口罩能保护人们远离冠状病毒吗？

作者
Can homemade DIY and surgical masks protect against the coronavirus

随着2020年初，冠状病毒在中国的爆发，数百万人不得不在一夜之间成为口罩专家。

但是，口罩种类很多，哪些口罩可以保护我们免受病毒感染？口罩能过滤冠状病毒吗？我们需要使用N95口罩来保护自己免受冠状病毒等病毒的感染吗？

Quora上有这样一个问题：口罩能避免我们感染上冠状病毒吗？

戴口罩可以避免人们感染冠状病毒吗 

幸运的是，科学家已经积累了能够回答这些问题的可靠数据。

冠状病毒颗粒有多大?

 

冠状病毒的病毒粒子（或“颗粒”）是直径约125纳米（0.125微米）的球形颗粒。最小的颗粒是0.06微米，最大的是0.14微米。

冠状病毒病毒颗粒多大

 

这意味着冠状病毒颗粒比PM2.5颗粒小，但比一些灰尘颗粒和气体大。

 与其他污染类型相比，冠状病毒的颗粒大小

 

现在我们知道冠状病毒颗粒有多大了，口罩能过滤掉这些颗粒吗？

让我们把这个问题分解成两个更简单的问题。

  

1.防空气污染的口罩能捕捉到冠状病毒颗粒吗？

怀疑派说：

冠状病毒(以及其他病毒)非常微小——比人类头发的直径小500倍。

况且，“口罩那么薄，他们怎么可能阻挡得了那些微小的冠状病毒颗粒呢？”

但是

科学的测试告诉我们：

爱丁堡大学的研究人员测试了不同种类的常用口罩。他们用了柴油发电机来模拟汽车排气装置，向不同口罩排放废气，然后用一个粒子计数器测出有多少颗粒穿透了口罩。

测试口罩是否可以过滤冠状病毒颗粒

一个重要的细节：他们使用的粒子计数器能够测量到0.007微米的颗粒。所以我们现在讨论的真的是微小颗粒！

他们测试了一系列口罩，他们的发现：

戴口罩可以过滤冠状病毒颗粒

3M的口罩能够捕捉到95%以上的微粒，而微粒的厚度只有0.007微米，这比冠状病毒小十倍。

有些人可能会感到惊讶的是，外科口罩也能够捕捉到80%的微小颗粒。

口罩的测试告诉我们：口罩（包括外科医用口罩和N95口罩）可以捕获比冠状病毒小10倍以上的微小颗粒。

即使是非常微小的颗粒，口罩也能过滤掉。

好，那我们继续进入下一个问题。

2. “好吧，口罩可以捕捉比冠状病毒更小的微粒，但如果空气从口罩边缘溜进去呢？”

怀疑派说：

“理论上口罩是管用的，但是这些测试不是在真人脸上做的。所以，当你戴的口罩不能和你的脸完美贴合时，它们还是没用。”

科学的测试告诉我们：

这个问题更难回答，因为你必须在真的戴着口罩的时候测试效果，而且，想要做的这一点，你需要一个非常昂贵的密封性测试仪器。

幸运的是，我们的确在这样一个昂贵且可靠的机器上做了很多关于口罩的测试。

口罩密封性测试 Smart Air聪明空气实验

蓝色的管子采集口罩外的空气，白色的管子从口罩内采集空气（密封测试细节）。

Smart Air 聪明空气的创始人Anna，和生活在北京的Dr. Richard Saint Cyr也做了口罩密封测试，所以我把我们三人的数据整理了一下。

这是不同口罩在我们脸上的密封效果：

不同口罩的密封效果

点击可查看完整的测试数据

一些3M口罩甚至能捕捉到超过99%的0.01微米微粒(比冠状病毒小10倍)。更重要的是，外科手术的口罩也特别有效，捕获了63%的微小病毒大小的颗粒。

阅读更多:戴口罩可以保护身体健康

最后，回到现在大家最关心的话题上：

口罩能保护我们远离2020新型冠状病毒吗?

