Low airflow exhaust canopy for biological cabinets   

This application claims priority to, and the benefit of, co-pending U.S. Provisional Application No. 61/003,967, filed May 28, 2008, for all subject matter common to both applications. The disclosure of said provisional application is hereby incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The present invention relates to canopies for biological cabinets, and more particularly to a canopy for a biological cabinet having one or more intake dampers and one or more outlet dampers for regulating the airflow through the canopy.

BACKGROUND OF THE INVENTION

A biological cabinet, known also as a biological safety cabinet or a biosafety cabinet, is a ventilated cabinet that uses a variety of combinations of air filters, unidirectional airflow, and systems of containment to provide personnel, product, and cross contamination against particulates or aerosols from bio-hazardous agents. Conventional biological cabinets include one or more High Efficiency Particulate Arresting (HEPA) filters, although other types of air filters may be used as well. A HEPA filter is a type of air filter that can remove at least 99.97% of airborne particles down to 0.3 micrometres (μm) in diameter.

Typically, biological cabinets have a front access opening allowing the user to gain physical access to a working area or a chamber within the cabinet. The user can close off the front access opening using a door, a panel, or the like, which is done for purposes of conducting experiments or some process within the cabinet that would emit hazardous byproducts or germicidal (ultraviolet) light. A biological cabinet may include a canopy provided on top of the work chamber. The entire air exhausted from the work chamber is introduced into the canopy that is hard-connected to an external exhaust system.

Existing canopy designs provide air chambers with gaps or openings sized to enable sufficient air flow through the cabinet should the exhaust system fail. If the exhaust air cannot leave the biological cabinet at the desired rate due to an exhaust system failure, the canopy provides a place for the air to flow to enable the cabinet to maintain a desired airflow in the work chamber. However, when the exhaust system is functioning normally, the gaps or openings still remain in the conventional canopies. The existence of these open gaps forces a requirement that more room air be pulled into the system and flushed out through the exhaust to keep up with and capture all the exhaust airflow leaving the biological cabinet. Exhausting more room air that comes through the cabinet results in losing more conditioned air and running the building exhaust system at a higher flow level, which equates to higher energy costs for the building.

SUMMARY

The present invention recognizes a need to reduce the volume of room air taken into the canopy when an exhaust system coupled with the canopy operates normally, while still maintaining the ability to offer air relief during exhaust system fluctuations or failures.

In accordance with one aspect of the present invention, a biological safety cabinet includes a plurality of walls defining a first chamber having an internal environment therein. A canopy is configured to receive exhaust airflow from the first chamber. The canopy includes a pair of side panels, a front panel, a top panel and a back panel defining a second chamber having an internal environment therein. One or more intake ports are provided on the canopy. Airflow through the one or more intake ports is controlled by one or more intake dampers. One or more outlet ports are provided on the canopy. Airflow through the one or more outlet ports is controlled by one or more outlet dampers. An opening is connected to an external exhaust system for exhausting air inside the second chamber to the external exhaust system. The external exhaust system pulls a pre-determined amount of air from the second chamber.

The one or more intake dampers may be configured to open toward the internal environment of the second chamber. The one or more intake dampers may open when the external exhaust system pulls more air than the pre-determined amount of air from the second chamber. The one or more outlet dampers may be configured to open toward an environment external to the biological cabinet. The one or more outlet dampers may open when the external exhaust system pulls less air than the pre-determined amount of air from the second chamber.

In accordance with various aspects of the present invention, a biological safety cabinet may include an air baffle provided below the top panel of the canopy. The air baffle may be configured to guide air from the internal environment of the second chamber to the opening connected to the external exhaust system.

In accordance with various aspects of the present invention, a biological safety cabinet may include one or more removable brackets inserted inside of the one or more intake ports. The one or more intake dampers may cover end portions of the one or more removable brackets.

