Particle Counting

1. How to make a filter for 166 RMB. 2. Tests showing that the DIY Cannon removes as much particulate as an IQ Air. 3. Live demonstration.

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What is a HEPA filter and how do HEPA filters work?

[:en]The term “HEPA filter” can be confusing. What does HEPA stand for? What is a HEPA filter made from, and what actually makes it a HEPA filter? We’ll cover all you need to know about HEPA filters in this article.

 

What Exactly is a HEPA Filter?

‘HEPA filter’ stands for ‘High-efficiency particulate air filter’. Sounds complicated. But HEPA filters are nothing fancy. They were invented back in the 1940s, and they’re just a mat of synthetic fibers used to capture particles. That’ similar to the material used in sports t-shirt.

What’s important about HEPA filters, is they’re really effective at capturing almost every size of particle. They can capture viruses, bacteria, pollen, PM2.5, allergens and more.

To see what the randomly mat of fibers look like, here’s a closeup of the HEPA filter Smart Air makes for The Sqair air purifier, and then alongside it a scanning electron microscope photo for a view at the nano-level.

What Makes an air Filter a HEPA Filter?

OK, so if HEPA filters were invented in the 1940s and they’re nothing fancy, then what makes any old filter a HEPA filter? Turns out using the term ‘HEPA’ has a strict set of requirements. HEPA filters must remove 99.95% (ISO/European Standard) or 99.97% (US Standard) of the most penetrating particle size (MPPS) – more on MPPS later.

Standard

Filtration Rate of MPPS

ISO / European (ISO29463 / EN 1822)

≥ 99.95%

US Standard (MIL-STD-282)

≥ 99.97%

 

When following the ISO or European rules, filters that capture ≥85% of particles but less than 99.95% are called ‘EPA filters’ or ‘efficient particulate air filter’. Filters that capture more than 99.999% of particles are called ‘ULPA filters’ or ‘ultra low penetration air filter’.

 

Designation

Filtration Rate

EPA (efficient particulate air filter)

85% - 99.95%

HEPA (high efficiency particulate air filter)

99.95% - 99.999%

ULPA (ultra low penetration air filter)

≥99.999%

 

How do HEPA Filters Work? 

The answer to this question is one of the most fascinating things about HEPA filters. Most of us might start out thinking HEPA filters work like a net, like this.

If a particle is smaller than the holes in the net, it gets through. Makes sense!

Direct Impact & Straining:

That intuition is true for big particles typically larger than 1 microns. When large particles fly into a HEPA filter, they’re too big to get through, so they get stuck. When particles hit directly into a HEPA fiber, that's called ‘direct impact’. When particles get stuck between two fibers, that's called 'straining'.

Interception:

For smaller particles that can fit between the ‘gaps’, they’ll try to follow the air around a HEPA filter fiber, but they’re not as light and nimble as air, so they might still get stuck. This method of capturing particles is called ‘interception’, and works well for medium sized particles (0.3 – 1.0 micron particles).

Diffusion:

For the really small particles, (less than 0.3 microns) it’s reasonable to think HEPA filters can’t capture them. But these particles that small have so little mass that they actually get bounced around like a pinball when they hit gas molecules (that’s called Brownian Motion). So they move in random zigzag patterns.

These particles are so small they could easily fit through HEPA filters. But sadly for their freedom, they don’t fly in straight lines. Because they fly in zigzag patterns, they end up hitting the fibers and getting stuck. That process is called diffusion.

Here’s how all three capture mechanics work:

And here’s how the three different mechanics work for different particles sizes. Impact captures large particles, interception captures medium particles, and diffusion captures the smallest particles.

What’s the Most Penetrating Particle Size (MPPS)?

Notice that dip in the last graph? That’s because diffusion works really well under about 0.3 microns. Straining and other mechanics that are more intuitive work really well above 0.3 microns.

Where those two mechanics intersect is the hardest particle size to capture. That’s because it’s not quite so small for diffusion to work its full strength, and it’s not quite large enough for straining to work its full strength. Call it the ‘weak spot’ of a HEPA filter. This ‘dip’ in the graph is called the most penetrating particle size (MPPS).

The dip in the graph most commonly occurs around the 0.3 microns mark, which is why people mention 0.3 microns all the time.

 

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What's The Difference Between N95 and KF94 Masks?

The difference between N95 and KF94 masks are minor for the factors that most users care about. KF94 is the “Korea filter” standard similar to the US N95 mask rating.

Difference Between N95 and KF94 Masks: Charted Out

They look similar, and they filter a nearly identical percentage of particles—95% versus 94%. This chart from 3M explains the differences between the N95 and “first class” Korean masks. The columns highlight these two types of mask.

On the metric that most people care about (filtration effectiveness), they’re nearly identical. In most circumstances, mask users will not care about a 1% difference in filtration.

KF94 Standards Borrow More From Europe Than US

However, of the differences between the standards, the Korean standards are more similar to the EU standards than the US standards. For example, US certification agencies test filtering performance using salt particles, whereas European and Korean standards test against salt and paraffin oil.

Similarly, the US tests filtration at a flow rate of 85 liters per minute, whereas the EU and Korea test against a flow rate of 95 liters per minute. However, these differences are minor.

Other Differences Between Mask Ratings

Besides the 1% difference in filtration, there are some small differences on other factors.

For example, the standards require N95 masks to be somewhat easier to breathe out of (“exhalation resistance”).

Korean masks are required to test for “CO2 clearance,” which prevents CO2 from building up inside the mask. In contrast, N95 masks don’t have this requirement.

However, concerns about CO2 buildup may be overblown. For example, one study found that, even during moderate exercise, women wearing N95 masks had no difference in blood oxygen levels.

To get the mask label certified, Korea requires human fit-tests, like the one I’m doing below. The US N95 certification does not require a fit test.

However, that doesn’t mean people shouldn’t do fit tests with N95 masks. The US agency that regulates workplace safety (OSHA) require workers in certain industries to get fit-tested once a year. It’s just that fit tests aren’t required for the manufacturer to get the N95 label.

N95 vs. KF94 Masks: Bottom Line

On the factor that most people care about (filtration) N95 and KF94 masks are nearly identical. However, there are small differences in other factors, such as breathing resistance and fit-testing.

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What Are N95 Masks Made From?

N95 masks made from synthetic plastic fibers are most common. These plastic fibers are similar to the fibers in synthetic and polyester shirts many people wear.

N95 Masks Made From Synthetic Plastic

For example, let’s take the 3M 9332 masks that I wear in Beijing. Technically this is an N99 (FFP3) mask, but the idea is the same.

    According to 3M, the filter material in the 9332 mask is made out of polypropylene fiber.

    N95 Masks Made From This Raw Material

Polypropylene in the filter medium is a plastic. That plastic is made from fossil fuels like oil.

  That means these masks are made from fibers similar to the ones in our clothes, like quick-dry shirts, rain jackets, yoga pants, or any stretchy fabric.

  The polypropylene material in masks is often given an electrostatic charge, to increase its filtration efficiency. 3M has a great video explaining  how static charge works in masks:

https://multimedia.3m.com/mws/media/989808O/advanced-electret-media-enhances-breathability.mp4

N95 Masks Also Contain These Materials

Besides the filter material, N95 masks can also include other materials, such as metal. For example, the 3M 9502 (that Smart Air tested for decontamination in the microwave) contains several metal parts. The mask uses steel for the staples (which secure the straps to the mask) and aluminum for the bendable nose clip.

