FAA test raises fears over carrying rechargeable batteries on planes

Dramatic US government test results raise new concern that bulk shipments of rechargeable lithium batteries carried as cargo on passenger planes are susceptible to fires or explosions that could destroy the airliners.

Yet US and international officials have been slow to adopt safety restrictions that might affect the powerful industries that depend on the batteries and the airlines that profit from shipping them. The batteries are used in products ranging from mobile phones to hybrid cars.

Shipments of rechargeable batteries on passenger planes are supposed to be limited to no more than a handful in a single box, under standards set by the UN's International Civil Aviation Organisation and adopted by the US and other nations. But a loophole permits shippers to pack many small boxes into one shipment and get around the rules. Tens of thousands of the batteries may be packed into pallets or containers and loaded into cargo holds.

In an April test by the Federal Aviation Administration, a cargo container was packed with 5,000 lithium-ion batteries and a cartridge heater added to simulate a single battery experiencing uncontrolled overheating. That triggered escalating overheating in nearby batteries, which spread in a chain reaction. Temperatures hit about 593 degrees Celsius. Once about 300 batteries had become involved, a fierce explosion blew open the container door and sent boxes flying, catching FAA and industry observers by surprise. Within seconds, the cargo container was in flames. The explosion came from a buildup of flammable gases.

A second test in September produced similar results, despite the addition of a fire suppression agent. Authorities have long known that lithium-ion batteries can fuel fires if they are defective, damaged, overcharged, incorrectly packaged or exposed to extreme heat. But they have been allowed to be shipped on passenger planes as it was thought the halon gas fire suppression systems in cargo compartments could extinguish any fire.

The tests have raised a new worry: that an explosion could increase pressure in the cargo hold, activating depressurisation valves that would let halon gas and smoke vent into the cabin and cockpit. That would dilute fire suppression in the hold and let a fire rage unchecked.