How one restaurant’s experiment may help diners breathe safely

A restaurant in California’s Big Sur tries a comprehensive approach to clean its air.

When California’s Monterey County allowed restaurants to reopen in March, indoor dining returned to the cliff-perched Sierra Mar, known for its spectacular views of the Pacific Ocean.

The Big Sur restaurant now featured some new pandemic touches: 18 tabletop mini-purifiers, 10 precisely distributed HEPA air purifiers, an upgraded heating and air conditioning system, and four sensors measuring the air quality in real time.

The bar was closed, and at a table in the back sat someone new: an engineering professor whose specialty is air quality.

“If this is going to work right, the ventilation keeps up with the head count,” explained the expert, Mark Hernandez of the University of Colorado. Every 15 minutes, he would walk to the front desk to check how many people were now seated indoors. Then he would compare that number to the air’s current levels of carbon dioxide and particulate matter, to see how much exhaled breath lingered in the air and what expelled aerosols it could contain.

Indoor dining remains risky, as the pandemic rages on, propelled by highly transmissible new coronavirus variants that threaten gains from widespread vaccination. The virus has been brutal for the restaurant industry. The National Restaurant Association estimates a loss of $240 billion in bar and restaurant sales and 2.5 million jobs during 2020. President Biden’s covid-19 stimulus package provides $25 billion in grants for restaurants and bars that lost revenue, but thousands of restaurants already have shut down permanently.

Those struggling to hold on are considering a broad range of air ventilation and filtration techniques to keep customers and staff safe. Sierra Mar’s new air-quality experiment, partly funded by a regional foundation, cost about $30,000. That’s a hefty expenditure that might be out of reach for many restaurants running on thin profit margins.

Mike Freed considers it a worthy investment. He’s the managing partner of the Post Ranch Inn, the exclusive resort that contains Sierra Mar and caters to an affluent eco-conscious traveler. Since the setup, if successful, could potentially be utilized in other restaurants and indoor spaces, the Washington Post asked several experts on indoor air to review the restaurant layout and strategy. They agreed it should work to make the dining experience considerably safer, while noting 100 percent safety is unattainable.

These experiments in the restaurant industry may usher in a new data-driven relationship with indoor air, with people able to judge where they dine, vacation and work based on the quality and transparency of real-time readings.

“I’ve become obsessed with indoor air quality,” says Freed, who spent about $7,500 to buy equipment. “I just think it’s so important to our health.”

The resort promises an “away from it all” experience, so air safety innovations need to be unobtrusive.

Staff glide through a dining room whose interior air circulation has been designed, says Hernandez, as a “seat belt in a place where you can’t control your peers … This is long overdue for public places.”

At a time when its vista is clouded by recurrent wildfires, the Post Ranch Inn now displays the restaurant’s air quality updates on its website, so diners can time their escape around what they want to eat — and breathe.

On the table

An air purifier about the size of a water bottle sits on each table. It can’t clean a lot of air quickly, but it can direct filtered air in a small area. And it runs on batteries.

While the portable air purifier can be tilted toward a person’s face, Hernandez positioned it straight up, to reduce the risk of unmasked diners infecting others by breathing across the table. Instead, the device, made by Wynd and marketed as a personal air purifier, should push any shared or unfiltered air aloft.

On the floor

A key feature in Hernandez’s design is a decades-old technology now deployed against the highly infectious coronavirus: the high-efficiency particulate air filter.

The pandemic has boosted an air purifier industry that already had expanded to curb air pollution’s toxic effect on people’s lungs and hearts. Some products make questionable claims, experts say. The most reliable and longstanding technology for cleaning air is to force it through a very fine filter made up of tiny strands of fiberglass.

“HEPA filtration has been a workhorse for decades, and it’s a proven technology,” said Richard Corsi, an indoor air expert at Portland State University.

Technically, to receive the HEPA rating, filters must capture 99.97 percent of particles that are .3 microns in size. The SARS-Cov-2 virus is slightly smaller than that.

HEPA filters capture smaller particles as well; and more importantly, the virus “is carried in aerosols that are larger because the virus comes out with lots of salts and proteins that are in respiratory fluid,” said Linsey Marr, an expert on aerosols at Virginia Tech. “And even if all the water evaporates, there’s still a ton of salt and protein compared to the virus.”

Many purifier models pull in air on only one side, so their motors work harder and can be noisy. Sierra Mar uses a Mila air purifier model that pulls in air from underneath and all four of its sides — and does so relatively quietly.

That is key in an environment like a restaurant, where people raise their voices when it is noisy — and spew particles that hang around longer in still air.

Out of sight

High above the ocean, Sierra Mar restaurant has plenty of advantages in providing fresh air. Floor-to-ceiling windows open freely to catch Pacific breezes. In winter, its HVAC floor registers pump out warm air that naturally rises upward, reducing risk of airborne germs lingering in colder months.

To try and thwart the virus, Sierra Mar upgraded its HVAC filters to MERV 13 level filtration, a level that experts say should be able to capture many particles that contain the coronavirus. The system was also modified to increase the amount of fresh outdoor air pulled into the space, and three room dividers were installed.

Front and center

Hernandez designed a monitoring system for the restaurant as part of a $22,500 grant to the University of Colorado, where he teaches, from the Community Foundation for Monterey County. Four indoor air monitors from SenseWare provide real-time readings of key air quality indicators in four zones of the restaurant.

The key readings, Hernandez notes, are two. First, there is carbon dioxide, which humans exhale. So the closer that indoor levels are to the outdoor baseline, typically around 400 parts per million, the closer patrons are to breathing in fresh air, rather than air that recently came out of someone else’s lungs.

Second are readouts of particulate matter, known as PM2.5 and PM10 for the size of the particles. (PM2.5 refers to particles2.5 microns in size and smaller, while PM10 refers to larger particles.) These are standard air quality measures of pollution levels most associated with the fruits of combustion, emerging from smokestacks and car tailpipes.

Hernandez’ research focuses on using these same measures to assess the quantities of biological particulate matter that people shed. Aerosols from human respiratory systems, which could contain infectious viruses, will also fall in this general size range, with the smaller particles potentially posing the larger risk.

Therefore, low levels of both PM2.5 and PM10 are desirable for controlling the coronavirus, just as they are for avoiding the damaging health consequences of air pollution.

Outdoors, the Environmental Protection Agency’s ambient air quality standards require PM2.5 levels to be below 12 micrograms per cubic meter of air (as an annual average). Hernandez’s data indicates the restaurant has managed to keep particulates closer to 1 or 2 micrograms per cubic meter, even with people in the space.

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.

[How to assess the safety of indoor dining]

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.”

About this story

Editing by Monica Ulmanu and Ann Gerhart. Photo editing by Olivier Laurent. Copy editing by Dorine Bethea.

(Melina Mara/The Washington Post)

Chris Mooney is a Pulitzer Prize winning reporter covering climate change, energy, and the environment. He has reported from the 2015 Paris climate negotiations, the Northwest Passage, and the Greenland ice sheet, among other locations, and has written four books about science, politics and climate change.
Aaron Steckelberg is a senior graphics editor who creates maps, charts and diagrams that provide greater depth and context to stories over a wide range of topics. He has worked at the Post since 2016.
Jake Crump is a designer and web developer for The Washington Post since 2015.