Normally, CPCSupport talks about condensation particle counters, like the TSI PortaCount, and the steps for using them. However, these are somewhat expensive devices, unnecessary unless you have a substantial interest in fit testing. For most people, Qualitative Fit Testing easier and cheaper way of testing to integrity of a purchased mask, by using human senses to determine mask-seal leakage. For most people that don’t require fit testing for work with asbestos, lead, or whatever, the qualitative approach should be more than adequate. Don’t feel pressured to buy a PortaCount because it’s what’s talked about a lot.

Each section here was originally written out in a separate Mbin/Lemmy post on Fedia.io. (Backup at Discuss.Online) Here, I’ve condensed them all into a single Wiki page (see bottom section for the original link), for ease of reading, and for (hopefully) better search engine reach.

Why do Fit Testing? (Abridged)

Did you know: There’s more to “masks” than one may think initially and, as the endless papers continue streaming out of academic journals and Google Scholar, contrary to popular belief, the pandemic that started in 2019 hasn’t ended? In the context of pandemic denialism, and unmitigated viral evolution, it has become increasingly important to wear good quality PPE, especially in the context of Long COVID.

(More pressing examples: Cell Paper, KABC Article, and that’s just scratching the surface. Also note: XBB is virtually extinct as of 2024. So a paper that’s literally not even 2 years old as of March 2024 is already out of date.)

In other words, the SARS-COV-2 COVID pandemic is becoming increasingly high stakes, sort of like that tiny, rookie unit conversion error on Mars. How do we know one error can substantially affect your fit factor? Well, due to the flood of low-quality PPE (cough surgical masks) that came out in 2020, people have increasingly sworn off taking any measures, (see also: survivorship bias), despite the fact people in NIOSH, MSHA, and the Bureau of Mines, have, since the Progressive Era, taken great pains to ensure masks work through qualitative fit testing, later quantitative fit testing.

See also: This link.

Although we aren’t going to cover quantitative fit testing in this short wiki article, we’ll bring up certain concepts, mainly used by quantitative fit testers, like the PortaCount, to provide context to the theory behind the use of qualitative fit testing. Then, we’ll cover the procedures, and finally, places to get cheap fit testing equipment, without having to buy a PortaCount.

Now, a couple paragraphs, ago, I brought up the term fit factor. What exactly does that mean?

Common Fit Testing Terms (source)

Fit Factors

The fit factor is how much cleaner a mask is inside, compared to outside. Hence the equation:

  • Fit Factor = Ambient Concentration / Mask Concentration It seems cryptic, but it really isn’t that hard if you imagine aerosol particles like apples inside the bucket vs outside the bucket. The number you get is essentially how much cleaner the air is inside the mask than it is outside. For example:
  • A fit factor of 10 means the air inside is 10 times cleaner than outside.

Total Inward Leakage

A fit factor of 10 also means that there’s a Total Inward Leakage of 10%. Which makes sense: if you have 10% of the count of apples outside the bucket equals the count of apples inside the bucket, then there are 10 times as many apples outside than inside. Here’s the equation:

  • Total Inward Leakage Percentage = 1 / Fit Factor * 100 For example:
  • For a fit factor of 20, 1/20 = 0.05, 0.05*100 = 5% total inward leakage. Hey, that’s the allowable filter penetration limit of N95 masks!

Assigned Protection Factor

There’s a lot of smoke and mirrors on how assigned protection factors came to be, but if you ever come across this term in NIOSH or OSHA literature, just remember this formula:

  • Assigned Protection Factor = Fit Factor / 10

Fit Factor Assumptions

OSHA assumes that if you pass a qualitative fit test, and you pass, your fit factor is at least 100, and vice versa. If you’re skeptical… well, yeah. Who came up with this arbitrary number for a subjective fit test? Not to mention, we hallucinate all the time, we lose our sense of smell, so how can one trust that we have at least a fit factor of at least 100? The short answer is, you can’t, really. However, when you take into account the risks of:

  • Doing no fit testing, and being forced to make assumptions about your mask leaking,
  • Versus going hundreds-to-thousands of dollars out of pocket for the security of a calculated fit factor, which may not be an option for you,
  • Versus doing qualitative fit testing for a few dozen USD, The third option starts to seem like a reasonable risk proposition, in the context of harm reduction, especially if you’re not doing work with asbestos or something. SARS COV 2 probably isn’t going to kill you if you happen to get infected occasionally due to a faulty qualitative fit test. But I should elaborate on the harm reduction benefits, because even qualitative fit testing actually more consequential than that these days:

Woof!

  • For people who don’t fit test, and wear surgical masks, still get a fit factor of 2. Let’s assume that means a coin flip chance of getting infected every 10 minutes with such a mask, if someone infected is around. Over an hour, that’s 0.5^6, which, if you plug that into your calculator, is basically indistinguishable from not wearing a mask at all. Woof. Not worth it.
  • However, if you can get a fit factor of at least 100, you can reduce an almost 0% chance of not getting infected, to a coin flip every 10 hours at 0.99^60. At 0.99^6, that’s a 94% chance of not getting infected. Pretty substantial improvement. Well, that certainly seems worth pursuing. Even if the numbers were worse, like a coin flip every minute at a fit factor of 2, that’s still a reduction of risk to a coin flip every hour at fit factor 100. Thus, any form of fit testing makes wearing a mask from being a pointless activity, on an individual level, to something worth pursuing. Especially considering:
  • If your effective mask fails the fit test, you’ll likely do little better than a fit factor of 2. Documented, unfortunately. Mars climate orbiter, anyone? Of course, it gets more complicated, more effective, and less burdensome on the individual the more people mask. This (admittedly stupid) model makes the assumption that no one else is wearing a mask, which… is unfortunately the case these days. But, if despite all this, you feel qualitative fit testing is inadequate for your risk management, then by all means, get a PortaCount. CPCSupport (backup) exists for a reason.

