SK On, the battery manufacturing unit of SK Group, passed a major fire safety test for its energy storage systems (ESS), clearing a key hurdle as the company seeks to expand in the global market for grid-scale energy storage. The company said Wednesday that its ESS products met evaluation criteria under UL 9540A, a North American standard used to assess how thermal runaway in batteries can spread heat and fire to surrounding equipment. The large-scale fire test recreates conditions resembling an actual energy storage system fire, examining whether flames or dangerous heat spread to neighboring battery containers. The requirements were tightened in March to establish clearer criteria for assessing fire propagation. During the test, battery cells inside adjacent containers did not experience thermal runaway caused by heat from the container where the fire originated, and temperatures inside the containers remained within the evaluation limits, SK On said. The company attributed the result to a system design that releases heat gradually over an extended period, limiting sudden increases in h