Get a deeper understanding of masks, and summarize them by principle

Update:29 May 2020

Many people's understanding of masks may only stay at t […]

Many people's understanding of masks may only stay at the level of knowing, and the in-depth understanding is almost insignificant.

Generally, the classification of masks is based on their use, such as decoration, cold protection, dustproof, etc. Here, we first propose a way to classify according to principles. You can't stop breathing at all times. If you don't breathe for half a minute, you will deeply understand the importance of breathing. Therefore, since breathing cannot be stopped, the role of adding a hood in front of the mouth and nose is clear at a glance .. The main purpose is to protect the mouth and nose from outgassing, that is, the main pollutants are inside the human body; Protection against inhalation, that is, the main pollutants (or stimuli) are outside the human body (in the surrounding environment). Of course, many masks can protect both the impact of harmful substances inside the human body on the outside world and the impact of pollutants on the human body in the environment, but for simplicity, they are temporarily divided into the above two categories.

First of all, first representatives: catering masks, protective masks for disease transmission, surgical masks

Second, the second category, inhalation protection, that is, the main pollutants (or stimuli) in the external environment. Most masks are produced to cope with various pollutants from the external environment.

At present, the hot is the dust mask (particulate protective mask). Therefore, all kinds of masks have come into the PM2.5 protection from the original industry, such as surgical masks, cold masks, anti-personal masks, and anti-virus masks (such as activated carbon masks). After five years, the eyes of the masses are getting brighter and brighter, so more and more people know which masks have a good protection effect on PM2.5.

PM2.5 masks can also be divided into two categories in principle:

First, rely on psychological protection to protect PM2.5 masks (basically no protective effect).

2. Masks that may have a great protective effect.

There are mainly the above two, and their common characteristics are the following two:

1. It may fit closely with the face;

2. The filter material that can filter PM2.5 is used.

Here I have to say that PM2.5, why need a mask to protect PM2.5, is simply because the body's own mechanism for defending particulate matter, nose hair, nasal cavity, respiratory tract, etc., can only protect large particles. For example, a large part of particles with a particle size exceeding 10 microns can be absorbed by the nose hair.

Now that you understand the characteristics of each particle size, why not protect PM2.5 is not a problem, the lungs are different from the stomach, the stomach can digest food, and then excreted through the body, the lung does not have this function, so, if you want the lungs If you are comfortable, you have to add less to it (the same is true for people).

There is no doubt that PM2.5 enters the human body and fails to block it. So when wearing a mask, if the mask and face do not fit well, how much PM2.5 can be filtered by a few hairs? Therefore, masks mainly for the purpose of exhalation protection basically have a large gap with the face, let them do inhalation protection PM2.5, simply do not wake up (dreaming).

The above is basically a description .. a problem-1, may be closely attached to the face;

Next is the second question, PM2.5 material can be filtered. Because PM2.5 is small, it cannot be expected to be filtered with fishing nets. The materials that can filter PM2.5 are basically materials with very small pore diameters. At present, the mainstream filter materials used in air purifiers are glass fiber filters and polypropylene melt-blown cloth. The mask can only use polypropylene meltblown cloth, the reason is very simple, the air purifier can use the fan to drive the air flow, but you can only breathe with the lungs. Because the glass fiber filter particles are purely a word-touch, and the polypropylene melt-blown cloth can rely on another secret-electrostatic adsorption, so the resistance of the glass fiber filter is very large, and the static melt-blown cloth resistance It can be very small. Look at the principle of fiber filtration PM2.5:

It is precisely because of the lack of electrostatic adsorption (for simple understanding, you can think of the electric field as a magnetic field and the particles as a magnet), so that the glass fiber filter lacks an effective filtering method.

Polypropylene, because of its low melting point, can be softened by more than 800 degrees of glass fiber. As long as polypropylene is more than 100 degrees, since the melting point is low, it is often very soft at room temperature. The better the static effect, this is the truth.

The composition of common masks: the middle layer is called the meltblown cloth, and both the inner and outer layers are spunbond cloth. Regarding spunbond cloth, it is also made of polypropylene. Its main function is to shape and protect the meltblown cloth in the middle. You have to say that it can filter PM50 or larger particles.

There is no doubt that the filter performance of PM2.5 is the middle melt-blown cloth. The filter materials used in current masks are basically all melt-blown cloth. What kind of PM2.5 protection effect can a mask with the above two basic points wear on your face? In theory, a mask with a nominal rating of KN90, if you wear a completely sealed, that is, if there is no air leakage anywhere on the edge of the mask, the protection against particulate matter will be higher than 90%. A mask with a nominal KN95 will be higher than 95% when you wear a completely sealed mask. However, because it is impossible to completely seal, the final result is that the KN90 mask is qualified when the particle protection is higher than 90%, and the KN95 mask is qualified when it is higher than 92%.

KN90 refers to the level where the filtration efficiency of sodium chloride particulate matter is greater than or equal to 90%, and KN95 is the level that is greater than or equal to 95%. Pay attention to one word, filtration efficiency, what is filtration efficiency?

filter efficiency is the percentage of particulate matter removed by the filter element under fixed detection conditions

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