In accordance with aspects of the present invention, a method of regulating air inside a canopy of a biological cabinet includes providing a biological cabinet. The biological cabinet includes a plurality of walls defining a first chamber having an internal environment therein and a canopy coupled to the first chamber. The canopy includes a pair of side panels, a front panel, a top panel and a back panel defining a second chamber having an internal environment therein. One or more intake ports are provided on the canopy. Airflow through the one or more intake ports is controlled by one or more intake dampers. One or more outlet ports are provided on the canopy. Airflow through the one or more outlet ports is controlled by one or more outlet dampers. An opening is connected to an external exhaust system for exhausting air inside the second chamber to the external exhaust system. The method further includes supplying air exhausted from the first chamber into the second chamber. The external exhaust system pulls a pre-determined amount of air from the second chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become better understood with reference to the following description and accompanying drawings, wherein:

FIG. 1A is a perspective view of a biological cabinet, in accordance with one embodiment of the present invention;

FIG. 1B is a perspective view of a canopy of the biological cabinet illustrated in FIG. 1A, in accordance with one embodiment of the present invention;

FIG. 1C is a close-up cutaway view of the side of the canopy;

FIG. 1D is a side panel of the canopy including an intake port and an intake damper covering the intake port;

FIG. 1E is a front cutaway view of the canopy including an internal air baffle and a pair of brackets;

FIG. 1F is a close-up view of a bracket illustrated in FIG. 1E;

FIG. 2A is a perspective view of the canopy illustrating the airflow inside the canopy with air entering the canopy through the intake ports;

FIG. 2B is a front view of the canopy illustrating the airflow inside the canopy with air entering the canopy through the intake ports;

FIG. 3A is a perspective view of the canopy illustrating the air exiting the canopy through the outlet port;

FIG. 3B is a side view of the canopy illustrating the airflow inside the canopy with air exiting the canopy through the outlet port; and

FIG. 4 is a flowchart illustrating a method of regulating airflow inside the canopy of the biological cabinet using the intake and outlet ports.

DETAILED DESCRIPTION

An illustrative embodiment of the present invention relates to a canopy with intake and outlet ports to be used with Class II, Type A1/A2 biological cabinets. Air exhausted from a Class II, Type A1/A2 biological cabinet may be exhausted back into the room. Alternatively, air exhausted from a Class II, Type A1/A2 biological cabinet can be exhausted into a canopy connected to a building exhaust system. A canopy exhaust connection is normally required when Class II, Type A1/A2 biological cabinets exhaust air from the cabinet to the outside atmosphere. The canopy is connected to an external exhaust system, i.e. a building exhaust system, and is positioned over an exhaust opening in the cabinet, surrounding the exhaust opening. The purpose of the canopy is to capture and pass through to the outdoors all of the air being exhausted from the cabinet when the building exhaust system is operating properly, and to relieve air to the room when the exhaust is inadequate to pull the correct volume of air from the cabinet, and conversely, to send more air directly from the room rather than from the cabinet when the exhaust air volume is more than the correct volume. The increase or decrease of air supply (as needed) enables the biological cabinet to maintain a constant volume of intake level of intake airflow at its front access opening.

Air relief is conventionally provided through a gap between the canopy and cabinet or opening(s) in the canopy. Room air being pulled in through the gap and/or opening(s) in the canopy by the building exhaust system allows the canopy to capture all of the air being exhausted from the working chamber of the biological cabinet. The size and location of the gap and/or opening(s) may greatly affect the canopy performance. In general, the larger the gap and/or opening(s), the more airflow required to capture all the cabinet exhaust air. If the building exhaust system fails to operate, the canopy gap and/or opening(s) will enable the cabinet exhaust air to exit back into the room. This air relief will enable the biological cabinet to maintain an acceptable level of intake airflow at its front access opening, and through the work chamber, as long as the gap and/or opening(s) are sized properly. In general, the larger the gap and/or opening(s), the easier it is for the cabinet to exhaust back into the room during building exhaust system failure. Accordingly, it is the requirement to adapt to a failed exhaust system that primarily dictates the minimum required size of the gaps and/or openings to result in the desired volume of air flow. However, when the cabinet is operating normally, the larger the gaps and/or openings, the greater the capacity must be of the exhaust system. With more airflow required through the exhaust system, there is an increased energy requirement to generate that airflow, and more conditioned air is unnecessarily exhausted.

