An explosion and fire ripped through a gasoline processing unit at an Exxon Mobil Corp refinery near Los Angeles on Wednesday, leaving California with the threat of higher gasoline prices. Investigators were trying to determine the cause of the blast in Torrance, California, which occurred shortly before 9 a.m. PST (12 p.m. ET). Four contract workers were injured and sent to Long Beach Medical Center for evaluation. Exxon said late on Wednesday that three of the workers had been released. The company said it was operating units that had not been affected by the explosion at its 155,000 barrel-per-day refinery. Torrance Fire Captain Steve Deuel said a small ground fire that followed the explosion had been quickly extinguished. He said firefighters and refinery crews also contained a gasoline leak that had been caused by the blast. Deuel said there was no evidence of foul play. […]