Best Practices to Improve Building Safety

It is common knowledge that COVID-19 is primarily transmitted via close contact with an infected individual, and key preventative measures are physical distancing, hand hygiene and masking.

However, lesser-known is that the virus can also be transmitted over longer distances by aerosols under (un)favourable conditions. The risk of transmission only increases with more time spent in crowded, inadequately ventilated environments. Activities that require heavy breathing, such as exercise and singing, also increase risk even further.

Indoor air quality can thus be mobilized as a tool to further reduce transmission through the regulation of environments and airflow to make transmission more unlikely. Ventilation and filtration mitigate virus spread by respectively diluting and removing virus-laden particles from indoor air.

It is important to remember that while ventilation and filtration are important for overall indoor air quality as well as COVID-19 risk reduction, they must be used in conjunction with all other measures to be effective at minimizing transmission risk.

Why is ventilation important?

It has been found that building ventilation and air movement within buildings are associated with the transmission of various infectious diseases, such as tuberculosis and measles.

A multidisciplinary review (LINK) focused on the relationship between COVID-19 and HVAC systems in public spaces concluded that while more evidence is needed to reach any solid conclusions, HVAC systems play a potential role in spreading and/or mitigating the risk of transmission.

However, there are many studies on ventilation-related factors that demonstrate an increased risk of transmission from inadequately ventilated indoor spaces and high occupant density. Hence, due to HVAC’s role in air distribution and thus impact on the transmission of airborne infectious diseases and dilution of particles in the air, it can have a significant effect on COVID-19 prevention efforts, particularly in closed spaces.

In addition, there is evidence that airflow (for example, fans moving air from an infected individual to others nearby) can be an important factor in either increasing or decreasing transmission. Avoiding direct airflow around people will reduce respiratory droplets being dispersed from person to person. Rather than having airflow at head level, options would be to direct the air upwards or to exhaust room air out of an open window while other open windows draw fresh air in.



There are a variety of different systems and methods to improve air quality. Which will be most effective in any given indoor environment will depend on:

  • occupancy
  • the type of building
  • the type of activity undertaken

In addition, some types of air circulators will be more effective than others. These different options, along with their pros and cons, are discussed below.


Mechanical filtration involves the use of different types of fibrous filters designed to remove particles from the airstream.

The particle removal efficiency of the filter, the rate of airflow through the filter, location of the filter, and size of the particles filtered by the filtration system all contribute to the reduction of indoor particle concentrations.

Mechanical and Natural Ventilation

Ventilation is the supply and/or distribution or removal of air from a space by mechanical or natural means. Ventilation can be for the purposes of controlling air contaminant levels, humidity, or temperature within the space.

While natural ventilation (i.e., by window opening) can improve indoor air quality, using this as the only means of ventilation can lead to excessive energy costs, particularly due to heat loss in the winter or loss of conditioned air in the summer. Window opening can also create challenges in managing relative humidity in the winter and summer.

Mechanical ventilation allows for control over individual factors and can thus be a more efficient and effective system.


An HVAC system is the equipment, distribution systems, and terminals that provide, either collectively or individually, the processes of heating, ventilating, or air conditioning to a building or portion of a building. Most HVAC systems also make use of filtration.

Some buildings may use Energy Recovery Ventilators (ERVs), which are HVAC systems that transfer energy (heat in winter, cold in summer) from indoor exhaust air to outdoor supply air within a building to lower energy costs associated with heating or cooling outdoor air used for ventilation.

When central HVAC systems are unavailable, and a space is poorly ventilated, portable air-cleaning units can be considered to help control concentrations of particles in the air. It’s important to note that the effectiveness of portable air filtration devices in reducing the transmission of COVID-19 hasn’t yet been demonstrated. As such, they should not be used alone or as a replacement for adequate ventilation.


Portable or ceiling fans or single-unit air conditioners circulate air within the room, but they do not exchange air or improve ventilation.

If using a window air conditioner unit or a fan is necessary, aim the air stream away from people to reduce the spread of potentially infectious droplets or particles.


While humidifiers do not remove COVID-19 from the indoor air environment, they could impact the duration that particles that contain the virus are suspended in the air. It is therefore important to maintain an optimal humidity level, between 30% and 50% in indoor settings. Humidifiers can be:

  • part of an existing HVAC system
  • standalone units designed to maintain adequate humidity in a space
  • used to add extra humidity to the air to help alleviate respiratory symptoms

Best Practices

COVID-19 prevention depends on a combination of interventions that vary in effectiveness and practicality day-to-day. The key is to always practice as many measures as consistently as possible.

Abide by standards

Standards for air change rates are available from the Canadian Standards Association (CSA) for HVAC systems in specific zones or areas. The CSA guidance for workplaces during the pandemic asserts that air exchange rates should be modified on a building-by-building basis. This should always be done with careful evaluation of the ventilation system because even small adjustments can lead to issues related to thermal comfort and humidity and undesired effects on air circulation.


Air quality improvement strategies can reduce the concentration of virus particles in the air by taking into consideration the unique characteristics and needs of your establishment.

In general, most guidance encourages ventilation with outdoor air to avoiding recirculation as far as practically possible and ensuring clean filters. The particularities of your ventilation factors will need to be suited to what will best protect your occupants.

Practice regular maintenance

Cleaning, disinfecting and maintaining fans and air conditioners should occur on a routine basis.

Regular inspection and maintenance measures for air handling systems (including inspection and replacement of filters, if applicable) are essential.

Adjustments to ventilation may require more frequent inspections and filter changes, so be sure to monitor any change you make with care.

System humidifiers should be inspected to ensure they are cleaned, maintained and operating properly.

Monitor, analyze, and improve

The indoor CO2 level can be used as an indicator for ventilation. CO2 is exhaled by people and is particularly prone to build up in indoor spaces as compared to normal outdoor ground-level CO2.

Ventilation can lower indoor CO2 levels by introducing fresh outdoor air, leading to its use as a proxy for indoor air removal or dilution.

There are a variety of ways CO2 levels can be measured and analyzed using sensor systems and data management systems, but in general, measurements are averaged over a period of time to capture the effect of ventilation on CO2 levels. Measurements can be used to verify whether ventilation has increased in a space to confirm the effectiveness of the changes.

Run systems for longer

Generally, most HVAC guidance recommends against a complete shutdown of the HVAC system, even during a building shutdown.

During normal operations, it is also a good idea to run systems for longer than usual and maintain outdoor air ventilation rates when the building has fewer occupants than the allowable capacity.

Additionally, in spaces that are continuously used, like classrooms, windows and doors should be opened regularly where possible. The space should be cleared of people regularly to limit the potential buildup of potentially infectious respiratory droplets or particles over time.


It is important to restate that improved ventilation cannot replace other public health measures such as physical distancing and proper hygiene but can only support such measures. Whenever possible, consider the use of an alternative space, or preferably gathering outdoors rather than indoors, when interacting with people from outside your household.

By upgrading and maintaining your current building systems and following the outlined best practices, you can help make every space a safe one for your occupants.