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Linsey Marr Profile picture
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24 Feb, 4 tweets, 1 min read
I have no doubt that infection can happen via eyes and that large droplets can land there, but aerosols are unlikely to deposit there. If I assume 1 cm jet directed at eye, it must be 6000 mph for a 1 μm particle, 300 mph for 5 μm, 73 mph for 10 μm. /1
Aerosol scientists know that it's pretty hard to collect small aerosols by impaction; need very high velocities and tight geometry. This was for Stokes number=1. Someone should check my calcs. /2
I still recommend eye protection for close contact situations to avoid large droplet spray. And stop rubbing your eyes! /3
Face shields also help divert aerosols in face-to-face conversations. /4

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More from @linseymarr

Linsey Marr Profile picture
29 Jan
I keep talking about HEPA filters as inserts for masks. How do you get one? I took inspiration from @SmartAirFilters (smartairfilters.com/en/blog/hepa-f…) and decided to get one and test it. My video here: TLDR: 2-ply >95% efficient. 🧵 /1
I picked up this HEPA filter from the HVAC filter aisle at the local big box store. It's pleated and comes in a frame, so you have to cut it out and pull off glue strips, as shown in the video in my first tweet. /2
How badly does the deconstruction process damage filtration efficiency? @isjinpan looked at three types of samples: 1) pristine, 2) spanning a crease, 3) under a glue strip that I pulled off. /3
Read 6 tweets
Linsey Marr Profile picture
27 Jan
Glad to see CO2 in my classroom indicates excellent ventilation. My class has been meeting online, but this is good news for our potential to meet in person. Other classes met there yesterday, and ~20 people were there when I picked it up today. More for calcs... /1
We used a mass balance approach, although we actual did the calculations in terms of volume of CO2. /2
Y's are volumetric concentrations of CO2 /3
Read 5 tweets
Linsey Marr Profile picture
26 Jan
I forgot my cloth mask today, so it was a good day to try a mask brace for my backup surgical-type mask. A 🧵on making it and my impressions of it. /1
I used the @fixthemask DIY mask brace V2.0. I printed the template, cut it out, and traced it on a rubber sheet, the recommended 1/32" Shore 40A material. /2
I cut it out carefully with scissors (thanks Twitter for the warning to trim smoothly to reduce the chance of tearing). The top loop goes around your head, the middle peak over your nose, and the bottom loop around your chin. /3
Read 6 tweets
Linsey Marr Profile picture
18 Jan
Airborne Transmission of SARS-CoV-2: What We Know academic.oup.com/cid/advance-ar… Paper from our @theNASEM #EnviroHealthMatters workshop. Source-to-dose framework, like for particulate matter and health effects, and 4 critical questions: /1
Q1: What size particles are generated by people & how do they spread in air? A: Large range of sizes and concentrations, aerosols+droplets important at short range (<1.5 m), aerosols dominate exposure at longer range (>1.5 m). /2
Q2: Which size particles are infectious and for how long? A: <5 μm and probably larger, half-life is around 1 hr /3
Read 5 tweets
Linsey Marr Profile picture
13 Jan
Our multidisciplinary team sought to correct some bits of conventional wisdom on transmission of viruses through the air. Still working with historian @ethomasewing and others to show how these bits became embedded. journalofhospitalinfection.com/article/S0195-… Myths... /1
Myth 1: “Aerosols are droplets with a diameter of 5 μm or less”

Myth 2: “All particles larger than 5 μm fall within 1-2 m of the source”

Myth 3: “If it's short range [close contact], then it can't be airborne”

/2
Myth 4: “If the basic reproductive number, R0, isn't as large as for measles, then it can't be airborne”

Myth 5a. “If it's airborne then surgical masks (or cloth face coverings) won’t work”

Myth 5b: “The virus is only 100 nm (0.1 μm) in size so filters and masks won't work”

/3
Read 4 tweets
Linsey Marr Profile picture
27 Dec 20
A 🧵on humidity and airborne viruses. Several articles have said that at higher relative humidity (RH), droplets/aerosols retain more water, are larger, and then fall out of the air faster. True, but the effect of RH on biological decay is probably more important. /1
.@DrWanYang and I studied this question in 2011, exploring different removal mechanisms from air as a function of RH. I thought we’d find that at high RH, droplets/aerosols would be a lot larger and settle out quickly. journals.plos.org/plosone/articl… /2
But the biological inactivation rate is more sensitive to humidity. See bigger steps in RH for inactivation than for settling in Fig. 5. We used decay rates for influenza from Harper 1961. Also note the difference ventilation makes at 1 vs. 10 ACH. /3
Read 13 tweets

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