According to a report released on July 27, 2020, an explosion on April 19, 2019 at Arizona Public Service’s (APS) McMicken Battery Energy Storage System (BESS) facility in Surprise, Arizona was caused by an internal cell failure in a single battery which led to a cascading thermal runaway event[1].[2] The report was written for APS by Davion Hill, a U.S. energy storage leader DNV GL, a Norway-based company that provides advisory and analytics services to the energy industry. The report found that abnormal lithium metal deposits likely led to the internal failure. Contributing factors to the explosion include: a lack of thermal barriers between battery cells, a fire suppression system ill equipped to stop the thermal runaway, a concentration of flammable off-gassing, and a lack of coordination with emergency responders.

The APS report concluded that four issues must be addressed in future BESS installations: barriers to limit cell-to-cell and module-to-module cascading; ventilation and cooling; a combined strategy of fire suppression followed by ventilation and cooling strategies; and response procedures that incorporate system monitoring, the detection of gases, ventilation practices, extinguishing methods, and critical information.

[1] A thermal Runaway occurs in situations where an increase in temperature changes the conditions in a way that causes a further increase in temperature.

[2] https://www.aps.com/en/About/Our-Company/Newsroom/Articles/Equipment-failure-at-McMicken-Battery-Facility