaust air is HEPA-filtered as it exits the microbiological safety cabinet, removing harmful bacteria and viruses. However, some classes of microbiological safety cabinet (Class II and Ill) have a secondary purpose -to maintain the sterility of materials inside the cabinet.

Class I cabinets take in air from outside the cabinet. Therefore, a Class I cabinet can provide personnel and environmental protection but no product protection, because the inward flow of air can contribute to contamination of samples. These microbiological safety cabinets are commonly used to enclose specific equipment (e.g. centrifuges) or perform procedures (e.g.aerating cultures) that potentially generate aerosols.

Class II cabinets provide both kinds of protection (of the samples and of the environment) since the inward flow of air is also HEPA-filtered before being exposed to the working chamber. The principle of operation involves using a fan mounted in the top of the cabinet to draw a curtain of sterile air over the products that are being handled. The air is then drawn underneath the work surface and back up to the top of the cabinet where it passes through the HEPA filters. The air that is exhausted is made up by air being drawn into the front of the cabinet underneath the work surface. The air being drawn in acts as a barrier to potentially contaminated air coming back out to the operator.

Microbiological safety cabinets are either ducted (connected to the building exhaust system) or unducted (recirculating filtered exhaust back into the laboratory). However, ducted installations are much more expensive, especially where the laboratory or the building does not have an existing exhaust system in place.

It is an object of the present invention to provide an improved microbiological safety cabinet.

SUMMARY OF THE INVENTION

In a first aspect of the present invention there is provided a microbiological safety cabinet comprising a housing, said housing comprising: a lower chamber providing a working space with a worksurface and an access aperture; an upper chamber appended to the lower chamber; and a front panel on said upper chamber comprising an air grille therein; a duct appended to the upper chamber for connection to an external exhaust system; the upper chamber comprising: a damper defining upper and lower sub-chambers; a double filter disposed in said lower sub-chamber; a second filter disposed in said upper sub-chamber; a fan disposed between the double filter and the damper; and an opening located in said upper sub-chamber between the damper and the second filter and positioned substantially behind the air grille; wherein the fan is arranged to draw air from the working space through said double filter with at least a proportion of air being drawn in through said access aperture, a remote fan of the external exhaust system being operative to draw air through the second filter which is a combination of filtered air from the lower chamber and room air entering through the grille and subsequently through the upper sub-chamber opening, characterised in that the upper sub-chamber opening comprises an airflow regulator there across.

The air flow through the grille is of low velocity, but speeds up rapidly as it enters the upper sub-chamber due to the action of the external exhaust system.

With turbulent air entering the upper sub-chamber via the damper, this high velocity air being drawn in through the grille causes a large amount of disruption to the airflow path of the air being extracted. This in turn, negatively effects the efficiency of air extraction through the third filter and the pressure in the upper sub-chamber.

However, with the above arrangement, the airflow into the upper sub-chamber is controlled by the airflow regulator, thereby evening out the airflow entering the upper sub-chamber and creating a smooth flow path into the upper sub-chamber despite the increase in velocity. This reduces turbulence in the upper sub-chamber and minimises disruption to the airflow path of the filtered air entering the upper sub-chamber through the damper. This in turn, improves the efficiency of air extraction through the third filter and maintains the required pressure in the upper sub-chamber.

The airflow regulator may comprise a perforated metal sheet. The perforated metal sheet may comprise circular perforations therein. The perforated metal sheet may comprise up to approximately 50% open area. More preferably, the perforated metal sheet may comprise up to approximately 60% open area.

Alternatively, the perforated metal sheet may comprise a plurality of substantially horizontal or vertical slots therein, arranged in rows and/or columns. The perforated metal sheet may therefore, comprise two or more substantially horizontal slots in substantially parallel arrangement.

With this arrangement, the airflow into the upper sub-chamber is controlled in small streams, thereby evening out the airflow entering the upper sub-chamber and creating a smooth flow path into the upper sub-chamber.

Preferably, the airflow regulator comprises a metal sheet with at least one substantially horizontal slot therein. Most preferably, the airflow regulator comprises a metal sheet with a single horizontal slot therein. The (or each) slot may comprise width:depth size ratio of between approximately 8:1 and approximately 5:1. Most preferably, the (or each) slot comprises a width:depth size ratio of approximately 20:3.

Therefore, the (or each) slot may comprise a width of approximately 400 mm and a depth of approximately 60 mm.

