It is a device used for preparing chemicals, drugs, and samples, designed to protect against biological or infectious agents and to help maintain quality control of the materials being worked with by filtering both the airflow and exhaust. It is sometimes referred to as laminar flow or tissue culture hood. The airflow is exhausted through B2 100% externally, meaning that the air drawn into the cabinet is exhausted 100% into the atmosphere. None of the air drawn into B2 is recycled, whether for internal or lower airflow within the air flow system.