Lithium-ion BESS thermal event with flare-ups over several days

In May 2024 a utility-scale battery energy storage facility in North America experienced a thermal event. The installation used nickel manganese cobalt (NMC) lithium-ion cells. After the initial event, intermittent flare-ups continued for approximately seven days before the site was declared secure. The response involved coordination between site operators, local fire services and environmental authorities, and air quality monitoring was carried out throughout the response period. Public reporting records that the site had experienced an earlier thermal event before this one. The account here is drawn from a publicly issued environmental agency case study on battery energy storage incident response.

No root cause findings were available at the time of writing and none are reproduced here. Industry literature, rather than any finding specific to this site, notes that NMC lithium-ion chemistry has a higher thermal runaway propensity than lithium iron phosphate, and that high cell density in utility-scale installations can allow a thermal event to propagate from cell to cell if it is not contained.

1. Provide physical separation between battery enclosures so that a thermal event in one unit is less likely to propagate to adjacent units.
2. Maintain extended thermal and gas monitoring after the initial event appears suppressed, because lithium-ion systems can re-ignite as stored energy redistributes.
3. Agree a joint emergency response plan with fire services and air quality or environmental authorities before an incident, including who takes air monitoring readings and how results are communicated.
4. Record cell chemistry and its thermal characteristics in the design safety case, and review whether the selected chemistry, energy density target and containment measures are consistent for the site in question.
5. Include any earlier thermal event at the same site in the response plan and in operator briefings, so that lessons from the first event inform the handling of any later one.