Gas explosion at Metsä Fibres’ Kemi pulp mill attributed to inadequate preparation and welding errors

A gas explosion at Metsä Fibres’ Kemi pulp mill, causing nearly 150 million euros in damages, can be attributed to inadequate preparation and welding errors. An investigation by the Finnish Safety and Chemicals Agency (Tukes) revealed three primary factors that led to the incident.

Firstly, the preparation for maintenance work on the evaporator was insufficient. Incomplete cleaning and emptying of the unit allowed for the accumulation of a potentially explosive air mixture. Secondly, the safety separation between the welding area and the rest of the piping was inadequate, as the gas side remained connected to the evaporator’s pipeline, increasing the risk of gas infiltration into the work area. Lastly, improper grounding during the welding process created a probable ignition source, leading to an electrical discharge that likely sparked the explosion.

The explosion occurred in March while the mill was offline for maintenance. Reportedly, the entire evaporator had not been properly emptied and cleaned before the hazardous work began, despite previous similar maintenance activities being conducted without incident. On the day of the explosion, gas measurements were not taken after having been measured the day before.

Metsä Fibres’ report emphasizes the need for rigorous protocols going forward, including fully emptying, cleaning, and ventilating evaporators before executing gas-hazardous work. It also suggests that critical areas must be distinctly isolated from the rest of the plant, with continuous gas monitoring throughout maintenance activities.

Moreover, the report calls for improved training for personnel writing work permits and recommends a dual-authorization system for permits related to gas-hazardous activities.