Southwest announced the new policy that will go into effect May 28 and said passengers may have already seen notifications about the rule when using the airline’s app. While Southwest is the first U.S. airline to restrict the use of portable chargers, several Asian airlines have taken action earlier this year after a devastating fire aboard an Air Busan plane waiting to take off from an airport in South Korea in January.

There is growing concern about lithium-ion battery fires on planes because the number of incidents continues to grow yearly, and devices powered by those batteries are ubiquitous. There have already been 19 incidents involving these batteries this year, following last year’s record high of 89, according to Federal Aviation Administration statistics.

The incidents have more than doubled since the pandemic-era low of 39 in 2020, and have climbed annually.

Compared to the roughly 180,000 flights U.S. airlines operate each week, the number of incidents is still relatively small and lithium batteries can overheat anywhere. However, this is a growing concern for the airlines.

In the Korean airline fire in January, all 176 people aboard the plane had to be evacuated because the blaze burned through the plane’s roof. The cause of that fire hasn’t been officially determined, but several airlines and Korean regulators took action against portable chargers afterward.

Korean airlines won’t allow the chargers to be stored in overhead bins anymore; they must either be packed in a plastic bag or have their ports covered with insulating tape to keep them from touching metal.

In addition, Singapore Airlines and Thai Airways both prohibit the use or charging of portable power banks at all during flights.

Last summer, a smoking laptop in a passenger’s bag led to the evacuation of a plane awaiting takeoff at San Francisco International Airport. In 2023, a flight from Dallas to Orlando, Florida, made an emergency landing in Jacksonville, Florida, after a battery caught fire in an overhead bin.

Southwest said that requiring these chargers to be kept out in the open when they are being used will help because “in the rare event a lithium battery overheats or catches fire, quick access is critical and keeping power banks in plain sight allow for faster intervention and helps protect everyone onboard.”

The airline will allow the chargers to be stored inside carry-on bags when they aren’t in use.

The Transportation Security Administration has long prohibited 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.

The FAA recommends passengers keep cell phones and other devices nearby on planes so they can access them quickly. The agency said flight crews are trained to recognize and respond to lithium battery fires. Passengers should notify the flight crew immediately if their lithium battery or device is overheating, expanding, smoking or burning.

A previous report released last year by UL Standards & Engagement said e-cigarettes overheated more often than any other device. More than one-quarter of passengers surveyed for that study said they put vaping cigarettes and portable chargers in checked bags. That is against federal rules.

UL Standards & Engagement, part of a safety-science company once known as Underwriters Laboratories, said it based its findings on data from 35 passenger and cargo airlines, including nine of the 10 leading U.S. passenger carriers.