The present invention differs from conventional devices in that it reduces the volume of air required to be handled by the exhaust system during normal exhaust system operation, and offers the same air relief as conventional systems. This is primarily achieved through the use of openings, referred as ports, in the canopy covered by air dampers, such as flaps, designed to open and close on an as-needed-basis. The dampers are unique and an integral part of the canopy design that allow operation at lower airflows during normal operation relative to conventional canopies. If the building exhaust system fluctuates or fails and tries to pull more or less air than is required, the canopy will compensate for the fluctuation by either letting more air in through one or more intake ports or more air out through one or more outlet ports, as needed.

Prior to discussing the details of the invention, a brief overview of the different biological cabinets will be provided. A biological safety cabinet is designed to reduce the potential escape of airborne research or experimental materials and byproducts into the worker\'s environment, i.e. the work chamber, and to remove contaminants from air entering the research work zone. A laminar flow biological safety cabinet is designed to provide three basic types of protection: personnel protection from harmful agents inside the cabinet, product protection to avoid contamination of the work, experiment or process, and environmental protection from contaminants contained within the cabinet. In addition, the cabinet will provide cross contamination protection in the work zone to prevent airborne particles from traveling from one side of the cabinet to the other side of the cabinet.

Over the years, the scientific community has adopted commonly accepted classification criteria to differentiate containment capabilities and performance attributes of biological safety cabinets. In general, biological safety cabinets are divided into 3 classifications as illustrated in Table 1.

TABLE 1 Biological Classification Level Application Class I 1, 2, 3 low to moderate risk biological agents Class II 1, 2, 3 low to moderate risk biological agents Class III 4 high risk biological agents

Biological Level 1 encompasses practices, safety equipment and facilities appropriate for work with defined and characterized strains of viable microorganisms not known to cause disease in healthy adult humans. Work is generally conducted on open bench tops using standard microbiological practices. For biological level 1, special containment equipment or facility design is neither required nor generally used.

Biological Level 2 encompasses practices, safety equipment and facilities appropriate for work done with a broad spectrum of indigenous moderate-risk agents present in the community and associated with human disease in varying severity. It differs from biological level 1 in that laboratory personnel have specific training in handling pathogenic agents and are directed by competent scientists; access to the laboratory is limited when work is being conducted; extreme precautions are taken with contaminated sharp items; and certain procedures in which infectious aerosols or splashes may be created are conducted in biological cabinets or other physical containment equipment. A Class I or Class II biological cabinet is recommended for work involving these agents.

Biological Level 3 encompasses practices, safety equipment and facilities appropriate for work done with indigenous or exotic agents with a potential for respiratory transmission which may cause serious and potentially lethal infection. More emphasis is placed on primary and secondary barriers to protect personnel in the contagious area, the community, and the environment from exposure to potentially infectious aerosols. A Class I or Class II biological cabinet is required for work involving these agents.

Biological Level 4 encompasses practices, safety equipment and facilities appropriate for work done with dangerous and exotic agents which pose a high risk of life threatening disease. Agents may be transmitted via the aerosol route, and for which there is no available vaccine or therapy. Access to the laboratory is strictly controlled by the laboratory director. The facility is either in a separate building or in a controlled area within a building, which is completely isolated from all other areas of the building. Class III biological cabinet or pressurized environmental suits are required for work involving these agents.

The Class I cabinet has the most basic and rudimentary design of all biological cabinets. A stream of inward air moving into the cabinet contains aerosols generated during microbiological manipulations. It then passes through a filtration system that traps all airborne particles and contaminants. Finally, clean, filtered air is exhausted from the cabinet. The filtration system usually consists of a pre-filter and a HEPA (High Efficiency Particulate Air) filter.

