Marathon Oil Corp. (MRO) shut a unit at its Catlettsburg refinery in Kentucky after a leak of hydrogen fluoride late yesterday, according to a filing with the National Response Center.

Hydrogen fluoride was released from a pinhole leak in piping, according to the filing. The unit was shut and workers were isolating it and planning repairs.

“The Catlettsburg refinery experienced a small HF release yesterday,” Shane Pochard, a company spokesman, said in an e- mail. “There was no offsite impact and the issue is being addressed.”

U.S. refineries must notify the center if they release hazardous substances in excess of reportable quantities, according to the Comprehensive Environmental Response, Compensation and Liability Act, commonly known as Superfund.

The refinery has a capacity of 240,000 barrels a day, according to data compiled by Bloomberg.