The straps of the 9332 mask are made from polyisoprene, which is in natural rubber and also synthetic rubber. Other masks have elastic fabric straps.

N95 Are Ratings, Not Materials

However, it is worth keeping in mind that N95 is a rating certification about performance, not materials. The N95 rating requires masks to capture 95% of particles. Thus, theoretically, N95 masks could be made out of any sort of material as long as they meet these requirements.

This chart explains exactly what’s required of masks to be certified as N95 in the US versus similar ratings in the EU, China, Australia, Korea, and Japan. Although there are differences on many aspects, none of the agencies require a specific mask material.

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Can Masks Filter Pollen and Protect Us From Hay Fever?

Every year, spring’s blossoms bring with them wave of pollen. For places like Beijing, it’s also the start of the ‘snowy season’, with the hundreds of willow trees producing their fluffy catkin friends and the sniffles that follow. But how can we avoid the uncomfortable coughing and sneezing? Which masks work best for protecting us from pollen? Can surgical masks, single-use face masks, respirators or even Pitta masks filter out pollen?

To answer which masks work best, let’s break this down into two parts:

1. How big are pollen particles?

Pollen particle sizes typically range from 10 microns up to 200 microns — about the width of a human hair. That makes them pretty ‘large’, as far as particles go. They’re bigger than most smog, PM2.5 and soot particles, but smaller in size than heavy dust and sand-like particles.

Looking at individual pollen types, they vary greatly in size. Most trees have pollen that are in the range of 50 – 200 microns. The smallest pollen known measures 9 microns, the pollen of mimosa pudica.

At four times bigger than PM2.5, pollen is much more likely to get stuck in our throat, nose and lungs, as opposed to being absorbed into our blood. That means keeping them out of our throat, nose and lungs, can help to reduce the impact they have on our bodies.

2. Can Masks Filter Out Pollen-Sized Particles?

Because pollen particles are fairly large, most masks will capture a high percentage of it. Data shows that even surgical masks can capture up to 80% of tiny PM2.5 particles. They even do a great job when wearing them. Since the size of pollen is bigger than PM2.5, surgical masks will do even better at capturing them.

Other masks, such as 3M respirators and masks focused at filtering out PM2.5 do an even better job of capturing particulates. The 3M masks tested by Smart Air were able to capture over 99% of particulates when being worn.

The Japanese Pitta Mask vs. Pollen

The Pitta mask is a popular mask in Asia, often worn by celebrities for its cool and stylish looks.

When we previously tested the Pitta mask, we found it scored poorly at capturing PM2.5 particles. It filtered just 64% of particles 2.5 microns in size – that’s even worse than surgical masks. For even smaller 0.3 micron particles, it was useless, capturing 0% of the particles.

However, the Pitta mask never claimed to be able to filter PM2.5 or other small particles. The Japanese Pitta mask brands itself as able to capture “99% of pollen”.

In our tests we only measured particles as large as 5 microns, because that was the limit of our testing machine. However, we can extrapolate the graph above up to 10 microns to work out how well the Pitta mask might capture PM10 particles. Doing so, we can see that the Pitta mask should be able to filter out over 99% of PM10 particles, including pollen.

What else can I do to protect myself from pollen?

1. Get an air purifier for indoor protection against pollen

Plenty of research data shows that any air purifier with a HEPA filter will capture pollen.

    HEPA filters can capture virtually 100% of particles over 2.5 microns. Since pollen particles are all larger than 5 microns, it makes sense that air purifiers can do an even better job of capturing them than PM2.5.

2. Make Your Own Low-Cost Pollen Destroyer

  Big air purifier companies charge outrageous prices for air purifiers, like this popular IQ Air that costs over US$2,000 in China. 

    Our open-source data shows that even simple DIY purifiers capture pollen and even tiny PM2.5 particles. You can skip the big company markup and build your own purifier for about $30 — here’s how.

    Bottom Line On How To Protect Yourself From Pollen and Hay Fever

Pollen particles are typically larger than 10 microns in size, meaning masks are very effective at filtering out pollen particles. Even surgical masks and the Japanese Pitta mask – which previously scored poorly in our tests – do a good job of capturing pollen-sized particles.

Other ways to protect yourself could be to use an air purifier in your home, or to make your own DIY pollen destroyer with just a HEPA filter and a fan.

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Sanitizing Masks With Alcohol Degrades Performance

With mask shortages during the coronavirus outbreak, some doctors are sanitizing masks with alcohol so they can re-use them. But this raises questions about whether alcohol actually works and whether it degrades the masks.

  Does Alcohol Kill Viruses?

The research on alcohol is clear. Alcohol kills viruses. Technically, viruses aren’t alive, so scientists focus on whether the virus is “deactivated” or no longer able to infect humans.

For example, a 2018 article summarized 17 studies where scientists put alcohol on people’s hands and measured the reduction in virus. Alcohol deactivated over 90% of viruses like the polio virus in most cases, depending on the dose and the particular virus.

However, in 23% of the trials, the alcohol deactivated less than 90% of the virus. Thus, alcohol does “kill” viruses, but not all of them all of the time.

Does Sanitizing Masks with Alcohol Degrade Masks? 

But before doctors can start spraying masks with alcohol, we need to know whether the alcohol degrades the masks. Even a “successful” disinfection is useless if it harms the mask.

Fortunately, scientists have tested this question already. Researchers at the National Institute for Occupational Safety and Health tested N95 masks before and after dipping them in rubbing alcohol (isopropanol). Then they dried the masks overnight.

After the alcohol disinfection, the masks captured 37% less particulate on average.

Why This Mask Test Overstates The Effect

A 37% drop sounds big, but to be fair, this number exaggerates the overall harm. That’s because they tested the particle sizes that are the most likely to be affected by alcohol treatment.

The researchers tested particles from around 0.05 to 0.40 microns. For comparison, the coronavirus averages 0.125 microns. Of course, many particles in the air are larger than 0.4 microns, including some bacteria and even some viruses.

  Why does this size range matter? This range around 0.3 microns is the hardest for masks to capture. This chart shows particle capture rates dipping around 0.3 microns. This chart is for HEPA filters, but masks follow the same pattern, with some small differences.

    To boost performance in this critical size range, many masks use fibers that have a static charge. Dipping in alcohol removes this charge.

That’s bad news for particles in this size range, but it also means that alcohol does less harm for capturing particles outside this critical range. For example, when the researchers measured even smaller particles, they found out alcohol sterilization harmed performance by less than 5%.

Read more: Bouncing explains why it’s actually easier for masks to capture smaller particles.

Bottom Line on Sanitizing Masks with Alcohol

Bottom line: Alcohol deactivates viruses, but it significantly reduces filtration effectiveness, particularly for particles around 0.3 microns.

    Better Options Than Sanitizing Masks With Alcohol

This finding is similar to results of washing masks with soap and water, which also harms performance. Instead, research is pointing to UV light and simply drying and waiting as better options for disinfecting masks.

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The Ultimate Guide to Homemade Face Masks for Coronavirus

One month ago, we published the first readily available data on the best materials for making face masks. Fast forward and the CDC is now recommending face masks for everybody, spurring a worldwide movement to make homemade masks.

The first data summary (viewed over 4 million times!) was a great start on face mask materials, but the data is incomplete. Over the past several weeks, we’ve been hard at work to cover crucial materials the earlier study left out, as well as guidelines for variables like thread count. From coffee filters and bed sheets, to non-woven polypropylene bags, flannels and blue shop towels, let’s jump into the data.

