In a pharmaceutical plant, during an operation intended to remove dimethylsulfide (an odoriferous compound), a violent explosion audible for several kilometres fractured equipment (rupture disc, manifolds…) on a tank containing a cyclohexane-rich flammable distillate, and blew windows out of a 500 m² fine chemical facility. As this treatment was not part of the antibiotic manufacturing cycle, the operation is performed in a 8 m³ reactor, by oxidising dimethylsulfide with hydrogen peroxide in an acidic environment. The establishment’s internal contingency plan was initiated.
The site’s internal firemen were able to bring an outbreak of fire under control in 15 minutes. An operator was severely injured by a falling electrical cabinet and died a few hours later. Two employees were injured (burns to heels and eardrum trauma), 12 others who were not directly injured were examined as a precautionary measure. The accident occurred while the tank was being rinsed after a blow through valve was opened. The valve had been erroneously connected to a compressed air network and not flushed with nitrogen.
The proposed hypothesis is that the ignition energy was created by the agitation or the transfer of 2 non-miscible liquids (cyclohexane and water, in this case), one of which is flammable and insulating and thus can easily capture a static electrical charge (Klinkenberg experiment). During acceptance inspections following modification operations conducted over the summer to launch new manufacturing operations in the existing workshop, the subcontractor and the operator did not notice the incorrect connection of nitrogen piping on the compressed air network just 10 cm away on the plant’s “purge nitrogen” branch connection. The Classified Installations Inspectorate recorded the facts:
Following this accident, the operator decided to abandon the deodorisation treatment, better identify all of the plant’s pipework with a colour-coding system, check for oxygen using an oxygen profiler and to form a working group dedicated to finding deficiencies in the qualification procedures and improving them. Two years later, the inquiry conducted following a judicial inquiry implicated 3 companies and lead to the indictment of 14 individuals.
Download the detailed report in .pdf format (70 Kb)
