A. Installation

The cabinet should be located in a space that is free from drafts and traffic. Air conditioning vents, opening doors, and personnel traffic can produce air currents, which may penetrate the air barriers at the front opening of the cabinet. The ideal location for BSCs is a “dead-end” area of the laboratory. Nearby HVAC vents should be directed away from the BSC. Provide a clearance of 12-14 inches (30-35 cm) above Class II, type A1, A2, cabinets to allow access for accurate exhaust flow measurements and filter replacement.

The Class II, type A1 or A2 BSC is built to exhaust air back into the laboratory; therefore, it is generally best not to connect a duct to the cabinet. If a duct is connected by a canopy, the remote exhaust fan must be the correct size to match precisely the exhaust air volume from the cabinet. The canopy duct must not interfere with requirements for certification tests and filter replacement. Make sure the exhaust filter is accessible.

Type A or A2 cabinets with a canopy connected and exhausted by a remote fan should have an audible and visual alarm to indicate a loss of exhaust airflow.

The exhaust fan should interlock with the cabinet fan switch, so that both fans are either “on” or “off” at the same time. If the cabinet fan is “off” on a Class II, type A1 or A2 cabinet but the exhaust fan is “on”, the exhaust fan will pull room air contaminants through the cabinet and the supply filter in the opposite direction of normal cabinet operation. The clean side of the supply filter is therefore contaminated. When someone turns “on” the cabinet, the airflow through the supply filter is now flowing in the correct direction, and contaminants can dislodge from the filter media into the clean work area of the cabinet.

Class II, type B1 and B2 cabinets by design must duct to the outside using a remote exhaust fan, usually located on the roof. Once the cabinet is set or certified in its acceptable airflow range, audible and visual alarms shall be required to indicate a 20% loss of exhaust volume within 15 seconds. The internal cabinet fans shall be interlocked to shut off at the same time the alarms are activated.

To size the exhaust fan correctly, consult the cabinet manufacturer to obtain the pressure drop through the cabinet with fully loaded filters. For some older models, the exhaust filter is located on the roof just upstream from the fan. The maintenance technician uses a bag-in / bag-out filter assembly so that he/she does not have to handle a contaminated filter directly. Upstream and downstream certification test ports and isolation dampers for formaldehyde gas decontamination are also necessary.

The use of open flame burners is not allowed in Biological Safety Cabinets of Type A1 and Type A2 at UNC. Biosafety Cabinets of Type A1 and Type A2 currently in use must have their gas lines removed or disconnected. New BSC installations of Type A1 and Type A2 will not be connected to gas lines. The full Policy on the use of Flammable Gases in Biological Safety Cabinets is on the UNC website.

B. Certification

A BSC certifier tests and evaluates the performance of each BSC after initial installation in the laboratory, prior to use, whenever moved, and periodically thereafter. The following are typical field tests: downflow velocity profile for the supply air, work access opening airflow, HEPA filter leak test, cabinet integrity test, and airflow smoke patterns.

NSF Standard No. 49 describes certification field tests. NSF also accredits BSC certifiers. Recertification of the cabinet is necessary when the HEPA filters are changed, maintenance repairs are required, or when a cabinet is relocated. BSCs require decontamination with formaldehyde gas before maintenance work or filter changes, after gross spills of biohazardous materials, and before moving the cabinet.

Contact EHS for recommended certifiers at UNC.