In an effort to assist engineers in designing healthier indoor environments for buildings, ASHRAE unveiled its new standard meant to reduce the risk of disease transmission. ASHRAE Standard 241, Control of Infectious Aerosols, establishes minimum requirements to reduce the risk of disease transmission by exposure to infectious aerosols, the tiny, exhaled particles that can carry disease-causing pathogens. Because of their size, these aerosols can remain in the air for long periods of time and be inhaled by facility users, spreading diseases such as COVID-19, influenza viruses, and other pathogens that cause major personal and economic damages every year.
Standard 241 represents a significant step forward in prioritizing air quality and is meant to be an essential tool for creating healthier indoor environments and promoting sustainable practices. It provides requirements for many aspects of air system design, installation, operation, and maintenance, including:
Infection risk management mode
The requirements of Standard 241 apply during an infection risk management mode (IRMM) that applies during identified periods of elevated risk of disease transmission. ASHRAE cites “authorities having jurisdiction” as bodies able to mark these periods, but the owner or operator of the space can also activate them during influenza season, for example. This aspect of Standard 241 introduces the concept of resilience—the ability to respond to extreme circumstances outside of normal conditions—into the discipline of indoor air quality control design and operation.
Requirements for equivalent clean airflow rate
Other indoor air quality standards, including ASHRAE Standards 62.1 and 62.2, specify outdoor airflow rate and filtration requirements to control normal indoor air contaminants. According to ASHRAE, Standard 241 is innovative because it sets:
- new requirements for equivalent clean airflow rate;
- the flow rate of pathogen-free air 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 gives the user of the new ASHRAE standard flexibility to select combinations of technologies to comply with the standard that best satisfy economic constraints and energy use goals.
Requirements for use of filtration and air cleaning technology
Standard 241 provides extensive requirements for use of filtration and air cleaning to achieve equivalent clean airflow requirements. 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
The new standard 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.
The Standard 241 committee will continue to work on improving sections of the standard, adding additional requirements, clarifying requirements, and developing tools to help the public use the standard effectively. Industry and consumer-friendly resources such as courses, podcasts, factsheets, and information events will be introduced in the future.
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