Indoor air quality in schools

Indoor air quality can have an effect on health, which can be impacted by ventilation and air filtration. This document provides guidance on ensuring good indoor air quality in school settings.

Why is indoor air quality important?

Most people spend the majority of their time indoors, including home, school, and work. Air pollutants that impact indoor air quality can originate from outdoor or indoor environments. Examples of indoor air pollutants can include gases (e.g. carbon monoxide), solid particles (e.g., in smoke), and biological contaminants (e.g. mould). Poor indoor air quality can have a variety of health impacts, and children may be more susceptible to some of these effects.

Indoor air quality can be improved by:

1. Controlling the source of the air pollutant
2. Ensuring good ventilation (moving outdoor air into indoor environments)
3. Cleaning the air (typically by filtering)

What is the role of ventilation in indoor air quality?

Ventilation refers to supplying outdoor air to an indoor environment. This may be by natural means (e.g. via open windows) or by heating, ventilation and air-conditioning (HVAC) systems.  Supplying outdoor air can dilute the concentration of contaminants in an indoor environment.

Building operators are encouraged to ensure HVAC systems are in good working order, functioning to appropriate standards, and running with the highest efficiency ventilation filter feasible for system function.

Natural ventilation can be helpful to improve indoor air quality, particularly in spaces without a mechanical ventilation system. Natural ventilation can be straightforward to implement (e.g. by opening windows), and can be used when it is safe, feasible, and does not impact the function of the existing ventilation system.

What is the role of portable air filters in indoor air quality?

Portable air filters (or “air cleaners”) function by mechanically filtering particles from the air, such as particulate matter (e.g., from wildfire smoke), and respiratory aerosols (small droplets from people’s breath, which may contain viruses).  Air filters require adequate filtration (i.e. HEPA filters, or filters rated MERV-13 or higher), as well as adequate airflow through the device.

Portable air filters have a specific clean air delivery rate (CADR), dependent on their filtration efficiency and rate of airflow. The device’s CADR must be sufficient for the room size to be effective. Air filters should be positioned to optimize air intake, avoid creating air currents between room occupants, and must be maintained according to the manufacturer’s recommendations. Ozone-generating indoor air cleaners are not recommended, as ozone can have negative impacts on health. Ideally, air filters should be certified for quality control.

Inexpensive homemade air filters can help to address poor air quality hazards such as wildfire smoke. (e.g. box fan air filters, with designs including Corsi-Rosenthal boxes)Instructions to build a homemade air filter are available from the BC Centre for Disease Control . Key factors for the effectiveness of homemade air filters are filter type (ideally MERV-13 or higher), filter fit within the device, and airflow. Well-constructed homemade air filters can achieve similar clean air delivery rates to commercial portable air filters, although they are not subject to regulatory quality control and require users to ensure that the filters are built properly and maintained regularly. As a primary measure to protect health, building operators should support indoor air quality through long-term measures, such as ensuring HVAC systems are in good working order, and running with the highest efficiency ventilation filter feasible.

What is the role of ventilation and air filtration in the transmission of respiratory infections?

Most transmission of respiratory infections is due to a close-range exposure to respiratory droplets/aerosols from a person infected with a virus or bacteria, and this direct exposure will not be reduced by ventilation and air filtration, regardless of the filter or system. Ventilation and air filtration may help to reduce less common long-range aerosol transmission of respiratory infections in crowded, poorly ventilated spaces. Indoor air quality measures should complement, and cannot replace, a multi-layered approach to the prevention of respiratory infection, including self-isolation of symptomatic individuals (i.e. staying home when sick), appropriate vaccination and hand/respiratory hygiene. While it has been shown that portable air cleaners with HEPA filters can reduce the concentration of some viruses from the air, according to the Public Health Agency of Canada, the effectiveness of portable air filters in reducing transmission of the SARS-CoV-2 virus has not been demonstrated to date.

What is the role of carbon dioxide (CO2) monitors in indoor air quality?

Indoor CO2 levels can be used as part of a professional assessment of indoor ventilation. Higher concentrations of CO2 in indoor spaces can be an indicator of a poor ventilation, with established thresholds based on comfort or direct risks of CO2 exposure (which can occur at very high concentrations). CO2 monitors are not designed to assess transmission risks for communicable diseases, and concentrations are not a direct indicator of infection transmission risk.

Ensuring good indoor air quality in schools

Protection of indoor air quality remains an important health issue in schools, and supports community resilience to climate change impacts such as wildfire events. Personnel with expertise in HVAC systems can support schools and other buildings to ensure that ventilation and air cleaning systems remain in good working order.