It means the ability to filter bacteria up to 3 micrometers in size. But viruses are much smaller than that. There are 1000 nanometers in one micron. (http://www.kylesconverter.com/Length/Nanometers-to-Microns) Viruses are sub-micron in size, so their size is measured in nanometers, abbreviated “nm”. Some common sizes of viruses (http://book.bionumbers.org/how-big-are-viruses/):
- Polio virus: .030 microns
- Adenovirus: 88-110 microns
- Influenza A: 80-120 microns
- COVID-19: 0.120 microns
N95 masks do not work by catching the dry virus particle, they work by catching the droplets people exhale when a person coughs or sneezes, and the droplets are much larger than the virus itself. Droplets in the air are the most common way to transmit viruses of many kinds, that’s why the 6 foot social distancing is recommend. However this recommendation is ridiculous and illogical because these microscopic water droplets can carry much further than 6 ft because most places have air currents to carry them around.
COVID-19 size is 0.120 microns across. It is one of the largest viruses we know of. (https://www.quora.com/What-is-the-physical-size-of-the-Coronavirus-CiVid-19?share=1)
