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This article comes from Pacific Internet

Author: Truth Lab

Masks are still in short supply recently, and netizens with strong hands-on ability have immediately developed a bunch of methods to “reuse masks”, including spraying alcohol, steaming, oven baking, microwave ovens, etc. There are also many netizens who leave messages asking for real monarchs , these “cooking” methods are not reliable.

To this end, Qiuzhenjun immediately collected a large amount of literature, consulted relevant experts, and summarized a set of tutorials on the reuse of masks for everyone. Before starting a long discussion, directly to the conclusion:

Possible disinfection methods

1. Baking method, set the oven to 70℃, put the mask in and bake for 1 hour.

2. Ultraviolet disinfection method, put the mask into the ultraviolet disinfection cabinet, and the sterilization time is 30 minutes to 1 hour.

Infeasible disinfection method

1. The high temperature and high pressure (pressure cooker) method will cause the mask to deform and destroy the air tightness of the mask.

2. The 75% alcohol (medical alcohol) method destroys the charged state of the filter material of the mask and affects the filtering performance of the mask.

3. Microwave oven method, the nose clip of the mask is made of metal and cannot be placed in a microwave oven.

Disinfection methods need to be situation-specific

Cooking method, when baking and ultraviolet disinfection methods cannot be used, N95 masks can be considered for this method. Cook in boiling water for 30 minutes, and then use it after drying. This method is not recommended for ordinary medical masks.

special reminder

1. Disinfection and reuse of masks is an insufferable move under the shortage of materials. N95 masks may be used multiple times, but in principle, disposable medical masks are not recommended for reuse.

2. After disinfection by the above method, if you find that the nose clip of the mask is not tight, or the air tightness of the mask is not as good as before, please stop using it immediately!

3. The disinfection method is only suitable for low-risk groups: not in Hubei, not medical staff and not entering the hospital, not contacting patients.

4. It is not recommended to use the disinfection method when entering and exiting closed places with dense people. The masks should be discarded directly after they are used up.

Back to the topic, are the various methods of mask disinfection reliable on the Internet? Qiuzhenjun really found a good piece of information, and I will share it with you here.

But before sharing, Mr. Qiuzhen thinks it is necessary to share with you why masks need to be replaced regularly.

Why do masks need to be changed regularly?

First of all, let’s start with the principle. Whether it is a medical mask or an N95-level dust mask, the filtering principle is to remove the particulate matter (including dust, bacteria) in the inhaled air through the barrier layer (made of polypropylene meltblown fibers) of the mask interlayer. , virus, etc.) to intercept and adsorb to prevent users from inhaling harmful particles.

In addition to fiber interception, electret treatment is generally performed on the barrier layer of the mask, so that the barrier layer is slightly charged, actively adsorbing particles, and enhancing the filtering effect.

▲This layer of polypropylene meltblown fiber is enlarged like this ▲This layer of polypropylene meltblown fiber is enlarged like this

The barrier layer of the mask is equivalent to a large net. Therefore, even if the sanitation of the mask is not considered, if the mesh of this large net is blocked by various particles and the mesh is filled to a certain limit, there is not enough air to come in. When we wear it, it will naturally feel difficult to breathe, and this mask will naturally not work.

Moreover, warm and humid masks are also a good environment for bacteria to breed. Considering that the masks are soiled by saliva and snot, deformed and damaged after long-term use and affect the air tightness, in principle, masks cannot be used for a long time.

The only difference is that ordinary medical masks have a short lifespan (about 4 hours), while N95 masks have a long lifespan (about 8 hours).

However, for low-risk personnel (non-medical staff, not in contact with patients, not in Hubei), Zhang Liubo, chief expert and researcher of disinfection at the Chinese Center for Disease Control and Prevention, suggested that during the period of mask shortage, if the masks are not stained, they can be reused after natural drying. Not washable.

The National Institute for Occupational Safety and Health (NIOSH) also mentioned that N95 masks can be worn up to 5 times when they are fully functional and not soiled. And some studies have shown that the filtration efficiency of N95 masks after 5 days of use is still 80%.

▲Strictly speaking, only N95 and above can be reused. ▲Strictly speaking, only N95 and above can be reused.