What New Face Mask Materials Do We Have?

We’ve tested 30 new materials in this round of tests, triple what the Cambridge researchers tested.

We chose materials based on popular demand, using this poll we set up on our crowd-funding page . However, we’re still testing, so if there’s a material you want to know about, let us know! We’ll update this list as we run more tests.

DIY Mask Test Procedure

We aimed to mimic the test setup the Cambridge researchers used, which is called a Henderson apparatus . In our setup, a fan on one end blows air and particles through the mask material.

On the other end, a Met One GT-521 laser particle counter measures the number of particles that penetrate the mask material. We tested for larger (1-micron) particles and smaller (0.3-micron) particles. These larger particles are approximately the size of the Ebola virus , and the smaller particles are the size of the smallpox virus . The Covid-19 coronavirus measures 0.06-0.14 microns in size, but 5-10 microns when in droplets.

Full details on the testing method are open source and available in our DIY mask material & fabric testing – supplemental data article.

  Results: Ebola-Sized Particles (1.0 microns)

For Ebola-sized particles, the N95 mask, surgical mask and HEPA filter performed best, capturing over 99% of particles 1.0 micron and above. Next up, the HERO coffee filter captured 98%. Paper towels, canvas and denim (10oz) and the bed sheet (100% cotton, 120 thread) also captured more than 90%.

All materials were far better than nothing, with the majority blocking more than 50% of particles. But the four worst-scoring materials were the wool scarf, Neck warmer (100% microfiber polyester), bandana (100% cotton) and light scarf.

  Results: Smallpox-Sized Particles (0.3 microns)

For 0.3-micron particles, there was a much wider range in effectiveness. The N95 mask, HEPA filter and surgical mask still did best, all capturing over 75%. However, they consistently captured fewer 0.3 micron particles than 1.0 micron particles.

Among the household materials, the HERO coffee filter came up next in the list, capturing 62%. But only 4 other materials filtered more than 48%: the 40D nylon, CHEMEX coffee filter, and kitchen towel and canvas (1.0-1.2mm thick).

Some materials were only slightly better than nothing. The bandana, neck-warmer, scarves and cleaning cloths and 100% cotton t-shirt (1 layer) all captured less than 10%.

The 100% cotton t-shirt result is worth highlighting, as this material was recommended by the Cambridge researchers. In our tests it captured just 3.4% of 0.3 micron and above particles. This is likely because the cotton t-shirt we tested was lightweight, thin material. Material weight and thickness of the material are important factors for face masks. 2 layers of 100% cotton t-shirt performed slightly better, capturing 15% of 0.3 micron particles.

The three scarves we tested all captured fewer than 10% of smallpox-sized particles. The worst scarf material – a 100% ramie (similar to linen) scarf – filtered just 2.8%. President Trump last week recommended using scarves for face masks, but this data shows that these materials rank among the poorest at capturing virus-sized particles.

Natural Fibers Better Than Synthetics

The data shows that natural fibers (like cotton and paper) generally filtered better than synthetic fibers (polyester and polypropylene). Synthetic fibers tend to be smooth and uniform, whereas natural fibers are rougher and more irregular. The irregularity of natural fibers are likely to make them better at capturing tiny particles through Brownian motion .

© Dr. J. Alba (Polytechnic Univ. of Valencia)

  The Best Material for Filtration—But Not For a Mask

Based on this data, it would seem easy to recommend the coffee filter and blue nylon as the best materials for homemade masks. But we will end up recommending the paper towel, denim (10oz), and 120 thread bed sheet.

Why? When Smart Air engineer Paddy put the coffee filter and nylon sheet up to his mouth, he found it almost impossible to breathe through. Breathability is crucial when choosing face mask materials.

How Easy is it to Breathe Through These Materials?

To measure the breathability of each material, we recorded the fan power needed to blow a fixed amount of air through each material. You can think of this as the power your lungs need to blow through the material. Here’s how the data pans out (more plusses denotes easier to breathe):

Material Breathability 3M Disposable Floor Cleaning Cloth ++++++ Velvet Synthetic Fiber ++++++ Quick-dry T-shirt (95% Polyester + 5% Spandex) ++++++ Synthetic Brocade Sheet ++++++ Wool Scarf (100% Merino) ++++++ HEPA Filter ++++++ 100% Cotton T-shirt ++++++ Non-woven Polypropylene Bag ++++++ Bandana (100% Cotton) ++++++ Wool Scarf (100% Cashmere) ++++++ Neckwarmer / Snood (100% Microfiber Polyester) ++++++ Light Scarf (100% Ramie) ++++++ Dusting Cloth ++++++ Canvas (0.4-0.5mm thick) ++++++ Surgical Mask +++++ 100% Cotton T-shirt (2 layers) +++++ Bra Pad (muslin + sponge) ++++ 70D Nylon ++++ Paper Towel For Hand Drying +++ Bed sheet (100% Cotton, 120 thread) +++ Bed sheet (100% Cotton, 80 thread) +++ Denim (10oz, 0.6-0.8mm thick) +++ 3M N95 mask +++ Kitchen Towel +++ CHEMEX Coffee Filter ++ Canvas (0.7-0.8mm thick) ++ 40D Nylon* + HERO Coffee Filter* + Canvas (1.0-1.2mm thick)* +

  We compared the breathability of the household materials to the surgical mask. Unfortunately, most materials that were the best at filtering particles were also the most difficult to breathe through. That makes sense. A really dense, thick coffee filter can capture particles well, but it won’t let much air through.

To help with gauging breathability, we also tested the breathability of an N95 respirator. They’re known to be a little more difficult to breathe through than a surgical mask.

The 100% cotton T-shirt (2 layers), bra pad, 70D nylon, paper hand drying towel, cotton bed sheet (120 thread) and denim (10oz) all fell between the breathability of the surgical mask and N95 mask.

  Breathability and Filtration: The Best Combos for Facemasks

Balancing breathability and filtration, we recommend the paper towel, denim (10oz), and 100% cotton bed sheets (80-120 thread). The bra pad performed fairly well, filtering 14% of 0.3 micron particles, and 76% of 1.0 microns. It could be used as a more quirky face mask material, although men might be too bashful to strap a bra cup to their face in public!

One material that’s easier to breathe through than a surgical mask, and still performed fairly well at filtering particles was the 0.4-0.5mm thick canvas material. This material even performed better than the 100% cotton t-shirt.

However, if you don’t have thicker fabrics at home, our data shows that 100% Cotton t-shirts, layered up, are also still effective options for homemade masks.

  Finding the Best Material: The Poor Man’s Fabric Test

One problem for using this data at home is that materials like T-shirts and bed sheets are different. Some are thicker; some are thinner. How can you be sure the material in your home will perform similar to the ones we tested?

Without a $3,000 laser particle counter , here’s one handy way to estimate this: try your own “Poor man’s Fabric Test” to help you out.

Hold your material up to the light.

See how much light passes through it.

Compare it to this rubric to estimate the effectiveness of your material.

  Face Mask Materials: Bottom Line

Materials like coffee filters perform exceptionally well at filtering tiny particles, but they are so difficult to breathe through they aren’t practical for making face masks. Based on a combination of breathability and filtration effectiveness, we recommend denim (10oz), bed sheets (80-120 thread), paper towel, canvas (0.4-0.5mm thick), and shop towel for homemade masks.

