“I don’t know how to be more direct than this. COVID is inhaled in aerosols in the air by people who are simply speaking. Proper protection needs to be provided to those who spend time indoors around people including grocery stores, dental offices, meat packing, the list goes on.”

– Kimberley Prather, PhD, scientist and professor, March 7, 2021 (Twitter)

Length of time exposed to viruses increases risk of infection

How long people are exposed to the SARS-CoV-2, the virus that causes COVID-19, also plays a critical role in infection. Erin Bromage, Comparative Immunologist and Professor of Biology (specializing in Immunology) at the University of Massachusetts Dartmouth, helped boil down how time spent with the virus increases the risk of infection in this equation:

Successful Infection = Exposure to Virus x Time.

While this reality has been illuminated thanks to the pandemic, it is certainly not limited to SARS-CoV-2. Bromage pointed to influenza studies showing that “a person infected with influenza can release up to 33 infectious viral particles per minute.”

In search of an analogy: the wasp and the pathogen

When asked for an analogy to explain the importance of quickly eliminating pathogens, we landed on a wasp. Not surprisingly, a wasp flying around in a room can be a cause for concern, many room occupants wishing to avoid an unpleasant, painful sting. And for those who are highly allergic to wasps, they are particularly keen for immediate, decisive action to dispatch the wasp. The possibility of being stung increases when a wasp is flying around a room for 30 minutes versus a wasp flying around for a few seconds.

Now, consider another “flying,” potentially deadly “bug” in an occupied room—SARS-CoV-2. However, instead of just one visible creature zipping around the room, there are hundreds, thousands, potentially millions of these microscopic pathogens in the air generated by people “who are simply speaking.”

As the pandemic has progressed, there have been a tumult of claims by products that they can kill 99.9% of SARS-CoV-2, but over what span of time? Does it take 30 minutes or a few seconds? How long are infectious pathogens (the legions of microscopic wasps) flying around?

Air purifiers vs. UVGI

The term “air purifier” is used to identify a variety of devices designed to remove pathogens from the air. For purposes of this article, air purifiers refer to devices that rely on filters to trap pathogens. Pathogens making their way to the air purifier could take, on average, 30 minutes or even several hours depending on the size air purifier you have relative to the space. Additional potential issues if relying on these types of air purifiers to eliminate pathogens:

• Air purifiers trap particles, they do not kill them. Moreover, not all of the particles going in with the air are trapped. A common size rating to determine the appropriate size device for a room are based on providing an 80% reduction in particles. See more on size ratings, below.*
• Because live organisms may be on the filter, precaution must be used when changing filters.
• If airflow is blocked due to air purifier’s location, or because the filter is full, you have no benefits as nothing is being cleaned.
• Because the air purifiers are at floor level, and depending on how many are required for the space, noise levels may be elevated beyond recommended decibel levels (a particular issue in schools and other learning environments).

The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) and the Centers for Disease Control and Prevention (CDC) both recommend utilizing higher MERV-rated filters to trap large particles but, crucially, they also recommend ultraviolet germicidal irradiation (UVGI) upper room units and in-duct UVGI (installed in ventilation systems) to help eliminate pathogens.

UVGI like that manufactured by Aerapy harnesses the power of UV-C light to kill the pathogens in the air. Although air naturally moves to the upper portion of rooms due to convection currents (“heat rises”), Aerapy’s upper air units include integrated fans to draw the air—and the pathogens—into the path of the UV-C to shorten kill time. The upper air UV is designed to clean the air in occupied spaces, continuously eliminating “bugs” in the air. Similarly, for UVGI used in ventilation systems, air circulates through the ventilation system, passing by the disinfecting UV-C, before sending out clean air.

But, as always, the type and amount of UVGI is critical. It must be the right UV. As emphasized by environmental engineering professor Shelly Miller, PhD, in a March 17, 2021 tweet:

“Do not confuse germicidal UV, UV-C, with other unproven technologies. there is a ton of science going back almost 100 years showing it an effective method to inactivate airborne infectious microbes.”

Aerapy manufactures UVGI—germicidal UV—products that are researched, tested, and study-backed to kill more than 99.9% of tested virus and bacterial pathogens, including SARS-CoV-2. In independent laboratory testing against the coronavirus, Aerapy UV achieved a 99.97% reduction of the SARS-CoV-2 pathogen in the air, in one air pass. Aerapy UV also achieved a 99.98% reduction on surfaces in two seconds 99.99% in three seconds.

Less time spent with the virus decreases the risk of infection.

*More on size ratings. From the EPA: “Sizing portable air cleaners: Portable air cleaners should have a CADR (clean air delivery rate) that is large enough for the size of the room in which it is operated. For example, an air cleaner that has a CADR of 250 for dust particles can reduce dust particle levels to the same concentration as would be achieved by adding 250 cfm of clean air to the space in question. Units tested according to procedures established by the Association of Home Appliance Manufacturers (AHAM) carry an AHAM-Verified® label that suggests the appropriate maximum room size for the device. The size rating is intended to provide an 80 percent reduction in particle levels (at equilibrium conditions) as compared to levels without the air cleaner operating. Portable air cleaners often achieve a high CADR by using a HEPA filter, although other technologies can also achieve a high CADR.”