With this arrangement, the airflow into the upper sub-chamber can be controlled in one or more planar streams, thereby further evening out the airflow entering the upper sub-chamber and creating a smoother flow path into the upper sub-chamber. The efficiency of air extraction through the third filter is further improved with this arrangement.

Preferably, the damper is electronically connected and operated by a control panel.

Preferably, the lower working chamber comprises a lower working space and a secondary sub-chamber. Preferably, the lower working space and secondary sub-chamber are separated by a third filter provided across an upper portion of the lower chamber. The lower chamber preferably comprises a channel leading from a location adjacent the access aperture to said secondary sub-chamber. The channel may travel below the worksurface and behind the rear wall of the lower chamber to said secondary sub-chamber. Preferably, in the secondary sub-chamber there is disposed a secondary fan operable to draw contaminated air from the working space and from outside the cabinet (laboratory air) through the channel. Preferably, the secondary fan re-circulates laboratory air from said channel downwards through the third filter into the working space as filtered air. Preferably, the secondary fan directs a proportion of the air in the channel upwards to the upper chamber.

Preferably, the damper isolates the lower chamber and the lower sub-chamber from the upper sub-chamber. Preferably, the damper ensures an airtight isolation of the lower chamber and the lower sub-chamber from the upper sub-chamber.

It is to be appreciated that the features of the first aspect of the invention also apply to the following further aspects of the invention.

In a second aspect of the present invention there is provided a microbiological safety cabinet comprising a housing, said housing comprising: a lower chamber providing a working space with a worksurface and an access aperture; an upper chamber appended to the lower chamber; and a duct appended to the upper chamber for connection to an external exhaust system; the upper chamber comprising: a damper defining upper and lower sub-chambers; a double filter disposed in said lower sub-chamber; a second filter disposed in said upper sub-chamber; a fan disposed between the double filter and the damper; and an opening located in said upper sub-chamber between the damper and the second filter; wherein the fan is arranged to draw air from the working space through said double filter with at least a proportion of air being drawn in through the access aperture, a remote fan of the external exhaust system being operative to draw air through the second filter which is a combination of filtered air from the lower chamber and room air entering through the upper sub-chamber opening, characterised in that the cabinet comprises an automated failure detection system for monitoring and reacting to the safety status of the external exhaust system.

It will be appreciated that the preferred features described in relation to the first aspect of the invention also applies to this second aspect of the invention and vice versa.

Preferably, the failure detection system comprises an alarm. Preferably, the alarm is an audible alarm. Preferably the alarm also comprises a visual alarm status message to the operator.

Preferably, the failure detection system allows for continued operation of the cabinet and exit of filtered air through the upper sub-chamber opening during failure of the external exhaust system.

Preferably, the failure detection system comprises at least one pressure sensor. The (or each) pressure sensor is provided on a printed circuit board (PCB). Preferably, the pressure sensor monitors and reacts to a change in pressure in one or more chambers in the cabinet. Preferably, the (or each) pressure sensor activates said alarm(s) when the sensor(s) detect(s) a change in pressure in one or more chambers of the cabinet that are outside of predetermined acceptable pressure parameters.

For example, an increase in pressure in a particular chamber beyond predetermined parameters may indicate a blockage or impairment in a filter. In contrast, a decrease in pressure in a particular chamber beyond predetermined parameters may indicate that a fan is not running or is not functioning correctly.

Preferably, the failure detection system comprises a no start override' function once the cabinet is switched off. The no start override' function preferably comprises an on-going pressure feedback routine that prevents re-start of a cabinet until all pressures return to being within the predetermined acceptable pressure parameters.

With this arrangement, the failure of the external exhaust system can be identified early, in order that an operator can make arrangements to safely complete the work being performed and if necessary, shut down the cabinet for repair.

In a third aspect of the present invention there is provided a microbiological safety cabinet comprising a housing, said housing comprising: a lower chamber providing a working space with a worksurface and an access aperture; an upper chamber appended to the lower chamber; and a duct appended to the upper chamber for connection to an external exhaust system; the upper chamber comprising: a damper defining upper and lower sub-chambers; a double filter disposed in said lower sub-chamber; a second filter disposed in said upper sub-chamber; a fan disposed between the double filter and the damper; and an opening located in said upper sub-chamber between the damper and the second filter; wherein the fan is arranged to draw air from the working space through said double filter with at least a proportion of air being drawn in through the access aperture, a remote fan of the external exhaust system being operative to draw air through the second filter which is a combination of filtered air from the lower chamber and room air entering through the upper sub-chamber opening, characterised in that the cabinet comprises a pressure detection system for monitoring the operational condition of the second filter.

