One thousand litres of diesel flowed into the wastewater collection system of an automobile manufacturer over a weekend. When workers arrived at the plant that Monday, they found diesel on the ground and in the sewers. The operator initially suspected that the pollution had leached up from the ground because, one year earlier, a video inspection showed that a 1-m-long section of pipe may be missing. After the accident, the operator drained and pigged the hydrocarbon separator. No pollution was found in the sewer whose manhole had not been confirmed.

A rupture of the diesel filter in the engine test room is what caused 12 m³ of diesel to leak into the drip tray. The diesel was pumped into a recovery tank provided for this purpose. No alarm was sent to the safety monitoring station. As the tank’s high-level sensor was not working, the fuel overflowed via the vent and spilt into the bund and onto the floor. As this bund was leaky, the diesel flowed into adjoining bunds. The outlet valves on these bunds are kept open when the tanks above them are empty so that rainwater can flow into the sewers via a hydrocarbon separator. The diesel flowed from the bund’s outlet valve into sewer and then through the hydrocarbon separator fitted with a high-level sensor, which was also defective.

The operator carried out a risk analysis and took corrective measures. The hydrocarbon separator was replaced. The various bunds were repaired using hydrocarbon-resistant materials and connected together to form a single 120 m³ bund. The recovery tank was fitted with a sensor that shuts off the engine test supplies and sends an alert to the test bench monitors. The sump pumps in the engine test room were fitted with devices that alert the safety monitoring station in the event of prolonged operation. The inspection authorities for classified facilities also asked the operator to beef up security on the days the facilities are closed.