Ventilation and contactless service help reduce the risk of dining out in indoor structures, like these domes at Rising Tide. Photo courtesy of Rising Tide Brewing Co.

The outdoor dining structures, like tents, shacks and plastic domes, that have popped up at restaurants and breweries during the pandemic have been mocked on social media and criticized as hypocritical: So it’s OK to eat inside, as long as it’s outside, their skeptics question.

But the structures, when used properly, can be safer than eating inside a restaurant, experts say. The amount of risk varies depending on the setup and the practices of the businesses and diners themselves.

“There is no restaurant dining experience that is completely safe right now,” said Dr. Michele Polacsek, who responded to questions via email with input from fellow University of New England public health professor Jennifer Gunderman.

Aside from avoiding eateries altogether, dining outside in the open air is best, they said. But domes, wooden shacks, tents and greenhouses can be reduced-risk options – the safest being properly maintained structures that hold only one party, which consists only of people who live together.

“They keep people safe who are in their bubble system. I think they are a great option; they provide people a safer way of eating out. They just need to be managed in a way that prevents exposure (to) the subsequent parties,” said Christine G. Crocker, executive director of the Maine Indoor Air Quality Council.

Crocker said the smaller, single-party structures can be adequately ventilated by allowing stale air out and fresh air in for 15 minutes between parties. Contactless service, in which customers place and receive orders without the server entering the structure, also reduces risk, Polacsek said.

That’s how it’s done at Rising Tide Brewing Co. in Portland, which has domes for individual parties. Reservations are spaced out by 15 minutes to give “5 minutes for the (dome) to air out after the party leaves, (about) 5 minutes for our staff to sanitize, (about) 5 minutes for it to air out again before the next party,” said Kailey Partin, Rising Tide’s director of branding and hospitality.

Servers do not enter the domes but instead place all food and drink on a barrel that is located outside the entrance to the structure.

For structures that hold multiple parties, the risk varies from restaurant to restaurant depending on many factors, including the size of the structure and the number of people in it, the distance between tables and whether patrons wear masks when speaking with the server, said Polacsek. But, in general, “the more space, ventilation/filtering and fewer people – the better,” she said.

An open door or window or a mechanical fan in the doorway all help airflow circulate in and out, Crocker said. Restaurants also should use air filtration devices within the structure that constantly filter out potentially contaminated air, as well as a high-efficiency particulate air – or HEPA – filter, which brings in clean air. Crocker said the latter is what she sees missing the most from restaurants.

In addition to ventilation and filtration, the personal practices of diners and restaurant staff, including physical distancing, proper mask wearing, hand washing and personal hygiene, all factor into the safety of any dining situation, and limiting contact between servers and guests helps reduce the risk.

One recommended practice – widely adopted by restaurants early in the pandemic but which hasn’t proved to significantly improve safety – is the sanitization of surfaces, like tables and chairs, but Polacsek said it’s still encouraged as a “better-safe-than-sorry practice at this point.”

If you are dining with people you don’t live with, without masks and not socially distant in structures that aren’t well ventilated, the risk of transmitting COVID-19 is no lower than dining inside, because once you add four walls and a roof “any outdoor space becomes an indoor space,” making ventilation less than ideal, and static air is what helps transmit the virus, Crocker said.