It is often our experience that when a customer inquires about the purchase of a Class II, Type B2 Total Exhaust biological cabinet, they have the misconception that this configuration offers superior biological containment to a Class II, Type A2 cabinet. The decision to use a Type B2 cabinet is one that should be carefully weighed. Type B2 cabinets are specifically designed for applications when the microbiological work requires the use of volatile toxic chemicals or radionuclides.
Airflow through a B2 cabinet is similar to that of a fume hood, externally exhausting 100% of the air pulled through the cabinet. The purpose of this design is to completely remove any toxic chemical vapors or radioactive compounds that are generated inside the cabinet. Room air is brought into the cabinet through both an opening in the top of the cabinet and through the inlet grille. This air flows through an initial HEPA filter and then downward through the work area. All of the contaminated air is then drawn into a negatively pressured plenum and exhausted through a second HEPA filter. A dedicated exhaust system and remote blower draw all of the filtered exhaust air out of the laboratory.
In contrast, Type A2 biological safety cabinets only exhaust about 30% of their total airflow, with the remaining 70% being recirculated within the cabinet. Room air is drawn into the cabinet through the inlet grille where it mixes with air that has just passed through the work area. This contaminated air is pulled by the blower through a negatively pressured plenum, where approximately 70% is recirculated through the supply HEPA filter and back over the work area. The balance of the contaminated air is forced though the exhaust HEPA filter and either exhausted back into the room or ducted externally using a canopy connection.
More often than not, Type B2 cabinets cabinets are unnecessarily chosen over Type A2 because there is a perception that they are either safer or more versatile. In terms of safety, Type A2 and Type B2 cabinets are equally safe. Since both types utilize HEPA filtration, the protection against biological contamination of the user, laboratory, and work area within the cabinet is the same. Both may be used with agents requiring Biosafety level 1, 2, or 3 containment. In terms of versatility, Type B2 cabinets are far more limited. Installation of a B2 cabinet requires permanent ducting whereas an A2 cabinet is usually installed without ducting, but, can be ducted if the work generates noxious odors or involves minute quantities of chemicals.
It is worth noting that the cost of purchasing, installing, and operating a B2 cabinet is usually 2-3 times higher than an A2 cabinet. Initial costs include ductwork and the dedicated remote blower. Operating costs include increased electrical power consumption over an A2 cabinet. This figure does not account for the enormous amount of tempered air removed from the laboratory, which itself is another significant expense.
When making a biosafety cabinet purchase, carefully consider the planned application of the equipment. Unless the work involves volatile toxic chemicals or radionuclides, a Type B2 cabinet is not the appropriate choice. A Type A2 cabinet will provide the same level of protection against biological contamination, while being more versatile and less expensive to purchase, install, and operate.
Purifier® Logic™ Class II Type A2 Biosafety Cabinet
Purifier Logic Class II Type B2 Biosafety Cabinet
Photos courtesy of Labconco