In light of Covid-19 we’ll look at the difference between respirator filtering standards such as N95 and FFP2/FFP3…
Masks vs Respirators
Before we go any further, let’s just clarify on a technical difference between a “mask” and a “respirator”. In day to day language we often say mask, when referring to what are technically called respirators.
Uses for Masks:
- Masks are loose fitting, covering the nose and mouth
- Designed for one way protection, to capture bodily fluid leaving the wearer
- Example – worn during surgery to prevent coughing, sneezing, etc on the vulnerable patient
- Contrary to belief, masks are NOT designed to protect the wearer
- The vast majority of masks do not have a safety rating assigned to them (e.g. NIOSH or EN)
Uses for Respirators:
- Respirators are tight fitting masks, designed to create a facial seal
- Non-valved respirators provide good two way protection, by filtering both inflow and outflow of air
- These are designed protect the wearer (when worn properly), up to the safety rating of the mask
- Available as disposable, half face or full face
Whilst surgical style masks are not redundant by any means (discussed more below), they aren’t designed to protect the wearer, whilst respirators are.
The US Center for Disease Control (CDC) cites the N95 respirator standard as part of the advised protective equipment in their Covid-19 FAQ and their SARS guidance (SARS being a similar type of Corona virus). Which suggests that an N95 or better respirator is acceptable.
N95 vs FFP3 & FFP2
The most commonly discussed respirator type is N95. This is an American standard managed by NIOSH – part of the Center for Disease Control (CDC).
Europe uses two different standards. The “filtering face piece” score (FFP) comes from EN standard 149:2001. Then EN 143 standard covers P1/P2/P3 ratings. Both standards are maintained by CEN (European Committee for Standardization).
Let’s see how all the different standards compare:
|Respirator Standard||Filter Capacity (removes x% of of all particles that are 0.3 microns in diameter or larger)|
|FFP1 & P1||At least 80%|
|FFP2 & P2||At least 94%|
|N95||At least 95%|
|N99 & FFP3||At least 99%|
|P3||At least 99.95%|
|N100||At least 99.97%|
As you can see, the closest European equivalent to N95 are FFP2 / P2 rated respirators, which are rated at 94%, compared to the 95% of N95.
Similarly, the closest to N100 are P3 rated respirators – with FFP3 following closely behind.
You could approximate things to say:
KN95 vs N95
According to 3M (source), the Chinese KN95 standard has an equivalent specification to N95/FFP2 respirators . To quote:
“It is reasonable to consider China KN95, AS/NZ P2, Korea 1st Class, and Japan DS FFRs as equivalent to US NIOSH N95 and European FFP2 respirators”
In practice the issue is more complex, and I wouldn’t take for granted that all KN95 respirators are up to the same standard.
Things to watch out for:
- Typically KN95 respirators are held in place by over-ear elastic loops, rather than behind the head elastics. This can result in a weaker seal. Fortunately there are methods for tightening – see this YouTube video for ideas. Products called “ear savers” can also aid with tightening, and can be found on eBay or you can 3D print them.
- There’s no guarantee that all KN95 respirators actually meet the Chinese KN95 standard. However, with the current respirator shortage, unfortunately the same goes for N95/FFP also.
The KN95 specification is referred to as GB 2626-2006 (preview here) – so you will generally see that written on the KN95 respirators. From July 1st 2020, it’ll be replaced by GB 2626-2019, an updated specification (preview here).
I’ve linked below to a supplier of KN95 respirators in the USA – in case it’s of use to some readers.
Valve vs Non-Valved Respirators
✅Valved respirators make it easier to exhale air. This makes them more comfortable to wear, and leads to less moisture build-up inside the respirator. Ideal for things like DIY/construction work.
❌The problem with valved respirators is that they do not filter the wearer’s exhalation, only the inhale. This one-way protection puts others around the wearer at risk, in a situation like Covid-19. It’s for this reason that hospitals and other medical practices do not use valved respirators.
One hack to protect (and respect) others when wearing a valved respirator is to put a surgical mask or “cloth face covering” over the valved respirator, to (partially) filter the out breath.
Table of Contents
- 1 Masks vs Respirators
- 2 Respirator Standards
- 3 Surgical Masks
- 4 DIY / Homemade Masks
- 5 What are respirators protecting us against?
