@merpreb Merry - N-95 are certified in the US. KN-95 masks are certified in China, supposed to be to the same standards as in the US, so they should be equivalent. They wear the double masks as an extra precaution to protect the KN-95 from contamination by patient droplets while their masks are off for cleaning & dental procedures. So far, so good for them - it has been 10 weeks since reopening, and no one on the staff has been infected.
However, the N-95 industrial masks with the exhaust port, like I wear when working with soil, are not meant to be used for Covid-19 protection of other people, because the port allows droplets to escape while preventing inhalation of particles (it's why they are more comfortable than medical N-95 masks - moisture doesn't build up in them.)
Sue