DILIGENT make Biological Safety Cabinets are partly-recirculating laminar airflow enclosures with high efficiency particulate air (HEPA) filtration of exhaust air and an air barrier at the work opening. HEPA-filtered vertical laminar airflow which is re-circulated in the work zone. An air barrier between the operator and the work zone is maintained by a flow of room air into a full width grill in the work opening. The barrier air mixes with the laminar flow air in a sump underneath the work surface, and is exhausted to the outside environment via a HEPA filter and an optional virus burn-out. All positive pressure zones and filter seats are surrounded by negative pressure zones, so as to contain potentially hazardous aerosols.