Dear Editor,

Thank you for your thoughtful reflection on September 11 (Twenty-Five Years Later, We Are Rebuilding Still, Sept/Oct 2026 issue). I particularly appreciated the hopeful conclusion. Indeed, I remember back then that I walked to campus that morning. It was a cloudless, cool, dry, early autumn morning that fills one with energy and hope….and then…

I also appreciated your reference to ASHRAE's then-President Bill Coad, a peerless engineering practitioner, educator, and communicator. He was a role model throughout my career and I was privileged to work with him on a number of ASHRAE committees. As President, he even came to visit our student branch at Penn State…and gave a technical presentation! As usual, he found just the right words to capture that moment.

Some time after 9/11, I was asked to serve on a National Academies Consensus Committee on protecting building occupants from CBR (chemical, biological, and radiological) events. One of the things we did was visit the Pentagon to observe their security systems.

I remember a few things about that visit more than two decades later:

1. Going onto the roof and discovering that it is slate!;
2. The annual maintenance cost on CBR detection and response systems was a seven-figure amount! And...
3. Standing at the window in the restored section where the plane hadf struck on 9/11, looking out on the newly completed memorial, and remembering that day... It was quite an emotional moment.

I wish I could say that the response to that moment would have been to consider the vulnerability of buildings to airborne threats – chemical and pathogenic – but the calculus was that while consequences were severe when an event occurred, the probability was miniscule.

Twenty-five years later, a novel pathogen unleashed by accident – whether you believe it was in wet markets or a laboratory accident – showed that buildings were still ineffective at protecting us from airborne hazards and the engineering community again proposed protections that are strikingly similar to those recommended decades earlier.

Today, we live under the dual threats of more novel, naturally emerging pathogens like avian influenza that have demonstrated some ability to spill over from animal reservoirs to humans and, added to that, the potential for A.I. to enable a new generation of terrorists to design pathogens as bad or even worse than SARS-CoV-2.

With that context, thanks also for publishing Jason Hartke’s cover story on the Global Framework for Action. I’m glad that there is a global conversation going on about the need to improve IAQ in buildings, including their resilience in the face of airborne disease outbreaks and increasing incidence of wildfire events in regions not accustomed to them. I do believe that there is a motivated professional community eager to help respond to these challenges.

The barriers, as I have been saying for quite a while, are at the regulatory level – laws, codes, enforcement. The release of the Global Framework is evidence that there is broad recognition of this problem. It’s a first step, but to achieve the vision, local action is needed and, in the U.S., that is challenging – but those of us who believe in the necessity of changing the status quo soldier on... Because we must.

Bill Bahnfleth, PhD, PE, FASHRAE, FASME, FISIAQ

Professor of Architectural Engineering,

The Pennsylvania State University