The U.S. Department of Transportation issued a safety alert for the transportation of hoverboards containing lithium batteries that are at risk to heat up, catch fire or explode if improperly handled.

Hoverboards are self-balancing devices designed to be ridden around in a manner similar to a Segway, but without handle bars. The devices, a hot Christmas gift for 2015, are sold under a variety of different names, including balance boards, gravity boards or self-balancing devices.

In the safety alert, the DOT’s Pipeline and Hazardous Materials Safety Administration included shipping guidance after investigators intercepted 32 cargo containers filled with hoverboards with lithium batteries that were improperly prepared for shipment of a hazardous material.

The PHMSA’s investigation of intercepted cargo determined that more than 80% of shippers were unable to produce valid test reports to prove that lithium batteries have been properly manufactured and packaged to maintain integrity during transport.

Cargo shipments of hoverboards containing lithium batteries should be identified on shipping papers, tested and prepared for shipment as required based on the mode of transportation. Failure to comply can carry large civil penalties and potential criminal liability.

“It’s critical that lithium batteries are packaged and transported according to the correct specifications because, under certain conditions, they can generate heat, catch on fire and explode during transportation,” said Marie Therese Dominguez, PHMSA administrator. “PHMSA is conducting a complete and thorough investigation to ensure that hoverboards containing lithium batteries are transported in accordance with federal hazardous materials regulations.”