Pollution
Humain
Environnement
Economique

In a cardboard production facility, a maintenance operation was planned on the dome cover of a 25-m3 tank containing water and paper fibres. The operation was assigned to 3 employees and consisted of repairing a flange by performing a weld. An explosion occurred and ripped open the tank roof. All 3 workers were killed as a result of the traumatisms suffered; two bodies were found at the foot of the tank. Another employee, who observed the event from a distance, was also hurt. An investigation was launched by the federal agency overseeing chemical accidents (CSB); their report indicated that anaerobic bacteria had proliferated in the tank containing fibre waste and wastewater, as well as in the water recycling system, due to the presence of organic waste. Site employees were not at all aware that the multiplication of anaerobic bacteria could produce combustible vapours, most likely hydrogen, and therefore did not measure the explosive potential in the tank before undertaking these works.