At around 7.25 a.m., an alarm detected overflowing of a mixture of 5-8m³ of water and 0.04m³ of methylene chloride at a pharmaceutical plant. The overflow took place through the vent connected to a pipe channelling VOC gases to a cryogenic tower used to remove these gases. The internal emergency plan was triggered and the site was evacuated. The retention basins were closed at 7.50 a.m. Two production units were shut down and secured at around 8.30 a.m. The fire department established a safety perimeter. Tests were conducted on the effluents spilled, suggesting that the product consisted mostly of water. The explosimetric and toxicological readings were below the equipment’s detection threshold. The effluents spilled drained towards a 15m³ underground retention tank which is itself discharged by gravity into a 55m³ tank which, for its part, is discharged into the 400m³ retention basin. The emergency responders covered the effluents and the 15m³ tank with a foam blanket. Recovering the product was left to the responsibility of the operator, who eliminated it using a treatment process appropriate for halogenated liquids.
A production technician initiated manual filling of a receiving tank with town water. During this operation, he performed other work and left the valve open. At the same time, at 6.55 a.m., filling of a waste container began. To empty the tank into the transport tank, the latter was pressurised with nitrogen. On completion of filling, at 7.25 a.m., nitrogen flushing was restored and the tank was breathing again on the VOC network. The nitrogen was naturally sent to the cryogenic tower. Following the first incident, the nitrogen pressure pushed the water column which caused the rupture disc of the cryogenic tower’s condensate pot to break (burst pressure 0.35 bar). The content of the pot, 48l of methylene chloride and water, spilled on the site.
The operator took the following actions:
- reminder to all the teams of the operating procedure for filling this tank with town water;
- revision of the processing unit’s risk analysis taking into account this event;
- sharing the lessons from this event within the group.
