A loud blast shook the walls at the Fatzo’s sub shop at 46 Green Bay Road, on Sturgeon Bay’s west side, Wednesday afternoon. The Sturgeon Bay Fire Department was alerted at 1:28PM and three units and five firefighters responded. As a precautionary measure, the occupants of the building were evacuated and natural gas and electrical services shut down. The incident was reported as an explosion that shook the building and left a sulfur-like smell. The restaurant was checked out and the fire crew did not find any evidence of damage, structural or otherwise. When firemen surveyed the basement, they noticed that the cover appeared to have been blown off the furnace and there was dust, dirt and other residue on the floor. It was speculated that the blast could have been caused by material in the furnace that contributed to a buildup of natural gas that somehow ignited. After thoroughly inspecting the building, the fire department decided to turn the matter over to the service providers for the sub shop. Sturgeon Bay firefighters left the scene shortly before 2PM.