看完文章，大家一定发现了，口罩可以过滤掉哪怕是最小的颗粒——比病毒小10倍的颗粒。更重要的是，我们也测试了佩戴上口罩后的实际效果，是非常好的。

另外一个大家都很关心的，就是医用的便宜口罩到底有没有用。不用担心，它们在过滤病毒大小的颗粒时，效果也是非常棒！

Smart Air会携科学数据，与你一起度过这些日子。

 

关注我们微信公众号SmartAir2013

你知道这些吗？

雾霾天，戴口罩真的有用吗？
pitta masks protect us from coronavirus日本Pitta口罩能阻挡冠状病毒吗?
Can DIY masks filter out viruses and coronavirus自制口罩能预防冠状病毒吗？
Do portable air purifiers work?穿戴式空气净化器有用吗？

《口罩能保护人们远离冠状病毒吗？》有94条评论

  1. I was a Combat Medic/ Surgery Tech., Big Pharma Rep. plus pharmacy school.The reason we wore sugical masks was to prevent respiratory dropplets [ flugge ]from contaminating a sterile field [ the operating theatre surrounding the area site to be debrided/ disected]. We knew bacteria and viruses would transfer through our masks bu, t thay were effective when inadvertently coughing into said field.Look around you..most people are wearing surgical style masks which are 63 percent or less effective according to the smart study. Add to that, most masks do not fit tightly and many wear them with nostils exposed ! We go to a restaurant and take off the mask to eat…thereby ..completely contaminating the “sterile field ” around us !..when this is done in close contact , such as in commercial airlines…we have destroyed any practical reason to wear them at all ! We learned in bio hazard warfare training that the only practical way to prevent exxposture to a dangerous bio agent or weapon was to use a hazmat suit with separate o2 supply. Masks, as chosen and worn today, give us a very false feeling of security and in reality, we are looking more at a herd immunity scenario such as we have seen for many years with flu virus variants.

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  2. What about these masks that are made from thin linen cloths? Are they safe to be used?

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  3. Hi
    I find this very interesting. I think you should also consider the fact that the virus is transmited mostly throughout the Flugge droplets, which are droplets produced by humans by coughing or sneezing, wich measure to 0.5 mcm to 10 mcm.

    – Epidemiology of Respiratory Infections. https://link.springer.com/chapter/10.1007/978-3-030-26961-6_28
    – Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and coronavirus disease-2019 (COVID-19): The epidemic and the challenges. https://www.sciencedirect.com/science/article/pii/S0924857920300674

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  4. I am a old army medic, now a retired RN. Want to help others and thinking out of the box by making DIY face masks for shelters that have no supplies. Putting a mask on persons with symptoms. Will layers from hippa furnace filters be useful material to capture virus? Any other ideas?

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    • Hi Richard, I’m really glad to read all those comments offering DIY masks for your local hospitals! We are working on more tests in the following week and will publish the results as soon as possible! Stay tuned!

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    • Have you even read your own reference? It says right there in the summary “Further studies … are required to better define the effectiveness of face masks …” This is one of those further studies. What is the problem?

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  6. Please,
    I am writing a PhD thesis in Engineering and I need scientific references on the interception of particles smaller than 0.3μm in the N95 filter mesh.
    You can provide me with references of scientific articles.
    I would be very grateful
    [email protected]

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    • I see in this article, they stated the N95 mask protects down to .3 microns..this is not right..it’s actually 3 microns..which is much bigger than .3..this whole article was based on a false narrative..being the C-19 virus is .1 micron or less,regardless of the Fact Checkers..research it yourself, and any opening around mask clearly compromises its ability to filter any particles of any size..full face respirator is truly the only way to stop a .1 particle..OTHERWISE people who remove asbestos could just wear a N95 mask RIGHT..

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        • Hi John, a link to the scientific study performed by researchers at Edinburgh university can be found in the article. I’ve copied the link here, for your reference: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2662779/

          It explains how these masks can capture particles as small as 0.007 microns.

