DULUTH, Minn. - Investigators were trying to determine on Monday the cause of the Sunday night explosions that destroyed a local ice arena and injured several broomball players and fans. People inside the building said they suspected the explosion came from a room containing an ice-grooming machine, which are often known by the brand name Zamboni. Fire Chief John Strongitharm said after the initial blast in the room, there were at least two subsequent explosions. He thought they were caused by propane tanks stored near the ice-groomer. Ice grooming machines often use the flammable gas as fuel. Strongitharm estimated the...