Vertical transmission of aerosols between building flats through drainage system: A review

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been demonstrate to be transmitted through fecal aerosols in building drainage systems (BDS), emphasizing the urgent need to understand its specific transmission pathways and mechanisms. This paper concludes the two periods of aerosols transmission in BDS: airflows caused by pressure fluctuations during toilet flushing and airflows induced by the chimney effect. It also compares the airflow velocity, air pressure, and transmission duration during these two periods. Subsequently, research methods (e.g., aerosol experiments, tracer gas experiments, and numerical simulations), influencing factors, and related conclusions regarding aerosols transmission in BDS were thoroughly concluded and analyzed. Finally, the advantages and limitations of the research methods are compared, offering valuable insights on essential future research directions and drainage system design. Although there is a qualitative understanding of the vertical transmission mechanism in BDS, which summarize the pathway of aerosols transmission as “respiratory/fecal aerosols-drainage pipes-faulty floor drains-bathrooms”, it is imperative to establish a quantitative understanding of the relative importance and duration of aerosols transmission during these two periods. Further research urgently needs to assess the risk levels of aerosols transmission during both periods and establish pressure-coupling curves for these two periods. Overall, both designers and scholars can utilize this review as a reference to mitigate the potential risk of vertical aerosols transmission in BDS, so that BDS can be appropriately designed to minimize pressure fluctuations and the water seal in floor drains can be regularly checked. •A review of vertical transmission of virus-laden aerosols in drainage pipes.•The air pressure, airflow and duration in pipes during different periods are analyzed.•The influencing factors and results of research methods are discussed.•The advantage and limitations of research methods are discussed.•Several challenging topics are proposed to provide guidance for future studies.