Pollution
Humain
Environnement
Economique

At 5:19 p.m., an explosion occurred at a pharmaceutical plant at the end of a hydrogenation reaction involving a chemical raw material, acetic acid, water and a catalyst (palladium). While conducting a hydrogen purge (pressurised hydrogen is sent into the reactor via the hydrogen vent), a technician heard a thud and saw a light above the hydrogen vent at the flame arrestor. He activated the emergency stop and initiated the internal emergency plan. The employees were evacuated. The other facilities were safely shut down. Finding nothing during their reconnaissance, the first responders did not have to intervene. The internal emergency plan was lifted at 5:47 p.m.

The reaction medium involved in the event was inerted with nitrogen and kept at 10 °C until analyses could be made.

An altogether similar incident had occurred on 4 June.

Upon dismantling the reactor, it was found that trace amounts of palladium were present in the vent line. The palladium in the vents was caused by foaming of the reaction medium. The palladium was carried towards the flame arrestor and dried over the course of purging operations. The palladium self-ignited at the vent’s outlet upon coming into contact with oxygen. In both events, the production run had been halted for a long period beforehand and probably enabled the palladium to dry in the vent line. The flame arrestor had been cleaned after the first event, but this cleaning proved insufficient.

New instructions telling technicians to empty the trap after each batch had been issued in May 2018. Before then, liquid in the trap prevented the catalyst from drying and self-igniting.

Since the accident, the operator:

  • has implemented measures to reduce the risk of foaming;
    • uses a non-foaming starting material;
    • has revised the inerting procedure (the vacuum is no longer applied because foaming observed in the vacuum);
    • uses a stick to scrape the wall and prevent foaming;
    • is looking into the possibility of adding a defoamer to the reaction medium.
  • injects nitrogen into the hydrogen vent to keep the hydrogen concentration below its lower explosive limit (LEL);
  • has reduced the decompression rate (hydrogen degassing and nitrogen inerting) to reduce entrainment;
  • is looking into adding a hydrogenation reactor with a larger capacity or reducing loaded quantities to keep the filling level at 50–75%;
  • has changed the cleaning instructions for the vent lines: they are to be cleaned at the end of each run, the flame arrestor is to be cleaned if production is halted for an extended period and annual cleaning is required after the line is completely disassembled.