Prioritising ventilation: 7 lessons from the pandemic

The COVID-19 pandemic revealed serious deficiencies in the way indoor air quality (IAQ) is managed on an official level — something that contributed to the virus’s devastating impact.

This is the finding of a group of experts who have analysed the relationship between ventilation and indoor airborne infection transmission in the wake of COVID-19. Their research has been published in the journal Science.

Air quality scientist Professor Lidia Morawska, from QUT’s School of Earth and Atmospheric Sciences, said the rapid global spread of COVID-19 had soon made it clear the world was unprepared to respond appropriately.

“In the early days of the pandemic the World Health Organization and many national health authorities claimed the virus was ‘not in the air’ but rather present in large quantities on surfaces. This led to a misconception about how the virus was transmitted,” Morawska said.

“Public health authorities rejected existing knowledge, which led to misguided control measures aimed at cleaning surfaces, instead of ventilation, filtration, face-masking and deactivation of airborne viruses.

“However, for science and building engineering experts there was no doubt from the beginning that the virus was transmitted predominantly through the air and the most important control measure to reduce infection risk was to remove the viruses from the air through ventilation or inactivate them through UVC radiation.”

In their paper, the scientists — Morawska, Professor Yuguo Li from The University of Hong Kong and Professor Tunga Salthammer from the University of Surrey — state that contemporary buildings are not designed with provision of good indoor air quality as a requirement, and specifically not with the aim of controlling airborne infection transmissions. Also, there are usually no measures in place to check whether ventilation is adequate in relation to the number of people occupying the space; whether it functions without faults; or whether it is effectively distributed throughout the space.

This has been a longstanding problem. Not even ‘sick building syndrome’ (SBS) — which occurred after the reduction of ventilation flow rates that followed the energy crisis in the 1970s — prompted better ventilation of public buildings, despite research showing a strong connection between poor air flow and SBS.

To address the issue, the experts have presented seven key lessons to emerge from the pandemic.

1. Interdisciplinary knowledge is vital for public health decision-making.

The experts who advised the WHO at the beginning of the pandemic were mostly public health experts, while the value of physical, chemical and engineering expertise was considered less relevant. For example, current epidemiological studies of outbreaks commonly do not include the measurement of ventilation rates, which results in incomplete assessment.

2. Ventilation must go beyond the ‘open window’ solution.

Modern society cannot rely solely on natural (open window) ventilation in buildings that are not designed to provide sufficient and effective air supply.

Mechanical ventilation must be part of the solution. An HVAC system can implement various air supply techniques such as mixing, displacement and personal ventilation. At the same time, HVAC offers the possibility of air disinfection using germicidal ultraviolet (GUV) and filtration.

The performance of the HVAC can be controlled using suitable indoor air quality and outdoor air parameters, which are measured and processed using a smart sensor system.

3. Building and ventilation design go hand in hand.

Different types of buildings — housing, offices, shopping centres, airports, railway stations, school buildings etc — are becoming increasingly complex, but are mostly planned and built with design and operation constraints.

Sufficient ventilation, which is the basic function to make a building livable, is often not considered among the key criteria. Building and ventilation design are closely related and should be equally important in planning and operation.

4. Equivalent ventilation is a solution for existing buildings.

Buildings such as aged care facilities and schools that are naturally ventilated cannot be easily or cost-effectively retrofitted. In such cases equivalent ventilation is needed, using the techniques of air filtration and GUV.

Filtering does not remove water, carbon dioxide and gaseous pollutants from the air, but it is “equivalent to ventilation” for particulate matter (eg, pollutants from a bushfire). GUV deactivates pathogens in the air, so it may be equivalent to ventilation in relation to infection control.

The researchers noted that there are some concerns that the operation of GUV systems may result in the formation of harmful secondary air pollutants, adding that these concerns are based on laboratory experimental studies or modelling studies. There is little evidence from real building studies, which are very rare.

5. Control and risk assessment tools should be considered in future.

Risk assessment tools have value in estimating the probability of airborne infection, but are too complex to be used as a day-to-day control measure in modern buildings. New technologies are being researched, developed or optimised to control the ventilation of buildings.

6. Monitoring is crucial.

Ventilation performance should be monitored at all the times when buildings are occupied to dynamically inform ventilation control in response to building occupancy and use.

Numerous CO₂ monitors are installed in modern buildings and a raft of low-cost CO₂ sensors are available for continuous monitoring of ventilation performance in housing and transport cabins, with the preferred method for measuring CO₂ being non-dispersive infrared (NDIR).

Modern devices are calibrated against reference methods and their performance can be improved using machine learning tools. Combining CO₂ measurement with other relevant parameters is possible and recommended.

7. IAQ must be mandated in public buildings.

Indoor air quality must be mandated and controlled like water and food by the relevant authorities. Without regulations, good IAQ cannot be assured by volunteer occupants’ efforts or even building operators if the building was not designed with this as an objective and/or equipped with adequate engineering systems.

“The COVID-19 pandemic showed us that not only is ventilation a key control measure to lower the risk of airborne infection transmission of any pathogens, but also that ventilation must be considered as part of the control of IAQ from outdoor generated pollution, beyond infection transmission,” the researchers said.

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