          You’re right that 3M don’t say this on their website, and they wouldn’t. It’s because the masks (N95 in this case) are only certified to filter 95% of 0.3 micron particles. However, that doesn’t mean the masks don’t do better at filtering smaller particles. Just that the masks haven’t been tested or certified to do that.

          In short: masks do an incredible job of filtering even smaller particles, but the N95 standard only tests 0.3 microns.

  7. I’m curious what happens when you use a mask like this many times? It’s impossible to buy a stack for several months.

    Does the filtering capacity stay the same? Is it ok as long as you wash your hands after touching the mask? And what about indirect contact? For example you touch the mask, then touch your head, arm, clothes whatever. You wash your hands, but then touch the same spot again, then touch your eyes/nose/mouth/optional vagina. What then? (and yes I realize this is probably way out of your area of knowledge).

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  8. Can I spray alcohol on both layers of a surgical mask to disinfect it after using it?

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    • Hi David, I only know that alcohol contained gel rub can help and wouldn’t do much to the mask efficiency. We will have an article posted soon regarding how to clean the mask, so stay tuned for more information!

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  9. Hi,
    i’m writting from Greece.
    The only mask type i can find here is a PM 2.5.(washable, reusable).
    Is it ok (safe) to use it for covid-19?

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  10. Paddy, very interesting! If this is the case, then why are health officials in Canada (and I presume elsewhere) telling the public that masks don’t work to prevent infection from COVID-19?

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    • Great question Robert, we saw the US Surgeon general saying the same thing in the US:

      US Surgeon general masks do not work

      I believe the key point here is that they’re trying to reduce panic buying to make sure enough masks are available for medical staff. Although, there are valid points that the virus is unlikely to travel >2 meters, so wearing masks outside in public places (not in crowded places) may well not be necessary.

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    • Because they know there are not enough masks for people. Same in Australia. They tell us not to wear masks because they know they don’t have enough for everyone, while China has shown that masks are needed to reduce infections. If it is true that masks don’t protect from the virus, then why do all the doctors need to wear them when they are treating infected people..

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  11. Does it really matter how effective a mask of any type is when Coronavirus can live on skin and surfaces for hours if not days. The efficacy of any disposable mask will deteriorate and ANY mask will be removed for eating and other necessary daily functions !

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    • You’re spot on Deborah. It’s quite likely that the main mode of transmission of viruses isn’t through the air, but through fomites (carrier objects) and the touching of face/mouth. Researchers who found that surgical masks are just as effective at preventing transmission of viruses as N95 masks (which seal much better on the face) were stumped as to why. The only suggestion they could come up with was that the mask reduced hand to face/mouth touching.

      Viruses generally survive on cloth-like materials for a few hours, so leaving your mask to dry overnight can be an effective way of killing any viruses on it. However you’re right that viruses can last much longer on other surfaces (e.g. stainless steel). Check out the data:

      Viability of viruses on different surgaces

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  12. Hi..great article..
    I’m writing from Milan..as you probably know we’re all lockdown here..the only mask I managed to find is a Ffp1 3M 9914…you think it can help against the virus? I m allowed to get out to get some food..

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  13. Excellent article! When I wanted to obtain information on the comparison of different masks, I didn’t expect such a through article. Thank you.

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  14. Something is not clear. When you say, “80% of particles were filtered”, it does not necessarily mean that 80% of virus-sized particles are filtered.

    It could be that 100% of larger particles are captured, but 0% of virus-sized particles… in total, “80% of all particles are filtered” but none of the virus-sized ones.

    Can you clarify?

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    • Spot on Kevin, those are sharp eyes you have! In theory, that’d be possible. However, if we look at the make-up of air pollution, then we find that the majority of smaller (PM2.5) particles (by weight) are in the range of 0.1 – 0.3 microns. What you say is certainly possible in a theoretical scenario, and we can’t rule it out. But that’s fairly unlikely, especially as the source of pollution was a diesel generator which can be considered a fairly typical source (diesel engine) for pollution.

