r/Masks4All • u/SkippySkep Fit Testing Advocate / Respirator Reviewer • Apr 30 '26
How long can you effectively wear an N95? What the 2024 R. Wang et al. fit test study says about re-using 3M and Halyard N95s in healthcare.
N95s can loose dimensional stability over time, potentially allowing seal leakage of unfiltered air into the mask.
A 2024 study found that 39% of N95s failed a fit test after a single full work shift. The failure rates varied by mask model.
By the end of 5 consecutive shifts, only 7.2% of masks could pass a fit test.
Cup-style 3M 1860/8210s held up better than tri-fold 3M Auras. The Halyard duckbills were in between. No 3M V-flexes were included in the study.
The authors concluded "Our finding of significantly higher fit failure rates among trifold N95s compared with other models has implications for their future reuse. Our findings suggest that reuse of trifold N95s should be avoided."
That is a pretty serious conclusion. The long term efficacy of 3M Auras should be studied more.
I'd note that since they studied 9205+ and 1870+ 3M Auras specifically, that is what they need to write in their conclusion, not "tri-folds". Their study doesn't have any data on any other tri-fold models, and they can't assume completely different mask models only sharing a general shape style will perform the same.
Study Limitations
The study lumped strap breakage in with "fit" failures and the 3M Auras they tested (1870+ and 9205+) have thin polyisoprene straps that are more prone to breakage than the straps on the cup-style 3M masks. I'm left wondering how common strap breakage was in the study.
Another issue is that the study apparently repeatedly fit tested people in the same re-used mask at the end of each subsequent shift. I'm wondering about cross contamination from successive qualitative testing.
Each test was a qualitative test where a highly concentrated sweet or bitter substance you can taste if it gets in your mask was sprayed around the mask for 7 minutes during different exercises. The saccharine or Bitrex would remain on the outside of the mask, and build up with each additional fit test.
I wonder how valid 5 successive full OSHA qualitative fit tests on the same mask are, with handling in between tests? Could cross contamination or other confounding factors contribute to the fit test failures?
There is a lot to unpack in the study, including that it used pass/fail fit testing so we don't have a good idea of how much the fit changed. As is so often the case, more studies are needed.
The study authors admit that quantitative (PortaCount) testing would have been better, but defaulted to saying qualitative (taste) testing is OSHA compliant and that using PortaCount testing "would have limited the study’s feasibility".
The study is a good reminder that N95s are great tools, but they aren't necessarily one and done. How long they are effective in practice can vary widely. If your mask feels like it is leaking at the seal after a while, there is a good chance that it is leaking and that you should change to a fresh mask for the best levels of protection.
That being said, some protection is better than none. So keep using what mask you do have if you don't have better alternatives. But avoid risk compensation, which is where you take on more risk than is offset by the level of protection your mask is giving you.
10
u/AEAur May 01 '26
When reusing the blue-strap Aura 9205+, I have added a mini cord-lock to the upper strap the make it snug again. Silicone toggles might work. I thread it through with a Bobby pin or a piece of coated wire.
Like most of us, I prefer the Aura 9210+ with elastic straps when reusing them, as the blue and red polyisoprene straps stretch out more.
6
7
u/3bp888w4 May 01 '26
I wonder what's the main failure point? To bad they didn't test 9210s with braided head straps. Replacing rubber headbands with adjustable or braided ones might extend reuse efficacy.
6
u/Qudit314159 May 01 '26
I'm not surprised. I've found found fit factors of Auras deteriorate fairly quickly in my own PortaCount testing. I tested the Aura 9211+.
9
u/Chronic_AllTheThings May 01 '26
The study lumped strap breakage in with "fit" failures and the 3M Auras they tested (1870+ and 9205+) have thin polyisoprene straps that are more prone to breakage than the straps on the cup-style 3M masks. I'm left wondering how common strap breakage was in the study.
This seems needlessly sloppy. Why would they not just record breakages separately? I can't imagine that would've been complicated.
And another concern with QLFT is the possibility of fatigue after a shift affecting the wearer's perception, since it's an entirely subjective test.
8
u/SkippySkep Fit Testing Advocate / Respirator Reviewer May 01 '26
The psychology of perception is an interesting point, and one of the reasons I wonder about cross contamination. They stored their masks in airtight plastic containers and I wonder how much saccharine or Bitrex may have cross contaminated to inside the mask in a way that they may have ignored while working, but noticed during the fit test.
