J. Wiss & Sons Co. evacuated 500 employes from its plant at 31 Littleton Ave. this afternoon when the oil in a metal tempering tank overheated and burst into flame.

Deputy Fire Chief George Schaeffer said the intense heat blistered the underside of the roof and the walls of the fireproof tempering room on the fourth floor of the scissors and shears plant. Carbon dioxide and a water line were used to put the fire out quickly.

Occupancy of the building was resumed 25 minutes after the alarm was sounded at 12:37 p.m.