  A Shout Out to Those Who’ve Helped Support Open-Source Tests

The response we received for our initial article covering the best materials for homemade masks was unprecedented. People from Spain to Vietnam have offered to help and shared their thoughts on the best materials for masks. Joni, a disabled veteran with pulmonary disease, and K. Sue, a 70 year old in Rochester, US who donated to our campaign as her 70 th birthday present, are just a few of the people who’ve supported this project and made this open-data possible!

If you’d like to help support us test more materials, check out our campaign here: https://fundly.com/best-diy-mask-materials

  What is 10oz denim anyway?

Denim is typically measured in weight per square ounce. A square yard of 10oz denim would weigh 10oz. Anything under 12oz is considered ‘lightweight’ in the denim trousers range, so you can think of the 10oz denim we tested as being similar to that from lightweight trousers.

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The Ultimate Guide to Homemade Face Masks - Supplemental Data

This article accompanies our Ultimate Guide to Homemade Face Masks for Coronavirus article, and covers our testing method and provides the original data.

WATCH: Smart Air’s Paddy Explain How We Ran These Tests

The Cambridge researchers used a fancy piece of kit called a Henderson apparatus to run their tests. This allows for the controlled generation of microbial aerosols and a close control of flow rate and relative humidity. In our tests, we chose to mimic this testing method as closely as possible, but with some noticeable differences. Here’s our setup:

First off, we used ambient air pollution for our tests. The air we breathe contains thousands of tiny particles, some of which are the same size as viruses. We did this so as not to have to work with any nasty viruses or bacteria. We lined two fans up in series to generate a strong airflow, enough to blow through each material at 0.3m/s. That’s similar to speed of the air when exhaling through your mouth.

At the end of our test tunnel, we placed a 10cm x 10cm specimen of each material on the end of the tube, and adjusted the fan to measure 0.3m/s on our anemometer. For some thick materials, our two-fan setup wasn’t powerful enough to reach this speed. Our results reflect which materials these were.

After setting up the material and the airflow, we then proceeded to use our Met One GT521 laser particle counter to measure the number of particles the materials could capture. Met One is the company that makes the big BAM monitors that most governments use to measure air pollution, so we’re in good hands here.

We tested the particle capture effectiveness of each material at capturing 1.0 micron and 0.3 micron particles. The 1.0 micron size mimics the Bacillus atrophaeus bacteria used by the Cambridge researchers (0.93-1.25 microns in size). It’s also a size that can be considered similar in range to coronavirus droplets (5-10µm). 0.3 micron particles are typically considered the most difficult to capture, and so was chosen here as a ‘worst case scenario’. It can give a reasonable estimate for effectiveness of each material at capturing 0.1 micron particles – the size of the coronavirus when not in droplet form.

For each material, downstream air was samples for 30s with and without the test specimen in place, and repeated 3 times. Averaging these values gave us our 0.3 and 1.0 micron capture effectiveness for each material.

  Open Data On Best Materials for Covonavirus Face Masks

  As part of Smart Air’s open-data policy, we are providing all the data in our experiments available for free for people to download and analyse. The data can be downloaded here:

Ultimate DIY Face Mask Materials for Protecting Against Coronavirus Virus.xlsx

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N95和KN95的口罩有什么区别?

N95口罩和KN95口罩有区别吗？

  这个简单易懂的图表解释了N95和KN95口罩之间的区别。N95口罩是美国口罩标准；KN95是中国口罩标准。虽然两种口罩之间有很多不同之处，但这两种口罩在大多数人关心的功能上是一样的。

    口罩制造商3M说，“有理由认为”中国的KN95“相当于”美国的N95。欧洲(FFP2)、澳大利亚(P2)、韩国(KMOEL)和日本(DS)的口罩标准也非常相似。

      N95和KN95的共同之处

  两种口罩都能捕捉95%的颗粒。在这个指标上，N95和KN95口罩是相同的。

    因为一些测试标准说N95和KN95口罩能够过滤95%的0.3微米和以上的颗粒，很多人会说它们只能过滤95%的0.3微米以上颗粒。他们以为口罩不能过滤小于0.3微米的微粒。举个例子，这是《南华早报》  的一张图。他们甚至说“N95口罩可以防止佩戴者吸入直径大于0.3微米的颗粒物”。

    但是，其实口罩比许多人以为的还能捕捉更小的颗粒。根据经验数据可以看到，实际上口罩在过滤更小的颗粒方面是非常有效的。

    N95和KN95口罩的区别

  这两种标准都要求口罩在捕捉盐颗粒(NaCl)时进行过滤效果检测，都以每分钟85升的速度进行测试。但是，N95和KN95之间有一些区别，在这里强调一下。

    这些差异都不大，对于一般使用口罩的人来说没有太大的区别。但是，这里有一些比较关键的差异：

  1.如果制造商要拿到KN95的标准，需要对真人进行口罩密封测试，而且漏率（从口罩侧面漏过去的颗粒百分比）需要≤8%。N95标准的口罩不要求密封测试。（记住：这是国家对商品的要求。很多工业公司和医院会自己要求员工做密封测试。）

    2.N95口罩对吸气时的压降要求比较高。这代表着它们需要更透气一点。

  3.N95口罩对呼气时的压降也有稍微严格的要求，这应该有助于提高口罩的透气性。

  总结：N95和KN95口罩的区别

  总结：虽然只有KN95口罩需要通过密封测试，但N95口罩和KN95口罩都是被认可能够过滤95%的颗粒。另外，N95口罩对透气性有比较强的要求。

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用紫外线消毒口罩，效果好吗？

在新冠病毒爆发期间，因为口罩供应短缺，人们开始考虑用紫外线来消毒口罩。这对一线医护人员来说是一个关键的问题，因…

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微波炉可以给口罩消毒吗？

因为新冠病毒的爆发，口罩供应不足，很多人不得已重复使用仅有的口罩。于是人们开始想尽各种办法给自己的口罩消毒。用微波炉加热口罩来达到杀菌作用，原本是个听起来非常疯狂的想法，现在也变成了一个很值得被思考的问题：

微波口罩能杀死冠状病毒和细菌吗？

  这个问题之所以重要的另一个原因是：Smart Air做了测试，发现用肥皂和水清洗N95口罩会降低口罩21%的颗粒过滤效果。其他的测试发现，就算只是把口罩泡在酒精中，不去摩擦清洗它，也会破坏口罩的效果。

    Smart Air为了找到问题的答案，对微波口罩进行了测试。首先，让我们把这个问题分解成两个更简单的问题。

  问题1：微波能消灭病毒吗？

首先，让我们来看看家用微波炉是不是真的能杀死病毒(严厉的科学家们都在说“消灭活性”，因为严格来说病毒是没有生命的)。德国的研究人员测试了用微波炉是否可以消灭注射器和香烟滤嘴上的丙型肝炎病毒和艾滋病病毒的活性。

    为什么要用香烟过滤嘴和注射器呢？因为吸毒的人经常使用香烟和注射器，他们可能会通过这两样东西感染病毒。

  研究人员用丙型肝炎病毒或艾滋病病毒污染了香烟过滤嘴和注射器的塑料部分。然后用不同功率，微波加热3分钟。

      结果表明，在360瓦的微波炉中加热3分钟就足以使大部分病毒失去活性。

    为了安全起见，研究人员建议用600瓦的微波炉加热2分钟或更长时间。好消息是，大多数家用微波炉的功率都可以达到600瓦。

      那么新冠病毒呢?

