Face mask primer

I know there’s a lot of confusion out there about face masks. I thought I would try to clear a few things up.
Basics. There are two purposes for a mask

  1. to protect the user
  2. To protect other people
    DIY facemasks are meant to protect other people, not to protect the user. This is important for the community. My argument is that it’s different inside hacker space.

Sorry had to go more to follow

Disclaimer, these are my opinions as an emergency room physician. Take them for what you will and do your own research.
Spoiler: my recommendation within Hackerspace as to wear

  1. An 95 mask with strap going around your head not over your ears or
  2. A P100 respirator or
  3. a PAPR For woodworking.

DIY masks are important to protect the community. We have other issues inside hackerspace. Most important of which is best. I believe we should protect the user. Let’s break it down
You will see different designations.
NIOSH it’s a US regulatory agency.
You will see a letter at the beginning of the designation.
N refers to whether or not it protects against oil based products. N means no. P means yes.
Next is a number which refers to what percentage of particles larger than .3 µm it filters out.
95 means 95% of particles greater than .3 µm
99 means 99% of particles greater than .3 µm
100 Means 100% of particles greater than .3 µm.
So an N 95 means it will filter out 95% of particles greater than .3 µm that are not oil based.

KN 95 is a Chinese designation. Although the designation which suggest it is as good as an N 95, it is not. But it’s pretty good. Better than the DIY or surgical masks people are wearing. At one time you could not get an N 95 but you could get a KN 95.

FFP is a European designation.
FFP1 filters out about 80% of particles .3 µm or greater
FFP2 filters about 94% of these particles. Roughly equivalent to N 95
FFP3 filters out about 99% of these particles
To make it even more confusing, air conditioner filters use a totally different system. And HEPA filters use a totally different system.

Here’s where it gets really confusing. The size of the
SARS-CoV-2 (which is the proper name of the coronavirus which causes the disease named COVID-19) it’s between 50 to 200 nm. Which converts to .05 to .2 µm. “But that’s much smaller than what the N 95 filters out“ True. But the multi layer fabric and nonwoven nature of the N 95 mask allows it to trap the coronavirus about 99.8% affectively. Confused yet? This is one of the reasons an N 95 is superior to the KN 95. It’s number of layers.
But we’ve left out a very important part, how the mask attaches.
The over the ear loops are convenient but not as tight as the around the head. After several hours your ears begin to hurt (believe me, it gets bad) most American N 95s have head straps. Many people have devised workarounds such as a head strap with buttons on it to hook the ear loops over and strap around your head. This could even be done with paper clips in a rubber band. The bottom line is it must be tight fitting against your face to be effective. One other factor when buying masks is breathability rating. Many of them are easier to breathe in. For people that start out with lung problems, this becomes a major issue on being able to continue wearing the mask. I prefer the 3M masks. I can give specific recommendations if people want. From personal experience I can tell you that wearing a mask with poor breathability gets better over time. It’s kind of like your lungs are pumping iron.
I could go on and on but I think it’s enough for now. I hope this is helpful for someone.

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Please do not authorize P100 mask as an alternative. The do not filter the breath being exhaled, and thus leads to saturation of the air column in the space. Not everyone will have the proper N95 and could be needlessly exposed.
While the virus can theoretically psss through the filters, those virus are suspended in essentially water droplets. That makes ghe effectively larger than the filter media.
We all do our part. Wear the best mask you can find, AND stay the proper distance apart.

To wear a mask that ONLY protects the wearer, is just selfish, at least, and wreckless, at worst.

Peace, Wolf

Sorry, I meant to address the Exhale valves Separately.
Exhale valves are available not just on P 100s but on many masks. The Center for disease control’s position on this is that they may be covered with a suitable covering or disabled.
In the hospital, people will cover the Exhale valve of an N 95 with a simple surgical mask.
The exhale control of Most of the DIY masks or surgical masks is almost nonexistent. With most of the woven materials, the virus goes straight through the mask. If the mask is not tight fitting, it leaks around the edges. A rule of thumb: if it fogs your glasses or Does not make it somewhat difficult to breathe in, it is leaking. Remember, the virus is 0.05 to 0.2 microns. It would also be just as selfish to wear an ineffective mask as one with an unprotected exhale valve. But this is not selfishness. People are trying to follow what they are being told.
That is not to say that these don’t give some control the spread. These diy masks and the masks with Exhale control Minimize the force and distance of the aerosolization pattern. Remember its primary mode is droplet spread. A Sneeze or a cough in any of these devices travels and much shorter distance. Social distancing remains important and it’s probably the reason we’re not spreading Covid at Hackerspace. We are naturally socially distanced because of the nature of the work.
Covid is not the only issue. Protection from the fine dust is as important. This is the main reason I was Advising to wear the N 95 or P 100 masks. I still think KN95 Are a good alternative to an N95 If they are not available. KN 95s Are readily available and far superior to a DIY mask or a surgical mask. This was an issue before Covid and will remain after Covid. The Type of masks people have been wearing for Covid provide a little protection for inhaled dust. They filter out the larger particles, but not the sub micron particles.
LET ME BE CLEAR! I want to protect everyone involved, both wearer and The community around the wearer of a mask From COVID-19 and other infections disease but also From the dust particles which are a major health risk. We are making a real effort to get our dust situation under control.

