By Eamonn Ryan
ASHRAE Journal Podcast Episode 26 features two of the most influential figures in building science and indoor environmental quality: William Bahnfleth and Max Sherman. Hosted by Emily Toto, ASHRAE manager of codes, the episode explores the intent, development and implications of ASHRAE Standard 241: Control of Infectious Aerosols, a landmark standard created in direct response to lessons learned during COVID-19. This is part five of a six-part series.
Lessons learned from COVID. Freepik.com
During COVID, the market for air-cleaning technologies exploded. Alongside proven solutions came a wave of devices with bold claims and little evidence. Building owners were left to navigate a confusing landscape where marketing often outpaced science.
ASHRAE Standard 241 confronts this challenge directly – but not by endorsing specific products or technologies. Instead, it establishes a governance framework for deciding what counts.
This distinction is crucial.
Why ASHRAE refused to pick winners
From the outset, the Standard 241 committee made a deliberate decision: the standard would not promote or prohibit specific technologies.
As Sherman explains, picking winners would have frozen innovation and invited controversy. Worse, it could have locked the industry into today’s solutions while excluding better ones tomorrow.
Instead, Standard 241 asks a simpler, more powerful question: Can this technology demonstrate that it is safe and that it delivers equivalent clean air?
If the answer is yes, it counts.
Appendix A: the gatekeeper for innovation
Appendix A is the mechanism that makes this approach work. It defines performance-based test methods that any air-cleaning technology – existing or emerging – can use to demonstrate compliance.
Appendix A does not lower the bar. In fact, it raises it by requiring:
- Credible evidence of effectiveness
- Verification of safety, including byproduct generation
- Transparent, reproducible testing
Technologies that pass these requirements can be used to meet ECA targets under Standard 241, even if no product-specific standard yet exists.
This is how Standard 241 encourages innovation without opening the door to snake oil.
Existing standards and the gaps they leave
Where possible, Standard 241 references established standards, including:
- ASHRAE 185 series for air-cleaning performance
- Emerging ASTM standards for byproduct testing
But as both speakers note, these standards are incomplete. New technologies often appear years before test standards catch up. Appendix A fills that gap. It acts as a bridge between innovation and regulation, ensuring that absence of a product standard does not mean absence of scrutiny.
One of the most subtle achievements of Standard 241 is how it maintains neutrality. No technology is presumed effective. None is excluded by default.
Instead, all technologies are treated equally under the same question: Show us the data.
This approach benefits everyone:
- Building owners gain confidence
- Designers gain flexibility
- Manufacturers gain a clear pathway to legitimacy
Innovation is rewarded, but only when it is real.
Lessons learned from COVID
The committee’s philosophy is rooted in experience. During the pandemic, well-intentioned guidance sometimes amplified unverified solutions simply because something – anything – was needed.
Standard 241 corrects that by embedding scientific discipline into the standard itself. It recognises that urgency must not override evidence.
As Bahnfleth emphasises, the burden is shared. The standard enables new technologies, but industry must meet the responsibility of proving safety and effectiveness.
The Appendix A framework may ultimately outlive Standard 241 itself. As new challenges emerge – wildfire smoke, chemical exposures, future pathogens – the idea of performance-based inclusion may become the dominant model for environmental health standards.
Rather than chasing specific threats or technologies, the standard defines how to evaluate solutions, whatever they may be.
That is governance, not advocacy, and it is one of Standard 241’s most enduring contributions.
