In a chemical plant, a 4-tonne leak of toluenediamine (TDA) occurred during the maintenance intervention, while the production workshop was operating at 90% capacity. This accident actually gave rise to a TDA spill, which crystallised on the shop floor with the liquid part flowing into the retention tank and releasing aerosols from there. The gas alarm in the workshop was activated. An absorbent material was spread over the spill and a water curtain was set up to break down the emitted vapours. Watering wound up introducing amine into the site’s stormwater drainage system.
The majority of TDA spilled was recovered for destruction with the exception of 46 kg channelled to the retention pond of the chemical platform for gradual release into the DRAC River while respecting the known no-effect concentrations (PNEC value set at 0.016 mg/l). The absence of water table pollution was to be checked by piezometric monitoring downstream of the pollution. Furthermore, TDA measurements carried out onsite during installation clean-up revealed atmospheric concentrations below 0.1 mg/Nm³.
The leak lasted about 30 minutes (the time required for responders to equip themselves with airtight overalls), emanating from a manual valve on the bottom of the unit’s second separator, containing 30 m³ of a mixture of liquid TDA (63%) and water (37%) at 135°C under a pressure of 3.5 bar. The cause of this leak might have been related to accidental movement of the quarter-turn valve (by shock or vibration) when reinstalling the automatic valve located downstream or by sudden release of a “sealing plug” formed by the catalyst. The technical investigation also indicated that the quarter-turn valve had not included a stop or position indicator. An underestimation of the risks associated with maintenance interventions during normal operations was called into question.
A press release was issued by the operator.