Pollution
Humain
Environnement
Economique

In an explosives manufacturing and storage plant, when a technician came on duty at about 3 a.m., he noticed that the flow alarm had been triggered on the oil circulation pump (OCP) of the ammonium nitrate-based stock emulsion manufacturing workshop. Upon entering the workshop, he saw that the pump had failed and that the 4,500-litre fatty phase tank was empty. Smoke, caused by fatty phase projections on the hot pipes surrounding the pump, was released in the workshop.

The oil phase leak reached the main sludge/oil separator of the stock emulsion workshop, then the storage tank located downstream from it. The tank overflowed, and the overflow (500 to 1,000 litres) was discharged into the rainwater system. At 5 p.m., the presence of the fatty phase was observed on the surface of the storm basin located below the manufacturing facilities. Closing the sludge/oil separator valve located behind the storm basin prevented the outside environment from being reached.

A specialised company intervened the next day to clean the fatty phase tank, the storage tank, the rainwater network and the stormwater basin. The final waste from the sludge/oil separator was sent to a specialised treatment centre. Clean-up of the pollution caused was estimated to have cost between 35,000 and 40,000 Euros.

After an initial on-the-fly analysis the day after the incident, a formal expert analysis meeting was organised to ensure an in-depth investigation into the causes of the incident.

The massive leak occurred through the seal on the pump shaft. The pump, installed in 2001, had operated for a cumulative duration of 5,000 hours. A maintenance inspection, carried out just a few days before the incident, had not revealed any anomalies. It had been impossible to monitor wear on the part of the pump involved. The leak could therefore not be anticipated.

The following actions were carried out before resuming production:

  • installation of a new oil circulating pump on a retention tank equipped with a high-level probe to stop the pump from being put into service,
  • installation of a float level probe on the fatty phase preparation tank, turning off the heating if this tank is empty,
  • installation of a motorised valve on the bottom of the fatty phase preparation tank (automatic closing if the pump is stopped and prevention of commissioning if this valve is closed),
  • installation of a high-level probe with an alarm on the storage tank located after the sludge/oil separator in the manufacturing workshop,
  • installation of a safety system on the pump motor to prevent dry running.

The inspection authorities for classified facilities required that the alarms of the various security systems installed be sent to an alarm control station with return via telephone transmitter to the on-call staff. Otherwise, there must be constant monitoring during the operation of the installations. Following the various modifications, the inspectors also required the operator to ensure the validity of the risk analysis contained in the existing hazard study.