Are outdoor dining bubbles safe? Here’s what experts want you to know

Outdoor dining has become increasingly common during the coronavirus pandemic — but experts are warning that some structures designed to keep diners warm and cozy in chillier weather aren't very safe.

Plastic bubbles and other enclosures might be less exposed to the elements, but the set-up may not be any safer than eating indoors.

"If you're putting together something that has a roof and four walls outside, it is called an indoor enclosure outside," said said Gregg Gonsalves, Ph.D., an assistant professor of epidemiology at the Yale School of Public Health in New Haven, Connecticut.

What are the risks with enclosed outdoor options?

The biggest problem with an enclosed outdoor set-up is the same risk as eating indoors: You may be in close proximity to others with no airflow, which can lead to the spread of the coronavirus.

"I think it's a very similar problem to indoor dining," said Dr. Colleen Kraft, associate chief medical officer at Emory University Hospital in Atlanta, Georgia. "A lot of these plastic bubbles are possibly more porous than a wall, so maybe more air can circulate, but they are not going to be as safe as a really open-air set up where a breeze can flow and there's lots of air exchange."

There could also be some concern about aerosols remaining in an individual tent or bubble after a party has left, but Kraft and Gonsalves both agreed that the risk was relatively minimal and that the greater concern is about contracting the virus from others in the enclosure.

Kraft advises wearing a mask to and from your seat, even if you are in an individual enclosure, and Gonsalves recommends restaurants open the entrance to individual bubbles before seating a new party.

"Maybe there's something lingering on (surfaces), but if you open the flap and the air comes in, that will help," Gonsalves said. "It's really spread person-to-person."

While the small bubbles may be safer, they still limit air flow and can lead to increased transmission. Some cities, including San Francisco, have shut down similar outdoor set-ups due to concerns about the potential spread of the virus.

"The key to outdoor dining is the free flow of air," Dr. Anne Rimoin, professor of epidemiology at UCLA told TODAY in August, when the city of San Francisco ordered a restaurant to remove their outdoor structures. "It’s not clear to me that these domes will keep people in them safe nor the servers who would have to enter the domes to serve the people inside them, who would be dining presumably without masks on, with poor airflow. Given the current setup, it seems that these domes might end up promoting transmission instead of preventing it."

Related: Officials said that, although the dining structures are outdoors, they don't allow enough airflow to be deemed safe.

What are some safer alternatives?

As it gets colder, it will be necessary for restaurants to try to keep diners warm if they want to continue outdoor dining. Most states in the country do currently allow for indoor dining, though some areas are limiting indoor dining again due to an increase in hospitalizations and coronavirus cases.

Gonsalves said that outdoor structures that had just one or two walls to block wind or other elements can be safe and still have a decent amount of airflow.

"Just think of it as a continuum of risk," he said. "Would you rather be inside, in a small room with no ventilation, or outside with two walls open?"

There is no coronavirus risk presented by heating devices like space heaters or fireplaces, according to Gonsalves, and it can help to look to other venues for creative ways to keep guests warm.

Related: Restaurant owners are turning to igloos, tents and other structures to keep their outdoor diners protected from the elements and warm as temperatures fall.

"Ski resorts have been doing this for a long time," he suggested.

One possible solution could be blankets given to diners to keep them warm, but Kraft and Gonsalves were divided on just how risky that could be.

"You should encourage people to BYOB. It really should be 'bring your own blanket,'" Kraft said. "That's just a lot of extra work and overhead, and I think providing them just has a risk of adding more things that people are touching and putting around them."

Gonsalves was less concerned about the practice, especially when compared with the risk of eating indoors or in a closed area.

"We want to maximize our time outdoors over the next few weeks, because going indoors is risky, so if people are giving out blankets, that's great if its helps people," he said. "It's going to get really difficult to eat outdoors. I would be comfortable eating outside with space heaters and blankets."