MADISON, Wis. — A fire at an apartment complex on Madison’s east side was contained by one automatic sprinkler Thursday night, preventing more extensive damage, according to the Madison Fire Department. Firefighters were sent to 6834 Milwaukee St. shortly after 8:30 p.m. after residents reported what they believed was a burst pipe. When crews arrived, alarms were sounding and residents had evacuated. Smoke was visible in a hallway, and firefighters shut off the sprinkler that had activated in a utility room. Investigators determined that improperly discarded smoking materials ignited a cardboard box. The box contained cigarette butts and other materials, officials said. Fire damage was limited to the box and miscellaneous items inside it. The sprinkler discharge affected an apartment in the unit below. Three people from two apartments were displaced, and the American Red Cross offered assistance, the Fire Department said. The department said the incident was the second time in the same week that a sprinkler had stopped a fire in an apartment building. On Sept. 5, a fire involving a cart outside a trash room at a student high-rise also triggered a sprinkler. Madison Fire officials used the incident to underscore the role of automatic sprinklers in multifamily housing and other buildings. The department said sprinklers can contain, control or extinguish fires before they grow and threaten additional households, residents or firefighters. “​​When a residence is not protected by automatic fire sprinklers, fire has time to grow in size and severity before firefighters arrive,” the department said, urging the installation of fire-protection systems in commercial and residential properties.