But now it is a very difficult time, and it is estimated that everyone will not be relieved if it is not disinfected… Based on a research data, Mr. Qiuzhen will analyze the feasibility of the folk disinfection method with everyone.

Research background on mask reuse

When SARS broke out in 2003, masks also became a scarce substance for a time. After the SARS epidemic ended, the Institute of Labor Safety and Health of the Labor Committee of the Taiwan Executive Yuan (hereinafter referred to as the Institute) conducted a study on “sterilization and reuse of disposable masks.” Feasibility Study”.

The purpose of the research is very simple, to see if the masks can still maintain a qualified working state after various sterilization methods for our use.

The institute purchased 6 masks for testing, of which 2 are Australian standard P2 level masks and 4 are American standard N95 (national standard KN95) level masks.

Although there were no disposable medical surgical masks in the study, because the protective principle of the masks is the same, they are all intercepted by the barrier layer made of polypropylene meltblown microfiber material, so the test results are still the same for general medical surgical masks. Very informative.

What were the results of the research test?

The institute’s test is mainly divided into two parts, 1 is to explore whether different sterilization methods can effectively kill germs, and 2 is to determine whether the filtering ability of the mask has an effect after an effective sterilization method.

Let’s start with Part 1:

The research institute took Escherichia coli as a simulated germ, and attached the germ to the test mask through an atomizer, and then used five common sterilization methods: dry heat, moist heat, high temperature and high pressure, ultraviolet light and 75% alcohol. Can the Escherichia coli on the mask be eliminated?

Finally, it was found that only the following conditions are required, and the five methods can effectively kill Escherichia coli.

Among them, the sterilization methods of moist heat cooking and alcohol spraying need to be used after the mask is completely dry, otherwise the condensation of water vapor on the mask will increase the air resistance, and at the same time, the filtering efficiency of the mask will be significantly reduced.

Next, the sterilized masks can be tested for filtration efficiency in Part 2:

The institute tested the filtration efficiency of 6 masks (5 samples each, and the data in the table below is the average of the test data of the 5 samples) before and after sterilization in 5 ways, including moist heat treatment (cooking), high temperature and high pressure and These three disinfection methods of alcohol treatment all have a certain impact on the filtration efficiency of some masks, and high temperature and high pressure can even seriously deform the masks.

Dry heat (baking): basically has little effect on the filtering performance of the mask.

Damp heat (cooking): The filtration efficiency of one sample in the No. 5 mask dropped to a level below 95%, and the No. 6 mask also had a significant performance decline.

▲The data marked in red indicates that the filtration efficiency of the mask samples in the repeated test is lower than 95% (the initial filtration efficiency of N95 masks is ≥95%) The initial filtration efficiency of the mask is ≥95%)

Regarding the cooking method, there are rumors on the Internet that the polypropylene fibers of the mask barrier layer will greatly affect the filtration efficiency when exposed to water. Is this true? If the mask is not completely dry, it does have an impact. But if the mask dries out, there is no such concern.

Because the moisture regain of polypropylene fiber is only between 0.01% and 0.1%, it hardly absorbs water, and there is no problem in drying it, and it will not affect the charged state of the barrier layer.

High temperature and high pressure (pressure cooker): a relatively less popular method, and the test results are not ideal, some masks are “stewed” to the point of deformation…

▲The data marked in red indicates that the filtration efficiency of the mask samples in the repeated test is lower than 95% (the initial filtration efficiency of N95 masks is ≥95%) The initial filtration efficiency of the mask is ≥95%)

Ultraviolet rays (ultraviolet disinfection cabinet): This method is possible. The research uses a biological disinfection cabinet, which kills E. coli in 30 seconds. Our home ultraviolet disinfection cabinet can be appropriately extended to half an hour to an hour.

75% alcohol (medical alcohol): the worst disinfection method, the filtration efficiency of masks 1, 2, 5, and 6 has dropped significantly.

▲The data marked in red indicates that the filtration efficiency of the mask samples in the repeated test is lower than 95% (the initial filtration efficiency of N95 masks is ≥95%) The initial filtration efficiency of the mask is ≥95%)

The problem with this method is that alcohol will melt the surface of part of the filter material of the mask, thereby reducing the escape energy of the ions implanted during the manufacturing process and affecting the filtration efficiency.