Qualitative Fit Testing Procedure (source)

Update: See a more detailed procedure here: https://www.youtube.com/watch?v=-UEKtJRI4pk

Oh, where to begin? To start, viruses are massive compared to other harmful substances. They’re made of proteins, which are made of organic compounds, which are massive compared to water, let alone individual atoms. That’s unlike gases, which are closer in size to water, since they’re usually small organic compounds, which as we’ve established, are smaller than proteins, which in turn, are smaller than viruses.

So you can imagine separating oxygen, nitrogen, and carbon dioxide from other gases requires an enormous amount of power, not unlike the energy requirements of running a desalination plant, so the only practical way to stop gases from going through requires a chemical reaction, like VOCs with activated carbon. Or VOCs and your nose, which is less desirable for obvious reasons.

Last time I checked, electrostatic filtration media doesn’t contain activated carbon. So each of these qualitative fit test methods has to be artifically packed into larger particles, to prevent “smelly particles” from making it through the mask, and you smelling it. Because surprise surprise, without an instrument telling you your fit factor, the only way you know you passed a fit test or not is your nervous system. Good luck to you if some of your nerves are disabled by COVID…

And some smells, no matter how minute they become after packing, get detected anyways. Maybe someone is hypersensitive to one Bitrex compound making it through, even if it would have no relevance in the real world. We call these people supertasters, the opposite problem of not being able to smell (or taste) at all. Good luck with consistency!

So with all that said, here are the general procedures for fit testing qualitatively, with some noted hazards and pitfalls:

Bitrex, Banana Oil, or Anything Else That Requires Sense of Smell

Update: See a more detailed procedure here: https://www.youtube.com/watch?v=-UEKtJRI4pk

Notes:

  • You need a nebulizer to pack these smelly compounds into a particle large enough to not pass through N95 electrostatic filtration media.
  • You’ll need a hood to contain whatever aromatic compound you’ve chosen.
  • Try to finish the fit test quickly, to avoid aromas making it through the mask due to evaporation.

Steps:

  • Without a mask, don the hood.
  • Have someone spray the substance inside the hood. Remember the smell. If you can’t smell it, try a different substance.
  • Take off the hood, and air it out.
  • Put on your mask.
  • Follow the fit test procedure outlined below the othe qualitative fit test methods. If you detect a smell, your fit test is a failure.
  • Ventilate before doing another fit test.

Irritant Smoke

Notes:

  • DO NOT USE IRRITANT SMOKE NEXT TO A PORTACOUNT.
  • Irritant smoke tubes are made to spec by manufacturers, and should automatically produce large enough particles for fit testing. DIYing it yourself is probably not a good idea, and would probably not be OSHA approved.
  • Try to finish the test quickly, or your respiratory system will have a bad time. This irritant smoke, after all, described in the MSDS as a bit of a hazard.
  • Do not use a hood. See above.
  • Unless your N95 scores at least 100 on a PortaCount in N100 mode, it will likely fail. This is because the N95 spec allows for filter penetration. That does not necessarily mean it runs afoul of any specifications.
  • Ignore any smells you detect. Failure is determined through involuntary coughing.
  • If you can’t feel pain, or have never coughed in your life, then this fit test method is probably not for you.

Steps:

  • Put on your mask. Hope your reflexes work.
  • Have your assistant wear a mask too, to avoid irritant smoke exposure.
  • Have your assistant read the instructions on how to activate the smoke tubes.
  • Once activated, follow the fit test procedure outlined below the other qualitative fit test methods. Have your assistant spray irritant smoke around your mask during exercises. If you audibly cough, even just a little, your fit test is a failure.
  • Ventilate before doing another fit test.

The Fit Test Exercises

Exercises last 1 minute each. Here’s the old OSHA protocol:

  1. Normal Breathing
  2. Deep Breathing
  3. Head Side to Side
  4. Head Up and Down
  5. Talking
  6. (optional) Grimace
  7. Bending
  8. Normal Breathing

Note: The CPC protocol includes grimace, but lasts only 15 seconds and doesn’t count towards the fit factor score. Grimace is completely excluded it from QLFT, but you can add it back in if you want.

Where to buy

Here are some known cheap options:

  • You can go onto Google Shopping and get the VeriFit if you’re comfortable with irritant smoke. Costs about $40-$70, depending on the vendor.
  • Fittests4all <dot> bigcartel <dot> com also ships a $40 fit test kit, however, they’re often sold out. So much for that…

One More Thing:

Don’t forget to do additional fit tests every few months. Especially if you’re under 30, your face could be changing rather dramatically. And if you’re wearing an elastomeric, a.k.a. a hard plastic, reusable mask, you don’t want to be caught off guard with a mask in the process of breaking.

Wiki page version

Wiki version here