Originally published on April 3, 2020 by BNP Media through the Building Enclosure Blog.

The coronavirus disease 2019 (COVID-19) crisis has certainly impacted most of our lives and the AEC industry in which we operate. As I write this article, our understanding of the coronavirus that causes COVID-19 continues to evolve in a very fluid manner.

In consideration of personal protective equipment (PPE) in social spaces, people have gravitated to variations of face masks. The U.S Food & Drug Administration (FDA) and Centers for Disease Control and Prevention (CDC) have both issued advice for proper respirator types and usage for respiratory protection preparedness. One of the primary challenges in filtering the coronavirus is that such virions are extremely small. According to emerging research, such as which is exhibited by the National Center for Biotechnology Information (NCBI), coronavirus virions are spherical with diameters of approximately 0.13 micrometers.

Just how small is a virus?

Let us put the size of a micrometer into perspective. Figure 1 exhibits a graphic representation of the relative diameter of a variety of particles. While bacteria exists in a wide variety of shapes and sizes, the figure categorically depicts bacteria as having a representative diameter of 1µm (micrometer). By comparison, the diameter of a strand of human hair can range between 17 to 181 µm (60 µm is depicted in the figure).

At the other end of the spectrum are viruses, which can range between 0.02 – 0.40 µm. Again, coronavirus virions tend to exist on the smaller end of the range. In simple and generalized terms, a coronavirus can be 1/10 of the size of a bacteria cell, which is 1/10 of the size of a dust particle, which is around 1/10 of the diameter of a strand of human hair.

Figure 1: Relative Particle Sizes. Illustration by Daniel Overbey.

Can HVAC filters stop viruses?

Among other issues, this crisis has renewed my personal interest in air filtration as a critical strategy for indoor air quality.