The virus that causes COVID-19 spreads primarily through the air during close contact with infected people. It spreads between people more easily indoors than outdoors. At times, the virus can also build up in indoor air and infect people further away.
Outdoors, even a light wind can dilute and disperse viral particles, but when we are indoors, we need to pay special attention to the amount of fresh air entering the space. The circulation of fresh air is crucial for diluting any coronavirus that may be present and preventing it from spreading between people.
Air circulation is especially important when people are inside for longer periods of time and when they are removing their masks (for example, to eat). That includes workplaces, stores, and restaurants, as well as settings like shelters or long-term care facilities, and schools and childcare buildings.
Public Health—Seattle & King County recommends that business owners and building operators implement strategies to improve indoor air quality. Along with wearing masks, keeping physical distance, and limiting the number of people who are indoors together, this is an important way to decrease people’s risk for COVID-19.
Public Health has published a new guidance pamphlet for facility managers, along with additional resources. The guidance highlights three main approaches:
1. Maximize outdoor air in indoor spaces
Increasing outdoor air flow is one way to dilute indoor air and virus particles. This can be achieved in several ways. The least expensive is to open windows and doors to increase the flow of outdoor air into the building. Do not do this when outside air is polluted (either during wildfires or if the building is right next to a busy highway) or when there is the possibility of small children or pets falling.
If you place a fan in a window, position it to blow air out, so that you don’t blow air across anyone’s face.
Outdoor air can also be introduced by adjusting the building’s Heating, Ventilation, and Cooling (HVAC) system. Increase the amount of outdoor air that is pulled in to 100%. If you’re not sure how to do this, ask your building maintenance or consult an HVAC specialist.
2. Clean the indoor air
There are also ways to remove pollutants from indoor air by filtering the air:
- Install high efficiency filters (rated MERV 13 or higher) in your HVAC system. Not all systems are capable of using MERV 13 filters, so consult with an HVAC specialist first. If your HVAC system is unable to use those filters, use the highest MERV rating that they can.
- Use portable HEPA (high efficiency particulate air) cleaners throughout the space. Select units that can provide 99% or higher filtration efficiency down to 0.3 microns. Depending on the size of your space, you will likely need more than one HEPA air cleaner. Refer to Public Health’s Indoor Air Ventilation guide to determine how many you will need.
- A low-cost option is to attach a MERV 13 furnace filter to the back of a box fan. Learn how from Puget Sound Clean Air Agency. Another low-cost idea is to use four MERV 13 furnace filters to create a cube design, which can increase filtration and prevent air from blowing at anyone in the room.
3. Inactivate virus in the air using upper air Ultraviolet Germicidal Irradiation (UVGI)
This technology is very specialized and can be dangerous if installed or used incorrectly. Always work with a UVGI specialist to consult and install this technology in your space. Upper air UVGI is the only UV technology recommended by CDC. It uses UV lights installed near the ceiling to kill germs in the air. UVGI is not appropriate for homes but may work well in some facilities.
UVGI systems inactivate virus in the air, but do not remove pollutants. UVGI may be a useful addition to ventilation and air filtration in certain situations.
Implementing these strategies in your facility
All of these strategies can play a role in improving the indoor air in your facility and reducing the risk of spreading COVID-19. Before implementing any of them, consult with your building manager or HVAC specialist to discuss which would work best for your situation.
Indoor air strategies will work best when combined with mask-wearing, avoiding crowding, keeping physical distance, and hand-washing.
For more information:
Find more resources to help business owners and building operators improve the indoor air quality in their facilities, on Public Health’s indoor air webpage – www.kingcounty.gov/covid/air.
- This page includes Public Health’s Indoor Air Ventilation Guide that discusses these strategies in detail.
- There are also considerations for specific sectors, including congregate settings, schools and child care settings, and restaurants.
- A companion fact sheet offers the same information in less detail.
Originally posted April 30, 2021