Multi-zone modeling of airflow in a free running building floor: Possible implications for disease transmission

Free running buildings are suspected of spreading viral aerosols from unit to unit; while modeling literature is limited in analyzing multi-zone airflow influenced by a large number of building openings. Question remains as whether windows or doors should be closed to mitigate hazard transmission in such conditions? This study aims to (1) model the multi-zone airflow in a large free running building, and (2) present intermediary evidence on the possible disease transmission associated with such flow. A COVID-19 outbreak in a high-rise apartment building in Hong Kong was investigated. A cascading strategy was developed to backcalculate the unit-to-unit airflows and hazard concentration. The model was partially evaluated using tracer-gas experiments conducted using 3D-printed mockup building placed inside a wind tunnel. Findings suggest that hazard emanating from the source unit are likely to migrate downwind through both indoor and outdoor pathways. Closing windows can reduce such risk by a factor of two to four. The cascading strategy can analyze airflow in a complex building with surrounding urban and topological context. The public health message is that windows and doors should be closed during hazard outbreaks such as fire, smoke, or infectious diseases.