At 4:12 p.m., a fire broke out in the incinerator stack of a Seveso-classified pharmaceutical plant. The stack had been shut down two hours earlier for maintenance. The fire released copious amounts of smoke. The plant’s internal emergency plan was implemented and the employees were evacuated from the smoke-filled buildings. The site’s firefighters extinguished the fire in one hour, then monitored the cooling of the stack. The alert was lifted at 6:20 p.m. One person was injured during the evacuation (torn muscle). The flue-gas cleaning system, in particular the wet electrostatic precipitator (ESP) and a portion of the stack, was damaged. The operator collected two plant samples and five soil samples in the environment that was most exposed to the smoke and analysed them (PAHs, heavy metals, dioxins and furans) to determine whether there was any environmental impact. While the incinerator is down (this could last for up to 18 months depending on the repairs required), liquid waste will be taken by lorry to other treatment plants and a portion of the gases will be released to the atmosphere above the shops. The operator will conduct a study on the impact of this degraded mode.
An internal working group analysed the accident (operating and maintenance data, comparisons between the current shutdown and other shutdowns, the manufacturer and electrostatic precipitator experts were contacted to find out if similar incidents had already occurred, etc.). It was found that the materials used to make the plates in the ESPs are combustible and that sparks (arcing) can cause these composite materials to catch fire if the ESPs are kept energised while no gas is flowing (filling the system with air increases the oxygen content in relation to the normal operating period) and no scrubbing sequences are underway (stopped during the shutdown). Experts confirmed this and listed several ESP fires that had occurred in previous years due to a lack of water flow. The operator pointed out that the duration of the shutdown (2 hours) and the outdoor temperature (+28 °C) most likely promoted the drying and ignition of the material of the ESP plates that were left energised. The scenario of ESP fires will now be taken into consideration in the plant’s risk analyses.