  德国的研究人员测试了微波对丙型肝炎和艾滋病病毒的影响，但没有针对冠状病毒做测试。虽然还没有关于微波加热Covid-19的研究，但科学家们已经用人副流感病毒进行了测试。人副流感病毒是一种RNA病毒，类似于传染人类的冠状病毒。

  这些科学家把病毒放在玻璃培养皿中，然后用微波炉加热20到200秒。

    数据显示，微波3分钟就足以使脊髓灰质炎病毒和副流感病毒失去活性。

      什么是“600W”？我的微波炉符合规格吗？

科学家用来消灭病毒的“600W”指的是微波的功率。你可以把它想象成你家微波炉的“低”、“中”和“高”档。大多数家用的微波炉功率会在700-1200W之间，所以按理来说你的微波炉是符合要求的，你也可以通过微波炉背面的标签来确认一下。

       问题2：微波口罩会影响口罩效果吗？

  实验表明微波可以消灭物品中的病毒，但对于口罩来说，我们还得知道，微波它会不会破坏口罩的效果。为了测试这一点，Smart Air的总工程师Paddy拿出一个用过的3M N95口罩，“霸占”了Smart Air办公室厨房里的微波炉。

    但在正式微波口罩之前，有一步非常重要：Paddy必须去掉口罩上所有金属的零件，但在去掉口罩上的金属部分后，N95口罩几乎变得不能用了，看来微波口罩并不是一个很理想的方法。如果你的口罩含有金属部件，那么你一定要在把口罩放进微波炉之前拆掉它们。但是，有些口罩不含任何金属部件，尤其是许多人们现在使用的DIY口罩。

    为了测试微波加热的效果，Paddy把3M N95口罩置于高温下微波了3分钟。

    大约两分钟后，微波炉开始散发出奇怪的味道，感觉再不关掉微波炉可能会坏掉…

但是Paddy不想放弃，他（冒着生命危险）坚持了下来！

口罩在微波炉里待了3分钟，然后等它冷却下来。Paddy拿了一个Met One GT521，测试了口罩捕捉0.3微米粒子的效果。测试这种大小的颗粒是很重要的，因为它是最难捕获的大小。

   阅读更多：自制纸巾口罩如何有效预防传染新冠病毒。

  令人惊讶的是，微波口罩并没有损破坏口罩的过滤效果。

    如果说微波口罩前后有什么变化的话，微波会略微增加颗粒的过滤率。

    不使用微波炉加热口罩的一个好理由

  虽然微波口罩是有效的，但这样做还是有点危险。比如，微波可能会融化口罩，而且更重要的是，据《卫报》报道，英国一名男子将一块洗碗布放入微波炉消毒，结果引起了一场火灾。

      结论：微波口罩可以消灭病毒的活性，但这并不是最安全的方式！

  测试发现，把受污染的物体放进600瓦的微波炉里加热3分钟，可以消灭受污染物品上病毒的活性。但是，如果口罩上有金属的部分，用微波炉消毒可不是一个好办法。而且微波口罩也会导致口罩融化甚至着火，所以是非常危险的！

可能有更有效的方法为你的口罩消毒。阅读我们的相关文章：

  阅读更多：这个有数据支持的方法可以既不损害口罩效果，又能消灭上面的病毒。

    P.S.微波究竟是如何消灭病毒活性的?

 在他们的报告中，德国科学家解释说，56-60摄氏度的温度足以消灭丙型肝炎病毒。

  即将上线，敬请期待：你必须加热到什么程度才能消灭冠状病毒？

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What’s a Reliable Way to Disinfect Masks from Viruses Without Harming Effectiveness?

The outbreak of the coronavirus led to a surge in interest in how to disinfect masks, as well as Google searches for “wash N95 mask” and “clean N95 mask.”

Yet answers to this question are in short supply. The standard guidelines say to throw masks out and use new ones.

But the standard guidelines are meaningless for people facing a global pandemic and widespread mask shortages.

Washing Masks Reduces Effectiveness

The simplest solution is to wash masks with soap and water. Yet test data shows washing masks reduces their filtration effectiveness.

Alcohol Disinfection Reduces Effectiveness

Maybe alcohol disinfection is better because it doesn’t require rubbing the mask? Unfortunately, tests found that dipping in rubbing alcohol reduced particle capture by 37%.

Thus, we’re in need of a data-backed way to disinfect masks without harming performance.

A Reliable Way to Disinfect N95 Masks

In times of panic, we often want to take action, yet one of the simplest ways to disinfect masks is to do nothing! Simply allowing masks to dry will kill viruses.

But the critical question healthcare workers need to know is how long we need to dry masks before they’re safe. In other words, how long do viruses remain viable? The question of viability is particularly important, because many studies measure whether viruses are “detectable.”

Viruses can remain detectable for scarily long periods of time, which has lead to incredible-sounding headlines about how long viruses last. But “detectable” is very different from “viable.” Viable is more important for mask users because “viable” means it’s still able to infect someone.

How Long Does It Take to Disinfect Masks?

Researchers at the University of Hong Kong tested how long viruses retain their ability to infect people on different types of surfaces. They sprayed H1N1 flu virus on six common household materials and tested viability up to 24 hours.

Unfortunately, they didn’t test masks, but the closest material they tested was J-cloth. This J-cloth material is somewhat similar to the electrostatic material used in masks.

The tests found that the virus was completely non-viable in under 5 hours.

The virus remained viable the longest on hard, non-porous surfaces—stainless steel and plastic. However, even for the worst surface, stainless steel, the flu virus was non-viable in under 10 hours. The researchers concluded that the H1N1 is “likely to survive up to a few hours.”

Thus, simply leaving a mask out to dry should kill the virus. This eliminates the need to degrade the mask with water or alcohol.

  Will Drying Masks Work for Covid19?

The study above is for H1N1 (influenza A), not the coronavirus. The researchers said results should be similar for other influenza A viruses, but they stopped short of saying they’re valid for all flu viruses.

There’s little data on how long the Covid19 coronavirus remains viable. The CDC says that the coronavirus may remain viable for hours to even days. A recent study (that has not been formally published yet) tested the viability of the new coronavirus (HCoV-19) and the “old” coronavirus, SARS (SARS-CoV-1). They sprayed the two viruses on plastic, stainless steel, copper, and cardboard.

They did not test cloth, but the closest material to a mask was cardboard. It took 48 hours for the coronavirus to be completely non-viable on cardboard. On stainless steel, a tiny amount of viable coronavirus remained at 72 hours, That’s 7 times longer than the earlier study found for H1N1.

Based on these two studies, leaving a mask to dry for 48 hours should be enough to kill coronavirus, SARS, and influenza A viruses. Leaving masks for 72 hours would be even more conservative.

However, it is important to remember that virus survival time is not a universal constant like the speed of light. Several factors will influence how long viruses survive:

Viruses survive longer at lower temperatures. For example, one study found that viruses died faster at 20C than 4C, and faster still at 40C.

Studies have found that viruses survive much longer on wet materials than dry materials.

Drying out a mask is more likely to kill the virus. One US hospital is telling its nurses to keep their masks in plastic bags, yet this would prevent the mask from drying and thus allow the virus to live longer.

    How to Disinfect N95 Masks: Bottom Line

Leaving masks out to dry should disinfect them from the coronavirus, SARS, and influenza A in under 48 hours. 72 hours would be even more conservative.

