Protecting Occupants

Protecting Occupants in Non Healthcare Environments from Airborne Infections

Recognized Practices

ASHRAE has communicated great concern about the possibility of transmission through the air of various pathogens, especially SARS-CoV-2, among staff and administration in healthcare facilities, workers in office environments, staff and patrons in retail settings, workers in manufacturing, residents in private and public facilities, and the general public in outdoor settings and in public transportation.

The ASHRAE Position Document on Infectious Aerosols includes HVAC-system recommendations for hospital and various healthcare facilities which are aimed at reducing occupant exposure to infectious aerosols. Practices addressed include ventilation-related strategies including dilution, airflow patterns, pressurization, temperature and humidity distribution and control, filtration, and other “best practice” approaches. But what about those non-healthcare occupancies, including but not limited to schools, offices, restaurants and other places of public work and assembly?

Briefly addressed in this same document are “facilities of all types” where it’s recommended that HVAC design teams should follow, as a minimum, the latest published standards and guidelines along with good (or best) engineering practice. Designers of new and existing facilities are told to look beyond the minimum requirements of these standards, using techniques covered in various ASHRAE publications, to be better prepared and control the dissemination of infectious aerosols within the built environment. ASHRAE states “These buildings should have a plan for an emergency response”, advising that the following modifications to building HVAC system operation should be considered:

• Increase outdoor air ventilation (disable demand-controlled ventilation and open outdoor air dampers to 100% as indoor and outdoor conditions permit).
• Improve central air and other HVAC filtration to MERV-13 (ASHRAE 2017b) or the highest level achievable.
• Keep systems running longer hours (24/7 if possible).
• Add portable room air cleaners with HEPA or high-MERV filters with due consideration to the clean air delivery rate (AHAM 2015).
• Add duct- or air-handling-unit-mounted, upper room, and/or portable UVGI devices in connection to in-room fans in high-density spaces such as waiting rooms, prisons, and shelters.
• Maintain temperature and humidity as applicable to the infectious aerosol of concern.
• Bypass energy recovery ventilation systems that leak potentially contaminated exhaust air back into the outdoor air supply.
• Design and build inherent capabilities to respond to emerging threats and plan and practice for them.

Understanding that healthcare facilities have ASHRAE criteria for ventilation design to mitigate airborne transmission of infectious diseases, same or similar transmissions may also occur in “ordinary” occupancies within the community. ASHRAE provides general ventilation and air quality requirements for these in Standards 62.1 and 62.2., but does not provide specific requirements for infectious disease control in homes, schools, prisons, shelters, transportation, or other public facilities.

Best Practices

Sufficient published data shows the effectiveness of different filtration and air-cleaning technologies in removing contaminants from indoors and outdoors. In conjunction with proper mechanical (media filtration), products incorporating technology such as in-duct and upper-room UV devices (UVGI), Needlepoint Bipolar Ionization (NPBI), Photocatalytic Oxidation (PCO), Liquid Desiccant Dehumidification (LDD), along with an assortment of others should be considered and perhaps “bundled” with traditional mechanical filtration to help improve the overall quality of the indoor environment. (Refer to “The HVAC System’s Role in Environmental Infection Control for Hospitals” as noted in this documents reference for more details on these). It’s cautioned that careful attention should be paid to generation of ozone (a known respiratory irritant) when applying alternative IAQ solutions, specifically any device that requires power to clean the air, including polarized media filters, electrostatic precipitators, negative ion generators, bipolar ion generators, needlepoint bipolar ion generators, dielectric barrier discharge ion tubes, corona discharge ion tubes, UV lights, etc. ASHRAE notes that extreme caution is warranted when using devices in which ozone is emitted, even unintentionally, during the air-cleaning process as a byproduct.


Addendum aj to ANSI/ASHRAE Standard 62.1-2016 Section 5.7.1 addresses this issue by requiring air cleaning devices to be listed and labeled in accordance with UL 2998. Underwriters Laboratories (UL) in Northbrook, IL, recently took on the task of creating the validation for zero ozone air cleaning devices. It requires that qualifying zero ozone emission products must demonstrate they emit less than the maximum ozone concentration limit of 0.005 ppm (5 ppb) which is below quantifiable levels for ozone testing. This is 10-fold less than permitted under test standard UL 867, which allows concentrations of 0.05 ppm (50 ppb). UL 2998 doesn’t guarantee product performance, it only certifies the technology is safe to use in respect to ozone generation.

