ASHRAE Journal - September 2020 - 21

TECHNICAL FEATURE

exposure,3 and ASHRAE has adopted that position.4
Environmental epidemiology provides the most direct
way to establish the significance of airborne transmission in the spread of COVID-19 and the efficacy of
measures to limit airborne exposure. Environmental
epidemiological studies require collaboration between
engineers and health scientists to consider the location
and timing of cases and environmental conditions associated with these.
The following epidemiological studies suggest airborne
transmission of COVID-19.
Poorly Ventilated Restaurant. A detailed engineering evaluation was performed of conditions at the
time of a COVID-19 outbreak at a restaurant in China.
After mapping case locations, conditions experienced
by both infected and unaffected customers and staff
were characterized. The role of different transmission
routes was evaluated by comparing factors influencing
exposure of the two groups. Findings from this study
included:
* Ten of the 73 restaurant customers were infected.
* Those 10 were seated at three adjacent tables on one
side of the dining room, approximately 1 m to 5 m (3 ft to
16 ft) from a customer who had just arrived from Wuhan
before community spread in the rest of China.
* HVAC consisted of five fan coil units (FCU) with no
outside air and exhaust fans (off at the time).
* Measured ventilation rates (infiltration only) were
an order of magnitude below ASHRAE Standard 62.12019.
* Modeling of airflow patterns established that a
"bubble" was formed by each FCU, dividing the room
into five separate zones containing contaminants released in that zone.
* Modeling results also suggested that discharge from
the FCUs directed air in the breathing zone between
customers.
* The three impacted tables were within the same
zone.
* Air from the contaminated zone did not mix significantly with the rest of the room, and no customers were
infected in those areas.
* Surveillance videos showed that close contact between individuals and fomite contact were not significant.

* Waiters did have brief contact with infected customers, but that was insufficient to cause infection.
This study concluded that SARS-CoV-2 was transmitted by a combination of close contact (i.e., droplet exposure within 2 m [7 ft]) and aerosol exposure
beyond that distance (extended short-range airborne).
Poor ventilation resulting in little dilution of the virus
was considered a very important factor. This study
cannot be used to draw general conclusions on the
prevalence of airborne transmission due to the atypical HVAC configuration. Lack of customer infection
in adjacent zones suggests that SARS-CoV-2 was sufficiently isolated to prevent disease transmission. Lack
of waiter infection suggests that brief contact was not
sufficient to transmit COVID-19.5
Poorly Ventilated Bus. One hundred twenty-six people traveled to a religious event in China in two buses,
each with a recirculating air-conditioning system (no
outside air). An infected individual from Wuhan was on
one of the buses. All passengers mixed with the infected
individual at a three-day religious event, along with 172
other attendees who had not been in the buses. Thirty
persons subsequently contracted COVID-19, and they
were classified as follows:
* No passengers on the bus without the infected individual had COVID-19.
* Seven attendees who had not been in the buses
contracted COVID-19 but were in close contact with the
infected individuals during the event.
* Twenty-three riders on the bus with the passenger
from Wuhan were infected. By location, there were
more cases in individuals sitting beyond 2 m (7 ft) of the
infected passenger.6
Poorly Ventilated Conference Center. Also in China,
30 people attended a three-day event with an infected
individual from Wuhan in a building with poor ventilation (HVAC cycled on only 15 minutes per four hours).
It was not determined who had been in close proximity to the infected individual, and thus within droplet
range. Fifteen attendees were subsequently infected.
Investigators concluded that some infections were due
to airborne exposure after comparing the infection
rate to similar outbreaks and that ineffective dilution
because of poor ventilation appeared to be a major
contributor.6

Ed Light, CIH, is president, James Bailey, P.E., is vice president and Reid Lucas is a controls specialist at Building Dynamics in Savage, Md. Laurence Lee, CIH, is owner and founder
of Pacific Industrial Hygiene in Kirkland, Wash.
SEPTEM BER 2020

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ASHRAE JOURNAL

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ASHRAE Journal - September 2020

Table of Contents for the Digital Edition of ASHRAE Journal - September 2020

Contents
ASHRAE Journal - September 2020 - Intro
ASHRAE Journal - September 2020 - Cover1
ASHRAE Journal - September 2020 - Cover2
ASHRAE Journal - September 2020 - 1
ASHRAE Journal - September 2020 - Contents
ASHRAE Journal - September 2020 - 3
ASHRAE Journal - September 2020 - 4
ASHRAE Journal - September 2020 - 5
ASHRAE Journal - September 2020 - 6
ASHRAE Journal - September 2020 - 7
ASHRAE Journal - September 2020 - 8
ASHRAE Journal - September 2020 - 9
ASHRAE Journal - September 2020 - 10
ASHRAE Journal - September 2020 - 11
ASHRAE Journal - September 2020 - 12
ASHRAE Journal - September 2020 - 13
ASHRAE Journal - September 2020 - 14
ASHRAE Journal - September 2020 - 15
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ASHRAE Journal - September 2020 - 17
ASHRAE Journal - September 2020 - 18
ASHRAE Journal - September 2020 - 19
ASHRAE Journal - September 2020 - 20
ASHRAE Journal - September 2020 - 21
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ASHRAE Journal - September 2020 - Cover3
ASHRAE Journal - September 2020 - Cover4
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