Devices powered by lithium-ion batteries are overheating more often during airline flights and passengers often put them in checked bags that go into the cargo hold, where a fire might not be detected as quickly.

Overheating incidents rose 28% from 2019 to 2023, although such events remain relatively rare, UL Standards said in a report released Monday.

E-cigarettes overheated more often than any other device, based on reports from 35 airlines, according to the report.

In 60% of the cases, the overheating — called thermal runaway — happened near the seat of the passenger who brought the device on board.

In July, a smoking laptop in a passenger’s bag led to the evacuation of a plane awaiting takeoff at San Francisco International Airport. Last year, a flight from Dallas to Orlando, Florida, made an emergency landing in Jacksonville, Florida, after a battery caught fire in an overhead bin.

More than one-quarter of passengers surveyed for the study said they put vaping cigarettes and portable chargers in checked bags. That is against federal rules.

The Transportation Security Administration prohibits e-cigarettes and chargers and power banks with lithium-ion batteries in checked bags but allows them in carry-on bags. The rule exists precisely because fires in the cargo hold might be harder to detect and extinguish.

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UL Standards, a division of UL Solutions Inc., a safety-science company previously known as Underwriters Laboratories, based its findings on data from 35 passenger and cargo airlines including almost all the leading U.S. carriers.

The Federal Aviation Administration reports 37 thermal-runaway incidents on planes this year, through Aug. 15. There were a 77 reports last year, a 71% increase over 2019, according to the FAA numbers.

Considering that airlines operate about 180,000 U.S. flights each week, incidents in the air are relatively uncommon, and lithium batteries can overheat anywhere.

“We also know that one of these thermal-runaway incidents at 40,000 feet does present unique risks,” said UL’s David Wroth.

Those risks have been known for many years.

After cargo planes carrying loads of lithium-ion batteries crashed in 2010 and 2011, the United Nations’ aviation organization considered restricting such shipments but rejected tougher standards. Opponents, including airlines, argued that the decision on whether to accept battery shipments should be left up to the carriers, and some no longer take bulk battery shipments.

The most common lithium-ion-powered devices on planes are phones, laptops, wireless headphones and tablets. About 35% of reported overheating incidents involved e-cigarettes, and 16% involved power banks.

UL Standards, a division of UL Solutions Inc., a safety-science company previously known as Underwriters Laboratories, based its findings on voluntary reports from 35 passenger and cargo airlines including almost all the leading U.S. carriers.