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Nicholas Schiefer
@nschiefer
Replying to
@nschiefer
(For a summary of the history of aerosols in the context of COVID, I really like this thread: twitter.com/jljcolorado/st)
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Prof. Jose-Luis Jimenez
@jljcolorado
1/ TIME FOR SOME AIRBORNE + DROPLET HISTORY Now that @WHO and @CDCgov have finally accepted *after a year of denial and delays* that airborne transmission is a major mode for COVID-19, it is time to review the history to try to understand why this response was so poor.
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Nicholas Schiefer
@nschiefer
Air filters are really good appliances! I have one to help with dust and it's cheap and quiet. They're basically zero effort once they're set up, unlike masks or shutting down businesses. Lots of people out west already have them for smoke season.
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Nicholas Schiefer
@nschiefer
The wonderful
@microcovid
estimates that a HEPA air filter with a high enough flow rate reduces COVID transmission risk by 3-6x, with longer (more dangerous) interactions getting the greater factor. That's comparable to having everyone wear a cloth mask (!!!)
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Nicholas Schiefer
@nschiefer
Air filters are a great complement to vaccines, since they filter particles regardless of what virus or variant lives on them! I wonder what the effect of this on flu or cold virus transmission would be. This might be worth it even for the post-COVID benefits alone.
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Nicholas Schiefer
@nschiefer
Despite this, I have heard very little about ventilation/filtration upgrades in offices or retail stores. Anecdotally, I've only noticed public air filters in a One Medical office (good job!)
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Nicholas Schiefer
@nschiefer
I have no idea how much commercial HVAC upgrades would cost, but as a lower bound: we could buy the same air filter that I have for dust control at home (~$400 MSRP for 350 cfm CADR) to cover all 97 billion commercial sq ft of real estate in the US for ~$110 billion.
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Nicholas Schiefer
@nschiefer
(Assumptions: retail prices of $400 per 350 cubic feet per minute of air flow, 97 billion sq ft of commercial real estate based on a random figure I found online, 12 ft average ceiling height to determine air volume, microCOVID goal of 5 air changes per hour.)
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Nicholas Schiefer
@nschiefer
Obviously, $110 billion is a lot! But... not that much on the scale of the trillions of dollars spent on COVID relief. I'd also expect that you could do a lot better than paying retail prices at country-sized volumes.
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Nicholas Schiefer
@nschiefer
The weirdest part is that I don't understand why this hasn't happened more? It's useful on the margin and doesn't require much coordination. As far as I know there are no regulatory barriers. I would preferably patronize businesses that advertised good ventilation or filtration!
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Nicholas Schiefer
@nschiefer
Replying to
@nschiefer
Apparently Belgium has mandated CO2 meters in many public spaces (restaurants, bars, gyms), using CO2 as a proxy for fresh air ventilation (that is, air brought from outside). Filtration won't affect that, but it seems like a pretty good attempt at making ventilation legible.
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Nicholas Schiefer
@nschiefer
Either I'm missing something (and please tell me if you think I am!), or we're... just collectively making a terrible decision for no good reason? We're trapped in a bad state, and it's not even like we need coordinated action to make it much better. Any ideas?
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Nicholas Schiefer
@nschiefer
(I've not verified this in any way) Apparently teachers are trying to use air filters in their classrooms and getting told that they are... fire hazards? A large air filter draws maybe a few hundreds Watts.
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Karyn TJ
@karyntess1
Replying to @j_g_allen
Fire codes- our district told us we couldn’t use them (we bought them for ourselves) because they’re a fire hazard.
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Nicholas Schiefer
@nschiefer
I wonder if this is an actual safety concern (albeit probably not one that outweight the benefit) a bureaucratic mixup, or someone on a power (ha!) trip.
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