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Occupational health branch

COVID 19 & Improving Indoor Air Quality at Work

 You can reduce the spread of COVID-19 at work by improving the air quality indoors. Some diseases (including COVID-19) spread through the air. This happens when people infected with a virus breathe it out. Other people in the room or nearby can then breathe in the virus and become infected.   

 The quality of the air inside a building can affect how much a virus builds up indoors. Improving indoor air quality can help lower the amount of virus in the room. Diluting, mixing, and filtering the air are three ways you can improve indoor air quality.​ 

Indoor Air Quality Webpage Summary ​(PDF)​ ​​​​​ 

Dilute, Mix, and Filter the Air​​

  • Dilute: Draw fresh air in 
    Use a Heating, Ventilation & Air Conditioning (HVAC) system or bring in outside air by opening windows and doors when weather permits. 
  • Mix: Move the air flow 
    Move around the air inside a room with fans (ceiling, wall-mounted, or portable), and/or through the vents in your HVAC system.  
  • Filter: Clean the air  
    Clean the air by trapping germs through HVAC system filters (MERV 13 rating and higher) and portable air cleaners with high efficiency particulate air (HEPA) filters.  

    The infographic shows two scenarios to enhance indoor air quality by diluting, mixing, and filtering the air. ​​
Improving Air Quality at work. BEST HVAC on, doors and windows closed, fans in use, portable air cleaner running. Heating, Ventilation and Air Conditioning (HVAC) Turned on (not auto) using MERV 13 filters or higher, dampers open. Doors and windows closed when operating HVAC system. Ceiling and Portable Fans. Turned on. Portable Air Cleaners (PAC) Running at highest speed. GOOD When no HVAC, doors, and windows open, fans in use, portable air cleaner running. Doors and Windows. Open when HVAC system is unavailable. Ceiling and Portable Fans. Turned on. Portable Air Cleaners (PAC) Running at highest speed.

Additional Tips to Dilute, Mix, and Filter the Air 

When an HVAC system is unavailable, you can use a portable fan, place it near an open window pointing towards the window and away from the room. Meanwhile, leave other windows and doors open--ideally on the opposite side of the room. This promotes a light cross draft to blow stale air out of the room and draw in fresh air.  

Fresh air comes in through open windows and stale air blows out through a portable fan facing a window.

Check out tips to reduce COVID -19 indoors (PDF) for more info. Workplaces can learn more about Ventilation and Filtration using the webpage.

T​ips for Portable Air Cleaners (PACs) 

Follow these tips to help your PAC work its best​:

The PAC draws in stale air, filters the air through the HEPA filter, and release into the room.

Before purchasing your PAC Select PACs that use HEPA filters.  

  1. Avoid devices that advertise "ionizer" or "ozone" technology.  
  2. Know the square feet (sq ft) of your space​.

  3. Choose a PAC that has a Clean Air Delivery Rate (CADR) that is 2/3 of the room's area (in sq ft). 

For example: 

  • 15x20ft room = 300 sq ft 
  • 2/3s of 300 is 200 
  • buy a PAC with at least 200 CADR

After purchasing your PAC 

  1. Where you place the PAC in a room matters. Notice the air inlets and outlets on your PAC, and make sure air can flow freely in and out of the unit. Avoid placing the PAC near open doors, windows, and/or directly under vents.   
  2. Cover the power cord to avoid tripping hazards.     
  3. Use the PAC at the highest fan setting acceptable for the noise level. 
  4. Follow manufacturer's recommendations for use and how often to replace the HEPA filter. 

Tips for HVACs ​

  • Make sure that vents are open with nothing covering or blocking them. 
  • Upgrade your filters to MERV 13 or higher. 
  • Change filters on a regular basis (follow manufacturer recommendations). 
  • Run systems continuously on “ON" mode instead of “AUTO." 
  • Only operate the HVAC in spaces or areas that are occupied if you can control it that way. This would reduce energy consumption, minimize equipment wear and tear, and extend the lifespan for filters. 
  • Make sure systems are regularly inspected and maintained to run properly. 
  • Inspect the outside air dampers to ensure they are open and the system is bringing in outside air. 

Tools for Workplaces  

California employers can review the Interim Guidance for Ventilation, Filtration, and Air Quality in Indoor Environments. ​

Group of masked doctors

Skilled Nursing Facilities                                       

Since COVID-19 transmission risk increases in poorly ventilated indoor environments, it's important to know how to set up well ventilated spaces. Read about frequently asked questions from skilled nursing facilities. 

Teacher in classroom


Improving indoor air quality creates a healthier school environment by reducing COVID-19 and other diseases that spread through the air. Learn more here: Information for School Districts on Purchase of Filtration and Air Cleaning Devices (PDF)

Additional Resources


Other resources 

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