Physical distance may not be enough to prevent viral aerosol exposure
indoors
Architectural engineering team investigated the effects of physical distancing, building ventilation as control strategies

Date:
September 14, 2021
Source:
Penn State
Summary:
Eighteen months ago, stickers began to dot the floors of most shops,
spaced about six feet apart, indicating the physical distance
required to avoid the COVID-19 virus an infected person may shed
when breathing or speaking. But is the distance enough to help
avoid infectious aerosols?


FULL STORY ========================================================================== Eighteen months ago, stickers began to dot the floors of most shops,
spaced about six feet apart, indicating the physical distance required
to avoid the COVID-19 virus an infected person may shed when breathing
or speaking. But is the distance enough to help avoid infectious aerosols?

==========================================================================
Not indoors, say researchers in the Penn State Department of Architectural Engineering. The team found that indoor distances of two meters --
about six and a half feet -- may not be enough to sufficiently prevent transmission of airborne aerosols. Their results were made available
online ahead of the October print edition of Sustainable Cities and
Society.

"We set out to explore the airborne transport of virus-laden particles
released from infected people in buildings," said Gen Pei, first author
and doctoral student in architectural engineering at Penn State. "We investigated the effects of building ventilation and physical distancing
as control strategies for indoor exposure to airborne viruses."
The researchers examined three factors: the amount and rate of air
ventilated through a space, the indoor airflow pattern associated
with different ventilation strategies and the aerosol emission mode
of breathing versus talking. They also compared transport of tracer
gas, typically employed to test leaks in air-tight systems, and human respiratory aerosols ranging in size from one to 10 micrometers. Aerosols
in this range can carry SARS-CoV-2.

"Our study results reveal that virus-laden particles from an infected
person's talking -- without a mask -- can quickly travel to another
person's breathing zone within one minute, even with a distance of two
meters," said Donghyun Rim, corresponding author and associate professor
of architectural engineering.

"This trend is pronounced in rooms without sufficient ventilation. The
results suggest that physical distance alone is not enough to prevent
human exposure to exhaled aerosols and should be implemented with
other control strategies such as masking and adequate ventilation." The researchers found that aerosols traveled farther and more quickly in rooms
with displacement ventilation, where fresh air continuously flows from
the floor and pushes old air to an exhaust vent near the ceiling. This
is the type of ventilation system installed in most residential homes,
and it can result in a human breathing zone concentration of viral
aerosols seven times higher than mixed-mode ventilation systems. Many commercial buildings use mixed-mode systems, which incorporate outside
air to dilute the indoor air and result in better air integration --
and tempered aerosol concentrations, according to the researchers.

"This is one of the surprising results: Airborne infection probability
could be much higher for residential environments than office
environments," Rim said.

"However, in residential environments, operating mechanical fans and
stand- alone air cleaners can help reduce infection probability."
According to Rim, increasing the ventilation and air mixing rates can effectively reduce the transmission distance and potential accumulation
of exhaled aerosols, but ventilation and distance are only two options
in an arsenal of protective techniques.

"Airborne infection control strategies such as physical distancing,
ventilation and mask wearing should be considered together for a layered control," Rim said.

The researchers are now applying this analysis technique to various
occupied spaces, including classrooms and transportation environments.

Mary Taylor, a graduate student at Penn State at the time of the research,
also contributed to this work, which was supported by the National
Science Foundation.

========================================================================== Story Source: Materials provided by Penn_State. Original written by
Ashley J. WennersHerron.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Gen Pei, Mary Taylor, Donghyun Rim. Human exposure to respiratory
aerosols in a ventilated room: Effects of ventilation condition,
emission mode, and social distancing. Sustainable Cities and
Society, 2021; 73: 103090 DOI: 10.1016/j.scs.2021.103090 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/09/210914184827.htm

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