      Particle size distribution

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  15. Thanks for your article. Please consider that: fine particles ( between 0.1- 0.3 micro meters) are the hardest to capture. They are harder to capture than even ultra fine particles ( below 0.1 micro meters).
    Usually all mechanical filters have the lowest efficiency at this particle size range.

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  16. Thanks for sharing this. While masks can no doubt cut the risk of infection, viruses can make their way into the human body thru eyes and ears as well. So, while masks maybe preventing us from breathing them in, I doubt it will make much difference in the end, particularly since rubbing a hand that touched a contaminated area on the face is one of the more common ways to get infected. I guess using them as part of a more holistic strategy would make more sense…

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  17. I got a PM2.5 rated gas mask, with sealed silicone around the face. Do you think it might still work well?

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  19. Hi

    How should you use and treat the mask between usage? When you put it on and off and how you should store it?

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  21. Hi,
    thanks for the article and a great job done in Edinburgh. I am still confused when it comes to codes and standards of different masks offered on internet.
    Is the standard EN 149:2001+A1:2009 automatically determining a specific type like: N95, 3M, FFP1 or FFP2?
    Can one masc, certified as EN 149:2001+A1:2009, be classified as FFP1 and another, with same certificate, as FFP2?
    How does EN 149:2001+A1:2009 refer to codes N95 and 3M?
    Sorry if I missed the answer in your article or in comments.

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    • Hey Greg, you’re absolutely right! The array of acronyms, numbers and standards really can be confusing. Let me try and summarise your questions below:

      N95, N99, FFP1, FFP2 and FFP3 are classifications or ratings of masks. The rating covers (most importantly for us) the filtration level, among other things. You can think of them like G, PG, PG-13, R etc. – the ratings for movies. The movie ratings cover who can watch them.

      EN 149:2001+A1:2009 are standards for masks. They specify the rules and testing methods companies should follow to rate their masks. These standards define the N95, FFP1, FFP2 etc. ratings above. Using the movie rating analogy, you can think of it like this: the people reviewing movies and choosing the appropriate movie rating must have a set of rules to decide if the movie is considered PG-13, R etc. They’ll follow these rules to rate the movie. These standards are the set of rules for masks.

      3M: This is the name of a company that makes masks (among other things). In many parts of the world, they have become synonymous with masks, however it’s still most important to look at the mask rating. You can of course find good quality masks from other brands and companies that are still N95 or FFP1 rated.

      You can learn more about the different ratings here

      Hope this clears it up for you!

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  22. Great article! So if i’m understanding correctly, a cotton mask with a PM2.5 insert will still be efffective against coronavirus, even though it is significantly smaller in size? What % would it be?

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    • If you’re using a PM2.5 insert in your mask, then it will be able to filter out the smaller 0.1 micron coronavirus particles – yes! In fact, PM2.5-type filters (e.g. those certified to N95, N99, FFP2, FFP3) do a really good job of filtering out the small 0.1 micron particles.

      Your cotton mask may well have leakage round the edge, since it’s unlikely to have a good seal, but new data we have just published shows that surgical masks – which also have a poor seal – were just as effective as N95 masks at preventing viruses like the coronavirus.

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      • Thank you! Are non-certified filters effective? For example, those sold on Amazon do not state any sort of certification.

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        • It’s very difficult to say. Since the coronavirus outbreak, hundreds of ‘opportunist’ companies have cropped up trying to sell facemasks. I would recommend you stick to certified masks, or to materials for which there’s open-data showing they work. Good luck, R L!

  23. Thanks for the article, it’s most helpful. I do have a question though. Those masks stating effective PM2.5 – does that mean the smallest virus it can catch is 2.5microns and hence they are not effective in clearing coronavirus which is 0.1microns in size?

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    • Hi Carol. The data above shows that these masks – including the PM2.5 masks – can capture particles as small as 0.007 microns. That’s means they are also effective at clearing the coronavirus at 0.1 microns!

      I’ve updated the post to clarify this point. Thanks!

