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OP here. Your confusion comes from comparing filter media performance to simulated as-worn performance. A good surgical mask media will very much likely provide

OP here. Your confusion comes from comparing filter media performance to simulated as-worn performance. A good surgical mask media will very much likely provide 17% penetration. Note that this is just the media. When you wear one, there are gaps everywhere. So that's why the paper says "penetration goes up to 76% when considering fit". 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.

ricardobeat 6y ago
> the masks perform as well as ones without the valve > 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-abstracts/1150-vol-26-no-3-2009-pp-54-70-rengasamy-open-access/file 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.
- mc32 6y ago
  FFRs have better elastic that hold fit much better than surgical masks which have weak elastic loops. (remember the pictures of nurses with red rings around their faces from wearing N95s 8hrs+ ? Thats due to tight fit.) Surgical masks are better than cloth or gaiters but N95s are better yet.
  - ricardobeat 6y ago
    Unfortunately the fit hypothesis was not tested in the study, so it doesn't answer any of those questions. 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 https://aip.scitation.org/doi/pdf/10.1063/5.0031996
    - simpleguitar 6y ago
      Right. In the visualization it looks bad, but actual penetration testing reveal that it's not so bad.
- simpleguitar 6y ago
  > There's quite a difference between as well as and better than. I think that qualifies as editorializing, which is discouraged by HN guidelines. 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.
- throwaway81523 6y ago
  You are supposed to fit-test N95's. They sell some kind of mint spray for the purpose. If your N95 is on properly, you aren't supposed to be able to smell the mint. 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.

ricardobeat 6y ago

> the masks perform as well as ones without the valve > 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-abstracts/1150-vol-26-no-3-2009-pp-54-70-rengasamy-open-access/file 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.

mc32 6y ago
FFRs have better elastic that hold fit much better than surgical masks which have weak elastic loops. (remember the pictures of nurses with red rings around their faces from wearing N95s 8hrs+ ? Thats due to tight fit.) Surgical masks are better than cloth or gaiters but N95s are better yet.
- ricardobeat 6y ago
  Unfortunately the fit hypothesis was not tested in the study, so it doesn't answer any of those questions. 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 https://aip.scitation.org/doi/pdf/10.1063/5.0031996
  - simpleguitar 6y ago
    Right. In the visualization it looks bad, but actual penetration testing reveal that it's not so bad.
simpleguitar 6y ago
> There's quite a difference between as well as and better than. I think that qualifies as editorializing, which is discouraged by HN guidelines. 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.
throwaway81523 6y ago
You are supposed to fit-test N95's. They sell some kind of mint spray for the purpose. If your N95 is on properly, you aren't supposed to be able to smell the mint. 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.