BISMARCK, N.D. (AP) -- Federal regulators say a lightning strike may have caused a pipeline rupture that spilled more than 20,000 barrels of oil in northwestern North Dakota.
The U.S. Department of Transportation's Pipeline and Hazardous Materials Safety Administration said Thursday that a preliminary investigation "points to a strong electrical discharge as the cause of the failure."
Agency spokesman Damon Hill says the exact final determination on cause hasn't been made. He says that could take months.
The agency also issued a safety order Thursday that sets conditions for Tesoro Corp. to restart the pipeline. The order requires the company to perform frequent aerial and ground inspections and install additional leak detection equipment.