By Katherine Ratliff, Ph.D., physical scientist, US EPA Office of Research and Development, Center for Environmental Solutions and Emergency Response, Homeland Security and Materials Management Division
When the COVID-19 pandemic started, researchers at the US Environmental Protection Agency (EPA)’s Office of Research and Development quickly focused efforts on how to reduce the spread of the virus through environmental exposure. 1 EPA scientists and engineers provided technical support to a wide variety of organizations, including other government agencies, industry, schools and transportation organizations.
Many of the questions that came in were related to what kinds of technologies could be used as effective engineering solutions for reducing concentrations of infectious virus in the built environment. An increasing number of technologies were being marketed to do this, but it often was challenging to assess how well these technologies would work in real-world settings. Researchers in EPA’s Homeland Security Research Program (HSRP), 2 which has conducted applied research on decontamination and disinfection for over two decades, quickly redirected some of their efforts to address many questions related to these technologies.
Given their well-known and historic use for inactivating microorganisms in water, air and on surfaces, researchers and stakeholders were particularly interested in germicidal ultraviolet (GUV) technologies. Many organizations were asking about how new and emerging technologies, including ionizers, photocatalytic and novel types of GUV devices, would work compared to increasing ventilation, filtration and traditional GUV. Another common question was whether these technologies live up to the performance claims in their marketing materials.
Challenges in GUV Device Assessment
As HSRP reviewed the available testing data, it became clear that it was challenging to assess how well many of these technologies would perform under real-world conditions. Because there was no routinely used standard test method for evaluating GUV effectiveness against pathogens on surfaces or in the air that related to real-world performance, researchers in academia, government and industry conducted experiments using a wide variety of laboratory methods. This made it very challenging to compare results across studies.
Moreover, testing often was conducted under conditions that were ideal for product performance, but not so representative of the true application setting. Laboratory data generated this way effectively can overstate technology performance against pathogens in the real world. Hence, there was an obvious need for robust scientific information on how well different types of mitigation technologies work to reduce the risk of exposure to pathogens in the occupied indoor settings.
Research Studies to Address Challenges
HSRP designed new research studies to address these challenges. Some of the initial work addressed questions related to how effectively different types of GUV devices would reduce SARS-CoV-2 concentrations on surfaces in high-touch settings, like transit environments. 3 HSRP conducted experiments to evaluate how exposing the virus to GUV on different materials (e.g., stainless steel, plastic, bus seat fabric) and in simulated saliva impacted technology performance.
Testing also showed that exposing the virus in a droplet that had dried on a surface could reduce GUV effectiveness, compared to GUV exposures with the virus in wet droplets. Stakeholders and decisionmakers used these important findings when developing strategies on how best to use different kinds of technologies as part of an overall layered approach for improving public health protections in the built environment.
As it became clear that COVID-19 primarily is transmitted in the air, HSRP also designed and executed a new research program to evaluate technologies that can reduce infectious aerosol concentrations. Many air cleaning and treatment devices are tested in small test chambers, which again can make it challenging to extrapolate their performance to more realistic settings.
HSRP adapted existing specialized laboratory facilities in Research Triangle Park, North Carolina, to create a new large bioaerosol test chamber, which can be used to conduct experiments at a scale that is more representative of real-world conditions. Experts across government, industry and academia provided input on designing the test chamber and experimental methods. To date, many different types of air cleaning and treatment technologies have been evaluated to quantify their effectiveness to reduce bioaerosol concentrations in this setup, including GUV, ionization and photocatalytic devices, along with portable HEPA and DIY air cleaners. 4,5 HSRP has found that even small changes to test methodology, including aerosolizing the microorganism in saliva (compared to deionized water), can have significant impacts on GUV effectiveness.
Motivated by these findings, HSRP is conducting additional experiments to evaluate how the composition of the media surrounding various microorganisms (beyond SARS-CoV-2) impacts GUV effectiveness at different wavelengths. Researchers also are conducting additional studies to inform choices on using different surrogate microorganisms, and other ongoing experiments are evaluating the impacts of combining air cleaning strategies.
GUV Standards Development
HSRP’s findings are helping to develop and improve standardized test methods for both air and surface treatment technologies, including GUV. These efforts support both EPA’s regulatory mission and industry stakeholders through organizations like ASHRAE and the American National Standards Institute (ANSI).
We need transparent, voluntary consensus standards for both effectiveness and safety to make informed decisions and investments on the optimal use of GUV technologies, as well as to drive innovation in the field. These standards also are critical for understanding how to use GUV and other treatment devices to achieve new indoor air quality targets, such as the five equivalent air changes per hour recommended as part of CDC’s ventilation guidance 6 and ASHRAE 241’s clean airflow requirements across different occupied spaces. 7 Additional research also is needed to improve understanding of how to bridge findings from laboratory testing to predicting GUV performance in application settings.
Right now, there is a great opportunity to leverage the sustained attention, scientific and technological developments, and industry activity to improve public health protections against disease transmission. Decision makers need a better understanding of how to balance different economic, health, energy and economic goals to make the most informed investments and develop the most holistic strategies for protecting public health and the environment. EPA and other federal agencies will continue to work on a wide range of related activities, from research to technical assistance, to financial sponsorship in low income and disadvantaged communities, to guidelines development for the nation’s built environment. Together, these exciting scientific and technological advances can be harnessed to ensure a healthier world.
References
- U.S. Environmental Protection Agency. “COVID-19 Research.” https://www.epa.gov/emergency-response-research/covid-19-research. Accessed 20 November 2024.
- U.S. Environmental Protection Agency. “Emergency Response Research.” https://www.epa.gov/emergency-response-research. Accessed 20 November 2024.
- Oudejans, L., and K. Ratliff. “COVID-19: UV-C Devices and Methods for Surface Disinfection”, EPA Emergency Response Research Webinar Series. https://www.epa.gov/emergency-response-research/covid-19-uv-c-devices-and-methods-surface-disinfection-webinar. 21 January 2021.
- Ratliff, K., and L. Oudejans. “COVID-19: Evaluating Aerosol Treatment Technologies”, EPA Emergency Response Research Webinar Series. https://www.epa.gov/emergency-response-research/covid-19-evaluating-aerosol-treatment-technologies-webinar. 9 February 2022.
- Ratliff, K., and A. Heffernan. “EPA’s Research and Regulation of Pesticidal Air Treatment Devices”, EPA IAQ Science Webinar. https://www.youtube.com/watch?v=BP_-poHzo1k. 6 September 2023.
- CDC National Institute for Occupational Safety and Health. “Ventilation Mitigation Strategies.” https://www.cdc.gov/niosh/ventilation/prevention/. Accessed 20 November 2024.
- ASHRAE (2023). Standard 241, Control of Infectious Aerosols. https://www.ashrae.org/technical-resources/bookstore/ashrae-standard-241-control-of-infectious-aerosols.
Dr. Katherine Ratliff is a physical scientist at the US Environmental Protection Agency’s Office of Research and Development and principal investigator in EPA’s Homeland Security Research Program. She uses numerical models, lab and field-scale studies to develop strategies aimed at reducing the risk of exposure to hazardous contaminants, including leading EPA’s research to evaluate the effectiveness of air cleaning technologies against airborne pathogens. Dr. Ratliff also is involved in developing standard methods and testing guidelines for these technologies and supports EPA’s regulatory mission under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA). She received her B.A. in Earth and Environmental Sciences from Vanderbilt University and a Ph.D. in Earth and Ocean Sciences from Duke University. For more information, visit www.epa.gov/emergency-response-research.
