SEATTLE — The U.S. Justice Department said Friday it will file no criminal charges following a four-year investigation into the April 2010 explosion that killed seven workers at the Tesoro Corp. refinery in Anacortes. The decision was shared with victims’ relatives earlier in the day, said Jenny Durkan, the U.S. attorney in Seattle. Prosecutors examined whether environmental and worker safety laws and regulations had been criminally violated, but there was no evidence that reached the “exacting bar for criminal prosecution,” Durkan announced. The U.S. Chemical Safety Board released its final report on the April 2, 2010, blast in May. It blamed the facility’s safety culture, industry standards, and state and federal oversight for the catastrophic rupture of a heat exchanger.The board called for more conservative standards for the use of carbon steel and called on the state of Washington to adopt more rigorous safety-management standards. “I believe this investigation, as well as those conducted by other agencies, have prompted changes in how the industry conducts itself,” Durkan said.Tesoro and the refinery’s previous owner, Shell Oil Co., agreed to settle a lawsuit brought by the families of six victims for $39 million, and the families are also suing an outside firm that they say gave Tesoro bad advice on the mechanism that failed in the blast.