Ventilation regimes of school classrooms against airborne transmission of infectious respiratory droplets: A review

Airborne transmission of small respiratory droplets (i.e., aerosols) is one of the dominant transmission routes of pathogens of several contagious respiratory diseases, which mainly takes place between occupants when sharing indoor spaces. The important role of ventilation in airborne infection control has been extensively discussed in previous studies, yet little attention was paid to the situation in school classrooms, where children spend long hours every day. A literature study was conducted to identify the existing ventilation strategies of school classrooms, to assess their adequacy of minimizing infectious aerosols, and to seek further improvement. It is concluded that school classrooms are usually equipped with natural ventilation or mixing mechanical ventilation, which are not fully capable to deal with both long-range and short-range airborne transmissions. In general, the required ventilation designs, including both ventilation rates and air distribution patterns, are still unclear. Current standards and guidelines of ventilation in school classrooms mainly focus on perceived air quality, while the available ventilation in many schools already fail to meet those criteria, leading to poor indoor air quality (IAQ). New ways of ventilation are needed in school classrooms, where the design should be shifted from comfort-based to health-based. Personalized ventilation systems have shown the potential in protecting occupants from aerosols generated within short-range contact and improving local IAQ, which can be used to compensate the existing ventilation regimes. However, more studies are still needed before such new ventilation methods can be applied to children in school classrooms.