HEPA air cleaners and face masks reduce the exposure to COVID-19 air particles up 90%

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HEPA air cleaners and face masks can reduce the exposure to Covid-infected particles in a room by up to 90%, CDC report finds

  • CDC simulated a conference room in which there was one COVID-19-infected meeting participant, an uninfected speaker and two other participants
  • HEPA air cleaners were placed around the room, and simulations were run in which the participants did or didn’t wear masks 
  • Just using air cleaners without masks reduced the exposure to infected particles by 65% and just masks without the air cleaners reduced exposure by 72%
  • When HEPA air cleaners were used in combination with masks, the exposure to COVID-19 aerosols was reduced by 90% 


Portable air cleaners and masking can dramatically reduce the number of COVID-19 droplets and aerosols, a new report published on Friday suggests.

Researchers from the Centers for Disease Control and Prevention (CDC) conducted multiple experiments in which high efficiency particulate air (HEPA) cleaners ere used in a conference and people wear face coverings.

On their own, the air cleaners reduced the exposure of particles spread by an infected person about 65 percent.

However, when combined together, it reduced the exposure to coronavirus-infected aerosols by 90 percent.

CDC researchers simulated a conference room in which there was one COVID-19-infected meeting participant, an uninfected speaker and two other participants (file image)

CDC researchers simulated a conference room in which there was one COVID-19-infected meeting participant, an uninfected speaker and two other participants (file image)

Just using air cleaners without masks reduced the exposure to infected particles by 65% and just masks without the air cleaners reduced exposure by 72%, but the combination reduced exposure by 90%

Just using air cleaners without masks reduced the exposure to infected particles by 65% and just masks without the air cleaners reduced exposure by 72%, but the combination reduced exposure by 90%

HEPA air cleaners consist of a filter that removes almost all particles from the air and fan to draw air through the filter.

They offer a way to boost the filtration of aerosols and droplets without modifying an entire’s building ventilation system.

The air cleaners are widely available in stores and online, and can be bought for as little as $95.

Because it’s widely-known, that the coronavirus mainly spreads through the air and not through surface transmission, the team conducted a simulation of a typical office conference room. 

In the simulation, there was one infected person at the meeting who was exhaling aerosols along with two uninfected participants and an uninfected speaker.   

HEPA air cleaners were placed around the room, and simulations were run in which the participants did or didn't wear masks

HEPA air cleaners were placed around the room, and simulations were run in which the participants did or didn’t wear masks 

A breathing aerosol machine mimicked an COVID-19 patient exhaling infectious particles, also called the source.

Three breathing machines were used to mimic the speaker and the other two meeting participants, also called the receivers.

Two HEPA air cleaners were placed at the front and back of the room and four were placed in the center, some near the source and others near the receivers.

Control simulations were also perfumed with no air cleaners used.

The face masks used were three-ply cotton masks – with two fabric external layers and filer inside – with ear loops. 

Results showed that when just using air cleaners without masks, the exposure to particles was reduced by 65 percent.

In the simulation, when just masks were used without air cleaners, it reduced the aerosol exposure of the receivers by 72 percent.

But the best method was using masks and HEPA air cleaners together.

In this scenario, it reduced the exposure of other participants to COVID-19 respiratory aerosols by up to 90 percent.

The CDC says that findings can be used for any indoor environment, such as offices, school, restaurants or theaters, as people slowly make a return to day-to-day activities.

‘The optimal location for HEPA air cleaners will depend upon the unique conditions in each room, but they are likely to be most effective when they are placed as close to the occupants as is practicable,’ the authors wrote.

‘Larger reductions in exposure occur when air cleaners are used in combination with universal masking.’    

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