LYNN – Firefighters are examining the second floor porch of 181 Henry Ave. as the origin of a two-alarm late-afternoon fire Wednesday that left a family homeless.Roxana Vargas was watching television in her second-floor bedroom when her brother banged on the door.”He said the dog was barking, something was wrong,” Vargas said.She fled her apartment with 2-1/2-year-old son, Harlem Lugo, and her brother, Brian, as flames and smoke climbed from the porch to the residence’s top floor.Firefighters credited an ambulance crew driving by Henry Avenue and police officers with ensuring Vargas and her family safely exited the home.Fire crews converged on the hilly dead-end street off Western Avenue and quickly extinguished the blaze as neighbors looked on.”I saw a big ball of flames,” said neighbor Chris Brown.Vargas credited the family dog, Sophie, with alerting her brother to the fire. Vargas’ mother, Rosa Mejia, also lives in 181 Henry. Vargas said the building’s first-floor residents are out of town for the summer.Fire investigators interviewed residents as part of their preliminary efforts to pinpoint the fire’s cause.