Read This Before You Even Consider Dining Indoors

Experts explain the many risks involved — and how to lower your risk if you decide to do it

11 min readNov 29, 2020

Photo: Jeff Gritchen/MediaNews Group/Orange County Register/Getty Images

Linsey Marr has not dined indoors at a restaurant since the pandemic began, and she won’t until it’s over. Because she knows the risk, better than just about anyone. Marr, PhD, is a scientist at Virginia Tech and an expert on the transmission of the coronavirus through the air. She and several of her colleagues agree that the riskiest environments for catching Covid-19 are crowded indoor spaces, including restaurants.

“Restaurants are among the higher-risk activities because you’re indoors with other people without masks for some of the time at least,” Marr tells Elemental.

The coronavirus spreads in three known ways: from infected surfaces, by large respiratory droplets that typically fall to the ground within a few feet, and in smaller droplets called aerosols that can stay suspended for minutes or hours — a particular risk in poorly ventilated buildings where the aerosol concentration can build up.

The risk of airborne transmission increases with several factors related to dose and duration.

The louder a person talks, the more aerosols are released.
If you’re closer to someone or more than one person in a room is sick (even if they don’t know it), the risk rises.
If you stay in an infected space for, say, an hour, your odds of getting sick are higher than if you spend less than 15 minutes there, but there are no firm thresholds given the many other variables.

The relative extent of each transmission mode is not known, so Marr, and other scientists and health experts encourage hand-washing as well as physical distancing, mask-wearing, and avoiding large crowds as the keys to slowing the spread.

The risk, they say, is much greater in a crowded, poorly ventilated restaurant than an uncrowded, well-ventilated one and much greater when people don’t wear masks. In an FAQ on the topic, 10 aerosol-transmission experts point out that many outbreaks have been documented in crowded indoor spaces where people spend a lot of time together and especially when there is a lot of loud talking, shouting, or singing — as in bars or choir practices — but there have been no documented outbreaks in movie theaters where there is little talking and good ventilation.

Measuring the risk

A limited case study of coronavirus infections that occurred in a restaurant in China found one infected person spread the virus to five people who were seated at other tables, each in the path of air-conditioning vents. Doors and windows were closed, and the restaurant was not filtering the conditioned air, a substandard ventilation scenario by modern U.S. building health standards.

Richard Corsi, PhD, dean of the College of Engineering and Computer Science at Portland State University, studies indoor air quality. He recently ran computer simulations using the data from the case study in China. Corsi’s hypothetical U.S. restaurant was relatively full, with a similar number of people per square feet as the restaurant in China. The main difference: The simulated restaurant meets ventilation standards set by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers.

The results of his unpublished findings: The amount of coronavirus potentially reaching the lungs of some patrons from a single infected person in the hypothetical U.S. restaurant would be about 20% of what occurred in the restaurant in China, Corsi says.

If a restaurant was running at 50% capacity, that not only allows for better physical distancing than a packed house but also cuts in half the probability that an infected person might be there, Corsi explains in a phone interview. Likewise, restaurants at 25% capacity, as planned for New York City starting September 30, further reduces risk. The risk could be lower still in restaurants that have upgraded air filters or have installed air purifiers, but short of asking the owner about precautions taken, there’s no way to guess or even measure how safe the air might be. (Though if an owner is baffled by your questions, that would be a clue.)

Corsi says he totally understands the emotional drain of the pandemic — what other experts are calling “Covid fatigue” — and why people want to get back to living normally, but under none of these conditions would he go to a restaurant right now. “I think there’s still too much of a risk there of getting sick,” he says. “I’m not going to a restaurant because I know they’re not safe.”

Weather permitting, restaurants can take one very useful and visible prevention step: Open doors or windows and create cross-ventilation so that fresh outdoor air dilutes the air in the shared space, says Shelly Miller, PhD, an environmental engineer at the University of Colorado, Boulder, who studies the indoor transmission of infectious diseases.

