You do need fancy equipment, but not quite that fancy. The one thing you absolutely can't do it without is a nebulizer. This is a sort of modified spray bottle which converts liquid into aerosol. A regular spray bottle won't work, because the droplets it produces are too large. The nebulizer I have works by having a channel which pulls liquid up and suspends a drop of it in the path of bursts of air, which you produce by squeezing a rubber bulb. This is an expensive item because it's in short supply, but it's a simple plastic part that would be very cheap if it were made in bulk, and it doesn't seem impossible for someone to make a replacement home with hand tools and some expertise.
(A commercial fit-test kit will typically contain two nebulizers, when you only need one. The reason for this is because if you're following the formal procedure, you first use a low-concentration version of the aerosol to make sure the person has a working sense of taste, then a high-concentration version for the real test, and if you're testing a bunch of people in a row you don't want to have to clean out the nebulizer each time. For home use, you only need one.)
(The liquid you put in the nebulizer is just saccharin in water; you might as well use a bottle that's labelled as being for fit tests, but if you can't get one you can get saccharin powder at a grocery store and mix it with water yourself. Some test kits use denatonium aka Bittrex instead, supposedly because some people can't taste saccharin. A saccharin test is much more pleasant. I noticed that saccharin solution sometimes clogged the nebulizer, by leaving a crystalline residue when it dries out, and denatonium doesn't.)
The formal fit test procedure also uses a hood, which holds aerosol in place while you hold your head at various angles and read a passage aloud, in case gaps open only while you do that.
When I've administered fit tests to people, about half fail. Cheap KN95s usually fail by having big gaps around the edges, which can be fixed by taping them down with medical tape, if you really need to. Rubber interface P100s fail by not having the straps tight enough or by having incorrectly installed filters.
I have an instant pot that can usually do a good job of turning water into mist. If an atomizer doesn't work, how about simply creating steam with my instant pot?
Do you have tips on how to not fail without having one of these test kits? Which N95s work best? Do rubber P100s tend to fit better?
This paper from engineers at Cambridge University claims that a standard aroma diffuser and plastic bag is close to the performance of commercial equipment. That said, I'm not sure how much the total cost and prep time would compare to the nebulizer approach that jimrandomh suggests.
Paper Link
Abstract
Objective:
Qualitative fit testing is a popular method of ensuring the fit of sealing face masks such as N95 and FFP3 masks. Increased demand due to the coronavirus disease 2019 (COVID-19) pandemic has led to shortages in testing equipment and has forced many institutions to abandon fit testing. Three key materials are required for qualitative fit testing: the test solution, nebulizer, and testing hood. Accessible alternatives to the testing solution have been studied. This exploratory qualitative study evaluates alternatives to the nebulizer and hoods for performing qualitative fit testing.
Methods:
Four devices were trialed to replace the test kit nebulizer. Two enclosures were tested for their ability to replace the test hood. Three researchers evaluated promising replacements under multiple mask fit conditions to assess functionality and accuracy.
Results:
The aroma diffuser and smaller enclosures allowed participants to perform qualitative fit tests quickly and with high accuracy.
Conclusions:
Aroma diffusers show significant promise in their ability to allow individuals to quickly, easily, and inexpensively perform qualitative fit testing. Our findings indicate that aroma diffusers and homemade testing hoods may allow for qualitative fit testing when conventional apparatus is unavailable. Additional research is needed to evaluate the safety and reliability of these devices.
This didn't work for me. I could taste the saccharin when wearing a surgical mask, but I couldn't taste it (but should have) when wearing two surgical masks. I suspect that the diffuser isn't creating the correct sizes of particles and/or is creating too many (the mask did become somewhat damp) and this may cause the smaller particles to combine into sizes that are too big or heavy to penetrate smaller gaps.
Trying to detect leaks by smelling stuff is useless, since smells aren't affected by particulate filters.
This is how to do a fit test correctly without using fancy equipment:
That was actually the procedure for doing a seal check, not a fit test.
This is how to do a fit test (assuming you have a test kit):
https://www.youtube.com/watch?v=Syj_zeNtLGI
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The "paranoia" can justified for several reasons.
Lugging around oxygen tanks is not as practical or necessary.
Commercial fit-testing for masks needs quite fancy equipment like the Allegro Saccharin Fit Test Kit 2040 which combines undesireable features of being currently unavailable to order, expensive and having to take up room in my apartment after beign ordered.
It seems to me that there should be a way to get fit-testing done without as fancy equipment as it's just about exposing oneself to the smell of one of the substances that are are suitable for fit-testing (that have the right molecular size). Has anybody here found a way to do reliable fit-testing for themselves without the commerical equipment?