United/DOD study using mannequins sheds light on infectious particle spread on airplanes

Could a mannequin help quell COVID-19 fears on an airplane?

The U.S. Department of Defense embarked on a six-month, $1 million study to find out.

"This was a study to look at the potential for transmission of infectious particles," Chris Hogan, an aerosol expert with the University of Minnesota, said.

The DOD, partnering with United Airlines, used a mannequin equipped with an aerosol generator to reproduce breathing and coughing, with and without a mask.

"What they would look at was the concentration of particles in the seat next to the person who they pretended is infected, where the tracer particles are coming from," Hogan explained.

The researchers used 40 sensors throughout the plane to detect the spread of droplets.

They found, with a mask on, only 0.003% of particles made their way to another passenger’s breathing zone.

"Virtually non-existent," said Josh Earnest, United’s Chief Commercial Officer. "And again, this is the U.S. military study."

The study, conducted during 38 hours of flight time and 48 hours of ground testing in United aircraft, has not yet been peer-reviewed but United is applauding the research.

"What I am telling people is if you are inclined to travel or thinking about air travel, there is reason today for this independent study that you can feel confident that you can travel safely," Earnest said.

5 EYEWITNESS NEWS asked Hogan to take a closer look.

He obtained a copy of the 53-page report.

"I believe it is safe to breathe the air on planes, I would put it that way," he said. "That you don’t have to worry about the air being infected."

Full KSTP COVID-19 coverage

Hogan said the air exchange rate on planes, typically about 30 times an hour, is a major factor.

HEPA filters eliminate 99.9% of airborne particles, including viruses, every two to three minutes.

"Even hospital operating rooms aren’t as high as 30," Hogan noted. "So they’re really clearing that air very, very quickly."

There are some caveats.

Researchers didn’t try to replicate what happens when an infected person stands up or moves about the cabin.

"I’m an epidemiologist. I have not gotten on a plane since early March, and I’m not ready to do that yet," Cathy McCarty, with the University of Minnesota Medical School, Duluth campus, said.

McCarty agrees the study is comprehensive and well-researched but she notes the mannequin is always face-forward, wearing a surgical mask that never moves.

"Two things: people have to be wearing their masks, No. 1," McCarty explained. "They take their mask off to eat, to do whatever, and that mask is not working, obviously."

Hogan is also concerned about human contact.

"They’re not saying anything about if someone sneezes, that’s still on a surface, and that’s potentially a concern or contact," he said. "If someone touches you, or touches something you touch. They didn’t investigate that portion of it."

Still, he said the study shows slightly higher particle concentrations close to the mannequin.

He said, because of that, it would be better to fly on planes that allow safe distancing.

United Airlines issued a statement to 5 EYEWITNESS NEWS, which says in part:

"We still proactively notify customers when their flight is going to be fairly full, to give them the option of rebooking to a different flight or receiving a travel credit. When presented with all of the information, the overwhelming majority of our customers choose to keep their travel plans the same."

United also said its customers are required to wear masks on their planes when they are not eating or drinking.

The Centers for Disease Control and Prevention strongly recommends in-flight mask use, and virtually all airlines require it.

The CDC says it has identified nearly 11,000 people potentially exposed to the coronavirus on airplanes.

According to the International Air Transport Association, there have been tens of millions of flights since the start of the COVID-19 outbreak, resulting in less than 50 confirmed cases.

But experts say the pandemic is changing every day.

In the last couple of weeks, case numbers have surged, nationwide.

KSTP medical expert Dr. Archelle Georgiou said other studies published by the CDC show similar results to the one done by United and the DOD, suggesting with masks and social distancing, it’s relatively safe to fly.

But right now, she advises against it.

"My first recommendation would be to stay home, don’t fly," Georgiou said.

"Don’t even get together with family for Thanksgiving, that’s my first piece of advice," she added. "But if you have to fly, be extra careful about wearing a mask, washing your hands, and social distancing, keeping the space around you as clean as possible. But I really want to go back to that first recommendation. We are in a surge right now. People should be staying home."

Minnesota Gov. Tim Walz and his administration are recommending the same thing — celebrate Thanksgiving with people in your immediate family only.

Meanwhile, the DOD says the study is a "launchpad for further research," since it didn’t include variables such as multiple infected passengers, large projectile droplets containing the virus or people moving about the cabin.

The DOD also says its researchers will review time periods for how long service members and their families move through air travel, and will potentially revise its policies, including capping flights at between 80% and 90%.

"It still seems that reducing capacity on planes is still helpful here, to keep people from contact," Hogan said. "In terms of the environment being higher risk, I would say no. But people’s actions are a different thing."