Perfect is the enemy of good enough. Water droplets expelled by talking/breathing are large enough and heavy enough to be predominantly affected by gravity and as such fall to earth within about 5 to 6 feet, hence the 6 foot recommendation. Some could exceed that radius if expelled more forcefully as in a sneeze, hence the recommendation (finally) to wear a mask to not only minimize the droplets expelled but also stop some of those in the air you might breathe in. Droplets of a small enough size to form aerosols are predominantly governed by air currents and take longer to settle/disperse further so 'perfect' interception of potential contamination is not possible, but 'good enough' protection can be implemented
The size of individual WuVid 19 particles has been characterized as between 0.06 and 0.14 microns and an N95 is only good down to 0.3 microns. There is no perfect protection, after all it likely broke (carelessly implemented?) Level IV containment at the lab in Wuhan. If you want 'perfect' containment until you can get a vaccine you'll need to go full Howard Hughes
That isn't quite right. The N95 or P95 standard is to stop 95% of 0.3 micron and larger particles. The filtering is called tortuous path filtering and is pretty much a statistical thing. The filters will certainly stop some particles smaller than 0.3 microns but just at some rate less than 95%. There is no sharp cutoff.
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