SSAB has suspended operations at its new steel plant in Luleå after gas detectors registered low levels of hydrogen cyanide.
The incident marks the second work stoppage at the facility, raising fresh questions about the safety protocols and operational stability of the company's flagship green steel project.
The stock reversed course in trading, selling off on the news of the disruption.
Investors are increasingly sensitive to execution risks at the Luleå site, where the transition to fossil-free steel production has faced a series of technical and logistical hurdles.
The latest alarm underscores the complexity of managing hazardous materials in a high-pressure industrial environment.
This development adds to a challenging week for the Swedish market, which closed lower on Friday amid renewed concerns over AI sector volatility.