MADISON, Wis. — Discarded cigarette butts ignited a small fire Thursday night at an apartment complex on Madison’s east side, but an automatic sprinkler limited the damage, according to the Madison Fire Department. Firefighters were called to the 6000 block of Milwaukee Street at about 8:31 p.m. after alarms sounded and residents evacuated the building. Crews found smoke in a hallway and traced the fire to a utility room inside one apartment, where a sprinkler head was operating. After shutting down the sprinkler system, firefighters found a burned cardboard box filled with cigarette butts. The smoking materials were identified as the fire’s ignition source. The fire was extinguished by the single activated sprinkler. Damage was limited to the box and other items inside it, though water from the sprinkler affected the apartment below. Three people from two units were displaced. The American Red Cross assisted those residents.