Covid Risk airborne, a tool to test the risk of aerosol transmission of SARS-CoV-2 under different scenarios: a pre-school classroom case study

Abstract

The COVID-19 emergency has shown that airborne transmission of SARS-CoV-2 is especially relevant in poorly bad ventilated spaces with high occupancy density, like non-university classrooms, a widespread space typology with very sensitive occupants. Of these, pre-school classrooms stand out, due to the vulnerability of children. Thus, this study has estimated the existing transmission risk of SARS-CoV-2 in a pre-school classroom, due to the especial vulnerability of the children, regarding to different indoor CO2 excess levels. This statistical evaluation has been performed through 68 calculation hypotheses, grouped into 4 cases, according to who is the primary infected occupant (one of the children or the teacher) and depending on whether the teacher wears a mask or not. It can be concluded that, to have acceptable risk conditions for airborne disease transmission (with one infected occupant) in pre-school classrooms, it is necessary to maintain sufficient ventilation conditions to reach a maximum average excess CO2 level exhaled of 150 ppm, while teachers should wear well fitting N95 respirators. In this way, infection risk is much higher when the primary infected occupant is the teacher and is wearing no mask or a surgical one - 5 or 6 times more.