HVAC Systems and COVID-19
Do we need to protect employees from our building’s air conditioners?
Cause for concern?
In one study, available online as a preprint and has not undergone scientific review, researchers in Oregon collected samples from various places inside a hospital’s HVAC system and found genetic material from the virus that causes COVID-19. This demonstrates that it may be possible for the virus to be transmitted through HVAC systems.
The research started late; the final evidence is not in yet
However, researchers did not assess if the genetic material they found was able to cause infection, and they noted there were no confirmed COVID-19 cases associated with the samples found in the ventilation systems.
There is currently no conclusive evidence documenting the possibility of COVID-19 transmission through an air conditioning unit.
The known risk is non-circulation indoors
The known risk is that hot weather outside makes people seek air-conditioned comfort indoors. And indoors, there is less ventilation and more opportunity to spread disease. The risk to healthcare workers is that we are indoors and, on occasion, not socially distancing and rebreathing the air that people have just exhaled.
When we shut the doors and windows to keep the hot air outside, we are essentially eliminating the flow of fresh air, so everyone in the room is breathing and rebreathing the same air. If someone in the room is infected with COVID-19, then they are breathing out the virus, which can linger in airborne droplets and be inhaled by another person, potentially causing infection.
By comparison, if you were outside and near an infected person who breathed out some viral particles, there is a much larger volume of air flowing to disperse and dilute those particles quickly, reducing the risk of spread to another person nearby. That is why infectious disease experts consider outdoor gatherings and activities less risky than indoor ones (though not completely risk-free).
Another suspected risk of air conditioning
The other significant risk is that air conditioning units, fans, or even an open window can create strong enough air currents to move virus-containing droplets around a room. This happened in January at a restaurant in Guangzhou, China, where a person with COVID-19 infected five other people sitting at neighboring tables from 3 to 6 feet away, according to a study by scientists from the Chinese Center for Disease Control and Prevention. After examining video footage of the diners who were infected and simulating the transmission of the virus, scientists concluded that the small outbreak was caused by strong air currents from the air conditioning unit above the diners, which was blowing virus-containing aerosols from an infected person to those nearby. The restaurant also had no windows — and thus no ventilation bringing in fresh air and diluting virus particles in the air.
A clue: Flu particles can travel 30 feet in the air
The fact that aerosolized viral droplets can move in air currents in this way means that if you are in a room with an infected person and fresh air is not circulating, even if you are socially distancing to keep 6 feet apart at a minimum, you may not be safe. Although there are currently no published studies that have examined precisely how far airborne COVID-19 particles can travel, previous research on influenza found that viral particles may travel upward of 30 feet in the air.
To be clear, this is only a concern in shared public places. At home, the risk of contracting COVID-19 through air currents or air conditioning units is no more likely than spreading the virus through close contact or touching contaminated surfaces.
CDC Engineering recommendations for protecting employees right now:
- Modify or adjust seats, furniture, and workstations to maintain social distancing of 6 feet between employees, where possible.
o Install transparent shields or other physical barriers where possible to separate employees and visitors where social distancing is not an option.
o Arrange chairs in reception or other communal seating areas by turning, draping (covering the chair with tape or fabric so seats cannot be used), spacing, or removing chairs to maintain social distancing.
- Use methods to physically separate employees in all areas of the building, including work areas and other areas such as meeting rooms, break rooms, parking lots, entrance and exit areas, and locker rooms.
o Use signs, tape marks, or other visual cues such as decals or colored tape on the floor, placed 6 feet apart, to show where to stand when physical barriers are not possible.
o Replace high-touch communal items, such as coffee pots and bulk snacks, with alternatives such as pre-packaged, single-serving items. Encourage staff to bring their own water to minimize the use and touching of water fountains or consider installing no-touch activation methods for water fountains.
o Consider taking steps to improve ventilation in the building, in consultation with an HVAC professional, based on local environmental conditions (temperature/humidity) and ongoing community transmission in the area:
o Increase the percentage of outdoor air (e.g., using economizer modes of HVAC operations) potentially as high as 100% (first, verify compatibility with HVAC system capabilities for both temperature and humidity control as well as compatibility with outdoor/indoor air quality considerations).
o Increase total airflow supply to occupied spaces, if possible.
o Disable demand-control ventilation (DCV) controls that reduce air supply based on temperature or occupancy.
o Consider using natural ventilation (i.e., opening windows if possible and safe to do so) to increase outdoor air dilution of indoor air when environmental conditions and building requirements allow.
o Improve central air filtration:
- Increase air filtration to as high as possible without significantly diminishing design airflow.
- Inspect filter housing and racks to ensure appropriate filter fit and check for ways to minimize filter bypass.
o Consider running the HVAC system at maximum outside airflow for 2 hours before and after occupied times, in accordance with industry standards.
o Generate clean-to-less-clean air movements by re-evaluating the positioning of supply and exhaust air diffusers and/or dampers and adjusting zone supply and exhaust flow rates to establish measurable pressure differentials. Have staff work in “clean” ventilation zones that do not include higher-risk areas such as visitor reception or exercise facilities (if open).
- Consider using portable high-efficiency particulate air (HEPA) fan/filtration systems to help enhance air cleaning (especially in higher-risk areas).
- Ensure exhaust fans in restroom facilities are functional and operating at full capacity when the building is occupied.
- Consider using ultraviolet germicidal irradiation (UVGI) as a supplemental technique to inactivate potential airborne virus in the upper-room air of common occupied spaces, in accordance with industry guidelines.
CDC References and links for these recommendations are found here: https://www.cdc.gov/coronavirus/2019-ncov/community/office-buildings.html