The Post asked three indoor air experts to examine Sierra Mar’s layout, including the location of vents and air filters, and some of the results Hernandez has gathered. They generally agreed that the devices used, and principally the HEPA filters, are known to work, so the design is likely creating a safer indoor experience.
Nothing is perfectly safe, as Hernandez himself acknowledges. The aim is reducing risk, and Virginia Tech’s Marr said the system Hernandez and Freed devise will do that “substantially.”
“It relies on proven technologies: a combination of excellent ventilation and filtration,” she said. “Real-time monitoring that is publicly available provides valuable information to the public, giving people confidence that the space is indeed low risk.”
Portland State University’s Corsi added that mixing air together indoors is very important, on top of good air ventilation and filtration. The air purifiers are spaced out in part to help do this.
“When you do increase mixing in a space, that does break up that plume of concentrated aerosols between you and an infector,” Corsi said. “That additional mixing causes dispersion, which makes the receptor inhale a lot lower amounts of the infector’s respirable particles.”
Donald Milton, who studies indoor air at the University of Maryland and pushed health authorities early on to recognize the virus’s airborne transmission, also thought the system designed by Hernandez would make dining safer in general. But he drew a distinction between people eating at the same table — where the smaller cordless device, made by Wynd, pushes the air upward — and those who are further away.
“Maybe that system could protect you from the people you’re eating at the same table with. That’s a very challenging thing,” Milton said, noting a device sitting on a crowded tabletop is more likely to be bumped or shifted into the wrong direction.
“But by having good mixing, good filtration of the air in the restaurant generally, you will reduce exposure to people at other tables.”
Marr did note something that Hernandez has been careful about, but that could undermine others attempting the approach: You have to be very careful about where your air purifiers are located. You do not want them pulling air in such a way that you are actually “spreading aerosols between tables,” Marr cautions.
In other words, do not line up two tables and then a purifier, or the air from the farthest table will travel across the central table to the machine, coursing around those seated at the central table along the way. That is the kind of simple, but consequential, mistake that we will learn to avoid in this new world of still invisible, but now demystified, air.
After collecting his measurements at the restaurant, Hernandez shared the data with The Post. It showed the setup worked, he said.
In the north sector of the restaurant, even as occupancy increased to 18 diners, airborne levels of fine particulate matter (PM2.5) never rose above 2 micrograms per cubic meter. That is even though outdoor PM2.5 levels that evening were at around 10 micrograms per cubic meter.
Indoor carbon dioxide levels rose across the restaurant as the occupancy level increased, but never eclipsed 600 parts per million. Outdoor levels are generally around 400 parts per million.
That rise is not enough to be dangerous, Hernandez suggests, and is actually in a sense good news when compared with the particle findings, since tiny molecules of carbon dioxide gas fly right through filters.
“The gases go up but the particles don’t. That’s the result of an engineering control,” he said.
Hernandez, who has also implemented indoor air quality monitoring for a number of Colorado schools, argues that even once the current pandemic is over, the kind of design that he has created will remain in demand.
“It applies to the next pandemic, colds, flu, whooping cough, you name it,” he said.
For restaurant owner Mike Freed, he is just hoping that California health regulators, and other restaurants, pay attention.
“I don’t think this is rocket science,” says Freed, “which is why it’s mind-boggling to me that the public health officials aren’t talking to the building scientists.”
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