According to officials, at 6:40 a.m., units were sent to 12 Millbrook Road, the location of Plainfield Renewable Energy, for a report of a fire inside.
At the scene, firefighters located material burning on a metal storage rack and extinguished the flames.
One employee was treated at the scene for injuries but refused transportation to a hospital.
No other injuries were reported.
Officials did not say what caused the fire.