In a plastics factory, the internal emergency plan was activated at 2 pm subsequent to a smoke release on the variable speed stirrer of a tank located inside a workshop. Technicians stopped the stirring, began cooling the tank and sounded the alarm. Factory personnel were evacuated. The site’s intervention team cooled the machines using CO2 extinguishers; 20 min later, employees were allowed to return to work. No injuries and no spreading or discharge was reported either in the workshop or within the atmosphere. Mechanics disassembled the stirrer in order to provide a diagnosis. The stirring turntable was composed of a motor clamped to a pulley (driving pulley) with a manual mechanical device to enable varying the speed of a gear set, which was also clamped to a pulley (driven pulley) fitted with a spring compensation device installed on a timing belt connecting the 2 pulleys. The driving pulley was equipped with sealed ball bearings (permanently lubricated). The entire assembly was covered by a plastic hood placed on the upper ball bearing, thereby protecting it from grease. After disassembly and appraisal of the gear motor assembly, the following conclusions were drawn: heating of the upper ball bearing (unknown temperature), cast iron present in the plastic hood, and a heavy smoke release. The cause of ball bearing heating could not be determined.