
Video showing microdroplets suspending in air - jennyyang
https://vimeo.com/402577241
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keenmaster
Incredible video. I strongly recommend watching the whole thing. It changed my
priors on the dynamics of micro-droplets. The part showing how a single cough
can create a room-wide cloud of virus that lingers for 20+ minutes in spaces
with poor circulation was especially enlightening. I won’t feel paranoid for
vacating an area with a sick person anymore, unless it’s outside or in one of
those premium buildings where you can feel the air flow.

Shouldn’t the government subsidize good HVAC (not just energy efficient HVAC)?
It already subsidizes green energy, which helps avert a far off semi-
existential risk. Good HVAC could partially mitigate an existential risk in
the near future, in addition to loss of productivity and life due to seasonal
flus. Of course, we should all be wearing masks when we go out during a
pandemic. Less intuitively for people, we should expect sick individuals to
wear masks outside of home regardless of a pandemic, and we should never ever
physically go to work or school sick.

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vanniv
To be fair, they were simulating an airtight room with zero movement.

Even just people walking around would create some airflow -- an HVAC would
create both airflow and temperature gradient.

Blowing the droplets away is effective, but also blowing them in to either
each other or a surface is also effective.

Evaporation also occurs -- the smallest droplets likely would evaporate long
before this model shows them hitting the ground or dissipating.

To your final point, I direct you to the hygiene hypothesis -- you definitely
want to periodically encounter low levels of non-lethal pathogens.

Yeah, people should take reasonable precautions when they are sick, and you
should wash your hands whenever they're dirty or before you eat/stick your
fingers in your nose (or at least 5x per day just on general principle), but
we shouldn't stop having human social contact, and you shouldn't live in a
Cleanroom.

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keenmaster
Sure, we shouldn’t be extra paranoid and literally live in a clean room. Yes,
the simulated room had zero circulation, which is unrealistic. However, the
point stands that micro-droplets linger far more than you’d think. We should
find ways to systematically improve the health of the population. Guidelines
to cough into our elbows just don’t cut it. Flu vaccines are great but they’re
not enough and they’re not universal.

My logic for subsidizing good HVAC also applies to other pathogen mitigation
technologies. No-touch sinks in public areas are one example.

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DoingIsLearning
I am really struggling to understand the recommendations for SARS-COV2 at this
point.

WHO claims that the virus is transmitted via contact or heavy droplets and
some other study previously linked on HN refered that aerosolization was only
a risk in ICU when extubating a patient.

But this video seems to contradict that, no?

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SZJX
The professor only said that "they're now becoming aware of the possibility of
the virus being transmitted via droplets". So they're not totally sure either.
It's all at an early exploratory phase.

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PeterStuer
The 1.5m distancing rule that so many governments (and sadly once more their
lackey scientific experts) has very little to do with physical properties, but
is chosen so as to allow for the least possible required adaptations to
factories and offices.

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gowld
The video shows both real sensors and a simulation showing the vast majority
of particles contained in a 6-ft range and then falling to the ground.

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PeterStuer
Your observations are correct, but your implied conclusion is not.

In the 'real' environment micro-droplets are shown to be suspended for
minutes. It is the larger droplets that are pulled down by gravity and do not
make it far. But the micro droplets can contain more than enough virus
particles.

It is shown that the room gradually accumulates more and more suspended
droplets as people continuously produce them, not just through sneezing and
coughing, but just by talking and breathing.

In a typical office environment there is continuous low velocity air
circulation spreading these droplets through the room and saturating the whole
space with them.

The video shows also that cross drafts, which produce a high air replacement,
can take the droplets outside of the room which is a good thing. The moment
the draft is closed the accumulation starts anew.

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downshun
Their model doesn't seem to account for static charges and evaporation, which
typically results in accumulation on surfaces and less of endlessly
freefloating in a room.

~~~
keenmaster
Isn’t that almost as bad? That means that if you don’t breath them in, they’ll
have another chance of infecting you through surface contact and inevitable
migration toward your face.

~~~
gowld
Not if you don't rub the walls, ceiling, and floor.

~~~
keenmaster
What about the other things that could be in a room? Tables, couches, food,
etc...