- 6 Roundup
TL;DR – yes, respirators with high efficiency at 0.3 micron particle size (N95/FFP2 or better) can in theory filter particles down to the size of the coronavirus (which is around 0.1 microns). What that doesn’t tell us is how much protection respirators will provide against coronavirus when in use – we will need to wait for future studies to confirm.
Read on to learn more…
A recent paper shows that the coronavirus ranges from between 0.06 and 0.14 microns in size. Note that the paper refers to the coronavirus particle as 2019-nCoV, which was it’s old name. The virus is currently called SARS-CoV-2, and the illness it presents in people is called Covid-19.
Respirator’s are measured by their efficiency at filtering particles of 0.3 microns and bigger (noting that the coronavirus is smaller than that).
The reason for the focus on 0.3 microns is because it is the “most penetrating particle size” (MPPS). Particles above this size move in ways we might anticipate, and will get trapped in a filter with gaps smaller than the particle size. Particles smaller than 0.3 microns exhibit what’s called brownian motion – which makes them easier to filter. Brownian motion refers to a phenomenon whereby the particle’s mass is small enough that it no longer travels unimpeded through the air. Instead it interacts with the molecules in the air (nitrogen, oxygen, etc), causing it to pinball between them, moving in an erratic pattern.
According to researchers this point between “normal” motion and brownian motion is the hardest particle size for filters to capture.
What we can take away from this, is that high filter efficiency at 0.3 micron size will generally translate to high filter efficiency below this size also.
For more discussion and details on the subject of respirator filters and brownian motion – see this great post at smartfilters.com.
Now lets look at specific research that measures the filter efficiency at 0.3 microns and below (coronavirus territory)…
- This article by 3M discusses research showing that all 6 of the N95 respirators they tested can efficiently filter lower than 0.1 micron size with approximately 94% efficiency or higher. The graph below is from that article, and illustrates this:
- Additionally, smartfilters.com have a great article on this subject, citing research showing that the respirators tested could filter down to 0.007 microns (much smaller than Covid-19). For example the 3M 8812 respirator (FFP1 rated) was able to filter 96.6% of particles 0.007 microns or larger. Suggesting FFP2 or FFP3 would achieve even greater filtration.
The below image (click it to expand) shows the size of the coronavirus, relative to other small molecules like a red blood cell, or the often talked about PM2.5 particle size.
N vs P respirators? (Oil Resistance)
The CDC explains that in the USA there are 3 ratings for protection against oils; N, R or P:
- N = Not resistant to oil
- R = somewhat Resistant to oil
- P = strongly oil Proof
What this means in practice, is for industrial settings, where the air might contain a lot of oil particles, if the mask isn't P rated, then over time the oil may degrade and reduce the filter performance.
For the vast majority of people trying to reduce exposure to Covid-19, it won't be necessary to protect against oils - this is primarily designed for industrial use settings.
Surgical vs Non-Surgical Respirators?
Alongside "regular" respirators, there are also what are often referred to as "surgical" or "surgically approved" respirators. These carry the aforementioned ratings such as N95/FFP2, but are also approved for fluid resistance. A qualification governed by ASTM F1862 - which covers the edge case in which an artery is punctured, and high pressure blood is sprayed directly at the respirator. To pass the test, the mask has to withstand this spray without leaking fluid inside the mask.
You can see why this type of mask if important for surgery, but it's not clear outside of that setting how much extra benefit it would provide. Regular N95/FFP2 masks will block things like coughs and sneezes.
The comparison table below shows how a regular N95 mask (8210), stacks up against 2 surgical N95 masks (1860 and 1870+).