Although the Class I cabinet protects the operator and the environment from exposure to biohazards, it does not prevent samples being handled in the cabinet from coming into contact with airborne contaminants that may be present in room air. Naturally, there is a possibility of cross-contamination that may affect experimental consistency. Class I biological cabinets are suitable for work with microbiological agents assigned to biological safety levels 1, 2 and 3.

Like Class I biological cabinets, Class II biological cabinets have a stream of inward air moving into the cabinet. This is known as the inflow and it prevents the aerosol generated during microbiological manipulations to escape through the front opening. However, unlike Class I cabinets, the inflow on Class II cabinets flows through the front inlet grille, near the operator. None of the unfiltered inflow air enters the work zone of the cabinet, so the product inside the work zone is not contaminated by the outside air.

A feature unique to Class II cabinets is a vertical laminar (unidirectional) HEPA-filtered air stream that descends downward from the interior of the cabinet. This continuously flushes the cabinet interior of airborne contaminants and protects samples being handled within the cabinet from contamination and is known as the down flow. Some cabinets may exhaust air directly back to the laboratory, while others may exhaust air through a dedicated ductwork system to the external environment.

Class II cabinets, like Class I cabinets, protect both the operator and environment from exposure to biohazards. In addition, Class II cabinets also protect product samples from contamination during microbiological manipulations within the cabinet interior and are all suitable for work with agents assigned to biological safety levels 1, 2 and 3. Class II cabinets are further classified according to how they exhaust air.

The Class II Type A biological cabinets exhaust air directly back to the laboratory, and they may contain positive pressure contaminated plenums. When toxic chemicals must be employed as an adjunct to microbiological processes, these cabinets are not used. Exhaust HEPA filtration only removes airborne aerosols including biohazards, and not chemical fumes.

In the Class II, Type A1 and Type A2 biological cabinets, Hepa-filtered exhaust air may be recirculated into the room or exhausted to the outdoors through a canopy exhaust connection. The Class II, Type A1 and Type A2 biological cabinets offer product, personnel and environmental protection. Product protection in the Class II, Type A1 and Type A2 biological cabinets is offered by unidirectional (commonly called “laminar”) downflow air in the work chamber, generated by the cabinet blower pushing air through the supply HEPA filter. Personnel protection comes from the intake air pulled into the front access opening of the cabinet. Environmental protection is provided by HEPA filters in the exhaust air stream of the cabinet. Class II, Type A1 and Type A2 biological cabinets may be used with biosafety levels 2 and 3.

The main difference between Class II type A and type B cabinets is that the type B cabinets must be operated with an external blower, which exhausts air to the external environment via a dedicated ductwork system. Without the external blower, the cabinet\'s internal blower will blow the air (and microbiological agents) inside the work zone through the front operator, toward the operators face, creating a dangerous situation.

The Class II Type B1 biological cabinets have a dedicated exhaust feature that eliminates re-circulation when work is performed toward the back within the interior of the cabinet.

In the Class II Type B2 cabinet all inflow and down flow air is exhausted after HEPA filtration to the external environment without recirculation within the cabinet. Type B2 cabinets are suitable for work with toxic chemicals employed as an adjunct to microbiological processes under all circumstances since no re-circulation occurs.

The Class III biological cabinet provides an absolute level of safety, which cannot be attained with Class I and Class II cabinets. Class III cabinets are usually of welded metal construction and are designed to be gastight. Work is performed through glove ports in the front of the cabinet. During routine operation, negative pressure relative to the ambient environment is maintained within the cabinet. This provides an additional fail-safe mechanism in case physical containment is compromised.

On Class III cabinets, a supply of HEPA filtered air provides product protection and prevents cross contamination of samples. Double HEPA filtered exhaust air is required and may also be incinerated. Class III cabinets exhaust air via a dedicated ductwork system to the external environment. When a dedicated ductwork system is employed, they are also suitable for work employing toxic chemicals as an adjunct to microbiological processes. Class III biological cabinets are frequently specified for work involving the most lethal biological hazards.

