Airborne Infection Isolation (AII) rooms, commonly called negative pressure rooms, are single-occupancy patient care spaces designed to isolate airborne pathogens to a safe containment area. AII rooms are a specialized application of a hospital’s HVAC system, where the airflow supplied into the room is balanced with exhaust airflow to create at least -0.01” WC negative differential pressure with respect to an adjacent space, usually the hallway or an anteroom. In simple terms, this provides a gentle flow of air under a closed doorway and into the room so that no airborne particulates escape into nursing staff or public areas. Exhaust from these rooms is not recirculated in the HVAC system. Instead, exhaust air typically moves in dedicated ductwork to ventilation stacks on the rooftop, where atmospheric air provides sufficient dilution to make the resulting air safe.