In the past year, the Federal Aviation Administration (FAA) has made a strong case against lithium batteries on airplanes. While passengers are still allowed to bring most phones and laptops that contain lithium batteries onto their flight, spare or uninstalled lithium batteries must be carried in carry-on baggage only.

What makes these batteries so dangerous? Being so compact and powerful is exactly what puts the batteries at risk for exploding and having the potential to cause fires. If they short-circuit and overheat, they can create a chain reaction that makes them emit gas that could spark an explosion. Loose batteries, especially in large quantities, create a risk for fire in aircraft cargo and baggage compartments. In the confines of a cargo hold, a battery fire has the potential to spread so quickly that it overpowers existing fire-suppression systems, and there have been multiple reports of lithium battery-related fires on cargo planes.

The most recent warnings from the FAA include the ruling on spare batteries, the ban on Galaxy Note 7 phones on all US flights, and the urging of airlines to warn passengers of the risks of carrying loose batteries in both their checked luggage and carry-ons. The greater risk to a plane would come from large shipments of the batteries, and as a result, the FAA is pushing for an international ban on carrying such cargo on passenger airliners. Some airlines have voluntarily banned such cargo. Among them are the four largest domestic airlines (American, Delta, United, and Southwest), as well as international lines including British Airways, Lufthansa, Emirates, Etihad, and Qantas. Due to the fact that many of these big shipments often originate in Asia, carriers like Cathay Pacific, Singapore, and Dragonair are also supporting the ban.