An explosion occurred around 1:40 am in a formulation reactor upon completion of camphorsulfonic acid loading into the toluene for the purpose of drying by means of azeotropic distillation. The explosion injured 1 technician due to the direct (blast) effect and caused the upper part of the distillation column to burst, in addition to roof damage (asbestos cement tiles torn off) and debris projections (mainly pieces of glass) spewed 20 to 30 m outside the building. The top of the column (nominal diam.: 300, 1 bar) split, the temperature transmitter was found on the building roof, and a flange (0.5 – 1 kg) wound up 20 m from the building. A large quantity of soot was also discovered on the reactor walls, dome, the manhole surface, the stirring shaft, and in the glass pipes and settling tank (continuous sedimentation). Moreover, the reactor’s rupture disc burst.
The site operator’s investigation confirmed the presence of an explosive mix inside the free volume of both the reactor and distillation column subsequent to a defective inerting step conducted by the technician, though the ignition source could not be clearly identified (self-heating of the product vs. electrostatic discharge?). Several remedial measures were implemented:
- Additional investigations on the causes of potential formation of a sodium methylate deposit leading to product self-heating;
- Revision of all process execution instruction sheets in manufacturing workshops, with a systematic indication of pressure in the reactors on operations control sheets, plus the requirement to obtain an oxygen value below 8% for a pressure below 150 mm Hg (or 200 mbar) during the inerting phase;
- Production of a specific instruction devoted to the inerting of formulation reactors;
- For the targeted process, drafting of an operations procedure that specifies the continuous oxygen content measurements inside the reactor, along with replacement of the glass column by an enamel column;
- Recall of the importance of technicians’ compliance with inerting instructions and procedures when completing the phase of introducing an insulating liquid into a reaction medium; a training session on inerting techniques was once again proposed for synthesis workshop staff;
- The damaged reactor was fitted with a stationary oxygen probe; this measure would gradually be extended to all onsite reactors.