As pupils across Switzerland soon start returning to school, some might wonder how well ventilated school classrooms are.
A study published by Switzerland’s Federal Office of Public Health (FOPH) in 2019 estimates that the air quality in two thirds of Swiss classrooms was inadequate.
The study, which ran over two years, sampled the air quality in 100 classrooms in the cantons of Bern, Vaud and Graubunden.
An online simulator shows how the air quality drops rapidly below acceptable levels across a school day if classrooms are not aired. With no airing during the day, a typical Swiss classroom would have good air for only 10% of the day, satisfactory air for another 12% of the day and unacceptably poor air for the remaining 78% of the time. With airing the unacceptably poor percentage drops to 13%.
Shelly Miller, a professor of mechanical engineering at the University of Colorado Boulder focused on how to control the transmission of airborne infectious diseases indoors, points out that the vast majority of SARS-CoV-2 transmission occurs indoors. According to her, the safest indoor space is one that constantly has lots of outside air replacing the stale air inside.
Generally, six air changes an hour are recommended for a 9 m2 room with 3 or 4 people in it. One study suggests a rate of nine times per hour reduced the spread of SARS, MERS and H1N1 in a Hong Kong hospital.
Post-obligatory schools in some parts of Switzerland are requiring pupils to wear masks at school when they return. Fresh air would help too.