I grew up in a time before widespread central air conditioning and during a time when windows opened and buildings leaked like sieves. In recent decades building maintenance have perfected sealing leaks and minimizing number of air changes per hour. First there was sick building syndrome, then SARS-CoV-2, the virus that causes COVID-19 arrived and we remembered why we might want fresh air. Ensuring proper ventilation with outside air can help reduce indoor airborne contaminants, including COVID-19, and other viruses. Also, HEPA air filters are good for removing wildfire smoke and we should consider investing in one for our homes.
In a study recently reported at the World Health Organization Europe Indoor Air Conference, researcher Catherine Noakes reported on the University of Leeds study where thirty primary schools were assigned to three groups balanced for school type (building; ethnicity; free school meals; total student numbers). These were randomly allocated to three groups: control; HEPA-Air Cleaning Technologies; UVC-Air Cleaning Technologies. All schools were predominantly naturally ventilated and relied on manual opening of windows and doors to ventilate classrooms. All classrooms were equipped with air quality monitors.
The researchers found that air quality data indicated comparable ventilation rates between groups, and a 48% mean reduction in particulate matter in the HEPA classrooms which were equipped with a free standing HEPA blow filter about the size of 20 gallon kitchen trash can. The HEPA filter in classrooms was found to reduced the number of covid-19-related sick days by more than 20%.
Only absences related to covid were tracked, but the researchers also believe that the HEPA filters probably also cut other respiratory illnesses like colds and flu. Air filters can cost several hundred dollars and can be noisy, but really produce results. Other studies of the use of HEPA air filters in a hospital in Cambridge UK is expected in the near future.