HAMPDEN – An explosion Wednesday afternoon at a propane storage facility on Western Avenue split sections of a building’s roof at the seams and shattered windows but caused far less damage than was feared.

Three large white holding tanks in the back of the building were not damaged in the explosion that Hampden fire officials said appears to be connected to a malfunction in the propane-burning boiler room. The resulting fire spread to an adjacent bathroom but was quickly extinguished, said Hampden Deputy Fire Chief Mike Andersen.

Two workers were in the rear of the building at the time of the explosion, but they were uninjured, he said. They shut off the main tanks. Outside, with the potential for more substantial explosions, emergency vehicles blocked off a section of busy Western Avenue, rerouting traffic.

Some damage to the building was clearly visible from a distance. A large ripple in the roof made by the explosion vented white smoke from inside the building.

Initial reports of an explosion at the plant, where gas is stored and transferred to railroad tank cars, raised concerns for firefighters.

“It was quite heart-jumping at first,” Andersen said.

Firefighters had the fire under control within a few minutes, he said. One minor hitch was reported, however.

In a mishap that Fire Department officials said didn’t hamper the effort to extinguish the fire, a passing train severed a secondary water line. Water sprayed for a few minutes before firefighters could turn it off. By that time, however, the fire had been extinguished.

Bangor firefighters backing up Hampden had put down the support line to supplement the primary water supply.

The secondary line was placed across the railroad tracks, and fire officials said the railroad company was notified, however, citing some confusion over the ownership of the railroad, the wrong company was contacted.

About 2:45 p.m., the train crossed the track and carried the water-inflated line along with it, lacerating it and pulling it from the hydrant.

The cost of the damaged hose was not immediately available.