SK On Says ESS Passed UL 9540A Large-Scale Fire Test, No Spread
SK On says its container storage system met UL 9540A criteria, with no thermal runaway in the adjacent container. It is converting 3 GWh of 7 GWh at Seosan to LFP storage lines.
2 min readAI-assisted
SK On says its container ESS met UL 9540A criteria in a large-scale fire test; the company's claim has no independent check yet.
Illustration (AI-generated)
SK On said on Oct. 28 that its containerized energy storage system met the evaluation criteria of UL 9540A, the North American standard for how battery fires spread, in a large-scale fire test, according to The Korea Times.
In the test, battery cells inside the container next to the one where the fire began did not go into thermal runaway, and temperatures inside the containers stayed within the evaluation limits, the company said. The result is SK On's own account of the test. No independent verification has been published.
For developers and data-center operators weighing grid-scale storage, fire propagation between containers is a core site-safety question, and SK On is now pointing to a North American test result as it courts US buyers. The claim covers one tested design, not every SK On product.
How SK On explains the result
The company credits a system design that releases heat gradually over a long period, which limits sudden spikes in the heat release rate and lowers the risk of fire reaching nearby containers. Korea Times and DigitalToday both said the test was run under requirements that were tightened in March to set clearer pass criteria for propagation.
SK On did not say which container, cell model or energy rating was tested, nor which lab ran it. Both outlets gave no capacity figure for the tested unit.
Supply deals and production behind the push
SK On said it will use the report to expand in global storage. In August it signed an LFP battery supply agreement with US storage company NeoVolta Power, after a 1 GWh storage supply deal with US renewable developer Flatiron in September 2025, the outlets reported.
SK On is converting 3 GWh of the Seosan plant's 7 GWh of production lines to LFP for storage, according to The Korea Times.
Illustration (AI-generated)
In Korea, SK On secured 284 MW of the 565 MW offered in the second central contract market in February. At its Seosan plant in South Chungcheong Province it is converting 3 GWh of 7 GWh of production lines to dedicated LFP lines for storage.
Rivals are making similar claims. As Voltgrid reported, Sungrow said its PowerTitan 3.0 fire test showed no spread at 28.56 MWh, a different product tested under the 2026 version of the standard.
What is not confirmed yet
The reports we read do not include the full test report, so the tested system's size, the cell chemistry in that unit and the test lab are unconfirmed. The commercial terms of the NeoVolta deal and the timing of the Seosan conversion were not given in the reports we read. We found no independent check of the fire-test data.
