IAQ: Airborne Pathogens—The Problem

Do you worry about COVID-19? Here is more to worry over.

Our human nature wants tangible, visible evidence of threats to our persons. This works to our good when a threat is a reckless driver or a pothole in a road. But airborne pathogens are invisible threats. The graphic depicts the relative sizes of a wide range of these threats from fungi spores to tiny viruses.

Source: ResearchGate.com

Early in the COVID-19 pandemic, the CDC emphasized droplets as the primary transport mechanism of the communist Chinese virus designated SARS-CoV-2. SARS-CoV-2 stands for severe acute respiratory syndrome coronavirus 2. SARS-CoV-2 is the strain of coronavirus that causes the COVID-19 disease. (WebMD)

To better understand droplets, look to the first four letters: drop. These drop down. Not up.

In October 2020, the CDC described droplets as the principal mode by which people are infected with SARS-CoV-2 (the virus that causes COVID-19) is through exposure to respiratory droplets carrying infectious virus. Most infections are spread through close contact, not airborne transmission.

The same CDC brief differentiates between ‘larger dropletsthat fall out of the air rapidly within seconds to minutes and ‘smaller droplets and particlesthat can remain suspended for many minutes to hours and travel far from the source on air currents.

In September 2020, the CDC first warned against infectious aerosols then abruptly changed its mind. The question of ‘following the science’ arises.

Before reading on, I suggest taking a few moments to review some Fun Facts and Physics of Water to aid in the understanding the difference between aerosols and droplets.

One month before the CDC report on aerosols, Time Magazine reported COVID-19 Is Transmitted Through Aerosols. We Have Enough Evidence, Now It Is Time to Act

Many diseases, including COVID-19, infect most effectively at close proximity. Since droplets are visible and fall to the ground between 3-6 feet, we can readily see and understand this route of infection. In fact, it was thought for decades that tuberculosis was transmitted by droplets and fomites, based on ease of infection at close proximity, but research eventually proved that tuberculosis can only be transmitted through aerosols. I believe that we have been making a similar mistake for COVID-19.

Time Magazine, 25 Aug 2020

For clarity, the word aerosol used in this brief means a suspension of fine solid or liquid particles in gas, specifically airborne aerosol transmission of infective viral particles.

What has physical separation got to do with transmission of the disease?

“There is growing evidence those aerosols can travel well beyond a six foot distance and linger in the air. It could be a few minutes, it really depends. It could be a few seconds and someone has the the time to inhale it and it could be hours and we know that some particles will remain airborne forever. They will never settle down, so it can be from a few minutes to forever.” Caroline Duchaine is a professor at the Université Laval in Quebec City. She’s also a bio-aerosol expert. Excerpt from the above video starting at minute 02:06.

In order for a person to become ill from the SARS-CoV-2/COVID-19 virus, the infective dose must be breached. No one knows what this number is but we know from experience with other airborne pathogens that there is a threshold for infection.

By no means does the writer intend to present himself as an expert on epidemiology; the purpose of this briefing is to point to HVAC systems and processes by which the density of airborne pathogens can be minimized toward the goal of preventing infections and transmissions of the virus between humans.

For more information: FAQs on Protecting Yourself from COVID-19 Aerosol Transmission

The Science of Social Distancing – Perhaps Not What You Think

What do radiation (all kinds), light, sound, odors, and airborne pathogens share in common? Intensity varies as a function of distance between the source and the affected person. The common function is the inverse square law.

Diagram for purposes of predicting relative concentration of airborne pathogen vs distance | Spread of the virus-laden aerosols depends on wind direction and speed.

In the world of engineering and science, the usual and customary application of the inverse square law is to evaluate changes in the intensity of light or changes to the loudness of a source of sound as the observer moves closer to or farther from the source of sound or light.

I suggest we take a scientific approach to understanding the transmissibility of airborne pathogens like Sars-CoV-2/COVID19 from an infected person to persons in the proximity of the infected person. Application of the principle of the inverse square law can help us understand how we are more susceptible to infection as we approach an infected person.

The CDC recommends 6 feet or more, the WHO about half that distance, but experts say the science is far from settled. [Smithsonian Magazine 22 Sep 2020]

Back in the early 1960s, my cousin Norman would hold his breath while driving past the tuberculosis hospital in Corpus Christi. Holding one’s breath is probably not the best solution to avoiding infection.

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Back to Understand the problem: An Airborne Pathogen

Published by John White

A lifetime (over 50 years) of experiences with automation and control systems ranging from aerospace navigation, radar, and ordinance delivery systems to the world's first robotic drilling machine for the oil patch, to process-control systems, energy management systems and general problem-solving. At present, my focus is on self-funding HVAC retrofit projects and indoor air quality with a view to preventing infections from airborne pathogens.

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