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ASHRAE Approves New Standard on Infectious Aerosols

June 26, 2023
Groundbreaking move signifies "major step forward" in reducing risk of infectious disease spread in buildings, society says.


ATLANTA (June 24, 2023) – ASHRAE announced the approval for publication of its highly anticipated airborne infection risk mitigation standard for buildings, bringing numerous benefits to occupants and promoting healthier environments.

ASHRAE Standard 241, Control of Infectious Aerosols establishes minimum requirements to reduce the risk of disease transmission by exposure to infectious aerosols in new buildings, existing buildings, and major renovations. Infectious aerosols are tiny, exhaled particles that can carry disease-causing pathogens and are so small that they can remain in the air for long periods of time and be inhaled. Use of this standard would reduce exposure to SARS-COV-2 virus, which causes COVID-19, influenza viruses and other pathogens that cause major personal and economic damage every year. Standard 241 provides requirements for many aspects of air system design, installation, operation, and maintenance.

Important aspects of the standard include:

Infection Risk Management Mode – Requirements of Standard 241 apply during an infection risk management mode (IRMM) that applies during identified periods of elevated risk of disease transmission. AHJs (Authorities Having Jurisdiction) can determine when the enhanced protections of Standard 241 will be required, but its use can also be at the discretion of the owner/operator at other times, for example, during influenza season. This aspect of Standard 241 introduces the concept of resilience – ability to respond to extreme circumstances outside normal conditions - into the realm of indoor air quality control design and operation;Requirements for Equivalent Clean Airflow Rate – Other indoor air quality standards, including ASHRAE Standards 62.1, 62.2, specify outdoor airflow rate and filtration requirements to control normal indoor air contaminants. Standard 241 breaks new ground by setting requirements for equivalent clean airflow rate, the flow rate of pathogen free air flow into occupied areas of a building that would have the same effect as the total of outdoor air, filtration of indoor air, and air disinfection by technologies such as germicidal ultraviolet light. This approach allows the user of the standard flexibility to select combinations of technologies to comply with the standard that best satisfy their economic constraints and energy use goals;Requirements for Use of Filtration and Air Cleaning Technology – Dilution of indoor air contaminants by ventilation with outdoor air can be an energy intensive and expensive way to control indoor air quality. Standard 241 provides extensive requirements for use of filtration and air cleaning to effectively and safely achieve meet equivalent clean airflow requirements efficiently and cost effectively. These include testing requirements to establish performance and to demonstrate that operation does not degrade indoor air quality in other ways, for example by elevating ozone levels;
  • Planning and Commissioning – Standard 241 provides assessment and planning requirements culminating in the development of a building readiness plan, a concept carried over from the work of the ASHRAE Epidemic Task Force. It also describes procedures for commissioning systems to determine their installed performance.
  • "Standard 241 represents a significant step forward in prioritizing indoor air quality," said 2022-23 ASHRAE President Farooq Mehboob, Fellow ASHRAE. "By implementing the requirements outlined in this standard, we can improve the health, well-being and productivity of building occupants. This standard empowers building owners, operators and professionals to take proactive measures in safeguarding indoor environments. It's an essential tool for creating healthier indoor environments and promoting sustainable practices."

    While not an ANSI standard, the consensus process from project approval, development and final approval of this standard, including a public review, took six months from authorization to completion and only four months of development time dating from the first meeting of the project committee.

    “Volunteers and staff dedicated their expertise and thousands of hours of their time to address this urgent industry and societal need,” added ASHRAE Presidential Fellow and Standard Project Committee 241 chair William Bahnfleth, Ph.D., P.E. “The development of this standard shows not only ASHRAE’s ability to respond rapidly to a societal need, but also a steadfast commitment to the health and safety of people in buildings everywhere. This is a significant achievement and milestone in connecting building design and operation with public health.”

    The Standard 241 committee will continue and work on improving sections of the standard adding additional requirements, clarifying requirements and developing tools to help the public use the standard. Industry and consumer-friendly resources such as courses, podcasts, factsheets and information events will be introduced in the future.

    Standard 241 is available now for presale in the ASHRAE Bookstore. 

    About ASHRAE

    Founded in 1894, ASHRAE is a global professional society committed to serve humanity by advancing the arts and sciences of heating ventilation, air conditioning, refrigeration and their allied fields. As an industry leader in researchstandards writingpublishingcertification and continuing education, ASHRAE and its members are dedicated to promoting a healthy and sustainable built environment for all, through strategic partnerships with organizations in the HVAC&R community and across related industries.

    Media Contact:

    Karen Buckley Washington, Senior Public Relations Specialist, [email protected].