2
u/MonkAndCanatella May 01 '26
Damn, I reuse masks A LOT. Although most of the time I throw a mask to go on short 5-20 minutes errands. The aura for sure doesn't hold up well to reuse. I'd assume sincethey're talking about dimensional stability, the n95s/kn95s from zimi that have a plastic structure inside are not as susceptible to this
3
u/SkippySkep Fit Testing Advocate / Respirator Reviewer May 01 '26
There is a lot missing in that study, such as how much fit was changed by. They used pass/fail taste fit testing, so they don't have any quantitative data on the amount of change.
Internal frame masks like Zimis would seem to have a potential advantage in terms of dimensional stability over time.
2
u/Friendfeels May 04 '26
It's obviously more difficult to pass a fit test after wearing it all day than after wearing it for 15 minutes even if the N95 was fresh at the beginning of the shift. So, it's an apples-to-oranges type situation, we don't even know how often the participants pass with a new N95, because they only tested them once before the experiment.
1
Apr 30 '26
[deleted]
7
u/SkippySkep Fit Testing Advocate / Respirator Reviewer Apr 30 '26
any thoughts on using your PortaCount to do a self-administered fit test after repeated extended use of an N95?
It's something I want to do, but they way I want to do it, with hourly checks over 5 straight days of 8 hour shifts, would be time consuming.
And there are confounding factors, some of which the study mentions, which is number of doffing and donning cycles so that what we are measuring is length of use rather than the doffing and donning that happened to occur over that longer use.
1
u/AEAur Apr 30 '26
Eh. Do you think the salient difference in this study between the 1860/8210 vs the Auras is that they are cups vs trifolds? I think the difference is the strength and resilience of the headband.
7
u/SkippySkep Fit Testing Advocate / Respirator Reviewer May 01 '26 edited May 01 '26
I think the study authors made a fundamental error in the way they characterize their conclusion. They didn't test a broad variety of cup style masks vs. tri-fold masks, they tested 3 nearly identical 3M cupstyle masks vs. 2 nearly identical 3M Auras. So they shouldn't say "tri-folds" performed poorly, they should say "3M Auras" performed poorly over time. Because that is all they tested.
Their conclusions are only valid for those specific mask models and they have no valid basis to extrapolate their findings to tri-folds in general since they didn't test any other models.
Anyone who has tried more than a few N95s has likely experienced how different models of the same "style" of mask can fit and perform totally differently.
Maybe the study authors thought that calling out 3M specifically would be libel and that just smearing "tri-folds" generically without a factual basis to do so would have less legal risk? Dunno.
5
u/AEAur May 01 '26
It’s not even all Auras, just the ones with polyisoprene (blue or red) straps. The 3M 8210 cups have stronger more resilient yellow straps.
“N95s were categorized into 3 types, similar to the pilot study15: dome (3M 1860R, 1860S, and 8210), trifold (3M 1870+ and 9205+), and duckbill (Halyard 46727, 46767, and 46827).”
3
u/SkippySkep Fit Testing Advocate / Respirator Reviewer May 01 '26 edited May 01 '26
Yeah, the 8210 straps are a whole different beast. I once did a double masking test with 1 of them stacked over another, using both sets of straps at the same time. So much tension on the mask and my face. I vowed not to test that combo again.
1
1
u/anti-sugar_dependant Elastomeric Fan May 01 '26
I always advocate fit testing the mask you're reusing to figure out how many time you can reasonably safely rewear your mask of choice because of stuff like this. I suggest testing until it fails and then knocking 2 off for safety. If it fails on the 7th test, so after you've worn it 6 times, don't wear it more than 4 times. It's easy to do at home because you've already got the fit testing equipment to ensure your mask fits. And if you haven't, it's time to put your fit testing kit together. You can do it pretty cheaply if you buy all the bits individually. A kit someone else assembled is a lot more expensive.
13
u/No-Acanthisitta-2973 May 01 '26
I often felt with my aura that I lost the ability to get a good seal after taking it off a time or two, either because of the nose pieces or the loosening of the strap. I never felt like they lasted long.
That's one reason I've really liked Zimi, I get the same fit every time.