Four people are being treated for shock after an explosion at the Rio Tinto plant in Sorel-Tracy this morning. The Surete du Quebec said the explosion occurred around 4:30 a.m. A gas line ruptured, according to Sorel Mayor Serge Peloquin. Company spokesperson Claudine Gagnon told Radio-Canada no one was hurt. More than 1,400 people work at the site. There is no word on damage to the plant, which is about 90 kilometres northeast of Montreal.