The pathogen of this epidemic is a new type of coronavirus, and the transmission route can be determined mainly by droplets. Larger droplets will fall to the ground quickly, while smaller droplets will float in the air. As the water evaporates, it becomes a disease-causing aerosol, which is the air containing many droplet nuclei.
82% of the droplet nuclei produced by coughing are concentrated in the range of 0.74-2.12 microns, and the size of the droplet nuclei that can float in the air is between 0.74-2.12 microns. The filtration efficiency of N95 masks for particles of this size exceeds 99%; Surgical masks are also over 80%, so they can all be used for virus protection.
There are actually two national standards for medical masks, namely medical surgery YY0469-2011 and medical nursing YY0969-2013. These are generally stated in the package. The filtering effect of medical nursing masks is relatively poor, but for those who are not in severely affected areas , For us who are not often in hospitals or densely populated places, it is also sufficient.
N95 masks also have two national standards: medical N95 GB19083-2010, ordinary N95 GB2626-2006 one is for medical use, and the other is for anti-haze. Medical N95 masks have a hydrophobic layer on the outer side, which is completely unnecessary for our daily protection, so please leave this standard mask to those who need it.
In addition, sponge masks, cotton masks, activated carbon masks. Because the filter layer has relatively large holes and has no electrostatic effect, their filtration efficiency for droplet nuclei is below 10% and does not play a protective role.
We must first understand the working principle of mask filtering. Whether it is an N95 mask or a medical surgical mask, the main function is the middle layer of meltblown cloth. This layer of material is composed of polypropylene fibers with a diameter of 0.5-1 microns. The difference between N95 masks and surgical masks is that the quality of this layer of materials is different.
When the area of the mask is about the same, the mass of meltblown cloth used for N95 masks is about 40-50 grams, which is relatively thicker, while the meltblown cloth used for medical surgical masks is about 20g, which is the thickness of this layer of material. The difference causes the difference in their filtration efficiency.
These polypropylene fibers are interlaced with each other, using physical barriers for large particles, while for particles with diameters smaller than pores, it uses electrostatic adsorption. At present, officials have confirmed that 75% alcohol, ultraviolet light, and high temperature above 56 degrees. The new coronavirus can be effectively inactivated, and the above method is indeed effective if it is only disinfected. But when it comes to reusing masks, it is necessary to disinfect the mask without destroying the filtering effect; neither changing the size of the holes nor eliminating the static electricity effect.
Large particles rely on blocking the adsorption of small particles, and filtration is completely fine. Then the difficulty in filtering lies in particles with a diameter smaller than the pores and not easily affected by static electricity: 0.3um particles are the most difficult to filter. According to my country's standard regulations, 0.3 micron sodium chloride particles are used as the test index, and the filter effect of 95% is the N95 mask, and so on, there are N99, N90, N80 and so on. The general medical surgical mask has a filtering effect of about 60% for particles of this size.
Are there other options besides N95 and medical surgery? In addition, there are many KN95, KF94, FFP and other standards on the market. What does this mean?
N95 is in line with American standards, and KN95 is in line with Chinese standards. In fact, there is no difference from Chinese standards
KF94 is a Korean standard. It requires a filtering effect of more than 94% for 0.3 micron particles, so it can also be used for virus protection
FFP is a European standard. Among them, FFP2 means that the filtration effect for 0.3 micron particles is above 94%, FFP3 means 97%, and FFP1 means 80%
In addition, there are more complicated Japanese standards. Instead of directly giving you several models like other regions, it uses three letters plus a percentage number to represent the filtering efficiency of the mask, PFE BFE VFE%
PEF (Particle Filtration Efficiency) 0.1 um particulate matter
BFE (Bacteria Filtration Efficiency) 3um particles
VFE (Virus Filtration Efficiency) 0.1-5um particulate matter
N95 mask machine