While there is no consensus on the safe level of ozone, ASHRAE’s Environmental Health Committee (2011b) issued an emerging issue brief suggesting “safe ozone levels would be lower than 10 ppb” and that “the introduction of ozone to indoor spaces should be reduced to as low as reasonably achievable (ALARA) levels.” In the ASHRAE Position Document on Filtration and Air Cleaning it’s stated that “even though the ozone is an unintentional by-product of operation, it may represent a net negative impact on indoor air quality and thus should be used with caution. If possible, non-ozone-emitting alternatives should be used.

Regardless of make or model, all filtration and air-cleaning technologies should be accompanied by data documenting their performance regarding removal of contaminants and production of any ozone. This data should be based on established industry test standards, and if not available should then consist of scientifically controlled third-party evaluation and documentation.

COVID-19 Recommendations

ASHRAE has recognized that the transmission of SARS-CoV-2 through the air is sufficiently likely and that airborne exposure to the virus should be controlled. Changes to building operations, including the operation of heating, ventilating, and air-conditioning systems, can reduce airborne exposures.

What about measures to specifically address concerns with the SARS-CoV-2 virus which caused the disease COVID-19? HVAC technologies that are proven to “kill” COVID-19 are not yet available with reliable testing to back-up this claim. Until now, the novel virus was not available for study. With the understanding that it can take more than a year to get a viral claim approved by regulatory agencies, the United States Environmental Protection Agency (EPA) has enacted a “hierarchy-based” policy. This means if a company’s product has been found to be effective against harder-to-kill viruses, its “likely” to kill a virus like COVID-19. A product that is likely to provide the greatest protection to you from COVID-19 will have claims against at least one non-enveloped virus such as Norovirus, Feline Calicivirus, Poliovirus, Rhinovirus, or Reovirus. Once we have products available with evidence-based test results our options will be more clearly defined, but this may take considerable time. It’s always best to use products that have been qualified for the specific viral pathogen of concern. Until then, the EPA says that if you cannot obtain those products, then use products that are effective at killing Human Coronavirus because it’s expected those products will also be effective against SARS-CoV-2.

ASHRAE’s statement on operation of heating, ventilating, and air-conditioning systems to reduce SARS-CoV-2/COVID-19 transmission:

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. Unconditioned spaces can cause thermal stress to people that may be directly life threatening and that may also lower resistance to infection. In general, disabling of heating, ventilating, and air-conditioning systems is not a recommended measure to reduce the transmission of the virus.

Closing Thoughts

HVAC system design for buildings is a blend of code and standards compliance along with a healthy dose of engineering best practice. Professionals involved in the design, construction, and service of any complex

structure must keep abreast of ever-changing needs and requirements, while taking keen interest in the rapid evolvement of shifting dynamics in the built-environment. Many building owners and operators are financially incentivized to improve the occupant experience which places tremendous value on the benefits garnered from productivity, safety, and health. After the events of the worldwide coronavirus disease 2019 pandemic, the building-industry will never return to status quo. Engineers responsible for the systems which produce the temperature, humidity, air movement, ventilation and filtration within these environments are under increased pressure to assure facility owners and operators that their designs meet stringent code mandates while also contributing to the complex dynamics of occupant wellbeing and improved outcome.


  1. ASHRAE Position on Infectious Aerosols.
  2. ASHRAE Position Document on Airborne Infectious Diseases.
  3. ASHRAE Position Document on Filtration and Air Cleaning.
  4. ANSI/ASHRAE Standard 62.1-2016 Addendum aj.
  5. Aaron Engle, Fresh-Air UV North America.
  6. David N. Schurk, Whitepaper: The HVAC System’s Role in Environmental Infection Control for Hospitals. 7. Center for Biocide Chemistries Answers Your Questions about COVID-19 by Sarah J. Scruggs | March 11, 2020.