The appeals court overturned earlier acquittals, 11 years after the blast that tore apart the AZF plant in Toulouse with the force of a 3.4-magnitude earthquake. Some 2,000 people were injured.
The appeals court cited negligence by factory chief Serge Biechlin, saying it "created or contributed to the situation" that caused the accident, according to the Sipa news agency. It said Total subsidiary Grande Paroisse was his employer and, therefore, also responsible.
Grande Paroisse and Biechlin said they would appeal the new ruling to the nation's highest court. "They cannot serve as scapegoats when no proof was determined," the company said in a statement.
The blast occurred 10 days after the Sept. 11 terror attacks in the United States, raising fears of terrorism, but it proved to be an accident. However, it took years to determine the exact cause behind the explosion, which killed and injured Toulouse residents beyond the factory site, where 21 people died.
The factory chief was convicted Monday by the appeals court of manslaughter and involuntary injury and destruction of goods and sentenced to three years in prison with two of the years suspended. He was fined (EURO)45,000 ($58,446). The Total subsidiary Grande Paroisse was fined (EURO)225,000
A 2006 report by judicial investigators blamed the explosion on negligence that allowed ammonium nitrate to come into contact with other chemicals.
In 2009, an initial ruling by the lower court acquitted both defendants, giving them the "benefit of doubt."
However, the presiding judge at the appeals court, Bernard Brunet, stressed that the "chemical track has been demonstrated indisputably," Sipa reported.
France's top court, the Court of Cassation, is ruling Tuesday on another appeals case involving Total and an industrial accident, a 1999 oil spill that blackened much of France's Atlantic coastline. In a 2008 trial, the company and three others were found criminally responsible for the spill from the Erika tanker.