It will be appreciated that the preferred features described in relation to the first and second aspects of the invention also apply to this third aspect of the invention and vice versa.

Preferably, the pressure detection system comprises at least one pressure sensor.

Preferably, a first pressure sensor is operable to monitor the pressure in the double filter. Therefore, a pressure sensor is located between the lower chamber and the double filter. The pressure sensor may be one of several types of flow meter that measure the differential pressure within a constriction, or by measuring static and stagnation pressures to derive the dynamic pressure.

Preferably, the double filter comprises a fixed orifice plate. The orifice plate may comprise a plate with a hole through it, which constricts the flow, and measures the pressure differential across the constriction to provide the flow rate.

With this arrangement, the pressure and therefore, the requirement for a replacement filter can be detected early, in order that an operator can make arrangements to safely replace the filter in order to maintain the relevant standard of air being extracted into the duct. In this respect, the cabinet can detect when the pressure drops below a certain level (typically below 50 Pa for HEPA filters), in order to make the most of the filters and maintain a required operational efficiency for the whole system.

Preferably, a second pressure sensor is operable to monitor the functionality of the second filter and the external extraction system. Preferably, therefore, the further pressure sensor is located between the extraction duct and the second filter in the upper sub-chamber. Preferably, the pressure sensor comprises a static pressure sensor.

With this arrangement, the pressure and therefore, the requirement for a replacement filter or a faulty external extract system can be detected early, in order that an operator can make arrangements to safely replace the filter! repair the extract system.

Preferably, where the lower working chamber comprises a secondary sub-chamber as previously described, an third pressure sensor is operable to monitor the functionality of the third filter and the secondary fan in order to ensure a constant flow of air through the access aperture. Preferably, therefore, the further pressure sensor is located in the secondary sub-chamber. Preferably, the pressure sensor comprises a static pressure sensor.

With this arrangement, the requirement for a replacement third filter or a faulty secondary fan can be detected early, in order to ensure that there is no leakage of contaminated air through the access aperture to the external environment).

Preferably, each pressure sensor activates said fault detection system when the sensor(s) detect(s) a change in pressure in one or more chambers of the cabinet that are outside of predetermined acceptable pressure parameters.

In a fourth aspect of the present invention there is provided a microbiological safety cabinet comprising a housing, said housing comprising: a lower chamber providing a working space with a worksurface and an access aperture; an upper chamber appended to the lower chamber; and a duct appended to the upper chamber for connection to an external exhaust system; the upper chamber comprising: a damper defining upper and lower sub-chambers; a double filter disposed in said lower sub-chamber; a second filter disposed in said upper sub-chamber; a fan disposed between the double filter and the damper; and an opening located in said upper sub-chamber between the damper and the second filter; wherein the fan is arranged to draw air from the working space through said double filter with at least a proportion of air being drawn in through the access aperture, a remote fan of the external exhaust system being operative to draw air through the second filter which is a combination of filtered air from the lower chamber and room air entering through the upper sub-chamber opening, characterised in that the damper is located wholly internally of the cabinet and is controlled electronically.

It will be appreciated that the preferred features described in relation to the first, second and third aspects of the invention also apply to this fourth aspect of the invention and vice versa.

Preferably, the damper is electronically connected to and operated by a control panel.

With this arrangement, the external housing of the cabinet is easier to clean since there are no manual levers for operation that may harbour pathogens.

Furthermore, with the electronic control, should the cabinet need to be shut down, there is less room for human error with the opening! closing of the damper.

In a fifth aspect of the present invention there is provided a microbiological safety cabinet comprising a housing, said housing comprising: a lower chamber providing a working space with a worksurface and an access aperture; an upper chamber appended to the lower chamber; and a duct appended to the upper chamber for connection to an external exhaust system; the upper chamber comprising: a damper defining upper and lower sub-chambers; a double filter disposed in said lower sub-chamber; a second filter disposed in said upper sub-chamber; a fan disposed between the double filter and the damper; and an opening located in said upper sub-chamber between the damper and the second filter; wherein the fan is arranged to draw air from the working space through said double filter with at least a proportion of air being drawn in through the access aperture, a remote fan of the external exhaust system being operative to draw air through the second filter which is a combination of filtered air from the lower chamber and room air entering through the upper sub-chamber opening, characterised in that the fan is energy-efficient and is electronically controlled.

