Estimating the real-life infection risk of the SARS-CoV-2 virus in a typical metro compartment

Abstract

The metro has been an essential means of commuting for Hong Kong citizens, even during the pandemic. To evaluate the real-life infection risks of airborne SARS-CoV-2 in a typical half-metro carriage, field tests were first carried out to obtain thermo-fluid boundary conditions, air exchange rates, and passenger locations in metro compartments. Computational Fluid Dynamics (CFD) models of half of a metro carriage integrating real-world passenger distribution were built for different crowdedness level with 37, 57, and 75 passengers to determine the infection risk for commuters during typical metro trips. A total of 2449 cases were evaluated, and the study found that the infection risk of SARS-CoV-2 in the benchmark case (one source passenger talking continuously for 26 min in a lightly crowded compartment) varied from 0 % to 7.1 % depending on passenger location, and the corresponding overall infection risk was 1.75 %. No risk existed during a short metro ride of 2 min, and the infection risk increased with the talking durations/coughing frequencies, co-travel durations, and crowdedness levels. The infection risk for seated passengers was higher than that for standing passengers due to the shorter interpersonal distance for the former. Over 80 % of infections occurred within 1.5 m of the source passenger, and 100 % occurred within 2.6 m in metro carriages with different crowdedness levels. A safe social distance of 2.6 m from a potential source passenger is recommended in metro carriages. This study's findings provide guidelines for safeguarding the health of metro commuters for seasonal illnesses and the future pandemics.