Now turning to the present invention, FIGS. 1A through 4, wherein like parts are designated by like reference numerals throughout, illustrate an example embodiment of a biological cabinet canopy with intake and outlet ports. Although the present invention will be described with reference to the example embodiment illustrated in the figures, it should be understood that many alternative forms can embody the present invention. One of ordinary skill in the art will additionally appreciate different ways to alter the parameters of the embodiment disclosed, such as the size, shape, or type of elements or materials, in a manner still in keeping with the spirit and scope of the present invention. The airflow bypass system described herein is primarily intended for use in Class II, Type A1/A2 cabinets, but can be utilized with other cabinets if environmental and safety conditions allow.

FIG. 1A illustrates a biological cabinet 150 in accordance with one embodiment of the present invention. The biological cabinet 150 has a first chamber 160 used as the work chamber and a canopy 100 provided on top of, and connected to, the first chamber 160 for collecting air exhausted from the first chamber 160. The user may access the work area through a front access opening 162. The front access opening 162 may be a sliding door, for example. The canopy 100 may be made of sheet metal that is bent and welded into a rectangular shape. Alternatively, the canopy 100 may be made of one or more of materials such as plastic, aluminum, fiberglass, or the like.

According to an embodiment of the present invention, the canopy 100 may be formed integrally with the first chamber. According to yet another embodiment of the present invention, the canopy may be formed integrally with the first chamber and further separated from the first chamber using a partition.

FIG. 1B illustrates a perspective view of the canopy 100 of the biological cabinet illustrated in FIG. 1A. The canopy 100 has a pair of side panels 104, a front panel 106, and a top panel 102. The canopy 100 is open at the bottom and fits on top of the first chamber 160, also referred as the work chamber, of the biological cabinet 150. The front panel 106 may be a slanted panel. A pair of intake ports 108 is provided on the pair of side panels 104. An outlet port 110 is provided on the front panel 106. An opening 116 is provided on the top panel 102. The opening 116 may be connected to an external exhaust system, such as a building exhaust duct. The outlet port 110 may be a one-piece opening. Alternatively, the outlet port 110 may be divided in two or more openings. The outlet port 110 is covered with an external outlet damper 114. The outlet damper 114 is a one-way directional damper that may rotate around a horizontal axis and that can only open toward the environment external to the canopy 100 and cannot open toward the chamber enclosed in the canopy 100. The pair of intake dampers 112 covers the pair of intake ports 108. The pair of intake dampers 112 is one-way directional dampers that may rotate around a horizontal axis and that can only open toward the chamber enclosed in the canopy 100. The intake dampers 112 are restricted from opening toward the environment external to the canopy 100. One of ordinary skill in the art will additionally appreciate that the intake dampers 112 and the outlet damper 114 are interchangeable as to direction of airflow allowed therethrough, location, and plurality. In other words, the present invention is described using an illustrative embodiment in which the air may enter into the canopy 100 through the side and exit from the canopy through the front, however, the locations of these dampers 112 and 114 on the canopy are relocatable during the design and manufacture stage to other locations on the canopy, including on the top of the canopy.

One ordinary skill in the art will appreciate that the intake port 108 and the outlet port 110 may be of a variety of shape and dimensions. According to various embodiments of the present invention, the intake 108 and outlet 110 ports may be of similar shape and dimensions. In alternative embodiments, the intake port 108 and the outlet port 110 may be covered by a flap, a blade, a valve or a similar type of membrane that may serve the same purpose as the intake and outlet dampers 112 and 114.

