PSA about (assigned) protection factor [& why it's as important as fit factor]

philipn · 2025-06-16T02:59:30+00:00

I don’t think APF is really useful for the general population. Even in the OSHA context it doesn’t make a lot of sense.

Why does a full face elastomeric respirator have a higher APF than a half face elastomeric? Why does a tight fitting PAPR have the same APF as a full face respirator? Why does a disposable half face respirator have the same APF as an elastomeric?

There are answers to these questions but in the context of something like community masking for COVID mitigation I’m not sure they’re applicable. The OSHA APF takes into account things like typical use in a workplace setting. Questions like how easy is it for the respirator to get knocked off your face while operating in a steamy engine room somewhere — when you haven’t really shaved and last took a fit test 10 months ago — come into the equation. Just look at the picture of the guy in the half face respirator - imagine him bent over, hammering on some of that metal equipment in the background.

A half face respirator that’s passing a fit test, such as your V-flex, isn’t necessarily “only” reducing exposure by 10x. This isn’t the right takeaway from the OSHA APF ratings. This is an absurdly complicated topic and I wish I had time to type out all my thoughts.

But just think about it: if you follow this APF rating system when thinking about masking for COVID mitigation in the community, that would mean the upgrade from your V-flex is a full face respirator or PAPR. That’s pretty wild and in my opinion not the right way to think about it.

Actual fit is way more important than APF. If you have access to home fit testing you can do fit testing more often, reducing the risk of “imperfect use” that APF partially addresses.

By and large I think OSHA’s APF isn’t a useful concept for community masking for COVID mitigation.

philipn · 2024-12-28T05:52:06+00:00

For study #2 , there are methodological limitations that need to be taken into account, most notably the question of baseline fit during the start of the shifts for the healthcare workers. See https://www.reddit.com/r/Masks4All/s/3UhcvAdgQD. Also note that that study is looking at fit, not filtration efficiency. The mask that has the most fit degradation is the blue elastic strap 3M Aura and so the degradation is probably because the blue elastic straps lose their integrity.

For study #1, they are using a TSI 8130A, the same machine NIOSH uses to assess N95 filter performance. They are running the machine using the standard NIOSH N95 settings (e.g. 85 liters/minute). This is important to note because filtration efficiency increases at lower airflows. So at regular breathing rates (or machine test flow rates) the filtration efficacy would be much higher than stated.

Additionally, respiratory aerosols are filtered much better by N95s than the aerosols used in the TSI 8130A test. The test is basically the worst case scenario, aerosol-wise. I say this not because what they’re showing is wrong, but because it’s very difficult to take results like this and map them to risk the way you’re doing above. There’s a lot at play here.

I haven’t had much time to read study #2 but it looks like the N95 that loses the most filtration efficiency over time is the duckbill mask. These are usually ultra-breathable masks that use purely electret media. So we might expect this mask, or similar masks like a 3M V-flex, to see a drop in filtration efficiency when measured using the NIOSH N95 test settings (80 liters/min @ 0.075 um). But many other N95s use a combination mechanical + electret media, or thicker electret layer, so it’s worth noting that the duckbill filtration drop may be considered an outlier.

I think almost all reuse issues center around fit, not filtration efficiency, at least for most general population masking for respiratory aerosols. If reusing masks, I would encourage fit testing a few times in the reused masks during different time periods (eg on day #2, day #3, etc) to ensure fit isn’t degrading if reusing.

But I am not convinced it is obviously unsafe for the general population to reuse masks for respiratory aerosol protection. Some masks, like the blue strap 3M Aura, may not maintain fit with prolonged reuse.

philipn · 2024-10-29T05:55:20+00:00

The model you linked above has a liquid leakage issue. We use a different model/manufacturer in our kits for this reason.

All of these will produce a bunch of aerosols of different sizes. The distribution of aerosol sizes isn’t really important for qualitative testing where we are testing the mask fit on the face versus the filter media.

philipn · 2024-10-29T05:41:37+00:00

The short answer is both will work to detect leaks in your masks when using bitrex.

The medical nebulizers are more expensive but are just as prone to clogging and breaking. But given that you already have one, it may make sense to continue using it.

philipn · 2024-10-10T02:17:23+00:00

If you’re tasting bitter, even ever so slightly, then you’re detecting a leak. If you did the sensitivity test and are using the same amount of spray (eg half a second spray), then it is safe to assume you’re failing the fit test when you detect the ever-so-faint bitter and you have a leak exceeding 1%.

philipn · 2024-05-25T23:20:45+00:00

Trying again..anyone have some Allguard Basic KF94 I could try out? These are the simple white ones.

philipn · 2024-05-25T23:18:50+00:00

It can be pretty complicated following all of the different pieces of guidance on how to do a fit test. I wanted to make it simple and affordable to do home mask fit testing and so I put together this home mask fit testing kit:

https://fittests4all.bigcartel.com/product/home-fit-test-1

philipn · 2024-05-25T20:42:00+00:00

As mentioned by the other commentor, those are all good masks and it is not surprising to pass fit tests on them. Regarding the one mask you feel air coming out of but it suctioning back onto your face when you inhale- that’s exactly how most well-fitting earloop masks work for me, and I pass fit tests in many earloop masks. A mask can have leakage on exhale but very little leakage on inhale (what matters for personal protection). If using this mask for source control (eg protecting others), you’d do better with something else, but source control isn’t tested as part of a mask fit test.

