Inside an electric power plant, a transfer of domestic fuel oil from the primary tank (2,450 m³) to the daily supply tanks, initiated around 4 pm, did not stop automatically even though the high level had been reached. At 11 pm, the watchman noticed an accidental overflow of fuel oil in the retention basin associated with the daily supply tanks. The transfer process was halted. Since the retention basin was not completely sealed, fuel oil seeped out in several places, polluting the soil. In all, nearly 22 m³ of fuel oil had spilled. The plant operator estimated operating losses at €25,000. A control room operator had forced continuation of the fuel oil transfer by overriding the high and very high alarm levels on the daily tanks. The environmental inspection also noted: the absence of guidelines for combustible transfers, no sound alarm in the event of overpassing high and very high levels, plus the lack of personnel response upon activation of the supervisory system alarms both on-site and on remote sites.