Air purifiers in lifts (elevators) and other poorly ventilated confined spaces could actually increase the spread of airborne virus droplets, according to researchers who have called upon the health authorities to look for such places which might be turning out to be super spreader for Coronavirus which is spreading like a raging fire.

When people infected with the Cov-SARS-2 virus, responsible for the current Covid-19 pandemic, sneeze, talk or simply breathe, they expel thousands of contaminated saliva droplets.

These droplets are now recognized as being the main way in which the virus spreads to other individuals and people are being advised to wear masks to curb contamination. Regularly airing indoor spaces to reduce the concentration of viral particles is also important.

Since the quality of air in a small space can quickly deteriorate even when there is just one person in that space (mainly because of the increased CO2 levels produced as we breathe out), lift manufacturers routinely include ventilator systems. These can, however, increase the rate at which air – possibly laden with bacteria and viruses – circulates. While adding an air purifier to the lift in addition to the ventilator should help in theory, the way in which the purifier affects air circulation, and thus transmission of airborne viruses is unclear, said the researchers.

Air purifiers work by sucking in stale air and exhausting cleansed air, but this adds to the overall circulation of air – an aspect that previous studies, or indeed air purifier manufacturers themselves, have not considered.

To investigate this issue, Dimitris Drikakis and Talib Dbouk of the University of Nicosia analysed air circulation and found that the air purifier actually increases the spread of saliva droplets in the cabin.

“This is because the air intake integrated inside the purifier equipment induces flow circulation that can add to the transport of these droplets,” explains Drikakis.

They also found that the risk of airborne virus transmission is lowest for low ventilation rates. This is due to reduced flow mixing inside the lift, says Dbouk.

“The broader implications of the present findings are that health and safety authorities must revise guidelines accordingly by considering the flow circulation and droplet dispersion effects arising from air purifiers and sanitisers in confined spaces,” say Drikakis and Dbouk.