Ventilation Can Impact the Spread of Communicable Disease

There is an increased risk of transmission when viruses accumulate in an indoor space, such as those that are crowded and when people spend long periods of time together in close proximity. This type of transmission is dependent on several factors, including ventilation rate, room size, occupancy, type of activity taking place, and amount of virus released. Good ventilation can decrease the concentration of respiratory particles in the air that contain infectious viruses and may reduce the spread of communicable disease in the ventilated space.

While it has been suggested that airflow within a space may spread disease between people in that space, there is no evidence at this time that a building’s ventilation system, in good operating condition, contributes to the spread of the virus to people in other spaces served by the same system.

Improving Ventilation 

Indoor Air Quality is a term used to define the overall quality of air in a building. Poor indoor air quality can lead to performance and health issues for occupants. Improving this may be accomplished by supplying more outdoor air to indoor spaces through ventilation. Ventilation can be controlled in two ways:

• Natural Ventilation. This is the simplest form of ventilation that involves opening windows and doors to the outside.
• Mechanical Ventilation. This involves the use of heating, ventilation, and air conditioning (HVAC) systems, which filter, heat, and/or cool outside air before circulating it throughout the building. This differs from air circulation which simply moves air within a space without a filtration process (i.e. use of ceiling fan, floor fan or ventilation fan).

Increasing ventilation can decrease the concentration of aerosols that may be suspended in the air. However, it is important to remember that strategies for indoor air quality improvement will not eliminate the risk of communicable disease transmission in instances where individuals are in close contact.

Optimize Natural Ventilation

One of the easiest ways is to improve ventilation is to open windows and doors and allow outside air in, as weather permits and if it does not pose a safety risk to the occupants. Doing so, even for a few minutes at a time throughout the day, can improve ventilation with minimal impact on indoor temperature.

The use of fans to circulate air is not recommended in spaces where there are several people present. Circulating air within a space may help spread viruses and other contaminants. If the use of fans is unavoidable, ensure that fans are positioned to blow inside air to the exterior, and minimize air blowing from one person directly to another to reduce the potential spread of any airborne or aerosolized viruses.

Maintain Your HVAC System

Your HVAC system is responsible for exchanging indoor air with outdoor air a certain number of times per hour, as part of regular operation and maintaining indoor air temperature and humidity at healthy and comfortable levels. These strategies will help you ensure your HVAC system is operating effectively to keep your staff and residents safe and healthy.

• Comply with WorkSafeBC Regulations by ensuring your HVAC system is designed, operated and maintained per standards and specifications. This should be done within the specifications of your HVAC system and in consultation with an HVAC professional.
• Have your HVAC system inspected, maintained, and cleaned according to the manufacturer’s recommendations on a regular basis¹.
• Check the filters in your HVAC system regularly, to ensure that they properly fit in the filter racks and have their edges sealed to limit airflow bypass.
• Replace the filters in HVAC systems when they reach the end of their useful life.
• Install the highest level of filtration that the HVAC system is intended to use if you haven’t already done so.
• Consult an HVAC professional about installing the highest rated Minimum Efficiency Reporting Values (MERV) or High-Efficiency Particulate Air (HEPA) filters compatible with your ventilation system(s). Review filter replacement schedules as new filters could require more frequent changes.

¹ Maintenance workers of HVAC systems are required to follow their usual safe work procedures, including the use of personal protective equipment (PPE) normally worn to conduct maintenance.

Other Strategies

• Air purifying and/or cleaning technologies can exist as a part of a building’s HVAC system. Consult with an HVAC professional for options that may be compatible with your HVAC system when considering air purifying, filtering or air exchange system upgrades.
• Consider humidity levels and try to maintain an optimal humidity level (between 30% and 50%) in indoor settings. Humidifiers can be part of an existing HVAC system or standalone units to maintain adequate humidity in a space.
• If fresh air input from mechanical ventilation is not adequate and natural ventilation is not possible, think about avoiding the area and moving to a better-ventilated space.
• Portable air filtration devices with high-efficiency particulate air (HEPA) filters may be an option if used in combination with established public health infection control measures². Portable systems can vary in size and are usually intended for use in localized areas within a building such as a single room. When using a portable unit in the workplace consider the following:

Cost. In addition to the cost of the unit itself, also consider maintenance costs and filter replacement costs.

Noise. If the portable unit is always running and/or operating at the highest setting noise may be a factor.

Size of the Room. Consider the size of the room, as well as the placement of the unit within the room (improperly placed devices may continue to recirculate the same volume of air) when choosing a portable unit. Follow manufacturer’s instructions on place and operation of the unit within the space.

Ozone. Health Canada advises against using products that intentionally release ozone as a method of cleaning indoor air. Ozone generators may produce levels of ozone that are harmful to health.

² The effectiveness of portable air filtration devices in reducing the transmission of the COVID-19 virus has not yet been demonstrated. As such, they should not be used alone or as a replacement for adequate ventilation and personal preventive practices (e.g. avoiding closed spaces, crowded places, and close contact settings; wearing a well-constructed and well-fitting mask; physical distancing).