Last week, an international group of scientists and indoor air quality (IAQ) experts called for a “paradigm shift” in combating airborne pathogens such as COVID-19 by improving indoor ventilation systems. They say that the potential benefit to public health is comparable to that achieved in the 1800s when cities started organising clean water supplies and centralised sewage systems.
To achieve this, those involved recommend a shift in ventilation standards and guidance, from the World Health Organization down to individual countries and their building codes. In Australia, it has been suggested that the National Construction Code (NCC) could play a key role in establishing ventilation and IAQ requirements for different types of buildings. But is this the right tool for the job?
Standards and awareness
Queensland University of Technology air-quality expert Distinguished Professor Lidia Morawska led the group of researchers. She says that any requirements for improved ventilation must consider many factors.
“We cannot just go straight into the construction code and change the ventilation rate per hour, per person – it’s not that simple,” she says. “With a huge number of different types of buildings, different solutions, and different building settings, this has to be worked out.”
Professor Morawska notes that ventilation requirements for CO2 are relatively simple to calculate. But when pathogens are involved, it will depend on the specific pathogen, occupancy rates, how long people spend in the space, and what they are doing – for example, talking, exercising or singing. This makes it harder, but by no means impossible.
“There are tools now for such calculations,” she says. “So far they’ve been ignored.”
Another critical aspect of ventilation, which Professor Morawska says is rarely taken into account, is the direction of airflow.
“You design the space for some activities and then someone puts in a barrier or something and the flow direction changes,” she says. “This almost calls for something like CFD simulations for every interior, which will be very difficult if not impossible. But still there are ways of doing this – there are means for providing personalised ventilation, and specific distributed flow direction. It’s just that we need to put our heads together to see how it would work on a more general scale.”
Such systems will be complex and costly, but Professor Morawska says that governments must conduct a serious economic analysis.
“All the analysis we’ve seen so far points out that the initial investment is significantly lower than the cost of health effects, pandemics, epidemics and so on,” she says. “The issue, however, is that the money comes from different pockets. This is something that has to be realised at the society level.
“Who pays the cost? Ultimately, the whole society pays. So as a society we need to think like this, and actually this is the biggest element of the paradigm change.”
Part of the problem with getting governments involved is that IAQ is not an election issue. Professor Morawska agrees that greater public awareness of air pollution is vital.
“Let’s say you are choosing a seat in a restaurant on the kerbside and inhale [the pollution from] all the cars passing by, is anybody worried about this? It’s the most desirable seat outside.
“This comes down to teaching,” she says. “It should go into the curriculum from kindergarten through all the education and people should learn that air pollution is an issue, and what they do has an impact.”
In the meantime, Professor Morawska says that indoor air sensors and monitors would help.
“If there was a display on the wall showing that the CO2 concentration is high, some people would start querying whether this a problem.”
“We need to start somewhere“
Vince Aherne, F.AIRAH, is the author of the indoor air quality handbook recently published by the Australian Building Codes Board (ABCB), the body that updates and maintains the NCC. Aherne sees various options for improving ventilation standards to control airborne pathogens.
“The NCC would be an appropriate place to set a requirement, preferably a performance requirement,” he says. “But technical solutions would be better placed in documents like Australian Standards or Technical Guidelines.”
Aherne notes that the NCC verification method for ventilation excludes microbial control, and deemed-to-satisfy mechanical ventilation provisions refer to AS 1668.2 and AS/NZS 3666.1, which do not address control of airborne transmission of respiratory infections or pathogens.
“Control of airborne infections has not been a primary objective of current building codes or ventilation and microbial control standards outside of specialised healthcare applications,” he says. “But current experience has clearly exposed a need to develop standards in this area.
“It is not just a matter of increasing outdoor airflow rates either. There needs to be a lot more thought to providing the correct air pathways and controlling infiltration and exfiltration between spaces as well as outdoors. Air follows the path of least resistance, which can be influenced by internal and external air pressures. Regulators have only ever looked a building sealing from an energy-efficiency perspective, never from an IAQ or ventilation perspective.”
According to Aherne, there would be many difficulties in setting indoor air quality standards for microbial control, including airborne pathogens and infections, and extensive research would be required.
“But we need to start somewhere,” he says, “so addressing this within the existing standards infrastructure would be a relatively quick way to set minimum standards in the area.
“WHO would be the organisation best placed to set IAQ standards. Local application of WHO standards in building codes is another matter. I expect a hierarchy of standards could be applied based on building use/risk, from hospitals and aged care all the way through to residential and industrial.”
Combinations of mechanical and natural ventilation, filters, air-cleaning technology and IAQ monitoring would also have to be considered in standards, says Aherne, to support any mandatory requirements.
He suggests an alternative approach could be to mandate disclosure of ventilation or indoor air quality performance, similar to energy performance through the Commercial Building Disclosure scheme using NABERS energy ratings.
“Most building occupants don’t really think about ventilation and are more concerned with thermal comfort, lighting and views,” he says. “If we could develop a rating system, so people could visually see and compare the IAQ performance of buildings, that could motivate the industry to improve performance above minimum standards.”
Health departments best placed to lead
World-renowned expert on microbial control, Clive Broadbent AM, L.AIRAH, was heavily involved in addressing the original SARS outbreak. In 2003 he flew to China at the request of the WHO to analyse the spread of the virus and produce guidelines on laboratory standards, hospital practices and appropriate ventilation for SARS patients.
Broadbent says a conversation on the role of the NCC would be useful, but may not get anywhere due to the vast variety of buildings it covers. Because COVID-19 is a health issue, he sees government health departments as central to new codes.
“They are best set up to prepare acts and regulations,” he says, “and, with industry support, could prepare new guidelines supporting new regulations in much the same way as, for example, NSW Health has now handled the challenge of Legionnaires’ disease.
“NSW Health has a specific act, regulation, and guideline, and these are supported by risk-management procedures plus annual audits, all to minimise transmission of this disease. Such strategies are ideally suited to the protection of health in any number of buildings.”
Following this approach, Broadbent says health departments would take responsibility for producing best-practice materials.
“They do know what public health is about, whereas we in the HVAC industry are into functional requirements of building services or simply temperature, humidity, and ventilation needs, where no contagion is anticipated. When in the realm of microorganisms, it’s surely the health departments that should take the leadership.”
A greater focus on relative air pressures may also help, he says.
“Respective room air pressures are much more relevant to aerosol control than the straightforward air conditioning system features,” Broadbent says. “Air moves from a zone of high pressure to one of lower pressure. So a movement from a corridor, to each room, to the outdoors via an exhaust fan – or arguably even an openable window – then releases any contagion back to the outdoors where it will dissipate.
“The outdoor factor is our great assistant in dissipating aerosol-bearing particles such as microorganisms and virus in particular.”