A fire that destroyed a FedEx Corp. truck in Canada exposed a loophole in lithium-battery testing standards that could have led to a fatal blaze on a flight, U.S. investigators said.

The shipment by Braille Battery Inc. of Sarasota, Florida, in 2016 had earlier prompted federal regulators to charge the company with violating shipping rules. But, since the batteries were low-production models, they were exempt from more rigorous safety tests and shipping rules, the National Transportation Safety Board concluded on Monday.

Braille makes batteries for race cars and motorcycles and other uses.

“The NTSB is concerned that similar accidents involving low-production or prototype special permitted lithium-ion batteries could occur on an airplane during transport, potentially leading to the loss of the airplane and its crew and, catastrophic property damage on the ground,” the safety board said in a recommendation letter.

Lithium-based batteries have been linked to two fatal air cargo crashes and scores of other fires on passenger planes. The safety board is separately investigating battery fires on electric vehicles.

Because Congress in 2012 prohibited U.S. regulators from enacting battery standards that are more rigorous than those imposed by the United Nations’ International Civil Aviation Organization, the NTSB called on the government to petition the international agency to tighten its standards.

The recommendation was addressed to the Pipeline and Hazardous Materials Safety Administration. The agency will review the recommendations, it said in an emailed statement.

Braille didn’t respond to an email seeking comment.