WISCASSET – A small fire broke out in an abandoned chemistry lab at Maine Yankee on Monday.

The cause of the electrical fire remains under investigation. The fire, which extinguished itself, did not spread to other areas of the shuttered nuclear power plant or other rooms in the building, according to John Merry, first assistant chief of the Wiscasset fire department.

Maine Yankee spokesman Eric Howes said the room was being used to evaporate mop water. He said state environmental regulations don’t allow Maine Yankee to simply pour the wastewater down the drain and that evaporating the water is the best way to dispose of it.

An electric heater was being used on two 55-gallon drums of wastewater when the fire broke out shortly before 6 p.m. Merry said the power pack supplying the heater may have sparked the fire.

Merry said there were only a few small areas with flames in the room when firefighters arrived and that the fire burned itself out after the supply of electricity stopped flowing.

Howes said five employees suffered minor smoke exposure and were seen by rescue personnel who were called as a precaution.

The plant is about halfway through the decommissioning process.