It’s clear that many of the hastily assembled dining structures in place right now, especially the ones that are essentially outbuildings, aren’t actually a COVID-safe dining alternative—they’re an unintentionally deceptive option that sometimes fits legal definitions that are themselves removed from reality.
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Yes, true. This type of an essentially fully enclosed “outdoor” area is a stretch of the intent and meaning of “outdoor”, any time of the year.
… one person (Case B) infected two other people (case A and C) from a distance away of 6.5 meters (~21 feet) and 4.8m (~15 feet). Case B and case A overlapped for just five minutes …
A very interesting article. Here’s part of it, for those who don’t want to read the whole thing:
“What can we conclude from all this? I think there are three broad lessons here. One, small data can be extremely illuminating. Two, air flow and talking seem to matter a great deal. Three, sadly, indoor dining and any activity where people are either singing or huffing and puffing (like a gym) indoors, especially with poor ventilation, clearly remains high risk. However, given these pieces of information, it also seems that both masks (which dampen the emission of droplets/aerosols from the infected person and which can also lessen the amount one breathes in) and ventilation remain crucial tools.,We should follow Japan’s lead and discourage talking, especially loud talking indoors or on public transportation.”
Memo to restaurants when restrictions relax: Turn down the music.
So, the only thing that the CA government has done is to shut down restaurants, along with other “non-essential” businesses. No steps have been taken and no money spent to help restaurants and other businesses have “safe air”.
Meanwhile, billions in tax revenue are being lost. Those billions, managed differently than brute force sledgehammer closures, might have been spent on helping restaurants to be made safe during the pandemic.
One of the justifications that I read in a local news article for closing restaurants is that they’re gathering places.
I think that properly-placed portable HEPA filters, while not the whole answer, could help greatly in restaurants. I also think that the government should subsidize them.
https://www.washingtonpost.com/health/2021/02/10/carbon-dioxide-device-coronavirus/
[Washington state] egulators introduced a new policy, which appears to be one of the first of its kind, allowing certain restaurants to count as “open air” dining even if they have four walls. In a new pandemic trend, these establishments can open up large windows or doors and actively measure levels of carbon dioxide, the gas we all exhale when breathing, as a key indicator of how much fresh air is circulating.
Excellent concept, although the C02 concentration levels would need to be measured at each table location. An average or, worse yet, a single measurement in the dining space would be pretty meaningless.
CO2 is typically evenly dispersed. That’s why it’s a handy way to measure ventilation quality.
What leads you to believe that CO2 is typically evenly dispersed, any more so than anything else that’s airborne, such as sub-microscopic particles? Like smoke.
Gases and tiny airborne particulates mix in pretty much the same way and by the same mechanisms. Molecular diffusion is almost negligible in real scenarios. Mixing is by way of convection and the shear-induced development of initially “large-scale” turbulent eddies.
The initially “large” eddies break down through a cascading process to smaller and smaller sizes. The cascade continues until the eddies are so small that they’re prevented from further relative motion by aerodynamic drag; i.e., turbulent diffusion. The contents of the smallest eddies are deposited in the flowing (or still) air where they stop.
The degree of heterogeneity or homogeneity of the overall mixing in a volume is dependent in a first-order way on the size and location of objects in the primary convection paths, due to their direct effect on the sizes and locations of the largest-scale eddies. “Objects” includes both boundaries (walls, floor, ceiling) and things like tables, dividers, and people.
The human sources of CO2 are themselves dispersed. Especially when pandemic distancing rules are in effect.
Agree, which is why I think that the Washington State concept of using measurements of excess CO2 concentration (above that found in open air) is an excellent one. I just don’t think it should be assumed to be uniform throughout a restaurant space.
The Washington guidelines require that the CO2 monitor be in the seating area farthest from the outdoor air source.
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I’m almost at a loss to describe how near-perfect the substance of this document is. I actually printed it out.
I feel that the WA State approach should be held in nomination for our much-needed nation-wide standard.
I (we?) can only hope that Biden’s team is aware of this outstanding WA State effort, and that people in the medical professions like Dr. Fauci and others will also endorse and publicize it. It represents by far the best physics-based approach to assessing dining safety I’ve seen – in every detail.
The one and only thing I might add is that a tare reading should probably be made of the local ambient atmospheric (outdoor) CO2 concentration. There’s some allusion to this in the document, but it doesn’t go far enough and is a bit vague.
The requirement would then be that the CO2 concentration at the designated test location in the restaurant space should not exceed the tare (background) level by more than 50 ppm. But I’d be happy to bypass that nit and just go with 450 ppm as being the max.
The basis and details of this approach, to the credit of what was obviously the product of a very thorough and thoughtful WA State study, needs (urgently, I think) to get widespread distribution and attention.
I’m sure it will be well managed by owners and staff . Thumbs up . A step forward.
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Yes. Absolutely.
Here’s a related item, a computational fluid dynamics (CFD) simulation carried out at Harvard last month and also published by NYT in Wednesday’s newspaper (much better online, actually), illustrating covid spread by airflow in classrooms.
They certainly appear to have reached the right conclusions/recommendations (portable HEPA filter plus exhaust fan blowing out of the window, with a cracked-open lower window for outdoor air intake), although the default placement of the filter that’s suggested (center of room) could be debated.
It doesn’t appear that they included turbulence shear/diffusion (e.g. k-epsilon model or direct) in their simulations, however.
The same principles hold for restaurants.
A corner table is a bad place to be in any case. Corners tend to be semi-stagnant accumulation zones. Restaurants should put artwork or plants in corners, not people, until the pandemic-related danger has passed. Whenever that will be.
I was encouraged to read that classrooms that re-opened to limited in-person instruction yesterday in San Diego Unified (after a year) included HEPA filters among steps taken to reduce virus transmission.
Excellent. And I agree with the quote at the end of the article:
“I don’t think this is rocket science,” says Freed, “which is why it’s mind-boggling to me that the public health officials aren’t talking to the building scientists.”