Using air purifiers in confined spaces, such as elevators, could increase the circulation of saliva droplets, actually exacerbating the spread of Covid-19, researchers said.
A team from the University of Nicosia in Cyprus said air purifiers are expected to help limit the spread of the virus, but they can actually increase it. Air quality in small spaces can deteriorate quickly without ventilation.
Adding ventilation will increase the rate at which air, possibly laden with viruses, can circulate in the small space. Elevator manufacturers have included air purifiers to solve this problem, but the systems are not designed to account for their effect on overall air circulation.
Air purifiers use ultraviolet radiation to kill viruses and other microbes, but they also circulate, draw in and remove pure air. This contributes to overall circulation, an aspect that the team said was not addressed in previous research.
Previous studies show that saliva droplets can travel 5.5 meters in five seconds when an unmasked cough.
Researchers performed calculations for a 3D space equivalent to an elevator that can accommodate five people.
A mild cough was simulated in one position in the room and air inlets and outlets were added in several places to study their influence on circulation. An air purifier has also been included in the simulation.
“We quantified the effect of air circulation on airborne virus transmission and showed that installing an air purifier in an elevator significantly changes air circulation, but does not eliminate airborne transmission,” said author Dimitri’s Drikakis.
The researchers found that the risk of virus transmission through the air is lowest at low ventilation rates.
“This is due to reduced flow mixing in the elevator,” said author Talib Dbouk. “Regulatory authorities must therefore define the minimum required ventilation, depending on the type of building.”
The study looked at the role of an air purifier, considering only the air inlet and outlet of the purifier, but not the mechanism in the purifier that kills the virus.
Even with an air purifier, the transmission of viruses in the air is still significant. “Our results show that installing an air purifier can increase the dispersion of droplets,” said Drikakis.
“The air inlet integrated into the air cleaning equipment induces flow circulation that can contribute to the transport of contaminated saliva droplets into the booth.” The observed effect increases with the number of infected persons in the elevator.
Limiting the number of people allowed in an elevator would minimize the spread of the virus, as well as better design air cleaners and ventilation systems.
Last year, a new carbon-based air filter was developed that can trap and destroy animal coronaviruses, which are close relatives of the SARS-CoV-2 virus strain that causes Covid-19.