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      • Thanks Paddy for your clarifications. I have further questions regarding effectiveness of other types of filter. I will send you an email at [email protected] and hopefully you will be able to help me. Thanks.

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  24. Hi, Thanks for this article.

    What do you think about N95 mask that is washable, mind you that the filter is not, so only the mask. Any idea how often we should change the filter? It is said to have 5 layers of protection

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  25. Thank you for this article! It’s very helpful!
    How long can you wear a surgical mask before you have to replace it?
    What if the mask is N95 and washable?
    Also do I have to replace the PM 2.5 filters to make it effective against corona?

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    • Hey Sariah, glad you found this post useful! We haven’t tested the lifespan of surgical masks ourselves, but we have tested N95 masks. They showed no reduction in effectiveness even after using them for 30 days! There is one report of scientists testing surgical masks after they’ve been worn for 3 hours, and they saw no reduction in effectiveness!

      As for washing N95 masks – we tested this, and found that washing N95 masks drastically reduces their effectiveness. We wouldn’t recommend this.

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      • Hi. Thanks for the information! My question is regards to disposable masks. My understanding is the particles get trapped in the material/layers. If so, would this make it dangerous to reuse as it would be unknown by the user if its contaminated?
        Also do you have any information re washable masks used for sports graded as filtering pm2.5? Are they effective against viruses and continue to be so after washing?

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        • Hi, Elaine, we are working on a new article about how to clean your mask. It will be posted this week, so stay tuned!

    • Hi Sariah,

      I am not an expert in masks myself but I was living in Hong Kong when SARS happened. Experts in Hong Kong recommended the use of a surgical mark to be no longer than 4-5 hours straight (but people commonly use one mask for a whole day due to shortage of supply). So if you have wore a mask for, let’s say a couple of hours, you could keep it clean and re-wear it if you want to save on the mask.

      To temporarily storing a used mask, some doctors suggest the following steps:

      1. Wash your hands with soap / clean with hand gel.
      2. Take off the mask by only touching the earloops.
      3. Without touching the surface of the inner and outer layers, put it into a clean paper envelop. If there is no envelop in hand, cover the top and bottom with two pieces of tissues and put it aside (e.g. on a clean surface, say on a table if you take off the mask for a drink or a meal).
      4. When ready to put the mask back on, wash your hand / clean with hand gel again.
      5. Take the mask out from the envelop and put it on by only touching the earloops.
      6. Dispose the envelop / tissues
      7. Use a new envelop / new pieces of tissues if you need to re-use the mask again.

      The most important thing is to avoid cross-contamination between the top and bottom surfaces of the mask 🙂

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  26. Your claim is misleading. The measuring capability of the device does not tell us if it measured particles of 0.007 micron. in that study.
    I read the article and could not find a single conclusion saying or somehow claiming “3M industrial filters were able to capture over 95% of particles down to 0.007 micron.”

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    • You’ve got really sharp eyes, Grifin! I understand how that point could be confusing. You’re right that the paper doesn’t specifically specify the researchers tested down to 0.007 microns. However the device they used for monitoring is the “condensation particle counter [CPC] model 3022, TSI Instruments, High Wycombe, UK”. Looking at the specifications, you’ll find that this device can measure down to 0.007µm (see Table B-1 in the manual here: https://epic.awi.de/27246/1/TSI1999a.pdf ).

      Effectiveness of masks to capture 0.007 micron particles

      Most scientists don’t quote ‘filtration effectiveness’, but use what’s called ‘penetrance’. That is the inverse of filtration effectiveness. We took Figure 2 from the scientists’ data, and simplified it for this blog post.

      Great to see you checking your sources and analysing the open-data. That’s exactly the spirit of Smart Air. Keep it up!

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  27. How often(hrs use) do I need to change the mask/cartridge filters for them to remain effective?

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  28. I have this “BROAD” air mask with me. The mask is connect with Filter (HEPA H-13) and battery air pump connect.
    Do this can help to protect from Corona Virus better than conventional air mask. It has the filtered air thru the mask and make a positive pressure in the mask to protect leak air to the nose.

