SAUGUS – Hot steam vented from the Wheelabrator incinerator started a two-alarm fire Wednesday night on the Route 107 facility’s rooftop, said Fire Capt. Michael Newbury.Newbury said the fire burned a 60-foot-long stretch of a wall at the roof’s edge along the rear of the incinerator building. He said an 8:55 p.m. call from a Wheelabrator worker to the Fire Department sent Engine 1, commanded by Lt. James Hughes, to the fire.Newbury arrived minutes later and realized firefighters would have to climb up 10 flights of stairs wearing protective gear and carry equipment to fight the fire. Hughes had already declared a working fire and Newbury struck a second alarm, bringing firefighters from Lynn, Wakefield, Melrose and Malden to assist town firefighters.”One of my main concerns was the safety of the men. I knew it was going to be a labor-intensive fire,” Newbury said.Twenty-one firefighters carried portable hoses to the rooftop and connected them to a water standpipe to fight the fire. After axes and chainsaws proved cumbersome, Newbury said firefighters used utility knives to cut away the rubber roof membrane before spraying water on insulation beneath the membrane.He said firefighters had to extinguish the fire before it could weaken structural beams holding up the roof.”At about 9:49 p.m., we got control of the fire,” Newbury said.He ordered firefighters finishing up work at the fire scene off the roof at 11 p.m. after lightning struck near the incinerator. Newbury declared the fire out at 12:25 a.m.Newbury said steam released on the incinerator roof “heated to the point where there was combustibility.” Wheelabrator Technologies spokeswoman Michelle Nadeau said company officials “are working closely with the Saugus Fire Department to determine the cause of the incident.””The fire caused minimal damage and resulted in no impact to operations,” she said.Thor Jourgensen can be reached at [email protected].