ABSTRACT
Escalating demands of assessing airborne disease infection risks had been awakened from ongoing pandemics. An inhalation index linked to biomedical characteristics of pathogens (e.g. TCID 50 for coronavirus delta variant) was proposed to quantify human uptake dose. A modified Wells-Riley risk-assessment framework was then developed with enhanced capability of integrating biological and spatiotemporal features of infectious pathogens into assessment. The instantaneous transport characteristics of pathogens were traced by Eulerian-Lagrangian method. Droplets released via speaking and coughing in a conference room with three ventilation strategies were studied to assess occupants' infection risks using this framework. Outcomes revealed that speaking droplets could travel with less distance (0.5 m) than coughing droplets (1 m) due to the frequent interaction between speaking flow and thermal plume. Quantified analysis of inhalation index revealed a higher inhalation possibility of droplets with nuclei size smaller than 5 µ m , and this cut-off size was found sensitive to ventilation. With only 60-second exposure, occupants in the near-field of host started to have considerable infection risks (approximately 20%). This risk was found minimising over distance exponentially. This modified framework demonstrated the systematic analysis of airborne transmission, from quantifying particle inhalation possibility, targeting specific disease's TCID 50 , to ultimate evaluation of infection risks.
ABSTRACT
Urgent demands of assessing respiratory disease transmission in airliner cabins had awakened from the COVID-19 pandemics. This study numerically investigated the cough flow and its time-dependent jet-effects on the transport characteristics of respiratory-induced contaminants in passengers' local environments. Transient simulations were conducted in a three-row Boeing 737 cabin section, while respiratory contaminants (2 µm-1000 µm) were released by different passengers with and without coughing and were tracked by the Lagrangian approach. Outcomes revealed significant influences of cough-jets on passengers' local airflow field by breaking up the ascending passenger thermal plumes and inducing several local airflow recirculation in the front of passengers. Cough flow could be locked in the local environments (i.e. near and intermediate fields) of passengers. Results from comparative studies also revealed significant increases of residence times (up to 50%) and extended travel distances of contaminants up to 200 µm after considering cough flow, whereas contaminants travel displacements still remained similar. This was indicating more severe contaminate suspensions in passengers' local environments. The cough-jets was found having long and effective impacts on contaminants transport up to 4 s, which was 8 times longer than the duration of cough and contaminants release process (0.5 s). Also, comparing to the ventilated flow, cough flow had considerable impacts to a much wider size range of contaminants (up to 200 µm) due to its strong jet-effects.