1/ Reviewing data from past school study in Texas. On average ventilation rates are considerably higher in portable than in permanent classrooms, but with much greater variability.
2/ Portables are much more connected to outdoor environment - greater infiltration and opportunity for natural ventilation (open door/windows).
3/ But interestingly, portables (on average) appear to have higher rebreathed fraction of air (fraction of inhaled air that was exhaled by others in the indoor space) than permanent classrooms due to higher density (occupants per classroom volume).
4/ While portable classrooms generally have other IAQ problems, during COVID-19 times if density is controlled they might actually provide greater opportunity for increasing ventilation. I will discuss this Thursday in my ISIAQ/AIHA webinar hosted by USEPA. More to come.
And thanks much to @S_Kumar22 for providing data!!!!!

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More from @CorsIAQ

16 Nov
1/ As a senior in high school I ran for Mayor of @TorranceCA, Calif, against a sitting Councilmember (James Armstrong). At the time I believe I was the youngest candidate to ever run (& lose!) in California. Gr8 experience and learned a new meaning for the term "landslide".
2/ I conceded immediately after the votes were counted. Within a couple of days my "opponent" and I had lunch together at the Good Earth in the Del Amo Mall. We kept in touch over the years until Jim's passing & would occasionally discuss our campaign and debates.
3/ We had several public debates, including one on the radio that I wish I could find. To this day, I am haunted by a question regarding my views on binding arbitration.
Read 4 tweets
15 Nov
1/ As inferno of infection kills & drives nation to the abyss, many governors starting to take stricter action. Many waited too long, frozen in headlights, or in denial. Need strong leadership (courage) to reduce inhalation dose (& so cases & deaths). Just Do It!
2/ "Fits & starts" has been a HORRIBLE approach & only added to suffering, deaths, economic crisis, lost jobs, detriment to education of children. The correct approach was all-out assault on reducing inhalation dose to "starve" virus of hosts and then manage it like others did.
3/ Much more difficult to do this now because of lack of leadership & long delay in listening to experts related to transmission by and control of aerosol particles that are ride share for virus. Need an all-out assault to reduce inhalation dose now to save lives. Let's do it!
Read 6 tweets
15 Nov
1/ Much of US is on fire w/ COVID-19 infection & the flames are only getting hotter. Politicians & the general public who continue to be cavalier about, or blind to, this inferno are adding fuel to fire. People are burning. People are dying.1st responders are exhausted & dying.
2/ We know what to do. Wear a mask in indoor spaces outside of own home w/ immediate family, avoid non-essential indoor spaces, limit time in indoor spaces where you must go, physically distance. Just do it!
3/ Business or building owners/building managers: Require masks, design for physical distancing, reduce density, increase ventilation, improve filtration and/or employ UV. Just do it!
Read 5 tweets
13 Nov
1/ Heading to 200K/day this month & 300K/day in Dec. Increased death rates to follow. What got us here is obvious. Failed leadership. Ill preparedness. Stubbornness. Failed communication. Irresponsible behavior. Water under bridge now. Learn from it, but move on w/ urgency.
2/ Do we act now to save hundreds of thousands more from gasping for breath & dying without family around them, the heartache of losing loved ones, the struggles of those who survive, the horrific impacts on our economy? Acting now is responsible, empathetic, and patriotic.
3/ Please be a patriot. Act. Wear a mask in any indoor space other than your own home w/ immediate family present. Visit only essential indoor spaces where everyone wears a mask. Reduce time in those spaces. Distance. Ventilate. Filter. Sanitize hands. Help to educate others.
Read 5 tweets
12 Nov
1/ Complexity of Close Contact

Inhaled deposited dose of aerosol particles via close contact is difficult to model, even if two people stay facing each other at 4 - 6 feet apart, due to huge variations in emissions as well as dispersion of the plume between them.
2/ If the indoor space is a crowded event (e.g., wedding reception, bar, etc.) in which people move around, the complexity becomes even greater. How often does a person come in close contact with one or more infectors? What is the average contact time?
3/ I have been thinking back to my PhD dissertation (way back in the day) when I studied and applied surface renewal theory for gas transfer at interfaces where liquid-phase mass transfer dominates.
Read 5 tweets
11 Nov
1/ Gr8 that @cdc has discovered the dual (lower emissions & less inhalation dose) benefits of masks. A 5 min Sci Citation Index search leads to several past papers of relevance. Here is one by researchers @cdc's very own @NIOSH from 2010.

2/ This paper was cited in tweets by several researchers earlier in the pandemic & shows 40% to 60% removal efficiency (100% - penetration%) for 1 um particles at receptor end (& so even better for > 1 um) for some materials (much worse for others).
3/ More recent results reported by @linseymarr, @Smogdr, & their colleagues/teams significantly increase knowledge of different materials, layered materials, particle size effects, etc.

My previous tweet illustrating dual benefits. 40+40 = 64%, 50+40 = 70%, 60+60=84%, etc.
Read 4 tweets

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