Again, these are my personal opinions. Do your own research. But be responsible. Hackerspace has an incredible resource of brain power. Let’s use it to get past these problems.

Fred R. Martin, M.D.

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Dr Martin

My point is, do not promote the idea that ANY mask with an exhaust valve, as suitable for COVID19 requirements. You can’t disable the valve on a cartridge (P100) mask, there are valves on the intake side that prevent breathing back through the cartridge, which severely shortens the life/effectiveness of the cartridge. One of my duties in my 20 year Naval career, was a gasfree tech, I know all about particulate concentration (PPM) rates.

No mouth/nose mask, however perfect the fit, seals 100%. Talking, moves the jaw, causing temporary gaps…
Creases in your face, cause problems, compounded during speach…
Then there is facial hair, compounded during speach…
Perfect seals are only achieved with a full head hood.

I am completely on board, wearing masks. Any mask, worn properly over mouth AND nose. Yes, there are great masks, and there are poor examples, but to suggest the the poorer variety are equivalent to no mask, in my opinion is blatant negligence.

At this point there is very little, “confusion” as you said, about masks, just ignorance and political polarization. 70M Americans just proved that beyond a doubt.

I have been out there in the real world, wearing my mask and keeping my distance from the idiots. I no longer bother, wasting my time, or risking my health, trying to help those individuals that are not complying. I just avoid and move on. Maybe it is nature’s way of cleaning up the gene pool.

Stepping down from my, soap box.

Peace, Wolf

I agree with @Fmartin that dust is another important problem that surgical masks and DIY masks seem ill equipped for, and I agree with @LoboFPV that masks with exhalation valves, and without further protection like another mask on top (seems like a hassle) are not adequate in the current pandemic – for that matter, face shields alone are not either.

I was looking into masks that could potentially solve both of these issues and came across the RZ mask, which seems like a good option in the wood shop. They have exhalation valves, but they also sell an exhalation valve cap that plugs the valve and doesn’t allow exhalation to escape that way. They strap behind your head, as Fred mentioned, as well.

I’ve been looking into getting a good dust filtering mask and these (with the valve cap) seem like a good option to me.


Here’s another option. The Gill mask. I have been using this for the last couple of weekends. Silicone face seal. Very comfortable. Make your own filters. Not rated, since there isn’t testing for it. I’m also posting the material I am using. That is where you can go crazy, going through material processes, MERV ratings, if supplied, etc… At 3 layers, I can still breath pretty easily.

$8 for 5m of material that is about 8 1/4 (Amazon listing says 7 1/4, but my tape measure disagrees) inches wide. The filter frame is about 1.5 x 2.5, so I can get 4 filters across. I triple fold it first, then place the frame over it, and cut it out. If you want to quad fold, cut it 2.5 inches long. If you were to quad fold, you’ll get 78 refills out of the 5m length. At triple fold, a little over 100 refills, etc… You can game the orientation and folding to optimize, but you get the idea.

The frame is pressed against the silicone for a seal.

KN-95 are between $1 and $3 each. At 75 filter changes per $8, these are .10 each. Then it’s just a matter of how often you change one or the other.

Finally, you can wash the entire mask when you change the filter.

I have an old RZ mask, and while I like it, the Gill is far more comfortable and seals around my nose better.

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Thanks Charlie! They even sell N95/kn95 inserts in bulk for other reusable masks which could be cut to fit. Is the seal tight against the cut piece?

Fred R. Martin, M.D.

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The cut piece fits in a plastic frame. The frame is 2 pieces with a hinge at one end. So yes. The frame is under compression, sealing against the silicone.

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Do you happen to know what the Merv rating is of the fabric you’re using?
I like that it is non-woven. Some people are using MERV 13 in their homemade filters. Hepa Filters are roughly equivalent to Merv 17 to 20. None of these rating systems directly correspond. Merv 13 is said To filter larger viruses. Corona as a smaller virus. still better than the normal DIY stuff. The manufacturers won’t tell you that it’s OK to breathe directly through these. Lots of people are doing it though. It is possible that some other chemical or binder may be being released. I know if no apparent damage from using these (in fact I did it myself when 95’s and kn95s were unavailable.). I’m still sticking with the N 95/KN95 regular masks. This is probably a good solution though. I may buy one to do a hands-on evaluation. Thanks again.

