At a 40-ha chemical facility located on the outskirts of an urban area, the safety disc set at 1.5 bar on a 15.2-m3 reactor burst in a plant working with formo-phenolic resins used for glues applied to agglomerated material. The operator informed the Classified Facilities inspector, who promptly made a site visit. The batch production of a formo-phenolic resin lasted 10 hours. Both formaldehyde and phenol were loaded into the warmed reactor, then the soda used as a catalyst was gradually introduced into the device, which was maintained in a vacuum. The reactor’s cooling system (consisting of two double shells) and the return of emitted vapour condensates served to control this highly exothermic chemical reaction. At the time of this event, all 3 reagents were inside the reactor when the reaction started to run away, with a rise in both the temperature and pressure of the enclosure, followed by bursting of the adjusted safety disc protecting the installation; 6 tonnes of reactive media (formaldehyde at 11.5%, phenol at 0.6%, soda and resin) released from the roof fell both inside and outside plant premises, at distances as far as 400 m. Vegetable gardens and several vehicles received residue on their surface. The Classified Facilities Inspectorate proposed shutting down operations of the malfunctioning reactor, given that its service start-up was contingent on filing a report indicating the exact accident causes and suggesting a framework to avoid repetition of the incident. The operator was also required to submit within 24 hours a precise and readable map of the zones affected by this chemical fallout, so as to notify local elected officials and set the stage for implementing appropriate measures. This submission was to include all documentation and information (e.g. on toxicology) required to ensure an effective assessment of the risks potentially posed to residents and occupants of the identified zones. The operator was moreover asked to propose remedial measures for treating the polluted zones, e.g. disposal of affected plantations, soil treatment. The operator performed site cleanup work: 1,000 m3 of washing water were stored in an onsite basin. Soils and plant life were analysed, yielding: 0.02-0.87 mg/kg of phenol in the soil samples, and 0.17-4.08 mg/kg in plants. A selection of vegetables grown in neighbouring gardens was retrieved, and a wheat field in the line of chemical substance fallout was mowed; all damages incurred were reimbursed. After an overly rapid injection of soda, exacerbated by a high reactor loading level, reactor cooling was initiated too late (12 min after the temperature increase according to equipment recordings). The quantities of products introduced were considerable, although the plant operator insisted that the operating protocol had not been violated (15,190 kg measured by a mass flow meter, i.e. 15,792 kg per load cell for a 15.2-m3 reactor). The reaction ran away while reactor cooling devices (which had reached 127°C) were malfunctioning. The reactor loading level, combined with insufficient available cooling capacity and inappropriate temperature settings, impeded control over the reaction process. Also, the loading of all primary reagents at the beginning of the cycle, noncompliant with good professional practices, facilitated this runaway reaction. The plant had not been granted the necessary regulatory authorisations to produce this new type of resin, and no safety report for either the process or installation had been previously conducted. The operator modified the relevant process in favour of a continuous injection of formaldehyde, leading to improved control over reaction exothermicity and runaway protection by stopping formaldehyde injection. Reagent quantities were reduced, and the monitoring of both reactor operating parameters and chemical reaction stages was improved.

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