Masks are again required in many indoor spaces to slow the spread of COVID-19, but not all masks protect against airborne viruses and they are not required in all public places.
Key points:
- People with a COVID-19 infection can exhale particles and droplets that contain the virus
- Mixing fresh air with the air inside a building helps lower the risk of transmission
- Current building standards do not address the risk of airborne infection, an occupational hygienist says
Like other virus variants, Omicron can be exhaled by a person with an infection, carried through the air and inhaled by someone else, causing them to become infected.
Some public places are riskier than others, but there are measures business owners can take to improve the air quality in their premises and lower the risk of customers and staff becoming infected.
We took two workplace safety experts to indoor spaces to find out what makes a place less of a COVID-19 risk.
Risk in retail spaces
As the owner-operator of a small plant and gift shop in Cronulla, Sydney, Andy Gray is a one-man band and cannot risk having to close if he or a customer catches COVID-19.
“No-one wants to be the spot that other people are getting infected at,” he said.
Mr Gray said he has had no advice from government sources about keeping his business COVID-19 safe, so was grateful to get some tips from occupational hygienist Andrew Orfanos.
“It’s all about reducing the risk,” Mr Orfanos said.
With staff spending many hours in a shop, any particles they exhale can build up in the air. If they had COVID-19, it could be a risk to any visitors.
Vaccinated staff have less chance of catching COVID-19 and less chance of passing it on, which helps protect customers.
However, customers with an infection are less of a risk because they only spend about five to 10 minutes in the shop.
“That’s something in your favour,” Mr Orfanos told Mr Gray.
To review a building’s ventilation systems, Mr Orfanos uses a smoke tube, which releases white curlicues that waft along with moving air.
“That’s the best visual. It’s a very simple tool,” he said.
Mr Gray keeps a back door open to encourage a draft of fresh air to move through his shop and Mr Orfanos’s smoke tube shows the air does move through the place.
But Mr Orfanos noted the shop only had a split-system air conditioner cooling the air inside, and no mechanical ventilation helping to dilute the air in the shop with fresh air from outside.
In Mr Orfanos’s view, that could mean the property Mr Gray is renting is not compliant with building regulations that require indoor spaces to be adequately ventilated.
Mr Orfanos said landlords should be able to show their tenants that the ventilation system in their building was working well.
“It’s one thing to have something installed. It’s another thing for it to be working and being maintained,” he said.
He would like to see government regulators inspect occupied buildings to ensure they meet current standards, instead of simply requiring buildings meet the code when they are erected.
Restaurants and cafes
Kate Cole, president of the Australian Institute of Occupational Hygienists, takes a carbon dioxide (CO2) monitor with her wherever she goes.
On a recent visit to Mexican restaurant Calle Rey in inner-Sydney, she set it up in a back corner to test the air quality where she suspected the area was least ventilated.
With its front doors opening wide onto the street, and a fully functional HVAC system churning fresh air through the place, the Newtown restaurant impressed the engineer and scientist.
“This is what you’d aspire to,” she said.
Because people sit close together, generally don’t wear masks and spend an hour or more at a table, restaurants can be places where staff and customers are at risk of being infected with COVID-19.
Ms Cole said to reduce the risk of COVID-19 or other airborne diseases being transmitted in public spaces, indoor air should be constantly mixed with fresh air from outside.
“The key to reducing COVID transmission is dilution,” she said.
She said when she offers advice on improving ventilation in an indoor space, she first tests to see whether there is a problem using the CO2 monitor.
CO2 is itself not a risk. But because we all exhale it as we breathe, measuring how much of the gas is in a space can indicate whether exhaled disease-causing particles would also build up there.
“We use CO2 as a proxy for infection risk,” Ms Cole said, adding that a reading below 800 parts per million shows an area was safe.
When she retrieves the CO2 monitor from the back of the Mexican restaurant, it shows readings of around 500ppm as she approached the restaurant from outside, then up over 900ppm when the monitor was placed in the back corner.
Placed on a table in the main part of the restaurant where it is well ventilated, the monitor settles around 600-700ppm.
“We can’t eliminate [risk] but we can lower it,” Ms Cole said.
Gyms
Both experts said gyms were challenging spaces to ventilate safely.
Mr Orfanos said many gyms used split-system air conditioners for temperature control, together with fans.
Neither draws fresh air into the space.
“Fans just distribute the virus evenly in the room,” he said.
Ms Cole agreed that the size of the space, what people are doing in there and how often the air is being changed would determine the risk in a gym.
A large room with high ceilings could be less risky than a smaller enclosed space, she said.
And she said a high-intensity class would be higher-risk than yoga because participants are breathing more heavily.
Ultimately, the onus is on the public.
“It’s about the choices we make as an individual,” she said.
“I choose to spend my time and money in businesses that reduce the risk to their customers and employees.”
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