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Dr. Richard Corsi

14 Jan, 10 tweets, 3 min read

1/

Total US COVID-19 deaths = 385K (400K by end of weekend)

1 of every 855 Americans dead by COVID-19
1 of every 43,600 S. Koreans dead by COVID-19

End of Feb 2020
US deaths = 20
South Korean deaths = 17

By end of Feb 2021 US likely exceeds 500K
S. Korea may exceed 1,400

2/ Yes, the vaccine will ultimately help. But unless we work relentlessly to starve this virus of its hosts the case and death count will remain out of control until then. And the new variant means that we need to quadruple down on reducing inhalation dose.

3/ Inhaled dose (D) is important in BOTH the near (close) and far fields.

D = C x B x t x f

D = # virus-laden particles deposited (ultimately convert to vol), C = concentration in breathing zone (#/L), B = resp minute volume (L/min), t = time (min), f = fraction deposited.

4/ Note that D, C and f should be taken as a function of aerosol particle size. For near field, universal mask wearing (reduced C) and physical distancing (reduced C) are both critical, as is reduced t & reduced B (avoiding being around others while doing aerobic exercise, etc.)

5/ For indoor far field, C can be reduced by universal mask wearing, increased ventilation, improved engineering controls for particles, and lower B and t.

6/ Avoid non-essential indoor environments. Wear a mask in essential indoor environments (other than own home with immediate family unless someone is quarantining or isolating). Avoid indoor environments where universal mask wearing is not required and enforced.

@trimet

7/ Practice sufficient distancing in essential indoor environments other than home (w/ caveats listed above).
If on a bus see whether windows can be opened for cross-flow (@trimet in Portland does a good job with this) and distance from others.

8/ If taking ride share / taxi make sure you AND your driver wear masks and ask driver if windows can be opened. If driver says "no" ... seek another ride.

Running out of steam ... more to come

I've tweeted extensively about layered dose reduction for schools & businesses.

9/ Info on inhaled deposited dose and layered dose reduction here: corsiaq.com. A screening model to explore layered inhalation dose and risk reduction in far field at safeairspaces.com.

@Wymelenberg

10/ @Wymelenberg & I will also be offering a short course on layered risk reduction for businesses w/ half days on Feb 4 and 5. More to come ...

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More from @CorsIAQ

Dr. Richard Corsi

@CorsIAQ

13 Jan

A record day for US COVID-19 deaths at > 4,200.

Total to date = 381K

US = 1 out of every 862 Americans dead by COVID-19
S. Korea = 1 out of every 46,000 dead by COVID-19

By end of Feb 2020 the US deaths by COVID-19 = 20

By end of Feb 2020 we will likely exceed 0.5 million

Despite an extraordinary time frame for an effective vaccine, things will continue to get worse until widespread vaccination occurs if Americans continue to fail to accept and relentlessly employ layered inhalation dose reduction. It's not rocket science, folks.

See my previous twitter threads as well as those of others. Explore here: safeairspaces.com. A blog on inhaled deposited dose and key factors here: corsiaq.com.

Read 4 tweets

Dr. Richard Corsi

@CorsIAQ

4 Jan

Particle settling: In case anyone wants to see a derivation of Stokes equation for particle settling - here is one of my old course notes. Note that aerosol particles achieve terminal settling velocity almost instantaneously, unlike someone jumping out of an airplane. more ...

This derivation assumes spherical particles & does not adjust for different shapes that affect drag force. It also does not adjust for particle "slip" as diameter approaches the mean free path of air molecules & drag is reduced as the no slip condition is violated. more ...

A 0.1 micron particle settles three times faster for this reason than is shown at the bottom off the page. A 1 micron particle settles about 17% faster. Slip correction becomes smaller and smaller for larger particles. More ....

Read 5 tweets

Dr. Richard Corsi

@CorsIAQ

31 Dec 20

1/ Dealing with an inferno of infectiousness.
We failed to do what was needed to keep this mess from getting out of control. Our situation is horrific and will soon get much worse due to end-of-year holidays + more infectious variant. Vaccine distribution also F grade to date.

2/ All of this means even greater mass casualties (for both those who live and die) in the coming months.

3/ Expect one-half million dead by end of February, a lot more of the following: refrigerated trucks outside of hospitals, hospitals faced with triage, schools that will not re-open, business closures, lost jobs, homeless, and (unfortunately) more.

Read 25 tweets

Dr. Richard Corsi

@CorsIAQ

27 Dec 20

1/ Teaching Indoor Air Quality

I taught both undergraduate and graduate indoor air quality classes for many yrs at UT Austin. Proud of the fact that many current professors (and some department chairs) took my courses as students & are now teaching a new generation.

2/ I loved infusing my research into lectures, having students bring different scented products to the classroom, exposing them to a small amount of ozone and measuring ultrafine particle formation (image). We also measured rebreathed fraction in the classroom, etc.

3/ Every class would have an assignment with CO2 analyzers checked out to groups w/ 1 wk to measure avg CO2 concentrations and rebreathed fraction & then use the Rudnick-Milton model to estimate probability of common cold & flu transmissions across campus (50+ locations/class)

Read 12 tweets

Dr. Richard Corsi

@CorsIAQ

25 Dec 20

https://twitter.com/HuffmanLabDU/status/1342336300611903491

1/ "To prevent the virus from spreading, companies that needed employees to return to in-person work put up plexiglass barriers, implemented daily temperature checks and required workers to wear masks while in proximity to others." What's wrong with this picture?

https://twitter.com/HuffmanLabDU/status/1342336300611903491

2/ Plexiglas barriers are not very effective at reducing transmission by aerosol particles. Temperature checks do not catch pre-symptomatic, asymptomatic, or symptomatic infectors w/o fever. Masks "while in proximity of others" = unacceptable. Masks at all times indoors.

3/ And we wonder why there are outbreaks in the workplace. LRRS = Layered Risk Reduction Strategy, not LRR Shortcut. LRRS must be done based on layered interventions that make scientific sense. Performance = sad. Almost a year in, folks. What will it take to get this right?

Read 5 tweets

Dr. Richard Corsi

@CorsIAQ

23 Dec 20

1/ More results (year 1) of our Healthy High School PRIDE study. Here we show a cumulative distribution plot of average rebreathed fraction (RF) of air in classrooms during the occupied day. RF is actually converted to a percentage on the vertical axis.

2/ Note that a rebreathed fraction of 0.03 (3%), for example, means that 3% of every inhaled breath originated from the collective respiratory systems of others in the indoor space (including anyone infected with COVID-19).

3/ In my recent USEPA webinar on layered risk reduction strategies for schools I argued for a maximum RF < 0.008 (0.8%) for classrooms during this pandemic. That translates to an average CO2 concentration of less than 700 ppm.