FARMERSVILLE, Texas — A valve leak and a spark of unknown origin combined to cause a North Texas natural gas pipeline explosion last year that killed two workers and injured two others, federal investigators said.
A report by the National Transportation Safety Board followed the agency’s investigation of the June 28, 2021, explosion near Farmersville, about 35 miles (55 kilometers) northeast of Dallas.
In the report issued Wednesday, the NTSB said a work crew was using a steel rod to insert an inline tool into the Atmos Energy pipeline when an explosion in front of the tool shot it from the chamber and at the workers standing in front of the door.
Investigators said they found scratches and gouges in a mainline valve seal in front of where the tool was, creating leak paths. Workers had suspected the leak existed the week before, tightened the valve until the leak stopped or was reduced to undetectable levels, then marked the valve’s position to avoid a recurrence.
The leak persisted, however, the NTSB said. Also, Atmos procedures and training did not prepare workers to recognize the developing hazard. Although the work crew had many years of collective experience, the workers were not qualified as required by federal regulations and were not using gas monitors to watch for a hazardous atmosphere, the board said.
Dallas-based Atmos has upgraded its procedures in response to the explosion, the NTSB said. Atmos officials did not immediately respond to a message seeking comment on the NTSB report.