SPRINGFIELD, Mass. (AP) â¿¿ A natural gas explosion that injured 18 people and damaged 42 buildings in Springfield's entertainment district was blamed Sunday on a utility worker who accidentally punctured a high-pressure pipeline while looking for a leak. State Fire Marshal Stephen Coan said the Friday night blast in one of New England's largest cities was caused by "human error." He didn't name the Columbia Gas Co. worker who pierced the pipe while responding to reports of a gas leak. The worker damaged the underground pipe while using a metal tool to locate the source of the leak, Coan said. A flood of gas then built up in a building that housed a strip club, and some kind of spark touched off the blast, officials said. Coan said the employee was following older markings on a sidewalk that indicated the location of the gas line. He appeared to be an appropriate distance from the line, but the markings were incorrect and the worker accidentally punctured the pipe. A message left for a Columbia Gas spokeswoman wasn't immediately returned. Columbia Gas, a subsidiary of public company NiSource Inc., said earlier Sunday that it plans to open a claims center at City Hall on Monday for residents and businesses affected by the explosion. Preliminary reports show the blast damaged 42 buildings housing 115 residential units. Three buildings were immediately condemned, and 24 others require additional inspections by structural engineers to determine whether they are safe. The building that housed the Scores Gentleman's Club was destroyed. After the pipe was ruptured, authorities evacuated several buildings. Most of the people injured were part of a group of gas workers, firefighters and police officers who ducked for cover behind a utility truck just before the blast. The truck was demolished. Some officials said it was a miracle no one was killed. Springfield Fire Commissioner Joseph Conant praised the actions of city firefighters.