Some notes from Alana about the fit testing data
Ideally you should use the mask that you got the highest overall fit factor in.
Hopefully fit-testing gives you more confidence in the ability of your mask to protect you, while keeping in mind that masks are just one layer of protection. Obviously the best mask in the world can't protect you when you're not wearing it or not wearing it properly, which is why it’s always good to do a quick fit check every time you put on a mask - make sure the straps and nose are properly in place and exhale while checking if you can feel any air leaking around the sides.
Fit-testing standards recommend retesting annually as face shapes and therefore mask fit can change over time.
I've written a bit more about fit testing data below, but most of it isn't necessary to know for day to day purposes. All you really need to know is to use the highest scoring fit factor mask you got, noone failed all masks, so there's a decent mask out there for you. You could also consider doing a diy qualitative fit test test at home or testing more masks with the portacount in the future.
Fit Factor
A fit test asks you to perform a series of exercises. Each exercise is given a score based on a calculation that looks at how well the mask fit during that exercise (based on an equation relating to how many particles were counted inside the mask vs outside the mask). The overall fit factor is an average of these scores. Higher fit factor = better mask fit = better protection.
What is a good fit factor score?
For a fit test in N95 mode, I suggest aiming for a minimum of 100+ and ideally aiming for 200+ (this is the maximum score for this test).
For a fit test in N99 mode, we get a bit more information (it can give scores above 200) but we need to keep in mind that testing disposable half-face masks in N99 mode is an off-label use, as it's really designed for resuable respirators. A test done in N99 mode is also testing for much smaller particles than those it looks for in N95 mode. If you got a good result in N99 mode, your mask is doing a great job of filtering even smaller particles sizes, and therefore is likely filtering out way more than just covid. The standards for N99 mode recommend 500+ or 1000+ depending on what the mask will be used for, but keep in mind that these are recommendations for respirators that are both reusable and designed for hazardous environments.
How fit testing works
A fit test basically measures how well a mask fits, based on its ability to prevent particles from entering.
The fit test machine measures how many particles of a certain size are in the mask, versus how many are in the air around the mask, and therefore how well the mask is preventing those particles from entering. Particles can either enter through the filtration media (mask fabric) or around the edges of the mask (if the mask doesn't create a good seal / doesn’t fit properly).
For a test running in N95 mode, we can assume that the filtration media is doing a decent job (based on other fit testing data out there and mask standards) of preventing particles of a certain size, and therefore any particles that enter the mask are because of poor fit/seal.
For N99 mode, the higher the score the better, and while anything 500+ is great and 1000+ is even better, we need to keep in mind that this mode is designed for testing particles smaller than covid, and for testing full face respirators used in scenarios beyond covid mitigation. If you got a high fit factor score in N99 mode, this doesn’t necessarily mean it provides the correct level of protection for all hazardous environments, as this can be context specific, so please don't rely on it in for hazardous fumes or in hazardous scenarios etc.
N99 mode vs N95 mode
My basic understanding is that N99 mode tests for much smaller particles than N95 mode, and this can explain why the scores you get in N99 mode are lower than N95 mode - because extremely small particles may be getting through the filtration media (particles that are likely way smaller than covid) but not around the edges of the mask (alternatively, you may be exhaling them if you recently ate/drank). If you pass a fit test (200+) in N95 mode this is likely to confirm that your mask seals to a decent standard. N95 mode only gives the highest score of 200+, as this is the highest standard required of N95 masks.
If you get a really good score in N99 mode, then that mask is filtering even very small particles, so will also likely filter particles much smaller than covid.
If you passed a test in N95 mode (200+) and then in the same mask got a lower score on the test designed for N99 - this likely means yes it is letting in some particles, but because you previously confirmed that the mask had a good fit by passing N95 mode, and assuming you are still wearing it correctly and didn’t recently consume food/drink, it’s likely that those particles are coming in through the filtration media (fabric) as the n99 test measures much smaller particles (down to as small as 0.2 microns). So yes it is letting in some smaller particles, but is still likely to reduce risk of covid/respiratory transmission as covid particles are generally larger than this size.
Because of this, it’s probably ideal for each user to first test in N95 mode, and move onto testing in N99 for masks that pass mode. Though this shouldn’t really be an issue if we are testing masks which we know have reliable filtration media (ie. masks that are made to standard and known to pass N95 tests)
Fit test scores for individual exercises
Each mask fit test asks you to undertake a series of exercises. Each exercise receives an individual fit factor score, which are then collated and averaged to give you an overall fit factor score. For tests that had 'grimace' as an exercise, this value is excluded as the purpose of a grimace is to break the seal of the mask, and then to see how well the mask reseals. This is also something to be aware of in daily use of your mask - your facial expressions and body movement influence the fit of your mask in that moment. Maybe lay off the grimaces!
