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things look for the invitation I'm going to talk today about why a mask is is not a mask and some face masks are better than others um to understand this topic we need to start by understanding how the virus
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systems needed um at the beginning of the pandemic we were told that infected people when they cough with these knees they produce projectiles also called droplets and this project tells could help you inside
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the eye inside the nostrils inside the mouth and you could get infected that way or you could touch an object with one of these droplets had landed and you could touch again your eyes your nostrils and that's how you got infected
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this is the droplets and the surfaces CBC and who and everybody told us that that was how this virus was transmitted there was a third way that was known to be possible is that in addition to these
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large projectiles there is also a smaller particles called aerosource that can also contain the virus but they are too small to behave like a projectile instead they float and then they can be inhaled an inhalation of aerosols but
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within the mean is what we call Urban transmission at the beginning of the pandemic we were told in no uncertain terms by who that this did not happen and that it was misinformation to say that it happened
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now the pandemic has really changed things a lot and this is a paper we published over a year and a half ago where we showed that this is 10 FM who was completely wrong there is lots of
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evidence from many different types of studies and they all point to Urban transmission being the only important way in which this viruses needed so basically we're breathing the virus in
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everything else is very small and this paper has had a huge impact but but Public Health agencies are still kind of resisting communicating this clearly you know for for other reasons that are not science
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now when does this happen it happens primarily in two situations when we are close to someone that's where the aerosols are the most concentrated like if you were talking to a smoker so this is in this situation of close proximity
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or close contact that's what you're gonna see the most effective people and this can happen indoors or Outdoors but in addition to this when you have people sharing a room just like this person who's at a certain distance will
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eventually smell the smoke from this smokery that was the case they can also breathe in some of those other sources after they are trapped in a room and every Super spreading event that has been studied in detail is caused by by
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this by sharing the the room error without being close to someone else and we know that super spreading event is very important for the pandemic it's estimated to to lead to about 50 of of
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the cases now before we talk about masks and and how they work in filtering the virus we need to dispel to uh myths about about how this works this myth was published
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no nowhere else than the German of the American Medical Association so they published this cartoon for a paper and here you see that the virus is floating in the air in this basically water droplet the water will evaporate and you
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have something very very small that's basically the size of the virus that's floating in the air that is what a lot of people think and it is completely wrong what science really tell us is that is much bigger Autosource they're
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still small enough to float and to be inhaled but they're much bigger than the virus and most of the aerosol is saliva or respiratory fluid and then there is a small fraction of wireless oxidate and this is what we have to filter
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um the next thing is that a lot of people have the idea from the macroscopic world in which we leave that what we need is then a sieve a colander a strainer we need some fibers on the
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filter that are so small that this aerosols get stuck in there like they would be in a sea If you're receiving some dirt that's not how it works I mean that may be intuitive but that's not how it works we're dealing with microscopic
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physics that people don't have experience of and they are really different physical mechanisms that are much more efficient and and you don't need the fibers to be so close they can be much further apart and they still it
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works very well okay so but this is yet another misconception that that's floating around now okay so we know that we're gonna wear a mask and the idea is that it's gonna remove the aerosols that we are
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exhaling if they have the virus or they were inhaling they may also have the virus we want these Mass to have good filtering efficiency meaning when the air goes to it it removes the viruses to be breathable to not oppose much
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resistance to the air otherwise it can be difficult to wear for a long time and to fit well and not have any gaps otherwise if the air goes through gaps then it is not filtered now these are the results from a study from the CDC on
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Cafe results and there are many similar studies um and here they tested the efficiency so this is how well the mass Works in removing um aerosols as a function of the size
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right and these are the sizes that are relevant for for this problem and you see what we call an n95 which is uh is basically something like this it filters you know 95 or 99 I tested one of these
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on myself with professional tools and it was 99.9 so this definitely work very well but one detail that's important is a real n95 or ffp2 or 3 as they call in Europe it needs to have the straps
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behind the bug this is essential for them to fit well to seal all the gaps and to really have this level of protection many people think that this type of mask what we call a kn-95 or kf3
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is an n95 is not true this one's the material tends to be good quality as well but because they go through our ears they don't push as as strongly against our face and they don't seal as
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well study after a study they see you know half the people or a third of the people they don't fit as well so I mean is the next best thing if this is intolerable for whatever reason but it's not as good
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now the third type of mask that we have is this surgical or procedure masks and if they may be good filters but the problem is a lot of the air goes through the gaps okay and the results here of the efficiency you know they depends on
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particle size but it's like maybe 40 50 80 depending on the size you know let's call it 50 so now 50 protection is nothing just Nissa this is good right
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but but it's nowhere near what can be done with a master not not much more complicated okay now we have to remember one thing 50 percent protection is if you are the only one wearing the mask but if everybody is wearing a mask
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what's called two-way masking then you get the square of the benefit because let's say only 50 of the virus goes out but now only only 50 of that 50 is what you're breathing in so in this in this
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study they they said you know if everyone is wearing surgical masks which in this case they were assuming were a little better then the risk is only 10 or what it would be if nobody was wearing a mask but if everybody is
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wearing well fitted ffp2 mask or n95 then the risk is 1 000. of of what it will be with this with a mask or a hundred times less than with surgical masks okay so surgical masks you know if
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that's all you have you should definitely wear it but you can do so much better and it's not difficult now keep talking about fit and what do we mean well we mean that if again if you have gaps the air goes through there
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and then that air is not filtered and in this video that's on YouTube you see how the air escapes through the gaps in the surgical mask and that's really defeating the purpose if you wear an a mask that fits better that's going to work a lot better
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and this is a study where they Quantified that this is the relative efficiency as a function of how big were the gaps and the key thing here is that a tiny Gap really does a lot of damage a
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gap does one percent of the size of the mass or a masters so you're standing up here in the nose that you often see 30 40 50 of the air is going through there and is not being filtered so it's really it's really hurting
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one last misconception is you see these videos in which people are vaping and then they say you look the other source go through the mask this is another error this is really gases are going through the map through the mask and they are condensing on the other side
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and this is what's causing this problem um if you cannot afford the 95s or for whatever reason in your country so then there are these braces that can be used with surgical mass and turn them into
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something close to 195. what are they doing they are closing the gaps it's just a piece of plastic or rubber that is gonna it's gonna put pressure in the places where the mask would not really have a gap otherwise and I have many
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colleagues who have tested this and this works you know it's not as good as a n95 but it's almost as good and definitely worth the effort um finally the last type of mask I wanted to talk about are elastomeric
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masks and this is basically the same filter that you have in an n95 but now in a plastic enclosure and then now the plastic enclosure is reusable and it has some mechanism like this silicon o-ring
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in this case that does a better job of sealing so it deals with this issue of fit better than you would in an n95 mask by itself so for hospitals or for people at high risk this would be the the
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choice of mask but it costs a little more the initial purchase so finally just you know so I have summarized what they said the best is really n95s next is KN 95s and then it
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goes down from there and you know I'm a I'm a scientist working on another source but here you have an infectious disease doctor from Harvard or the former head of the CDC telling you the same thing thank you very much for your attention I
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hope this was useful
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