Of course, more data is needed. Particularly needed is direct tests of viability on masks and with virus concentrations that would be common on masks.

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Is Washing Masks Effective After Virus Exposure?

With the shortage of masks during the coronavirus outbreak, many people are wondering if washing masks is an effective way of cleaning them, to let you re-use them.

There are companies that claim to have washable anti-pollution masks. This company in India claims their mask is washable and can capture air pollution, bacteria, and “germs.”

  Yet one thing that seems to be lacking is any actual data on this question–until now.

The Test: Washing Masks with Soap & Water

Smart Air tested this by washing a dirty 3M N95 mask our engineer Paddy had been using during the coronavirus outbreak.

Step 1: Use a Met One GT-521 laser particle counter to test what percentage of tiny 0.3 micron particles the mask filters.

Read more: Here’s why these 0.3 micron particles are they key for mask effectiveness.

Step 2: Wash in soap and water. Smart Air used Walch hand soap, which claims to remove 99.9% of bacteria, although it doesn’t say how effective it is at removing viruses.

Step 3: After drying overnight, test mask particle capture again.

Testing Mask Filtration Effectiveness

Although the mask was used for over a week, it still very captured 99% of particles. This fits with previous Smart Air results where masks retained effectiveness nearly unaffected after being worn 11 days, 20 days, and even 30 days.

However, washing the mask was much worse than natural “aging.” Washing decreased particle capture by 21%.

  That is still better than the effectiveness of some surgical masks, but it’s a large drop.

Why Is Washing Masks So Harmful?

The answer to this question lies in the fibers masks are made from. Many N95 and other pollution masks are made from a mat of randomly aligned, very thin fibers.

Manufacturers then give these sheets an electrostatic charge.

See More: 3M explains static charge in masks in this video.

https://multimedia.3m.com/mws/media/989808O/advanced-electret-media-enhances-breathability.mp4

  Washing removes that static electric charge, which decreases performance. Vigorous washing may also damage the fibers, making it easier for particles to pass through.

Bottom line: Washing masks with soap and water decreases particle capture effectiveness. Washing is not a solution for extending mask lifespan.

Why Do Some Companies Claim to Have Washable Masks?

Companies might not know that washing mask filter media can drastically reduce effectiveness. Or maybe the masks claiming to be washable aren’t actually N95 standard masks, but just cotton masks that can be washed with potentially less damage to the fibers.

Another common so-called “washable” masks is made up of a washable cotton mask and a non-washable N95 filter.

Yet this filter still can’t be washed. What’s more, masks with replaceable filters tend to score worse on fit tests than 3M N95 masks. That pattern is clear in mask fit tests run by Beijing-based doctor Richard Saint Cyr.

Is Washing Masks with Alcohol Effective?

Perhaps another solution for washing masks is alcohol. If soap and water require rubbing, maybe alcohol will do less harm because it can disinfect without rubbing. 

A group of researchers at the National Institute for Occupational Safety and Health tested N95 masks before and after dipping them in rubbing alcohol. After drying overnight, the masks captured 37% less particulate on average.

To be fair, this test exaggerates the harm. That’s because the test above was for particle sizes that are the most likely to be affected by alcohol treatment. Many masks capture particles in the range around 0.3 microns using fibers with static charge. Dipping in alcohol removes this charge.

However, when the researchers looked at even smaller particles, they found out alcohol sterilization did much less harm.

Read more: This is why the graph above makes no intuitive sense but is real.

Looking for an effective way of cleaning your mask from viruses?

This method kills viruses without affecting mask performance.

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Comparison of Mask Standards, Ratings, and Filtration Effectiveness

Mask standards can be confusing: N95, KN95, FFP1, P2, or surgical mask? This quick run-down covers mask types, mask ratings, and their effectiveness at filtering particles.

First off, let’s start with mask types (or certification types). In general, there are 3 (or sometimes 4) types of commonly used, disposable masks. They are single-use face masks, surgical masks, and respirators.

Mask Standards and Effectiveness Bottom Line

Single use masks (normally one layer, very thin) are typically only effective at capturing larger dust particles, but can do so fairly well.

Surgical mask standards have higher requirements for capturing virus-sized (0.1 micron) particles, however they vary by region.

Pollution masks (respirators) typically capture >90% of virus-sized particles. You can use the rating system in the table above to see the exact proportion each certification requires. This includes ratings such as N95, KN95, FFP1, FFP2 and FFP3.

Mask Standards Vary by Country

Each country has their own certification standard for each mask type. For example, Europe uses the EN 14683 standard for surgical masks, whereas China uses the YY 0469 standard. Each standard varies a little by country, however they are broadly similar. For respirator masks, China uses the KN standard (e.g. KN95) and the US uses the N standard (e.g. N95).

Read more: what’s the difference between KN95 and N95 masks »

Requirements Are Lowest for Single Use Face Masks

The standard with the lowest requirements on filtration effectiveness are the single use face masks (not to be confused with surgical masks). Surgical masks have higher requirements, and respirators have the highest requirements. Respirators also usually fit tighter around the face (data shows they score higher on fit effectiveness) than surgical masks and single-use face masks.

Coronavirus & Mask Livestream

Wondering whether masks work to protect you against the coronavirus? Check out our livestream recap covering all the info here!

  3M or FFP1 or N95 or KN95? What Do Mask Numbers and Letters Mean?

A visitor to the website asked this in the comment section on coronavirus and Pitta masks a few days back:

Could you please explain: if a mask is FFP2 or 3, but NOT 3M – what does it mean exactly concerning coronavirus? thank you!

Here’s an explanation on the difference between N95, 3M and PM2.5, to help you out.

N95, N99, FFP1, FFP2 and FFP3 Masks

The ratings cover (most importantly for us) the filtration level, among other things. You can think of them like G, PG, PG-13, R ratings for movies. The movie ratings cover who can watch them.

EN 149:2001+A1:2009 / ASTM F2100 / NIOSH

These are standards for masks. They specify the rules and testing methods companies should follow to rate their masks. These standards define the N95, FFP1, and FFP2 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 or R. They’ll follow these rules to rate the movie. These standards are the set of rules for masks.

Why are there so many? Standards labelled “EN” are for the EU. ASTM F2100 (NIOSH) is for the US. Many other countries will have their own rating systems too.

3M Masks?

3M is a company that manufactures masks. They generally produce masks that meet KN95 or N95 standards

PM2.5 vs. N95

As we now know, N95 is a mask rating. PM2.5 refers to “particulate matter” or a fancy way of saying “pollution particles” that are in the air. The 2.5 refers to the size of these particles as being 2.5 microns or smaller. This picture can give you a visual example of how big PM2.5 particles are.

  Important Tips for Understanding Mask Ratings

1. Three randomized studies have found surgical masks are just as effective as N95 masks at preventing virus transmission. They hypothesize the main reason for this is that any mask can reduce the hand-to-face contact, although we don’t know this for sure.

2. If you’re wearing a mask with a valve, you are protected. The valve does not bring in any outside air into the mask. Fit-test data has found that masks with valves are often among the highest scoring.

However, valves will not protect other people as well. If you are sick, and you breathe out, some of the moisture from your breath can expel through the valve, potentially putting others in danger.

3. Tests have found that DIY masks can filter a percentage of virus-sized particles. While they’re not as effective as surgical or N95 masks at filtering viruses, they can still provide some benefit. They can also reduce hand-to-face contact.

