LYNN – A firefighter was taken to the hospital for heat exposure but no residents were harmed in a two-alarm fire that burned the middle floor of an apartment building near Lynn Common Thursday night.”The guys did a great job containing it before it got the third floor,” Lynn District Fire Chief Jack Barry said at the scene. He said the firefighter was taken to the hospital for precautionary measures and that all the building’s occupants escaped safely.The fire department responded to 7 Hanover Circle at 8:59 p.m. Thursday and the second alarm was rung at 9:03 p.m., according to fire officials. Barry said the fire broke out on the second floor of the building, a three-story building with a single apartment on each floor. He said the first floor of the building had smoke and water damage while the third floor suffered some flame damage.That damage appeared primarily at the rear of the building, where blackened and burned siding extended from a second-floor window up to the window and roofline of the floor above.Barry said it was too early to determine the cause of the fire.But a bystander, although she declined to give her name, said people were setting off fireworks in the parking lot behind the house prior to the incident.”They’re all over the place, it’s the Fourth of July,” Barry replied when asked if he could confirm whether fireworks were set off in the area before the fire. Several exploding fireworks and brightly colored flashes in the sky emphasized his point.Several firefighters rested outside the building after the flames appeared doused, with emergency medical responders handing out wet towels and bottles of water. Barry said that jakes were being rehydrated and their body temperatures monitored after exposure to the flames and heat at the fire.He said that residents would not be able to return to their homes that evening.Cyrus Moulton can be reached at [email protected].