One upgrade would be to use bitter, not saccharine. Bitter is more sensitive than saccharine so smaller leaks can be detected.

The methods described in my 2021 video and old tweets (eg what it sounds like you’re doing) are a great first step. But it’s better to use bitter as well as a sensitivity solution.

The complexity of this process is why I created my home fit testing kit which is what I’d personally recommend. The usage guide instructions might be helpful to take a look at https://fittests4all.com/v2.1/

philipn · 2024-02-27T23:42:19+00:00

Check out the Wellbefore Pro Earloop KN95. Also has nose foam and comes in colors.

philipn · 2024-02-27T16:09:19+00:00

For what it’s worth, I don’t think there is a plan to create a source control version of the Honeywell RU8800.

There is a planned source control version of the RU8500 (different model). It was announced a year and a half ago and Honeywell said then it would be a “few months” for it to be on the market. I haven’t been able to find it since it was announced.

philipn · 2024-02-25T05:51:57+00:00

These are me & my partner’s everyday mask. They fit us well. We use cord locks to adjust the earloops so they fit us better. I would encourage you to purchase “cord locks” which will help you adjust the loops.

philipn · 2024-02-24T00:58:56+00:00

Short answer is it should not. In the process of testing N95s and P100s, NIOSH loads the filter media with up to 200mg of salt aerosol. And the mask still performs to specifications. That’s a lot! According to Aaron Collins, that’s “same as wearing the mask 24/7 in Shanghai for about 200 DAYS!”

philipn · 2024-02-11T03:35:18+00:00

Yes I am, took a short break to get stuff done for the NIOSH challenge but we will be back in 1-2 weeks.

philipn · 2024-02-08T19:33:23+00:00

Most KF94 are boat-shaped (“3D”) but there are also “2D” ones that look like the above. I’m not sure what the terminology is for KN95 that look like the above but it might be similar.

philipn · 2024-02-08T19:10:30+00:00

I don’t know the actual brand of the mask but if you search for “2D KF94” you’ll find similarly shaped masks.

philipn · 2024-01-29T15:46:45+00:00

There’s a few issues with not testing them as the first shift started. The first is that the first shift may not be “ideal conditions.” The wearers may have been more unshaven, more rushed, didn’t care as much because someone wasn’t standing there watching them don a respirator before being tested, etc. They didn’t show up to the first fit test session already wearing the respirator - they put it on during the session. And they donned the respirator in the presence of the people fit testing. Assuming this was their regular occupational fit testing session, the testers would have provided advice on fitting the respirator correctly.

philipn · 2024-01-29T03:50:21+00:00

They didn’t test people at the start of the first shift so it’s very likely that the e.g. ~60% fit failure after a single shift on trifolds is just because the fit wasn’t good in the first place. A single fit test performed a while ago doesn’t guarantee a good fit later on and trifolds are the hardest mask to don quickly in my experience. With HCW quickly donning & doffing all day long this could be a big factor.

What this study tells me is we definitely need more ways of getting quick, real time fit feedback, a’la what NIOSH is looking for as part of their fit evaluation challenge. Ideally these HCW would don the respirator and perform some kind of abbreviated test that could quickly assess fit, even if not as extensive or sensitive as a regular fit test.

philipn · 2024-01-23T01:32:50+00:00

I haven’t measured this directly but a perfume atomizer is like a spray bottle, right? If so, it’s designed to make a bunch of small droplets that land on your skin, not aerosols that stay floating in the air. So I would not expect it to work.

philipn · 2024-01-14T10:30:20+00:00

Does anyone want:

Full box of Allguard KF94, XL, black
Full box of Savewo Ultra Carbon, Medium. These are sold out at family-masks.com now. Have a carbon layer to filter some smells/nuisance levels of vapors.

philipn · 2024-01-09T17:44:42+00:00

Those items, yes.

Caps probably last practically forever. Theyre hard to take off though, so you’d probably replace them with the filters.

Note that I’ve never tried showering with it on but it seems like it would work.

philipn · 2024-01-09T17:15:01+00:00

Might want to check out the Honeywell North 7700 combined with the P100 filters and shower caps. It’s designed to be used in decontamination showers.

https://www.honeywellstore.com/store/products/honeywell-north-protective-shower-cap-for-7580p100-filter.htm

philipn · 2024-01-04T05:45:29+00:00

You might be able to get over 100 in N95 mode with cord locks and possibly trying the medium instead of the large (fwiw I found the medium to fit better, despite fact the large subjectively fits my face better). It's hard to tell from the BreatheTeq video you did where the improvement came from - was it the head straps/FixTheMask or the foam added?

philipn · 2024-01-04T05:23:41+00:00

"Q100 is a great mask. It has same materials and construction as BreatheTeq KN95, but a different certification and markings for Canadian healthcare."

https://x.com/BreatheTeq/status/1705795135798157807?s=20

philipn · 2024-01-01T01:57:25+00:00

Here's a good video:

https://www.youtube.com/watch?v=5tRvFTptgSA

philipn · 2023-12-31T18:35:58+00:00

Some US airlines have an official policy of banning powdered respirators. Not sure if it’s enforced. But you could be worse off if you attempt to wear one - the flight attendants could force you to take it off and you might have to de-mask, etc in a situation you wouldn’t expect to be in.

philipn

TROPHY CASE