Miller just made reservations for dinner indoors at a fancy restaurant for her son’s 18th birthday — her first dining-in experience during the pandemic. She didn’t make the decision lightly. The restaurant has high ceilings, lots of space, and the owners have upgraded their ventilation. Still, she’ll be packing a carbon dioxide detector. It won’t reveal whether there’s coronavirus in the air, but it will measure how much fresh air is being mixed into the building, diluting any virus that might be wafting about.

Don’t have $100-plus for a CO2 detector? “If you walk into a place and it feels hot and stuffy to you, and there’s a lot of people in there, you should walk back out,” Miller says.

“If you have 100 people in a restaurant, there’s going to be infected people there in most parts of the country right now.”

What to look for before you sit down

All three of these scientists are sensitive to the economic consequences of avoiding restaurants, and they’re eager to support their favorite local establishments by doing takeout or delivery where available. They also recognize that as states and cities relax regulations on indoor dining, some people won’t be able to resist the craving to eat out. Here, then, are their collective suggestions on what to look for to suggest a restaurant is taking the pandemic risk seriously:

Masks on all employees
Tables spaced to keep several feet between groups
Respectful distancing and minimal talking from wait staff and hosts
Good ventilation from open doors or windows if practical weather-wise
Frequent and serious cleaning of tables and menus
A quiet atmosphere

“I’d be looking for a place where it’s uncrowded, there’s no music or TVs in the background, at least not audio, no sound, so that people don’t have to talk over it,” Marr says. Also consider whether your state, city, or community is experiencing strong outbreaks or not, the experts say. And do a headcount.

“If you have 100 people in a restaurant, there’s going to be infected people there in most parts of the country right now,” Corsi says. “If you have a third as many there, you can cut the probability that there’s an infected person there by two-thirds.”

Importantly, the guideline you’ve heard for six feet of separation is just that: a guideline. It’s a useful distance to separate you from most large respiratory droplets but not from aerosols, experts agree. Corsi does not think it’s sufficient distance for indoor dining given the length of time people could be exposed to others who won’t be wearing masks throughout a meal.

What you can do to lower risk

As with any activity that goes against the advice to avoid crowded indoor spaces, lowering risk in a restaurant involves layered measures, starting with mask-wearing.

“I would suggest that, ideally, people would be wearing their masks anytime they’re not eating or drinking,” Marr says. While face masks are effective primarily at protecting others, Marr’s research lab is finding, in ongoing research on mannequins that’s not yet published, that good-quality, properly fitted homemade masks can protect the wearer from infection more than has been suggested. “If it fits well with no gaps and you have at least a couple of layers of densely woven material, then it probably protects you against at least half if not 80% or more of the droplets and aerosols that we think are most important for transmission.”

Effectiveness also presumes a person avoids touching the mask, their face, or their eyes.

The scientists cite other simple ways to cut down intensity and duration of exposure, all of which, admittedly, veer from some of the attractions of eating out:

Go during off-hours or on slow days
Ask for the bill early and eliminate the wait to pay
Take a walk outside while waiting to order or waiting for your food

Experts also suggest sitting only with people you live with, unless you’ve created a small social “quaranteaming bubble” agreeing to prevention rules while dining and in other activities.

Of course, any activity done outside, including dining, is safer than the same activity indoors in terms of Covid-19 prevention. But even outdoor dining has risks. The experts say tables should still be well-spaced-apart outdoors, servers should still wear masks, and diners should don masks if seated close to others, especially if downwind.

Even with all these precautions, eating in restaurants runs the risk of increasing coronavirus infections in any community. Health experts urge policymakers and individuals to consider which aspects of “returning to normal” are most important.

“I still think that restaurants and bars are nonessential, and opening them for indoor service now puts a lot at risk, including the opening of schools if infection rates increase,” Corsi says. “We need to have priorities as a nation if we are going to get past this without three times as many deaths and a destroyed economy.”

WRITTEN BY

Robert Roy Britt

Explainer of things, independent health and science journalist, author, former editor-in-chief of LiveScience and Space dot com.

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