International News
HEATING, VENTILATION AND
AIR-CONDITIONING SYSTEMS
IN THE CONTEXT OF COVID-19
By the European Centre for Disease Prevention and Control
Evidence for transmission in closed spaces and the role of
heating, ventilation and air-conditioning (HVAC) systems.
Air-conditioning systems usually form part of integrated
HVAC systems or stand-alone, providing cooling/warming and
dehumidification. Stand-alone systems usually recirculate the air
without mixing it with outdoor air. Ventilation in indoor spaces is
associated with increased transmission of respiratory infections.
WHAT IS KNOWN ABOUT COVID-19 RELATED TO
HVAC SYSTEMS
• There have been numerous COVID-19 transmission events
associated with closed spaces, including some from
presymptomatic cases.
• The role of ventilation in preventing COVID-19 transmission
is not well-defined (that is, by preventing dispersal of
infectious particles to minimise the risk of transmission,
or preventing transfer of an infectious dose to susceptible
individuals).
• COVID-19 is thought to be primarily transmitted via large
respiratory droplets, however, an increasing number
of outbreak reports implicate the role of aerosols in
COVID-19 outbreaks. Aerosols consist of small droplets
and droplet nuclei which remain in the air for longer than
large droplets.
• Studies indicate that SARS-CoV-2 particles can remain
infectious on various materials, as well as in aerosols in
indoor environments, with the duration of infectivity
depending on temperature and humidity.
• So far, transmission through fomites has not been
documented, but it is considered possible. Several
outbreak investigation reports have shown that COVID-19
transmission can be particularly effective in crowded,
confined indoor spaces such as workplaces (offices,
factories).
• There are also indications that transmission can be
linked to specific activities that may be characterised
by increased production of respiratory droplets through
speech or singing.
Web MD
• The only case of outdoor transmission identified in this study
involved two people. However, outdoor events have also
been implicated in the spread of COVID-19, typically those
associated with crowds, such as celebrations, highlighting
the risk of crowding even outdoors.
• The length of time that people stay in indoor settings
appears to be associated with the attack rate.
• The authors also concluded that the length of time people
were in contact played the most important role in spreading
of COVID-19
• From the reports published to date, it is not as yet possible
to clarify the role of physical proximity and direct contact,
and the possibility of indirect transmission through
contaminated objects and surfaces, or longer distance
transmission through aerosols.
• The current body of evidence demonstrates the risk of
transmission in crowded indoor settings and the importance
of combining bundles of prevention measures. Several
studies have addressed the role of ventilation in COVID-19
outbreaks.
• High Efficiency Particulate Air (HEPA) filters have
demonstrated good performance with particles of the
SARSCov-2 virus size (approximately 70−120 nm) and are
used in aeroplanes and in healthcare settings.
Continued on page 13
Case studies
indicate that the
HVAC systems
in buildings
can play a
significant role
in management
of air-borne
diseases such as
Covid-19.
www.hvacronline.co.za RACA Journal I September 2020 11