Air purifiers may do more harm than good in confined spaces with airborne viruses

The location of airspace inlets and outlets at limited locations, such as elevators, greatly affects airborne virus transmission. In Physics of Fluids, researchers at the University of Nicosia in Cyprus point out that help would be expected from air purifiers, they could actually increase the spread.

Air quality in small spaces can degrade quickly without ventilation. However, adding ventilation will increase the rate at which air, possibly virus-laden, can move in a smaller space. Lift manufacturers have added air purifiers to take care of this problem, but the system is not designed keeping in mind their effect on overall air circulation.

Air purifiers use ultraviolet radiation to kill viruses and other microbes, but they circulate air, suck it up and expel clean air. This adds to the overall circulation, an aspect that has not been considered in previous research.

Previous work by scientists indicated that droplets of saliva can travel 18 feet in five seconds, when an unmatched person coughs. The authors extended the same model to examine the effects of face masks and weather conditions.

Investigators calculated for the 3-D space, which is equivalent to an elevator, capable of holding five people. A mild cough was simulated at one position in space, and air inlets and outlets were added in various locations to study their effect on circulation. An air purifier was also included in the simulation.

“We determined the effect of air circulation on airborne virus transmission and showed that installing an air purifier inside an elevator significantly alters air circulation, but does not eliminate airborne transmission,” author Dimitris Drakkis said.

Investigators found the risk of airborne virus transmission to be the lowest for low ventilation rates.

“This is due to less mixing inside the lift,” said writer Talib Dubok. “Regulatory authorities should thus define the minimum ventilation required based on the type of building.”

The study looked at the role of an air purifier considering only air intake and exhaust associated with the air purifier, but not the mechanism inside the purifier that killed the virus. Even with an air purifier, airborne virus transmission is still important.

“Our results show that installing the air purifier can cause a small droplet to spread,” Drikkis said. “Integrated air intake flow inside the purge device induces circulation that can combine the transport of contaminated salivary droplets into the cabin.”

The observed effect increases with the number of infected individuals in the lift. Limiting the number of people allowed in the lift will reduce the spread of the virus because of better design of air purifiers and ventilation systems.

Air quality in small spaces can degrade quickly without ventilation. However, adding ventilation will increase the rate at which air, possibly virus-laden, can move in a smaller space. Lift manufacturers have added air purifiers to take care of this problem, but the system is not designed keeping in mind their effect on overall air circulation.

Air purifiers use ultraviolet radiation to kill viruses and other microbes, but they circulate air, suck it up and expel clean air. This adds to the overall circulation, an aspect that has not been considered in previous research.

Previous work by scientists indicated that droplets of saliva can travel 18 feet in five seconds, when an unmatched person coughs. The authors extended the same model to examine the effects of face masks and weather conditions.

Investigators calculated for 3D space equivalent to an elevator capable of holding five people. A mild cough was simulated at one position in space, and air inlets and outlets were added in various locations to study their effect on circulation. An air purifier was also included in the simulation.

“We have determined the effect of air circulation on airborne virus transmission and have shown that installing an air purifier inside an elevator significantly alters air circulation, but does not eliminate airborne transmission,” author Dimitris Drakkis said.

Investigators found the risk of airborne virus transmission to be the lowest for low ventilation rates.

“This is due to less mixing inside the lift,” said writer Talib Dubok. “Regulatory authorities should thus define the minimum ventilation required based on the type of building.”

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