The masks are almost identical in performance to the N95 masks that hospitals and other institutions are struggling to find.
With doctors, nurses and other health care workers facing acute shortages of protective masks, the Food and Drug Administration announced on Friday that it will allow use of a more widely available mask that meets Chinese standards instead of American ones.
Hospitals across the United States are running out of N95 masks, which filter at least 95 percent of particles that are 0.3 microns or larger, including the new coronavirus. N95 masks are tested and certified by the National Institute for Occupational Safety and Health, or NIOSH, a research agency that is part of the Centers for Disease Control and Prevention.
On Friday, the F.D.A. issued an emergency use authorization for KN95 masks. Regulated by the Chinese government, they are almost identical in performance to N95 masks. There are slight differences in their specifications, like a variation in the maximum pressure the masks must be able to withstand as a person inhales and exhales.
The C.D.C. lists KN95 masks as a suitable alternative when N95s are not available.
The F.D.A. said KN95 masks were eligible for authorization if they met certain criteria, including documentation that they were authentic.
Effectively block fine particles in the air, four-layer filtration structure, PM2.5 filtration efficiency> 95%
What about homemade face masks?
If wearing homemade masks is recommended, there is lots of advice online about how to make them. Suggestions include using common household items, such as cotton fabric from old T-shirts or bedding. However, homemade masks are not regulated, whereas officially-made ones have to meet safety requirements. Reusable cloth masks are not recommended and may even increase the chance of infection, say European advisers. This is because there is a high chance virus particles could go through cloth, and moisture in it could retain the virus, they warn.
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