During the pumping of a batch of naphtha, a hydrocarbon leak occurred inside the warehouse enclosure on a pipe branch conveying the product to the refinery, located a few kilometres away. This phenomenon was the consequence of a pressure jolt inside the 12″ pipe, which caused the safety valve to open along with the partial destruction of a flange joint upstream of the valve. This pressure jolt was related to the disturbance of pipeline operations experienced by site personnel subsequent to a violent thunderstorm (lightning) at the beginning of the evening in the region around Chalon-sur-Saône. According to the operator, no significant impact on the environment could be detected, as the level of coordination between the pipeline operator and the warehouse manager was deemed to be effective and the arrival of response teams at the site rapid. The product that had spread was recovered, but a strong odour still created nuisances for the neighbourhood.