From the FAA warning today on the carriage of lithium batteries, of which the UPS flight was carrying a large number.
The FAA's safety directive said that recent research conducted by its scientists shows that when batteries are exposed to high temperatures they have the potential to create "thermal runaway," a chain reaction leading to self-heating and the release of a battery's stored energy.
A cargo compartment fire can be hot enough to ignite batteries even if they aren't involved the initial fire, "creating a risk of a catastrophic event," the safety directive said. Once one battery experiences thermal runaway, it generates enough heat to trigger thermal runaway in other nearby batteries. Lithium metal batteries — the kind normally used in watches and cameras, for example — can create explosions forceful enough to damage cargo compartments.
FAA tests of as few as six loose lithium metal batteries stored in steel containers found that when exposed to heat they created enough explosive force to blow the lids off the containers, the directive said.
"There are currently no approved and tested containers that can sufficiently contain the known effects of accidental lithium metal battery ignition," the safety directive said. "Common metal shipping containers, pails and drums are not designed to withstand a lithium metal cell fire."