A decomposition reaction occurs around 7 pm on the line 51 of an ethylene polymerisation reactor in a plastics manufacturing plant. The safety mechanisms were activated: dilution and cooling of the decomposition gases. The effects noted were a noise related to rupture of the overpressure disks, as well as the emission of carbon black and carbon monoxide.

On 10/07, the operator indicated to the inspection authorities for classified facilities that it was continuing its investigations on the equipment and had considered starting the restart procedure for line 51 that same evening. The operator was requested to provide an incident report specifying the causes and circumstances of this decomposition, the effects on people and on the environment and the measures considered to prevent a similar incident.