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Comment by ehsankia | Hacker News Reader

I'm curious, I've been seeing a lot of calls for 3D printing similar looking Face shields, which are very different from face masks. What is the use for this? Are they actually useful to health care professionals? Face mask + goggles fully covers the 3 places the virus can enter (mouth, nose and eyes), but these shields seem like they would be more useful for people who have the virus than those who don't.

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COVID-19 is very likely only marginally spread by aerosols (I take this from Robert Koch Institute, Germany information [1]), approximately 10% by contact spread and mainly by direct transmission of droplets.

Faceshield therefore protects from the main transmission vector. It's not impossible to get infected otherwise, simply much less likely. Your main enemy are getting coughed/sneezed/talked at in close proximity.

Surface spread is likely also extremely limited (source: Prof. Hendrik Streecke who continues to study COVID-19 in the German epicenter of Heinsberg [2]). Money quote from source:

> "Wir waren in einem Haushalt, wo viele hochinfektiöse Menschen gelebt haben, und trotzdem haben wir kein lebendes Virus von irgendeiner Oberfläche bekommen.“

English: "We have studied a household where highly infectious individuals resided and have still been unable to find any living virus on any surface."

All virus residues found have been dead virus material.

[1, German] https://www.rki.de/DE/Content/InfAZ/N/Neuartiges_Coronavirus...

[2, German] https://www.deutschlandfunk.de/covid-19-wie-lange-sich-das-c...

So this is likely a dumb idea, but if things got truly desperate I wonder if a snorkel mask would be a decent improvised protection. Your eyes and nose would be completely covered and your mouth is getting air from a direction/location that is unlikely to be in the "line of fire" from someone coughing or sneezing.

Definitely. A snorkel/scuba mask is going to be better protection than most masks, though relatively expensive to produce and clean and can't be treated as disposable.

But if you have to breathe in infected air, doing so with your nose is far better than your mouth, since your nasal cavity has thicker membranes and a lot of mucus and hairs to catch particles, whereas through your mouth the particles are going straight into your lungs.

In fact, that effect might be so significant evolutionationary that it is the reason we have a seperate nose and mouth, rather than combining the two.

A nose lets you breathe while you eat.

Put a peg on your nose... You won't have any trouble eating after a few minutes practice. You just breathe between chewing.

The biggest problem is actually eating hot food - it seems the mouth can withstand hotter foods than the lungs, which get painful if you breathe in the steam from the half chewed food in your mouth.

They already are, actually: European researchers retrofit snorkel masks for coronavirus fight - https://www.reuters.com/article/us-health-coronavirus-czech-...

Face shields also stop you from accidentally touching your face through habit which is the main transmission vector

Face shields provide specific protection against bodily fluids: sneezes, blood sprays, etc., that would further soil the masks you wear underneath them.

This study talks through the advantages of adding them to the repertoire for infectious disease control as part of your PPE: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5015006/

> Face mask + goggles fully covers the 3 places the virus can enter (mouth, nose and eyes)

I believe face masks are only 95% effective at best and that's only with a proper N95 which a lot of medical staff appear not to be able to get hold of. Hence they're wearing things like Buffs or cycling masks to make do. In that situation, having another layer that can stop droplets etc. from reaching the mask in the first place makes sense to me.

Plus it stops a whole lot of messy body fluids from reaching the mask and goggles which cuts out a swap/clean cycle (again, difficult if there's no spares!)

[Edit to correct 'googles' to 'goggles', FFHS]

An N95 respirator is rated to block at least 95% of 0.3 μm particles. It’ll do waaay better than 95% at blocking droplets! They’re much larger.

(though N99 and N100 respirators do exist)

But remember that a respirator blocks 0% of particles getting in your eyes.

I see, so are they wearing these shields on top of the usual mask?

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