LYNN – Officials said a fire at a Boston Street Burger King early Saturday morning was accidental and investigators are examining the ductwork of the restaurant’s broilers.Burger King employees arrived at the 108 Boston St. location at approximately 5 a.m. Saturday. Employees reported they began noticing smoke in the kitchen area of the building, near one of the restaurant’s broilers, just before 6 a.m., according to an email from Lynn District Fire Chief Stephen Archer. The first alarm was struck at 6:02 a.m. and three engines, two ladder trucks and a medic unit were sent to the scene of the working fire, Archer said.Crews remained on scene until a little after 8 a.m. and no injuries were reported, according to Archer. He said the building sustained “extensive damage” but no estimate on the cost of damage was available. The building was boarded up and there appeared to be several holes in the building’s roof this afternoon.The Lynn Fire Investigation Unit and a member of the State Fire Marshal’s Office determined the cause to be accidental, Archer said.District Fire Chief Tim Collier said Sunday night that investigators were still examining the ductwork of the restaurant for the cause of the fire.