Firefighters knocked down a building at 147-151 East Merrimack St. on Saturday after extinguishing a fire that ignited around noon and caused smoke damage to two other buildings. Deputy Chief Jeff Winward arrived at 5:30 p.m., after the flame was put out, and said that two companies remained in the commercial and residential area of downtown Lowell past 11 p.m. hosing down hot spots and debris. There were no injuries, but the Red Cross provided emergency funds for food and clothing to three residents from the apartment building next door, which sustained smoke and water damage. A barber shop, a Brazilian variety store, and law offices, including those of state Representative Colleen Garry, were destroyed by the fire. Preliminary investigations suggest the fire was accidental.