No need to use air purifiers at home, natural ventilation is key to reducing risk of Covid

SINGAPORE - It is not necessary to use air purifiers at home, and people should instead adopt practices like opening doors or windows as much as possible to maximise natural ventilation to reduce the risk of getting exposed to Covid-19, says the National Environment Agency (NEA).

This advice comes as sales of air purifiers went up in recent weeks following concerns that Covid-19 may spread through airborne transmission in some settings.

While using the appropriate air purifiers can remove virus aerosols in the air, they cannot act as a substitute for good ventilation, NEA told The Straits Times.

They also cannot act as protection for other household members if one already has or is exposed to the virus.

An NEA spokesman said: "Good ventilation can prevent the accumulation of virus aerosols in the air, and reduce the risk of exposure to the virus. Members of the public do not need to buy or use air purifiers at home, but may improve ventilation via natural means such as opening doors and windows as much as possible."

It is also more likely for transmission within the household to be via contaminated surfaces and droplets, as household members spend much time in close proximity without wearing masks, NEA added.

But this does not mean that air purifiers have lost their value. They can still be used as an interim measure in enclosed, poorly ventilated spaces with a high risk of disease transmission, such as where masks are removed, or at medical procedures such as swabbing.

Some experts said air purifiers may also come in handy in a confined space, such as when someone from the household would want to isolate himself from the rest of the family over Covid-19 concerns.

But they emphasised that people cannot rely on air purifiers alone, as other health measures, such as social distancing and wearing masks, are still critical.

Associate Professor Ernest Chua from the National University of Singapore's Department of Mechanical Engineering said: "The use of portable air purifiers with an efficient Hepa filtration system can certainly help to reduce the risk of airborne transmission of Covid-19. However, they are not silver bullets to combat Covid-19. Instead, they are part of a larger strategic mitigation plan, rather than being the only plan."

He said that when virus aerosols are present, having a large amount of outdoor air would dilute any contaminants, including viruses, in a building.

"Air purifiers work with small volumes of air flow rates to reduce indoor pollutants and contaminants. Ventilation is the preferred option for spaces of different sizes while air purifiers are effective in handling small spaces, particularly when they are unable to get enough outside air for dilution," he added.

Associate Professor David Cheong from NUS' Indoor Air Quality Research Unit at the Department of Building said an air purifier can provide localised cleaning but may not be able to clean the whole room effectively.

Dr Cheong, along with two other professors in the research unit, said: "Performance of air purifiers degrade with time and, if not adequately maintained, the cleaning effectiveness may be compromised."

If air purifiers are used as a mitigation measure for enclosed spaces, they should be fitted with high-efficiency filters, such as a Hepa filter, to remove aerosols, NEA said. Consumers should also look at the clean air delivery rate of the air purifier to determine the size and the number of air purifiers needed.

The clean air delivery rate is a measure of the speed at which air is being cleaned. A large number means faster cleaning in an enclosed room.

NEA said that many models of air purifiers have additional cleaning features, such as ionisers, but their added benefits are uncertain. Some air purifiers also use ultraviolet radiation (UVC) to treat the air.

The spokesman said: "Care must be exercised when using UV for disinfection, as exposure to UVC radiation could cause eye or skin injuries, and increase risk of skin cancer from chronic exposure. Some UVC devices emit ozone, which can irritate the nose, throat and lungs."

Pre-school teacher Lim Yan Hui, 24, had been thinking of buying an air purifier, especially after reading reports about the possibility of Covid-19 being transmitted through the air in some settings. She is also worried for her parents, who are in their late 50s.

But she has changed her mind, saying: "I now find natural ventilation the most simple, yet effective, way to reduce the exposure of the virus.

"We intend to use less of the air-conditioner and open the windows of our home... I find that air purifiers are redundant and not necessary, as my home would not be an enclosed space."

Additional reporting by Cha Hae Won

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