Preventing the Spread of Respiratory Viruses in Public Indoor Spaces

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This page provides guidance for schools, offices, and commercial buildings on implementing a comprehensive suite of building system and indoor air quality strategies to reduce the spread of common respiratory viruses indoors.

On this page:

Implementing a Multi-Layered Indoor Air Approach
Ventilation, Filtration and Supplemental Air Cleaning, and Air Treatment
Administrative Controls
Reconfiguration of Building Spaces and Furnishings
Cleaning and Disinfection

On other pages:

Implementing a Multi-Layered Indoor Air Approach

The Centers for Disease Control and Prevention (CDC) recommends a suite of preventive actions to protect individuals and communities from respiratory viruses, especially when:

Respiratory viruses are causing a lot of illness in your community.
You or the people around you were recently exposed to a respiratory virus, are sick, or are recovering.
You or the people around you have risk factors for severe illness.

Visit CDC’s webpage on Respiratory Viruses to find information about how to reduce your risk of getting sick from these viruses, and if they are spreading in your community.

Each year, respiratory viruses are responsible for millions of illnesses and thousands of hospitalizations and deaths in the United States. In addition to the virus that causes COVID-19, there are many other types of airborne respiratory viruses, including influenza (flu) and respiratory syncytial virus (RSV), that can spread more easily indoors than outdoors, since their concentration can build up indoors and people are often closer to each other.

Organizations can implement strategies to reduce the spread of respiratory viruses indoors and promote good indoor air quality, including:

Ensure proper ventilation indoors.
Filter particles from the air.
Provide supplemental air cleaning and air treatment.
Implement administrative controls and space reconfiguration.

On their own, these individual indoor air strategies are not likely to be sufficient for preventing the spread of respiratory viruses indoors, making it essential to implement each of them, as is needed, in a multilayered strategy.

However, several factors may influence whether these strategies can be implemented in a particular building, including differences in building type, occupancy, and use of the space. Therefore, you may consider consulting with a professional to understand your building’s capabilities and with implementing a multilayered strategy.

Ventilation, Filtration and Supplemental Air Cleaning, and Air Treatment

Ventilation and filtration are important components of a multilayered approach for reducing the spread of respiratory viruses indoors. Increasing the amount of outdoor air coming indoors is one of the most important ways to reduce the likelihood that viruses are spread. When it is challenging to enhance the ventilation to a space, consider cleaning or treating the air to reduce virus particles. Air cleaning, by filtering virus particles from the air through furnace filters in your heating, ventilation, and air conditioning (HVAC) system or portable air cleaning devices, is another approach for reducing the spread of respiratory viruses indoors.

Air treatment devices are typically designed to remove or inactivate airborne and/or surface virus particles indoors using technologies besides particle filtration. However, the effectiveness of some emerging air treatment technologies is less well-documented than for more established options.

This section will help you develop a multi-layered strategy for improving the amount of ventilation indoors, as well as considering supplemental air cleaning to reduce the spread of respiratory viruses indoors. Please note that these strategies will vary by building and may also depend on the building type, age and capability of HVAC systems in a building. You may need to consult with a professional to implement your strategy.

Ventilation

Increase outside-air ventilation to the maximum extent practical.
Adjust or reconfigure air flows to minimize the spread of viruses between people. This may include redirecting airflows to prevent air from blowing directly from person to person, when feasible, exhausting restrooms directly to the outdoors, and other targeted steps.

Visit Ventilation and Respiratory Viruses to learn how to increase ventilation to reduce the spread of respiratory viruses indoors. For additional guidance and information, please visit:

Centers for Disease Control and Prevention:

Filtration and Supplemental Air Cleaning

In addition to improving ventilation for a building or a space within a building, consider the following filtration and supplemental air cleaning approaches to reduce the amount of viral particles in the air:

Increase air filtration by filtering the air that is re-circulated by the HVAC system through the building to remove more aerosol particles (i.e., very small airborne particles, including those containing viruses). Increase air filtration by upgrading HVAC filters to MERV 13 (or the highest MERV rating a building’s ventilation system can accommodate).
Place portable air cleaners in areas that are hard to ventilate with outside air or that have high density or occupancy.

For additional guidance and information, including on how to select a high-performance air filter or air cleaner, please visit:

Air Cleaners, HVAC Filters, and Coronavirus (COVID-19).
Guide to Air Cleaners in the Home, 2nd edition (printable) (pdf) (2.94 MB, August 2018)

Air Treatment Technologies

Upper Room Ultraviolet Germicidal Irradiation (UVGI) is a well-established air treatment based on the ability of light in the ultraviolet spectrum to kill or inactivate microorganisms, including respiratory viruses, by damaging their genetic code. Upper-room UVGI can provide a germicidal effect in a space where it is properly installed and maintained. Upper-room UVGI is not a replacement for effective ventilation or filtration but can be used to further reduce disease transmission in combination with adequate ventilation and filtration.

