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Dr. Richard Corsi Profile picture
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9 Oct, 4 tweets, 2 min read
1/ At very beginning of this pandemic (late February/early March) we placed CO2 monitors w/ data loggers in several locations of the library @Portland_State, counted occupants on several floors, and flux in/out of the library to get an average time of approximately 2 hrs/visit.
2/ We used the data to determine the average rebreathed fraction of air on floors & occupancy numbers & average occupancy time to estimate reproductive numbers if infectors were present (w/ a range of quanta generation rates) using the Rudnick-Milton model. Upshot ...
3/ BIG differences in rebreathed fraction between floors, but small in general. However, w/ large # of occupants, even small rebreathed fractions can lead to predicted site-specific reproductive # between 1 and 5 for a single infector in teh space depending on quanta gen rate.
4/ For collective (emphasized) infection potential related to virus-laden particles in the far field, it is not all about how high the CO2 concentration is. Amount of time in a space and # of occupants (which also influences potential for one or more infectors) also important.

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More from @CorsIAQ

Dr. Richard Corsi Profile picture
5 Oct
1/ Many years ago I was trying to get permission to do extensive IAQ sampling in a large school district in Texas. After weeks of trying I finally got to meet the then superintendent. I think I wore him down. In the end he looked at me and said ......
2/ "Alright. Do it. But if you find ANYTHING wrong I never heard about it." I was shocked. My team did find a lot that was wrong (w/ woefully poor ventilation being the root of many problems). We informed facilities staff and specific school officials.
3/ The want of anonymity was common between all five school districts that I worked w/ over 20 years. But some districts were more accommodating, were receptive to help, and in ONE case took our findings and acted positively to improve indoor air quality in their schools.
Read 4 tweets
Dr. Richard Corsi Profile picture
4 Oct
1/ It is important to recognize that as long as an infected individual is in an indoor space, virus-laden aerosol particles will accumulate to higher concentrations in that space until (in a well-mixed space) an approximate steady-state concentration occurs. more ....
2/ The steady-state condition is reached when the rate of emissions from the source is equal to the rate of removal by ventilation, deposition onto surfaces, & filtration. At this point the rate of change of concentration with time is zero. more ...
3/ The time to achieve 95% of steady-state is 3/B (where B is the sum of removal mechanisms, each w/ units of inverse hours). I have observed K-12 classrooms with outdoor air change rates as low as 0.5/hr. w/o filtration and little deposition this = 6 hrs to steady-state. ....
Read 4 tweets
Dr. Richard Corsi Profile picture
1 Oct
1/ Aerosols

I am seeing a lot of what seems like tension and chatter about aerosols vs. airborne and disciplinary differences in how the latter is defined.

a lot more ...
2/ My "go to" source for all things aerosols is WC Hinds' great text - Aerosol Technology: Properties, Behavior, and Measurement of Airborne Particles.

Anyone who studies aerosols should know of Hind's text. I am old enough to have a tattered copy of the (cough) 1st ed. more
3/ Note the title of the book carefully.

Please also note that aerosols are a binary system consisting of particles AND the gas in which they are suspended. Aerosol particles refers to the particle (liquid or solid) phase of aerosols.

more
Read 14 tweets
Dr. Richard Corsi Profile picture
26 Sep
1/ Wish it had not taken this long given that many bright scientists/engineers have known & warned of same for 6+ mos. But GR8 to have Dr. Fauci on board. Hope he speaks often & underscores signif' role of aerosol transmission.
2/ I hope this becomes a pivot point & educational moment for deniers among policy makers & public to stop propagating this deadly disease so that more schools can eventually re-open, our economy does not continue to struggle through fits and starts, & less people suffer and die.
3/ Remember what many of us have been saying for months & months. Avoid non-essential indoor environments, and particularly those that are densely occupied and poorly ventilated. Always wear a mask inside buildings other than your own home, physically distance,
Read 5 tweets
Dr. Richard Corsi Profile picture
26 Sep
1/ An elderly friend has been hospitalized w/ COVID-19.

It has bothered me that in many discussions about COVID-19 & its skewed impact on seniors there is a subtle undertone that "it's mostly just old people," which implies that there lives are not worth all that much.
2/ I get that from a purely "economic" perspective they do not contribute as much as someone in prime of life. I get the philosophical perspective that many have lived long lives & others still have long lives ahead of them. But, ...
3/ I also strongly believe that those who have paved the way for younger generations have a right to die w/ dignity. Dying in a hospital, gasping for oxygen on a ventilator, and w/o your loved ones present is not a dignified way to find the door.
Read 4 tweets
Dr. Richard Corsi Profile picture
19 Sep
1/ A follow-up on gyms. A couple of months ago I modeled the volume of particles deposited in the respiratory system of those infected in an outbreak in Restaurant X in Guangzhou China with assumed infector emission profiles. More ...
2/ I then placed the infector from Restaurant X in different scenarios w/ ratio of volume deposited in new scenario to that of restaurant X. That ratio (omega) for a specific gym is shown in figure here. The vertical axis is omega for several ventilation/control scenarios. Image
3/ In this analysis, infector X is a staff member in the gym emitting aerosols that are well mixed into the gym. The receptor did 75 minutes of aerobic exercise w/ a heavy breathing rate (greater inhalation dose than if not doing aerobic exercise).
More ...
Read 5 tweets

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