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
I tried it on without a mask first. Looks super dorky, so this would not be my first choice of mask. It feels tight (could enlarge the template a little if needed), so it should greatly improve performance of my surgical mask, which was very leaky around the sides. /4
The brace will get me closer to the material filtration efficiency of this mask (ASTM level 1), going from ~30% to 60% at 0.5 μm and from ~30% to 80% at 1 μm. /5
Verdict: Very useful. it's tiny and lightweight, so I'll keep it with my backup surgical mask. Good for backup but I wouldn't want to wear it all day. Also, I need to upgrade to an ASTM level 2 surgical mask, as it will filter particles much better than ASTM level 1. /6

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More from @linseymarr

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 Image
We used a mass balance approach, although we actual did the calculations in terms of volume of CO2. /2 Image
Y's are volumetric concentrations of CO2 /3 Image
Read 5 tweets
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
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
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
14 Dec 20
Absolute 🔥 from the inimitable @edyong209! So much insight, so succinctly written, with input from scientists with deep expertise (from well before 2020) on viruses. Excerpts with my thoughts follow... /1
Their movements through the air have been poorly studied, too. “There’s this very entrenched idea,” says Linsey Marr at Virginia Tech, that viruses mostly spread through droplets (short-range globs of snot and spit)... /2
rather than aerosols (smaller, dustlike flecks that travel farther). That idea dates back to the 1930s, when scientists were upending outdated notions that disease was caused by “bad air,” or miasma. /3
Read 8 tweets
23 Nov 20
We started studying cloth masks in March. Preprint now at medrxiv.org/content/10.110… Take-home: Cloth masks are not an N95, but they work reasonably well for aerosols 1-2 microns and larger, which is the size that we think mostly mediates transmission. See thread. /1
.@jinpan @charbeleharb & Leng tested vacuum bag, microfiber, coffee filter, MERV 12 filter, cotton, acrylic, bandana, CDC sewn & non-sewn designs, surgical mask, face shield for material filtration efficiency in a filter holder and inward and outward protection on a manikin /2
For submicron particles, vacuum bag, microfiber, and surgical mask filtered out >50% of aerosols. Other materials were way below 50%. /3
Read 6 tweets

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