Comment by saurik | Hacker News Reader

Comment by saurik | Hacker News Reader

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As I imagine you are expecting to test for smoke in that case by seeing if you can smell it: of course you can smell it, as what you are smelling there is a gas. An N95 mask filters particles larger than some reasonably large size, which hopefully includes giant encapsulated viruses filled with genetic material but is not going to include the odor from smoke which is made up of individual molecules of stuff like syringol. An N95 mask is not some kind of "only oxygen and nitrogen and carbon dioxide (and whatever else you absolutely need from air)" filter: it is just that most scents thankfully aren't harmful, but happen to be correlated with stuff that is.

FWIW, when I wear an N95 mask I do not get steam from its edges (that is either a ludicrously poor fit or you are expecting to be able to breath out too quickly for your mask design), but you also need to remember that breathing out is "safe" while breathing in is not, and yet the pressure in the two cases is very different, so something can be very effective even if it has the issue you are complaining about (and some masks are even designed specifically like that, with pressure vents to make breathing easier so you can exhale quickly without a problem and then pull air in more slowly where the feedback is more clear).

This a thousand times.

I wear a p3 mask to cycle to work, because I work in central london and don't want to fill my lungs up with crap(as fast).

a P3 mask filters 99% of >0.3 micron particles. It stops diesel fumes, but not smell. I've not tried it with wood smoke, but I suspect that'll fill up the filters much quicker.

you can 100% smell sewers still.

I have recently got some filters that claim to get rid of "troublesome" smells as well, by bundling a carbon filter on the inside. I was forced to by these as everyone had panic bought normal filters. When I replace my filters next week, I'll see if it makes a difference.

> giant encapsulated viruses filled with genetic material

Somewhat tangential, but viruses are actually _really_ small. Some approximate sizes for comparison:

* Pollen: 20 - 35 um

* E. coli: 2 um

* HEPA filter: 99.97% capture at 0.3 um

* N95: 95%+ at 0.1 - 0.3 um [1]

* Sterilizing filter pore size: 0.22 um

* Virus: 0.004 - 0.1 um

Even the sterilizing filter in the lab doesn't remove viruses. I'm not actually sure what mechanics are going on in this case that allow an N95 to protect you.

[1] https://www.ncbi.nlm.nih.gov/pubmed/9487666

Masks actually have kind of a funny response curve (see 5th page of linked PDF).

The masks are basically made out of layers of tiny (as small as 1um) fibres that force the air to weave through them to get to you. Larger particles tend to hit fibres on their way through, while smaller ones tend to get pushed out of the way of bigger things like air molecules rushing through and get bumped into the fibres and captured. The things that get though are the ones in the sweet spot of being small enough to make their way around the fibres in the air, but large enough to not simply be knocked out of the path by the air molecules themselves.

The lowest efficiency is around 0.04-0.1um on the models tested (so perfect range for most viruses) but even then they were still only dropping to like 94% effectiveness. I expect “94% effective” is still enough to see a significant different but that’s just my gut feeling.

All kind of moot, though, as coronaviruses (per 4th page of linked PDF) are actually closer to 0.125um, which is veering back to 100% effectiveness. And if we expect that a lot of transmission is happening in droplets, those are much larger and easily caught by the filter.

https://multimedia.3m.com/mws/media/409903O/respiratory-prot...

I asked this same question to a doctor and his response was: The particles of concern are likely to be more than just a single virus cell on its own so an n95 mask does help to some degree.

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