"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.