After being called to the Legislative Office Building for a reported structure fire, firefighters concluded that cigarette butts began to smolder–causing foam insulation to ignite and send smoke through the building’s ventilation system.

A firefighter on the scene tells me that discarded cigarette butts were getting pushed into the cracks of the stone tiles outside the east exit of the building (and probably a similar situation at other exits around the plaza). Over time, “thousands” accumulated underneath, he said.

The tile, which had visible char marks and emitting smoke, was removed and shortly after workers were told they could reenter the building just before 4 p.m.

more images after the jump: