Australia needs to deliver better infection control in buildings to help prevent the spread of COVID and other infectious diseases, a leading academic says.
In a recent address to the Building Ventilation Sumit hosted by the Air Conditioning and Mechanical Contractors Association of Australia, Professor Lidia Morawska, director of the International Laboratory for Air Quality and Health at Queensland University of Technology (QUT), called for action across several areas to prevent the spread of infectious diseases within buildings.
In particular, Morawska called for:
- A shift away from reliance upon natural ventilation such as opening windows and doors to prevent infection spread
- Clear indoor air standards which prescribe concentrations of indoor air pollutants and which are monitored and enforced
- Inclusion of ventilation as part of HVAC as an element in enforcement of the above standards; and
- Supplementation of ventilation with other means such as GUV (see below) in shared spaces to disinfect the air and control airborne infection risk.
Morawska’s comments come as the World Health Organisation last year acknowledged the airborne nature of COVID transmission at short range or in crowded and poorly ventilated spaces despite earlier having insisted that COVID was transmitted via touch.
Whilst the WHO at the time insisted that science about airborne transmission was still emerging, Morawska says understanding of the role and mechanisms of airborne infection and transmission was well advanced before the pandemic.
Essentially speaking, particles are generated by all respiratory activities including breathing but are generated in particularly high concentrations during speaking.
With COVID specifically, smaller particles contain higher loads of the virus as these originate from deeper parts of the respiratory tract where the virus is located. As a result, breathing and speaking are the main sources of emission of particles containing high loads of COVID transmission.
Once in the air, particles do not necessarily fall straight on the ground within one meter as commonly believed. Indeed, many of these smaller particles can remain in the air for minutes or even hours – depending on specific particle size. They can travel meters or tens of metres.
When it comes to building design for indoor air quality, Morawska acknowledges that indoor atmosphere is affected by various factors. These include meteorological conditions, outdoor pollution, building characteristics, ventilation rates, indoor air sources, air mixing, building uses, indoor pollutant sinks and air cleaners.
She also stresses that building design needs to account not only for indoor airborne infection but also thermal comfort, dampness/mold, prevention of ingress of outdoor pollutants, control of indoor anthropogenic sources and finally minimising energy consumption and cost.
What should be done?
According to Morawska, several measures need to be considered.
First, there is natural ventilation, which can occur by opening windows and doors.
Whilst this is ideal in quieter environments during good weather, it cannot be relied upon as a complete solution in itself as windows need to be closed when conditions are too hot, cold or noisy.
In such cases, Moraskwa says natural ventilation is equivalent to no ventilation at all.
Next, there are filter-based air-conditioners.
When used in the right size and number, Moraskwa says these have been shown to reduce infection risk.
Better yet, these can also address outdoor particle pollution along with outdoor pollution which occurs because of bushfires.
However, these are not a complete solution in themselves without ventilation as any absence of ventilation will lead to the build-up of carbon dioxide, VOCs and other indoor generated air pollutants.
These pollutants will still accumulate notwithstanding the filtration.
As a result, Moraskwa says building engineering controls are critical.
- Sufficient and effective mechanical ventilation
- Avoiding air recirculation
- Particle filtration and air disinfection; and
- Avoiding overcrowding.
On the first point, Morawska says ventilation needs to be supplied in sufficient quantities and needs to be provided throughout entire rooms in a manner which prevents air flow from person to person.
In working out how much ventilation is sufficient, guidance is available for minimum ventilation rates.
In non-residential settings, the World Health Organization recommends a minimum rate of 10 liters per second per person.
A similar recommendation is adopted by The Federation of European Heating, Ventilation and Air Conditioning Association in relation to typical non-residential buildings.
Different recommendations are adopted by the American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE).
ASHREA has a table of recommendations which vary according to different settings.
For an art class involving activities such as painting, for example, ASHRAE recommends a minimum ventilation rate of 9.5 liters per second per person.
For a seated lecture theatre, this drops to four liters per second per person.
Even where these minimum rates are achieved however, ventilation does not offer a complete solution in and of itself.
During a recent study, Moraskwa and her team at QUT recently assessed the individual risk of an exposed person along with the expected number of new infections which arises from a single infectious individual. They compared this with past scenarios for which previous research work provided robust data for a classroom and military barracks.
The analysis covered ten known viruses: influenza, SARS-CoV-1 (initial COVID strain), Coxsackievirus, TB-on treatment, MERS, Rhinovirus, measles, TB-untreated, SARS-COV-2 (Delta variant) and adenovirus.
It also took account of different activities being undertaken by those in the room (resting, oral breathing, standing, speaking).
Even at high ventilation rates of 14 liters per person per second – well above minimum rates referred to above – that analysis found that infection was still likely to occur for four of the viruses studied: measles, TB-untreated, SARS-COV-2 (Delta variant) and adenovirus.
For each of these viruses, each infectious person was likely to infect at least one other.
For this reason, Morawska says mechanical ventilation must be supported by other measures.
Fourth, it is important to disinfect the air in a way that no additional pollution is generated indoors.
Whilst there are many ways this can be done, Morawska says a particularly effective technology is Germicidal ultraviolet (GUVV) air disinfection. This has low energy requirements, does not in itself generate additional new pollutants in the air, does not make noise, requires little maintenance and is low cost.
Finally, we need enforceable air quality standards.
As things stand, Moraskwa says the WHO issues air quality guidelines for indoor and outdoor air (these were updated to more stringent standards last year).
In addition, most countries including Australia have outdoor air quality standards which are monitored by stations around the country,
However, most including Australia DO NOT have indoor air quality standards.
As a result, indoor air quality operates in a ‘no man’s land’ from a regulatory viewpoint.
This, Morawska says, must change.
Going forward, she says standards are needed for indoor air quality which are monitored, measured and enforced. This means that concentration levels of selected pollutants need to be monitored and measured in every indoor space.
Morawska says the importance of action cannot be underestimated.
“It took two thousand years from the time that asbestos was recognised as a health risk (during Roman times) for regulations against asbestos to be introduced,” she says.
“I hope it will not take two thousand years before we have healthy air in all our interiors.
“Hope it not a strategy. We all have to continue working toward change.”