LYNN – Fire officials said they are still investigating the cause of a four-alarm fire that displaced 40 to 50 city residents Tuesday.Firefighters responded to 12 Bennett Circle and 6-8 Bennett Circle at approximately 4:10 p.m. Tuesday after firefighters at the nearby station saw smoke and rang an alarm, Lynn Fire Chief Jim McDonald said Tuesday.Crews arrived on scene to find heavy fire at 12 Bennett Circle and residents already outside the home. Firefighters reportedly helped residents of 6-8 Bennett Circle evacuate that building as flames spread.McDonald said initial reports suggest the fire started in either the alleyway between the two triple-deckers or on the porch of 12 Bennett Circle. Flames scorched the adjacent side of 6-8 Bennett Circle, with damage extending almost completely to the back of the house and the roof.No residents were hurt, but a firefighter reported a minor case of heat exhaustion from the blaze.Lynn District Fire Chief Arthur Richard said Wednesday afternoon that investigators had not determined the cause of the blaze and were still investigating.Richard said that approximately 25 people displaced by the fire had stayed at Lynn Classical High School overnight Tuesday. But he reported the Red Cross, which also responded to a fire in Waltham Tuesday, had found alternative housing for the victims on Wednesday.”They worked just as hard as we did,” he said of Red Cross workers.