FOCUS HVAC
CLEARING THE AIR
Until the majority of the population has been vaccinated it is critical
that workplaces maintain good levels of ventilation to help reduce the
risk of airborne transmission says Hywel Davies, Technical Director of
the Chartered Institution of Building Services Engineers (CIBSE)
Assuming the vaccine roll-out goes
to plan, businesses will still need
to operate strict COVID-19 measures
to ensure their sta and visitors are
protected. The situation is evolving:
the scale of e ectiveness of the vaccine
is still to emerge; how long vaccineinduced
protection will last has yet to
be established; and how e ectively the
vaccine will reduce transmission is still
unknown.
The situation is under review, but there
is an expectation that restrictions could be
li
ed so that businesses could be reopening
as early as Easter, when a large proportion
of the working age population may not have
been vaccinated. That means the focus
in workplaces and other multi-occupant
30 FEBRUARY 2021
spaces, especially those open to the public,
must remain on limiting transmission to
prevent the spread of Coronavirus to unvaccinated
people.
Advice from the Government’s Scientific
Advisory Group for Emergencies (SAGE)
in its document Role of Ventilation in
Controlling SARS-CoV-2 Transmission(i),
is that “Ventilation should be integral to
the COVID-19 risk mitigation strategy for
all multi-occupant public buildings and
workplaces”.
The SAGE publication follows the World
Health Organisation’s acknowledgement
last July of the possibility of airborne
transmission of Coronavirus. This in
turn confirmed the lead provided by the
Chartered Institution of Building Services
Engineers (CIBSE) in its COVID-19 Ventilation
Guidance, issued in May, and referenced in
the SAGE document.
The need for e‘ ective ventilation in
helping limit the spread of COVID-19 is based
on growing evidence that Coronavirus can
be spread by tiny particles called aerosols.
The acts of breathing, talking, coughing
and sneezing all produce droplets and
aerosols that may, if the host is infected,
contain pathogens. Larger droplets fall by
gravity onto surfaces within 1 - 2m from the
source, which is why 2m social distancing
is recommended. The droplets fall onto
surfaces and can therefore get onto hands
and eating utensils - hence the importance of
regular hand washing and avoiding touching
the face. Smaller aerosols, however, can
stay airborne for hours, which enables them
to travel longer distances where they could
infect secondary hosts, particularly in poorly
ventilated spaces.
The advice from SAGE, based on
modelling, is that “exposure to aerosols
approximately halves when the ventilation