AS ONE of the foremost experts in the field of airborne pathogen transmission, I have a question: Who was the person(s) who recommended the plexiglass barriers in our restaurants, grocery stores, and nearly every other public place?

Over the past year, as the president elect of the Granite State ASHRAE (American Society of Heating, Refrigeration and Air Conditioning Engineers), I have hosted multiple webinars on airborne pathogen transmission from top scientists and airflow modeling experts in the world, and not one of them has said plexiglass is an effective strategy for mitigating the transmission of COVID-19, or any other airborne pathogen.

There is absolutely no scientist or scientific evidence that supports this solution, yet I (literally) bump into it everywhere I go. And when professionals in my area of expertise are asked where this idea came from, no one knows. The only condition in which plexiglass would possibly help is the case of someone sneezing or coughing directly in front of you without turning away or covering their nose/mouth. But that was very rare prior to the COVID-19 pandemic, and is even more rare now.

The CDC has (finally) just announced the primary means of SARS-CoV2 transmission is airborne. Those of us who have been following the science and modeling airflow have known this for over a year now. The probability of contracting COVID-19 from direct (handshake) or indirect (doorknob) is “considered to be very low,” according to the most recent CDC April 5th guidance. The dominant path is through the air, and air does not abide by the rules of plexiglass. Airborne pathogens can remain active in room air currents for hours. In fact, there is a strong argument that it makes it worse. To become infected with COVID-19, a person must inhale enough “viral load” to start a reaction in the human respiratory system. The viral load is measure as a density, so its concentration matters. By putting plexiglass in place, the viral load concentration is increased, and so is the probability of infection. Removing the plexiglass would reduce the concentration, along with the probability of infection.

The science proves that cleaning the air is much more effective and can be done at approximately the same cost as the plexiglass installation.

For those who may doubt my assertion, let me ask a simple question? If plexiglass is so effective, why not allow smoking in restaurants where plexiglass has been installed in the booths? The idea seems absurd to most, but smoke and airborne pathogens follow the same laws of physics. They are both light particles that travel with air currents in the room.

Surely, we have learned that a smoker in a restaurant will contaminate others with passive smoke that is determinantal to human health. So why are we treating airborne pathogens differently?

Paul Bemis is a mechanical engineer and president elect of Granite State American Society of Heating, Refrigeration and Air Conditioning Engineers. He lives in Bristol.

Thursday, May 06, 2021
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AS ONE of the foremost experts in the field of airborne pathogen transmission, I have a question: Who was the person(s) who recommended the plexiglass barriers in our restaurants, grocery stores, and nearly every other public place?

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