FARMERSVILLE, Texas (AP) — 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., The Safety Board’s investigation of a natural gas explosion and fire that resulted in three fatalities in North Carolina in 197511 determined that the gas had accumulated because a concrete drain pipe resting on a plastic service pipe had precipitated two cracks in the plastic pipe., A pipeline explosion and fire at an offshore natural gas pipeline in Louisiana's Plaquemines Parish, has left a worker dead, authorities reported, adding that the incident was under investigation., The Pennsylvania Public Utility Commission has finalized a statewide mandate requiring natural gas utilities to identify and replace older plastic piping prone to brittle cracking, following a , 1965 (March 4): A 32-inch (81 cm) gas transmission pipeline, north of Natchitoches, Louisiana, belonging to the Tennessee Gas Pipeline exploded and burned from Stress corrosion cracking (SCC) on March 4, killing 17 people., .