In a petrochemical plant, an explosion followed by a huge fire occurred during the polymerization of dicyclopentadiene (DCPD). Inside the plant, 3 people died and 11 are injured inside the plant. Heavy parts of the installation are found in a range of 1 km from the plant. The neighbourhood is evacuated within 600 m. The company fire brigade (12 people) is assisted by external fire brigade (about 50 people). The violence of fire makes it difficult to intervention. The water used for fire fighting caused a water pollution. Due to a mistake of the operator (inadequate training/instruction) during the filling of a polymerization reactor, the vessel was loaded with about 40 t of a mixture of monomers containing about 75% of DCPD instead of the required 50%. The high concentration of DCPD caused a runaway reaction that burst the reaction vessel (a safety valve was provided but with a wrong capacity) and resulted in an explosion followed by a huge fire.