- The space you're in can either keep you safe or infect you with the Covid-19 virus
- Keeping the air safe is therefore an important way to curb the spread of the virus
- One way to achieve this is through good ventilation
The new coronavirus, SARS-CoV-2, typically lingers in public spaces. And while strict non-pharmaceutical interventions (NPIs), such as physical distancing and good hand hygiene, can be highly effective in reducing transmission, they have their limits.
Since schools have reopened, along with restaurants and office buildings and other indoor spaces, good ventilation, air filtration and humidity levels are key to reducing the spread of the virus.
The purpose of ventilation
According to the World Health Organization (WHO) guidelines published in July, a “well-maintained and operated system can reduce the spread of the virus in indoor spaces by increasing the rate of air change, reducing recirculation of air, and increasing the use of outdoor air”.
The general purpose of ventilation in buildings, the organisation adds, is to provide healthy air (and remove stale air) for breathing, in other words, to maintain the quality of air in that space.
No sign of ventilation? Best to stay away
A number of studies have shown that airborne transmission of the virus can effectively take place within confined spaces, as the tiny virus particles linger in the air.
If you enter a room or building and smell stuffy air, take it as a sign that the carbon dioxide concentration is high, and the ventilation is poor, Qingyan Chen, a mechanical engineering professor at Purdue University, told Business Insider US.
Air-conditioning may not always be protective
WHO states that heating, ventilation and air-conditioning (HVAC) systems are used to maintain indoor air temperature and humidity at healthy levels, but that recirculation modes (which recirculate the air) should be avoided.
If you spot an air-conditioning system in a shop or room, have a quick look at what type of system it is. The split air-conditioner, for instance, is commonly installed in malls and restaurants, but may not be the healthiest option in our current setting, as it recirculates the air.
A limited study by Chinese researchers earlier this year suggested this type of air-conditioner may spread the virus in a restaurant setting.
Their paper includes a diagram of the arrangement of a restaurant’s tables and air-conditioning airflow, and they explained that an asymptomatic (infected but displaying no symptoms) person released the virus as he breathed and talked and that the air-conditioning unit blew air in the direction of several tables, which was likely the cause of infection of nine other people that were also at the restaurant at that time.
Managing air quality: indoor humidity
Recent evidence suggests that SARS-CoV-2 survives better in low-humidity environments. Health24 reported on an Australian study, published last month, where researchers found a link between lower humidity and an increase in community transmission.
"When the humidity is lower, the air is drier and it makes the aerosols smaller," said Professor Michael Ward, an epidemiologist in the Sydney School of Veterinary Science at the University of Sydney, and lead author of the study.
According to Dr Stephanie Taylor, M.D. of Harvard Medical School who spoke to PBC Today, maintaining indoor humidity levels to 40–60% will decrease exposure to infectious particles and therefore reduce viral transmission.
If you don’t spot any heating or ventilation systems, or portable humidifiers, it’s best to ask the building owner, for example, whether they have sufficient humidification mechanisms in place.
Avoid fans in certain situations
As we ease into the warmer weather, most of us are likely to bring out our table and pedestal fans. The WHO notes that these fans are perfectly safe for air circulation among family members living together, who are not infected with the virus, but that these fans should be avoided when you have outside visitors, since some people are asymptomatic.
“If the use of a table or pedestal fan is unavoidable, it is important to increase outdoor air changes by opening windows and minimise the air blowing from one person (or group of people) to another person (or group of people),” the guideline reads.
In the case of ceiling fans, the organisation adds that good outdoor ventilation – which can be achieved by opening windows – is critical when using this type of fan.