Droplet fate, efficacy of face mask, and transmission of virus-laden droplets inside a conference room

The second and third waves of coronavirus disease-2019 (COVID-19) pandemic have hit the world. Even after more than a year, the economy is yet to return to a semblance of normality. The conference/meeting room is one of the critical sections of offices that might be difficult not to use. This study analyzes the distribution of the virus-laden droplets expelled by coughing inside a conference room, the effect of ventilation rates, and their positioning. The efficacy of masks is studied to get quantitative information regarding the residence time of the droplets. The effects of evaporation, turbulent dispersion, and external forces have been considered for calculating the droplets' trajectories. We have analyzed six cases, of which two are with masks. Change in the ventilation rate from four air changes per hour (ACH) to eight resulted in a $9\%$ increment in the number of droplets entrained in the outlet vent, while their average residence time was reduced by $\sim 8s$ . The shift in the vents' location has significantly altered droplets' distribution inside a conference room. It results in $\sim 1.5\%$ of the injected droplets reaching persons sitting across the table, and a similar indoor environment is not recommended. Wearing a mask in the case of eight ACH has presented the best scenario out of the six cases, with a $6.5\%$ improvement in the number of droplets entrained in the outlet vent and a $9s$ decrease in their average residence time compared to the case without a mask. No droplets have reached persons sitting across the table when the infected person is wearing the mask, which follows that a social distancing of $6\mathrm{ft}$ with a mask is adequate in indoor environments.