FIG. 1C illustrates a close-up cutaway view of the side of the canopy 100. A bypass bracket 118 is disposed in each intake port 108 of the canopy 100 and held in place with screws 120 in accordance with one example embodiment of the present invention. According to alternative embodiments, the brackets 118 may be attached to the canopy 100 using various fastening mechanisms such as clamps, glue or welding techniques. According to an alternative embodiment, the brackets 118 and the canopy 100 may be formed as a single piece of hardware. The brackets 118 may be removable to allow access to the fasteners 124 (illustrated in FIG. 1D) used to mount the canopy 100 to the top of the work chamber 160 of the biological cabinet 150. The brackets 118 hold the intake dampers 112 at an angle that gravitationally pushes the dampers toward their closed position. The brackets 118 also deflect air entering the canopy away from the intake ports 108, to prevent the exhaust air from escaping out through the intake ports 112.

FIG. 1D illustrates the side panel 104 of the canopy 100 including an intake port 108 covered with an intake damper 112. As illustrated in FIG. 1D, the bottom of the canopy 100 has a gasket 122 around its perimeter and a plurality of fasteners 124 to attach the canopy 100 to the top of the work chamber 160 of the biological cabinet 150. As further illustrated in FIG. 1D, the outlet port 110 is covered with an outlet damper 114. The outlet damper 114 is held in place at the top with a flexible hinge 130. The hinge 130 allows the outlet damper 114 to rotate freely in an upward fashion outside the canopy 100. However, since the outlet damper 114 is a one-way directional damper, it cannot open toward the chamber enclosed in the canopy 100. The use of hinges 130 to attach the outlet damper 114 to the canopy 100 should not be construed as limiting, different mounting hardware may be used to attach the outlet damper 114 to the canopy 100.

FIG. 1E is a front cutaway view of the canopy 100 including an internal air baffle 126 and a pair of brackets 118. An end of the brackets 118 that stays inside of the chamber enclosed by the panels of the canopy 100 is covered by the intake dampers 112. According to an alternative embodiment, the intake dampers 112 may cover the intake ports 108 directly, without providing the brackets 118, so long as preparations are made to avoid exhaust air escaping through partially open intake ports 108. The internal air baffle 126 helps to capture the cabinet exhaust air 202 (illustrated in FIG. 2A-3B) and direct it out of the opening 116 connected to the building exhaust duct. The air baffle 126 may have a bell mouth exhaust collar that reduces airflow turbulence, or other configurations generally known to those of ordinary skill in the art.

FIG. 1F is a close-up view of a bracket 118 illustrated in FIG. 1E. The bracket 118 is held in place on the side panel 104 of the canopy 100 using a plurality of screws 120. The intake damper 112 is held in place at the top with a flexible hinge 128. The hinge 128 allows the intake damper 112 to rotate freely in an upward fashion toward the interior environment of the canopy 100. However, since the intake damper 112 is a one-way directional damper, the intake damper 112 cannot open toward the environment exterior to the canopy 100. The use of hinges 128 to attach the intake dampers 112 to the canopy 100 should not be construed as limiting, different mounting hardware may be used to attach the intake dampers 112 to the canopy 100.

According to various embodiments of the present invention, the intake and outlet dampers 112 and 114 may be driven mechanically and/or electrically driven instead of by the static pressure differential between the internal environment of the canopy 100 and the external environment. The intake and outlet dampers 112 and 114 may further be sliding, or affixed in another manner suitable for their operation as described. The intake and outlet dampers 112 and 114 may alternatively be counterbalanced or driven by static pressure differential driven by electro-servo mechanisms.

The intake and outlet dampers 112 and 114 are unique and integral part of the canopy 100 that allow the canopy 100 to operate at lower airflows when compared to traditional exhaust canopies. This is because the existence of the intake and outlet dampers 112 and 114 reduces the ability for room air to enter the canopy and be pulled into the exhaust system, thus a lower overall airflow rate and volume pass through the exhaust system. The intake and outlet dampers 112 and 114 are made of light weight material and are easily moved by changes in static pressure between the canopy 100 and room.