For more information on UVGI please see CDC’s Upper-Room Ultraviolet Germicidal Irradiation (UVGI).

Some emerging air treatment devices can use technologies such as the addition of chemicals, charged ions, or photolysis. These technologies can be found in a variety of devices and building types. They either use non-traditional filter technology or incorporate particle filtration among multiple other air treatments. Some emerging air treatments may adversely impact indoor air through, for example, the generation of ozone and the evidence for their safety is less well-documented than for more established ones.

Alert
Caution

Avoid devices that generate ozone. Ozone is a lung irritant.

Some emerging air treatments may generate ozone. When possible, look for evaluations and safety certifications from third parties. One such certification is the UL standard 2988 which certifies that a tested device produces ozone below the limit of detection of the test instruments (5ppb).

Setting Ventilation and Filtration Goals

How is Ventilation Measured?

Ventilation is commonly measured in terms of air exchange rate.

Air Changes Per Hour (ACH) A common measure of ventilation is known as air changes per hour (ACH). This measure (the airflow per hour divided by the volume of the space) indicates the number of times per hour the entire volume of air in a room would be replaced with outside air.

Equivalent Air Changes Per Hour (eACH) Strategies that involve supplemental filtration, such as the use of a portable air cleaner, or other technologies such as ultraviolet germicidal irradiation (UVGI), can be compared to ventilation using equivalent air changes per hour (eACH). The eACH is based on the volume of treated air per hour plus the outdoor airflow provided to the space.

When setting a goal for ventilation and filtration improvements, it is important to determine the feasibility of that goal given the current system. This may require consultation with an experienced HVAC technician to ensure the building’s HVAC system can operate properly with proposed changes without damage or unacceptable loss of performance.

Some buildings and indoor spaces might not have the capacity to reach aggressive ventilation goals while maintaining thermal comfort, particularly goals that might be established during periods of heightened disease transmission, by solely relying on dilution with outdoor air. In these instances, an "equivalent ventilation” approach may be useful.

"Equivalent ventilation” is generally expressed in Equivalent Air Changes Per Hour (eACH) and can be calculated as the volume of filtered, treated, or outside air supplied per unit time, divided by the volume of the room. Equivalent ventilation, unlike ventilation with outdoor air alone, relies in part on air filtration and air treatment. Air filtration and air treatment help control particles and biological contaminants like respiratory viruses, but do not necessarily reduce other important indoor air pollutants, such as gases, chemicals, and odors) in the same way as ventilation with clean outdoor air. As a result, equivalent ventilation is a helpful approach for considering how best to control the spread of respiratory viruses in public indoor spaces, but it is not a substitute for meeting minimum outdoor air delivery requirements that may be specified in national, state, and local building codes.

CDC recommends, when possible, to aim for one of two ventilation goals to help reduce the number of viral particles in the air in public indoor spaces:

5 ACH (Air Changes per Hour) using outdoor air ventilation alone; or
5 eACH (Equivalent Air Changes per Hour) using a combination of ventilation from outdoor air, filtration, and other air treatment

More specific guidance on setting a ventilation rate for different buildings to control infection can be found in ASHRAE Standard 241 (see the following link).

For more information and detailed guidance setting a ventilation and filtration goal, please visit:

Administrative Controls

Administrative controls are steps taken to modify the occupancy of a space and are also important components of a multilayered approach to reducing the spread of respiratory viruses in a building or other indoor space.

Administrative controls may include:

Practices designed to reduce crowding or occupancy such as telework, staggered schedules, remote/video meetings, etc.
Limiting the use of small spaces that are shared, such as meeting rooms, laundry rooms, and lobbies.

Reconfiguration of Building Spaces and Furnishings

Reconfiguration of building spaces is another approach that can help reduce the spread of respiratory viruses indoors. The goals of reconfiguration of building spaces and furnishings are to increase the amount of space or separation between individuals indoors, minimize direct air flow between people, and reduce their interaction in high-traffic areas of buildings.

Reconfiguration efforts may include:

Reconfiguration of building layouts and/or of individual rooms.
Reorientation of office furniture or cubicles. For example, reorienting adjoining workstations so employees do not face each other can be an important component of an overall plan to address the virus.

Cleaning and Disinfection

Cleaning frequently touched surfaces and being diligent about hygiene when you may be sick with a respiratory virus are core strategies for preventing the spread of illness. For more information and best practices for cleaning and disinfection, please visit:

Return to Indoor Air and Coronavirus (COVID-19).