In a refinery, a diesel fuel leak occurred in a vacuum distillation unit. It flowed into the cooling water evacuation channel then reached the Tancarville canal. The leak was caused by the penetrating corrosion of three tubes in a water-cooled open-circuit heat exchanger (the three tubes, on which early signs of corrosion had been detected during the last inspection, were to undergo more thorough testing during the next shutdown). The product had migrated into the cooling water and then reached the canal. According to the feedback, heat exchangers of this type (water open-circuit) installed on the site are now monitored more closely than before (complete inspection on every cycle instead of every 2 cycles). Furthermore, a floating boom on the cooling water evacuation channel will eventually be added to existing installations along with another boom on the stormwater outfall.