During normal operation, as illustrated in FIG. 2A, the outlet damper 114 will be closed and the intake dampers 112 will be slightly open due to a slight negative static pressure inside the canopy 100. The outlet damper 114 blocks the outlet port 110 so that any turbulent air streams inside the canopy 100 created by the cabinet exhaust air 202 do not escape the canopy 100. The intake dampers 112 are pulled slightly open due to the slight vacuum or negative pressure caused by the pull of the exhaust system, which allows a small amount of room air 201 to be pulled into the canopy 100. This small volume of room air passing through the canopy captures any cabinet exhaust air 202 trying to escape through the openings of the biological cabinet 150. Intake and outlet dampers 112 and 114 covering the canopy intake and outlet ports 108 and 110, respectively, help to reduce the need for room air 201 passing through the canopy, thus lowering the overall airflow required for the canopy 100 to operate.

If the building exhaust system fluctuates and tries to pull more air than is required, the intake dampers 112 illustrated in FIG. 2B will open more to allow more room air in through the intake ports 108, thus helping the cabinet 150 to maintain an acceptable level of intake airflow at its front access opening 162.

The intake ports 108 in the canopy 100 provide means for room air 201 to enter the canopy 100 helping to capture the cabinet exhaust air 202 and provide air relief if the building exhaust system fluctuates and pulls more air than is required. The intake dampers 112 with flexible hinge 128 help to reduce the amount of room air 201 required by the canopy to capture the cabinet exhaust air 202. Bypass bracket 118 helps to deflect the cabinet exhaust air 202 away from the canopy intake ports 108 and provides support to the intake dampers 112 when they are closed. Flexible hinge 128 attaches the intake dampers 112 to the bypass brackets 118. The hinge 128 allows the intake dampers 112 to rotate freely in an upward fashion inside the canopy 100.

If the building exhaust system fluctuates or altogether fails and does not pull a sufficient amount of air, as illustrated in FIGS. 3A-3B, the outlet damper 114 will open and let some of the cabinet exhaust air 202 out through the outlet port 110, thus enabling the cabinet to maintain an acceptable level of intake airflow at its front access opening 162. The internal air baffle 126 helps to capture the cabinet exhaust air 202 and direct it out through the opening 116 connected to the building exhaust duct (not illustrated).

The slanted outlet port 110 in the canopy 100 and outlet damper 114 provide means for the cabinet exhaust air 202 to exit back into the room when the building exhaust system fails or fluctuates and does not pull a sufficient amount of air. When the building exhaust system is operating properly, the outlet damper 114 blocks the slanted outlet port 110 in the canopy 100 so that any turbulent air streams inside the canopy 100 created by the cabinet exhaust air 202 do not escape. The internal air baffle 126 helps to capture the cabinet exhaust air 202 and direct it out of the opening 116 connected to the building exhaust duct.

FIG. 4 illustrates a method of regulating the air inside the canopy 100 of a biological cabinet 150 when the external exhaust system fails to pull a pre-determined amount of exhaust air from the canopy 100. If the external exhaust system is operating normally (step 402), i.e. the external system is pulling a pre-determined and desired amount of exhaust air from the canopy 100, the outlet damper 114 is closed and the intake dampers 112 are slightly opened (step 404). If the external exhaust system is not operating normally, the external exhaust system may be pulling more air than the pre-determined amount (step 406) or the external exhaust system may be pulling less air than the pre-determined amount (step 410). If the external exhaust system is pulling more air than the pre-determined and desired amount, the outlet damper 114 remains closed and the intake dampers 112 open more, allowing room air to enter into the canopy 100 (step 408). If the external exhaust system is pulling less air than the pre-determined and desired amount, the outlet damper 114 opens and the intake dampers 112 close allowing exhaust air exit the canopy 100 to the external environment, i.e. the room where the biological cabinet 150 is situated. According to the method illustrated in FIG. 4, the dampers are returned to their original position, i.e. outlet damper 114 is closed, intake dampers 112 are slightly opened, when the external exhaust system is back to normal operation.

Numerous modifications and alternative embodiments of the present invention will be apparent to those skilled in the art in view of the foregoing description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the best mode for carrying out the present invention. Details of the structure may vary substantially without departing from the spirit of the invention, and exclusive use of all modifications that come within the scope of the appended claims is reserved.