ASHRAE Journal - January 2021 - 60

IEQ APPLICATIONS
Column

Tool Evaluates Control
Measures for Airborne
Infectious Agents

BY W. STUART DOLS, MEMBER ASHRAE; LISA NG, PH.D., MEMBER ASHRAE; BRIAN J. POLIDORO; DUSTIN POPPENDIECK; STEVEN J. EMMERICH, FELLOW ASHRAE; ANDREW PERSILY, PH.D.,
FELLOW/LIFE MEMBER ASHRAE

The purpose of the new online tool Fate and Transport of Indoor Microbiological
Aerosols (FaTIMA) is to model the fate of infectious aerosols (e.g., those associated with
SARS-CoV-2) generated within the built environment and the potential impact of various control measures.1 Pathogen-containing aerosols can be generated by an infected
person through breathing and other activities involving the respiratory system, such as
coughing. Larger emitted droplets fall rather quickly to the ground due to gravitational
settling; these can impact various surfaces or ballistically enter the respiratory tract of
another, nearby occupant.2 Smaller droplet nuclei can remain airborne for longer periods, and these aerosolized particles are the focus of FaTIMA.
FaTIMA models the fate of such indoor microbiological aerosols based on the effects of ventilation, ﬁltration,
deposition and inactivation. FaTIMA can be used to evaluate relative effects of control measures on airborne infectious agents but does not model the risk of infection.
The underlying model (Figure 1) consists of a single
zone, served by a mechanical ventilation system, that
incorporates source and removal mechanisms of an
aerosol having a single, user-deﬁned representative size
and a uniform concentration. (Users who need to understand spatial variations in airborne concentration should
consider using computational ﬂuid dynamics instead.)
The mechanical ventilation system model allows speciﬁcation of supply, return, exhaust and outdoor air intake

rates. Aerosol sources may be speciﬁed as any combination of continuous (e.g., breathing) or intermittent (e.g.,
coughing) emissions. Aerosol removal mechanisms
include ﬁltration (within the ventilation system and via
a room air cleaner), deactivation and deposition onto
ﬂoors, walls, ceilings and other surfaces. Simulations
run for 24-hours, with results provided as a time history
of the airborne concentration and surface loading and
the integrated exposure of an occupant.
W. Stuart Dols and Lisa Ng, Ph.D., are mechanical engineers, Brian J. Polidoro is an
IT Specialist, Dustin Poppendieck is an environmental engineer, Steven J. Emmerich
is a group leader, and Andrew Persily, Ph.D., is a division chief in the Engineering
Laboratory at the National Institute of Standards and Technology, Gaithersburg, Md.
Dols and Ng are members of and Persily is a consultant to SSPC 62.1. Emmerich is
chair of GPC 44 and a member of SSPC 62.2.

This peer-reviewed column does not represent ofﬁcial ASHRAE guidance. For more information on ASHRAE resources on COVID-19, visit ashrae.org/COVID19.
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ASHRAE JOURNAL

ashrae.org

JAN UARY 2021

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ASHRAE Journal - January 2021

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