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This does not pose a safety risk for experiments only handling biological agents since the exhaust air has already passed through the HEPA filters.

When airflow is disrupted (typically because an exhaust fan has failed or lost capacity), the alarm will alert the operator they have lost containment of exhaust and the cabinet is now recirculating back into the lab.Airflow alarms monitor the airflow passing through the canopy and measures whether it is sufficient to capture the exhaust air exiting the cabinet: NSF standard 49 requires that canopy connected Class II Type A2 biosafety cabinets have an airflow alarm. Negatively charged particles (such as some viral particles) are removed by electrostatic attraction to the slightly positive charge of the fibers.Very small particles move by Brownian motion and are removed by diffusion when they come in contact with fibers.Smaller particles are removed by interception.Large particles are removed by straining effect when particles become trapped between two fibers.Fast-moving particles are filtered through direct impact with fibers.HEPA filters remove biological aerosols through several mechanisms: Increased surface area drastically increases the efficiency of filtration.Multiple, folded sheets of fibrous material drastically increase the surface area of the filter.Particles are “trapped” by the fibers and removed from the air as it flows through the filter.Fibrous material is used to separate biological material from air passing through the filter.This particle size is the Most Penetrating Particle (MPP) size. To be designated as HEPA, the filter must remove 99.97% of all particles at a 0.3 um size. The edges are sealed with Epoxy or polyurethane. HEPA filters consist of a metal or wood frame holding a long, folded strip of cellulose or borosilicate fiber. HEPA filter (High-Efficiency Particulate Air or High-Efficiency Particulate Arresting filters) are fibrous filters that remove particles from air passing through them.