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[quote=Anonymous][quote=Anonymous]Name of your school district and is it using 3 or 6 feet distancing? If 3 feet was it always using 3 or only after CDC updated guidance? Thanks![/quote]

It should make no real difference in re risk.  But masks and ventilation will.

We first apply our guideline to a typical American classroom, designed for an occupancy of 19 students and their teacher, and choose a modest risk tolerance, ϵ=10% (Fig. 3A). The importance of adequate ventilation and mask use is made clear by our guideline. For normal occupancy and without masks, the safe time after an infected individual enters the classroom is 1.2 h for natural ventilation and 7.2 h with mechanical ventilation, according to the transient bound, SI Appendix, Eq. S8. Even with cloth mask use (pm=0.3), these bounds are increased dramatically, to 8 and 80 h, respectively. Assuming 6 h of indoor time per day, a school group wearing masks with adequate ventilation would thus be safe for longer than the recovery time for COVID-19 (7 d to 14 d), and school transmissions would be rare. We stress, however, that our predictions are based on the assumption of a “quiet classroom” (38, 77), where resting respiration (Cq=30) is the norm. Extended periods of physical activity, collective speech, or singing would lower the time limit by an order of magnitude (Fig. 2).

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In both examples, the benefit of face masks is immediately apparent, since the CET limit is enhanced by a factor p−2m, the inverse square of the mask penetration factor. Standard surgical masks are characterized by pm=1to5% (73, 74), and so allow the CET to be extended by 400 to 10,000 times. Even cloth face coverings would extend the CET limit by 6 to 100 times for hybrid fabrics (pm=10to40%) or 1.5 to 6 times for single-layer fabrics (pm=40to80%) (75). Our inference of the efficacy of face masks in mitigating airborne transmission is roughly consistent with studies showing the benefits of mask use on COVID-19 transmission at the scales of both cities and countries (22, 33, 83).

Air filtration has a less dramatic effect than face mask use in increasing the CET bound. Nevertheless, it does offer a means of mitigating indoor transmission with greater comfort, albeit at greater cost (22, 72). Eq. 5 indicates that even perfect air filtration, pf=1, will only have a significant effect in the limit of highly recirculated air, Zp≪1. The corresponding minimum outdoor airflow per person, Q/Nmax, should be compared with local standards, such as 3.8 L/s per person for retail spaces and classrooms and 10 L/s per person for gyms and sports facilities (72). In the above classroom example with a typical primary outdoor air fraction of Zp=20% (22), the air change rate λa could effectively be increased by a factor of 4.6 by installing a MERV-13 filter, pm=90%, or a factor of 5.0 with a HEPA filter, pm=99.97%. At high air exchange rates, the same factors would multiply the CET bound.

https://www.pnas.org/content/118/17/e2018995118[/quote]

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