Fred R. Martin, M.D.

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They don’t provide a MERV rating. Looking at other sites on this, there are discussions over spun bond PP fabric vs meltblown PP fabric. One site claims that MERV fabrics can shed fine particulates, and that meltblown can shed, though they admit they say “might” and provide no back up. I am seeing conflicting statements on N-95 being spun bond vs melt blown. One website, Makermasks, says to only use spunbond, and NOT to use melt blown. Yet N-95 are melt blown.

In general, PP material is static charged, which increases the filtration effectiveness by attracting contaminants. That is one reason why these fabrics are preferred over cotton or other materials.
Some of the PP fabrics are probably crap. No great way to pick through them.

When I double layered, I saw some of the dust on the inside layer. At that time, I was resawing long lengths of wood, and the vacuum doesn’t do a great job (if you use one at all). My head had sawdust all over it. When I went to triple layer, no dust on the inside. I’m cutting pecan, so it’s easy to see the dust layer. Not seeing dust on the inside is not absolute proof, but I smelled less of the pecan as well. I actually need to experiment with a 4th layer. I do notice some reduced breathability from 2 to 3 layers. But even at 3 layers, it’s easy breathing. And what I have is a pretty thin film to begin with.

Where this falls on the spectrum, I don’t know. Closer to N95 than fabric, for sure. Better than N-95, not sure. I do think that with the right material, thickness or layers, it can be better. The face seal is very very good, so it’s really down to the filtration media.

You could put disposable surgical mask material on the inside layer to help catch stray filter pieces

Fred R. Martin, M.D.

I haven’t researched this at all but seems to me that one of the potential benefits of a P100 respirator with valves (or any respirator with valves) would be the ability to use different materials for inhale vs. exhale path. I could imagine a substrate on the exhale side that is more likely to disrupt the virus envelope than standard filter material, but might not be something you necessarily want to inhale through.

I wonder if something as dumb as parallel soap/detergent soaked layers would work? Presumably droplets would land on soapy surface and deactivate. I wonder if copper mesh would work? I’ve heard that copper surfaces have some antibacterial properties but don’t have any clue if they can disrupt the coronavirus as well.

Just spitballing. In the mean time, is there a best practice for using a P100 style respirator with vent that will minimize transmission to others? I prefer them in a shop environment for dust protection.

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Copper is known to inhibit the virus. There is an Israeli company that sells a copper impregnated mask (not copper mesh over a mask, it is soaked with copper nano particles) that was developed for cancer chemotherapy patients. They are susceptible to a wide range of infections. Other metals have antiviral and antibacterial activity such as silver and zinc.

Fred R. Martin, M.D.

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Here is the link to the Israeli mask

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I’ve made 3d printed adapters that fit into the 3M 7000 series exhaust valve and allow for the attachment of standard 3M bayonet filters for the exhaust or printed filter holders. Different attachments are easily swapped with Meshmixer. The parts can use nanocopper flexible materials where appropriate to lower self-innoculation / cross-contamination risk and copper coatings for the original 3M PBT / ABS / PE parts can be added. This solves the majority of the problems and is more cost-effective with daily use. I had initially planned to use the space equipment but have been able to do it at home.

If people would like to use them I can fwd some files with materials and print settings. Cost for materials for the exhaust adapter are about $1 ea, $4-8 if using nanocopper. There are simple changes that can improve them that would only take 15min-1hr if someone is experienced with Solidworks/Fusion360 and would like to do that. I spliced other parts together to get something that worked well enough in a short time frame and simply don’t have the time to re-learn CAD to add them myself and this worked “well enough”.

Most exhaust covers / filter add-ons don’t provide sufficient surface area for the exhaust. The too-small filter will be restrictive, collect moisture from the user’s breath, and become more restrictive. Excess exhaust restriction also exacerbates poor fit / looser elastic where the exhalation pressure breaks the seal of the facial gasket, especially around the nose. This is one reason why the higher quality mask gaskets loop backwards inside for a pseudo-double wall. Initial exhalation flow redirects against the inner raised fold instead of the skin/gasket intersection and has time to open the valve / filter pores instead of breaking the seal.

If you know someone with compromised respiratory function, 3M has a newer series of P100 electret filters with about half the resistance of a standard one. These are hard to come by, but are the “TWO HUNDRED” designation for circular bayonet filters. 2091 vs 2291. 2291 refers to the newer version. Please don’t waste the two hundred series if the easier breathing isn’t medically necessary. Before COVID 3M was phasing out the traditional cartridges to transition fully to these.

