A court Monday convicted seven former senior employees of Union Carbide’s Indian subsidiary of “death by negligence” for their roles in the 1984 leak of toxic gas that killed an estimated 15,000 people in the world’s worst industrial disaster.

Survivors of the Bhopal accident, some of whom gathered in this central Indian city chanting slogans, said the light sentences — two years in prison — are too little, too late given the scale of the damage. In India’s notoriously slow justice system, the appeal process could drag on for years, even decades, while those convicted remain free on bail.