International News
Continued from page 11
• The role of HEPA filters in buildings outside of healthcare
settings in preventing transmission of infectious diseases is
unclear. A modelling study of the infection risk from SARS-
CoV-1, the virus causing SARS, conferred by three types of
ventilation systems in relatively large commercial aeroplanes,
found that mixing ventilation systems had the highest risk
and conventional displacement systems had the lowest risk.
• Well-maintained HVAC systems, including air-conditioning
units, securely filter large droplets containing SARS-CoV-2.
It is possible for COVID-19 aerosols (small droplets and
droplet nuclei) to spread through HVAC systems within a
building or vehicle and stand-alone air-conditioning units if
air is recirculated.
• Air flow generated by air-conditioning units may facilitate
the spread of droplets excreted by infected people longer
distances within indoor spaces.
• HVAC systems may have a complementary role in
decreasing transmission in indoor spaces by increasing
the rate of air change, decreasing recirculation of air and
increasing the use of outdoor air.
GUIDANCE
Infection control measures with proven evidence for reducing the
risk of SARS-CoV-2 transmission should be emphasised.
Organisers and administrators responsible for gatherings and
critical infrastructure settings should provide guidance material
to participants regarding the application of other preventive
measures, including:
• Physical distancing
• Meticulous hand hygiene
• Respiratory etiquette
• Appropriate use of face masks, if required for staff, and in
areas where physical distancing cannot be maintained due
to structural or functional impediments.
Building administrators should maintain heating, ventilation, and
air-conditioning systems according to the manufacturer’s current
instructions, particularly in relation to the cleaning and changing
of filters.
There is no benefit or need for additional maintenance cycles
in connection with COVID-19. Energy-saving settings, such as
demand-controlled ventilation controlled by a timer or CO₂
detectors, should be avoided. Consideration should be given
to extending the operating times of HVAC before and after the
regular periods of use.
Direct air flow should be diverted away from groups of
individuals to avoid pathogen dispersion from infected subjects
and transmission. Organisers and administrators responsible
for gatherings and critical infrastructure settings should explore
Pinterest
options with the assistance of their technical/maintenance teams
to avoid the use of air recirculation as much as possible.
They should consider reviewing their procedures for the use
of recirculation in HVAC systems based on information provided
by the manufacturer or, if unavailable, seeking advice from the
manufacturer.
The minimum number of air exchanges per hour, in
accordance with the applicable building regulations, should be
ensured at all times. Increasing the number of air exchanges per
hour will reduce the risk of transmission in closed spaces.
This may be achieved by natural or mechanical ventilation,
depending on the setting. The application of the above guidance
should be in accordance with national and local regulations (for
example, building regulations, health and safety regulations) and
appropriate to local conditions.
Technical specifications and standards for mechanical
ventilation systems to reduce the risk of COVID-19 transmission
in indoor spaces still need to be defined on the basis of scientific
studies that are tuned to COVID19 research developments that
are continuous.
The technical specifications will need to be defined for
categories of room or location type, taking into account the room
size, the degree of enclosure and non-mechanical ventilation, and
the probable purpose for which the room will be used.
Moreover, options should be provided for protected buildings
that be subject to engineering modifications. The technical
standards should ideally recommend minimum criteria to be
met in order for authorities to permit the intended use of an
enclosed space. The technical specifications regarding the
logistical arrangement of enclosed spaces, including the physical
placement of mechanical ventilation systems, also need to be
informed by scientific evidence and technical expertise, so as to
minimise the risk of transmission.
These specifications will also need to take into account
the expected number of users, the types of user and the user
activity. For example, in supermarkets, cashiers and customers
have different levels of mobility and durations of occupancy. As
a general principle, mechanical ventilation should be arranged
to minimise the direction of sustained air flow for stationary
persons. RACA
The study
shows that
the direction
of airflow also
plays a major
role in buildings
catering to many
occupants and
infection rates.
www.hvacronline.co.za RACA Journal I September 2020 13