At around 7.20 p.m., a saline leak (950°C) occurred in a black liquor boiler at a paper mill. The overflow of saline into the gutters created a reaction with liquid present in the gutters. Sounds of explosion were heard. The gutters’ metal grilles were lifted up. A release of smoke was detected. At 8.35 p.m., the emergency responders were called in by an employee. The operator triggered its internal emergency plan. Staff were evacuated. A 200m safety perimeter was put in place around the facility and the spill remained contained within the plant limits. The boiler’s supply of black liquor was stopped. The plant’s natural gas supply was shut off. That stopped the saline flow. Sandbags were placed in the vicinity of the heaps of saline to prevent any contact with liquid products. Production was shut down. Two tanks of boiler water treatment product had melted, releasing liquid substances which fuelled the reaction with the saline. 20m³ of combustion residues were spilled on the floor over 100m² and cooled. 200m³ remained in the boiler. No impact on the environment was observed. The SO2, CO and NO levels measured in the air showed no anomaly. Two days later, the site was cleaned. Boiler restarting depended on the approval of the Prefect.

A tightness defect on the boiler (between the first lateral tubes and the hearth tube) caused the saline leak. The presence of moisture in the gutters caused a reaction with the melted sodium. The nearby presence of containers of liquid chemical products was a negative factor. Moreover, as a consequence of staff turnover in the firm, the technicians present on the day of the incident had not encountered this type of event.

Following the event, the operator took the following actions:

• reconstruction of the leak test chambers;
• modification of the maintenance plan for leakproofing systems;
• change of location of boiler water treatment products;
• updating of the instructions for swift shutdown of the boiler.