A series of tests by the US Federal Aviation Administration (FAA) shows that the flames created by just one lithium ion battery overheating could overwhelm the fire suppression systems in commercial passenger airliner cargo holds and potentially down the entire plane, according to the American Journal of Transportation (AJOT).

Obviously, this is a troubling finding for safety officials who believed that the automated extinguishing – an essential feature of all aircraft because cabin crew cannot get into the hold to combat fires – was sufficient to alleviate the growing threat of battery fires.

Lithium-ion batteries, often referred to as Li-ion, are the most popular type of rechargeable battery due to their high energy efficiency and long lifespan. Currently, they are used in almost every type of portable electronic device, including laptops, music players, cameras, tablets, and cell phones. And while you may not be aware of how many of your possessions are powered by Li-ion batteries, you may have heard that they very rarely experience a malfunction that causes them to overheat to the point that a temperature-raising positive feedback loop, called thermal runaway, is initiated. This self-destructing process culminates in an extremely hot, smoking battery that may catch fire, or – as several 2006 laptops and one particularly infamous 2016 smartphone demonstrated – explode.   

Due to this risk, the FAA and the UK Civil Aviation Authority have both implemented bans on passengers putting spare Li-ion and similar lithium metal batteries in their checked baggage; batteries must be brought in carry-on baggage so that if a fire breaks out, the crew and others onboard can fight the flames. The agencies recommend, but have yet to require, that devices with lithium batteries inside also be put in carry-on baggage. If the device must be inside a checked bag, they emphasize the importance of turning it off and not placing it next to flammable substances like perfumes or hairspray.

As reported by the AJOT, it is the presence of such combustibles that could make a stored runaway battery a deadly event. The FAA tests, conducted last year, demonstrated that planes’ automated halon gas-emitting fire suppression systems cannot put out a lithium-ion battery fire but can prevent the flames from spreading to nearby clothing or paper items. However, in a set-up mimicking a suitcase with an overheating Li-ion battery stored next to an aerosol product, the halon gas was incapable of preventing the gas canister from exploding.

“There is the potential for the resulting event to exceed the capabilities of the airplane to cope with it,” the FAA said in a notice to airlines. The findings prompted them to petition the UN International Civil Aviation Organization for a complete ban on electronics larger than cell phones in checked bags, but the proposal was rejected.