Airflow in South Korean Restaurant
Airflow in cars
Two studies recently released build on earlier work to inform our understanding of airflow and how it spreads the SARS-CoV-2 virus. Fred reviews the airflow in cars and highlights important actionable information on optimum means of diminishing the risk of spreading the disease to other passengers in the car and Nick reviews the study out of South Korea that detailed a far greater distance for transmission of the virus indoors that is driven by airflow
🌾Outdoor air is best
🧭Airflow direction is important
📐Transmissibility seen as far as 21’
🏎Open all car windows, if not opposite side to passengers
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Transcript:
Nick van Terheyden
Hi, this is Dr. Nick on the incrementalist here with incremental insights for better business and better health.
Fred Goldstein
And I’m Fred Goldstein with accountable health here working with Nick and others, his companies seek to reopen and operate safer during the COVID pandemic. So one of the areas we focused on a bunch, Nick over the last couple months, and actually identified this earlier, I believe it was back in March from one study is this whole issue of airflow. And there have been a number of really interesting studies that have come out over the last week or so about this. So could you talk about that first one we took a look at?
Nick van Terheyden
Yeah, so I think, first of all, let’s talk about the historical studies, there was the choir in Washington State, and I’m blanking on whatever the location was, but it’s sort of named after that, then there was the restaurant study, that was really informative in terms of transmission that was detailed. And what came out of South Korea was an extraordinarily detailed analysis of a single restaurant. And they even went back to CCTV footage, to actually determine times of contact position, and so forth. So it wasn’t just memory, which is flawed, for the most part in terms of people’s ability to remember what happened, where they did, and so forth. And here’s what’s interesting. So first of all, all credit to the people that went there. I mean, this is a really detailed, deep dive. And it’s what we need, because that helps us understand and really get to the bottom of the transmission process. But here’s what came out of that. They were seeing transmission over distances that you would not expect, given the current guidance that says six feet, they were seeing somewhere of the order of 20 feet, 15 feet, in the case of specifics, where the individuals had not gone to, or been in close proximity for the 15 minutes have total, whatever they would distance they were wearing, face coverings and so forth. Although here’s the thing about food and restaurants, you can’t eat whilst you’re wearing the face covering, although there are people that is to do this. And if fat culturally, this is boats that managed to achieve that. So it is possible source, but it’s very, very difficult. So you end up sort of letting your guard down, not deliberately, and exposing yourself. And they even dive in further and looked at the airflow based on the air conditioning, and it was reflected. So this wasn’t just pure airflow coming out of the ducts, it was actually coming out and then bouncing off walls and showing a essentially a flow. And, you know, I don’t know if this is true, but I always get the sense that airflow wants to be laminar it tries to sort of case stick to one direction unless it gets diverted. And that was what was happening. So we have evidence of transmission across across longer distances. What they suggested was that the viral particles and it’s the smaller ones that cause the problem because they tend to stay airborne. for longer periods of time, this whole issue of aerosols and droplets, it’s really the size of the particle allows it to stay airborne, anywhere from three to six hours or so potentially. But what it informs is a whole different thinking in terms of the way that you approach any kind of indoor activity And we’ve certainly talked about fans and opening doors and so forth. But finding flow that doesn’t force the flow so that it crosses other people. So I think we’re going to see more of this over time. But there are some other circumstances where air flow is very significant. And that’s the study I know you looked at, which is in the car, which we’re all sort of doing. We still do, but with somebody else, right.
Fred Goldstein
Sure. And before we get there, Nick, a couple questions for you on that study. One was, I believe the distances were pretty far, weren’t they?
Nick van Terheyden
Yep. So 21 feet in one case and about 15. And another.
Fred Goldstein
And the other was the duration of time was shorter, wasn’t it? Yeah,
Nick van Terheyden
it, it was nowhere near the sort of extended time that we think is required. So this is this is the deal, infected, deposited dose is obviously higher. And I think it’s the concentration through that flow that says, we’re going to get that and it’s coming at you in a position where you don’t have a face covering on because you’re eating.
Fred Goldstein
So take away from this, what should people be considering now if it’s further distance, and shorter time?
Nick van Terheyden
Run in, don’t go near anybody and run out again? Absolutely no, in itself?
Fred Goldstein
Yeah. And that’s that whole question. Now we’re even seeing the CDC say, hey, restaurants are one of the five places that are really high risk. And so reducing the number of people in there, obviously now, considering airflow is critical. And as you pointed out, this study that I looked at was on automobiles, people are traveling in them, it’s really kind of an Uber scenario, too. Because what these folks did in this study, which was called air flows inside passenger cars, and implications for airborne disease transmission, was they looked at window openings, and analyze pressure gradients, the flow of air inside the car. And they essentially placed in this was a model a computer model simulation. So not quite as advanced as that study you talked about where they actually had people sitting in the seats do recreate the situation. But they did put in a person that driver seat front left and a posture and the person the passenger seat rear, right, and essentially began to look at what the airflow is where with the windows closed, with one window, open two, windows open three, and four. And what they found was fascinating. Based on these pressure gradients Was it the best way to sit, although force for windows open makes a ton of sense, and does create the sort of split was if you open windows opposite the person. So the front right window is opened and the left rear window is open, creates this flow that goes counterclockwise, and essentially reduces the amount of potential particles you could be exposed to sitting in that car. By expelling it whether the front persons infected to the back, you don’t know which, but that appeared to be the best scenario if you couldn’t open all four of them. So So break it down as simply as possible best options for Windows and passenger seating. For people, if they’re in a car, thinking about somebody potentially being infected and reducing that infection, yeah, instead of thinking about, I’m going to open my window and they’re going to open theirs, you open the opposite windows, which is very much different than you would think of. But if you can obviously open all four, it does create a huge amount of air change per hour, well over 100 changes per hour. And it also sort of divides the car. But if you can’t open those opposite windows, and it creates this flow that that essentially ejects particles from the people who are potentially infected in certain cases, and then creates sort of a zone of less exposure in those two areas, the front and the back for the two years.
Nick van Terheyden
So top choice open all for Windows. And for those of you that, you know, thinking about this, I always used to talk about it when I was doing skydiving, if you wanted to know what skydiving was like, open the windows and stick your head out of the car driving at 70 miles an hour. That’s exactly what skydiving was. It’s lots of airflow going on. Typically, you can’t so it’s the opposite windows. I think that’s you know, useful information and then not necessarily the way that we were thinking about it, right. So this is actually really helpful.
Fred Goldstein
Absolutely. And it really gets to the same point that there identify now indoors, it really is about that flow of air between individuals. And obviously if you’re in a car, this was not wearing a mask, they weren’t measuring, hey, here’s, here’s how much more safe you are. But they were measuring the potential exposure of the two individuals in the car. So really a fascinating study and something everyone should take to mind as they’re looking at potentially traveling with other individuals. I can say we had a potential individual who thought they might be infected and I was as and we were at a location and we said okay, now you’re driving with this other person sit in the furthest back seat, you You can find, which happened to be three rows back and then open every window as you transport yourself home and make sure you’re both wearing masks. But obviously this study is beginning to help us figure out what really does work to limit that airflow, which is becoming possibly the critical issue associated with the spread of this virus.
Nick van Terheyden
Fresh air is king. That’s what I would say.
Fred Goldstein
Well, it’s Fred Goldstein. And thanks so much for joining us this week. Nick once again. Fantastic.
Nick van Terheyden
And this is Nick van Terheyden I’m the incrementalist here with incremental insights for better business better health. Alright, perfect. Great. me Stop that.
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