An exothermic runaway reaction triggered an explosion and subsequent fire in a workshop at a pharmaceutical plant during a reduction step carried out inside a reactor inerted with nitrogen; this reduction was being performed in an anhydrous environment on an amine imide in the presence of sodium borohydride activated by aluminium trichloride. At the time of the accident, the imide was being transferred into the reactor by means of a flexible pipe connected to a mobile pneumatic metering pump. The operation began at 6:30 am, a half-hour before the end of the work shift. According to plant procedure, this operation required at least 8 hours with a reaction medium temperature not to exceed 65°C. At 6:45 am, once the mandated temperature limit had been reached, technicians prepared to cool the reactor and maintain it at approx. 65°C. At that point, the reaction suddenly ran away, accompanied by a rise in temperature and pressure. The technician nearest the reactor noticed a strong unpleasant smell. Through the reactor’s glass window, he detected a glow before the explosion. Employees positioned within 15 m of the reactor felt the blast. A flame crossed the workshop; other flames spewed from the reactor via a joint and damaged taps. Employees outside the building also felt the blast just prior to the explosion. A flame several meters high was visible for a few seconds at the outlet of a chimney, which allowed for a drop in reactor pressure should the rupture disc burst. Operational malfunctions caused this accident, which occurred at the end of the shift. Erroneous manual settings on both a pump and group of valves led to an excessive flow of imide. The runaway reaction released a significant quantity of H2 not consumed by the reaction medium. The sudden gas ignition might have been due to static electricity, a hotspot or the eventual presence of diborane and traces of water. The instructions did not provide the settings to apply during transfers, relying instead on technicians’ know-how. The agents assigned to the shift were certified, but this technician was the newest member of the team and had never before transferred imide. In large part, the unit was operated manually and lacked a pump flow measurement meter and an alarm for aberrant reaction parameter values. Four of the 8 personnel inside the workshop were injured (2 seriously); property damage was assessed at 14 million francs.

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