Twelve oxygen tanks exploded inside of a burning Lancaster house Saturday night, fully engulfing the structure in flames, the town’s fire chief said. The fire began at 10:56 p.m. Saturday on Kilbourn Road and grew to three alarms after the explosion, Chief Michael Hanson said in a statement. Live power lines were down on the road when firefighters arrived, forcing them to attack the flames from outside the 2½-story house. The roof collapsed at the height of the fire, which completely destroyed the house. Damage was estimated at $300,000, the fire chief’s statement said. Two dogs were inside when the fire broke out. One dog was found safe; the other was revived, the statement said. There were no other injures.