A guideline to limit indoor airborne transmission of COVID-19

https://doi.org/10.1073/pnas.2018995118 

In nursing homes in New York City, law requires a maximum occupancy of three and recommends a minimum area of 80 ft2 per person. In Fig. 3B, we plot the guideline for a tolerance of =CF=B5=0.01  transmission probability, chosen to reflect the vulnerability of the community. Once again, the effect of ventilation is striking. For natural ventilation (0.34 ACH), the Six-Foot Rule fails after only 3 min under quasi-steady conditions, or after 17 min for the transient response to the arrival of an infected person, in which case the Fifteen-Minute Rule is only marginally safe. With mechanical ventilation (at 8 ACH) in steady state, three occupants could safely remain in the room for no more than 18 min. This example provides insight into the devastating toll of the COVID-19 pandemic on the elderly (86, 88). Furthermore, it underscores the need to minimize the sharing of indoor space, maintain adequate, once-through ventilation, and encourage the use of face masks.

Eight students in a second-grade classroom at Penn Valley Elementary have tested positive for the virus in what officials say marked the district's first instance of significant in-school transmission.

Due to the scope of the outbreak, district staff evaluated the classroom's HVAC system and found that a part within the ductwork above the ceiling "was too far closed, allowing only (approximately) 30% of the maximum amount of fresh air it should have into this specific room," Terry Quinlan, lead supervisor of school health and student safety for the district, said in an email to families Friday.

The district "cannot say definitively whether the diminished fresh airflow contributed to the outbreak; however, it could be a factor," Quinlan said. She added that the Montgomery County Office of Public Health "also noted the possibility of a variant strain of COVID-19 being a factor, citing both the rapid spread within the class and the fact that two vaccinated family members of impacted students have also tested positive."