It will be appreciated that the preferred features described in relation to the first, second, third and fourth aspects of the invention also apply to this fifth aspect of the invention and vice versa.

Preferably, the fan is electronically connected to the control panel.

Preferably, the fan is switched on and off through the controlled supply of power thereto by the control panel.

With this arrangement, the energy Gonsumption of the Gabinet can be significantly reduced. Furthermore, with the electronic control, should the cabinet need to be shut down, there is less room for human error with the operational status of the fan.

It will be appreciated that the preferred features described in relation to the above aspects of the invention apply to each of the other aspects of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, and to show how exemplary embodiments may be carried into effect, reference will now be made to the accompanying drawings in which: Figure 1 is a perspective view of one embodiment of a microbiological safety cabinet according to the invention; Figure 2 is a side cross-sectional view of the cabinet of Figure 1; Figure 3 is a front view of the cabinet of Figure 1; Figure 4 is a side view of the cabinet of Figure 1; Figure 5 is a perspective view of another embodiment of a microbiological safety cabinet according to the invention; Figure 6 is a side cross-sectional view of the cabinet of Figure 5; Figure 7 is a front view of the cabinet of Figure 5; Figure 8 is a side view of the cabinet of Figure 5; Figure 9 is a front view of a control panel of a cabinet of Figure 1 or 5; Figure 10 is an explanatory legend of the control panel of Figure 9; Figure 11 is an alternative operative function of the control panel of Figure 9 for operation of an Engineer's menu; and Figure 12 is a flowchart showing the Engineer's menu operation menu for the control panel of figure 9.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

As shown in Figures 1 to 8, a microbiological safety cabinet according to the invention comprises a housing (10, 100) having a lower working chamber (11, 110) providing a working space (12, 120) and an upper chamber (13, 130). The lower working chamber (11, 110) is accessed via an access aperture (14, 140) in a front panel (15, 150) thereof. The base of the lower working chamber (11, 110) provides a worksurface (16, 160).

A first filter arrangement (17, 170) is disposed between the lower working chamber (11, 110) and the upper chamber (13,130), such that the first filter arrangement (17, 170) is located at an inlet to the upper chamber (13, 130). The first filter arrangement (17, 170) is a double HEPA filter.

An air flow sensing device (18, 180) is provided between the lower chamber (11, 110) and the first filter arrangement (17, 170). The sensing device (18, 180) comprises a fixed orifice plate being a plate with a hole through it, placed in the flow; it constricts the flow, and measures the pressure differential across the constriction to give the flow rate.

A first fan (20, 200) is located between the first filter arrangement (17, 170) and the second filter (19, 190) in the upper chamber (13, 130). The fan (20, 200) is an energy-efficient fan of compact design, thereby contributing significantly to a reduction in the running cost of the cabinet. The fan (20, 200) is located towards a rear wall of the lower sub-chamber (22, 220) in order to minimise disruption to the airflow path.

A damper (21, 210) is located between the first fan (20, 200) and the second filter (19, 190). The damper (21, 210) is located internally of the upper chamber (13, 130), thereby creating two distinct lower and upper sub-chambers (22, 220, 23, 230) there within. The damper (21, 210) is also controlled automatically via an externally located control panel (28, 280). The use of an internal automatic damper (21, 210) provides numerous advantages over a manual external damper by making operation of the cabinet more efficient and more safe. Furthermore, by reducing the number of external manual mechanisms, the Gleaning of the outside of the cabinet is much more efficient and much more thorough, thereby reducing the chance of pathogen transfer.

A duct connector (24, 240) provides an outlet in the upper chamber (13, 130) for connection to an extraction duct (not shown), which connector (22, 220) is located beyond the second filter (19, 190).

A second air flow sensing device (37, 370) is provided between extract duct (24, 240) and the third filter arrangement (19, 190). The sensing device (37, 370) comprises a static pressure sensor.

An air regulator (25, 250) is provided in a front wall of the upper sub-chamber (23, 230). The regulator (25, 250) corresponds with an air grille (26, 260) provided in a door (27, 270) of the upper chamber (13, 130). The regulator (25, 250) comprises a horizontal slot approximately 400 mm by 60 mm in size.

