Thick smoke was seen billowing from the Lubrizol plant – which manufactures additives for lubricants and is considered “high risk” – with more than 200 firefighters sent in to tame the blaze.
Pierre-André Duran, the government's top official in Normandy, said the fire risked polluting the nearby Seine – one of France's main rivers, which passes through Paris before flowing through Rouen and into the Channel at Le Havre.
Incendie dans une usine classée Seveso à Rouen: le préfet affirme "qu'il n'y a pas de toxicité aiguë" sur les premiers relevés pic.twitter.com/TSRCmpLWuoBFMTV (@BFMTV) September 26, 2019
Reports say the fire began at 2:48am Thursday morning in a storage facility at the factory, located on the right bank of Rouen not far from the city centre.
Some residents were awakened by the sounds of explosions. There were no casualties, and it’s unclear what caused the blaze.
Seine-Maritime regional authorities said preliminary analysis found the smoke was not toxic. Schools and nurseries were however closed in 13 municipalities.
Residents of Rouen and its surrounding areas have been told to limit their movements as a precautionary measure, with Interior Minister Christophe Castaner saying there was no need to panic.
Lubrizol is a US multinational owned by billionaire investor Warren Buffett.
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The factory – which has been operating since 1954 – gained notoriety in 2013 when a foul smell emanating from its premises sparked a national health crisis.
The nauseating gas mercaptan had formed in a tank at the plant, causing a stink that spread all the way across the Channel to England.
An investigation found the mercaptan leak was caused by human error.