Are we ready to close schools’ windows?

...On September 29, the Royal Society (the UK equivalent of the US National Academy of Sciences) issued its report, “The Ventilation Of Buildings And Other Mitigating Measures For COVID-19: A Focus On Winter 2020”. It is by far the most comprehensive analysis of this issue that I have seen to date. 

Critically, it contains tools that school districts and health departments can use to quantify the risk of contracting Covid-19 from indoor exposure to aerosols containing the SARS-CoV-2 virus.

This risk is a function of the amount viral aerosols that accumulate in a space over time. In turn, this depends on a number of controllable variables, including:

• The volume of an enclosed space, in cubic feet (all else being equal, smaller is riskier).
• The number of people in the enclosed space (more is riskier).
• How long they are in the enclosed space (longer is risker).
• An assumption about how many of these people are shedding viruses (more is riskier).
• The activity the people are performing (more active is riskier, e.g., listening to a teacher versus having choir practice).
• And the parameters at which the HVAC system is operating, including the efficiency of its filters (lower MERV rating is riskier), the amount of air changes per hour (fewer is riskier), and the amount of outdoor air entering the space each hour, from open windows or through HVAC system (less outside air is riskier).

This methodology is essentially the same one that has been used in the past to measure the accumulation of carbon dioxide in classrooms, which has been shown to reduce students’ cognitive function (for example, see “Indoor Air Quality and Academic Performance,” by Tess Stafford)...

https://fordhaminstitute.org/national/commentary/are-we-ready-close-schools-windows