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Investigation of Rönnskär fire completed

After the fire at Boliden Rönnskär’s tankhouse in June 2023, an investigation into the cause of the fire was initiated and has now been finalized. In summary, the investigation concluded the following: the fire started in the part of the tankhouse called group 4. The cause of the fire was deterioration of the contact surfaces in a vacuum circuit breaker due to the release of the vacuum. The exact reason for the release of the vacuum cannot be determined.

The result of the investigation was presented Thursday, June 27, 2024, to Rönnskär’s management team as well as engineers, who are now working intensively on Rönnskär’s new tankhouse, scheduled for commissioning in 2026.

“My assessment is that the fire cause investigation has been conducted in a professional manner. The investigation confirms my opinion that our staff performed excellent during the course of the fire. It is positive to now get a kind of formal closure of the fire episode itself, and be able to put our entire focus on the future and the new tankhouse,” says Linn Andersson, General Manager of Boliden Rönnskär.

The fire cause investigation has been conducted by Boliden’s insurance provider, in coopeation with an external fire investigation partner and a fire spread specialist from Lund University acting as an independent analyst. The insurance provider deems the investigation to be successful and  progressed further than initially expected given the conditions after the fire. All Boliden staff approached by the investigators have contributed in a crucial way to this. The investigation also clearly shows that Boliden’s operators on duty did everything expected according to applicable routines.  

The investigation in brief

Damage after the fire was extensive, posing challenges when investigating the cause of the fire.  Based on the testimonies from operators on site, the investigation could be restricted to a limited area of the tankhouse. In this area there were few plausible incendiaries except one circuit breaker in group 4, which after being examined in a laboratory proved to have been damaged in a contact and lost the vacuum required for the circuit breaker to function fully. Around the circuit breaker were signs of extreme heat development, which according to the manufacturer indicates the malfunction of a contact. This process does not occur in a matter of seconds but over a longer time, which is in line with the scenario as the switch had been turned off a few days earlier. Eventually, the circuit breaker became so hot that it could ignite material in its proximity.  

Continued dialog about fire prevention routines

The investigators have to the furthest possible extent examined the circumstances of the fire to, if possible, help Boliden prevent a similar situation from happening in the future. Risk engineers will likely have a contiued dialog with concerned parties within Boliden and at other operators of tankhouses, in order to examine if routines can and need to be changed to prevent similar fires from happening again.  


Boliden Head Office

Boliden Group
Klarabergsviadukten 90
P.O. Box 44, SE-101 20 Stockholm 
Tel: + 46 8 610 15 00
Fax: + 46 8 654 80 90