Really good overview of ventilation, filtration, & a few other air-cleaning strategies, via @B_resnick & @voxdotcom. Many of the right experts were consulted for this.
But many districts & universities have yet to fully address these issues... 1/
due to a) decades of deferred maintenance: linkedin.com/pulse/2016-sta…, linkedin.com/pulse/addressi… & b) lethargic, inconsistent responses (from the local to national level, & by districts/universities themselves) to devote needed $, resources, expertise, driven by the lack... 2/
20% RH (winter condition), MERV 7 filters, 455 CFM of outside air (OA or ventilation) required by code, which = 3.0 air changes per hour (ACH), 1.7 ACH of recirculated air.
1 infected individual, a quanta value = 100, coughing, 6 hours of exposure, 0% vaccination, no masks, the total removal efficiency at 15 minutes (from 1 single cough) is 72.2%. The probability of infection (PI) for the kids after 6 hours is 33.3%. For adults it's 26.5%. 5/
This is a simple model, & you can refer to the supporting documentation for the details & assumptions. But generally the removal efficiencies are more directly comparable to SARS-CoV-2 & the probabilities of infection only in a general sense.
classroom's ventilation to 900 cfm to achieve the 6.0 ACH recommended in the article, & keep everything else constant. Removal efficiency = 86.2%, Child PI = 22.8%, Adult PI = 17.9%.
Now let's also change the filters to MERV 13. Removal efficiency = 88.7%,... 7/
deltas than the absolute values (also based on influenza). This points out the importance of ventilation, probably more important than building system filtration. But time of exposure is also critical, as is the volume of the space (not emphasized in this example). 9/
Which is why moving learning activities to larger spaces (or outside) & reducing the time in the classroom / on campus are also strategies to consider, along w/ reducing density.
As many building systems won't be capable of achieving 6.0 ACH of ventilation in any,... 10/
space, or consistently throughout the year during the more extreme external temperature conditions (particularly since we haven't devoted the needed time/resources - in the last six months or the last few decades), multiple strategies, that vary by,... 11/
district, university, & building, will have to be considered. The article covered some of these additional strategies. But be wary of some as the article points out. Their use could lead to evolutionary mismatches, e.g. linkedin.com/pulse/evolutio….
some of the complex building/operational issues that must to be addressed. There are a whole host of behavioral issues we haven't fully wrapped our heads around either: linkedin.com/pulse/reopenin….
One of the most basic, mask wearing, is still controversial. Which is...13/
unfortunate, considering the risk reduction benefits offered. The excel tool our online version is based on currently accounts for mask wearing (which will make it into v2 of the online tool). Using the same parameters as above (going back to 6 hours of exposure),... 14/
if everyone is wearing a basic cloth mask, the Child PI = 15.8% and the Adult PI = 9.8%, vs 21.1% & 16.5% respectively for not wearing a mask. This conservatively assumes so-so fits of the mask to the face.
If we want to have even hybrid forms of school/university...15/
during a pandemic, we must have more consistent efforts to understand and address all of the relevant variables. But short of a national, coordinated effort, I fear we may continue to limp along. 16/
Our new office policy we're finalizing essentially takes this viewpoint. In 3 of our offices, we've assessed high vaxx rates combined w/ addressing the Delta far field risk via ventilation/filtration is adequate enough for vaxxed employees (almost 100%) to go sans masks. 1/
Even in metro areas currently deemed by the CDC as having high or substantial community transmission.
To have vaxxed employees go sans masks in our other 2 offices, relative to their current lower office vaxx rates, the Delta far field risk needs to be addressed through... 2/
some combination of additional ventilation/filtration improvements, increasing vaxx rates, setting lower occupancy limits, or having non-vaxxed employees WFH - we are still assessing the best path forward for each of those locations.
. That we haven't had more districts close for a period of time is pretty fortunate considering everything. 2/
That we're still arguing over the basics of how to respond to a pandemic driven by a predominantly airborne virus demonstrates a multi-level failure of public health & government, exacerbated by a history of underfunding public health, public education, current levels of... 3/
A few questions for the UV specialists. 1st, are the studies/modeling that have been done so far relative to Far UVC impacts on eyes/skin sufficient to answer questions regarding a) potential negative impacts from chronic (continuous or repeated) exposure,... 1/
b) age/developmental specific concerns related to short term or chronic exposure, & c) concerns for those w/ pre-existing eye/skin conditions after experiencing short term or chronic exposure?
2nd, have studies been done looking at the impacts on the built environment's... 2/
microbiome, & the subsequent impacts on human health? And for this 2nd question, not just relative to Far UVC, but also for more traditional upper room UVGI systems.
Manufacturers are already marketing fixtures exposing occupants to Far UVC. Do the answers to either of the... 3/
This is an all hands on deck moment. In-person school is starting. W/ the #DeltaVariant, even w/ the majority of the relevant strategies in place, it’s going to be difficult to prevent transmission in our schools (linkedin.com/pulse/in-perso…). 🧵1/
In an elementary classroom w/ unvaxxed students, generally ASHRAE compliant ventilation/filtration, the addition of (1) portable HEPA filter unit, & theoretical 100% mask wearing (double layer cloth mask), max exposure is only about 1.2 hrs before an additional student... 2/
is potentially infected at full occupancy (assuming 1 infected student is present).
Accounting for the potential reality of younger kids not always effectively wearing their masks (50% mask wearing), the max exposure is under an hour before an additional student is infected. 3/
These are the type of actions our pharmacies, hair salons, retail stores, offices, universities, k-12 schools, individual residences, etc., need to be taking, particularly w/... 1/
a more transmissible strain spreading in the U.S. & months left before vaccination levels are where needed to be.
CO2 levels can be used to estimate ventilation levels, though it's important to account for factors like the number of people present, the size of,... 2/
the space, & the use of portable air cleaners. Pages 23-24 of this document from @HarvardChanSPH & @j_g_allen provide a means for estimating ventilation rates based on measured CO2 levels. 3/
I would challenge your point that “No matter what we do, resources will remain scarce and people will compete over them.” First, there’s an abundance of evidence from the archaeological, historical, & contemporary ethnographic records of individuals & groups cooperating... 1/
(employing some or all of Ostrom’s principles) to survive in environments of scarce resources (& not just hunter/gatherer groups). Not saying the evidence for competition (including violent competition) isn’t also there, or that the competition between groups isn’t also... 2/
what often drives the cooperation among group members (because it does), only that cooperation seems to have been most effective when these principles are applied (even as part of a larger competition between groups).