No one was injured in a fire at a Mountlake Terrace apartment Sunday night that displaced three residents and caused more than $110,000 damage. The fire was reported at 6:20 p.m. by an alarm company receiving a system activation at the Lakeside Apartments in the 6000 block of 219th St. S.W. Firefighters responding for the fire alarm arrived to find heavy black smoke and flames inside a first-floor unit in a two-story building at the apartment complex. South County Fire crews had the fire under control within 10 minutes of arriving and kept the flames from spreading to other apartment units. The residents were away when the fire started. Other residents of the building evacuated safely. No one was injured. According to South County Fire spokesperson Leslie Hynes, fire investigators determined this was an accidental fire, most likely started by a mattress located too close to a baseboard heater.