Although there are many kinds of medical masks, they are mainly divided into two categories, general surgical masks and N95 respirator. Initially, the purpose of surgical face masks was to prevent liquid splashing and prevent the person wearing the mask from transmitting the germs to others, so the mask was designed so that the inner lining is rough and the outer layer is smooth. Later surgical masks were more widely used and also used to prevent infections.
N95 means that it can block 95% of bacteria. The N95 face mask is a respirator, which needs to be sealed, and the air is exchanged through the mask, instead of going in and out like a mask. Therefore, the use of N95 masks needs to pass a fitting test. Speaking and deep breathing will not affect the seal. At this time, fat people have an advantage and the seal is good. 1860 is hard, generally better than 1870 (soft) seal, but more uncomfortable; the better the seal, the more difficult to breathe. N95 masks are suitable for low-intensity work, otherwise breathing is difficult. The masks with valves are not real medical masks, and can not be used to prevent infections. It is possible to prevent smog.
The N95 mask sounds good, but because the minimum pore size of the fiber can only be 0.3 microns, although the coronavirus is relatively large, the maximum is not more than 0.15 microns. No matter how many layers are made, it can only be delayed and cannot completely block the virus, because the virus is alive.
The MIT study found that the sneezing liquid velocity is 35m / s, and it depletes with distance. There is basically no velocity after 2 meters; it spreads in the air for about 8 meters; so if the patient is not protected, the N95 mask cannot be protected; Wearing a mask, especially the lining of N95, most of the virus was left behind. The virus that went out had no speed, and it was impervious to the N95 for a while. Why effective time? This is an estimate. There are viruses on the mask, how long can it penetrate.
Therefore, everyone should wear a mask in public, and people infected with the virus wear masks, which is much more important than healthy people.