Which subtype of BSC Class II indicates that most of the work surface area is exhausted outside?

The subtype of BSC Class II that indicates most of the work surface area is exhausted outside is indeed B1. This subtype is designed specifically to protect the sterile materials and the personnel working in the biosafety cabinet while allowing for a greater portion of airflow to be exhausted directly from the cabinet to the outside environment.

In Class II B1 biosafety cabinets, the airflow dynamics are structured such that they create a balance between the sterile environment needed for compounding and the safety required to handle hazardous materials. This design minimizes the risk of exposure to contaminants while maximizing the efficiency of exhaust ventilation.

In contrast, other subtypes like A1 and A2 have different airflow configurations that may recirculate some of the air back into the work area. B2, while also a Class II cabinet, relies on a different exhaust system that often requires connection to a dedicated external vent. Therefore, it does not focus as much on exhausting most of the work area directly outside as B1 does.