Abstract: An incident occurred in the vinyl department of a plant. The equipment involved was a two-roll plastic mill. The operation involved dispersion of dry pigment powder into a liquid binder by mechanically squeezing the mixture between the steel rolls which were rotating in opposite directions. The binder in this instance was a copolymer of polyvinyl chloride and polyvinyl acetate, which was premixed as a dry powder with the pigment prior to introduction onto the mill. The second steel roller of the mill was steam heated to a temperature high enough to melt the vinyl copolymer powder, so that the liquid resin could wet the dry pigment during the dispersion on the mill. There were end plates at the sides of the rolls to prevent the batch on the mill from running off the sides. Due to improper maintenance of these end plates, an inordinate amount of space existed between the mill roll and the end plate on one side of the mill. An excessive quantity of paste tended to accumulate at this point. Apparently, these accumulations were never sufficiently removed after each batch had been completed, and a hard layer of dry dispersion had built up in the end plate. This caused the clearance between the steel roll and the end plate to become greatly diminished. This apparently was the condition of the mill at time of the incident. When the batch was running on the mill on the date of the occurrence, the friction, created by the unusually narrow clearance, caused the material on this side of the mill to overheat, until some of the resin close to the faulty end plate became hot enough to burn. These burning pieces dropped into the catch pan below the rolls, causing the dry vinyl resin powder there to smolder, and creating the toxic smoke, which affected the employees who came to extinguish the fire. Polyvinyl chloride, when it decomposes at 148 degrees centigrade, emits hydrogen chloride vapors. This caused the symptoms experienced by all the involved employees.