Example of Surgical vs Non-Surgical Respirators
See this comparison table below for the key differences (source: 3M website):
|N95 Respirator 3M Model 8210||Surgical N95 Respirator 3M Model 1860||Surgical N95 Respirator 3M Model 1870+|
|Designed to help protect the wearer from exposure to airborne particles (e.g. Dust, mist, fumes, fibers, and bioaerosols, such viruses and bacteria)||✅||✅||✅|
|Designed to fit tightly to the face and create a seal between the user’s face and the respirator||✅||✅||✅|
|Meets NIOSH 42 CFR 84 N95 requirements for a minimum 95% filtration efficiency against solid and liquid aerosols that do not contain oil||✅||✅||✅|
|Cleared for sale by the U.S. FDA as a surgical mask||❌||✅||✅|
|Fluid Resistant - Meets ASTM Test Method F1862 “Resistance of Medical Face Masks to Penetration by Synthetic Blood” which determines the mask’s resistance to synthetic blood directed at it under varying high pressures||❌||✅ 120 mm Hg||✅ 160 mm Hg|
According to the 3M wesbite:
 "ASTM F1862 is a standard test method for resistance of medical facemasks to penetration by synthetic blood. This test is required because during certain medical procedures, a blood vessel may occasionally be punctured, resulting in a high-velocity stream of blood impacting a protective medical facemask. The test procedure specifies that a mask or respirator is conditioned in a high-humidity environment to simulate human use and is placed on a test holder. Synthetic blood (2cc) is shot horizontally at the mask at a distance of 30 cm (12 inches).
Surgical masks and respirators are tested on a pass/fail basis at three velocities corresponding to the range of human blood pressure (80, 120, and 160 mmHg). The inside of the mask is then inspected to see if any synthetic blood has penetrated to the inside of the facemask. Fluid resistance according to this test method is when the device passes at any level."
In essence, all 3 of these masks should be adequate, as per CDC guidance on 2019-nCoV and SARS. As mentioned above, where the 1860 and 1870+ are superior to the 8210 is when faced with high velocity liquid spray - which is possible during surgery (e.g. punctured artery), but unlikely in day-to-day usage.
Risks With Using Respirators
There are a number of possible risks with respirators that it’s worth being aware of, so that you can avoid making them.
- Not fitting and wearing respirators correctly – A respirator can’t fully protect you if it doesn’t fit your face. See OSHA guidance on fit testing and fit checking for more info.
- Touching the front of the respirator (which catches viruses etc) and then transferring that to other objects, which could eventually lead back to your mouth and nose.
- Taking unnecessary exposure risks because you’re wearing a respirator. Don’t let it give you false confidence. The safest thing is maintaining social distance.
For further discussion on these 3 points, see the expandable box below:
1. Not fitting and wearing respirators correctly
It's important to make sure that the respirators we use form a tight fit on our face, such that all air is being filtered and not passing in through the sides. Under ideal situations, one would try on a number of respirators to find one that fits perfectly. After that, you would "fit test" the respirator by putting it on tightly, then checking if you can smell or taste a chemical that you hold nearby. If you can, the seal may not be adequate. If you can't, that suggests you passed the fit test. See more about this process on the OSHA website - including details on their list of approved chemicals for fit testing. However, currently we're under pandemic conditions with shortages on both respirators and the chemicals used for fit testing them. Therefore we have to make-do as best we can with what we've got available. However, a focus on correctly fitting respirators is crucial.
2. Touching the front of the respirator
The front of the respirator can be thought of like a net - catching and filtering viruses and bacteria as we breathe. The problem then occurs if we touch the front of the mask and then touch our faces. In essence we need to treat the front of the mask like it's a hazardous material, and always wash hands carefully after touching it. Also avoiding touching the outside, and then the inside of the mask, because the inside has to make tight contact with your face, and is difficult to clean.
3. Taking unnecessary exposure risks
Don't let wearing a respirator give you confidence to take unnecessary risks. The efficacy of respirators is less than 100%, unfortunately. Both due to their filtering capacity limits (<100%) and due to the 2 points discussed above. So for example, don't go to an event with lots of people (especially if it's indoors), and think it's safe because you're wearing a respirator. The safest thing you can do is practice social distancing.
Examples of well known, reliable manufacturers of respirators include:
For more options, the CDC maintains a list of N95 approved respirators.
Surgical masks are generally speaking a 3-ply (three layer) design, with 2 sheets of “non-woven” fabric sandwiching a “melt-blown” layer in the middle. It’s the melt-blown layer that provides the filtering capability. A melt-blown material is also used in respirators, and thus you can imagine it’s more expensive and hard to come by recently, due to demand.
The melt-blown fabric is made by melting a plastic, then blowing it from either side at high velocity onto a rotating barrel. Done right, this results in a fabric composed of tiny filaments. For a more technical (!) explanation of the process – see here.
Not all melt blown fabric has the same filtering capability, some are better than others. Unfortunately we can’t test the filtering capability of the melt-blown layer without specialized knowledge and equipment. What we can do, however, is at least check that the melt-blown layer is present.
