ASHRAE Journal - March 2021 - 28

TECHNICAL FEATURE

The thermal plume can be affected by body position
(sitting vs. standing) and clothing, but is still significant
while wearing pants and long sleeves.33

Droplet Release with Masks and Shields
When looking at face masks (Figure 3, page 27), there are
all types of masks from commercial to homemade. A study
by Viola, et al., found that all of the face covers they tested
reduced the frontal jet by more than 90%.32 A similar
study by Verma, et al., found that for a simulated cough a
stitched mask limited the frontal respiratory jet to 64 mm
(2.5 in.); a commercial mask to 203 mm (8 in.); a folded
handkerchief to 381 mm (1 ft, 3 in.); and a bandana to 1 m
(3 ft, 7 in.).29 During normal breathing, when the expelled
flow is weak, the air is slowed down by the mask or redirected through the narrow gaps such that air can be
captured by the upward convection of the thermal plume
without being displaced significantly horizontally.29,32
The face shield (Figure 4) has been shown to deflect the
expelled frontal respiratory jet downward and limit the
horizontal travel of large droplets. Smaller droplets, however, can move around the bottom of the shield and leak
around the gaps on the sides and top of the shield. As
these droplets move forward and laterally, they begin to
rise upward after a few seconds, since they are warmer
than the ambient air, and have the potential to spread
approximately 0.9 m (3 ft) in these directions. Studies also
showed that masks, shields and ambient disturbances can
cause the airflow to spread toward a person's back.32,34

Conclusions
This article has taken a look at what makes up a virus,
how it can be released into the space through droplets
and aerosols and the effect of certain environmental
conditions like temperature and humidity on the droplets. The next article will cover airborne virus transmission and the effect of air distribution.

References

1. Lodish, H., A. Berk, Zipursky, S.L., et al. 2000. Molecular Cell
Biology, 4th edition, " Section 6.3, Viruses: Structure, Function, and
Uses. " New York: W. H. Freeman. https://tinyurl.com/yyofaa67
2. Oldstone, M.B.A. 2014. " History of virology. " Encyclopedia
of Microbiology 2014:608 - 612. http://doi.org/10.1016/B978-0-12801238-3.00078-7
3. Goldsmith, C.S., S.E. Miller. 2009. " Modern uses of electron microscopy for detection of viruses. " Clin Microbiol Reviews
22(4):552 - 563. https://doi.org/10.1128/CMR.00027-09
4. Eames, I., J.W. Tang, Y. Li, P. Wilson. 2009. " Airborne
transmission of disease in hospitals. " J. R. Soc. Interface

28

ASHRAE JOURNAL

ashrae.org

MARCH 2021

6(Suppl6):6S697 - S702. http://doi.org/10.1098/rsif.2009.0407.focus
5. Wells, W.F. 1934. " On air-borne infection. Study II. Droplets
and droplet nuclei. " American Journal of Epidemiology 20(3):611 - 618.
https://doi.org/10.1093/oxfordjournals.aje.a118097
6. Luongo, J.C., K.P. Fennelly, J.A. Keen, Z.J. Zhai, et al. 2016.
" Role of mechanical ventilation in the airborne transmission of
infectious agents in buildings. " Indoor Air 26(5):666 - 678. https://
doi.org/10.1111/ina.12267
7. Kutter, J., M. Spronken, P. Fraaij, R. Fouchier, et al. 2018.
" Transmission routes of respiratory viruses among humans. "
Current Opinion in Virology 28:142 - 151. https://doi.org/10.1016/j.
coviro.2018.01.001
8. HHS. 2012. Principles of Epidemiology in Public Health Practice:
An Introduction to Applied Epidemiology and Biostatistics. Atlanta: U.S.
Department of Health and Human Services, Centers for Disease
Control and Prevention. https://tinyurl.com/y3jb3t96
9. Bischoff, W.E., K. Swett, I. Leng, T.R. Peters. 2013. " Exposure
to influenza virus aerosols during routine patient care. " J Infect Dis.
207(7):1037 - 1046. https://doi.org/10.1093/infdis/jis773
10. Giovanni, A., T. Radulesco, G. Bouchet, et al. 2020. " Transmission of droplet-conveyed infectious agents such as SARS-CoV-2 by
speech and vocal exercises during speech therapy: preliminary
experiment concerning airflow velocity. " Eur Arch Otorhinolaryngol.
https://doi.org/10.1007/s00405-020-06200-7
11. Stadnytskyi, V., P. Anfinrud, C. Bax, A. Bax. 2020. " The airborne
lifetime of small speech droplets and their potential importance to SARSCoV-2 transmission. " Zenodo.org. http://doi.org/10.5281/zenodo.3770559
12. Xie, X., Y. Li, A.T. Chwang, P.L. Ho, et al. 2007. " How far
droplets can move in indoor environments-revisiting the Wells
evaporation-falling curve. " Indoor Air 17(3):211 - 225. https://doi.
org/10.1111/j.1600-0668.2007.00469.x
13. Jennison, M.W. 1942. " Atomizing of mouth and nose secretions
into the air as revealed by high-speed photography. " In Aerobiology, F. R. Moulton (Ed.), pp. 106 - 128. American Association for the
Advancement of Science. https://tinyurl.com/y57vxtxs
14. Hatch, T.F. 1942. " Behavior of microscopic particles in air
and the respiratory system. " In Aerobiology, F.R. Moulton (Ed.), pp.
102 - 105. American Association for the Advancement of Science.
https://tinyurl.com/y57vxtxs
15. Riley, E.C., G. Murphy, R.L. Riley. 1978. " Airborne spread of measles in a suburban elementary school. "  American Journal of Epidemiology
107(5):421 - 432. https://doi.org/10.1093/oxfordjournals.aje.a112560
16. Riley, E.C. 1980. " The role of ventilation in the spread of measles
in an elementary school. " Annals of the New York Academy of Sciences
353(1):25 - 34. https://doi.org/10.1111/j.1749-6632.1980.tb18902.x
17. Sze To, G.N., C.Y.H. Chao. 2010. " Review and comparison
between the Wells-Riley and dose-response approaches to risk
assessment of infectious respiratory diseases. " Indoor Air 20(1):2 - 16.
https://doi.org/10.1111/j.1600-0668.2009.00621.x
18. Fernstrom, A., M. Goldblatt. 2013. " Aerobiology and its role
in the transmission of infectious diseases. " Journal of Pathogens
2013:Article ID 493960. https://doi.org/10.1155/2013/493960
19. Morawska, L. 2006. " Droplet fate in indoor environments, or
can we prevent the spread of infection? "  Indoor Air 16(5):335 - 347.
https://doi.org/10.1111/j.1600-0668.2006.00432.x
20. Tang, J.W. 2009. " The effect of environmental parameters
on the survival of airborne infectious agents. " Journal of the Royal
Society Interface 6(Issue Suppl_6):S737 - S746. https://doi.org/10.1098/
rsif.2009.0227.focus
21. Nikitin, N., E. Petrova, E. Trifonova, O. Karpova. 2014. " Influenza virus aerosols in the air and their infectiousness. " Advances in
Virology 2014:859090. https://doi.org/10.1155/2014/859090
22. Bolashikov, Z.D., A.K. Melikov. 2009. " Methods for air
cleaning and protection of building occupants from airborne
ASHRAE Journal - March 2021

Table of Contents for the Digital Edition of ASHRAE Journal - March 2021