Moreover, the operation of using medical alcohol to sterilize the bottom is not easy. It needs to be sprayed evenly inside and outside. Moreover, there is a waterproof layer on the outside of the medical mask, which will block the penetration of alcohol. The operation of ordinary people may not completely kill the bacteria adsorbed on the barrier layer of the mask. Viruses, the secondary use of such masks is also very risky.

Relatively speaking, dry heat (baking) and ultraviolet methods have less impact on masks.

Except that high temperature and high pressure will deform the mask, masks can generally maintain a filtration efficiency of more than 90% after disinfection by other methods. Only some masks have a filter efficiency of less than 90% after alcohol disinfection.

Some friends may think that this only reduces the filtration efficiency by a few percent? There are still more than 80%, 90%, what are you afraid of?

But please note that the test uses a brand new mask, just spraying a quantitative amount of Escherichia coli, but in reality, the mask will absorb various dust particles, bacteria and viruses, and the filtration efficiency will continue to decline during use, and the situation after disinfection is definitely not. Ideal for experimentation.

To sum up, among the 5 sterilization methods for the secondary use of N95 masks, 2 are desirable, namely dry heat and ultraviolet rays, and the filtration performance of masks after disinfection is basically unaffected.

Therefore, in the period of shortage of masks, if there is an oven or ultraviolet disinfection cabinet at home, it can be disinfected according to the conditions (the new coronavirus is inactivated at a high temperature of 60 degrees Celsius for 40 minutes, and it is also afraid of ultraviolet rays):

1. Set the oven to 70℃, put the N95 mask in and bake for 1 hour.

2. Put the N95 mask into the UV disinfection cabinet, and the sterilization time is 30 minutes to 1 hour.

If there is no oven and no UV disinfection cabinet, according to the experimental results, steam the N95 mask in water for 15 to 30 minutes, and then continue to use it after it is completely dried. However, it was also mentioned above that the filtration efficiency of one of the samples of No. 5 masks dropped to less than 95% after wet steaming, and at the same time, the service life would also decrease.

But watch out! ! ! One thing that the research institute did not test is the air tightness of the mask after disinfection, especially after disinfection and drying under high temperature and high humidity conditions! ! !

If you find that you use the above methods to disinfect and completely dry before wearing it, and find that the nose clip of the mask is not working, or it is obvious that the fit and air tightness of the mask is not good, please stop using it immediately! ! !

Can ordinary medical masks do this?

Yes, the institute’s test is only for N95 masks. Can the above feasible disinfection methods be used for medical surgical masks and ordinary medical masks?

Under normal circumstances, ordinary medical masks are not recommended to be reused at all. Now, in special circumstances, Qiuzhenjun recommends referring to the test of the research institute. Two disinfection methods, dry baking and ultraviolet light, can be used, but wet steaming is not recommended.

1. Set the oven to 70℃, put the medical mask in and bake for 1 hour.

2. Put the medical mask into the ultraviolet disinfection cabinet, and the sterilization time is 30 minutes to 1 hour.

Because it can be seen from the data that the wet steaming method has an impact on the filtration effect of the mask, while the filtration efficiency of medical surgical masks for particles with a particle size of 0.03 μm is only 30% (N95 level is 95%), and the filtration efficiency drops again. Really can’t prevent anything.

Moreover, high-temperature cooking may also damage the water barrier layer and accelerate the failure of the mask barrier layer, so do not cook.

As for the alcohol method of Internet celebrities, the above research also mentioned that it will have a great impact on the filtering efficiency of masks. And only spraying alcohol inside and out does not guarantee that the alcohol will come into contact with the bacteria adsorbed in the barrier layer. If it cannot effectively kill the virus, it is meaningless to use it for a second time, so it is also not recommended.

Last but not least, if you find that the nose clip of the mask is not working after the disinfection operation, or the fit and air tightness of the mask is obviously not good, please stop using it immediately! ! !

　

▲If the airtightness of the mask is found to be damaged, it can no longer be used.

Then the research on the reuse of masks is over here, and I hope to give you some help. As mask manufacturers resume work one after another, the supply of masks will definitely catch up. If the supplies are sufficient, try not to reuse masks.