New York City mandated every classroom have at least one operable window to help with ventilation, even in the winter. So let’s see what happens when we open a window.

You can see a marked improvement: The fresh air dilutes the contaminants as they move around the room. “Simple and inexpensive measures can make schools much safer,” said Scott E. Frank, whose engineering firm JB&B assisted with these simulations.

We managed to achieve four total air exchanges by opening just one window in this simulation, which was dependent on specific weather conditions. To get to six air exchanges, we will have to do more.