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DIY Masks: Is Paper Towel Effective at Blocking Viruses?

In a recent study, researchers tested household materials that could be used to make DIY masks, but they left out one common material—paper towel (also called “kitchen paper”). Could paper towel be an effective material for making homemade masks in times of crisis and shortages? Smart Air Engineer Paddy tested its effectiveness in the Beijing lab.

  Putting Paper Towel to The Test

Paddy used a Met One GT-521S particle counter to test how well a single and double layer of paper towel filtered out particles down to 0.3 microns. Paddy ran the Met One for one minute, measuring the total number of particles passing through the kitchen paper versus the same setup with no filter.

  How Big Are Viruses?

Just how small is 0.3 microns compared to viruses? On average, coronavirus particles measure approximately 0.1 microns in diameter, so 3 times smaller than measured in our test. However, 0.3 microns is an important size to test, because 0.3 micron particles are the most difficult to capture.

The crazy reality is that particles smaller than 0.3 microns are actually easier to capture. Don’t believe us; believe the data. Here’s the science behind it »

Paper Towel Particle Capture

The results weren’t great. A single layer of kitchen paper captured just 23% particles. Adding an extra layer only increased particle capture to 33%.

For larger 2.5 micron particles, paper towel performed better. The single layer of kitchen paper captured 52% of these larger particles.

Do Paper Towel Masks Fit Tight?

One thing this test doesn’t cover is fit effectiveness–how leaky a DIY mask would be. Not surprisingly, masks that fit better will let fewer particles in. That’s one of the reasons why surgical masks score lower on fit tests than N95 masks.

  Yet Studies Find Mask Leakage Has Small Effect on Flu Virus Transmission

Although surgical masks (and presumably DIY masks) are more leaky than N95 masks, randomized studies that have tracked infection rates have found that surgical masks are just as effective as N95 masks at preventing the transmission of viruses. Researchers don’t know the exact reason for this. However, some scientists hypothesize that masks help, in part, because they prevent us from touching our face. That helps keeps us from “planting” viruses our mouth, nose, and eyes.

Bottom line: Paper towel captured fewer particles than other DIY mask materials tested by researchers at Cambridge. However, if it is the only material you have, it is better than nothing.

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What Are The Best Materials for Making DIY Masks?

Update 9th April: We’ve had hundreds of requests from people looking for data on more materials for making face masks. We are working hard to provide MORE data on MORE materials for DIY masks.

To help with this, we have created a campaign on Fundly.com where you can vote and recommend what materials we should test. Please support this campaign and help us use data-backed science to fight Covid-19!

With masks sold out during the coronavirus outbreak, many people will have to make do with what some scientists have called “the last resort”: the DIY mask.

Data shows that DIY and homemade masks are effective at capturing viruses. But if forced to make our own mask, what material is best suited to make a mask? As the coronavirus spread around China, netizens reported making masks with tissue paper, kitchen towels, cotton clothing fabrics, and even oranges!

The Best Material for Making a Homemade DIY Mask

Researchers at Cambridge University tested a wide range of household materials for homemade masks. To measure effectiveness, they shot Bacillus atrophaeus bacteria (0.93-1.25 microns) and Bacteriophage MS virus (0.023 microns in size) at different household materials.

They measured what percentage the materials could capture and compared them to the more common surgical mask.

Not surprisingly, the surgical mask performed best, capturing 97% of the 1-micron bacteria. Yet every single material filtered out at least 50% of particles. The top performers were the vacuum cleaner bag (95%), the dish cloth (“tea towel” in the UK! 83%), the cotton blend shirt fabric (74%), and the 100% cotton shirt (69%).

Homemade Masks vs. Viruses

The test above used bacteria that were 1 micron large, yet the coronavirus is just 0.1 microns – ten times smaller. Can homemade masks capture smaller virus particles? To answer this question, the scientists tested 0.02 micron Bacteriophage MS2 particles (5 times smaller than the coronavirus).

On average, the homemade masks captured 7% fewer virus particles than the larger bacteria particles. However, all of the homemade materials managed to capture 50% of virus particles or more (with the exception of the scarf at 49%).

Are some materials missing from the list?

We are working on more comprehensive tests with more materials. Check out our ‘Best Mask Materials’ Campaign for more info.

Are Two-Layered DIY Masks More Effective?

If the problem is filtration effectiveness, would the masks work better if we doubled up with two layers of fabric? The scientists tested bacteria-size particles against double-layered versions of the dish towel, pillow case, and 100% cotton shirt fabrics.

Overall, the double layers didn’t help much. The double-layer pillowcase captured 1% more particles, and the double-layer shirt captured just 2% more particles. Yet the extra dish cloth layer boosted performance by 14%. That boost made the dish cloth as effective as the surgical mask.

Looking at the data, the dish towel and vacuum cleaner bag were the top-performing materials. However, the researchers didn’t choose these as the best materials for DIY masks:

Instead, they concluded the pillowcase and the 100% cotton t-shirt are the best materials for DIY masks. Why?

What DIY Mask Materials Are The Most Breathable?

The answer lies in breathability. How easy it is to breathe through your mask is an important factor that will affect how comfortable it is. And comfort isn’t merely a luxury. Comfort will influence how long you can wear your mask.

Fortunately, in addition to particle effectiveness, the researchers tested the pressure drop across each type of fabric. This gives us a good indication of how easy it is to breathe through each material. As a benchmark, they compared breathability of each DIY mask material to the surgical mask.

Although the dish cloth and the vacuum bag captured the most particles, they were also the hardest to breath through. With two layers, the dish cloth was over twice as hard to breathe through as the surgical mask. In contrast, the pillow case, t-shirt, scarf, and linen were all easier to breathe through than the surgical mask.

  Researchers’ Pick for Best-Performing Homemade Mask Material

Based on particle capture and breathability, the researchers concluded that cotton t-shirts and pillow cases are the best choices for DIY masks.

Are there any other materials we can use? The Cambridge researchers left out one common material: paper towel. We tested how well paper towel masks capture sub-micron particles.

Making DIY Masks with Household Materials

Bottom line: Test data shows that the best choices for DIY masks are cotton t-shirts, pillowcases, or other cotton materials.

These materials filter out approximately 50% of 0.2 micron particles, similar in size to the coronavirus. They are also as easy to breathe through as surgical masks, which makes them comfortable enough to wear for several hours.

Doubling the layers of material for your DIY mask gives a very small increase in filtration effectiveness, but makes the mask much more difficult to breathe through.

  Here’s What Else You Should Know About DIY Masks

Still not sure if DIY masks really work? See the real-world test data on the effectiveness of homemade DIY masks.

Some health authorities claim that masks are only to keep sick people’s germs in, but do masks actually prevent healthy people from getting infected? Randomized studies say “yes.”

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Believe It Or Not: Beijing Sees Worse Pollution During Coronavirus Shutdown

Recent news reports have proclaimed a dramatic reduction in China’s air pollution during the coronavirus lockdown, yet data shows Beijing has actually seen pollution levels rise during this period. The headlines are based on images from NASA, finding that air pollution dropped 10-30% compared to the same period in 2019.

  NO2 Pollution During Coronavirus Down 10-30% Over Prior Year

Smart Air analyzed data from the Beijing Environmental Protection Bureau, comparing 6 different pollutants for the period 2019 to 2020. In contrast, the NASA study looks only at NO2 (nitrogen dioxide). NASA estimated that NO2 fell 10-30% across the whole of China during January and February, when compared to 2019.

