The U.S. Consumer Product Safety Commission announced on Wednesday that it’s currently investigating various self-balancing board manufacturers, importers, and distributers following a string of safety issues related to the products. Consumers have reported explosions and fires.

Some of those being investigated include Smart Balance, Hover-Way, Swagway, and E-Rover. The agency has yet to determine the safety of any of these brands, and is currently testing models at its evaluation center in Rockville, Maryland.

The CPSC says that many of the incidents took place indoors and “could have resulted in serious injuries if not for the quick actions of consumers to extinguish the fire.” The agency has described this as a “priority investigation,” and will continue to dedicate its time and resources until it discovers the cause of these combustive episodes, which are most likely caused by lithium batteries.

In a statement, the CPSC specifically lauded Amazon for taking cautious action and offering full refunds to consumers who purchased hoverboards through the e-commerce website. It added that there are no safety standards in place for these types of products, but ASTM International and Underwriters Laboratories (UL) are currently working to develop them.