How a Class II, Type B2 Biosafety Cabinet Works

Class II Type B2 biosafety cabinet, the inflow into the front access opening provides personnel protection, the filtered and laminar downflow in the work zone provides product protection, and the filtered exhaust provides environmental protection, just like they do in any Class II biosafety cabinet. However, the Type B2 cabinet cannot function autonomously. It must be matched with an external exhaust blower that has enough power to not only pull the inflow into the front of the cabinet but also continue to pull the exhaust air through and out of the cabinet and inside the ductwork towards itself. The internal motor’s only contribution is to draw new air in from the room through an opening at the top of the cabinet and propel it past the supply HEPA filter towards the work zone to provide downflow. Suppose the external exhaust blower stops working and no longer creates enough “pull” to keep air flowing toward the work zone. In that case, it is critical that the internal blower no longer force air down into that work zone where it can ultimately flow out towards the user and carry hazardous particles with it. Under normal operation, the air that the internal blower pushes down into the work zone merges with the air that is sucked into the front access opening. Together, both are pulled out of the cabinet entirely by the external exhaust blower. No air is ever rerouted back to the work zone downflow.

REFERENCES

• NSF International. NSF/ANSI 49-2019. Biosafety Cabinetry: Design, Construction, Performance, and Field Certification. 2020.
• Centers for Disease Control and Prevention. Biosafety in Microbiological and Biomedical Laboratories (BMBL) 5th edition. Appendix A. Atlanta, GA: CDC, 2009.
• Controlled Environment Testing Association. CETA Application Guide for the Exhaust System Requirements of Class II, Type B Biosafety Cabinets. CAG-007-2010. March 24, 2010.
• Controlled Environment Testing Association. CETA Application Guide CAG-007: Exhaust System Requirements of Class II Biosafety Cabinets. CAG-007. Revised September 2020.