The rate of incidents involving lithium-ion batteries overheating on passenger planes hit a five-year peak last year, with e-cigarettes being the biggest culprit, according to a report from a nonprofit organization focused on safety standards. 

Incidents involving so-called thermal runaway, which occurs when the batteries overheat and can result in fires, have increased 28% over the five-year period from 2019 through 2023, the report from UL Standards & Engagement found. After vaping devices, which contributed to 35% of the reported incidents last year, power banks for charging electronics were the second-leading cause, according to the report released Monday. 

“Rechargeable devices like phones, laptops, tablets, and portable power packs are integral to the air travel experience, but with wide and increasing usage of lithium-ion batteries in these and other consumer products comes an increase in the safety hazards they present,” the organization said in the report. 

The Federal Aviation Administration has also found this issue to be a growing problem, with lithium-battery air incidents rising from 16 in 2015 to 77 in 2023, according to data compiled by the agency. Already this year, there have been 37 verified events, including a July case involving a passenger’s e-cigarette overheating on a Delta Air Lines Inc. flight. 

The UL Standards & Engagement report was based on a database of incidents voluntarily reported by airlines.