I’m not sure where the 6′ number comes from, and I’m skeptical it really holds up as something I’d be comfortable maintaining for an extended period of time (If someone with c19 coughed at me from 6′ away I would not feel very safe). I’m guessing the 6′ is more like a quick rule for people who are only interacting briefly.
How much does it matter whether you’re up/downwind? I’ve heard conflicting things about how airborne it might be.
I’m interested in this largely for “Okay, assuming we need to be careful about this for months at a time, what sort of practices could we use to maintain in-person social ties, indefinitely, without risk?” (i.e. going on long walks, visiting each other’s house where 1-2 people hang out in the street or sidewalk and house denizens hang out on the porch, etc)
I’m guessing this has separate answers for “outdoor” and “indoor.”
Current Answers:
Indoors: Basically it’s not safe.
Outdoors: 10 meters (30 feet) seems safe, if nobody is upwind/downwind of each other. But I’m unclear what the falloff range is.
Another reference (being reported in the news): Turbulent Gas Clouds and Respiratory Pathogen Emissions—Potential Implications for Reducing Transmission of COVID-19
So indoors basically no distance is safe, outdoors maybe 10 meters is safe if people aren’t up/down wind of each other.
Thanks, this is great.
I think the main followup question I have is “what’s the rate of falloff for outdoors?” (given that my goal here is not “100% safe”, its “the risk is comparable (i.e. within a factor of 2ish) to the usual background default level of micromorts”, for the range of stuff humans typically do.)
Found this link, which I think corroborates the paper Wei Dai linked. Haven’t review it yet.
https://globalnews.ca/news/6815551/cough-chamber-physical-distancing-coronavirus-western-university/?fbclid=IwAR2mdghjc-3x6S2PyAIrjdyx6J0mUTDxXdT4FJCV5jPMkeMtgoZ8Gzq8gXo
From “A choir group had 60 people show up for practice. Now 45 are sick.”:
Given that they were spaced out and 1 asymptomatic person probably infected all 45 out of 60 in what must be a reasonably large room, it seems just impractical to keep sufficient distance to be safe indoors.
Talking emits droplets and aerosols just like coughing does. In fact, I’m increasingly thinking that face-to-face conversations (especially without facemasks) are a major cause of asymptomatic transmissions. According to that theory, an indoor choir practice, with everyone singing loudly for extended periods, has to be one of the worst imaginable transmission risks. If the same type of super-spreader event happened in, say, a movie theater, I would be much more confused about it.
That makes sense, and does update me against public gatherings (but, I’m thinking of things on the timescale of a months to a year. I’m guessing it’ll get increasingly hard to keep people apart. I’m also thinking less in terms of groups of 60, and more more like groups of 2-5)
I was thinking of thresholds that were more like “at least 12 feet apart, maybe 20 feet”, with nobody touching any objects. (Also, I’m assuming this is all outdoors)
My point is that since 45 out of 60 people were infected and they were spaced out, the farthest person infected in that group must have been quite far from the source of the infection, and keeping a even longer distance to be safe is probably impractical for most indoor spaces.
ETA:
Didn’t notice this part earlier. I would be much less worried outdoors where virus particles are more likely to disperse instead of hang around, but don’t have any quantitative answers to offer.
Ah, okay yes that makes sense.
I suspect the inside issue is something that will eventually have to be addresses via ventilation and filtration (as in planes) and attention to just how the air flows seems important here. That probably doesn’t get us back to distances pre-COVID-19 but at least gets to some new workable normal. (Unless we’re giving up direct social interactions and go to pure virtual reality solutions).
Outside might still need some work I think. If you’re thinking not overly crowded settings not nearly as much to worry about. However, things like open air markets, rallies, large spectator sporting events outside or even tightly packed streets may still be a bit problematic. I think a lot there will depend on infection density at that point. I would expect some type of cloud to still emerge from the crowd of people that may remain localized in a lot of weather settings.
I have roughly two use cases in mind here:
a) the sort of person who wasn’t that trustworthy in the first place and was probably going to start hanging out with friends within a few weeks even if official quarantines weren’t lifted, but who might follow basic precautions if they were spelled out clearly.
b) small high trust networks where everyone has been quarantining (and documenting their quarantine), nobody has been interacting with anyone outside the network, etc. (but, still with a margin of error added so that a single person who’s been exposed unknowingly doesn’t end up auto-infecting everyone)
You might try this article and the many references therein. Sorry I don’t have time for a better answer at the moment :-)
Thanks. Gave it a quick skim and will hopefully comb through and pull out useful bits later tonight.
I’m not yet sure how related this is to Wei_Dai’s answer, but found a medium article exploring “how far away to be from others who are walking in front of you”. It references a couple other non-english articles, and one english… translation (I think?) on urbanphysics.
Some researchers ran computer modeling of what happens to saliva
There is a critique of this here. I haven’t yet read it thoroughly.
This suggests to me that we don’t just want to consider distance. Time and speed are both elements here too. I think that is actually something people can understand intuitively if they get some basic information. Most people are not challenged with knowing where they need to be to catch the fly ball. Here they just need to have a reasonable sense of where not to be.
So the message really isn’t X distance but several factors that can include a distance metric.
However, the other aspect here is not safe (pick you metric) versus not safe. It’s about level or risk and what that implies about actions to take. This could be anything from what types of PPE one uses to thinks like everyone adopting inside versus outside clothing (a bit like biohazard suits in those labs but probably more like a mechanic’s overalls) and increased use of “mud rooms” in housing.