CDC now says valved N95 has better source control than cloth/surgical masks [pdf]
cdc.gov
cdc.gov
A cloth (medical) mask is not what people are wearing.
Nitpicking on differences in real, tested, filtered and/or non-woven and/or paper medical PPE... Might be useful.
But not while 90% of the public are wearing woven-material marketed on any other product as being breathable.
It's like debating head safety of NFL vs MLB, and then complaining about someone wearing a football helmet without a chinstrap, while you stand there in a baseball hat.
And valved N95s are now around $2-3 each from established (not pandemic profiteering) online sources.
Well... yeah?
For the layperson, that's fine. For a scientific study, that's a problem.
https://www.costco.com/face-masks-coverings.html
Maybe a bit much for a household (100 masks I mean).
wellbefore.com also has various brands of N95.
With mitigation measures such as surgical tape or an ECG
pad secured inside, the FFRs can perform nearly as well
as an FFR with no exhalation valve
the maximum particle penetration through the unmitigated
FFRs evaluated in this study was 55%, which occurred at
55 lpm, while the maximum penetration for surgical masks
was 17% for the filter media and 76% when considering fit
FFRs with exhalation valves can reduce 0.35-μm MMAD
particle emissions more consistently than surgical
masks, procedure masks...
With mitigations that cover the exhalation valve, 0.35-
μm MMAD particle emissions can be limited to 5% if the
filter media does not interfere with providing a good
seal to the exhalation valve
the exhalation valves could be improved by establishing
criteria for valve performance
The conclusion is that taping with micropore performs just as well as a non-valved mask, but blocking the valve completely with an ECG pad performs better than not having a valve at all. How?
Are there other design differences in valved masks that account for the difference? If I attach an ECG pad to the center of a non-valved mask would it improve performance?
The best valves filtered particles very well without any mitigation. If there was a standard there might not be anything to talk about (they could all be better than other masks).
I think the statement about improving them is sort of misplaced in the flow (it's related to the containing paragraph and previous 2 paragraphs).
That's not supported by the study: 17% max penetration for surgical masks vs 55% for valved masks without any 'mitigation'. They only perform similarly for inwards flow, which is expected when both have an N95 rating.
Based on a sample size of 13 models, this study found that unmitigated FFRs with an exhalation valve that were tested in an outward position(with particles traveling in the direction of exhalation) have a wide range of penetration, emitting between <1% and 55%. Further testing could measure greater particle penetration.
See where it says "between <1%"?
And Figure 5 shows the variation between the models.
Presumably if the goal was to standardize on good valve performance, the performance would align with the best models rather than the majority.
As for the rest, the paper is saying that with a good tape/blocking the exhaust valve, the masks perform as well as ones without the valve. And they speculate that with a better designed exhaust valve, even better source control than as-is valve might be achievable, but there is no standards to measure it.
PS: As for your last points, figure 4 answers it.
> CDC now says valved N95 has better source control than cloth/surgical masks
There's quite a difference between as well as and better than. I think that qualifies as editorializing, which is discouraged by HN guidelines.
> penetration goes up to 76% when considering fit
They quote a separate study for that. The numbers from their own testing are 2%-17% for surgical masks, and fit doesn't seem to be factored in for the FFR ones - all the testing was done completely sealing the mask edges. On top of that, most of the FFR models perform worse than the 17% baseline, as seen in Figure 5.
My last point was: what can be the physical explanation for a covered valve performing better than not having a valve? The numbers are there for the specific model that achieved it, yes, but I'm surprised there is no hypothesis put forward.
EDIT: I looked into the study where the 76% figure comes from: https://www.isrp.com/the-isrp-journal/journal-public-abstrac... - again ranges don't tell the truth, a single model tested went into the 76% range, most stayed around 20%.
In addition to that, the study says "76% when considering fit [Rengasamy et al. 2009]" but the results in the 2009 article are also from a mask sealed around the edges, they didn't actually test for fit.
Enough masks for a day now... these inconsistencies just trigger my curiosity.
Surgical masks are better than cloth or gaiters but N95s are better yet.
The real issue addressed here is with the valves, not the mask type or fit - outflow is not filtered through the valve, only inflow. The difference is stark: https://aip.scitation.org/doi/pdf/10.1063/5.0031996
The "as well as" is comparing valved and un-valved N95s. The "better than" is between valved N95 vs cloth/surgical masks. Many jurisdictions in the US put valved N95 in the same category as no mask, where as this study says that they maybe better than the mandated face coverings.
If you look at figure 6, you'll see that surgical masks performed at 20% penetration. The dotted line on that figure is what was reported in Rengasamy 2009. But not all surgical masks are the same. ASTM level 1 is I believe 80% filtering media. The wearer will get less than that due to fit. Most of the "surgical" masks in stores now (not in hospitals) has no ASTM rating at all, and the cotton masks that are sold also does very poorly in controlled penetration tests, even before considering their fit.
Covid virus particles are about 0.125 micron, so it's not clear whether the measurements at 0.3 microns are of much help re leakage around the mask.
Random website with a fit test kit: https://www.allegrosafety.com/product/sweet-fit-test-kit/
My one issue is that long term it's hard to wear both. Air restriction can be bad for the wearer. It's important to know this.
They are not supposed to be a tight fit. It is to stop virus/spit going directly into another persons face (or, originally, a wound). They aren't made to actually filter the air. If you want filtered air you need a N95 mask.