In a second embodiment of the invention, shown in figures 5 -8, the lower working chamber (110) is divided into the working space (120) and a secondary sub-chamber (290) by a third (double HEPA) filter (310) provided across an upper portion of the lower chamber (110). The lower chamber (110) further comprises a channel (330) located between the worksurface (160), rear wall and upper part of the lower chamber (110) and the outer casing of the cabinet. An opening (340) adjacent with the opening in the front panel (150) provides air flow into the channel (330). In the upper part of the channel (330), there is disposed a secondary fan (320) which communicates with the channel (330) and the secondary sub-chamber (290). A third air flow sensing device (380) is provided in the secondary sub-chamber (290). The sensing device (380) comprises a static pressure sensor.

The control panel (28, 280) of both embodiments, shown in Figure 9, comprises a key switch (29), a fan! control circuit button (30), a lights button (31), solenoid gas valve button (32), a fumigation activation button (33), a mute alarm button (34) and a activate UV lights button (35).

The control panel (28, 280) also has an LCD display (36) which displays details of the operative condition of the cabinet, displays warnings and also displays useful information both at request of an operator.

The key switch (29) allows a supervisor to prevent or authorise use of the cabinet through the use of a mechanical key. By turning the key clockwise to point to the numeral 1', the supervisor is allowing use of the cabinet. By turning the key anti-clockwise to point to 0', the supervisor is preventing against use of the cabinet.

To operate any of the other buttons (30 -35), each button is pressed to obtain the positive condition and pressed again to obtain the negative condition.

Once pressed a first time, the positive condition e.g. on' or activate' is achieved and this is displayed on the LCD display (36) with a pictorial representation of that button. When a button is pressed again, the negative condition e.g. off or de-activate' is achieved and this is displayed on the LCD display (36) by removal of the pictorial representation of that button.

The fan! control circuit button (30) starts or stops a power supply to the fans and the control circuits. The lights button (31) starts or stops a power supply to the lights to turn them on and off. The solenoid gas valve button (32) starts or stops a power supply to the gas valve to operate the damper, but is subject to the cabinet being in AIRFLOW SAFE condition for the power to be started. The fumigation activation button (33) will only fumigate the cabinet when the key switch (29) is set to the 0' condition and therefore, the cabinet is off'. The mute alarm button (34) will mute an audible alarm, but the indication of the muted alarm will remain on the LCD display (36) until the fault has been rectified. The UV lights button (35) will start or stop a power supply to the UV lights to turn them on and off, but will only switch the UV lights on when the key switch (29) is set to the 0' condition and therefore, the cabinet is off' and the lights button (31) is off.

The control panel (28, 280) monitors, reports on and reacts to a number of cabinet conditions which ensures that a safe working environment is maintained.

In order to do this, the control panel (28, 280) comprises a number of predetermined limits for a variety of conditions stored in a memory.

Should any of the monitored conditions exceed, drop below, or have not yet reached the predetermined limit then the LCD display (36) will display an appropriate alarm or status message along with the pictorial representation of the fan button (30). The LCD display (36) conveys the following alarm! status messages: AIRFLOW STABILISING -status message displayed when the fan button (30) is activated whilst the control system (pressure sensors (18, 180! 37, 370! 380)) checks and confirms that the main extract system is operating within safe limits, the filters (17, 170! 19, 190! 310) are in working order and the fans (20, 200! 320) are in working order (checks that the pressure in the relevant chambers are within predetermined limits) -this message delays the start of the internal fan (20, 200); AIRFLOW SAFE -status message displayed once the control system checks have been completed and the pressure sensors (18, 180! 37, 370! 380) corroborate that the internal fans (20, 200! 320) are up to speed.

MAIN EXHAUST FAIL -alarm displayed when the control system (pressure sensor (37, 370)) confirms that a low pressure, which indicates that the main extract system is not operating within safe limits and audible alarm is triggered.

DOWNFLOW LOW -alarm message displayed when pressure sensor (380) detects either a low pressure (second fan (320) is not operating fully! at all) or a high pressure (third filter (310) is blocked or impaired) which are outside of the predetermined parameters, implying that there could be insufficient filtered air being provided to the working space -displays alongside the alarm button (30) and audible alarm is triggered.

INFLOW LOW -alarm message displayed when inflow airflow drops below a predetermined limit -displays alongside the alarm button (30) and audible alarm is triggered.

