ASHRAE Journal - January 2021 - 63

COLUMN IEQ APPLICATIONS

Example Application of FaTIMA
FaTIMA was used to evaluate the effect of face coverings (masks) and HVAC-related controls in a classroom
for children ages 5 to 8 years.13 In this example, the
integrated exposure was modeled for a single contagious
occupant (modeled as a continuous source from 9 a.m.
to 3 p.m.) in a classroom ventilated according to ANSI/
ASHRAE Standard 62.1-2019, Ventilation and Acceptable
Indoor Air Quality. The space was assumed to be served by
a terminal unit with a 70% recirculation rate and a MERV
6 ﬁlter. Simulations were performed for 1 µm aerosols to
evaluate the following control methods separately and in
combination: face coverings with a 30% ﬁlter efﬁciency,
MERV 13 ﬁltration, and a portable air cleaner (PAC) with
a clean air delivery rate (CADR) of 142 L/s (300 cfm).
Scenarios implementing these controls were compared
to the baseline case by dividing their integrated exposure
by that of the baseline case to calculate a normalized integrated exposure (NIE) as shown in Figure 4. For example,
face coverings resulted in an NIE of 0.49, meaning the
exposure over the 6 hour period was reduced by approximately 50%. Figure 4 shows that increasing to MERV 13 ﬁltration also reduced exposure by approximately 50% and
that the PAC reduced exposure by 40%. A larger capacity
PAC unit could reduce exposure further. When combined
with face coverings, each of the two ﬁltration controls
reduced exposure by over 70%.
FaTIMA can be accessed here: https://pages.nist.gov/
CONTAM-apps/webapps/FaTIMA/index.html. A report
providing more detail on the tool,1 including a user
guide, is here: https://doi.org/10.6028/NIST.TN.2095.
Readers are encouraged to explore the tool and use it to
study the relative effectiveness of control measures for
microbiological aerosols in indoor spaces. Plans exist to

FIGURE 4 NIE results for example case.

1.4
1.2
NIETU,nocontrols

exposure period and the full 24-hour simulation period.
A set of summary pie charts presents the numerical
results visually to show relative values related to fate,
source, surface deposition and ﬁltration.
After a simulation is complete, the user can download
a CONTAM project ﬁle and a comma-separated value
(CSV) ﬁle containing the inputs and simulation results.
A spreadsheet is provided into which the CSV ﬁle can be
imported to allow comparisons between different scenarios. For those familiar with CONTAM, the project ﬁle can
be used directly in CONTAM, which allows the exercise of
CONTAM capabilities not implemented in FaTIMA.

1.00

1.0
0.8
0.6

0.49

0.60

0.51

0.4
0.2
0.0

0.29

0.25
No Control

Face
Coverings

MERV 13

PAC
MERV 13
(300 CADR) + Face
Coverings

PAC
+ Face
Coverings

further develop the tool; suggestions are welcome and
can be sent to the authors at NIST.

References

1. Dols, W.S., B.J. Polidoro, D. Poppendieck, S.J. Emmerich. 2020.
A Tool to Model the Fate and Transport of Indoor Microbiological Aerosols
(FaTIMA). National Institute of Standards and Technology.
2. Zhu, S., S. Kato, J.-H. Yang. 2006. " Study on transport
characteristics of saliva droplets produced by coughing in a calm
indoor environment. " Building and Environment 41(12): 1691-1702.
3. Dols, W.S., B.J. Polidoro. 2015. CONTAM User Guide and Program
Documentation. National Institute of Standards and Technology.
4. Grot, R.A., A.K. Persily. 1986. " Measured air inﬁltration and
ventilation rates in eight large ofﬁce buildings. " In Measured Air
Leakage of Buildings, ed. H. Trechsel and P. Lagus. ASTM International.
5. Persily, A.K., L.K. Norford. 1987. " Simultaneous measurements
of inﬁltration and intake in an ofﬁce building. " ASHRAE Transactions
93(2):942-56.
6. Ng, L.C., N.O. Quiles, W.S. Dols, S.J. Emmerich. 2018. " Weather
correlations to calculate inﬁltration rates for U.S. commercial
building energy models. " Building and Environment 127:47-57.
7. Kowalski, W.J., W.P. Bahnﬂeth, T.S. Whittam. 1999. " Filtration
of airborne microorganisms: modeling and prediction. " ASHRAE
Transactions 105(2):4-17.
8. Duguid, J.P. 1946. " The size and the duration of air-carriage of
respiratory droplets and droplet-nuclei. " Epidemiology and Infection
44(6):471-79.
9. Milton, D.K., M.P. Fabian, B.J. Cowling, M. L. Grantham, et al.
2013. " Inﬂuenza virus aerosols in human exhaled breath: particle
size, culturability, and effect of surgical masks. " PLoS Pathogens
9(3):e1003205.
10. Leconte, S., G. Liistro, P. Lebecque, J.-M. Degryse. 2011. " The
objective assessment of cough frequency: accuracy of the LR102
device. " Cough 7(1):11.
11. Lindsley, W.G., et al. 2010. " Measurements of airborne inﬂuenza
virus in aerosol particles from human coughs. " PLoS One 5(11):e15100.
12. Lai, A.C.K., W.W. Nazaroff. 2000. " Modeling indoor particle
deposition from turbulent ﬂow onto smooth
surfaces. " Journal of Aerosol Science 31(4):463-76.
13. Ng, L.C., D.G. Poppendieck, B.J. Polidoro,
W.S. Dols, et al. 2020. " Simulation of controls for
reducing aerosol exposure in educational spaces
using FaTIMA. " National Institute of Standards https://bit.ly/3khhdC5
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https://pages.nist.gov/CONTAM-apps/webapps/FaTIMA/index.html https://pages.nist.gov/CONTAM-apps/webapps/FaTIMA/index.html https://www.doi.org/10.6028/NIST.TN.2095 https://www.bit.ly/3khhdC5 http://www.ashrae.org

ASHRAE Journal - January 2021

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