1/ In the indoor air quality field, source removal (or avoidance of ever having the source in a space) is a fundamental principle.
“If there is a pile of manure in a space, do not try to remove the odor by ventilation. Remove the pile of manure.” Max von Pettenkofer (1858)
2/ During the pandemic that means doing all that's possible to avoid having infected persons in a space with others. Stay home if feeling symptoms. Test and isolate.
3/ If source removal is not possible, then source reduction becomes important. Lowering density lowers the probability of a source being present, but does not assure removal of source. Everyone wearing high-quality, e.g., N95, masks dramatically lowers source emissions.
4/ Couple with other means of lowering inhalation dose to virus-laden aerosol particles. Tools: Increase ventilation, improve filtration in HVAC systems, use right-sized portable HEPA air cleaners and/or @CorsiRosenthalBox es, upper-room UVGI.
5/ Complete this sentence ....
None of this is R_________ S__________, folks.
• • •
Missing some Tweet in this thread? You can try to
force a refresh
1/ A context slide from my CITRIS webinar on 3/16/22.
We know it is possible to achieve a CADR > 800 cfm for a Corsi-Rosenthal box. So, let's compare its impact in a realistic dorm room & classroom relative to air changes per hour in, say, a hospital infection isolation room.
2/ In a standard 2-person dorm room (where masks are unlikely to be worn when two people are sleeping 10 ft away from one another for 8 hours!) the CR box yields an aerosol particle reduction equivalent to 24 air changes per hour (ACH).
3/ Without any other ventilation, this is 2 x a hospital isolation room! Measurements of natural ventilation in my home garage with the large garage door wide open have been in the range of 15 to low 20s for ACH depending on outdoor wind conditions.
Involves a novel method to assess near- and far-field exposures using specific terpenoids/VOCs in breath mints & a PTR-ToF-MS. Teaser below for distance from human source.
1/ 3 hours in the late night & a seed tossed into the social media wind. Origin of the #CorsiRosenthalBox.
There were 2 motivations for the concept.
Motivation 1. Make effective air cleaning more accessible to those who cannot afford $300 HEPA air cleaners.
2/ Motivation 2. Help schools employ effective air cleaning at a cost that would not be prohibitive given financial constraints. In summer 2020 school districts seemed overwhelmed, confused, & vulnerable to purchasing shiny objects that might not actually be all that effective.
3/ Three criteria were considered for the device: (1) Effective, removing a reasonable amount of virus-laden aerosol particles from indoor air. (2) Inexpensive, much lower cost than HEPA air cleaners. (3) Open source, not a “money maker” for anyone or any organization.
1/ I always go in for my asymptomatic PCR testing @ucdavis on Sunday mornings & take the time to walk around campus before & after. It is such a gift to work at a great university w/ such a wonderful campus. A few images taken on those walks today & previously .....
2/ Our beautiful arboretum - Such a nice play to walk away from the office to clear one's mind and get some exercise.
1/ It would be easy to put a #CorsiRosenthalBox in a 3 m3 chamber with 0.05 ACH, inject particles, switch the system on, and show a dramatic downward trajectory of particle concentrations to effective 0 ug/m3 in 10s of seconds. But we do not do that, for it would be deceiving.
2/ Instead, studies are being done in actual classrooms, home environments, etc., and showing remarkable effectiveness at reducing aerosol concentrations. Further, experiments are being done to determine highly-relevant metrics like clean air delivery rate (CADR).
3/ Data indicate CADR of 400 to 800 cfm depending on fan and fan speed. These results can then be translated to estimate benefits in actual building spaces.
1/ Inhalation dose of virus-laden respiratory aerosol particles w/ at least one infector in shared indoor space (two contrasting scenarios).
Everyone wearing a (mediocre vs. high-quality) mask vs. nobody wearing a mask.
2/ Everyone wearing a mask serves to reduce emissions, lower concentration in air, and reduce inhalation by receptor. Nobody wearing a mask leads to neither benefit.
3/ Let's assume mediocre cloth masks (or poorly fitted better masks) yield 50% reduction at source and receptor vs. 95% for high quality masks with good fit & compare to no masks at all (lifting the mask mandate and forgetting about sources amongst the population).