SPRINGFIELD, Mass. (AP) -- A utility worker responding to reports of a natural gas leak in one of New England's largest cities punctured a pipe and an unknown spark ignited a massive explosion that injured 18 people and damaged 42 buildings, the state fire marshal announced Sunday.

Friday night's natural gas blast in Springfield's entertainment district was caused by "human error," State Fire Marshal Stephen Coan said at a news conference. He didn't name the Columbia Gas Go. worker who pierced the high-pressure pipe.

The worker was trying to locate the source of the leak with a metal probe that tests natural gas levels when the probe damaged the underground pipe, Coan said. A flood of gas then built up in a building that housed a strip club, and a spark touched off the blast, officials said.

Columbia Gas planned a news conference for later Sunday afternoon. A message left for a company spokeswoman wasn't immediately returned. Columbia Gas, a subsidiary of public company NiSource Inc., announced earlier Sunday that it planned to open a claims center for residents and businesses affected by the explosion at City Hall on Monday.

Preliminary reports showed 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 completely destroyed.


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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.

"The firefighters did an excellent job evacuating the area which certainly prevented additional civilian injuries and saved many lives," Conant said.

Columbia Gas officials have been cooperating with investigators and have determined that there are no more gas leaks in the neighborhood, Mayor Domenic Sarno said.

Coan said the investigation is being turning over to the state Department of Public Utilities. It's not clear whether investigators will ever be able to determine what caused the spark that ignited the explosion.

Springfield, which is 90 miles west of Boston and has about 150,000 residents, is the largest city in western Massachusetts. It's known as the home of the Basketball Hall of Fame, which is not near the blast site.

The city has been rebuilding from damage caused by a tornado in June 2011.