The individual exercise score for the first exercise you undertook may be falsely low (looks as if a lot of particles entered the mask) due to particles from the surrounding air getting trapped in the mask when you first put it on. For this reason, it's recommend you wear the mask for a few minutes before starting the test. For tests that had 'normal breathing' as the first and last exercise, this can be an explanation for cases where the first exercise received a lower fit factor score than the final one. Similarly, food or drink consumed prior to the test also has the possibility of contributing to particle count. It's reassuring that both of these factors are likely to make a mask look like it works worse than it does, and not the other way around (ie. it’s not going to give you a false positive/false sense of security).
While a lower individual exercise score indicates when your mask is likely to let in more particles, scores that look low in comparison to other individual exercise scores in the same mask might still be viewed as providing a good fit, as the equation that formulates a fit factor value is not a straightforward scale. If the mask passed the overall fit test, I wouldn't find a low value overly concerning, however it may help provide some additional information to inform your mask use or personal risk assessment (eg. I got a low score on the head up and down exercise so maybe I’ll go to the metal show but won’t be doing any headbanging).
Particle sizes
My understanding is that an N99 test is looking for particles as small as 0.2 microns, whereas N95 mode only looks at particles 0.5 micron or greater. While covid aerosols are likely 0.34 microns or larger, most are in the range 0.94-2.8 microns(source), so masks with a high fit factor score in either mode are providing a decent level of filtration, though obviously the higher score the better.
I want a higher score
From what I can understand, the way that a fit factor score is calculated is not a straightforward scale, so don’t be concerned that you got a lower fit factor score than someone else - the aim should be to find the highest scoring mask available to you. I also do wonder if scores were likely to be worse as the day progressed due to particles building up in elements of the machine (next time we could try to keep note of times/usage, particle generator use and when the portacount filters/tubes are changed). If you're having trouble interpreting your mask test info and/or feeling negative about any aspect of it, I'm happy to go through it with you to try to help you understand why your mask is doing a really decent job actually! It’s worth keeping in mind that the standard used in healthcare is simply to get an N95 fit factor score of 100+ or 200+ (depending on the service). You could also undertake diy qualitative fit testing for some extra reassurance/data, or test more masks with the portacount at a future date.
DIY qualitative fit testing
There are some decent DIY fit tests you can do easily enough at home - it basically involves wearing a mask and seeing if you can taste specific sweet/bitter sprays while in an enclosed space. Annabelle has done these with our household and we were happy with how the results lined up with our portacount fit test results. Links on how to do these are here, and she is happy to talk anyone through how to do this.
https://fittests4all.com/v2.0/ <- website explaining how to do diy fit test with the kits they sell, but you can buy your own supplies linked below and use a paper/plastic bag
Tablets to make diy saccharine solution: https://www.woolworths.com.au/shop/productdetails/612562/sugarine-sweetener-tablets (testing solution: 1.66:2 ratio of tablets to distilled water - eg. 16.6g tablets - 20g of water)
Extra stuff
If you want to hire the Portacount yourself or organise a community fit testing day we’re happy to talk more about the logistics. It can be done outside, but you might need to run the supplied particle generator depending on conditions. Hiring place: Kenelec Scientific - 1 day hire cost: $302 + delivery (approx $44 one way or machine can be collected/dropped off directly to Mitcham)
If you tested multiple masks, the fit factor values are only comparable if you tested them under the same protocol (eg. OSHA n99) and did the same set of actions for each one (eg. if you jogged in one test but didn't when testing another mask, then that's not really equivalent data). Although really our personal goal I assume is just to get a reliable fitted mask, so any mask that has a decent fit factor is a good mask, with the higher the score the better.
This link gives some info on protocols and why protocols might differ a bit. Basically, different calculation methods of protocols and different exercises and duration of fit tests are used to balance the social aspect of fit testing. If we do another fit testing day, it might be good to have a think about what the more strenuous and common actions/movements a user is likely to undertake in their mask and choose/edit the protocol according to this. https://accutec.com/osha-fast-fit-protocol/
Here’s a link to Aaron collins mask docs
Something to keep in mind if comparing multiple masks, is that the fit factor number is not a straightforward scale where the distance between 1 and 2 is the same as the distance between 3 and 4 and so forth. I imagine it looks more like a line on a graph getting higher quite quickly - this table from Aaron Collins (mask nerd on youtube) gives a good idea. For me it drives home why people say "the best mask is the one you will wear" as even poorly fitting masks still provide some level of filtration.
And some personal anecdotal takeways:
fit tests are recommended annually, because face shapes can change, and so can mask availability. For me, I passed an N95 fit test in my Trident when I did the same fit test at my healthcare job in 2022 (fit factor of 200+) but did not pass it this time around (fit factor 17).
for me, how a mask felt like it fit on my face did not correlate with the actual fit factor value
the diy fit tests (using bitterant or saccharine solution in an enclosed space,) we did in our household (v small sample size of 3 people) correlated with our portacount fit test results, so this could be a good way to retest your mask if you feel you want to down the track, or for others who are unable to attend a portacount fit test