    Ballang Sathorn

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    • Most probably – yes! If your mask is certified to capture PM2.5, then it will likely also be good for capturing the coronavirus. The data in this post explains how pollution and dust masks (for example, the 3M masks discussed in the Edinburgh study above) are able to capture particles as small as 0.007 microns – much smaller than the coronavirus.

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  31. Maybe this is a strange question, if I use 2 mask PM 2.5 is not probably that I get similar protection as an 1 Mask N95 3M ? Thank you for your time.

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    • Doubling up on the layers of masks is unlikely to give you much more protection, Manuel! I suggest you save the 2nd mask for when your first one becomes too dirty or old!

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  33. I’m confused when i search for refillable filter N95 I get results for PM2.5 filters… Is there a difference between N95 and PM2.5?

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    • Hey Gio! PM2.5 refers to very small particles that are 2.5µm in diameter or smaller (See this graphic in the post: covid-19 particle size of virus)

      N95 is a certification standard for masks. Think of it like a performance certificate for masks to verify that they can capture over 95% of tiny particles. The test covers particles 0.3µm in size, so 8 times smaller than PM2.5. That means that N95 masks can capture 95% of 0.3µm particles but definition, but as explained above they can also capture PM2.5 (particles 2.5µm in diameter) and also 0.1µm particles (those the same size as the Covid-19)

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  34. I am not sure about if anyone ask. Does p95 work? As I know, if I am right p95 is for industrial use and no layerfor blocking water, so some people say it does not work.

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    • We haven’t tested the 3M 7502, so can’t give you a definite answer. However it will depend on what 3M cartridges you have in the filter. I see that it’s compatible with 3M™ Cartridge 6000 Series; 3M™ Filters 2000, 2200, 7000 or 5000 Series; or 3M™ Dual Airline Systems. Most of these filters seem to be P95/N95 or P100/N100 rated, which means they’ll be able to capture 95% of 0.3µm particles. By the amazing phenomenon of Brownian motion, these masks therefore should be able to block 0.01 micron particles too!

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        • Any mask that is marked N95 will filter the same amount of particles. What’s then important to you is to find the mask that fits YOUR face best. Different people find different types of masks more comfortable, so if you have a mask you like, then I suggest you stick to it!

          One note on the 3M 8511 N95 mask – it has a valve, which is used when breathing out to release air and moisture out of the mask. This means this mask isn’t recommended for people who are sick to wear, since you will still be breathing out any viruses from your own mouth! The recommended masks for protecting both you (the wearer) and other people (from you) is a mask without a valve.

  36. the airborne virus is .1 microns while n95 protects up to .3 microns. how can it offer protection?

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  38. Sorry Still a bit lost here, so technically the effectiveness of those cotton Mask with PM 2.5 Filter are similar to surgical mask? or totally useless against viruses?

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    • Based on the research done at Edinburgh university, a cotton handkerchief can capture around 28% of tiny, virus-sized particles. That’s not amazing, but it’s certainly better than nothing.

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      • He asked about a cotton mask with a PM2.5 filter, not a cotton hankerchief. Could we get clarification on this?

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  39. But I suppose the virus usually doesn’t come alone, but rather with slime/water droplets from coughs or sneezes. How do the masks perform in that case?

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    • That’s correct Oskar! Viruses typically travel in larger ‘droplet’ form (50-100 microns), however these can dessicate quite quickly to become much smaller in a matter of seconds (as the moisture quickly evaporates). For droplets 50-100 microns, the masks will also be able to capture these. However this is where things can get a little bit complicated. If virus droplets do fall onto the mask, then there may be a higher risk of transmission of viruses due to touching the mask or placing the masks on various surfaces which will transfer the virus. It’s worth bearing this in mind when deciding how often to replace your mask, and also how to store it.

      One good resource to read about the transmission of viruses in the air (called Aerobiology) can be found here.

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