Something we’ve known for a while here at The Fifth Estate is that Covid can likely spread through small airborne droplets, even though the risk appears to be far lower than the better publicised touch and sprayed droplet routes.
Almost two months ago, more than 200 scientists, including QUT’s International Laboratory for Air Quality and Health director Professor Lidia Morawska, penned an open letter calling on the World health Organisation and the broader medical community to get serious about airborne virus spread.
The letter is based on the growing body of research that shows that the virus can be spread through miniscule respiratory particles (of five microns or less in diameter) that hang in the air and can infect people far further away than the 1.5 metres social distancing recommendations.
The research has covered a range of mysterious spreading incidents, including a lengthy bus trip that saw a passenger infected; they were sitting 4.5 metres away from the Covid case.
There was a restaurant outbreak that pointed a finger at the airconditioning and the well-known case Skagit Valley Chorale rehearsal hall case where 33 people contracted the disease, resulting in two deaths, despite taking all the advised precautions.
From these examples, the dangerous settings for aerosol virus spread indoors tend to be a lengthy stays, crowding and a lack of fresh air moving through an enclosed space.
The World Health Organisation has since taken a serious stance on airborne transmission. In late July, it advised that ventilation is indeed “an important factor” in preventing COVID-19 from spreading indoors.
It’s put together handy guidelines to keep “fresh, clean air” in buildings, starting with natural ventilation – that is, the simple act of opening the windows. It also issued advice on mechanical ventilation: increase the percentage of outdoor air using economiser modes of HVAC operations, “potentially as high as 100 per cent”.
WHO also warns against air recirculation in buildings, especially for buildings with high risk of exposure such as in retail premises and hotels, with filters to be cleaned regularly if air recirculation is the only practical option.
All reasonable advice as far as The Fifth Estate is concerned. But what about tenancies such as small shops and restaurants that rely on customers walking into their shop and opening doors as their only source of fresh air (as current regulations allow)?
The real danger in these sorts of tenancies is a lack of awareness, according to a recent AIRAH article, with some ground floor establishments keen to keep their doors or window firmly shut to keep out odours, noise or pollution that might bother their customers.
Small shops and restaurants aren’t the only spaces prone to airborne spread – offices, schools, kindergartens, libraries, cruise ships, elevators, conference rooms and public transport are other higher risk examples.
Older sealed buildings with ageing HVAC systems are also tricky.
Fortunately, CETEC principal consultant Adam Garnys, who’s company has carried out almost 100 Covid risk assessments, says the risk factor is being well managed in office buildings with less-than-optimal ventilation.
Basically, he isn’t seeing any businesses rocking 100 per cent occupancy in a 1970s building.
He says that at current disease rates (outside of Victoria) there will be some poorly ventilated office buildings that won’t safely be able to achieve full occupancy. For these buildings, businesses will need to rely on the many other Covid risk mitigation measures in the playbook, including working from home, hand washing and social distancing.
Garnys says there’s been pretty clear government guidance around maximising ventilation, where you can and reducing occupants per square metre, and the market has adapted accordingly.
He did note, however, that not everyone has made it back to the office (even Sydney, which is not in lockdown, is rumoured to have only around 20 per cent occupancy in the CBD), making it difficult to determine the relationship between lacking ventilation and Covid infection rates.
Industry split on the best way to achieve fresh clean air indoors
In the HVAC community, the fresh air advice seems to be feeding into the enduring mechanical versus natural ventilation argument that predates the virus.
An article published in early August in The Conversation penned by the well-respected Susan Roaf, Emeritus Professor of Architectural Engineering at Heriot-Watt University spruiked the benefits of windows as a cheaper and often overlooked alternative to its mechanical counterparts.
The UK-based author took aim at the modern preoccupation with expensive mechanical ventilation, going as far as suggesting self-serving HVAC engineers purposefully specify expensive mechanical kit in the building codes they help write.
The article kicked up a bit of a stir, including in Australia.
One source contacted by The Fifth Estate suggested that the piece was written in the context of an ideological disagreement in the UK where long-standing proponents of hybrid and naturally ventilated buildings are unhappy about the rise of closed and controlled buildings.
The same source also suggested that the natural ventilation route is not always practical in Australia’s cooling-centric climate, where offices are mostly sealed buildings with few openable windows to allow for efficient cooling.
In a response to Roaf’s piece, chief executive of Australia’s HVAC engineering body AIRAH, Tony Gleeson, warned against declaring natural ventilation a “panacea” to reduce airborne Covid spread, drawing attention to WHO’s advice around air flows in buildings moving from “clean to less-clean areas”.
“Does air travelling from a busy reception area, past employees and out an open window produce a healthier workplace? We believe more work still needs to be done here,” Gleeson says.
He also noted that his organisation is a supporter of low carbon emissions HVAC systems, which includes lowering the heating and cooling load required using design features such as windows so less mechanical heating and cooling is needed at all.
As such, Gleeson told The Fifth Estate that the organisation is not, in fact, for “ever more machinery” but for “reducing the need for that machinery” through holistic building design and operations.
While supportive of using natural ventilation to better indoor air quality, Gleeson says that it can’t be relied on solely in some of Australia’s climatic zones. In many instances, a combination of both passive design principles and mechanical AC (mixed mode) will be a good option.
Windows are great but there’s one glaring problem
While The Fifth Estate is a ready supporter of carefully controlled, air quality-enhancing mechanical ventilation systems such as those used in a Passive House building, it’s also hard to go past low energy windows to keep the fresh air circulating, where it makes sense.
In Brisbane, the council wants to make the most of its temperate subtropical climate – characterised by sunny days, cooling breezes and a pleasant mean annual temperature range of 15 to 25 degrees – with its “Buildings that Breathe” guidelines.
It’s now ramping up incentives that will see more of Brisbane populated with buildings that have plenty of natural ventilation and operable windows and doors.
For indoor air quality specialist Jon Dalton of Viridis, windows are great low tech air quality-improving devices but they have their drawbacks.
When it comes to virus control, one benefit of using windows for ventilation is that unlike a centralised airconditioning system, there’s no risk of windows distributing the contaminant to other floors of the building.
Another tick for windows, according to Dalton and his colleagues, is that they require virtually no maintenance.
The downside of windows, which has already been alluded to in the restaurant/shop example mentioned earlier, is that occupants actually have to use them.
“Sometimes they don’t want to, it isn’t appropriate (for example, noise, security), or, they just couldn’t be bothered.”
Dalton points out that occupants can often mistake cool indoor air with “freshness” despite it sometimes being stale and polluted.
As air quality specialists particularly focused on mould, Dalton knows these sorts of ventilation issues well pre date Covid.
He says many new apartments are plagued with mould and air quality issues despite meeting the National Construction Code standards. While there’s some instances where the occupant is not opening their windows as required, a recent article in The Fifth Estate by Brisbane architect Russell Hall argues that the building code’s requirements around ventilation are weak.
The code requires 5 per cent of habitable floor area to be for ventilation. But the way the code is worded, according to Hall, often results in windows that only open a crack.
As such, there’s a good chance we’re occupying less than optimally ventilated buildings.
Covid might be the prod we need to rethink our approach to ventilation so we can live and work in healthier, more comfortable buildings.