The claim: "N95 masks block few, if any" COVID-19 particles due to their size
As many states and communities ease restrictions related to the COVID-19 pandemic, the debate over mask usage has intensified.
Businesses, churches and governments have implemented all manner of policies — some requiring masks, some leaving it up to each person, some even banning masks. And that has spurred many armchair epidemiologists to weigh in, including a Facebook page with nearly 1 million followers.
Virus particles don’t exist alone
The science of mask functionality gets really small, really fast. The unit of measurement here is microns — 1/1000th of a millimeter.
The size-based argument against N95 laid out in this claim assumes mask filtering works something like water flowing through a net — particles in the water smaller than the net opening pass through, while larger items don’t.
But the physics involved don’t work like that at all.
The COVID-19 particle is indeed around 0.1 microns in size, but it is always bonded to something larger.
“There is never a naked virus floating in the air or released by people,” said Linsey Marr, a professor of civil and environmental engineering at Virginia Tech who specializes in airborne transmission of viruses.
The virus attaches to water droplets or aerosols (i.e. really small droplets) that are generated by breathing, talking, coughing, etc. These consist of water, mucus protein and other biological material and are all larger than 1 micron.
Size matters, but not how you think
But that’s not the only logical flaw in this claim.
The N95 filter indeed is physically around the 0.3 micron size. But that doesn’t mean it can only stop particles larger than that. The masks are actually best for particles either larger or smaller than that 0.3 micron threshold.
“N95 have the worst filtration efficiency for particles around 0.3,” Marr said. “If you’re smaller than that those are actually collected even better. It’s counterintuitive because masks do not work like sieving out larger particles. It’s not like pasta in a colander, and small ones don’t get through.”
N95 masks actually have that name because they are 95% efficient at stopping particles in their least efficient particle size range — in this case those around 0.3 microns.
Our ruling: False
We rate this claim FALSE because it is not supported by our research. The COVID-19 virus itself is indeed smaller than the N95 filter size, but the virus always travels attached to larger particles that are consistently snared by the filter. And even if the particles were smaller than the N95 filter size, the erratic motion of particles that size and the electrostatic attraction generated by the mask means they would be consistently caught as well.
