ASHRAE Journal - March 2021 - 24
TECHNICAL FEATURE
Virus Transmission Modes and Mitigation Strategies, Part 1
Defining Viruses
And Droplet Release
BY JONATHAN BURKETT, P.E., HFDP, MEMBER ASHRAE
The recent COVID-19 crisis has led to increased concern about the transmission of
viruses. One particular area of concern has been the transmission of viruses in classrooms and other spaces served by single-zone HVAC systems. Therefore, it's essential
to understand how viruses are commonly transmitted and what mitigation strategies are available, which is the topic of this article. An article in next month's ASHRAE
Journal will cover airborne virus transmission and the effect of air distribution.
A virus is a small, intracellular parasite consisting
of RNA or DNA enclosed in a protein coat that cannot
reproduce by itself, but can direct a susceptible host cell
to produce more viruses.1 This virus, consisting of the
nucleic acid (RNA or DNA) and an outer shell (capsid), is
called a virion.1 The study of viruses is a relatively recent
endeavor with the isolation of individual viruses and
their assignment to specific diseases occurring about
1898.2 With the invention of the electron microscope in
1931, viruses could finally be visualized, and in 1939 the
first virus (tobacco mosaic virus) was visualized using
electron microscopy.3
In 1897 Carl Flügge, a German bacteriologist, showed
that droplets from the nose and mouth contained bacteria, and the idea of droplet transmission was born.4
Then in 1934 William F. Wells released his study " On
Air-Borne Infection. Study II. Droplets and Droplet
Nuclei. " 5 In this study Wells showed the relationship
between droplet size, evaporation and falling rate.
Since Wells' study, continued research has expanded
our understanding on virus transmission and infection
mechanisms.
Virus Transmission
Viruses are commonly transferred from an infected
person to a susceptible person in two ways:
* Direct Transmission
* Direct contact: contact between an infected
person and a susceptible person (i.e., skin-to-skin
contact, kissing, etc.); and
* Droplet spread: large, short-range droplets
produced during sneezing, coughing, talking, etc., that
make direct impact with a susceptible person.
* Indirect Transmission
* Vehicles: food, water, blood and fomites (inanimate objects or materials that can carry pathogens
Jonathan Burkett, P.E., is a mechanical engineer at Buford Goff & Associates in Columbia, S.C.
This peer-reviewed article does not represent official ASHRAE guidance. For more information on ASHRAE resources on COVID-19, visit ashrae.org/COVID19.
24
ASHRAE JOURNAL
ashrae.org
MARCH 2021
http://www.ashrae.org/COVID19
http://ashrae.org
ASHRAE Journal - March 2021
Table of Contents for the Digital Edition of ASHRAE Journal - March 2021
Contents
ASHRAE Journal - March 2021 - Intro
ASHRAE Journal - March 2021 - Cover1
ASHRAE Journal - March 2021 - Cover2
ASHRAE Journal - March 2021 - 1
ASHRAE Journal - March 2021 - Contents
ASHRAE Journal - March 2021 - 3
ASHRAE Journal - March 2021 - 4
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ASHRAE Journal - March 2021 - Cover3
ASHRAE Journal - March 2021 - Cover4
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