ASHRAE Journal - July 2022 - 20

TECHNICAL FEATURE
FIGURE 8 TRANSCOM in-flight breathing study and the CFD breathing study resulted in similar masses inhaled.
Comparing the eight seats nearest the index (as a worst case), on average the six CFD breathing simulations
resulted in higher localized exposure than the nine TRANSCOM 777 mid-aft in-flight breathing experiments.
Horizontal bars represent the maximum, 97.5th quantile, 90th quantile, 75th quantile (Q3), median, 25th quantile
(Q1), 10th quantile, 2.5th quantile and minimum values.
0.5%
0.4%
0.3%
0.2%
0.1%
0.0%
CFD 737 Breathing
TRANSCOM 777 Mid-Aft
In-Flight Breathing
Both the CFD and empirical studies conclude that
there was low exposure to aerosol for neighboring passengers.
The median nonvolatile mass for worst-case
occupants was 0.075% in the CFD model, compared to
0.009% for the TRANSCOM empirical study, while the
maximum was 0.469% for the model and 0.461% from
the empirical study.
The good, and slightly conservative, alignment of the
CFD model to the empirical results demonstrate the
applicability of the CFD model.
Discussion
The airplane cabin is a mixed-flow system that shares
more characteristics of a plug flow system than a uniformly
mixed system. This results in higher concentrations
of infectious agent particles near the infected individual,
and lower concentrations present in the seats at
greater distance. Distance alone is a poor predictor of
the nonvolatile mass inhaled under all circumstances on
an aircraft and, at least in the case of a cough-plume, for
a building environment.
While the airplane cabin is a unique environment
compared to other spaces, there are some areas where
ICS can benefit from understanding the airplane cabin
environment. In some ICS configurations, the lack of
high efficiency filtration assists in spreading aerosols
from one occupant to another. However, for a cough
with exposure prior to recirculation, better filtration
would not help the ICS. Similarly, an ICS with standard
configurations can be designed to minimize exposure,
through changes in designed airflow gradients, rather
than emphasizing mixing within a space.
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ASHRAE JOURNAL ashrae.o rg
J U LY 2022
For the case of the COVID-19
pandemic, the plume from either
coughing, talking or breathing at
close range, where air-handling is
not well managed, may be the most
important form of disease transmission.
Future efforts should look to
confirm how breathing and talking
models behave within an ICS space,
as it will add clarity to physical distancing
guidelines that are currently
recommended by government agencies.
However, since occupants are
able to move around freely within
an ICS, a well-mixed environment
may be a more reasonable assumption. It is not easy
to trace who was exposed to the cough plume when
occupants are in motion. Additional information
regarding airflow in the room at the time of the cough,
where the index person was located, what direction
they coughed and where each susceptible person was
located is required. Therefore, it is recommended to
minimize exposure risk for occupants of an ICS by
implementing best practices of increased ventilation,
improved filtration and improved airflow patterns
(where practical).
Similarly, it is difficult to model human behavior in an
aircraft cabin. This study does account for movement of
occupants up and down the aisles and assumes forwardfacing
occupants. This study does not attempt to calculate
infectiousness of SARS-CoV-2 or other viruses and
does not consider fomite or droplet transmission and
focuses instead on the inhaled mass of aerosols. In environments
where there is poor airflow that is not confined
to a specific direction of flow where people spend
long periods of time in close proximity, there is of course
risk of transmission.
Conclusion
The results of CFD analysis and test results demonstrate
the necessity of an advection-dispersion model
using a large dynamic set of data points to model
aerosol exposure within the aircraft cabin. The cough
simulation in an aircraft cabin shows that the system
is neither well-mixed nor steady state. This was verified
by the TRANSCOM empirical study. The breathing
model shows that while an infected person's emission
Nonvolatile Mass Inhaled,
% of Release

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ASHRAE Journal - July 2022

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