Below I show an example of a surgical mask (left) that came without the melt-blown layer. You can imagine that, given the extra cost and current scarcity of melt-blown fabrics, manufacturers might cut corners with this layer, so it’s worth keeping an eye on.
Choosing surgical masks that have been tested according to a set of standardized test methods (ASTM F2100, EN 14683, or equivalent) will help avoid low quality products. The ASTM standard for surgical masks (particularly levels 2 & 3) are primarily focused around fluid resistance during surgery. These higher levels don’t offer much extra in the way of protection from Covid-19 under non-surgical conditions.
If you see reference to BFE95/BFE99 - BFE = "Bacterial Filtration Efficiency" - and the score = % of particles blocked, with a mean particle size of 3 microns (+/- 0.3microns) - source.
Similarly, PFE = Particle Filtration Efficacy. ASTM F2100 measures the PFE down to 0.1 microns (source).
This table by Nelson Labs gives more examples of surgical mask specifications, including BFE/PFE.
Whilst FFP2/FFP3 or N95/N100 are the gold standard as far as face protection goes, what about surgical masks, do they provide any protection?
Strictly speaking, surgical masks are primarily designed to protect vulnerable patients from medical professionals. Stopping the wearer (e.g. surgeon) from spreading their germs when coughing/sneezing/speaking. So they’re designed to protect patients, not to protect the wearer.
An obvious flaw with surgical masks compared to respirators is their lack of a tight face fit, which leaves gaps around the edges.
There isn’t currently research available on the efficacy of surgical masks (or even respirators), for protecting wearers against the coronavirus. Although this isn’t totally surprising given how new the virus is.
In lieu of that, the below looks at research around the use of surgical masks and N95 masks in the context of influenza, looking specifically at the protection given to the wearers. Influenza may be a good virus particle to compare it to, as they are both transmissible through droplets and aerosol, both cause respiratory infection, and both are similar in particle size.
N.B. Please don’t conflate the comparison to the influenza particle as suggestion that they are comparable illnesses – current data suggests that the coronavirus may have a higher mortality rate.
In the first study we will look at, 2,862 US health care personnel were split into 2 groups, those wearing N95 masks and those wearing surgical masks1. There were 207 lab confirmed influenza events in the respirator wearing group, compared to 193 in the mask wearing group – a difference that was not statistically significant.
In the next study, Canadian nurses were split into 2 groups, those wearing N95 masks and those wearing surgical masks. There were 50 cases of influenza in the surgical mask group, compared to 48 in the N95 respirator group2. Again, no significant difference.
So where does this leave us? Those 2 studies suggest that surgical masks are approximately comparable to N95 masks when it comes to preventing influenza illness in close contact clinical settings. What this doesn’t tell us, is whether they’re better than wearing nothing on our faces.
To find that out, we need a study that has a control group that doesn’t use any facial protection. Due to ethical considerations, those studies aren’t abundant, but we do have at least one.
In this Australian study, they looked at 286 adults in 143 households who had children with influenza-like illness3. For clarity, influenza-like illness is not the same as laboratory confirmed influenza. It’s diagnosed by symptoms like fever, dry cough and feeling sick, which could mean influenza, but could also be caused by the common cold or other viruses. They found that adults who wore masks in the home were 4 times less likely than non-wearers to be infected by children in the household with a respiratory infection. There is nice analysis of the study here by Imperial College London.
It’s definitely fair to note that this Australian study was very small, and could not be considered definitive by any means. That being said, we’ve got to work with what he have, and this at least gives us some data points:
- Wearing a surgical mask or N95 (FFP2) respirator was better (in the study) at protecting against influenza-like illnesses than wearing nothing at all
- Whilst we can anticipate surgical masks to be inferior to respirators, the studies above suggest they are not as inferior as one might assume. For example the first two studies didn’t find a significant difference between surgical masks and N95 respirators, when protecting wearers against influenza.
- Important to note that we’ve used influenza protection as a proxy for SARS-CoV-2 (coronavirus). This is done because SARS-CoV-2 is new and there are no comparable studies on it. But of course the drawback is that it still leaves a lot of uncertainty, as SARS-CoV-2 may act quite differently in terms of transmission.