I’m unaware of a scientific reason that high quality respirators with filtered exhaust aren’t standard by now. Vocal clarity can be improved with the addition of acoustic membrane windows if necessary.

One reason why mfg’s are reluctant to approve materials such as Halyard/medical instrument wrap for filters is that ethylene oxide is used for sterilization followed by chamber evacuation. There is a small residual that was considered negligible with the intended use but would be inhaled if used as a filter. Ethylene oxide is a known carcinogen and since there isn’t a way for the mfg to control the use case they don’t know what residual dosage would be inhaled and are simply saying don’t. Furnace filters and fabrics such as military BDU’s often include fire retardants.

Apologies for run-ons and lack of organization. I thought that some might want to use the space to make their own to use with the COVID situation getting worse and I lack the time(and sleep) to write more concisely.

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Great job! I think this is the meaning of discourse. Great brainstorming. Lots of differing opinions. these are the seeds from which solutions come.
I would be interested in the files.
I got one of the masks that @cfstaley recommend (The Gill mask). I was quite impressed. Great fit, very comfortable, filters both incoming and outgoing. Washable. I found two rolls of Merv materials (Merv is it rating system used for air conditioning filters.) There was Merv13 and Merv 16. I bought a roll of the Merv 16 which states it is to be used with masks. It can be cut to size. Because of the nature of the Gill mask, It is tightly bound in the holder at all edges. I also found HEPA filters which would be the equivalent of P 99/P100. They were a bit more expensive but still very affordable. I think these mask will provide protection for both COVID-19 And for dust. They don’t come with a filter, just so you know. About $25. Parole of the Merv 16 material Which was 11.8 inches by 59 inches Was about $39. But it will make a ton of filters. I ordered four more for other family members. This would also be great just mowing the lawn. Will filter out dust and pollen.

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Thanks @fmartin for starting this thread, and to the participants who shared their knowledge. Call it confusion (or ignorance if one prefers that label) on my part, there was a lot I didn’t know. No I do! I appreciate the excellent reference material.

Note: Edited typo

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Many N-95 configurations use SMS layer configurations. Hydrophobic spunbound, meltblown electret, hydrophobic spunbound. This is not because of shedding. They’re typically charged with Corona discharge very high voltage. Moisture reduces the charge carrying capacity so the hydrophobic layers help keep it dry while also acting as a splash guard.

Some commonly used solvents like isopropyl alcohol permanently insert themselves into the polypropylene polymer chains and they will no longer hold a charge - an issue with people using hand sanitizer and rearranging their mask.

While the Gill mask is much better than most I’ve seen, I don’t see a reason these days to not just get 3m or Honeywell 7000 series mask, also with silicone seals, and convert the exhaust for a filter now that they’re more available. The P100/P3 filter much more and can last months in an indoor setting. The lifespan rating for the P series filters is referring to the ability to protect vs aerosolized oils in a factory environment. The remaining particulate lifespan is actually much, much longer. They are easier to breath in with the greater surface area provided by two cartridges and don’t get increase resistance / decreased filtration capacity from your breath wetting the filter. The exhaust filter can be changed at lunch along with a moisture absorber pre-filter.

It is common for people to think of filters like smaller hole versions of kitchen strainers or spider webs, but this is not the primary method of capture for air filters. The maze-like mat of ultrafine fibers and/or layers force the air to wind around and the larger particulates smash into the fibers and get embedded in them through impaction. Smaller particles, less than 0.3 Microns, are subject to Brownian motion where you stop assuming air is uniform “air” and the relative amounts of individual gasses, chemical reactions, and electrostatic effects dominate the microscopic movement. The charge carrying filters are actually much more efficient at removing these smaller particles, like aerosolized droplets, than their listed rating. 0.3 Micron particles are a problem because they are both too small impaction and too large for Brownian dynamics, but I’m not aware of concern for COVID related sizes being common in this range.

Welders/metal grinders and certain dangerous solvent/adhesive chemical users do need to be concerned, which is why filters exist specifically for them.

Rubber band and gaffing tape added for redundancy if it gets knocked or printer filament impurities / extrusion inconsistencies cause unexpected part weakness.
Exhaust uses standard 3m bayonet attachment to simplify part management. Bayonet orientation angle can be adjusted to increase visibility for right or left handed users. Inside of the red adapter you can place a cut piece of shop towel, loosened Q-tip, or cotton ball to absorb moisture and increase filter lifespan. I’ve subsequently copper coated most pieces and keep a couple so I can place one in a container and come back to it later with low chance of surface cross-contamination. COVID surface cross-contamination isn’t much of a concern with freq. hand washing, but all the other hazards like MRSA still exist and are reduced.