Who knows?
Based on the limited contract tracing studies to date, it seems likely to me that there’s a threshold concentration of virus particles below which infection is rare. Since infection outdoors is so rare, maybe if there’s a flow of fresh air sufficient to carry virus particles outdoors so they don’t accumulate, dining rooms might be safe without modification.
But those are two open questions: is there such a threshold, and how much ventilation do you need to stay under it?
Damn.
Have they taken winter weather, wind, and rain into account? (It never rains in California, right?)
I’ll bet that in SD, both 5th Ave. (downtown) and parts of Little Italy’s India St. will be next. The parking in those areas is so tight already that for several years I’ve only taken the trolley to get there. But do I really want to get on a trolley right now? (That’s rhetorical.) Shutting down streets on weekends or for special occasions is one thing, but…is this the best mid-term solution?
On the other hand, we took a walk in Little Italy just today, where every other establishment (so it seems) is a restaurant and all of course are now closed or open only for takeout. Dreary is a kind word. Without all of the people on the sidewalks and all of the sidewalk tables filled with diners, it had no character or color. It was drab and pretty ugly, actually. Very, very sad.
It’s not a done deal in Berkeley, and to my knowledge, no one is even talking about that here. The article sounded like it wasn’t all of the streets in town, as could easily be inferred from the headline, just some of them. We’ll see come June 2.
Great idea! I wish more cities could do that.
This article speaks to both air flow and talking, singing and yelling.
Thanks, DD. This is a nicely written article expressed in a way that people can understand. The author has delineated important general concepts and provided useful data and examples of trouble areas.
I have what I think is an important if semantic issue with it, though. The word “dose” is used correctly throughout most of the article, but in a couple of places it’s misused. I think that pointing this out is important because miscommunication is often due to differing understandings of word meanings.
In one place, “dose” is used where volumetric concentration (particles per unit volume) is the intended meaning. And right at the end of the article “dose” is again misused, where the term “dose rate” was intended.
Dose rate is the number of viral particles inhaled per unit time (as in, per minute), which is (breaths taken per unit time) x (the number of viral particles inhaled in each breath). In turn, the number of viral particles inhaled in each breath is a function of the volume of air that’s inhaled in each breath and how many infectious particles there were per unit volume of that air (i.e., the volumetric concentration of particles in the air that was inhaled).
In overall concept, the author is spot on. But the article needs editing to prevent misunderstandings.
“Dose” is the total amount of infectious particles inhaled over a specified period of time: Dose = (Dose Rate) x (Time). That’s really all there is to it.
But the author used the term “dose” when he really meant dose rate in his simple expression a the end (i.e., “dose and time”), a potential source for confusion in this otherwise worthy article.
Next time your shopping at your local store . Look up at the ventilation. That’s right. Recirculated air . Your already doing it . Game on .
HEPA filters are very expensive and retrofits difficult, but in recirculated air in enclosed spaces they would go a long way towards mitigating that part of the equation.
Their already broke . Sure that’s not going to happen .HVAC one of the most expensive of the building trades .
I agree and won’t argue with that at all. Being “already broke” is also another reason I wonder about the proposed expansion of restaurants into closed-off streets. Who’s going to pay for that?
Maybe the State could direct some of its covid mitigation money towards restaurant HEPAs? Just a thought.
Stores are quite different from restaurants. Supermarkets have a much larger volume of air in which the virus particles can be dispersed. You’re not next to any one customer for very long, let alone sitting in an eddy of recirculated air with them for an hour. You can wear a mask, and in civilized areas everyone is wearing a mask, which from health department stats seems to be effective.
Here’s my “In Your Dreams” wish list for restaurants to be made safe – and desirable – places to go to again. Yeah, it’s mostly science fiction and fantasy, but…
A hand-held sanitary breath analyzer or litmus paper instant test at the greeter station or entrance to immediately determine if you have covid, even if asymptomatic, before being seated.
A health department-produced video that’s required viewing for restaurant owners and employees, illustrating what the visible signs of a moderate covid infection looks and sounds like, such as the dry cough and shaking. And also things that don’t mean covid (like a productive cough, clearing your throat, and sinus drainage). Certification for opening and staying open would require this.
Esthetically-pleasing “bead curtains” or the like hanging (or on stands) between tables, and arranged so as to inhibit respiratory droplet convection by the ventilation system from one table to the next. This would reduce table spacing requirements.
HEPA filters required in all recirculating ventilation systems; fully subsidized by State government. These would effectively eliminate re-introduction of viral particles by the restaurant’s HVAC system (if it has one).
Sound conditioning to reduce overall ambient noise, and by doing so reduce the volume of speech by patrons so that it remains below 60 db (“normal conversational level”); fully subsidized by State government. This would reduce the number of potential virus-containing spray droplets and mists at the source (i.e., due to loud speech).
Bars retrofitted with exhaust fans located directly overhead and with sufficient vertical airflow as to enable people to sit next to one another – with greatly reduced likelihood of getting or giving infection. Retrofitting fully subsidized by the State. This would enable bars, pubs, and restaurants to have real “bars” again.
If we had magic instant tests, nothing else would be necessary.
Bead curtains wouldn’t stop air circulation and would be a nightmare to clean.
Magic instant tests probably represent the most fanciful wish-list item. (Like Tamicov being available next month.)
Well, maybe not beads, but some kind of esthetic baffling that wouldn’t make for claustrophobic spaces and would reduce spray/mist movement, if not by reducing convection, then perhaps by capture. Once again, a fanciful wish-list item.
Every viral test has a significant issue with sensitivity and specificity so that you will always get false positives and negatives - with less deadly virus one doesn’t care too much but the current sensitivity and specificity of the available covid-19 test (even if we could make them in really large numbers) wouldn’t be even close to enough that wouldn’t “nothing else”. (and it is not even likely that it is technically possible to the time improve these issues very significant. (Instant) tests will always be an important tool but never the only one
That’s why we also need “Tamicov”.
Right, that’s why we need magic.
The development time for something like Tamicov to market (if we cut many (dangerous) corners will be 4-6 years. (and as I said the repurposing efforts don’t look to promising so far - beside HCQ of course thanks to the orange idiot)
Hopefully less than 4-6 years, but yes. Which is why I added Tamicov to a list of “In your Dreams”.
BTW - Tamiflu is an overhyped drug which has actually very little effect and just shortens the disease minimally - one could argue we have Tamicov already - it’s called Remdesivir