A heavy metals fire in a dust collector prompted the evacuation of a plant at Arconic early Tuesday morning.About 30 employees were evacuated from plant No. 4 after the fire was discovered just after 6 a.m. Feb. 14, said White Lake Fire Authority Chief Gregory M. Holman. The plant, formerly Alcoa, is located at 555 Benston Road in Whitehall. White Lake firefighters, assisted by Montague firefighters, extinguished the fire with a dry chemical powder, Holman said. Because the fire was burning at such high temperatures - estimated at between 1,800 and 2,000 degrees - spraying water on it could have caused an explosion, he said. The fire, discovered by employees, occurred when a spark ignited titanium, copper and brass particles collected in a large dust collection system, Holman said. Such fires occur a couple of times a year and the plant keeps the dry chemical for fire suppression on site