Each of the predetermined limits can be accessed and setl re-set through an Engineer's menu. In this case, each of the buttons (30 -35) also provides a second function in the event that an Engineer's menu has been accessed. The second function of each button transition is shown in Figure 11.

To enter the Engineer's menu, the button (32) is held down for more than seconds. The first item of the Engineer's menu is displayed on the display (36).

In this mode, the fan! control circuit button (30) operates instead as a NEXT button (30a) to shunt through the various predetermined limits as shown down the left hand side of Figure 12, the fumigate button (33) operates instead as an ENTER button (33a) to allow the limits of a predetermined limit to be selected, the lights button (31) and the mute alarm button (34) operate instead as an button (31a) or.j button (34a) to increase or decrease a value of a predetermined limit, respectively. To exit the Engineer's menu, the button (32a) is held down for more than 5 seconds. To start or stop the fans in this mode, the button (35a) is used.

Once in the Engineer's menu, the first item of the Engineer's menu (LOW ALARM SETPOINT) is displayed on the display (36). The sequence of menu items is shown in Figure 12. To view the limit for a particular predetermined limit, the NEXT button (30) is used to navigate to the required predetermined limit.

ENTER (33) is used to select a predetermined limit and view the limit. The button (31a) or the j. button (34a) is used to re-set the limit of a predetermined limit, respectively.

In everyday use, the cabinet start-up sequence is as follows: 1. Switch cabinet ON using the fan button (30).

2. The control system checks and confirms the main extract system is operating correctly within safe limits (pre-set) -display AIRFLOW STABILISING.

3. Once confirmed that the main extract system is operating correctly within safe limits, the internal fans (20, 200, 320) will start to run -display AIRFLOW STABILISING.

4. The internal fans (20, 200, 320) reach optimum speed -display AIRFLOW STABILISING.

5. The airflow limits are checked and confirmed to be within pre-set limits -display AIRFLOW SAFE.

6. The cabinet is operational and can be used as normal.

The control panel (28, 280) is pre-programmed to provide a no-start override" operation in response to an operator's re-start command following a mandatory shut-down in the event of an external extract system failure. The cabinet will not re-start until the problem has been rectified due to a constant pressure feedback from the pressure sensors (18, 1801 37, 370/ 380) overriding the re-start operation if the pressures are not detected within the predetermined limits.

The control panel (28, 280) improves the efficiency of the operation of the components in the cabinet. Furthermore, the pre-programmed operations of the control panel (28, 280) also work to remove human error.

In the first embodiment of the invention (a Class I cabinet), as shown in Figures 1 -4, the upper chamber (13) comprises an auxiliary unit mounted upon the top of a basic unit forming the lower working chamber (11). The control panel (28) is provided below the air grille (26) in the door (27). In use, the fan (20) is arranged to draw contaminated air in from the working space (12) through the first (double) filter arrangement (17) into the lower sub-chamber (22) as indicated (now filtered air), thereby indirectly drawing laboratory air through the opening (14) in the front panel (15) and into the working space (12). The first fan (20) also forces the filtered air into the upper sub-chamber (23) and through the damper (21). A remote external second fan (part of an external extract system -not shown) located in the extraction duct (24), draws the filtered air along with laboratory air through the regulator (25), through the second filter (19) and into the extraction duct (24). Therefore, the airflow through the second filter (19) is a mixture of filtered air originally from the lower working chamber (11) and laboratory air entering via the regulator (25).

In the second embodiment of the invention (a Class II cabinet), shown in figures 5 -8, the secondary fan (320) is arranged to draw contaminated air from the working space (120) and from outside the cabinet (laboratory air) through the channel (330) for circulation downwards through the third filter (310) back into the working space (120) as filtered air. This function continuously replenishes the working space (120) with filtered air and removes the contaminated air, but further functions to ensure that no contaminated air from the working space leaks out through the access aperture (140), by making sure that air is constantly being drawn in through said access aperture (140). The secondary fan (320) also directs a proportion of the air in the channel (330) upwards to the upper chamber (130) which helps to maintain the necessary intake of air through the opening (140) when the unit is being used. The first fan (200) located in the upper chamber (130) draws the air from the channel (330) (a mix of laboratory and contaminated air) up through the first filter arrangement (170) into the upper chamber (130). The first fan (200) also forces the filtered air into the upper sub-chamber (230) through the damper (210). A remote external second fan (part of an external extract system -not shown) located in the extraction duct (240), draws the filtered air along with laboratory air through the regulator (250), through the second filter (190) and into the extraction duct (240). Again, the airflow through the second filter (190) is therefore, a mixture of filtered air originally from the lower working chamber (110) and laboratory air entering via the regulator (250).

