ASHRAE Journal - December 2020 - 12

LETTERS

following COVID-19. " https://tinyurl.com/y2al8rjy. Accessed 8:01AM
PST, October 8th 2020.
2. I. Duncan, " Nearly 11,000 people have been exposed to the
coronavirus on flights, the CDC says. " The Washington Post, Sept.
19, (2020). https://tinyurl.com/y2524fsw.
3. J. Chen J, H. He, W. Cheng. Potential transmission of
SARS-CoV-2 on a flight from Singapore to Hangzhou, China:
An epidemiological investigation. Travel Med Infect Dis. (2020);
36:101816. https://doi.org/10.1016/j.tmaid.2020.101816
4. C. Eldin, J.-C. Lagier, M. Mailhe, P. Gautret, Probable aircraft
transmission of Covid-19 in-flight from the Central African
Republic to France; Travel Medicine and Infectious Disease 35 (2020).
https://doi.org/10.1016/j.tmaid.2020.101643
5. A. Pavli, P. Smeti, S. Hadjianastasiou. In-flight transmission of
COVID-19 on flights to Greece: An epidemiological analysis; Travel
Medicine and Infectious Disease, Vol 38, (2020) Sept 17.
https://doi.org/10.1016/j.tmaid.2020.101882
6. S. Hoehl, O. Karaca, N. Kohmer, Assessment of SARSCoV-2 Transmission on an International Flight and Among
a Tourist Group; JAMA Netw Open. 3(8):e2018044, (2020).
https://doi.org/10.1001/jamanetworkopen.2020.18044
7. E. M. Choi, D. K. W. Chu, P. K. C. Cheng, D. N. C. Tsang,
M. Peiris, D. G. Bausch, In-flight transmission of severe acute
respiratory syndrome coronavirus 2, Emerging Infectious Diseases 26
(2020).
8. D. O. Freedman, A. Wilder-Smith, In-flight Transmission of
SARS-CoV-2: a review of the attack rates and available data on the
efficacy of face masks, Journal of Travel Medicine, taaa178, (2020).
https://doi.org/10.1093/jtm/taaa178
9. S. H. Bae, H. Shin, H-Y. Koo, S. W. Lee, J. M. Yang, D. K. Yon,
Asymptomatic transmission of SARS-CoV-2 on evacuation flight.
Emerging Infectious Diseases 26 (2020). doi.org/10.3201/eid2611.203353
10. IATA, " COVID-19 and borders, Considerations relating to travel
and aviation " . https://tinyurl.com/y5keo3bb. Accessed 9:53AM PST,
October 9th 2020
11. H. Speake, A. Phillips, T. Chong, C. Sikazwe C, A. Levy, J.
Lang. Flight-associated transmission of severe acute respiratory
syndrome coronavirus 2 corroborated by whole-genome
sequencing. Emerg Infect Dis. (2020).
https://doi.org/10.3201/eid2612.203910
12. Boeing, Travel Confidently with Boeing. Computational Fluid
Dynamics Modeling and the Transport of Cough Particles in an Aircraft
Cabin https://tinyurl.com/y5ww2tkx. Accessed Nov. 1st, 2020.
13. United States Transport Command. TRANSCOM/AMC
Commercial Aircraft Cabin Aerosol Dispersion Tests. (2020). https://
tinyurl.com/y5qm7u2c. Accessed 12:30PM PDT, Nov. 9th 2020.
14. CDC, Coronavirus Disease 2019 (COVID-19), Symptoms
of Coronavirus. https://www.cdc.gov/coronavirus/2019-ncov/
symptoms-testing/symptoms.html. Accessed 9:31AM PST,
10/29/2020
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removal by HEPA - Rated Media Filters and Packed Beds of Granular
Materials. https://ntrs.nasa.gov/citations/20170005166 (2016).
Accessed 9:57AM PDT, November 9th, 2020
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Components and Related Products: Performance Test Methods,
MIL-STD-282, 28 May 1956 https://tinyurl.com/y3r3jkd3; Accessed
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17. ASHRAE Standard 62.1-2019 - Ventilation for Acceptable
Indoor Air Quality (ANSI Approved). https://tinyurl.com/y5vxgwfl.
Accessed 3:13PM PST October 11th 2020.

ASHRAE JOURNAL

ashrae.org

D ECEM BER 2020

The Author Responds
Viral infections such as from SARS-CoV-2 are spread
from an ill person to others via three very different
mechanisms:
* Sporadic cough and sneeze droplets that supposdly
travel 6 feet or less;
* Surface contamination by fomites; and
* Continuously exhaled breath aerosols (≤5 microns)
that various researchers have found can stay aloft 30 minutes or even longer and move around with air currents.1
Since infections take several days to manifest, case
studies have difficulty in identifying the infecting
mechanism(s) and the setting(s) of origin. This situation should improve for COVID-19 infections given the
screening, testing, surface disinfection, social distancing, and mask wearing measures in place. One just
completed case study, for example, concluded there was
a 9.8% to 17.8% COVID-19 attack rate on persons spread
throughout the cabin during a 17% full, 7-hour international flight to Ireland.2

Uniform Mixing

I commend the Boeing letter authors CFD analysis in
this section. Figure 1 showing a high degree of cough
aerosol mixing row-wise but not between rows has been
done to a level of detail reflecting accuracy and grid
refinement beyond the computer resources of most
researchers. Past analyses indicate a lateral ventilation
airflow velocity between 30-70 fpm and vertical plug
flow velocity of about 3 fpm do indicate a highly mixed
exposure row-wise as implied by Figure 1. However,
the USTRANSCOM aerosol dispersion tests simulating coughs found glass beads were deposited several
rows both fore and aft from the point source with a bias
towards aft. My analysis also assumes exhaled breath
particles disperse several rows fore and aft as this dispersion has been previously shown in other studies.

Particle Removal Dynamics CFD-Model Analysis

The Boeing cough modeling shows the rapid particle
airborne concentration decay after a single cough or
sneeze does not apply to exhaled breath modeling with
its ongoing particle generation. As to virus exhalation
rates from normal breathing, they have been found to be
higher than USTRANSCOM used for coughs.3

https://www.tinyurl.com/y2al8rjy https://www.tinyurl.com/y2524fsw https://www.doi.org/10.1016/j.tmaid.2020.101816 https://www.doi.org/10.1016/j.tmaid.2020.101643 https://www.doi.org/10.1016/j.tmaid.2020.101882 https://www.doi.org/10.1001/jamanetworkopen.2020.18044 https://www.doi.org/10.1093/jtm/taaa178 http://www.doi.org/10.3201/eid2611.203353 https://www.tinyurl.com/y5keo3bb https://www.doi.org/10.3201/eid2612.203910 https://www.tinyurl.com/y5ww2tkx https://www.tinyurl.com/y5qm7u2c https://www.tinyurl.com/y5qm7u2c https://www.cdc.gov/coronavirus/2019-ncov/symptoms-testing/symptoms.html https://www.cdc.gov/coronavirus/2019-ncov/symptoms-testing/symptoms.html https://ntrs.nasa.gov/citations/20170005166 https://www.tinyurl.com/y3r3jkd3 https://www.tinyurl.com/y5vxgwfl https://www.ashrae.org/

ASHRAE Journal - December 2020

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