Commentary: Parents should demand stronger safety measures before Huntington Beach high schools reopen
Now that airborne transmission and reinfection with the SARS-Cov-2 virus are established facts, I wish to draw attention to the critical role HVAC systems will play in the Huntington Beach Unified High School District once Nov. 3 rolls around and the hybrid, in-person model of face-to-face instruction will commence for general education students (special education students have been brought back to campuses in the district as of Oct. 5).
I am an academic physicist with a close-to-30-year career as a researcher and teacher, and while I cannot make predictions on transmissibility and epidemiology, I can certainly put some physics facts out for consideration.
Droplets the size of a human hair (1/10 of a millimeter, or 100 microns) are projected in speech, singing, shouting, etc., and these particles do settle out of quiescent air with a drift velocity of about two seconds per inch.
Released from 6 feet, these particles would take about three minutes to drift to the ground, about a minute to drift downward to any hard surface such as a desk or computer keyboard.
These particles are capable of drifting a foot or so laterally (if there are no prevailing drafts) so the social-distancing and plexiglass shields contemplated in HBUHSD are well-designed to stop the spread of these large droplets.
Droplets a factor of 10 smaller take quite a bit longer to settle: three minutes for a 100-micron particle becomes 300 minutes — five hours — for aerosol particles to settle to the ground when released in a cough or sneeze.
When you walk into an enclosed space that is not well ventilated, you may as well be kissing everyone who was in that space during the last five hours, which is essentially the way I have caught every cold I have ever had.
When the weather starts to turn blustery in November, the HVAC systems at each of the school sites will (as they are designed to do) recirculate air that has been heated, thus lowering the relative humidity of the air in classrooms, hallways and restrooms.
It takes about 10 seconds for a 100-micron droplet to “dry” in a low-humidity environment, which will render the 6-foot social distancing and plexiglass shields of limited use.
I want my children to be able to interact face-to-face for their senior years in high school, but I insist that that interaction be safe.
The district has had since March 20 to study the ventilation situation, and it has been at least since June that aerosol transmission has been a recognized mechanism of infection — and now what is believed to be reinfection with the SARS-CoV-2 virus.
The problem with the aerosol particles is that no one can see them. No one can smell them. They give no taste.
A region in a classroom with a backwash or an eddy from the ventilation system will accumulate aerosol particles throughout the school day, and the “hot” spots in a classroom, bathroom or hallway will be totally undetectable to any student or staff member.
The HBUHSD board of trustees and the administration of the district should immediately purchase electrostatic air-purifiers and N95 masks for every useable space on each of their campuses and for every staff member.
The focus for too long has been, “What is the minimal steps we need to satisfy arbitrary benchmarks?” and it should now be, “What can we do proactively to ensure the safety of in-person instruction?”
If there are neither resources nor the political will to expend resources in this manner, I urge every parent in the district to think very carefully about sending their children back to face-to-face instruction, and I would also urge those parents to think very carefully about reelecting any current board member in this or any future election.
And I would expect the superintendent, should anyone be harmed by neglecting the aerosol hazard, would consider resigning.
The writer is a professor in the Department of Physics and Astronomy at Cal State Long Beach.
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