A multi-purpose Seoul skyscraper showed us why office life may never be the same again. In March, officials issued coronavirus tests to 1,143 people who worked or lived inside: 97 came back positive. The infection rate was particularly high in an 11th-floor call centre, where 94 workers were infected. Almost all had desks on the same side of the building.
Five months later, countries are restarting their economies. Prime minister Boris Johnson has encouraged employers to open their office doors and dropped the two-metre rule for a one-metre-plus approach, despite uncertainty as to whether workplaces can be made safe. But what happened in Seoul is a warning about what could happen without proper precautions.
Research by Arup, the engineering, design, and consultancy firm, has given more reason for concern. Using software to model the motion of air and simulate crowds, researchers have demonstrated how aerosols — the microscopic droplets we breathe out — move through a typical, well-ventilated office space.
The simulation, based on Arup’s own offices, shows an 80 per cent increase in people exposed to aerosols exhaled by colleagues when offices are full. Researchers found that office partitions can create stubborn pockets of aerosols across the a floor.
“If you’re going back to full capacity in a densely populated office space then you need to be looking at doing more than business as usual to minimise the risks,” says Paul Lynch, a specialist in airflow modelling at Arup.
Lynch’s uneasiness centres on one contentious point: that Covid-19 is airborne — that it can spread via aerosols suspended in the air over distances greater than one meter. The World Health Organisation (WHO), like Public Health England, has long said that the primary form of coronavirus transmission comes from respiratory droplets — small particles of fluid, larger than aerosols — passed through direct or close contact.
This remains the most efficient mechanisms of transmission, but after months of pressure from experts, including a letter signed by 239 scientists, the WHO has acknowledged that indoor airborne transmission of the coronavirus may be possible. (Epidemiologists differentiate Covid-19 from classic airborne diseases like measles but agree that transmission can occur over longer distances when aerosols are concentrated in poorly ventilated spaces.)
A number of experts still deny that Covid-19 is airborne at all, but Lynch urges caution. He argues that the Seoul call centre findings are consistent with the aerosol spread his team is modelling because it was a crowded office space with workers spending all day talking. And if the virus is airborne, densely packed offices could become transmission hotspots.
The same conditions apply to any indoor space, but offices are unique because of how long people spend at work. The Seoul contagion showed that prolonged proximity, rather than sharing an elevator, was what allowed the virus to spread. “Your exposure level comes down to how many of these aerosols you’re breathing in and how long you’re exposed to them, and in an office space you could be there for eight hours a day,” Lynch says. “It’s therefore paramount that employers manage these risks to avoid extended periods of exposure.”
In this battle for safety, not all offices are equal. According to national building regulations, commercial premises must provide each occupant with between five and ten litres of mechanically ventilated fresh air per second alongside fresh air from windows. Most ventilation systems bring in the “bare minimum” because that means less to heat up in winter and cool down in summer, says Andrew Corney, a mechanical engineer.
The problem is that this is just enough for workers to breathe and remove odours but it can’t be relied on for anything more, Corney says. “Commercial ventilation systems aren’t designed to prevent airborne pollutants generated from one occupant from reaching others; they are designed to maintain adequate CO2 levels, consistent temperatures, and the removal of odours.”
Because of this there will always be a mix of air and internal pollutants around the space, Corney says. He describes office air like a cordial drink: pollutants generated by workers are mixed with filtered air, and it’s “constantly stirred” and “kept at an acceptable overall proportion”. The quality depends on the volume of outdoor air allowed in and the filtration system’s quality. In a modern office the air changes approximately every hour, but unless you’re in a cellular office separately ventilated from other workers, you're breathing the same air as them.
The safest offices will have natural ventilation, with large windows located on opposite sides of the floor. Unfortunately, the majority of offices don’t fall into that category. Most have windows that don’t open, partly to save energy and because modern filtration systems are thought to increase the quality of recirculated air. There’s also no guarantee that employers will open windows, especially in winter when heating systems struggle to cope with uncontrolled ventilation.
If aerosols aren’t being flushed out then they’ll circulate through the air within the heating, ventilation, and air-conditioning systems because they aren’t designed to filter out small particles. In Guangzhou, China, the coronavirus spread to three separate families eating in a restaurant sitting in proximity to an air conditioning unit.
But even if enough fresh air is being brought into the building, the office layout — including partitions installed to stop people from sneezing or coughing on each other — can create pockets of stagnant air. Imagine a cubicle connected to a thoroughfare where the aerosols will diffuse out. “Whoever is walking past will get a blast,” says Lynch. Or a meeting room bustling with aerosols waiting to greet the next unwitting visitor.
At the same occupancy density, open-plan offices are better, but the move from cubicles has decreased the average space per employee – and that includes a reduction in space for meeting rooms, breakout spaces and kitchenettes. While these setups use less energy, they can become breeding grounds for infection.
The desk areas are particularly potent because they’re so densely packed. Cubicles are small but in an open plan office desk space is, on average, half as small. Lynch suggests spreading the desks across the floor space to spread out aerosols.
Besides the extent to which the virus is airborne, no one knows how long stagnant, coronavirus-ridden air can linger in office spaces. Scientists have developed the Wells-Riley mathematical model to predict the risk of other airborne diseases, but Covid-19 is new. “The absolute risk is hard to nail down because we have an incomplete picture,” Lynch says.
Because of this, Amesh Adalja, an expert on emerging infectious diseases at Johns Hopkins University, believes we can’t label offices as more dangerous than any other public space. Even though scientists have demonstrated that you can isolate the virus from the air, nobody has proven this to be important when it comes to transmission, he says. Ventilation is important only in that it’ll whisk away the droplets faster. “Aerosols don't equate to transmission risk because we are not commonly seeing airborne transmission, if at all,” he says. “The primary consideration is social distancing and everything else is secondary.”
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This article was originally published by WIRED UK