In both embodiments, overall, through a combination of positive and negative pressures created by the first fan (200) and the secondary fan (320), air flow through the cabinet is efficient and the air in the upper sub-chamber is either filtered to a high standard or required no or little filtering in order to be considered uncontaminated and safe. Therefore, should the external extraction system fail, the cabinet can still operate to provide decontaminated air.

Furthermore, in both embodiments, by the time any previously contaminated air is being extracted to the external environment through the duct (24, 240), it has been filtered by no less than three HEPA filters and meets the standards for extraction.

Further still, in both embodiments, the regulator serves a valuable function:-by providing laboratory air intake into the upper sub-chamber, the lower chamber (11, 110) and the lower sub-chamber (22, 220) can be isolated from external extraction (by closing the damper (21, 201)) or the cabinet can be shut off, without having to shut off the external extraction system, because laboratory air would still be extracted. In contrast, if no laboratory air intake was provided in the upper sub-chamber (23, 230) and the damper (21, 210) was closed, this would create an unwanted vacuum in the upper sub-chamber (23, 230). The constant laboratory air intake into the upper sub-chamber offers constant extract volume irrespective of cabinet state and maintaining negative room pressures whether the cabinets is on, off or being fumigated.

However, the problem with providing laboratory air intake at this point is that the laboratory air intake disturbs the airflow path of the damper extracted (filtered) air, which causes unwanted turbulence and inefficient extraction through the second filter (19, 190) and the duct (24, 240). The use of the regulator (25, 250) at the intake point controls the flow of the air into the path of the damper extracted (filtered) air, thereby reducing turbulence and improving the efficiency of the extraction process, thereby solving the turbulence problem.

Although a few preferred embodiments have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention.

Claims

CLAIMS1. A microbiological safety cabinet comprising a housing, said housing comprising: a lower chamber providing a working space with a worksurface and an access aperture; an upper chamber appended to the lower chamber; and a front panel on said upper chamber comprising an air grille therein; a duct appended to the upper chamber for connection to an external exhaust system; the upper chamber comprising: a damper defining upper and lower sub-chambers; a double filter disposed in said lower sub-chamber; C') a second filter disposed in said upper sub-chamber; a fan disposed between the double filter and the damper; and 0 an opening located in said upper sub-chamber between the 8 damper and the second filter and positioned substantially behind the air grille; wherein the fan is arranged to draw air from the working space through said double filter with at least a proportion of air being drawn in through said access aperture, a remote fan of the external exhaust system being operative to draw air through the second filter which is a combination of filtered air from the lower chamber and room air entering through the grille and subsequently through the upper sub-chamber opening, characterised in that the upper sub-chamber opening comprises an airflow regulator there across.
2. The cabinet according to claim 1, wherein the airflow regulator comprises a pertorated metal sheet.
3. The cabinet according to claim 2, wherein the perforated metal sheet comprises circular perforations therein and comprises up to approximately 50% open area.
4. The cabinet according to claim 2, wherein the perforated metal sheet comprises at least one substantially horizontal or vertical slot therein, arranged in a row(s) and/or column(s) and comprises up to approximately 50% open area.
5. The cabinet according to claim 4, wherein the (or each) slot comprises a width:depth size ratio of between approximately 8:1 and approximately 5:1.
6. The cabinet according to any one of claims 1 to 5, wherein the damper is electronically connected and operated by a control panel.
7. The cabinet according to any one of claims 1 to 6, wherein the lower working chamber comprises a lower working space and a secondary sub-chamber. C')
8. The cabinet according to claim 7, wherein the lower working space and secondary sub-chamber are separated by a third filter provided across an 0 upper portion of the lower chamber.

