PLUM, Pa. (AP) — The owners of a home that exploded in western Pennsylvania last weekend were having issues with their hot water tank, authorities said, but the cause of the blast that killed five people — including two municipal officials — remains under investigation.

The explosion in Plum destroyed three structures and damaged at least a dozen others. It occurred shortly before 10:30 a.m. Saturday at a home owned by Heather Oravitz, the town’s community development director, and her husband. The town is about 20 miles (32 kilometers) east of Pittsburgh.

Plum Mayor Harry Schlegel said Oravitz, 51, and Plum Borough Manager Michael Thomas, 57, were killed in the blast, along with three others who lived in the neighborhood: Kevin Sebunia, 55; Casey Clontz, 38; and Clontz’s 12-year-old son, Keegan.

Oravitz’s husband, Paul, suffered severe burns over most of his body and remained hospitalized Tuesday in critical condition, Schlegel said. Two others injured in the blast were treated at a hospital and released.

Emergency responders said people were trapped under debris when they arrived to the scene. County spokesperson Amie Downs said the blast leveled one house and two others were on fire.

Crews from at least 18 fire departments worked to douse the flames.

Fifty-seven firefighters were treated at the scene for minor issues, according to Steve Imbarlina, deputy director of fire and emergency services for Allegheny County.

The cause of the explosion is under investigation by the Allegheny County fire marshal’s office, along with local law enforcement. The investigation was expected to be a “slow and long process,” Imbarlina said.

The fire marshal’s office said in a statement Monday that it was aware of the reported hot water tank issues at the home. The agency planned to investigate the cause of the blast, with the hot water tank issue in mind, and “along with any and all other possibilities,” the statement said.

Michael Huwar, president of Peoples Gas, said official checks by the company indicated that “our system was operating as designed.”

Gas and electric service had been cut off in the area as a precaution, but a plan was in place as of Sunday to restore services.