In a lab setting, with artificial conditions, we find that surgical masks are able to block 80% of particles down to 0.007 microns. Compared to the 3M 8812 respirator in this study which blocked 96% (FFP1 rated). This generally aligns with our discussion above.
In conclusion: we don’t know how much protection surgical masks provide against the novel coronavirus. However, the above at least suggests that a surgical mask may provide more than zero protection – and that’s worth being aware of. It makes sense to only wear them for protection as a method of last resort – with respirators being the primary choice.
It is much safer to avoid the company of people who are sick or potentially sick, and to reduce social contact overall, especially to large groups of people (see the social distancing section below). To repeat, the use or surgical masks would have to be a last resort – and wearing one should not encourage anyone to take unnecessary exposure risks.
If we are in the presence of someone sick, who has/might have the coronavirus, it makes sense for them to wear a mask or respirator to reduce their ability to spread the disease.
DIY / Homemade Masks
Early on in the pandemic, the CDC announced guidance to American citizens that “cloth face coverings” should be used in public settings where social distancing measures are difficult to maintain. At the time, there was quite a shortage of masks, so people were making their own. I’ve left this section of the article up, as it briefly covers the efficacy of household materials.
So how does one make their own mask?
Firstly, it’s worth noting how various household items compare in terms of filter efficacy and breath-ability. For that, we can refer to a Cambridge University study (link), which revealed “the pillowcase and the 100% cotton t-shirt were found to be the most suitable household materials for an improvised face mask”.
Interestingly, other items such as vacuum cleaner bags and dish towels showed greater filtration capacity, so why didn’t the study pick them? Unfortunately those items performed badly in the breathability tests. A mask is little good if you can’t breathe out of it. See this write-up of the study for more details (and nice graphs!)
Of course, it goes without saying that generally the protection these DIY masks is below that of surgical masks and respirators.
What are respirators protecting us against?
A primary reason for wearing a respirator is to protect from droplets. For example if a sick person coughs or sneezes when in close proximity to us, the respirator forms a barrier to prevent their bodily fluids reaching our face.
Droplets are generally large, and gravity drags them down to land on objects, rather than staying in the air. So they don’t travel very long distances. There is however research into micro droplets, which get ejected even during talking. This Vimeo video made by Japanese researchers, captures micro droplets on video using high speed cameras. We know large droplets play a role in transmission, but it’s not yet clear what role micro droplets play.
What may remain in the air for some time are aerosolized virus particles. So for example, you could imagine someone creating two issues when sneezing, the first are ejected droplets, which travel a short distance, then second, aerosolized virus particles that stay in the air for longer.
Currently there is debate and uncertainty around how long Covid-19 can remain aerosolized, and how much of a risk that vector is compared to others.
What we can do is be aware of what research currently says, and err on the side of caution until its been confirmed.
Scientists at the National Institute of Allergy and Infectious Diseases (NIAID) published a study in NEJM (link) on what can happen under controlled lab conditions. They used a nebulizer, which creates an aerosol from liquids, and tested how long the virus remains measurable in the air whilst aerosolized. They also tested how long the virus was measurable on other surfaces. Their results showed the virus remained measurable for the full duration of the aerosolization experiment; 3 hours.
See the graph below for more details:
Dr John Campbell has a YouTube video discussing the NIAID paper in more detail.
Mouth & Nose
Then lastly, whilst the respirator covers our face, it makes it very hard for us to touch an object with the virus and transfer it to our mouth and nose. This is a kind secondary benefit, in addition to the two mentioned above. We just need to make sure we wash our hands carefully as soon as we take the respirator off.
Hopefully if you’ve stumbled across this article, and you were confused about the difference between N95, KN95 and FFP2/FFP3 masks, this has cleared things up for you.
If you have any further questions, please leave them below in the comments.
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- N95 Respirators vs Medical Masks for Preventing Influenza Among Health Care Personnel – A Randomized Clinical Trial – Lewis J. Radonovich Jr, MD et al. – JAMA – Sept 2019
- Surgical Mask vs N95 Respirator for Preventing Influenza Among Health Care Workers – A Randomized Trial – Mark Loeb et al. – JAMA – Nov 2009
- Face Mask Use and Control of Respiratory Virus Transmission in Households – MacIntyre et al. – Emerging Infectious Diseases Journal – Feb 2009