An explosion at a metal casting plant killed one and injured nine others Tuesday morning, authorities said. The accident occurred at Tec-Cast, an aluminum castings company, while workers were performing maintenance on an air pressure vat used to pour molten metals into cast machine parts, police said. Workers were fixing a door on the approximately 1.22-meter wide vat shortly after 8 a.m. when it exploded because of air pressure that had built up in the back, said Capt. Franklin Smith of the Carlstadt Police Department. A 61-year-old maintenance supervisor was killed when the door blew off the vat and struck him and the other workers, police said. The man was pronounced dead at the scene; the others were taken to area hospitals.