Firefighters in Bangor say a fire at a senior housing complex, that’s still under construction, caused around $400,000 worth of damage. State fire marshal investigators are probing the possibility the fire was set.Construction workers arrived at work Thursday morning to find the damage to the building on Harlow Street.A worker on the scene tells us it appears as though someone broke a window to get in some time last night and set fire to some carpeting on the second floor. Three floors sustained damage, with the second floor getting the brunt of it.Bangor Assistant Fire Chief Rick Cheverie says the damage is extensive. “Since the building is under construction, the products of the fire, smoke, heat, and such extended beyond that room and pretty much the entire second floor has some damage to it,” he says. “Primarily in the form of smoke and since there was no ceiling or anything else up all the conduit all the wiring and many of the utilities that were up there.”Cheverie says there appears to be evidence of a break-in but they don’t expect to know the official cause until Friday.Contractors say they were hoping to have residents moved in by February, they still think that’s possible.