Evaluating the Impact of Air Cleaning and Ventilation of Airborne Pathogens and Human Bio-effluents at Two Primary Schools in Belgium

The COVID-19 pandemic increased the awareness and importance of infectious pathogens as contaminant in the indoor air, especially for non-residential buildings with a high occupational density like schools. During the COVID-19 pandemic air cleaning is often proposed as mitigation strategy for infectious risk in these types of buildings. However, indoor air quality (IAQ) in general comprises of a large range of possible contaminants and factors that can equally impact the health, comfort and well-being of occupants. In this context, a study was conducted in Flanders (Belgium) with the aim of investigating the potential impact of ventilation and air cleaning on the IAQ and infection risk control in Flemish public spaces. This paper describes part of this larger study, focusing on the assessments carried out in two primary schools.
In the first school, which did not have a mechanical ventilation system, 4 classrooms were assessed for three weeks. In the second school, 4 classrooms connected to a centralized mechanical ventilation system were assessed in two separate measurement campaigns of 3 weeks. Between the two measurement campaigns in school 2, the defects in the mechanical ventilation system which were observed during the first campaign were corrected.
In each school, in three of the four classrooms, specific interventions were done after the first week of monitoring, among which the introduction of air cleaners. The fourth class was monitored without intervention. In each classroom, CO2 concentrations and biological air samples were collected 2 days per week for in-lab qPCR analysis of over 20 genetic markers of respiratory pathogens. The results for SARS-CoV-2 are presented.
Unfortunately, in both schools, the effectiveness of the interventions on airborne pathogens (incl. SARS-CoV-2) could not be quantified due to the lack of infected schoolchildren and other measures like the wearing of face masks at that time resulting in mostly negative or borderline results. In general, the results indicate the importance of proper commissioning and maintenance to mechanical ventilation systems and show an overall better expected perceived indoor air quality when the ventilation system works properly. In the school without mechanical ventilation system, manual airing through the opening of windows can achieve the same level of expected perceived indoor air quality if operated correctly.