CDC in its latest report, recommends a layered strategy to reduce exposures to SARS-CoV-2, the virus that causes COVID-19. This includes using multiple mitigation strategies with several layers of safeguards to reduce the spread of disease and lower the risk of exposure.
Ventilation interventions
Below is a list of ventilation interventions that can help reduce the concentration of virus particles in the air, such as SARS-CoV-2. They represent a list of “tools in the mitigation toolbox,” each of which can be effective on its own.
These ventilation interventions can reduce the risk of exposure to the virus and reduce the spread of disease, but they will not eliminate risk completely.
Considerations to Improve Ventilation
Some of the recommendations below are based on Guidance for Building Operations During the COVID-19 Pandemic from the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE).
In addition to buildings, ventilation considerations are also important when you have multiple persons within vehicles, including public transportation (buses, subways, trains, school buses, carpools, and rideshares). Not all considerations are applicable to all scenarios.
Ventilation improvements may include some or all of the following considerations:
- Increase outdoor air ventilation, using caution in highly polluted areas.
- When weather conditions allow, increase fresh outdoor air by opening windows and doors. Do not open windows and doors if doing so poses a safety or health risk (e.g., risk of falling, triggering asthma symptoms) to occupants in the building.
- Use fans to increase the effectiveness of open windows. To safely achieve this, fan placement is important and will vary based on room configuration. Avoid placing fans in a way that could potentially cause contaminated air to flow directly from one person over another. One helpful strategy is to use a window fan, placed safely and securely in a window, to exhaust room air to the outdoors. This will help draw fresh air into the room via other open windows and doors without generating strong room air currents.
- Decrease occupancy in areas where outdoor ventilation cannot be increased.
- Ensure ventilation systems operate properly and provide acceptable indoor air quality for the current occupancy level for each space.
- Increase airflow to occupied spaces when possible.
- Turn off any demand-controlled ventilation (DCV) controls that reduce air supply based on occupancy or temperature during occupied hours. In homes and buildings where the HVAC fan operation can be controlled at the thermostat, set the fan to the “on” position instead of “auto,” which will operate the fan continuously, even when heating or air-conditioning is not required.
- Open outdoor air dampers beyond minimum settings to reduce or eliminate HVAC air recirculation. In mild weather, this will not affect thermal comfort or humidity. However, this may be difficult to do in cold, hot, or humid weather.
- Improve central air filtration:
- Increase air filtration to as high as possible without significantly reducing design airflow.
- Inspect filter housing and racks to ensure appropriate filter fit and check for ways to minimize filter bypass.
- Check filters to ensure they are within their service life and appropriately installed.
- Ensure restroom exhaust fans are functional and operating at full capacity when the building is occupied.
- Inspect and maintain local exhaust ventilation in areas such as kitchens, cooking areas, etc. Operate these systems any time these spaces are occupied. Consider operating these systems, even when the specific space is not occupied, to increase overall ventilation within the occupied building.
- Consider portable high-efficiency particulate air (HEPA) fan/filtration systems to help enhance air cleaning (especially in higher risk areas such as a nurse’s office or areas frequently inhabited by persons with a higher likelihood of COVID-19 and/or increased risk of getting COVID-19).
- Generate clean-to-less-clean air movement by re-evaluating the positioning of supply and exhaust air diffusers and/or dampers (especially in higher risk areas).
- Consider using ultraviolet germicidal irradiation (UVGI) as a supplement to help inactivate SARS-CoV-2, especially if options for increasing room ventilation are limited. Upper-room UVGI systems can be used to provide air cleaning within occupied spaces, and in-duct UVGI systems can help enhance air cleaning inside central ventilation systems.
Note
The ventilation intervention considerations listed above come with a range of initial costs and operating costs which, along with risk assessment parameters such as community incidence rates, facemask compliance expectations, and room occupant density, may affect considerations for which interventions are implemented.
Cost estimates per room for the listed ventilation interventions in cost. Here are some examples:
In non-residential settings, consider running the HVAC system at maximum outside airflow for 2 hours before and after the building is occupied.
- No cost: opening windows; inspecting and maintaining local exhaust ventilation; disabling DCV controls; or repositioning outdoor air dampers
- Less than $100: using fans to increase the effectiveness of open windows, or repositioning supply/exhaust diffusers to create directional airflow
- $500 (approximately): adding portable HEPA fan/filter systems
- $1500 (approximately): adding upper room UVGI
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Source: CDC
