Data shows face masks can protect you from the coronavirus, but how about air purifiers? How effective are HEPA air filters at capturing the coronavirus?
Can HEPA Filters Capture The Coronavirus?
To answer this question, we need to first answer if HEPA filters can capture particles as small as the coroanavirus. The coronavirus measures 0.06 – 0.14 microns in diameter.
HEPA filters – the workhorse of any purifier – must remove 99.97% of particles “greater than or equal to” 0.3 microns.
But the definition only mentions particles 0.3 microns and above. What about smaller particles like the coronavirus, can HEPA filters capture these?
This exact question has led to years of confusion and false advertising claims about HEPA filters, and is now leading to more misinformation about whether HEPA filters can or cannot capture the coronavirus that causes COVID-19.
Why HEPA Filters are Great at Capturing the Coronavirus
The fact that HEPA filters are so good at capturing tiny particles like the coronavirus is suprising. It’s surprising because our intuition about filters is wrong. Like most people, I had the intuition that HEPA filters work like a net.
If a particle is smaller than the holes in the net, it gets through. Makes sense! However, it turns out that particles as small as the coronavirus, and other nano-particles get captured using a scientific phenomenon called diffusion.
Diffusion is surprisingly effective at capturing tiny virus-sized particles. According to NASA, HEPA filters capture “virtually 100% of particulates.”
Researchers at the University of Minnesota tested this question with weaker fiberglass furnace filters and higher-grade HEPA filters. In their test, they shot particles of silver from 3 to 20 nanometers at the filters (that’s roughly 5 to 30 times smaller than coronavirus particles).
The results showed that filters captured 99.99% of particles smaller than 5 nanometers. Bingo! HEPA filters are incredibly effective at capturing nanoparticles–even smaller than the coronavirus.
Caveat: It’s not clear that HEPA air purifiers would be useful in a home, office, or school, since there is less recirculated air and viruses often (but not always!) travel on large water droplets, which tend not to linger in the air. However, if there are virus particles in the air entering a purifier, the HEPA filter will filter them out.
Paddy is the CEO of Smart Air, running operations from Beijing. He has a Masters in aeronautical engineering from Bristol University, UK having specialised in aerodynamics. An advocate for open data, free information and transparent business, he spends his spare time promoting honest business and social enterprise.