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Why masks block inward droplet passage better than outward -- possible explanation?

Posted by akauffman on 16 May 2020 at 15:36 GMT

When a mask-wearer coughs, sneezes, talks, or merely exhales, the particles expelled hit the inside of the mask at a range of speeds, which can be quite high in the case of a sneeze or cough. And these expelled particles have only a very short distance to travel before hitting the mask's inner surface, so they are not slowed down appreciably.

When, however, external particles hit the outside surface of the mask, they are likely to have been slowed down considerably by passage through the air, even if they have travelled only a short distance, say 300mm. Many such particles would be expected to 'drift' onto the mask rather than 'hit' it at speed.

Therefore exhaled particles are likely on average to penetrate the mask further, and perhaps pass right through it, compared with the on average slower particles heading the other way.

No competing interests declared.