Pollution
Humain
Environnement
Economique

At 7:45 a.m. in a synthetic fibre chemical plant, a leak was discovered on an internal pipe elbow during the start-up phase of a solvent regeneration distillation system (after shutdown). It was estimated that the leak lasted for roughly 20 minutes. The installation was shut down. Nearly 300 litres of distilling juice (70% water and 30% 1,3-dimethyl-2-imidazolinone (DMI) was recovered from the building’s retention facility using absorbent mats placed on the workshop floor. The municipal wastewater treatment plant and the Classified Facilities Installation Authorities were informed.

The unit was restarted the following day after the elbow had been repaired. While making rounds at 8 p.m., a security officer noted liquid exiting the facade via the overflow of a “small waters” distribution pot (riser stub) of the pre-concentration column. The liquid (70% water, 30% DMI) formed a puddle on the asphalt outside the facility. The unit was switched off again, and steps were taken to limit the spread of the spill. Based on the level measurement records, the leak was estimated to have lasted approximately 15 minutes.

The operator contacted a specialised engineering consultant to define the soil remediation measures in the area affected by the spill:

  • excavation of soil to a depth of 1.2 m, i.e. 30 t of soil excavated;
  • pending analyses, protection of the stormwater network by covering the area affected.

The leak on the pipe elbow resulted from erosion of the piping, although the solvent used is non-corrosive. The cause of the leak of the 2nd day was attributed to human error, namely:

  • forgetting to close a column shut-off valve after a test;
  • no check was performed before restarting;
  • the restart was not performed in accordance with the general procedures to be followed in terms of modification projects, servicing/maintenance works, lock-out and tag-out.

Several root causes were accumulated:

  • absence of a restart procedure after leakage and repair;
  • failure to take column isolation into account in the risk analyses (HAZOP initially performed with 2 columns, and then 3 when an element is added, without considering the possible isolation of the 3rd column; operation with two columns, with the 3rd isolated (not analysed initially);
  • clearance of the alarms of the 3rd column in the control room, in order to simplify operation with two columns (fewer alarms to manage, otherwise the management of flows and alarm levels is complex).

The operator updated the procedures following intervention on the column, updated its risk analysis and internal emergency plan, bolstered operator training, redefined the roles and responsibilities of each operator and improved the ergonomics of the operating interfaces.