CO
9. The cabinet according to any one of claims 7 or 8, wherein the lower chamber comprises a channel leading from a location adjacent the access aperture to said secondary sub-chamber and travels below the worksurface and behind the rear wall of the lower chamber to said secondary sub-chamber.
10. The cabinet according to any one of claims 7 to 9, wherein in the secondary sub-chamber there is disposed a secondary fan operable to draw contaminated air from the working space and from outside the cabinet (laboratory air) through the channel.
11. The cabinet according to claim 10, wherein the secondary fan re-circulates laboratory air from said channel downwards through the third filter into the working space as filtered air and a proportion of the air in the channel upwards to the upper chamber.
12. The cabinet according to claim 11, wherein the damper isolates the lower chamber and the lower sub-chamber from the upper sub-chamber.
13. A microbiological safety cabinet comprising a housing, said housing comprising: a lower chamber providing a working space with a worksurface and an access aperture; an upper chamber appended to the lower chamber; and a duct appended to the upper chamber for connection to an external exhaust system; the upper chamber comprising: a damper defining upper and lower sub-chambers; a double filter disposed in said lower sub-chamber; a second filter disposed in said upper sub-chamber; C') a fan disposed between the double filter and the damper; and an opening located in said upper sub-chamber between the damper 0 and the second filter; CO wherein the fan is arranged to draw air from the working space through said double filter with at least a proportion of air being drawn in through the access aperture, a remote fan of the external exhaust system being operative to draw air through the second filter which is a combination of filtered air from the lower chamber and room air entering through the upper sub-chamber opening, characterised in that the cabinet comprises an automated failure detection system for monitoring and reacting to the safety status of the external exhaust system.
14. The cabinet according to claim 13, wherein the failure detection system comprises an alarm.
15. The cabinet according to any one of claims 13 or 14, wherein the failure detection system allows for continued operation of the cabinet and exit of filtered air through the upper sub-chamber opening during failure of the external exhaust system.
16. The cabinet according to any one of claims 13 to 15, wherein the failure detection system comprises at least one pressure sensor provided on a printed circuit board (POB).
17. The cabinet according to claim 16, wherein the pressure sensors monitor and react to changes in pressure in one or more chambers in the cabinet and the (or each) pressure sensor activates said alarm(s) when the sensor(s) detect(s) a change in pressure in one or more chambers of the cabinet that are outside of predetermined acceptable pressure parameters.
18. The cabinet according to any one of claims 13 to 17, wherein the failure C') detection system comprises a no start override' function once the cabinet is swilched off.

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19. The cabinet according to claim 18, wherein the no start override' function CO comprises an on-going pressure feedback routine that prevents re-start of a cabinet until all pressures return to being within the predetermined acceptable pressure parameters.
20. A microbiological safety cabinet comprising a housing, said housing comprising: a lower chamber providing a working space with a worksurface and an access aperture; an upper chamber appended to the lower chamber; and a duct appended to the upper chamber for connection to an external exhaust system; the upper chamber comprising: a damper defining upper and lower sub-chambers; a double filter disposed in said lower sub-chamber; a second filter disposed in said upper sub-chamber; a fan disposed between the double filter and the damper; and an opening located in said upper sub-chamber between the damper and the second filter; wherein the fan is arranged to draw air from the working space through said double filter with at least a proportion of air being drawn in through the access aperture, a remote fan of the external exhaust system being operative to draw air through the second filter which is a combination of filtered air from the lower chamber and room air entering through the upper sub-chamber opening, characterised in that the cabinet comprises a pressure detection system for monitoring the operational condition of the second filter. C')
21. The cabinet according to claim 20, wherein the pressure detection system comprises at least one pressure sensor.

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22. The cabinet according to claim 21, wherein a first pressure sensor located between the lower chamber and the double filter is operable to monitor the pressure in the double filter.
23. The cabinet according to claim 22, wherein the double filter comprises a fixed orifice plate, which constricts the flow, and measures the pressure differential.
24. The cabinet according to any one of claims 20 to 23, wherein a second pressure sensor located between the extraction duct and the second filter in the upper sub-chamber is operable to monitor the functionality of the second filter and the external extraction system.
25. The cabinet according to claim 20, wherein where the lower working chamber comprises a secondary sub-chamber, a third pressure sensor is operable to monitor the functionality of the third filter and the secondary fan in order to ensure a constant flow of air through the access aperture.
26. The cabinet according to any one of claims 21 to 25, wherein each pressure sensor activates said fault detection system when the sensor(s) detect(s) a change in pressure in one or more chambers of the cabinet that are outside of predetermined acceptable pressure parameters.
27. A unit substantially as described herein with reference to the accompanying Figures. C') Co