Efficient pollution control measures

The hydraulic oil from a rolling mill in a steel plant polluted a lagoon. The abnormal presence of oil was detected during an inspection of the water pit of the rolling mill’s cooling system. The internal emergency plan was initiated after the extent of the pollution had been determined. The firefighters set up a dam on the site’s sewer system outlet and absorbent materials were placed in the sewers to absorb the pollution. The next day, following a period of rainfall, a slight iridescence was observed on the banks of the lagoon. A skimming operation was performed.

A lack of proper inspection/testing was blamed for the pollution

The causal analysis conducted by the operator indicates that the origin of the leak came from a cylinder seal on the rolling mill following a maintenance operation on the seal. No leak testing was performed following this maintenance operation. The oil, therefore, leaked into the rolling mill’s cooling water pit. At the same time, another maintenance operation to drain off the scale from this cooling system resulted in the rolling mill’s cooling water circulating pump to become blocked. The correct operation of this pump was not checked before it was restarted. The water, loaded with oil, then overflowed into the basin of the site’s general cooling system, which itself then overflowed into the sewers. The lack of high-level alarm reporting on this basin resulted in the discharge of effluents into the sewers that went undetected.

Strengthening of inspections/tests and process monitoring equipment

Following this accident, an alarm sent to the agent on-call was set up in the event the cooling system’s overflow pump, discharging to the sewers, is switched on. Monitoring equipment was also installed, including an oil presence sensor linked to the operation of the cooling system’s overflow pump discharging to the sewer, a water containment valve on the sewer outlet. The operator also reinforced the organisation of these inspections by drafting a procedure formalising the need to conduct operational testing after maintenance work has been carried out. A daily visual inspection to assess the water quality of the general cooling system was implemented.