Text Equivalent - Chapter 11 - Biological Safety Cabinets - Canadian Biosafety Standards and Guidelines (CBSG) - First Edition

Figure 11-1a: Class I BSC

In this figure, a Class I BSC is hard-ducted and used in conjunction with the building’s HVAC system. Room air is drawn through the front opening of the cabinet and moves across the negatively-pressurized workspace. It is then drawn through an air grille situated at the rear of the cabinet, and flows up a duct where it is HEPA-filtered and is discharged to the outside environment.

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Figure 11-1b: Class I BSC

In this figure, a Class I BSC is shown with a motor and blowing assembly. Room air is drawn through the front of the cabinet and moves across the negatively pressurized workspace. It is then drawn through an air grille situated at the rear of the cabinet and flows up a duct where it is HEPA-filtered. The filtered air is discharged into the containment zone.

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Figure 11-2: Class II Type A1 BSC (with a positively pressured contaminated plenum)

In this figure, a Class II Type A1 BSC is shown with a thimble connection and a positively pressured plenum. HEPA-filtered air from the top of the cabinet flows downwards towards the work surface. Above the work surface and halfway between the front and rear grilles, the potentially contaminated downflow air splits in two. One half of the downflow air passes through the front grille while the other half passes through the rear grille. Room air is also drawn into the front grille. The room and downflow air are drawn through the grilles and into the negatively pressured chamber underneath the work surface. The air is then collected in the positively-pressured plenum and flows to the top of the cabinet. A portion of this air is recirculated and passes through the HEPA filter in the plenum before flowing once again towards the work area. The other portion passes through the HEPA filter located at the base of the thimble connection and is exhausted into the containment zone. The Type A1 BSC shown here only contains a positively-pressured plenum.

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Figure 11-3: Class II Type A1 (with a negatively pressured plenum)/Type A2 BSC

In this figure, the BSC contains a thimble connection, and a positively pressured plenum surrounded by a negatively pressured plenum. HEPA-filtered air from the top of the cabinet flows downwards towards the work surface. Above the work surface and halfway between the front and rear grilles, the potentially contaminated downflow air splits in two. One half of the downflow air passes through the front grille while the other half passes through the rear grille. Room air is also drawn into the front grille. The room and downflow air are drawn through the grilles by the negatively pressured plenum underneath the work surface. The air flows up the negatively pressured plenum and into the positively pressured plenum at the top of the BSC. A portion of this air is recirculated and passes through the HEPA filter in the plenum before flowing once again towards the work area. The other portion passes through the HEPA filter located at the base of the thimble connection and is exhausted into the containment zone or directly to the outside atmosphere through the thimble connection.

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Figure 11-4: Class II Type B1 BSC

In this figure, a Class II Type B1 BSC is shown with a hard-ducted connection to the building’s HVAC system. HEPA filtered air from the plenum flows downward and splits into two streams directly above the work surface, halfway between the front and rear grilles. More than half of the air is directed through the rear grille and flows up the side plenums. Meanwhile, room air and less than half of the downflow air are drawn through the front grille, passes through the HEPA filter beneath the work surface, and collected in the positively pressured plenums. The filtered air flows up the side plenums and accumulates at the top of the BSC. A portion of HEPA filtered air flows downwards over the work area while the other portion flows through a HEPA filter before being exhausted out of the BSC.

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Figure 11-5: Class II Type B2 BSC

In this figure, a Class II Type B2 BSC is shown with a hard-ducted connection to the building’s HVAC system. A supply blower draws room air into the top of the cabinet. The air from the plenum and the room air from the supply blower are physically separated. Room air is drawn into the top of the cabinet by the supply blower and is directed past the HEPA filter before being discharged downward into the cabinet work space. The downflow air splits into two streams directly above the work surface, halfway between the front and rear grilles. Room air is also drawn through the front grille before it can reach the work surface. The air directed through the grilles is collected in the negatively pressured plenum beneath the work surface and flows to the top of the cabinet. It then passes through the HEPA filter and is directly vented to the outside atmosphere.

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Figure 11-6: Class III BSC

In this figure, a Class III BSC is shown with hard ducted supply and exhaust air. The BSC is completely enclosed; all penetrations are air-tight, and the BSC is kept under negative pressure. Manipulations are performed through attached heavy-duty long-sleeved gloves. Air from the supply duct is HEPA-filtered before entering the cabinet and circulates within the work space. The air from the work space is drawn into the exhaust duct and passes through two consecutive HEPA filters before being vented to the outside atmosphere.

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