Around 9 pm, 150 litres of 50% hydrogen peroxide (oxygenated water) overflowed from a buffer tank and then from the retention basin in a paper mill. The oxygenated water came into contact with a sewer outlet connected to the site treatment plant and reacted with iron oxide (rust). Employees were evacuated. Maintenance staff reversed the rotational direction of the electrical utility room aeration system in order to prevent vapour from entering and degrading the transformer, then shut off the peroxide filling pump and locked out both the pneumatic and electric valves. Their intervention ended at 11:45 pm.

A dysfunction in the tank level sensor was the suspected cause of this spill. The sensor was replaced, along with the mother boards, input/output cards and pump contactor. An analogic gauge, fitted with a relay box, and a spring-activated return valve were both installed. Moreover, the cable-connected logic level control redundancy was doubled and the control program was modified to stop the installation if the gauge signal is lost. In addition, the subsequent on-site peroxide delivery operation was to undergo close scrutiny and monitoring.