What are the precautions for the frequency of mask replacement?

Regarding the frequency of replacement of masks, the above-mentioned technicians said that if they are dirty, they will be replaced, ranging from three to five days, or if medical staff go to the contaminated area, they will be replaced.
In fact, regarding the frequency of replacement, at present, foreign countries, including WHO, have not made clear conclusions on the best wearing time of N95 masks, and my country has not yet made relevant regulations on the use time of masks. Some researchers have done related research on the protection efficiency and wearing time of N95 medical protective masks. The results show that the filtration efficiency of N95 masks remains above 95% when worn for 2 days, and the respiratory resistance does not change much; the filtration efficiency is reduced to 94.7 after wearing for 3 days. %.
But when the following situations occur, the mask should be replaced in time:
1. When the respiratory impedance increases significantly;
2. When the mask is broken or damaged;
3. When the mask and face cannot be closely attached;
4. The mask is contaminated (for example, when it is stained with foreign objects such as blood stains or droplets);
5. It has been used in individual wards or in contact with patients (because the mask has been contaminated);
6. If it is a mask containing activated carbon, there is a peculiar smell in the mask.
In addition, there are a few points to pay attention to when wearing a mask:
1. Wash your hands before wearing the mask, or avoid touching the inner side of the mask during the process of wearing the mask to reduce the possibility of the mask being contaminated.
2. Never use your hands to squeeze masks, including N95 masks, which can only isolate the virus on the surface of the mask. If you squeeze the mask with your hands, the virus will soak through the mask with droplets, and there is still a chance of infection.
4. Make sure that the mask is in good contact with the face as much as possible. The simple test method is: After putting on the mask, exhale forcefully so that the air cannot leak from the edge of the mask.