This fits with results from our analysis. Beijing’s NO2 fell 21% compared to the same period in 2019.

Why? The major source of NO2 is from transport – cars, trucks and buses. The coronavirus lockdown has closed entire cities and roads, which has meant fewer cars on the road.

  Beijing PM2.5 Pollution During Coronavirus Lockdown: Up 17%

However, NO2 is only one type of air pollution. According to the World Health Organization, particulate pollution “affects more people than any other pollutant.” For that sort of pollution, Smart Air analysis finds that PM2.5 has actually increased 17% during January and February, compared with the same period in 2019.

So why, even with Beijing under lockdown, has PM2.5 worsened over the prior year? With less traffic on the roads – up to 77% fewer trucks and 36% fewer buses in some cases – and hundreds of factories closed, it is reasonable to expect decreasing pollution during the coronavirus lockdown.

  Heavy industry surrounding Beijing is up and running

The area surrounding Beijing is China’s biggest steel manufacturing hub.

What’s more, these heavy industry factories are typically state-owned enterprises that have remained open despite the coronavirus lockdown. For example, a map of Beijing’s factory activity from 2nd March, 2020 shows almost all factories back online, except for a few (gray) points on the map.

However, some factories have closed due to the coronavirus. Why, then, is PM2.5 higher than 2019?

Unfavorable winds in 2020

A map of winds around Beijing as of February 13th show stagnating air around Beijing.

Weaker winds and fewer northerly winds can increase PM2.5. Data shows that wind—particularly northern wind—slashes PM2.5 in Beijing. Thus, less wind means fewer chances to blow away the air pollution. This, coupled with the atmospheric effect known as inversion, could explain why Beijing’s PM2.5 has been higher during the coronavirus lockdown.

  Bottom Line: Beijing’s PM2.5 Pollution During Coronavirus Lockdown

Beijing’s NO2 pollution has dropped during the coronavirus shutdown, but PM2.5 has increased 17%. This is critical because data has linked PM2.5 to heart attacks, strokes, and even lower IQ.

  Studies Document Protective Effects of Purifiers, Masks

Despite the harms of PM2.5, studies have found that wearing masks prevents effects on blood pressure and heart rate variability. Placebo-controlled studies of air purifiers have found that reducing particulate in the home prevents harm to blood pressure, inflammation, and immune response—even among young, healthy twenty-year-olds.

Smart Air is a certified B Corp committed to combating the myths big companies use to artificially inflate the price of clean air. To help people living in polluted cities protect themselves, Smart Air provides empirically backed, no-nonsense purifiers and masks, helping to lower the cost of clean air.

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自制口罩能预防冠状病毒吗？

戴上自己DIY的口罩来抵御冠状病毒听起来是个疯狂的主意。

因为数据显示很多口罩的效果都非常好，一些性能最好的口罩也是最便宜的。

比如一个外科口罩只需要几美分，它可以过滤掉80%的大小只有0.007微米（比冠状病毒小14倍）的微粒。

但是，2019年爆发的冠状病毒(Covid-19)带来了一个新问题：口罩都卖光了。

    买不到口罩，人们都开始开始自制口罩，但自制的口罩真的能保护你远离冠状病毒吗？

  一名用户自制“杀毒”面具

  自制口罩测试 —— 能过滤微小颗粒吗？

  在2009年H1N1流感爆发之后，剑桥大学的科学家提出了这个问题。他们认为，在全球流感爆发的情况下，我们可能会用完N95口罩。在冠状病毒爆发期间，他们的预言成真了。

    研究人员让志愿者们用棉质t恤和缝纫机自制一个设计简单的口罩。然后，研究人员在口罩上他们比较了棉质DIY口罩和外科口罩过滤微粒的效果。

研究人员让志愿者们用棉质t恤和缝纫机制作自己的面具，使用的是他们设计的简单程序。然后，研究人员在口罩上注射了1微米大小的细菌(称为“阿托菲菌”)，并测量自制口罩能够过滤的细菌百分比，这些颗粒的大小和炭疽、瘟疫病毒的颗粒大小差不多。

    自制口罩捕捉到的颗粒物比外科口罩少，但仍能捕获69%的1微米颗粒物。

但这就是自制口罩能过滤的最小的颗粒吗？研究人员在口罩上注射了0.2微米的“噬菌体MS2”粒子，提高了这个标准。它们甚至比冠状病毒颗粒还要小。

  同样，外科口罩捕捉了更多的颗粒，但是自制的棉口罩捕捉了51%的微米颗粒。

  好的，但是它们会漏的，对吧？

  在这一点上，聪明的怀疑论读者可能会想，“当然，布可以捕捉粒子，但它们可能不会很好的贴合在脸上，所以它们是没用的。”

幸运的是，研究人员也对自制口罩进行了测试。在佩戴测试中，有人戴好口罩，科学家测量口罩内和口罩外的颗粒物数量。

    这台用于机器的测量，可以检测到的颗粒大小在0.02到1微米之间，冠状病毒的大小就在这个范围内。

    在21名志愿者中，自制的棉口罩捕捉了50%的0.02-1微米颗粒，而外科口罩捕获了80%的颗粒。所以DIY口罩是可以在人们佩戴着的时候捕获颗粒的。根据这些数据，研究人员得出结论，自制口罩总比什么都不戴要好。

      只有一个自制口罩的测试吗？

  剑桥大学的数据显示，棉质口罩可以过滤掉一些0.02-1微米大小的微粒。这很好，但是其他材料呢？荷兰的一组研究人员测试了用桌布(在英国称为“茶布”)自制的口罩。

    他们也用一个合适的机器来测试人们实际带着口罩时的效果。

    自制的桌布口罩捕获了60%的0.02-1微米颗粒。当然，外科口罩和N95口罩能捕捉到更多的颗粒，但数据显示自制口罩在捕捉病毒大小的颗粒方面并不是毫无用处。

        自制口罩可以戴多久?

  然后他们测试了戴了3个小时后的口罩的效果，口罩上有了湿气后，效果会不会减弱呢？

    结果发现，口罩上的湿气和佩戴口罩的时间，对任一种口罩的有效性几乎都没什么影响。事实上，自制的口罩在3小时后过滤病毒大小的微粒的效率提高了5.8%。

所以，自制口罩在戴了几个小时后，并不会降低它们的有效性。

    自制口罩对儿童的防护效果如何?

  接下来，他们找了11个5-11岁的孩子，来测试了自制口罩的效果。当孩子们戴上自制的口罩时，0.02-1微米的颗粒物只被清除了52%，看得出来儿童的效果几乎比成人低15%。

    有趣的是，外科口罩和FFP2 (N95)口罩对儿童的效果也较差。这和Smart Air为印度儿童测试口罩效果的测试结果相似，该测试发现儿童佩戴口罩的效果低于成年人。数据表明，给孩子们佩戴非常合适的口罩是比较困难的。

      总结：自制口罩到底能不能对抗冠状病毒？

  数据显示，用一层棉布或一块桌布自制的口罩可以过滤大约50-60%的病毒大小的颗粒。这代表它们的效果比外科口罩和FFP2 (N95)口罩差。

戴自制口罩3小时对口罩的过滤效率并没有显著的影响。

DIY口罩也适用于儿童，但对儿童的防护效果不如成年人。