Science and Technical Resources related to Indoor Air and Coronavirus (COVID-19)
The importance of different routes of transmission for SARS-CoV-2 is an ongoing area of research. SARS-CoV-2 can remain airborne in indoor environments for hours, potentially increasing in concentration over time. Therefore, unless adequate precautions are taken, the longer a space is occupied and the more people that are present, the greater the potential for airborne transmission of the virus (See also Key References on Indoor Air and COVID-19).
As a result, lowering the concentration of SARS-CoV-2 by means of ventilation and filtration plays an important role in controlling transmission of the virus that causes COVID-19. In addition, physical distancing, wearing masks, and avoidance of crowded indoor spaces can play a role in controlling transmission of the virus. Consult guidance from the Centers for Disease Control and Prevention (CDC) and local authorities on current guidelines on the use of masks. Ventilation is also a critical measure that can be taken to reduce exposure to cleaning products, disinfectants, and the byproducts they produce as a result of chemical reactions in indoor air.
Links to additional information
CDC has stated: "SARS-CoV-2 viral particles spread between people more readily indoors than outdoors. Indoors, the concentration of viral particles is often higher than outdoors, where even a light wind can rapidly reduce concentrations. When indoors, ventilation mitigation strategies can help reduce viral particle concentration. The lower the concentration, the less likely viral particles can be inhaled into the lungs (potentially lowering the inhaled dose); contact eyes, nose, and mouth; or fall out of the air to accumulate on surfaces. Protective ventilation practices and interventions can reduce the airborne concentrations and reduce the overall viral dose to occupants."
The EPA SAB has stated: "There is evidence that inhalation of expelled aerosol from infected individuals is potentially a significant pathway in the spread of SARS-CoV-2 (Alford, 1966; Douglas, 1975; Little, 1979; Tellier, 2006). The SAB presented some of this evidence as part of the public teleconference on April 30, 2020 (Jayjock, 2020). A continuum of particle sizes ranging from less than 1 micron to over 1,400 microns is emitted when people cough, sneeze, speak or exhale (Nicas, 2005; Chao, 2009; Lindsley, 2010; Milton, 2013; Bourouiba, 2014; Skaria, 2014; MacIntyre, 2016; Bourouiba, 2020). These particles can deposit into the deepest part of the lung, the alveoli (Milton, 2013; Lindsley, 2010)."
CDC has stated: "COVID-19 can sometimes be spread by airborne transmission. Some infections can be spread by exposure to virus in small droplets and particles that can linger in the air for minutes to hours. These viruses may be able to infect people who are further than 6 feet away from the person who is infected or after that person has left the space. This kind of spread is referred to as airborne transmission and is an important way that infections like tuberculosis, measles, and chicken pox are spread."
CDC has stated: “Modes of SARS-CoV-2 transmission are now categorized as inhalation of virus, deposition of virus on exposed mucous membranes, and touching mucous membranes with soiled hands contaminated with virus.”
“Although how we understand transmission occurs has shifted, the ways to prevent infection with this virus have not.”
“The principal mode by which people are infected with SARS-CoV-2 (the virus that causes COVID-19) is through exposure to respiratory fluids carrying infectious virus. Exposure occurs in three principal ways: (1) inhalation of very fine respiratory droplets and aerosol particles, (2) deposition of respiratory droplets and particles on exposed mucous membranes in the mouth, nose, or eye by direct splashes and sprays, and (3) touching mucous membranes with hands that have been soiled either directly by virus-containing respiratory fluids or indirectly by touching surfaces with virus on them.”
ASHRAE (formerly the American Society of Heating, Refrigerating and Air-Conditioning Engineers) has stated: “Ventilation and filtration provided by heating, ventilating, and air-conditioning systems can reduce the airborne concentration of SARS-CoV-2 and thus the risk of transmission through the air.”
• Read CDC's Improving Ventilation in Your Home.
CDC has stated: People can be infected with SARS-CoV-2 through contact with surfaces. However, based on available epidemiological data and studies of environmental transmission factors, surface transmission is not the main route by which SARS-CoV-2 spreads, and the risk is considered to be low.
- Read the CDC article: Ventilation Improvement Strategies Among K-12 Public Schools — The National COVID-19 Prevention Study
- Read the CDC-authored article: Reducing SARS-CoV-2 in Shared Indoor Air
- Read the CDC report: Knowledge and Practices Regarding Safe Household Cleaning and Disinfection for COVID-19 Prevention — United States, May 2020
- Read the American Industrial Hygiene Association (AIHA) Covid-19 Resources
- Read Federation of European Heating, Ventilation and Air Conditioning Associations (REHVA) Resources on post-COVID ventilation
- Watch the EPA IAQ Science Series Webinar: SARS-CoV-2 in Indoor Air: Principles and Scenarios
- Read the ASHRAE guidance: Reopening of schools and universities (pdf)
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Watch the National Academies of Sciences, Engineering, and Medicine (NASEM) 2 day virtual workshop: Airborne Transmission of the SARS-CoV-2, featuring presentations by experts in aerosol science, virology, infectious disease, and epidemiology.