I doubt outdoor heaters have had a significant effect on cases.
I hope you’re right and there’s no evidence that they have had, but the physics are there. What then could possibly justify a ban on outdoor dining in LA? That your breath carries virus particles across the table to those with you at the same table?
In particular, fully unconfined tables with heaters, such as on a sidewalk, without any partial enclosure or cover, can’t possibly exacerbate case numbers. You’d have to sneeze directly into someone’s face, and how often does that happen?
The length scale for natural convection recirculation in such cases is essentially infinite even in still air, and there’s “flushing” if there’s any breeze at all. Dry active virus clusters in upward convection currents will simply rise to some height, move with the breeze, and decrease in concentration. In such cases, radiant heaters should actually help, and the closer to the heater the better.
In addition, when your breath is warm and the ambient air cold, your breath and any tiny particles in it will rise due to buoyancy, helping to prevent it from reaching others at the same table, “all in the family” or not. (In that connection, it’s worth noting that the human eye can’t see particles smaller than about 50 microns, so other than in special lighting conditions, you don’t usually see your “breath” unless the droplets you exhale are larger than that.)
The people making the rules seem only to know about one branch of science, to the exclusion of all others, including fluid dynamics. They should bring in a professor from one of the local universities who understands these things before clobbering outdoor dining.
I found The Monitor article (Starr County) in this post to be very interesting; in particular, that an ambient water vapor concentration of 10 gm/m**3 (which is reached at 72F and 50% relative humidity, for example, both comfortable levels) can have such a dramatic impact on reducing transmission. To be continued, I guess.
Another concern among some public health experts is people often come from different households to gather at outdoor restaurant dining tables. A safer approach would be to keep dining parties limited to members of one household at each table, experts say, but such an effort has been impossible to enforce.
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A good article. Surely those restaurant owners who have done what they had to but in the process taken advantage of the imprecise meaning of “outdoor” could at this juncture be offered the option to (ahem) re-think their layout, rather than closing down all outdoor dining in all restaurants in the county.
The problem is irresponsible customers, which discussion belongs here:
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Irresponsible patrons are another facet of the problem. Yes, perhaps that discussion belongs elsewhere, but the two threads overlap sometimes.
It’s hard to believe when seeing old posts like this that the FTC discussions on this topic go back so far. I remember when we were arguing what “real BBQ” was regionally, and where it was to be found locally…
I guess on T-Day, I’ll be thankful that 2020 is almost over. Time has passed both excruciatingly slowly and way too fast.
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Good preprint paper why a hard lockdown now could be beneficial longterm to have much less need for significant “control” mechanism
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That’s the “hammer and dance.” The problem in the US is that in places where lockdown resulted in low community spread, it was not followed by adequate TTI. Also, a lack of a national policy means any local gains are sooner or later erased by irresponsible travel.
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That’s why I hope Biden will show leadership and change things dramatically
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Nice tool to calculate risk in indoor settings (link to german newspaper but text is in English - just click the green button)
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And a good article in Boston Globe what went wrong over the last 9 months (a lot of obvious things but also topics which might not be this obvious, e.g. unions etc)
One thing that can be observed, just by looking the pictorial examples in this article, is that in almost every case, people in a corner or near a wall got infected. Corners and walls are locations in enclosed spaces where there are almost always trapped recirculation vortices, which by way of mixing with the room air and then trapping some of its particulate contents, will generally have higher concentrations of particles or fine droplets than other locations in the room.
Takeaway: If you’re in an enclosed space, don’t sit or stand too close to a corner or wall when others are present, for any length of time.
There can be no feedback control if people won’t cooperate with government guidelines, including travel.
On/off control is demonstrably unstable even without societal acceptance. I believe this has exacerbated the current “second wave” of viral spread in the US, simply due to our cultural, reflexive resistance to Big Brother.
It’s our culture, not our fault.
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You can close businesses but you can’t prevent, arrest, or cite and fine millions of people for violating a mandate that isn’t widely accepted; e.g., gatherings of friends at “speakeasy” residences.
In our society, at least in CA, “dimmer switch” feedback control might have prevented this second, astonishingly undamped surge in cases. The most extreme level of intrusive government, On/Off intervention, a full lockdown, is now once more being forced on the people of LA.
Has anyone here even read this article?
We just don’t know enough about Covid-19 yet or have detailed enough data. Notably, the sudden spike in LA doesn’t seem to be related to changes in behavior.
Certainly it would be more effective to ease or lift one restriction at a time and wait long enough to see what effect it has. E.g. reopen elementary schools and wait a month.
That would be a much more intelligent approach than what’s being done now.
but would cost even many more lifes…
What’s the math for that?
This regional / ICU-capacity approach makes way more sense to me than what the state.has done to date.
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It’s a move in the right direction, but too late and too harsh.
Using occupied ICU beds as a basis for the strength of restrictions, and regionally-applied mandates to reduce “mixing”, are both good ideas. (Not all patients in the ICUs are there due to covid, but that’s a secondary point.)
I presume that the projection that So. Cal. will reach the 85% occupied ICU threshold in a few days is based on an extrapolation of the slope of the ICU beds occupied vs. time. It’s that slope that should be used as the feedback control. Cutbacks and relaxation in the amount of allowed business activity should be based on the amount of departure of the actual slope from a safe slope – not the number or percentage of ICU beds in use itself.
Knocking back business occupancy from 50% to 20% capacity if we’re even the tiniest epsilon over 85% ICU capacity – and not doing so if we’re an epsilon under – is preposterous.
Instead, when the slope of the number (or percent) of ICU beds occupied vs. time curve exceeds some critical value that, if maintained for some specified minimum length of time, like a month, would lead to 85% ICU beds in use, allowable business capacity would drop from 50% to 40%, say. If the slope remains the same or goes up further, allowed occupancy would drop back further, from 40% to 25%, and so forth. Conversely, as the slope of the curve goes down, the allowed occupancy level would rise in the same manner, gradually approaching 100% as full control (i.e., the slope we’d have in the absence of covid) is reached. Which may not be until late next summer
The idea is to have at least a month of projected ICU capacity available at all times. Not wait until three days before an extrapolation shows that 85% of beds will be occupied, and then slam on the “emergency brake”.
Far less harsh, true feedback control, and it would have kicked in earlier.
Also, I don’t see the rationale for business closures and cutbacks across the board. What fraction of covid outbreaks have been traced to hair salons, for example? And how many have been traced to grocery stores? How many to outdoor dining other than in makeshift, essentially enclosed “tents” on the street?