ASHRAE Journal - October 2020 - 12

TECHNICAL FEATURE

COVID-19 and Beyond

A Brief Introduction
To Passenger Aircraft
Cabin Air Quality
BY DOUGLAS STUART WALKINSHAW, PH.D., P.ENG., FELLOW ASHRAE

The passenger aircraft industry says passenger cabin air quality is exceptionally good
compared with that of other public settings. Some airlines claim the air in aircraft
cabins is cleaner than that in ofﬁces and is on par with the air in hospitals. Another
airline says the air is particularly good because it is very dry, creating a sterile cabin
environment. Some say virus particles will only travel one or two rows. Nearly all say
the air change rate is high and recirculated air is passed through HEPA ﬁlters that
remove nearly 100% of airborne viruses.1 - 6 This article will review these claims.
Dry Air in Passenger Cabins

The air in passenger cabins is dry, with a relative humidity (RH) of 10% as the ﬂight progresses.
Meanwhile, a portion of the cabin air with its ventilation components (very dry outdoor air plus ﬁltered,
recirculated air) and humidity components, passes
from the cabin to behind the cabin insulation, drawn
there through liner leaks and openings by stack pressures. Some of this air is not lost as useful ventilation
air. However, all the air drawn there (perhaps 25% of the
cabin ventilation air) loses its humidity prior to recirculation, depositing its moisture as condensation on the
very cold fuselage behind the insulation. There it freezes
during ﬂight, adding nonproductive dead weight. When

the frozen water melts when the plane is back on the
ground, this moisture causes metal corrosion, hastening
metal fatigue and creating microbial growth.7
However, in addition to air at 10% RH being uncomfortable, it has been shown to impair nasal mucociliary
clearance, innate antiviral defense and tissue repair
function in mice and is, therefore, postulated to do so
in humans.8 Additionally, RH this low rapidly turns
droplets into aerosols,9 which disperse more widely, ﬁve
rows longitudinally either way (Figure 1).10 Aerosols are
more likely to inoculate the respiratory system, where
the minimum dose requirement to inoculate is lower
and the symptoms more severe than if the inoculation
occurs in the nasal system where the larger droplets are

This peer-reviewed article does not represent ofﬁcial ASHRAE guidance. For more information on ASHRAE resources on COVID-19, visit ashrae.org/COVID19.
12

ASHRAE JOURNAL

ashrae.org

O CTO B E R 2020

http://www.ashrae.org/COVID19 https://www.ashrae.org/

ASHRAE Journal - October 2020

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

Contents
ASHRAE Journal - October 2020 - Intro
ASHRAE Journal - October 2020 - Cover1
ASHRAE Journal - October 2020 - Cover2
ASHRAE Journal - October 2020 - 1
ASHRAE Journal - October 2020 - Contents
ASHRAE Journal - October 2020 - 3
ASHRAE Journal - October 2020 - 4
ASHRAE Journal - October 2020 - 5
ASHRAE Journal - October 2020 - 6
ASHRAE Journal - October 2020 - 7
ASHRAE Journal - October 2020 - 8
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ASHRAE Journal - October 2020 - 11
ASHRAE Journal - October 2020 - 12
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ASHRAE Journal - October 2020 - HR1
ASHRAE Journal - October 2020 - HR2
ASHRAE Journal - October 2020 - HR3
ASHRAE Journal - October 2020 - HR4
ASHRAE Journal - October 2020 - HR5
ASHRAE Journal - October 2020 - HR6
ASHRAE Journal - October 2020 - HR7
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ASHRAE Journal - October 2020 - HR10
ASHRAE Journal - October 2020 - HR11
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ASHRAE Journal - October 2020 - Cover3
ASHRAE Journal - October 2020 - Cover4
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