Necessity of ventilation for mitigating virus transmission quantified simply

Blackman, Eric G.; Ghoshal, Gourab

To mitigate the SARS-CoV-2 pandemic, officials have employed social distancing and stay-at-home measures. Less attention has focused on ventilation. Effective distancing practices for open spaces may be ineffective for poorly ventilated spaces, both of which are commonly filled with turbulent air. While turbulence initially reduces the risk of infection near a virion-source, it eventually increases the exposure risk for all occupants in a space without ventilation. Here we estimate the time-scale for virions injected into a room of turbulent air to infect an occupant, distinguishing cases of low vs. high initial virion mass loads and virion-destroying vs. virion-reflecting walls. An open window typifies ventilation and we show that its minimum area needed to ensure safety depends only on the ratio of total viral load to threshold load for infection. Our minimalist estimates complement more detailed approaches and present opportunities for generalization.