Office Building, Other Business Boston, MA – Sprinkler system activates in spontaneous combustion fire at downtown office building September 25, 2016 viking210 Firefighters believe a spontaneous combustion caused a small fire at a downtown Boston office building Thursday night, the fire department said. The fire started in a work room on the first floor of 50 Milk St. at about 8:55 p.m., said Steve MacDonald, a Boston fire spokesman. “It generated a lot of smoke,” he said, but the building was otherwise not damaged, and the Friday workday should not be affected. The department believes some rags in the work room had spontaneously combusted. MacDonald said the rags had some solvents on them and were in a room that was poorly ventilated. The room did have a sprinkler system, however, which activated when the fire began, MacDonald said. Fire companies left the scene by about 10:15 p.m. There were very few people in the building at the time of the fire, MacDonald said.